IceCube EHE Event search with 9 strings - unblinding request

A Quest for EHE Neutrinos with the 9-string IceCube detector Aya Ishihara for the EHE working group

* EHE Physics working group
* The first 9-string analysis page
* HTML version of the first unblinding proposal (for the analysis meeting @ 4/12/07)
* ICRC 2007 merida proceedings (pdf) (Aug, 07)
* EHE 9 string Paper Draft Wiki (Sept, 07)
* EHE 9 string summary and 22 string confirmation (ppt): 2007 Fall collaboration meeting (Oct, 07)


Please re-load this page.

marks below indicate new stuff since mid-June (namely corsika related stuff and new fluctuation effect included emperical model)

  1. Introduction
  2. EHE real sample
  3. MC sample
  4. MC Background
  5. Comparison with CORSIKA
  6. Real and simulation comparison
  7. Cut
  8. Systematics
  9. Results
  10. Comments from reviewer and replies
  11. FAQ


This page describes the EHE neutrino search with the 9-string IceCube detector on 2006 sample prior to accessing EHE signal part of sample.
Our target energy range is any neutrinos above 10^8 GeV. Cut are optimized for a GZK model. Our target sensitivity is to find GZK neutrinos within several years and competitive to the other EHE neutrino searches around world.
Relevant performance study has been performed prior to this analysis for the 80 string IceCube detector and described in the proceedings. Please find physics behind this EHE analysis strategy in this proceedings as the basic strategy is unchanged for 9 string analysis.
The point we need to address in the EHE neutrino search is that we do not have good understanding about the major contribution from atmospheric muon background in UHE/EHE regime, although still we do know for sure that the atmospheric muon distribution has much softer and steeper distribution than that of signal (gzk) neutrino (at both surface and deep in ice) and are able to reject background well if we could cut out lower energy events than signal energy domain. Thus, an empirical model construction using high enough energy range but lower than signal range is required.


EHE Sample

Data used for this analysis is level-1 filtering EHE sample which has filtering condition of number of channels larger than 53 or 80. The documentation of the Level-0 and Level-1 processing can be found here. Offline cut of Nchannel larger than 80 is applied to all data used in this analysis. Data is corrected from June 2, 2006 to Nov 20, 2006. Bad files listed here are excluded (plot). Before cleaning 1654 exist and after file cleaning 1260 files are left. List of files used in this analysis also found here. Also Carsten Rott has made a page on EHE sample verification. Removed are mostly the files which has length less than 300 sec and do not much contribute to livetime and so called "weasel" period. Livetime for current sample is 125.0 days.
The most difficult thing encountered in 2006 real data study is that the number of bins were reduced from what is designed/planned. In 2006, we have 128 bins of channel-0 (gain 16) ATWD which corresponds to 400ns but only 32 bins for channel 1 (gain 2) and 2 (gain 0.25) which corresponds to 100 ns (A combined waveforms look like this) and 50 bins read out for FADC of 1 micro second.

Real Event Distributions

MC sample

Detailed Monte Carlo simulation is performed using IceTray modules (relevant modules are included in the EHE meta-project) based on the simulation meta-project v01-09-06a. Droop is simulated for FADC and bin number is reduced for both ATWD and FADC. Muon and taus are injected at 860m from the center of IceCube 23 string. 400K of muon which follows E-1 spectra from 100TeV to 100EeV, 400k of muon with E-2 and 200K of taus with E-1 spectra in the same energy range are generated.

EHE MC Distributions

Signal and Background Simulation

In this study, JULIeT is used as the event simulator near the detector as well as propagator. The weighting schema for the JULIeT can be found in this internal report (pdf). Generated E-1 and E-2 samples are weighed by signal sample of a propagated GZK neutrino distributions in ice and the same with an empirical atmospheric muon model which we described in the following.

We have developed a relation between primary cosmic-ray energy and muon bundle sum energy (pdf), and this is convoluted with measured cosmic-ray fluxes. This indicates that possible muon bundles in ice is represented by single muons of which energy corresponds to the sum of muons in a bundle. A toy simulation shows this is good approximation at this EHE energy. Further explanation of the empirical atmospheric muon (bundle) model can be found here.
An example how flux changes with constant Ethres with varying alpha and similary constant alpha varying Ethres.

We have also checked corsika sample.

In addition to the model, we extracted fluctuation size from corsika sample (proton primary which gives a larger fluctuation value than from heavy primaries) in the relation between in-ice muon bundle energy and primary CR energy. Here one can find fluctuation sizes and corresponding fluctuation fig used in the model.

Plotted here are chi2(/dof) from simulated event NPE distributions weighed by model function using dE/dx ~ -beta(E)*E approximation and real data NPE distribution on the alpha and Ethres plane, in which above fluctuation effects are included. Chi2/ndof from fit without fluctuation effect old alpha and Ethres plane.

One can see a chi2 valley on the plane, in the plane, agreements between data and model are nearly equally good. There is not much difference in chi2 in the sets of the numbers of alpha and Ethres in the valley.
Initially we choose two extreme cases to estimate uncertainty in the model (shown below as old comparison without fluctuation).

Finally this model with two sets of parameters (note that if GZK cut off we are almost background free! and our main charm/bottom contribution is from the CR energy equal or above 10^20 GeV if any) is compared with the 9 string IceCube EHE real sample NPE distributions in the different linefit cos-theta range. Black points are real data and red histograms are obtained atmospheric muon (bundle) model (blue and light blue lines are from GZK model for reference) distributions in both plots.

Comparisons between data and simulation with fluctuation effect

Review iterations

Ordered by date


The BASIS on the EHE 9 string analysis

The other useful Information

Special Devices
Golden DOM (Chiba U.)
Standard Candle (Andres Morey)
Real Data
Verification Team
Chris's archive (Jan 06)
South Pole Logs
Mark's Page