Search for EHEEHE neutrinos

with the IceCube detectorAya Ishihara for the IceCube collaboration

Chiba University

EHE EHE Neutrino UndergroundNeutrino Underground

Fluxes at the IceCube depth

S. Yoshida et. al. (2004) Phys. Rev. D 69 103004

main signalGZK neutrino induced leptonsGZK neutrino induced leptons

background Atmospheric muonAtmospheric muon

Simple energy cut works!

atmospheric muon flux above 106 GeV is very

uncertain

Surface fluxes

atm

Target GZK neutrinoSurface energy range8 < Log(E/GeV) < 12

(energy at depth ~ 6-7 < Log(E/GeV) < 10-11)

EGZK >> EAtm

Energy !Energy !

e+e-

pair-creation

bremsstrahlung

photo-nuclear

e+e-

100 TeV

and tracks loose their energy by

radiative processesradiative processes.const

dx

dE

9 EeVE

dx

dE

??

The 9-stringThe 9-string realreal sample sample 20062006

Example Example BrightBright Events Events

NPE = integral of waveforms / single charge

20mV

0mV [ns]

Digital optical module waveform(ATWD / FADC)

Visible Energy vs. NPE correlation up to logVisible Energy vs. NPE correlation up to log1010 NPE ~ 4.5 NPE ~ 4.5

the resolution is then diffused by waveform saturation effectsthe resolution is then diffused by waveform saturation effects

NPE and Energy CorrelationNPE and Energy Correlationwith 2006 IceCube configurationwith 2006 IceCube configuration

log ( Energy / GeV ) log ( Energy / GeV )

66

log Cosmic-Ray Energy

Number of muon in a shower above threshold Energy Ethres (Elbert parameterization)

11

cos1

T

Bundle

thresCR AE

EAEE

This relation between cosmic ray energies

and the energy of the muon bundle

fixes atmospheric muon bundle fluxes

Nagano, Watson: Reviews of Modern Physics Vol 72 No3 (689)

Atmospheric Muon Bundles ModelAtmospheric Muon Bundles Model

77

Background simulationPartial experimental data

atmospheric simulation model 1atmospheric simulation model 2

cos log10NPE

4 < log10NPE < 5

Model Ethres[GeV]

1 1.9 300

2 2.0 1500

88

Atmospheric fluxes at IceCube depthAtmospheric fluxes at IceCube depthModel Ethres[GeV]

1 1.9 300

2 2.0 1500

with GZK cutoff !!

#1

#2

without GZK cutoff

#1 #1

99

Comparison with CORSIKAComparison with CORSIKAAtmospheric

empirical modelCorskiaProton

QGSJET01

CorsikaIron

QGSJET01

log (Primary CR Energy [GeV])

log

( B

un

dle

En

ergy

at

Dep

th [

GeV

])

log (Primary CR Energy [GeV])

overestimate bundle energy

1 PeV

bundle energy

100 TeV

bundle energy 10 PeV

underestimateproton and ion both underestimate the rate

Event Selection and NumbersEvent Selection and Numbers

Cut Level GZK events

e

Atmospheric model 1

Atmospheric model 2

1 (dotted brown) 0.055 0.003 0.006

2 (solid red) 0.046 < 10-4 < 10-4

3 (dotted black) 0.036 < 10-4 < 10-4

4 (solid brown) 0.024 < 10-4 < 10-4

GZK GZK Atm.

number of events

1111

Sensitivity for 2006

all flavors added

assuming 1:1:1 ratio

90 % C.L.

cut2106.5109.510-6 [GeV cm-2 sr-1 sec-1]

Neutrino Effective AreaNeutrino Effective Area

average over full solid angleCut level 2

SummarySummary

The IceCube 9 string array provided physics data sample in 2006 MC shows 9 string IceCube is capable of EHE neutrino search but

waveform saturation and its readout limits its capability For BG estimation, Elbert formula, derived from experimental

relation between EHE CR fluxes and surface mu bundle energy, used

Effective area, sensitivity of ~10-6 [GeV cm-2 sr-1 sec-1] for 2006 IceCube EHE region is obtained with optimized cuts with the assumption of zero background events from the empirical atmospheric background model

1414

backupbackup

1515

Comparison with CORSIKAComparison with CORSIKA

Proton QGSJET01

Iron QGSJET01

The The 9-string9-string realreal sample sample 20062006FADC FADC Waveforms Waveforms

saturated

1717

NPENPE

EHE waveforms

Integrating a waveform/single charge = NPE

= +

4.5V

0V

20mV

0mV

high gain

low gain4.5V

0V

120mV

0mV