appearance with KM3NeT/ORCA T. Eberl, S. Hallmann*, J. Hofestdt - - PowerPoint PPT Presentation

• T. Eberl, S. Hallmann*, J. Hofestädt

for the KM3NeT Collaboration 35th ICRC, Busan, South Korea, 15/07/2017 *speaker

ντ appearance with KM3NeT/ORCA

ICRC 2017 – 15/07/2017 – S. Hallmann (KM3NeT Collaboration) 2

KM3NeT/ORCA

Deep-sea neutrino detector consisting of a 3D array of Digital Optical Modules (DOMs) with 31 PMTs per DOM Dense instrumentation: ~ 20m horizontal spacing ~ 9m vertical spacing between DOMs Total: 2078 DOMs Instrumented volume: ~6 Mm³ see the Letter of Intent for KM3NeT 2.0 [J.Phys.G43 (2016) no.8, 084001] and the talk by A. Kouchner in this session for more information Recent developments in detector layout, trigger and reconstruction performance will improve the sensitivity presented here. A detector to study oscillations of the atmospheric neutrino flux (νe, νμ)

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Oscillation of atmospheric neutrinos

[oscillation probabilities: https://github.com/joaoabcoelho/OscProb] → Broad oscillation maximum from νμ → ντ at ~25 GeV for upward- going neutrinos → No large modulation due to matter efgects Region of interest for determination of neutrino mass ordering

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(Dis)appearance measurements

Broad oscillation maximum at ~25 GeV can be used to study

• dis-appearance of νμ

→ performed and ongoing measurements by many experiments (NOvA, T2K, SuperK, IceCube, ANTARES, …)

• appearance of ντ

→ challenging due to

• energy threshold for τ production (~3.4 GeV)
• prompt τ decay with similar signatures as other interaction channels

[Rev. Mod. Phys. 84, 1307 (2012)] ∟ I. Salvadori, PoS(ICRC2017)1169, poster board 152 ∟A. Habig, PoS(ICRC2017)1168, poster board 151

ICRC 2017 – 15/07/2017 – S. Hallmann (KM3NeT Collaboration) 5

Why are we interested in ντ`s?

• ντ channel currently least constrained

→ only non-appearance already excluded → normalisation not well determined

• 3x3 neutrino mixing via the PMNS matrix is assumed unitary

→ true, if the current picture of 3 flavours is complete → deviations from unitarity are an indirect evidence for new physics (sterile neutrinos,…)

[Phys. Rev. Lett. 115 (2015), 121802]

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Normalisation determination

[Phys. Rev. Lett. 115 (2015), 121802] [Phys. Rev. Lett. 110 (2013), 181802]

Current measurements:

• Able to exclude non-appearance
• Measured central values are high
• Large uncertainty on normalisation due to low statistics

OPERA: event-by-event vertex resolution, >5σ with 5 events Super K: statistical basis, tens of events per year using multivariate analysis Bands: 90% confidence level

ICRC 2017 – 15/07/2017 – S. Hallmann (KM3NeT Collaboration) 7

Normalisation determination

[Phys. Rev. Lett. 115 (2015), 121802] [Phys. Rev. Lett. 110 (2013), 181802]

Future experiments: Similar sensitivity

• Optimised for mass hierarchy studies (3-10 GeV range)
• Large effective volume at tau-appearance energies → large statistics
• More stringent determination of normalisation possible

Bands: 90% confidence level

[M. Larson (IceCube Coll.), Neutrino2016] [IceCube-Gen2 Coll., arXiv:1607.0267] this work

IceCube DeepCore:

• Sensitivity to exclude non-appearance on the 5σ-level

ICRC 2017 – 15/07/2017 – S. Hallmann (KM3NeT Collaboration) 8

Measurement on statistical basis

• Small kink produced by the τ lepton impossible to see for large volume

Cherenkov detectors → cannot measure ντ appearance on event-by-event basis Particle ID in KM3NeT/ORCA: 70% (90%) of νμ (νμ) identifjed as track >80% of ντ identifjed as shower → appearance measured on statistical basis by excess in the shower channel [J.Phys.G43 (2016) no.8, 084001]

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selected up- going shower events year νe C C νμ C C ντ C C ν N C 17k 11k 2.5k 6k

Relevant energy and zenith range

Relevant range: up-going and 10 GeV – 30 GeV energy Statistical per-bin significance in the shower channel: N(ντ CC)

√N(all neutrino interactions)

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Multi-parameter fitting

Take into account:

• uncertainties on oscillation

parameters

• uncertainties on atmospheric

neutrino fluxes (nuisance parameters) The fit result is robust against the

• ctant of θ23 and the assumed true

neutrino mass ordering → measurement is possible before knowing the true mass ordering Degradation due to nuisance parameters is moderate

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KM3NeT/ORCA sensitivity

→ Non-appearance excluded (5σ CL) after two months of operation → After 1 year of operation: ντ normalisation determined better than ±15% (90% CL) / ±40% (5σ CL) Expectation from 3x3 unitary mixing No ντ appearance

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Summary

Measurement of ντ appearance possible with KM3NeT/ORCA:

• Exclusion of non-appearance will be confjrmed within fjrst

months of operation → one of the early physics results of KM3NeT/ORCA

• In the longer run ντ normalisation can be determined with

high precision → possibility to test unitarity of 3x3 neutrino mixing Normalisation fjt is robust against

• uncertainties in neutrino oscillation

(mass ordering, octant of θ23)

• further uncertainties (nuisance parameters)

Thank you for your attention!

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