text: 6 A. Coutens et al. 10-6 Ziurys et al. 1989; Martin-Pintado et al. 1992; Requena- Torres et al. 2007). The bulk of Si is expected to be in the grain cores. ∼ − With the standard model (Si/H 10 7), the fractional × − abundance of SiO is about 5 10 8. The abundance of SiO is proportional to the initial Si abundance. In the case of − 10-7 an initial Si abundance of 10 7, the SiO abundance would × − ∼ range b−etween 1 10 9 (fo∼r models−with low density nI 103 cm 3, high den−sity−nI 106 cm 3, low cosmic ray io−ni- sation rate ζ = 10 16 s 1 or high ionisation rate ζ = 10 13 − × − s 1) and 5 10 8 (standard model). It should also be noted that the abundances predicted by a model that considers the 10-8 freezing of Si into solid Si (instead of SiH4) do not change 10 100 1000 signiﬁcantly. time (years) The main reaction that leads to the formation of SiO in our standard model is: Figure 2. Fractional abundance of gas-phase methanol with re- − → spect to H-nucleons as a function of time in phase I for the stan- SiOH+ +e SiO+H, dard model with episodic explosions of grain mantles. with SiOH+ formed by the reactions between SiO+ and H2 and between Si+ and H2O. Other reactions such as → Si+O2 SiO+O the explosion threshold abundance of H (fH) do not lead to and signiﬁcant variation of the abundance of methanol (lower → than a factor 2). The variation of phase II parameters such Si+OH SiO+H as the initial density (nII) and the three-body reaction rate contribute to the formation of SiO as well. (k3B) do not change the fractional abundances of methanol 4 DISCUSSION when the hydrogenation of CO is included, as it is the dom- inant mechanism. In the absence of the grain surface mech- In this section, we compare the results predicted by our anism, methanol is, as expected, produced more eﬃciently models with observations. As the observed abundances are with a higher initial density and a higher three-body reaction calculated with respect to H2 while the predicted abun- rate. The size distribution of the grains can also be investi- dances by the chemical models are with respect to H- gated by varying σH, the dust surface area per H-nucleon. nucleons, we corrected the latter to be expressed with re- A high value of σH increases the fractional abundance of spect to H2 (i.e. multiplied by a factor 2). methanol, both with and without the inclusion of the grain 4.1 Methanol surface hydrogenation of CO. Yusef-Zadeh et al. (2013c) estimated a fractional abun- We explored two cases with diﬀerent dust temperatures − dance of methanol in the CMZ ranging between 10 9 and for which we assumed diﬀerent fractions of volatile species − 10 7. Requena-Torres et al. (2008) estimated even higher desorbing at low temperatures. For a lower dust temperature ∼ abundances for three molecular clouds located in the CMZ ( 20 K), we assumed that, after depletion, 65% of CO, O2, (3 × 10−7 for G–0.02–0.07, 1.1 × 10−6 for G–0.11–0.08, and and N2 and 100% of CH4 remain frozen on the g∼rains. In 5 × 10−7 for G+0.693–0.03). With a conversion eﬃciency of the extreme case of a higher dust temperature ( 30 K), we consider that CO, O2, and N2 do not freeze at all, while CO into CH3OH of 10%, our standard model with episodic explosions is in agreement with the high abundances de- 30% of CH4 still remain frozen. As expected, in the latter rived in these studies (∼1.8 × 10−7). With high densities, case, we obtain the same results as in the absence of the × − × − the abundance is even higher (about 7 10 7–1 10 6), CO hydrogenation on the grains. For the lower temperature which is consistent with the high abundances derived for the case, the abundance of methanol is a factor 3 higher due to molecular clouds. On the contrary, in the absence of explo- the highest fraction of CO that remains on the grain. ≥ × − sion and for high densities ( 2 105 cm 3), the predicted Figure 2 shows the abundance of methanol as a function ≤ × − abundance of methanol is low ( 3 10 8) compared to the of time during phase I for the standard model. The cycle has a duration of 1.2 ×103 years. Right after the explosion observation∼s. It shou−ld be, however, noted that, for a high density of 106 cm 3, the gas and dust temperatures are phase, the abundance of methanol in the gas-phase reaches a value of 6 × 10−7 then decreases with the time until the certainly(cid:38)coupled, which would mean very high dust temper- atures ( 100 K) and the complete absence of ices. Based on next explosion. This shows that the explosion is required to these results, a scenario with cyclic explosions of grain man- reach high abundances of methanol. tles is suﬃcient to explain the observations. No additional 3.2.2 Silicon monoxide mechanism is required to reproduce the observational abun- The main uncertainty for the silicon chemistry is the dance of methanol in the CMZ and the cyclic aspect of our initial abundance of Si. Indeed, it is thought that Si is de- model can explain the continuous and widespread presence ∼ × − pleted with respect to the solar value (Si/H 3.9 10 5, of methanol. Asplund et al. 2009), but the depletion factor is not con- These results are, however, dependent on the fraction of sstilriacoinnedis. oInbsqeurvieesdcetnotbcelohuedasvliilkyedTepMleCte-1d,(LS1iO83/,Ha2nd(cid:46)L1104−4182,, CgeOnatthioant hoyfdCroOgeonnattehseingtroaiCnHs,3tOhHe .sWtanhdenartdhemreodisenl oprheyddicrots- MNRAS 000, 1–9 (2016) H/HO HC 3 ##LTFigure## ##LTLine## ##LTLine## ##LTLine## ##LTLine##

text: A.

text: Coutens

text: et

text: al.

text: Ziurys

text: et

text: al.

text: Martin-Pintado

text: et

text: al.

text: Requena-

text: Torres

text: et

text: al.

text: The

text: bulk

text: of

text: Si

text: is

text: expected

text: to

text: be

text: in

text: the

text: grain

text: cores.

text: With

text: the

text: standard

text: model

text: (Si/H

text: the

text: fractional

text: abundance

text: of

text: SiO

text: is

text: about

text: The

text: abundance

text: of

text: SiO

text: is

text: proportional

text: to

text: the

text: initial

text: Si

text: abundance.

text: In

text: the

text: case

text: of

text: an

text: initial

text: Si

text: abundance

text: of

text: the

text: SiO

text: abundance

text: would

text: range

text: b−etween

text: (fo∼r

text: models−with

text: low

text: density

text: nI

text: cm

text: high

text: den−sity−nI

text: cm

text: low

text: cosmic

text: ray

text: io−ni-

text: sation

text: rate

text: ζ

text: s

text: or

text: high

text: ionisation

text: rate

text: ζ

text: s

text: and

text: (standard

text: model).

text: It

text: should

text: also

text: be

text: noted

text: that

text: the

text: abundances

text: predicted

text: by

text: a

text: model

text: that

text: considers

text: the

text: freezing

text: of

text: Si

text: into

text: solid

text: Si

text: (instead

text: of

text: do

text: not

text: change

text: signiﬁcantly.

text: time

text: (years)

text: The

text: main

text: reaction

text: that

text: leads

text: to

text: the

text: formation

text: of

text: SiO

text: in

text: our

text: standard

text: model

text: is:

text: Figure

text: Fractional

text: abundance

text: of

text: gas-phase

text: methanol

text: with

text: re-

text: spect

text: to

text: H-nucleons

text: as

text: a

text: function

text: of

text: time

text: in

text: phase

text: I

text: for

text: the

text: stan-

text: SiOH+

text: +e

text: SiO+H,

text: dard

text: model

text: with

text: episodic

text: explosions

text: of

text: grain

text: mantles.

text: with

text: SiOH+

text: formed

text: by

text: the

text: reactions

text: between

text: SiO+

text: and

text: and

text: between

text: Si+

text: and

text: Other

text: reactions

text: such

text: as

text: SiO+O

text: the

text: explosion

text: threshold

text: abundance

text: of

text: H

text: (fH)

text: do

text: not

text: lead

text: to

text: and

text: signiﬁcant

text: variation

text: of

text: the

text: abundance

text: of

text: methanol

text: (lower

text: than

text: a

text: factor

text: The

text: variation

text: of

text: phase

text: II

text: parameters

text: such

text: Si+OH

text: SiO+H

text: as

text: the

text: initial

text: density

text: (nII)

text: and

text: the

text: three-body

text: reaction

text: rate

text: contribute

text: to

text: the

text: formation

text: of

text: SiO

text: as

text: well.

text: do

text: not

text: change

text: the

text: fractional

text: abundances

text: of

text: methanol

text: DISCUSSION

text: when

text: the

text: hydrogenation

text: of

text: CO

text: is

text: included,

text: as

text: it

text: is

text: the

text: dom-

text: inant

text: mechanism.

text: In

text: the

text: absence

text: of

text: the

text: grain

text: surface

text: mech-

text: In

text: this

text: section,

text: we

text: compare

text: the

text: results

text: predicted

text: by

text: our

text: anism,

text: methanol

text: is,

text: as

text: expected,

text: produced

text: more

text: eﬃciently

text: models

text: with

text: observations.

text: As

text: the

text: observed

text: abundances

text: are

text: with

text: a

text: higher

text: initial

text: density

text: and

text: a

text: higher

text: three-body

text: reaction

text: calculated

text: with

text: respect

text: to

text: while

text: the

text: predicted

text: abun-

text: rate.

text: The

text: size

text: distribution

text: of

text: the

text: grains

text: can

text: also

text: be

text: investi-

text: dances

text: by

text: the

text: chemical

text: models

text: are

text: with

text: respect

text: to

text: H-

text: gated

text: by

text: varying

text: σH,

text: the

text: dust

text: surface

text: area

text: per

text: H-nucleon.

text: nucleons,

text: we

text: corrected

text: the

text: latter

text: to

text: be

text: expressed

text: with

text: re-

text: A

text: high

text: value

text: of

text: σH

text: increases

text: the

text: fractional

text: abundance

text: of

text: spect

text: to

text: (i.e.

text: multiplied

text: by

text: a

text: factor

text: methanol,

text: both

text: with

text: and

text: without

text: the

text: inclusion

text: of

text: the

text: grain

text: Methanol

text: surface

text: hydrogenation

text: of

text: CO.

text: Yusef-Zadeh

text: et

text: al.

text: estimated

text: a

text: fractional

text: abun-

text: We

text: explored

text: two

text: cases

text: with

text: diﬀerent

text: dust

text: temperatures

text: dance

text: of

text: methanol

text: in

text: the

text: CMZ

text: ranging

text: between

text: and

text: for

text: which

text: we

text: assumed

text: diﬀerent

text: fractions

text: of

text: volatile

text: species

text: Requena-Torres

text: et

text: al.

text: estimated

text: even

text: higher

text: desorbing

text: at

text: low

text: temperatures.

text: For

text: a

text: lower

text: dust

text: temperature

text: abundances

text: for

text: three

text: molecular

text: clouds

text: located

text: in

text: the

text: CMZ

text: K),

text: we

text: assumed

text: that,

text: after

text: depletion,

text: of

text: CO,

text: for

text: for

text: and

text: and

text: and

text: of

text: remain

text: frozen

text: on

text: the

text: g∼rains.

text: In

text: for

text: With

text: a

text: conversion

text: eﬃciency

text: of

text: the

text: extreme

text: case

text: of

text: a

text: higher

text: dust

text: temperature

text: K),

text: we

text: consider

text: that

text: CO,

text: and

text: do

text: not

text: freeze

text: at

text: all,

text: while

text: CO

text: into

text: of

text: our

text: standard

text: model

text: with

text: episodic

text: explosions

text: is

text: in

text: agreement

text: with

text: the

text: high

text: abundances

text: de-

text: of

text: still

text: remain

text: frozen.

text: As

text: expected,

text: in

text: the

text: latter

text: rived

text: in

text: these

text: studies

text: With

text: high

text: densities,

text: case,

text: we

text: obtain

text: the

text: same

text: results

text: as

text: in

text: the

text: absence

text: of

text: the

text: the

text: abundance

text: is

text: even

text: higher

text: (about

text: CO

text: hydrogenation

text: on

text: the

text: grains.

text: For

text: the

text: lower

text: temperature

text: which

text: is

text: consistent

text: with

text: the

text: high

text: abundances

text: derived

text: for

text: the

text: case,

text: the

text: abundance

text: of

text: methanol

text: is

text: a

text: factor

text: higher

text: due

text: to

text: molecular

text: clouds.

text: On

text: the

text: contrary,

text: in

text: the

text: absence

text: of

text: explo-

text: the

text: highest

text: fraction

text: of

text: CO

text: that

text: remains

text: on

text: the

text: grain.

text: sion

text: and

text: for

text: high

text: densities

text: cm

text: the

text: predicted

text: Figure

text: shows

text: the

text: abundance

text: of

text: methanol

text: as

text: a

text: function

text: abundance

text: of

text: methanol

text: is

text: low

text: compared

text: to

text: the

text: of

text: time

text: during

text: phase

text: I

text: for

text: the

text: standard

text: model.

text: The

text: cycle

text: has

text: a

text: duration

text: of

text: years.

text: Right

text: after

text: the

text: explosion

text: observation∼s.

text: It

text: shou−ld

text: be,

text: however,

text: noted

text: that,

text: for

text: a

text: high

text: density

text: of

text: cm

text: the

text: gas

text: and

text: dust

text: temperatures

text: are

text: phase,

text: the

text: abundance

text: of

text: methanol

text: in

text: the

text: gas-phase

text: reaches

text: a

text: value

text: of

text: then

text: decreases

text: with

text: the

text: time

text: until

text: the

text: which

text: would

text: mean

text: very

text: high

text: dust

text: temper-

text: atures

text: K)

text: and

text: the

text: complete

text: absence

text: of

text: ices.

text: Based

text: on

text: next

text: explosion.

text: This

text: shows

text: that

text: the

text: explosion

text: is

text: required

text: to

text: these

text: results,

text: a

text: scenario

text: with

text: cyclic

text: explosions

text: of

text: grain

text: man-

text: reach

text: high

text: abundances

text: of

text: methanol.

text: tles

text: is

text: suﬃcient

text: to

text: explain

text: the

text: observations.

text: No

text: additional

text: Silicon

text: monoxide

text: mechanism

text: is

text: required

text: to

text: reproduce

text: the

text: observational

text: abun-

text: The

text: main

text: uncertainty

text: for

text: the

text: silicon

text: chemistry

text: is

text: the

text: dance

text: of

text: methanol

text: in

text: the

text: CMZ

text: and

text: the

text: cyclic

text: aspect

text: of

text: our

text: initial

text: abundance

text: of

text: Si.

text: Indeed,

text: it

text: is

text: thought

text: that

text: Si

text: is

text: de-

text: model

text: can

text: explain

text: the

text: continuous

text: and

text: widespread

text: presence

text: pleted

text: with

text: respect

text: to

text: the

text: solar

text: value

text: (Si/H

text: of

text: methanol.

text: Asplund

text: et

text: al.

text: but

text: the

text: depletion

text: factor

text: is

text: not

text: con-

text: These

text: results

text: are,

text: however,

text: dependent

text: on

text: the

text: fraction

text: of

text: sstilriacoinnedis.

text: CgeOnatthioant

text: .sWtanhdenartdhemreodisenl

text: oprheyddicrots-

text: MNRAS

text: H/HO

text: HC

text: ##LTFigure##

text: ##LTLine##

text: ##LTLine##

text: ##LTLine##

text: ##LTLine##


text: 8 A. Coutens et al. mechanism for the formation of methanol in the CMZ is the Lee H.-H., Bettens R. P. A., Herbst E., 1996, A&AS, 119, 111 grain surface formation through hydrogenation of CO fol- Longmore S. N., et al., 2012, ApJ, 746, 117 lowed by the desorption due to the explosion. Our model Martin-Pintado J., Bachiller R., Fuente A., 1992, A&A, 254, 315 also reproduces the SiO abundance in the case of a low Mart´ın-Pintado J., de Vicente P., Fuente A., Planesas P., 1997, − Si/H initial abundance of about 10 8. As both methanol ApJ, 482, L45 McElroy D., Walsh C., Markwick A. J., Cordiner M. A., Smith and SiO require grain surface formation mechanisms, shocks K., Millar T. J., 2013, A&A, 550, A36 could be another possible scenario to explain the presence of McGuire B. A., Carroll P. B., Loomis R. A., Finneran I. A., Jewell methanol and SiO in the CMZ. As shown by Rawlings et al. P. R., Remijan A. J., Blake G. A., 2016, in American Astro- (2013b), the episodic explosion models present the advan- nomical Society Meeting Abstracts. p. 203.04 tage that they can explain the presence of large and com- Meijerink R., Spaans M., Loenen A. F., van der Werf P. P., 2011, plex molecules after several cycles. This type of model could A&A, 525, A119 consequently also explain the presence of complex organic Minh Y. C., Irvine W. M., Friberg P., 1992, A&A, 258, 489 molecules such as glycolaldehyde and propylene oxide in the Minh Y. C., Liu H. B., Su Y.-N., Hsieh P.-Y., Liu S.-Y., Kim cold gas surrounding the star-forming region Sgr B2 (Hollis S. S., Wright M., Ho P. T. P., 2015, ApJ, 808, 86 O¨berg K. I., Boogert A. C. A., Pontoppidan K. M., van den Broek et al. 2004; McGuire et al. 2016). More experimental and S., van Dishoeck E. F., Bottinelli S., Blake G. A., Evans II theoretical work is however required to constrain the chem- N. J., 2011, ApJ, 740, 109 istry during the explosion phase. Pagani L., et al., 2009, A&A, 494, 623 ACKNOWLEDGEMENTS Pagani L., Lesaﬀre P., Jorﬁ M., Honvault P., Gonza´lez-Lezana T., Faure A., 2013, A&A, 551, A38 The authors would like to thank an anonymous referee Rawlings J. M. C., Williams D. A., Viti S., Cecchi-Pestellini C., for valuable comments and suggestions. The work of AC was Duley W. W., 2013a, MNRAS, 430, 264 funded by the STFC grant ST/M001334/1. Rawlings J. M. C., Williams D. A., Viti S., Cecchi-Pestellini C., REFERENCES 2013b, MNRAS, 436, L59 Ao Y., et al., 2013, A&A, 550, A135 Requena-Torres M. A., Marcelino N., Jim´enez-Serra I., Mart´ın- Asplund M., Grevesse N., Sauval A. J., Scott P., 2009, ARA&A, Pintado J., Mart´ın S., Mauersberger R., 2007, ApJ, 655, L37 47, 481 Requena-Torres M. A., Mart´ın-Pintado J., Mart´ın S., Morris Bayet E., Williams D. A., Hartquist T. W., Viti S., 2011, MNRAS, M. R., 2008, ApJ, 672, 352 414, 1583 Riquelme D., Bronfman L., Mauersberger R., May J., Wilson Bertin M., et al., 2016, ApJ, 817, L12 T. 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label: paragraph

text: A.

text: Coutens

text: et

text: al.

text: mechanism

text: for

text: the

text: formation

text: of

text: methanol

text: in

text: the

text: CMZ

text: is

text: the

text: Lee

label: reference

text: H.-H.,

text: Bettens

text: R.

text: P.

text: A.,

text: Herbst

text: E.,

text: A&AS,

text: grain

text: surface

text: formation

text: through

text: hydrogenation

text: of

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text: Millar

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text: A.,

text: Carroll

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text: 9 APPENDIX A: LIST OF REACTIONS IN Table A1. List of reactions in Phase I involving methanol PHASE I INVOLVING METHANOL AND SILICON MONOXIDE → Si+ + CH3OH → SiOH+ + CH3 H+ + CH3OH → CH3OH+ + H H+ + CH3OH → CH3+ + H2O H+ + CH3OH →HCO+ + H2 + H2 H3+ + CH3OH → CH3+ + H2O + H2 H3+ + CH3OH → CH3OH2+ + H2 He+ + CH3OH → OH+ + CH3 + HE He+ + CH3OH→ OH + CH3+ + HE C+ + CH3OH →HCO + CH3+ CH+ + CH3OH → CH3OH2+ + C CH+ + CH3OH→ H2CO + CH3+ CH3+ + H2O C→H3OH2+ + PHOTON CH4+ + CH3OH → CH3OH+ + CH4 CH4+ + CH3O→H CH3OH2+ + CH3 N+ + CH3OH → CH3OH+ + N N+ + CH3OH → H2CO+ + NH + H N+ + CH3OH → NO+ + CH3 + H N+ + CH3OH → NO + CH3+ + H O+ + CH3OH → CH3OH+ + O O+ + CH3OH →H2CO+ + H2O H3O+ + CH3OH→ CH3OH2+ + H2O O2+ + CH3OH →CH3OH+ + O2 HCO+ + CH3OH →CH3OH2+ + CO H2CO+ + CH3OH→ CH3OH2+ + HCO CH3OH2+ + NH→3 CH3OH + NH4+ Si+ + CH3OH− →SiOH+ + CH3 CH3OH+ + e− → CH + H2O + H CH3OH+ + e− → H2CO + H + H CH3OH+ + e − →OH + CH3 CH3OH2+ + e− → CH2 + H2O + H CH3OH2+ + e− → CH3 + H2O CH3OH2+ + e− → CH3 + OH + H CH3OH2+ + e− → CH3OH + H CH3OH2+ + e H2→CO + H2 + H − CH3OH + PHOTON → CH3OH+ + e CH3OH + PHOTON → H2CO + H2 CH3OH + PHO→TON OH + CH3 CH3OH+ + G →H2CO + H + H CH3OH2+ + G→ CH3 + OH + H CH3OH + G GCH3O→H GCH3OH + PHOTON CH3OH + G Notes : GCH3OH correspond to solid methanol. This paper has been typeset from a TEX/LATEX ﬁle prepared by the author. MNRAS 000, 1–9 (2016) ##LTLine## ##LTLine## ##LTLine##

text: APPENDIX

label: section

text: A:

text: LIST

text: OF

text: REACTIONS

text: IN

text: Table

text: List

label: caption

text: of

text: reactions

text: in

text: Phase

text: I

text: involving

text: methanol

text: PHASE

text: I

text: INVOLVING

text: METHANOL

text: AND

text: SILICON

text: MONOXIDE

label: table

text: Si+

text: SiOH+

text: H+

text: H

text: H+

text: H+

text: →HCO+

text: He+

text: OH+

text: HE

text: He+

text: OH

text: HE

text: C+

text: →HCO

text: CH+

text: C

text: CH+

text: PHOTON

text: N+

text: N

text: N+

text: NH

text: H

text: N+

text: NO+

text: H

text: N+

text: NO

text: H

text: O+

text: O

text: O+

text: HCO+

text: CO

text: HCO

text: Si+

text: →SiOH+

text: e−

text: CH

text: H

text: e−

text: H

text: H

text: e

text: →OH

text: e−

text: H

text: e−

text: e−

text: OH

text: H

text: e−

text: H

text: e

text: H

text: PHOTON

text: e

text: PHOTON

text: PHO→TON

text: OH

text: G

text: H

text: H

text: G→

text: OH

text: H

text: G

text: PHOTON

text: G

text: Notes

text: correspond

text: to

text: solid

text: methanol.

text: This

text: paper

text: has

text: been

text: typeset

text: from

text: a

text: TEX/LATEX

text: ﬁle

text: prepared

text: by

text: the

text: author.

text: MNRAS

text: ##LTLine##

text: ##LTLine##

text: ##LTLine##


text: Under consideration for publication in J. Plasma Phys. 1 Simulation study of the formation of a non-relativistic pair shock † M. E. Dieckmann1 , and A. Bret2,3 1Department of Science and Technology (ITN), Linkoping University, Campus Norrkoping, 60174 Norrkoping, Sweden 2University of Castilla La Mancha, ETSI Ind, E-13071 Ciudad Real, Spain 3Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real, Spain (Received xx; revised xx; accepted xx) We examine with a particle-in-cell (PIC) simulation the collision of two equally dense clouds of cold pair plasma. The clouds interpenetrate until instabilities set in, which heat up the plasma and trigger the formation of a pair of shocks. The fastest-growing waves at the collision speed c/5 and low temperature are the electrostatic two-stream mode and the quasi-electrostatic oblique mode. Both waves grow and saturate via the formation of phase space vortices. The strong electric ﬁelds of these nonlinear plasma structures provide an eﬃcient means of heating up and compressing the inﬂowing upstream leptons. The interaction of the hot leptons, which leak back into the upstream region, with the inﬂowing cool upstream leptons continuously drives electrostatic waves that mediate the shock. These waves heat up the inﬂowing upstream leptons primarily along the shock normal, which results in an anisotropic velocity distribution in the post-shock region. This distribution gives rise to the Weibel instability. Our simulation shows that even if the shock is mediated by quasi-electrostatic waves, strong magnetowaves will still develop in its downstream region. 1. Introduction Compact objects like neutron stars or black holes that accrete material can emit relativistic jets. These jets are composed of electrons, positrons and ions. The emission of relativistic jets by microquasars (Fabian & Rees 1979; Margon 1984), which are stellar-size black holes that gather material from a companion star, and by some of the supermassive black holes in the centers of galaxies has been observed directly (Bridle & Perley 1984). The ﬁreball model attributes gamma-ray bursts (GRBs) to ultrarelativistic jets, which are emitted during strong supernovae. A direct observation of the ultrarelativistic jets that trigger the GRBs and occur at cosmological distances is not possible. Their existence can thus not be established unambiguously (Woosley & Bloom 2006). However, observations of a mildly relativistic plasma outﬂow during the supernova 1998bw by Kulkarni et al. (1998) lend some support to the ﬁreball model. The eﬃciency, with which the accreting object can accelerate the jet plasma, is not constant in time. A variable plasma acceleration eﬃciency results in a spatially varying velocity proﬁle of the jet plasma. Internal shocks can form at locations with a large velocity change and these shocks can constitute strong sources of electromagnetic radiation (Rees 1978). The prompt emissions of gamma-ray bursts, which are associated † Email address for correspondence: mark.e.dieckmann@liu.se

text: Under

text: consideration

text: for

text: publication

text: in

text: J.

text: Plasma

text: Phys.

text: Simulation

label: title

text: study

text: of

text: the

text: formation

text: of

text: a

text: non-relativistic

text: pair

text: shock

label: author

text: M.

text: E.

text: and

text: A.

text: of

text: Science

text: and

text: Technology

text: (ITN),

text: Linkoping

text: University,

text: Campus

text: Norrkoping,

text: Norrkoping,

text: Sweden

text: of

text: Castilla

text: La

text: Mancha,

text: ETSI

text: Ind,

text: Ciudad

text: Real,

text: Spain

text: de

text: Investigaciones

text: Energéticas

text: y

text: Aplicaciones

text: Industriales,

text: Campus

text: Universitario

text: de

text: Ciudad

text: Real,

text: Ciudad

text: Real,

text: Spain

text: (Received

text: xx;

text: revised

text: xx;

text: accepted

text: xx)

text: We

label: abstract

text: examine

text: with

text: a

text: particle-in-cell

text: (PIC)

text: simulation

text: the

text: collision

text: of

text: two

text: equally

text: dense

text: clouds

text: of

text: cold

text: pair

text: plasma.

text: The

text: clouds

text: interpenetrate

text: until

text: instabilities

text: set

text: in,

text: which

text: heat

text: up

text: the

text: plasma

text: and

text: trigger

text: the

text: formation

text: of

text: a

text: pair

text: of

text: shocks.

text: The

text: fastest-growing

text: waves

text: at

text: the

text: collision

text: speed

text: and

text: low

text: temperature

text: are

text: the

text: electrostatic

text: two-stream

text: mode

text: and

text: the

text: quasi-electrostatic

text: oblique

text: mode.

text: Both

text: waves

text: grow

text: and

text: saturate

text: via

text: the

text: formation

text: of

text: phase

text: space

text: vortices.

text: The

text: strong

text: electric

text: ﬁelds

text: of

text: these

text: nonlinear

text: plasma

text: structures

text: provide

text: an

text: eﬃcient

text: means

text: of

text: heating

text: up

text: and

text: compressing

text: the

text: inﬂowing

text: upstream

text: leptons.

text: The

text: interaction

text: of

text: the

text: hot

text: leptons,

text: which

text: leak

text: back

text: into

text: the

text: upstream

text: region,

text: with

text: the

text: inﬂowing

text: cool

text: upstream

text: leptons

text: continuously

text: drives

text: electrostatic

text: waves

text: that

text: mediate

text: the

text: shock.

text: These

text: waves

text: heat

text: up

text: the

text: inﬂowing

text: upstream

text: leptons

text: primarily

text: along

text: the

text: shock

text: normal,

text: which

text: results

text: in

text: an

text: anisotropic

text: velocity

text: distribution

text: in

text: the

text: post-shock

text: region.

text: This

text: distribution

text: gives

text: rise

text: to

text: the

text: Weibel

text: instability.

text: Our

text: simulation

text: shows

text: that

text: even

text: if

text: the

text: shock

text: is

text: mediated

text: by

text: quasi-electrostatic

text: waves,

text: strong

text: magnetowaves

text: will

text: still

text: develop

text: in

text: its

text: downstream

text: region.

text: Introduction

text: Compact

text: objects

text: like

text: neutron

text: stars

text: or

text: black

text: holes

text: that

text: accrete

text: material

text: can

text: emit

text: relativistic

text: jets.

text: These

text: jets

text: are

text: composed

text: of

text: electrons,

text: positrons

text: and

text: ions.

text: The

text: emission

text: of

text: relativistic

text: jets

text: by

text: microquasars

text: (Fabian

text: Rees

text: Margon

text: which

text: are

text: stellar-size

text: black

text: holes

text: that

text: gather

text: material

text: from

text: a

text: companion

text: star,

text: and

text: by

text: some

text: of

text: the

text: supermassive

text: black

text: holes

text: in

text: the

text: centers

text: of

text: galaxies

text: has

text: been

text: observed

text: directly

text: (Bridle

text: Perley

text: The

text: ﬁreball

text: model

text: attributes

text: gamma-ray

text: bursts

text: (GRBs)

text: to

text: ultrarelativistic

text: jets,

text: which

text: are

text: emitted

text: during

text: strong

text: supernovae.

text: A

text: direct

text: observation

text: of

text: the

text: ultrarelativistic

text: jets

text: that

text: trigger

text: the

text: GRBs

text: and

text: occur

text: at

text: cosmological

text: distances

text: is

text: not

text: possible.

text: Their

text: existence

text: can

text: thus

text: not

text: be

text: established

text: unambiguously

text: (Woosley

text: Bloom

text: However,

text: observations

text: of

text: a

text: mildly

text: relativistic

text: plasma

text: outﬂow

text: during

text: the

text: supernova

text: by

text: Kulkarni

text: et

text: al.

text: lend

text: some

text: support

text: to

text: the

text: ﬁreball

text: model.

text: The

text: eﬃciency,

text: with

text: which

text: the

text: accreting

text: object

text: can

text: accelerate

text: the

text: jet

text: plasma,

text: is

text: not

text: constant

text: in

text: time.

text: A

text: variable

text: plasma

text: acceleration

text: eﬃciency

text: results

text: in

text: a

text: spatially

text: varying

text: velocity

text: proﬁle

text: of

text: the

text: jet

text: plasma.

text: Internal

text: shocks

text: can

text: form

text: at

text: locations

text: with

text: a

text: large

text: velocity

text: change

text: and

text: these

text: shocks

text: can

text: constitute

text: strong

text: sources

text: of

text: electromagnetic

text: radiation

text: (Rees

text: The

text: prompt

text: emissions

text: of

text: gamma-ray

text: bursts,

text: which

text: are

text: associated

text: Email

text: address

text: for

text: correspondence:

text: mark.e.dieckmann@liu.se


text: Nonrelativistic pair shock 17 instability by a ﬂow-aligned magnetic ﬁeld: testing the analytic threshold with pic simulations. Plasma Phys. Controll. Fusion 50, 025002. Stockem, A., Dieckmann, M. E. & Schlickeiser, R. 2009 Pic simulations of the thermal anisotropy-driven weibel instability: ﬁeld growth and phase space evolution upon saturation. Plasma Phys. Controll. Fusion 51, 075014. Stockem, A., Grismayer, T., Fonseca, R. A. & Silva, L. O. 2014 Electromagnetic ﬁeld generation in the downstream of electrostatic shocks due to electron trapping. Phys. Rev. Lett. 113, 105002. Trigo, M. D., Miller-Jones, J. C. A., Migliari, S., Broderick, J. W. & Tzioumis, T. 2013 Baryons in the relativistic jets of the stellar-mass black-hole candidate 4u 1630-47. Nature 504, 260–262. Umeda, T., Omura, Y., Yoon, P. H., Gaelzer, R. & Matsumoto, H. 2003 Harmonic langmuir waves. iii. vlasov simulation. Phys. Plasmas 10, 382. Weibel, E. S. 1959 Spontaneously growing transverse waves in a plasma due to an anisotropic velocity distribution. Phys. Rev. Lett. 2, 83. Wharton, C. B., Malmberg, J. H. & O’Neil, T. M. 1968 Nonlinear eﬀects of large- amplitude plasma waves. Phys. Fluids 11, 1761. Woosley, S. E. & Bloom, J. S. 2006 The supernova-gamma-ray burst connection. Ann. Rev. Astron. Astrophys. 44, 507–556. Zel’Dovich, Ya. B., Raizer, Yuri P., Probstein, Ronald F. & Hayes, Wallace D. 1967 Physics of shock waves and high-temperature hydrodynamic phenomena. London, New York, Sydney: Academic press.

text: Nonrelativistic

text: pair

text: shock

text: instability

text: by

text: a

text: ﬂow-aligned

text: magnetic

text: ﬁeld:

text: testing

text: the

text: analytic

text: threshold

text: with

text: pic

text: simulations.

text: Plasma

text: Phys.

text: Controll.

text: Fusion

text: Stockem,

text: A.,

text: Dieckmann,

text: M.

text: E.

text: Schlickeiser,

text: R.

text: Pic

text: simulations

text: of

text: the

text: thermal

text: anisotropy-driven

text: weibel

text: instability:

text: ﬁeld

text: growth

text: and

text: phase

text: space

text: evolution

text: upon

text: saturation.

text: Plasma

text: Phys.

text: Controll.

text: Fusion

text: Stockem,

text: A.,

text: Grismayer,

text: T.,

text: Fonseca,

text: R.

text: A.

text: Silva,

text: L.

text: O.

text: Electromagnetic

text: ﬁeld

text: generation

text: in

text: the

text: downstream

text: of

text: electrostatic

text: shocks

text: due

text: to

text: electron

text: trapping.

text: Phys.

text: Rev.

text: Lett.

text: Trigo,

text: M.

text: D.,

text: Miller-Jones,

text: J.

text: C.

text: A.,

text: Migliari,

text: S.,

text: Broderick,

text: J.

text: W.

text: Tzioumis,

text: T.

text: Baryons

text: in

text: the

text: relativistic

text: jets

text: of

text: the

text: stellar-mass

text: black-hole

text: candidate

text: Nature

text: Umeda,

text: T.,

text: Omura,

text: Y.,

text: Yoon,

text: P.

text: H.,

text: Gaelzer,

text: R.

text: Matsumoto,

text: H.

text: Harmonic

text: langmuir

text: waves.

text: iii.

text: vlasov

text: simulation.

text: Phys.

text: Plasmas

text: Weibel,

text: E.

text: S.

text: Spontaneously

text: growing

text: transverse

text: waves

text: in

text: a

text: plasma

text: due

text: to

text: an

text: anisotropic

text: velocity

text: distribution.

text: Phys.

text: Rev.

text: Lett.

text: Wharton,

text: C.

text: B.,

text: Malmberg,

text: J.

text: H.

text: O’Neil,

text: T.

text: M.

text: Nonlinear

text: eﬀects

text: of

text: large-

text: amplitude

text: plasma

text: waves.

text: Phys.

text: Fluids

text: Woosley,

text: S.

text: E.

text: Bloom,

text: J.

text: S.

text: The

text: supernova-gamma-ray

text: burst

text: connection.

text: Ann.

text: Rev.

text: Astron.

text: Astrophys.

text: Zel’Dovich,

text: Ya.

text: B.,

text: Raizer,

text: Yuri

text: P.,

text: Probstein,

text: Ronald

text: F.

text: Hayes,

text: Wallace

text: D.

text: Physics

text: of

text: shock

text: waves

text: and

text: high-temperature

text: hydrodynamic

text: phenomena.

text: London,

text: New

text: York,

text: Sydney:

text: Academic

text: press.


text: 8 M. E. Dieckmann and A. Bret 100 0 −0.5 −1 50 −1.5 −2 00 50 100 150 200 −2.5 (a) k λ y S 100 3 2 50 1 0 00 50 100 150 200 −1 (b) k λ y S Figure 3. The spatial power spectra of the in-plane electric ﬁeld E = E (x, y) + iE (x, y) at p x y the time t = 7.6 (a) and t = 14.7 (b). The color scale is 10-logarithmic and both spectra are 1 2 normalized to the peak value in (a). Figure 4. The phase space density distribution in the x, p -plane at the time t = 14.7 of x 2 electrons (a) and positrons (b). The phase space density distribution is averaged over all other dimensions. The momentum is normalized to p . The color scale is 10-logarithmic. 0 work; the range of wave numbers k that are unstable to the oblique mode instability is y large in a cold plasma, while the wave growth is concentrated at low values of k if the y plasma is hot (Silva et al. 2002). A ﬁrst and second harmonic along k have emerged. x The wave amplitudes have thus reached a non-linear regime (Umeda et al. 2003). Non-linear eﬀects in the wave distribution should be tied to changes in the lepton distribution. Figure 4 shows the phase space density distributions f(x, p ) of the electrons − x and positrons. The overlap layer of both clouds spans the interval 0.2 < x < 3. The counterstreaming clouds have not yet merged along p . However, the substantial particle x acceleration demonstrates that the instability is about to saturate. The density in the overlap layer is twice that of a single cloud and the density ﬂucutations caused by the − waves are of the order of 5% 10% (not shown). The ﬁlamentation instability starts to grow immediately but two-stream outgrows it. 3.2. Shock formation The two-stream instability saturates by forming stable phase space vortices in the electron and positron distributions (Berk & Roberts 1967) and the same holds during the initial saturation stage of the oblique mode instability (Dieckmann et al. 2006b). Sλ xk Sλ xk ##LTFigure## ##LTFigure## ##LTFigure## ##LTFigure## ##LTFigure## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine##

text: M.

text: E.

text: Dieckmann

text: and

text: A.

text: Bret

font: default

text: −1

text: −2

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text: k

text: λ

text: y

text: S

text: −1

text: (b)

text: k

text: λ

text: y

text: S

text: Figure

text: The

text: spatial

text: power

text: spectra

text: of

text: the

text: in-plane

text: electric

text: ﬁeld

text: E

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text: (x,

text: y)

text: iE

text: (x,

text: y)

text: at

text: p

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text: time

text: t

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text: and

text: t

text: (b).

text: The

text: color

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text: is

text: and

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text: spectra

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text: normalized

text: to

text: the

text: peak

text: value

text: in

text: (a).

text: Figure

text: The

text: phase

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text: density

text: distribution

text: in

text: the

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text: p

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text: at

text: the

text: time

text: t

text: of

text: x

text: electrons

text: (a)

text: and

text: positrons

text: (b).

text: The

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text: density

text: distribution

text: is

text: averaged

text: over

text: all

text: other

text: dimensions.

text: The

text: momentum

text: is

text: normalized

text: to

text: p

text: The

text: color

text: scale

text: is

text: work;

text: the

text: range

text: of

text: wave

text: numbers

text: k

text: that

text: are

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text: to

text: the

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text: the

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text: the

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text: A

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text: and

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text: k

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text: eﬀects

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text: lepton

text: distribution.

text: Figure

text: shows

text: the

text: phase

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text: density

text: distributions

text: f(x,

text: p

text: of

text: the

text: electrons

text: x

text: and

text: positrons.

text: The

text: overlap

text: layer

text: of

text: both

text: clouds

text: spans

text: the

text: interval

text: x

text: The

text: counterstreaming

text: clouds

text: have

text: not

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text: merged

text: along

text: p

text: However,

text: the

text: substantial

text: particle

text: x

text: acceleration

text: demonstrates

text: that

text: the

text: instability

text: is

text: about

text: to

text: saturate.

text: The

text: density

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text: the

text: overlap

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text: twice

text: that

text: of

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text: it.

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text: Roberts

text: and

text: the

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text: Sλ

text: xk

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text: XXV European Cosmic Ray Symposium, Turin, Sept. 4-9 2016 1 Prospects for measuring the neutrino mass hierarchy with KM3NeT/ORCA J. Hofest¨adt on behalf of the KM3NeT Collaboration Erlangen Centre for Astroparticle Physics, Friedrich-Alexander University of Erlangen-Nu¨rnberg, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany ORCA (Oscillation Research with Cosmics in the Abyss) is the low-energy branch of KM3NeT, the next-generation research infrastructure hosting underwater Cherenkov detectors in the Mediter- ranean Sea. ORCA’s primary goal is the determination of the neutrino mass hierarchy by measuring the matter-induced modiﬁcations on the oscillation probabilities of few-GeV atmospheric neutrinos. The ORCA detector design foresees a dense conﬁguration of KM3NeT neutrino detection technol- ogy, optimised for measuring the interactions of neutrinos in the energy range of 3–20 GeV. To be deployed at the French KM3NeT site, ORCA’s multi-PMT optical modules will exploit the excel- lent optical properties of deep-sea water to accurately reconstruct both shower-like (mostly electron neutrino) and track-like (mostly muon neutrino) events in order to collect a high-statistics sample of few-GeV neutrino events. This contribution reviews the methods and technology of the ORCA detector, and discusses the prospects for measuring the neutrino mass hierarchy as well as the potential to improve the measurement precision on other oscillation parameters. I. INTRODUCTION few-GeV atmospheric neutrinos that have traversed the Earth towards the detector [2]. Due to matter- induced modiﬁcations on the oscillation probabilities A variety of experiments with solar, atmospheric, in conjunction with diﬀerent cross-sections and atmo- reactor and accelerator neutrinos, spanning energies spheric neutrino ﬂuxes for neutrinos and antineutri- from MeV up to tens of GeV, demonstrated unam- nos, the expected event rates of neutrinos in the en- biguously that neutrinos change from one ﬂavour to ergy regime of 3–20 GeV are diﬀerent for NH and IH. another during propagation. Neutrino oscillations im- Next-generation experiments, such as ply non-zero neutrino masses, and that the masses KM3NeT/ORCA [3], PINGU [4] and Hyper- of the three neutrino states are diﬀerent. In the Kamiokande [5], are planned to perform this standard 3-neutrino scheme, the mixing matrix re- measurement with megaton-scale water/ice-based lating the neutrino ﬂavour eigenstates (ν , ν , ν ) e µ µ Cherenkov detectors. to the mass eigenstates (ν , ν , ν ) is parameterised 1 2 3 in terms of three mixing angles θ , θ and θ , In the following, the prospects for measuring the 12 13 23 and a CP-violating phase δ . Oscillation experi- neutrino mass hierarchy with ORCA (Oscillation Re- CP ments are mostly sensitive to mass-squared diﬀerences search with Cosmics in the Abyss) are presented, and − ∆m2 = m2 m2 (i, j = 1, 2, 3). Global ﬁts of avail- the potential to improve the measurement precision ableijdata iform aj coherent picture and provide the on θ23 and ∆m232 is discussed. values of these oscillation parameters with reasonable This contribution is mainly based on the ‘Letter of precision [1]. Intent for KM3NeT 2.0’ [3]. An open question is the so-called neutrino mass hi- II. THE KM3NET/ORCA DETECTOR erarchy (NMH). It refers to the ordering of the neu- trino mass eigenstates, which is either ν < ν < ν The KM3NeT detector design builds on the experi- 1 2 3 (normal hierarchy, NH) or ν < ν < ν (inverted ence of the successful deployment and operation of the 3 1 2 hierarchy, IH). The ordering of the ﬁrst two closely ANTARES detector [6], which has demonstrated the spaced mass eigenstates, ν < ν , is known from so- feasibility of measuring neutrinos with a large-volume 1 2 lar neutrino physics. Further yet unknown neutrino Cherenkov detector in the deep sea. The detection properties are: the value of δ , the absolute masses, principle is that of a 3-dimensional array of photo- CP the Dirac/Majorana nature of neutrinos. Knowing the sensors that register the Cherenkov light induced by NMH is important for constraining the models that charged particles produced in a neutrino-induced in- seek to explain the origin of mass in the leptonic sector teraction. From the arrival time of the Cherenkov and will allow to optimise the information obtained photons (nanosecond precision) and the position of ∼ from other neutrino experiments (targeting δ , ab- the sensors ( 10 cm precision), the energy and direc- CP solute neutrino masses and neutrinoless double-beta tion of the incoming neutrino, as well as other parame- decays). In addition, the NMH has a signiﬁcant im- ters of the neutrino interaction, can be reconstructed. pact on the measurement precision of the oscillation A key KM3NeT technology is the Digital Opti- parameters. cal Module (DOM), a pressure-resistant glass sphere The NMH can be determined by measuring the en- housing 31 3-inch PMTs and their associated elec- ergy and zenith angle dependent oscillation pattern of tronics. This multi-PMT design oﬀers several im- eConf C16-09-04.3

text: XXV

text: European

text: Cosmic

text: Ray

text: Symposium,

text: Turin,

text: Sept.

text: Prospects

text: for

text: measuring

text: the

text: neutrino

text: mass

text: hierarchy

text: with

text: J.

text: Hofest¨adt

text: on

text: behalf

text: of

text: the

text: Collaboration

text: Erlangen

text: Centre

text: for

text: Astroparticle

text: Physics,

text: Friedrich-Alexander

text: University

text: of

text: Erlangen-Nu¨rnberg,

text: Erwin-Rommel-Str.

text: Erlangen,

text: Germany

text: ORCA

text: (Oscillation

text: Research

text: with

text: Cosmics

text: in

text: the

text: Abyss)

text: is

text: the

text: low-energy

text: branch

text: of

text: the

text: next-generation

text: research

text: infrastructure

text: hosting

text: underwater

text: Cherenkov

text: detectors

text: in

text: the

text: Mediter-

text: ranean

text: Sea.

text: ORCA’s

text: primary

text: goal

text: is

text: the

text: determination

text: of

text: the

text: neutrino

text: mass

text: hierarchy

text: by

text: measuring

text: the

text: matter-induced

text: modiﬁcations

text: on

text: the

text: oscillation

text: probabilities

text: of

text: few-GeV

text: atmospheric

text: neutrinos.

text: The

text: ORCA

text: detector

text: design

text: foresees

text: a

text: dense

text: conﬁguration

text: of

text: neutrino

text: detection

text: technol-

text: ogy,

text: optimised

text: for

text: measuring

text: the

text: interactions

text: of

text: neutrinos

text: in

text: the

text: energy

text: range

text: of

text: GeV.

text: To

text: be

text: deployed

text: at

text: the

text: French

text: site,

text: ORCA’s

text: multi-PMT

text: optical

text: modules

text: will

text: exploit

text: the

text: excel-

text: lent

text: optical

text: properties

text: of

text: deep-sea

text: water

text: to

text: accurately

text: reconstruct

text: both

text: shower-like

text: (mostly

text: electron

text: neutrino)

text: and

text: track-like

text: (mostly

text: muon

text: neutrino)

text: events

text: in

text: order

text: to

text: collect

text: a

text: high-statistics

text: sample

text: of

text: few-GeV

text: neutrino

text: events.

text: This

text: contribution

text: reviews

text: the

text: methods

text: and

text: technology

text: of

text: the

text: ORCA

text: detector,

text: and

text: discusses

text: the

text: prospects

text: for

text: measuring

text: the

text: neutrino

text: mass

text: hierarchy

text: as

text: well

text: as

text: the

text: potential

text: to

text: improve

text: the

text: measurement

text: precision

text: on

text: other

text: oscillation

text: parameters.

text: I.

text: INTRODUCTION

text: few-GeV

text: atmospheric

text: neutrinos

text: that

text: have

text: traversed

text: the

text: Earth

text: towards

text: the

text: detector

text: Due

text: to

text: matter-

text: induced

text: modiﬁcations

text: on

text: the

text: oscillation

text: probabilities

text: A

text: variety

text: of

text: experiments

text: with

text: solar,

text: atmospheric,

text: in

text: conjunction

text: with

text: diﬀerent

text: cross-sections

text: and

text: atmo-

text: reactor

text: and

text: accelerator

text: neutrinos,

text: spanning

text: energies

text: spheric

text: neutrino

text: ﬂuxes

text: for

text: neutrinos

text: and

text: antineutri-

text: from

text: MeV

text: up

text: to

text: tens

text: of

text: GeV,

text: demonstrated

text: unam-

text: nos,

text: the

text: expected

text: event

text: rates

text: of

text: neutrinos

text: in

text: the

text: en-

text: biguously

text: that

text: neutrinos

text: change

text: from

text: one

text: ﬂavour

text: to

text: ergy

text: regime

text: of

text: GeV

text: are

text: diﬀerent

text: for

text: NH

text: and

text: IH.

text: another

text: during

text: propagation.

text: Neutrino

text: oscillations

text: im-

text: Next-generation

text: experiments,

text: such

text: as

text: ply

text: non-zero

text: neutrino

text: masses,

text: and

text: that

text: the

text: masses

text: PINGU

text: and

text: Hyper-

text: of

text: the

text: three

text: neutrino

text: states

text: are

text: diﬀerent.

text: In

text: the

text: Kamiokande

text: are

text: planned

text: to

text: perform

text: this

text: standard

text: scheme,

text: the

text: mixing

text: matrix

text: re-

text: measurement

text: with

text: megaton-scale

text: water/ice-based

text: lating

text: the

text: neutrino

text: ﬂavour

text: eigenstates

text: (ν

text: ν

text: ν

text: e

text: µ

text: µ

text: Cherenkov

text: detectors.

text: to

text: the

text: mass

text: eigenstates

text: (ν

text: ν

text: ν

text: is

text: parameterised

text: in

text: terms

text: of

text: three

text: mixing

text: angles

text: θ

text: θ

text: and

text: θ

text: In

text: the

text: following,

text: the

text: prospects

text: for

text: measuring

text: the

text: and

text: a

text: CP-violating

text: phase

text: δ

text: Oscillation

text: experi-

text: neutrino

text: mass

text: hierarchy

text: with

text: ORCA

text: (Oscillation

text: Re-

text: CP

text: ments

text: are

text: mostly

text: sensitive

text: to

text: mass-squared

text: diﬀerences

text: search

text: with

text: Cosmics

text: in

text: the

text: Abyss)

text: are

text: presented,

text: and

text: (i,

text: j

text: Global

text: ﬁts

text: of

text: avail-

text: the

text: potential

text: to

text: improve

text: the

text: measurement

text: precision

text: ableijdata

text: iform

text: aj

text: coherent

text: picture

text: and

text: provide

text: the

text: on

text: and

text: is

text: discussed.

text: values

text: of

text: these

text: oscillation

text: parameters

text: with

text: reasonable

text: This

text: contribution

text: is

text: mainly

text: based

text: on

text: the

text: ‘Letter

text: of

text: precision

text: Intent

text: for

text: An

text: open

text: question

text: is

text: the

text: so-called

text: neutrino

text: mass

text: hi-

text: II.

text: THE

text: DETECTOR

text: erarchy

text: (NMH).

text: It

text: refers

text: to

text: the

text: ordering

text: of

text: the

text: neu-

text: trino

text: mass

text: eigenstates,

text: which

text: is

text: either

text: ν

text: ν

text: ν

text: The

text: detector

text: design

text: builds

text: on

text: the

text: experi-

text: (normal

text: hierarchy,

text: NH)

text: or

text: ν

text: ν

text: ν

text: (inverted

text: ence

text: of

text: the

text: successful

text: deployment

text: and

text: operation

text: of

text: the

text: hierarchy,

text: IH).

text: The

text: ordering

text: of

text: the

text: ﬁrst

text: two

text: closely

text: ANTARES

text: detector

text: which

text: has

text: demonstrated

text: the

text: spaced

text: mass

text: eigenstates,

text: ν

text: ν

text: is

text: known

text: from

text: so-

text: feasibility

text: of

text: measuring

text: neutrinos

text: with

text: a

text: large-volume

text: lar

text: neutrino

text: physics.

text: Further

text: yet

text: unknown

text: neutrino

text: Cherenkov

text: detector

text: in

text: the

text: deep

text: sea.

text: The

text: detection

text: properties

text: are:

text: the

text: value

text: of

text: δ

text: the

text: absolute

text: masses,

text: principle

text: is

text: that

text: of

text: a

text: array

text: of

text: photo-

text: CP

text: the

text: Dirac/Majorana

text: nature

text: of

text: neutrinos.

text: Knowing

text: the

text: sensors

text: that

text: register

text: the

text: Cherenkov

text: light

text: induced

text: by

text: NMH

text: is

text: important

text: for

text: constraining

text: the

text: models

text: that

text: charged

text: particles

text: produced

text: in

text: a

text: neutrino-induced

text: in-

text: seek

text: to

text: explain

text: the

text: origin

text: of

text: mass

text: in

text: the

text: leptonic

text: sector

text: teraction.

text: From

text: the

text: arrival

text: time

text: of

text: the

text: Cherenkov

text: and

text: will

text: allow

text: to

text: optimise

text: the

text: information

text: obtained

text: photons

text: (nanosecond

text: precision)

text: and

text: the

text: position

text: of

text: from

text: other

text: neutrino

text: experiments

text: (targeting

text: δ

text: ab-

text: the

text: sensors

text: cm

text: precision),

text: the

text: energy

text: and

text: direc-

text: CP

text: solute

text: neutrino

text: masses

text: and

text: neutrinoless

text: double-beta

text: tion

text: of

text: the

text: incoming

text: neutrino,

text: as

text: well

text: as

text: other

text: parame-

text: decays).

text: In

text: addition,

text: the

text: NMH

text: has

text: a

text: signiﬁcant

text: im-

text: ters

text: of

text: the

text: neutrino

text: interaction,

text: can

text: be

text: reconstructed.

text: pact

text: on

text: the

text: measurement

text: precision

text: of

text: the

text: oscillation

text: A

text: key

text: technology

text: is

text: the

text: Digital

text: Opti-

text: parameters.

text: cal

text: Module

text: (DOM),

text: a

text: pressure-resistant

text: glass

text: sphere

text: The

text: NMH

text: can

text: be

text: determined

text: by

text: measuring

text: the

text: en-

text: housing

text: PMTs

text: and

text: their

text: associated

text: elec-

text: ergy

text: and

text: zenith

text: angle

text: dependent

text: oscillation

text: pattern

text: of

text: tronics.

text: This

text: multi-PMT

text: design

text: oﬀers

text: several

text: im-

text: eConf


text: 2 XXV European Cosmic Ray Symposium, Turin, Sept. 4-9 2016 trino sources with the ARCA detector [8], which will be deployed oﬀshore from Sicily, Italy. The main dif- ference between both detector designs is the density of photosensors, which is optimised for the study of neu- trinos in the few-GeV (ORCA) and TeV-PeV (ARCA) energy ranges. III. EXPECTED DETECTOR PERFORMANCE The key parameters for the NMH determination are the eﬀective mass of the detector and the experimental resolutions for the energy E and zenith angle θ of ν ν the incoming neutrino. Detailed Monte Carlo simulations have been per- formed using GENIE [9] for simulating neutrino in- teractions and GEANT-based simulation packages [10, 11] for particle propagation and Cherenkov pho- ton generation. Optical background from 40K decays FIG. 1: Photograph of a DOM (left) and schematic draw- in the seawater as well as the background from down- ing of an detection string (right). going atmospheric muons is taken into account. Fur- ther details are given in [3]. Two distinct event topologies are considered: tracks provements compared to traditional optical modules and showers. Showers are initiated by energetic hosting only a single large PMT (for example in electrons and hadrons emerging from the neutrino ANTARES), most notably: larger photocathode area, interaction, and develop over relatively short dis- wider ﬁeld of view, directional information and dy- tances. Muons produce elongated tracks in the de- namic range. The DOMs are arranged in strings held tector. Therefore, track-like events are induced by (cid:44) (cid:45) vertically by a buoy and anchored to the seabed. Fig- ν charged-current (CC) interactions, as well as µ (cid:44) (cid:45) ure 1 shows a DOM and a detection string. ν CC interactions with muonic tau decays. All τ In its current design, the ORCA detector will com- other neutrino-induced events are called shower-like, (cid:44) (cid:45) (cid:44) (cid:45) prise 115 such detection strings. Each string com- i.e. νe CC events, νe,µ,τ neutral-current events and (cid:44) (cid:45) prises 18 DOMs with a vertical spacing of about 9 m. ντ CC events with non-muonic τ decays. The horizontal spacing between adjacent strings is Dedicated reconstruction strategies for track-like roughly 20 m. The instrumented mass is about 6 Mton and shower-like events, as well as an event topology of seawater. This detector conﬁguration is the out- classiﬁcation algorithm, have been developed and are come of a optimisation study using the NMH sensi- described in [3]. The energy resolution is Gaussian- ≈ tivity as ﬁgure of merit. The proposed detector could like with σ /E 25%. The median zenith angle be built in three years, with an investment budget of resolution iEsνaboνut 5◦ for (cid:44)ν(cid:45) CC and (cid:44)ν(cid:45) CC events e µ about 45 Me [7]. with E = 10 GeV. Due to the long scattering length ν The ORCA detector will be deployed at the French of light in deep-sea water, the reconstructions are able (cid:44) (cid:45) KM3NeT site at a depth of 2450 m. The site is about to ﬁnd the lepton (e, µ) in ν CC events and are e,µ 40 km oﬀshore from Toulon and about 10 km west of therefore able to gain access to the interaction inelas- the operating ANTARES detector. ticity y. This allows a statistical separation of ν and The construction of the infrastructure has already ν interactions to further add to the NMH sensitivity started. The ﬁrst main electro-optical cable and [12]. This possibility has not yet been exploited in the ﬁrst junction box, needed to connect the detec- the estimated NMH sensitivity presented below. As tion strings, have been successfully deployed and con- shown in [13], the energy resolution is dominated by nected. The ﬁrst detection string is foreseen to be intrinsic light yield ﬂuctuations in the hadronic shower deployed in early 2017. An array comprising 7 detec- and the direction resolution is limited by the kine- tion strings is funded and expected to be concluded matic scattering angle between the outgoing lepton and operational by the end of 2017. It will serve to and the incoming neutrino. demonstrate the feasibility of the measurement and to The purity of the event topology classiﬁcation is validate and optimise the detector design. The full- about 90% (70%) for (cid:44)ν(cid:45) CC ((cid:44)ν(cid:45) CC) events with e µ size ORCA detector comprising 115 detection strings E = 10 GeV. The same event classiﬁcation algorithm ν could be operational towards 2020. also rejects downgoing atmospheric muons that are Within KM3NeT, the same technology is employed mis-reconstructed as upgoing. A contamination of less also for the search for high-energy astrophysical neu- than a few percent of atmospheric muons in the ﬁnal eConf C16-09-04.3 ##LTFigure## ##LTFigure## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine## ##LTLine##

text: XXV

text: European

text: Cosmic

text: Ray

text: Symposium,

text: Turin,

text: Sept.

text: trino

text: sources

text: with

text: the

text: ARCA

text: detector

text: which

text: will

text: be

text: deployed

text: oﬀshore

text: from

text: Sicily,

text: Italy.

text: The

text: main

text: dif-

text: ference

text: between

text: both

text: detector

text: designs

text: is

text: the

text: density

text: of

text: photosensors,

text: which

text: is

text: optimised

text: for

text: the

text: study

text: of

text: neu-

text: trinos

text: in

text: the

text: few-GeV

text: (ORCA)

text: and

text: TeV-PeV

text: (ARCA)

text: energy

text: ranges.

text: III.

text: EXPECTED

text: DETECTOR

text: PERFORMANCE

text: The

text: key

text: parameters

text: for

text: the

text: NMH

text: determination

text: are

text: the

text: eﬀective

text: mass

text: of

text: the

text: detector

text: and

text: the

text: experimental

text: resolutions

text: for

text: the

text: energy

text: E

text: and

text: zenith

text: angle

text: θ

text: of

text: ν

text: ν

text: the

text: incoming

text: neutrino.

text: Detailed

text: Monte

text: Carlo

text: simulations

text: have

text: been

text: per-

text: formed

text: using

text: GENIE

text: for

text: simulating

text: neutrino

text: in-

text: teractions

text: and

text: GEANT-based

text: simulation

text: packages

text: for

text: particle

text: propagation

text: and

text: Cherenkov

text: pho-

text: ton

text: generation.

text: Optical

text: background

text: from

text: decays

text: FIG.

text: Photograph

text: of

text: a

text: DOM

text: (left)

text: and

text: schematic

text: draw-

text: in

text: the

text: seawater

text: as

text: well

text: as

text: the

text: background

text: from

text: down-

text: ing

text: of

text: an

text: detection

text: string

text: (right).

text: going

text: atmospheric

text: muons

text: is

text: taken

text: into

text: account.

text: Fur-

text: ther

text: details

text: are

text: given

text: in

text: Two

text: distinct

text: event

text: topologies

text: are

text: considered:

text: tracks

text: provements

text: compared

text: to

text: traditional

text: optical

text: modules

text: and

text: showers.

text: Showers

text: are

text: initiated

text: by

text: energetic

text: hosting

text: only

text: a

text: single

text: large

text: PMT

text: (for

text: example

text: in

text: electrons

text: and

text: hadrons

text: emerging

text: from

text: the

text: neutrino

text: ANTARES),

text: most

text: notably:

text: larger

text: photocathode

text: area,

text: interaction,

text: and

text: develop

text: over

text: relatively

text: short

text: dis-

text: wider

text: ﬁeld

text: of

text: view,

text: directional

text: information

text: and

text: dy-

text: tances.

text: Muons

text: produce

text: elongated

text: tracks

text: in

text: the

text: de-

text: namic

text: range.

text: The

text: DOMs

text: are

text: arranged

text: in

text: strings

text: held

text: tector.

text: Therefore,

text: track-like

text: events

text: are

text: induced

text: by

text: vertically

text: by

text: a

text: buoy

text: and

text: anchored

text: to

text: the

text: seabed.

text: Fig-

text: ν

text: charged-current

text: (CC)

text: interactions,

text: as

text: well

text: as

text: µ

text: ure

text: shows

text: a

text: DOM

text: and

text: a

text: detection

text: string.

text: ν

text: CC

text: interactions

text: with

text: muonic

text: tau

text: decays.

text: All

text: τ

text: In

text: its

text: current

text: design,

text: the

text: ORCA

text: detector

text: will

text: com-

text: other

text: neutrino-induced

text: events

text: are

text: called

text: shower-like,

text: prise

text: such

text: detection

text: strings.

text: Each

text: string

text: com-

text: i.e.

text: νe

text: CC

text: events,

text: νe,µ,τ

text: neutral-current

text: events

text: and

text: prises

text: DOMs

text: with

text: a

text: vertical

text: spacing

text: of

text: about

text: m.

text: ντ

text: CC

text: events

text: with

text: non-muonic

text: τ

text: decays.

text: The

text: horizontal

text: spacing

text: between

text: adjacent

text: strings

text: is

text: Dedicated

text: reconstruction

text: strategies

text: for

text: track-like

text: roughly

text: m.

text: The

text: instrumented

text: mass

text: is

text: about

text: Mton

text: and

text: shower-like

text: events,

text: as

text: well

text: as

text: an

text: event

text: topology

text: of

text: seawater.

text: This

text: detector

text: conﬁguration

text: is

text: the

text: out-

text: classiﬁcation

text: algorithm,

text: have

text: been

text: developed

text: and

text: are

text: come

text: of

text: a

text: optimisation

text: study

text: using

text: the

text: NMH

text: sensi-

text: described

text: in

text: The

text: energy

text: resolution

text: is

text: Gaussian-

text: tivity

text: as

text: ﬁgure

text: of

text: merit.

text: The

text: proposed

text: detector

text: could

text: like

text: with

text: σ

text: /E

text: The

text: median

text: zenith

text: angle

text: be

text: built

text: in

text: three

text: years,

text: with

text: an

text: investment

text: budget

text: of

text: resolution

text: iEsνaboνut

text: 5◦

text: for

text: CC

text: and

text: CC

text: events

text: e

text: µ

text: about

text: Me

text: with

text: E

text: GeV.

text: Due

text: to

text: the

text: long

text: scattering

text: length

text: ν

text: The

text: ORCA

text: detector

text: will

text: be

text: deployed

text: at

text: the

text: French

text: of

text: light

text: in

text: deep-sea

text: water,

text: the

text: reconstructions

text: are

text: able

text: site

text: at

text: a

text: depth

text: of

text: m.

text: The

text: site

text: is

text: about

text: to

text: ﬁnd

text: the

text: lepton

text: (e,

text: µ)

text: in

text: ν

text: CC

text: events

text: and

text: are

text: e,µ

text: km

text: oﬀshore

text: from

text: Toulon

text: and

text: about

text: km

text: west

text: of

text: therefore

text: able

text: to

text: gain

text: access

text: to

text: the

text: interaction

text: inelas-

text: the

text: operating

text: ANTARES

text: detector.

text: ticity

text: y.

text: This

text: allows

text: a

text: statistical

text: separation

text: of

text: ν

text: and

text: The

text: construction

text: of

text: the

text: infrastructure

text: has

text: already

text: ν

text: interactions

text: to

text: further

text: add

text: to

text: the

text: NMH

text: sensitivity

text: started.

text: The

text: ﬁrst

text: main

text: electro-optical

text: cable

text: and

text: This

text: possibility

text: has

text: not

text: yet

text: been

text: exploited

text: in

text: the

text: ﬁrst

text: junction

text: box,

text: needed

text: to

text: connect

text: the

text: detec-

text: the

text: estimated

text: NMH

text: sensitivity

text: presented

text: below.

text: As

text: tion

text: strings,

text: have

text: been

text: successfully

text: deployed

text: and

text: con-

text: shown

text: in

text: the

text: energy

text: resolution

text: is

text: dominated

text: by

text: nected.

text: The

text: ﬁrst

text: detection

text: string

text: is

text: foreseen

text: to

text: be

text: intrinsic

text: light

text: yield

text: ﬂuctuations

text: in

text: the

text: hadronic

text: shower

text: deployed

text: in

text: early

text: An

text: array

text: comprising

text: detec-

text: and

text: the

text: direction

text: resolution

text: is

text: limited

text: by

text: the

text: kine-

text: tion

text: strings

text: is

text: funded

text: and

text: expected

text: to

text: be

text: concluded

text: matic

text: scattering

text: angle

text: between

text: the

text: outgoing

text: lepton

text: and

text: operational

text: by

text: the

text: end

text: of

text: It

text: will

text: serve

text: to

text: and

text: the

text: incoming

text: neutrino.

text: demonstrate

text: the

text: feasibility

text: of

text: the

text: measurement

text: and

text: to

text: The

text: purity

text: of

text: the

text: event

text: topology

text: classiﬁcation

text: is

text: validate

text: and

text: optimise

text: the

text: detector

text: design.

text: The

text: full-

text: about

text: for

text: CC

text: CC)

text: events

text: with

text: e

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