1 EHE A quest for EHE neutrinos with the IceCube detector proposal for EHE neutrino search in string sample Aya Ishihara for the IceCube EHE pwg

Introduction 2

Target Neutrinos of this analysis GZK neutrino The standard scenario of EHE cosmic-ray induced neutrinos The main energy range: E ~ GeV  e  e   EHE-CR Target Target Energy Range Log(E/GeV) > 8 Optimized for GZK neutrino

Competitors: On-going EHE Neutrino Search (GZK neutrino energy range ) Competitors: On-going EHE Neutrino Search (GZK neutrino energy range 10 8~11 GeV ) Air-shower Detector HiRes, Auger BG rejection based on near- horizon/upgoing young shower reconstruction EHE e  e e CR     Underground Ice Cherenkov Detector : IceCube Main BG rejection based on energy estimation Simple and robust  EHE  e  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 Neutrino Underground Fluxes at the IceCube depth S. Yoshida et. al. (2004) Phys. Rev. D tentative E GZK >> E Atm   main signal GZK neutrino induced leptons background Atmospheric muon Simple energy cut works! However, Structure of atmospheric muon flux above 10 6 GeV is very uncertain ! Surface Fluxes tentative atm 

How uncertain ? muon background in very high energy regime: NOT well-known (highly dependent on parton distribution assumption), e.g. charm production bundle structure Orders difference EHE regime Atmospheric muon Model fluxes From charmed meson decay  

7 Need models which describe our real data in UHE background regime Empirical model

8 Analysis

9 Analyzed 9-string real sample 2006 statistics  stable filtering condition for EHE sample with Nch>80 Physics runs since 2nd June, 2006 to 20th, Nov, 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 Frequency Before file cleaning Channel N >53 Hz Hz for Channel N > 80 After file cleaning Event interval

The 9-string real sample 2006 Example Bright Events

11 The 9-string real sample 2006 FADC Waveforms The 9-string real sample 2006 FADC Waveforms (integral ~ NPE) Saturated ~ 90mV DOM#31 1  s 90 mV

Typical ATWD EHE Waveforms Typical ATWD EHE Waveforms (integral ~ NPE) DOM#36 DOM#37 DOM#30 DOM#31 DOM#29 DOM#28 DOM#27 DOM#26 DOM#32 DOM#33 DOM#34 DOM# ns 402 ns 120 mV

Looking at a Very Typical Combined EHE Waveform String#29 – DOM#8 RunID Event ID Ch0Ch1Ch2 Combined ATWD FADC 105 ns 0 ns 402 ns0ns 105 ns 402 ns105 ns 1  s

Still have reasonable Energy vs. NPE correlation up to logNPE ~ 4.5 then, early saturation effect diffuse them The 9-string simulation: NPE and Energy Correlation  

15 NPE corresponds to signal region is quite reduced because of ‘reduced bin readout’ in 2006 data ‘Reduced Bin#’ reduced NPE  Signal NPE region based on full readout Signal NPE region based on reduced readout simulation

16 The 9-string real NPE distribution EHE region!! Channel N > 80 Filtering bias Very- high energy Background regime

17 Atmospheric Muon Bundles Model (see web page for further detail) web pageweb page cosmic-ray energy and total muon energy above E thres in a bundle measured cosmic-ray flux bundles of atmospheric  Cosmic-Ray   muon bundle flux

18 Single  represents bundled  NPE distributions of Toy model bundled muon events (50 muons in 100 m radius, 2*10 6 GeV each) and from single muon (10 8 GeV) events in 100 m radius    bundle single muon Log 10 (event-sum NPE) N channel Log 10 (channel wise NPE)

19 Flux after ice propagation (E 2 dF/dE [GeV/sec str cm2]) Flux at sea level (E 2 dF/dE [GeV/sec str cm 2 ]) Log 10 (E bundle/GeV) Log 10 (E bundle/GeV) Atmospheric Model Construction zenith zenith cos zenith down horizontal

20 In-ice fluxes with new model Model flux# E thres  1300 GeV GeV2.0 with GZK cutoff !! #1 #2 E T =14.5 GeV A=1

21 NPE distribution comparison set #1 simulation and real Set # E th 1 300 GeV GeV <Cos fg-theta < <Cos fg-theta < < Cos fg-theta < <Cos fg-theta < 0.4 Set # 1 Log 10 (NPE) GZK  GZK  atmospheric  real data

22 NPE distribution comparison set #2 simulation and real Set # E th 1 300 GeV GeV <Cos fg-theta < <Cos fg-theta < <Cos fg-theta < <Cos fg-theta < 0.4 Set # 2 Log 10 (NPE) GZK  GZK  atmospheric  real data

23 Signal and BG Simulation: NPE vs. Cos (  linefit ) Atmospheric muon model Log 10 (NPE) Cos fg-theta

Event Selection Set # 2 Set # 1 GZK  GZK  Cos fg-theta Log 10 (NPE) Cut level

25 Event Passing Rate zoom GZK  GZK  GZK  +GZK  atmospheric  set #1 atmospheric  set #2 Because of uncertainty from NPE/Energy relation, can not optimize the cut too aggressively Cut #8 is selected

Effective Area Signal condition Cut #8 Filtering condition Channel Number > 80 km 2

27 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! 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 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!!

30 FAQ 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

31 FAQ 2 Q-2) Energy resolution / standard-candle? A-2) 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.

32 FAQ 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) ). 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.

33 FAQ 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.

34 FAQ 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.

35 FAQ 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.

36 Extra

37 MC truth and LineFit  with Atm. Mu weight

38 Angular Resolution Atm. Mu weight

39 Memorandum for atmospheric muon fit using 9 string data

40 Event Properties