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

TeVPA 2018 Juliana Stachurska

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

Juliana Stachurska

Motivation

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• 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: 


νe:νμ:ντ =1:2:0 at source → νe:νμ:ντ ≈1:1:1 on Earth

• Other source flavor

compositions possible

Juliana Stachurska

Flavor Composition

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• M. Usner, PoS(ICRC2017)974

0.0 0.2 0.4 0.6 0.8 1.0

Fraction of νe IceCube Preliminary

68 % 95 % 68 % 95 %

νe:νµ:ντ at source

0:1:0 1:2:0 1:0:0

HESE with ternary PID IceCube APJ 2015

0.0 0.2 0.4 0.6 0.8 1.0

F r a c t i

• n
• f

νµ

0.0 0.2 0.4 0.6 0.8 1.0

F r a c t i

• n
• f

ντ

2 4 6 8 10 12 14 16 18 20

−2∆ log(Likelihood)

6 8

Juliana Stachurska

Flavor Composition

3

• M. Usner, PoS(ICRC2017)974

0.0 0.2 0.4 0.6 0.8 1.0

Fraction of νe IceCube Preliminary

68 % 95 % 68 % 95 %

νe:νµ:ντ at source

0:1:0 1:2:0 1:0:0

HESE with ternary PID IceCube APJ 2015

0.0 0.2 0.4 0.6 0.8 1.0

F r a c t i

• n
• f

νµ

0.0 0.2 0.4 0.6 0.8 1.0

F r a c t i

• n
• f

ντ

2 4 6 8 10 12 14 16 18 20

−2∆ log(Likelihood)

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• Flavor composition measurement needs tau neutrino sensitivity
• Vanishing atmospheric component → tau neutrinos are astrophysical

neutrinos!

• No tau neutrino inter-


actions in IceCube 


• bserved in 6 


years of HESE data

• Data reprocessing after recali-


bration of the detector for 7.5 
 year HESE analysis + improved 
 software, likelihood, ice model

• Now integral part of HESE, using


ternary topology for event 
 classification


Juliana Stachurska

Double Cascade Signal

• ντ interaction
• Charged current (71%)
• Tau decays into hadrons / electrons (83%)
• Mean length: 50m x energy/1PeV

4 simulated 10PeV Double Cascade event ντ ντ τ had had./ em. ντ

Juliana Stachurska

Background

5 Cascades: All nc interactions νe cc interactions ντ cc interactions with unresolvable lengths Tracks: νμ cc interactions Atmospheric muons ντ cc interactions with muonic tau decay

Juliana Stachurska

Analysis Overview

6 All HESE events in 7.5 years of data above 60 TeV

Juliana Stachurska

Analysis Overview

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

Juliana Stachurska

Analysis Overview

6 Observables from direct double-cascade reconstruction

> 1 m

All HESE events in 7.5 years of data above 60 TeV

Juliana Stachurska

Analysis Overview

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Track sample with ντ – cc interactions creating μ, νμ – and atm. μ – tracks Double cascade sample: 
 ντ + N τ + hadrons hadrons / electrons

>10m

Single cascade sample with not well- reconstructable ντ – cc interactions, all

• ther cascades

Observables from direct double-cascade reconstruction

> 1 m

All HESE events in 7.5 years of data above 60 TeV

Juliana Stachurska

Analysis Overview

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Track sample with ντ – cc interactions creating μ, νμ – and atm. μ – tracks Double cascade sample: 
 ντ + N τ + hadrons hadrons / electrons

>10m

Single cascade sample with not well- reconstructable ντ – cc interactions, all

• ther cascades

Observables from direct double-cascade reconstruction

> 1 m

Flavor composition All HESE events in 7.5 years of data above 60 TeV

Juliana Stachurska

HESE event class energy confinement cut energy asymmetry cut Topology ID sample single double track double single track

Selection

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length E1 E2 ντ ντ

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Juliana Stachurska

HESE event class energy confinement cut energy asymmetry cut Topology ID sample single double track double single track

Selection

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E1 E2 ντ ντ

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E1 E2

νμ

μ E1,C E2,C (E1,C+E2,C)/(E1+E2)≥0.99 E1,C E2,C

Juliana Stachurska

HESE event class energy confinement cut energy asymmetry cut Topology ID sample single double track double single track

Selection

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length E1 E2 ντ ντ

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length E1 E2 νe

• 0.98≤(E1-E2)/(E1+E2)≤0.3

Juliana Stachurska

Results

• 2 events in Double Cascade bin
• Soft spectral index: 2.9 → expect ~2.1 events (~1.4 signal + ~0.7

background)

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Juliana Stachurska

Results

• Best-fit νe:νμ:ντ = 0.29:0.50:0.21
• Consistent with previous measurements and

expectation of ~1:1:1 for astrophysical neutrinos

• Zero ντ flux cannot be excluded
• Systematic errors not included

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Maximum likelihood flavor composition fit based on 2D histograms:

• Zenith & energy for

single cascades, tracks

• Length & energy for

double cascades

Juliana Stachurska

10 20 30 40 50 20 40 60 80 100 120 140 160 50 100 150 200 250 300 350 400 100 200 300 400 500 20 40 60 80 100 120 140 10 20 30 40 50

saturated

Time Detected Photons

single cascade double cascade

• exp. data

reco with bright DOMs reco without bright DOMs

WORK IN PROGRESS

50 100 150 200

bright DOM* bright DOM*

* Bright DOMs are excluded from this analysis

Event #1

• Observed 2012
• Shows no clear

preference between a single cascade and double cascade hypothesis

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16 m 1.2 PeV 0.6 PeV (E1-E2)/(E1+E2) = 0.29

Juliana Stachurska

10.0 10.1 10.2 10.3 10.4 10.5 10.6 5 10 15 20 9.9 10.0 10.1 10.2 10.3 10.4 10. 5 10 15 20 25 30 35 40 9.8 9.9 10.0 10.1 10.2 10.3 10. 20 40 60 80 100 120 9.8 9.9 10.0 10.1 10.2 10.3 10.4 50 100 150 200 250 300 350 9.9 10.0 10.1 10.2 10.3 10.4 10. 50 100 150 200 250 20 40 60 80 100

Detected Photons Time

50 100 150 200 250 300 350

OM(20, 27): 1506.9 pe

single cascade double cascade

• exp. data

reco with bright DOMs reco without bright DOMs bright DOM* bright DOM* bright DOM* bright DOM* bright DOM*

WORK IN PROGRESS

* Bright DOMs are excluded from this analysis

Event #2

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• Observed 2014
• Observed light

arrival pattern clearly favors double cascade hypothesis

17 m 9 TeV 80 TeV (E1-E2)/(E1+E2) = -0.80

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 “tauness”

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Energy asymmetry for best-fit spectrum, and a νe:νμ:ντ = 1:1:1 composition

Juliana Stachurska

Summary

• Performed HESE ντ-induced Double Cascade

search and flavor composition measurement on 7.5 years of data

• Now feedback of topology into HESE sample
• Improved ice model, likelihood, software
• Data reprocessing “Pass 2”
• Identified 2 ντ candidate events
• 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

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• exp. data

WORK IN PROGRESS

=?

Updates coming soon - STAY TUNED

Juliana Stachurska

BACKUP

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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

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