New Measurement of the Flavor Composition of High-Energy Neutrino - PowerPoint PPT Presentation

New Measurement of the Flavor Composition of High-Energy Neutrino Events with Contained Vertices in IceCube TeVPA 2018 Juliana Stachurska

Motivation • IceCube observed astrophysical neutrinos, and identified first source • Measure flavor composition ? → learn about environment at production sites • Neutrino mixing → flavor composition at source ≠ flavor composition on Earth • Pion decay: 
 ν e : ν μ : ν τ =1:2:0 at source → ν e : ν μ : ν τ ≈ 1:1:1 on Earth • Other source flavor compositions possible 2 Juliana Stachurska

Flavor Composition ν e : ν µ : ν τ at source HESE with ternary PID 0.0 IceCube APJ 2015 1.0 0:1:0 20 1:2:0 18 0.2 1:0:0 IceCube 0.8 16 Preliminary ν τ F − 2 ∆ log(Likelihood) r f a 14 o 0.4 c t n i o o 0.6 12 n i t c o a f 10 r 0.6 F ν µ 8 0.4 6 0.8 6 68 % 68 % 8 0.2 4 95 % 95 % 2 1.0 0.0 0 0.0 0.2 0.4 0.6 0.8 1.0 Fraction of ν e M. Usner, PoS(ICRC2017)974 3 Juliana Stachurska

Flavor Composition • Flavor composition measurement needs tau neutrino sensitivity • Vanishing atmospheric component → tau neutrinos are astrophysical neutrinos! • No tau neutrino inter- 
 ν e : ν µ : ν τ at source HESE with ternary PID 0.0 IceCube APJ 2015 1.0 0:1:0 20 actions in IceCube 
 1:2:0 18 0.2 observed in 6 
 1:0:0 IceCube 0.8 16 Preliminary ν τ years of HESE data F − 2 ∆ log(Likelihood) r f a 14 o 0.4 c t n • Data reprocessing after recali- 
 i o o 0.6 12 n i t c o a f 10 bration of the detector for 7.5 
 r 0.6 F ν µ 8 0.4 year HESE analysis + improved 
 6 0.8 software, likelihood, ice model 68 % 6 68 % 8 0.2 4 • Now integral part of HESE, using 
 95 % 95 % 2 1.0 ternary topology for event 
 0.0 0 0.0 0.2 0.4 0.6 0.8 1.0 classification 
 Fraction of ν e M. Usner, PoS(ICRC2017)974 3 Juliana Stachurska

Double Cascade Signal • ν τ interaction • Charged current (71%) • Tau decays into hadrons / electrons (83%) • Mean length: 50m x energy/1PeV ν τ τ had./ ν τ ν τ em. had simulated 10PeV Double Cascade event 4 Juliana Stachurska

Background Cascades: All nc interactions ν e cc interactions ν τ cc interactions with unresolvable lengths Tracks: ν μ cc interactions Atmospheric muons ν τ cc interactions with muonic tau decay 5 Juliana Stachurska

Analysis Overview All HESE events in 7.5 years of data above 60 TeV 6 Juliana Stachurska

Analysis Overview All HESE events in 7.5 years of data above 60 TeV Observables from direct double-cascade reconstruction 6 Juliana Stachurska

Analysis Overview All HESE events in 7.5 years of data above 60 TeV Observables from direct double-cascade reconstruction m 0 1 > 6 Juliana Stachurska

Analysis Overview All HESE events in 7.5 years of data above 60 TeV Observables from direct double-cascade reconstruction m 0 1 > Single cascade Track sample with ν τ – sample with not well- cc interactions creating Double cascade sample: 
 reconstructable ν τ – μ , ν μ – and atm. μ – ν τ + N τ + hadrons >10m cc interactions, all tracks hadrons / electrons other cascades 6 Juliana Stachurska

Analysis Overview All HESE events in 7.5 years of data above 60 TeV Observables from direct double-cascade reconstruction m 0 1 > Single cascade Track sample with ν τ – sample with not well- cc interactions creating Double cascade sample: 
 reconstructable ν τ – μ , ν μ – and atm. μ – ν τ + N τ + hadrons >10m cc interactions, all tracks hadrons / electrons other cascades Flavor composition 6 Juliana Stachurska

Selection HESE event class track single double energy confinement cut energy asymmetry cut single double track Topology ID sample E 1 E 2 ν τ ν τ length 7 7 Juliana Stachurska

Selection HESE event class track single double energy confinement cut (E 1,C +E 2,C )/(E 1 +E 2 ) ≥ 0.99 energy asymmetry cut single double track Topology ID sample E 1 E 2 E 1 E 2 ν τ ν μ μ ν τ E 1,C E 2,C E 1,C E 2,C 7 7 Juliana Stachurska

Selection HESE event class track single double energy confinement cut energy asymmetry cut -0.98 ≤ (E 1 -E 2 )/(E 1 +E 2 ) ≤ 0.3 single double track Topology ID sample E 1 E 2 E 1 E 2 ν τ ν e ν τ length length 7 7 Juliana Stachurska

Results • 2 events in Double Cascade bin • Soft spectral index: 2.9 → expect ~2.1 events (~1.4 signal + ~0.7 background) 8 Juliana Stachurska

Results Maximum likelihood flavor composition fit based on 2D histograms: • Zenith & energy for single cascades, tracks • Length & energy for double cascades • Best-fit ν e : ν μ : ν τ = 0.29:0.50:0.21 • Consistent with previous measurements and expectation of ~1:1:1 for astrophysical neutrinos • Zero ν τ flux cannot be excluded • Systematic errors not included 9 Juliana Stachurska

Event #1 (E1-E2)/(E1+E2) = 0.29 single cascade double cascade exp. data reco with bright DOMs reco without bright DOMs 50 160 400 500 bright DOM* bright DOM* Detected Photons 140 350 1.2 PeV 0.6 PeV 40 400 120 300 100 250 30 300 80 200 20 200 60 150 40 100 10 100 20 50 16 m 0 0 0 0 200 • Observed 2012 150 100 • Shows no clear 50 preference between 0 140 a single cascade 120 saturated 100 and double 80 60 cascade hypothesis 40 20 0 50 40 30 20 10 WORK IN PROGRESS 0 * Bright DOMs are excluded from this analysis Time 10 Juliana Stachurska

Event #2 (E1-E2)/(E1+E2) = -0.80 single cascade double cascade exp. data reco with bright DOMs reco without bright DOMs 20 40 120 350 bright DOM* bright DOM* Detected Photons 35 9 TeV 300 100 80 TeV 15 30 250 80 25 200 10 20 60 150 15 40 100 5 10 20 50 5 17 m 0 OM(20, 27): 1506.9 pe 0 0 0 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 10 . 5 10 . 6 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 10 . 9 . 8 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 350 10 . 9 . 8 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 bright DOM* 300 • Observed 2014 250 200 150 • Observed light 100 50 arrival pattern 0 250 bright DOM* 200 clearly favors double 150 cascade hypothesis 100 50 0 100 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 10 . bright DOM* 80 60 40 20 WORK IN PROGRESS 0 * Bright DOMs are excluded from this analysis Time 11 Juliana Stachurska

Energy Asymmetry • Only a straight cut was used • Afterwards all events in Double Cascade bin treated the same regardless of energy asymmetry value • Mainly due to computational issues • Plan: incorporate all information into Energy asymmetry for best-fit spectrum, “tauness” and a ν e : ν μ : ν τ = 1:1:1 composition 12 Juliana Stachurska

Summary • Performed HESE ν τ -induced Double Cascade single cascade double cascade exp. data reco with bright DOMs reco without bright DOMs 20 40 120 350 bright DOM* bright DOM* Detected Photons 35 100 300 15 30 250 80 25 search and flavor composition measurement on 7.5 200 10 20 60 150 15 40 100 5 10 20 5 50 0 0 0 0 OM(20, 27): 1506.9 pe 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 10 . 5 10 . 6 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 10 . 9 . 8 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 350 10 . 9 . 8 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 years of data bright DOM* 300 250 200 150 100 • Now feedback of topology into HESE sample 50 0 250 bright DOM* 200 150 • Improved ice model, likelihood, software 100 50 0 100 9 . 9 10 . 0 10 . 1 10 . 2 10 . 3 10 . 4 10 . bright DOM* • Data reprocessing “Pass 2” 80 60 40 20 • Identified 2 ν τ candidate events WORK IN PROGRESS 0 * Bright DOMs are excluded from this analysis Time =? • One of which shows obvious signatures of a double cascade • A posteriori analysis of the events is ongoing • Incorporate more observables into likelihood • Complementary tau searches using “double pulse” signature are in preparation Updates coming soon - STAY TUNED 13 Juliana Stachurska

BACKUP 14 Juliana Stachurska

Improvements wrt. 6-year analysis • Data reprocessing after recalibration of the detector: • single photon electron (SPE) peak shift → reconstructed energy decreased by ~5% on average • “Pass 2” • Improved software: • minimizer tolerance decreased • various minor bugfixes • Improved ice model “Spice3.2”: • better constrained bulk ice parameters • 25% higher anisotropy • holeice modeling • New “SAY” likelihood: • takes into account limited MC statistics • Now integral part of HESE: • events classified using ternary topology ID based on observables 15 Juliana Stachurska