11

A quest for EHEEHE neutrinoswith the IceCube detector

proposal for EHE neutrino search

in 2006 - 9 string sample

Aya Ishiharafor the IceCube EHE pwg

Introduction

22

Target Neutrinos of this analysisTarget Neutrinos of this analysis

seXp K '7.2 ννμπγ +→+→+→ ±±±GZK neutrinoGZK neutrino

The standard scenario of EHE cosmic-ray induced neutrinos The main energy range:

Eν ~ 109-11 GeV

νμ νe

μ

e

πνμEHE-CR

TargetTarget Energy Range Log(E/GeV) > 8

Optimized for GZK neutrino

Competitors: Competitors: On-going EHE Neutrino Search On-going EHE Neutrino Search (GZK neutrino energy range (GZK neutrino energy range 108~11 GeV))

Air-shower DetectorHiRes, Auger

BG rejection based on near-horizon/upgoing young shower

reconstruction

EHE ν e

ee

CR

μ

μ

μ

Underground IceCherenkov Detector : IceCubeMain BG rejection based on

energy estimation Simple and robust

μ

EHE νμ

ν eμ

Background:Atmospheric muon

MC studies claim the target sensitivity of Auger/HiRes are almost the same as IceCube, although they are not neutrino detector!

No public results from 3 experiments yet. All claims result is coming very soon.

EHE EHE Neutrino UndergroundNeutrino Underground

Fluxes at the IceCube depth

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

tentative

EGZK >> EAtmμ

main signalGZK neutrino induced leptonsGZK neutrino induced leptons

background Atmospheric muonAtmospheric muon

Simple energy cut works!

However, Structure of atmospheric muon flux above 106 GeV is very uncertain !

Surface Fluxes

tentative atm μ

How uncertain ?How uncertain ?muon background in very high energy regime: NOT well-known (highly

dependent on parton distribution assumption), e.g.

charm productionbundle structure

Ord

ers

dif

fere

nce

EHE regime

Atmospheric muonModel fluxes

From charmed meson decay νμ

μ

77

Need models which describe our real data in UHE background

regime

Empirical model

88

Analysis

99

AnalyzedAnalyzed 9-string 9-string realreal sample sample 20062006statisticsstatistics

stable filtering condition for EHE sample with Nch>80

Physics runs since 2nd June, 2006 to 20th, Nov, 2006

124.148 days of livetime after file selection (a list of files not used and used in this analysis can be found at analysis web page)

Event interval

Event FrequencyBefore file cleaning

Ch

ann

el N

>53

Hz

0.134 Hz for Channel N > 80After file cleaning

Eventinterval

The 9-stringThe 9-string realreal sample sample 20062006

Example Bright EventsExample Bright Events

1111

The The 9-string9-string realreal sample sample 20062006FADC FADC Waveforms Waveforms (integral ~ NPE)

Saturated ~ 90mV

DOM#31

1 μs

90 mV

TypicalTypical ATWD ATWD EHEEHE Waveforms Waveforms (integral ~ NPE)

DOM#36

DOM#37DOM#30

DOM#31

DOM#29

DOM#28

DOM#27

DOM#26

DOM#32

DOM#33

DOM#34

DOM#35

105 ns

402 ns

120 mV

Looking at a Very Typical Combined EHE Waveform

String#29 – DOM#8RunID 89761- Event ID 1477531

Ch0 Ch1 Ch2

CombinedATWD FADC

105 ns0 ns 402 ns 0ns 105 ns

402 ns105 ns 1 μs

Still have reasonable Energy vs. NPE correlationStill have reasonable Energy vs. NPE correlationup to logNPE ~ 4.5up to logNPE ~ 4.5

then, early saturation effect diffuse themthen, early saturation effect diffuse them

The 9-string simulation:The 9-string simulation:NPE and Energy CorrelationNPE and Energy Correlation

μ

1515

NPE corresponds to signal NPE corresponds to signal region is quite reduced region is quite reduced because of ‘reduced bin because of ‘reduced bin readout’ in 2006 datareadout’ in 2006 data

‘‘Reduced Bin#’Reduced Bin#’reduced NPE reduced NPE

Signal NPE regionbased on full readout

Signal NPE regionbased on reduced readout simulation

1616

The 9-string The 9-string realreal NPE distribution NPE distribution

EHE region!!

Channel N > 80 Filtering bias

Very-high energyBackground

regime

1717

Atmospheric Muon Bundles ModelAtmospheric Muon Bundles Model(see (see wweb pageeb page for further detail) for further detail)

cosmic-ray energy and total muon energy above Ethres in a bundle

11

cos1 −

⎟⎟⎠

⎞⎜⎜⎝

⎛ −=

αμ ϑ

αα

T

Bundle

thresCR AE

EAEE

measuredcosmic-ray

flux

bundles of

atmospheric μ

Cosmic-Ray

μμ

muon bundle fluxmuon bundle flux

1818

Single Single μμ represents bundled represents bundled μμNPE distributions of Toy model

bundled muon events(50 muons in 100 m radius, 2*106 GeV each)

andfrom single muon (108 GeV) events in 100 m radius

μμ

μ

bundlesingle muon

Log10(event-sum NPE)

N channel

Log10(channel wise NPE)

1919

Flux after ice propagation (E2dF/dE [GeV/sec str cm2])

Flux at sea level (E2dF/dE [GeV/sec str cm2])

Log10(E bundle/GeV)5.4 8.2 Log10(E bundle/GeV)

5.4 8.2

Atmospheric Model Construction0.

0

0.

750.

0

0.

75 z

enit

hze

nit

h

0.0

0.7

50.

0

0

.75

cos

zen

ith

cos

zen

ith

down

horizontal

2020

In-ice fluxes with new modelIn-ice fluxes with new model1

1

cos1 −

⎟⎟⎠

⎞⎜⎜⎝

⎛ −=

αμ ϑ

αα

T

Bundle

thresCR AEE

AEE

Model flux#

Ethres α

1 300 GeV 1.9

2 1500 GeV 2.0

with GZK cutoff !!

#1#2

ET=14.5 GeVA=1

2121

NPE distribution comparison set #1 simulation and real Set #Set # EEthth αα

11 300 GeV300 GeV 1.91.9

22 1500 GeV1500 GeV 2.02.0

0.6<Cos fg-theta < 1.0-1.0<Cos fg-theta < 1.0

0.4 < Cos fg-theta < 0.6 -1.0<Cos fg-theta < 0.4

Set # 1Set # 1

Log10(NPE)

GZK μGZK atmospheric μreal data

2222

NPE distribution comparison set #2 simulation and real Set #Set # EEthth αα

11 300 GeV300 GeV 1.91.9

22 1500 GeV1500 GeV 2.02.0

0.6<Cos fg-theta < 1.0-1.0<Cos fg-theta < 1.0

0.4<Cos fg-theta < 0.6 -1.0<Cos fg-theta < 0.4

Set # 2Set # 2

Log10(NPE)Log10(NPE)

GZK μGZK atmospheric μreal data

2323

Signal and BG Simulation: NPE vs. CosSignal and BG Simulation: NPE vs. Cos((linefitlinefit))

Atmospheric muon model Atmospheric muon model

Log10(NPE)

Cos

fg-

thet

a

Event SelectionEvent Selection

Set # 2Set # 2Set # 1Set # 1

GZK GZK μμ GZK GZK Cos

fg-

thet

a

Log10(NPE)

Cut level0 1 2 3 4 5 6

7 8 9 10 11 12

2525

Event Passing RateEvent Passing Rate

zoom

GZK μGZK GZK μ+GZK atmospheric μ set #1 atmospheric μ set #2

Because of uncertainty from NPE/Energy

relation, can not optimize the cut too aggressively

Cut #8 is selected

Effective AreaEffective AreaSignal condition

Cut #8Filtering condition

Channel Number > 80

km2 km2

2727

Expected Sensitivity ...long journey toward GZK to be continued…

with cut #8

‘standard’GZK flux

with cut #10

Z-burst

TD

Strong ev.GZK

90 % C.L.

Summary

Ready to access EHE region!Ready to access EHE region!

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

early saturation and reduced bin numbers mainly has limited its capability

BG is estimated using empirical atmospheric muon bundle model Simple cut gives an event rate of ~0.02 GZK events in 124 days

and expected 10-3 background atmospheric events in the same interval.

22 string independent sample will steadily confirm any finding in 9 string data including empirical atmospheric muon model

No more bin number reduction!!

3030

FAQ 1FAQ 1

Q-1) CORSIKA? A-1) Use of CORSIKA for this analysis is not realistic because

of the lack of 1) reliable model (incl. bundle and prompt) in interested energy region at surface, 2) computational resources to obtain good stats at this energy and 3) very sensitive detector simulation for partially deployed partial DAQ operation to reproduce full NPE spectra

3131

FAQ 2FAQ 2

Q-2) Energy resolution / standard-candle? A-2) http://www.ppl.phys.chiba-u.jp/~aya/SC/gdom-1.html MC gives ~ a factor of two more NPEs. This will be put into

the systematic errors in finalizing the (unblinding) analysis. Let us also remark that GZK spectrum is so hard that the

shift of NPE (indirectly related to energy) threshold in the signal cut would not affect sensitivity in EeV regime too much.

3232

FAQ 3FAQ 3

Q-4) Contribution from GZK neutrino which make in-detector interaction?

A-4) There exists, but minor in the overall event rate (See S.Yoshida et al, PRD 69 (2003) 103004). We are, however, generating neutrino-induced events by JULIeT and the

event rate from the contained events are reported in the collaboration meeting.

Q-3) Baseline for NPE calculation? A-3) We have observed significant baseline shift/droop. Our

recipe to fix it was determined by looking at the baseline distribution of SC data estimated by the various algorythm.

http://www.ppl.phys.chiba-u.jp/~aya/SC/index.html

3333

FAQ 4FAQ 4

Q-5) IceTop to establish atmospheric muon bundle model? A-5) It is in our future plan. Insight of the mass composition

of Cosmic Rays will narrow the parameter space in the bundle model. We need more stats to realize this study.

3434

FAQ 5FAQ 5

Q-6) Is this analysis interfere with high energy cascade search?

A-6) No. Our study is not aimed at cascade ID but just looking for very bright events. This analysis is nothing to do with the cascade-likelihood. A (minor) contribution from EHE cascade events are just added to those from muons and taus to estimate the overall event rate. Moreover, our signal energy range (EeV) is mostly higher than that in the mainstream cascade search where you lower the energy threshold by identifying the cascade-like event topology.

3535

FAQ 6FAQ 6

Q-7) How the slight difference between bundle and our single muon representation in npe affects to this analysis?

A-7) It affects nothing. Our empirical formula has a flexibility in the relation between bundle energy (that determines NPE) and primary cosmic ray energy (that determines flux)

to make renormalization. The NPE/zenith angle distribution of the real data is well described by the model.

3636

ExtraExtra

3737

MC truth and LineFit MC truth and LineFit

with Atm. Mu weight with Atm. Mu weight

3838

Angular ResolutionAngular Resolution

Atm. Mu weight Atm. Mu weight

39

Memorandum for atmospheric muon fit using 9 string data

CR

CRCRIB

CR

CR

T

IB

IBthIB

dE

dJE

E

dE

dJ

AE

E

E

AEEFAll

3,

11

3,

3,3,

1

1

1

cos1

1

1),(cos

μ

αμ

μμ

α

ϑα

αα

ϑ

−=

⎟⎟⎠

⎞⎜⎜⎝

⎛ −−

=−

γκ −= )( CRCR FEJ

)(3, NPEfE IB =μ

)(coscos FGf ϑϑ =

11

min cos1 −

⎟⎟⎠

⎞⎜⎜⎝

⎛ −=

αμ ϑ

αα

T

Bundle

CR AEE

AEE

40

Event Properties