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Search for diffuse extraterrestrial contained neutrino-induced cascades using IceCube

79- and 86-string configurations

Mariola Lesiak-Bzdak Stony Brook University for the IceCube Collaboration

Outline: •  Motivation •  Analysis Method •  Unblinded Events •  Summary

Geographic South Pole"

Amundsen-Scott "South Pole Station"

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IceCube detector

07 April 2014, APS Meeting, Savannah, Georgia

Search for a Diffuse Neutrino Flux

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Diffuse Flux = effec&ve sum of neutrino fluxes from all extraterrestrial sources (e.g. AGNs) •  Signal:

–  Extraterrestrial ν from ~E-2

sources •  Background:

–  Atmospheric µ –  Atmospheric ν (conven&onal from

π/K and prompt from charmed mesons)

•  Sensitive to all three ν flavors •  Energy information used to

separate signal from background

Mariola Lesiak-‐Bzdak, APS 2014

Northern sky

Southern sky

GRBs AGNs Energy

Atmospheric ν, µ Harder

Spectrum ν (E-2)

Neutrino Event Signatures

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νμ N è μX

Color coding: red – earliest blue -‐ latest


νe Nè cascade

Cascade (data)

Tracks with length ~1km

§  angular resolution <1o

§  energy resolution log(E) ~ 0.2

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νµ +N→µ + XN -‐ target nucleon X -‐ hadronic shower

νµ (CC)

Track (data)

This Analysis Cascades §  e-m and hadronic cascades

§  energy resolution ~ log(E)~0.04 (above 10 TeV) §  angular resolution: ~8 degree

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νe(τ ) + N →e(τ ) + Xν l + N →ν l + X l = e, µ,τ

νe(τ)(CC) νl(NC)

IceCube Contained Cascade Analyses

•  Neutrino-‐Induced Contained Cascade Searches in IceCube based on Monte Carlo background simula&ons: –  IC22-‐strings (published PRD84 (2011) 072001) –  IC40-‐strings (accepted to PRD arXiv:1312.0104) –  IC59-‐strings (preliminary, ICRC2013 proceedings arxiv:

1309.7003)

–  IC79+IC86 – this analysis

4 Mariola Lesiak-‐Bzdak, APS 2014

IceCube detector string configura&on growth: IC9 = 9 strings (2006) IC22 = 22 strings (2007) IC40 = 40 strings (2008) IC59 = 59 strings (2009) IC79 = 79 strings (2010) IC86 = 86 strings (2011)

IC22 data events

IC40 data events

IC59 data events

E=40 TeV E=51 TeV

Mariola Lesiak-‐Bzdak, APS 2014 5

Search for Contained Cascades in IceCube with 79- and 86- strings

•  Signal: Extraterrestrial ν e CC and (ν e + ν µ) NC from ~E-2 sources

•  Background: Atmospheric µ and ν µ CC •  Analysis Strategy:

–  Demand spherical light distribution pattern and its reconstructed vertex to be contained inside the detector volume



•  Signal: Extraterrestrial ν e CC and (ν e + ν µ) NC from ~E-2 sources

•  Background: Atmospheric µ and ν µ CC •  Analysis Strategy:

–  Demand spherical light distribution pattern and its reconstructed vertex to be contained inside the detector volume

–  Combina&on of quality cuts on different variables op&mized using Monte Carlo background simula&ons

–  Selec&on criteria developed on 10% of the data

Example of Cascade Variable

TimeSplitPosi&on= difference between the reconstructed vertex posi&ons reconstructed for each event half

Selected events TimeSplitPosi?on



•  Good data vs Monte Carlo shape agreement •  Good data vs Monte Carlo rate agreement

Data vs MC rate agreement at different cut levels

Reconstructed Zenith

Example of Data/MC shape agreement

•  Energy range between 13 TeV and 5.3 PeV

•  Signal efficiency (final to trigger level) ~30% up to 3.5 PeV

•  Vertex resolution ~4 m •  Energy resolution: ~9% •  Angular resolution: ~8 degrees •  Purity (νAstr/(μ+νAtm+νAst)):

–  E>10TeV: 37% –  E>60 TeV: 83%

•  Muon Contamination (μ/(νAtm+νAst+μ)): –  E>10TeV: 8% –  E>60 TeV: 0.5%

Contained Cascades in IC79+IC86


Conv. norm. (Honda+H3a) = 1.0 Prompt norm. (ERS+H3a) = 1.0 Astro. Norm. (10-‐8E-‐2) = 1.0 Honda = Honda et al., PRD 75 (2007) H3a = Gaisser, Astropart. Phys. 35 (2012) ERS = Enberg et al., PRD 78 (2008)

Reconstructed energy ager final event selec&on (10% of the data)

Sta&s&cal uncertain&es only

Effective Area in Contained Cascades Search


IC79 Effec&ve Area

Factor of ~1.5 improvement

NuE

Comparison of Effec&ve Area for IC79 and IC59 Contained Cascades

Black Points = Toy Data MC

Likelihood Fit Test

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Input values: Conv. norm. (Honda+H3a) = 1.0 +/-‐ 0.5 Prompt norm. (ERS+H3a) = 1.0 Astro. Norm. (10-‐8E-‐2) = 1.0 Energy Scale = 1.00 +/-‐ 0.15


Toy MC LLh fit results for 1000 samples of toy Data MC

Honda = Honda et al., PRD 75 (2007) H3a = Gaisser, Astropart. Phys. 35 (2012) ERS = Enberg et al., PRD 78 (2008)

Physics Goal: perform likelihood fit to the 2-‐yr energy distribu&on and extract contribu&on of astrophysical E-‐2 normaliza&on

•  Toy Data MC results: –  Expected uncertainty on astrophysical

E-‐2 normaliza&on of ~35% –  All-flavor sensitivity: E2Φ90%CL < 0.90 x

10-‐8E-‐2GeV-‐1s-‐1sr-‐1cm-‐2

IC79+IC86 Contained Cascades vs HESE* analysis


HESE Analysis

•  Select cascades •  Background es&mated from Monte

Carlo simula&ons •  Contained cascade search above E>10

TeV (Total Charge>300 P.E.)

•  Select tracks and cascades •  Background es&mated from data •  Contained cascade and tracks search

at high energies (Total Charge>6000 P.E. àEnergy ~ 30 TeV)

IC79+IC86 Contained Cascades

ν

μ

ν

Veto

μ

*High Energy Star&ng Events (Science 342, 1242856 (2013))

Effective Area of Contained Cascades vs HESE


•  Below 150 TeV effec&ve area bigger than in HESE analysis

•  Same effec&ve area above 150 TeV -‐ 3 PeV as in HESE analysis

Spatial Distributions of Unblinded IC79+IC86 Contained Cascades

IC79+IC86 unblinded events

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Events well contained in the detector volume

Black dots denote IceCube strings loca&on


Vertex Posi&on X [m]

Vertex Posi&on

Y [m

]

Distance to the central string in IceCube [m] Ve

rtex Posi&on

Z [m

]

IC79 Unblinded Events E>60 TeV (3 events)

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E=114.2 TeV E=99.7 TeV E=64.2 TeV



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E=114.2 TeV E=99.7 TeV E=64.2 TeV


These events not in HESE sample (Science 342, 1242856 (2013))


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120.3 TeV 183.1 TeV

119.4 TeV

1. PeV 1.1 PeV

99.7 TeV 68.2 TeV 67.2 TeV

Events overlaping with HESE (Science 342 (2013) 1242856) Events not overlaping with HESE

200.2 TeV

71.7 TeV


Summary •  Search for diffuse neutrino-‐induced contained cascades in

IceCube data with 79-‐ and 86-‐strings –  Background es&mated from Monte Carlo simula&ons –  Energy range between 13 TeV and 5.3 PeV

•  Studies of the likelihood fit using toy data Monte Carlo: –  Expected uncertainty on astrophysical E-‐2 normaliza&on of ~35% –  Expected sensi&vity of E2Φ90%CL < 0.90 x 10-‐8E-‐2GeV-‐1s-‐1sr-‐1cm-‐2

•  2-‐year data sample unblinded: –  Total of 138 events observed

•  13 events (all cascade-‐like) have reconstructed energy above 60 TeV (40% overlap with HESE analysis, 8 addi&onal cascade events)

•  Stay tuned for likelihood fit results!


BACKUP SLIDES


Correlation Plots of the Best Fit Values

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Correla&on plots of the best fit normaliza&on values for LLh fit to the toy data MC (shown on slide 10) Input values: Conv. norm. (Honda+H3a) = 1.0 +/-‐ 0.5 Prompt norm. (ERS+H3a) = 1.0 Astro. Norm. (10-‐8E-‐2) = 1.0 Energy Scale = 15%


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