Filter Proposal for EHE analysis with IC40
Aya Ishihara for EHE PWG∗
January 28, 2008

1Physics Motivation

Purpose of this EHE filtering is to efficiently transfer high energy events i.e. EHE neutrino induced event
candidate and high energy muon bundle events. The main physics analysis from the EHE filtered sample
are the EHE neutrino search, high energy muon (bundle) structure study (collaboration with CR WG[1]) and monopole/exotic event search (Exotic WG [2]).

2Basis of the EHE Filtering 2008

EHE WG has been using number of photo-electrons (NPE) as the basis of the analysis, because the NPEparameter shows a good correlation with the energy of the particles near the detector. The muon energyand NPE relation is shown on the left plot in Fig. 1 and the muon energy and Nch relation is shown onthe right.
8Nch6log

10(NPE)

3000

42

2000
1000
06810log ( in-ice µ energy /GeV )6810log ( in-ice µ energy /GeV )1010Figure 1: Correlation between MC truth energy and NPE on the left and between MC truth energy andNch shown on the right. log NPE is more sensitive parameter to the particle energy compared to Nch.
In 2006 and 2007, Nch > 80 filtering (Nch filter) is used for EHE sample filtering because Nch filter
does select large NPE events. However, it is observed that Nch filter still retain some fraction of small
NPE events which have not been used for analysis. As the more number of strings, the more effecient
background filtering become important, we propose to use NPE as the basis of the 2008 EHE filtering in
stead of Nch filter. Also Nch cut biases to NPE distribution in mid-NPE region (up to approximately log
NPE ∼ 2.6) as seen in the left plot of Fig.2. These events in the NPE region are currently disregardedin the offline EHE analysis but for the further muon bundle background study and the improvement ofthe EHE neutrino sensitivity a portable access to the unbiased distribution is strongly preferred in 2008.
∗ Technical Contact:aya@hepburn.s.chiba-u.ac.jp

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number of events per day

80-dom filtering effect

IC22 event number above threshold NPE

106

106

105
104

104

103
102

correction factor

105

103
22.533.541022

2.53log (NPE)

log (NPE)

3.54thres

Figure 2: Left: IC22 event rate distribution normalized per day as function of log NPE. NPE distribution
indicate simple power-low behavior down to log NPE ∼ 2.6 and Nch filter effect is visible in the lower
NPE region. Right: the integrated IC22 event rate per day as function of threshold log NPE. To estimate
event rate without Nch filter bias, a correction factor multiplication will be applied on the Nch filteredintegrated event rate distribution assuming the high NPE slope is unchanged in the lower region.

3Event Rate and Data Volume Estimation

In this study, I used data from 4 runs, Run00108986, Run00108987, Run00108988 and Run00108989
in Aug. 2nd, 2007. The runs correspond to ∼ 25 hours of livetime containing 115635 events after Nchfilter. The total event size after Nch filter of these 4 runs are 2.7 GB. The average EHE event size canbe approximately converted to 23kB/events. As it can be expected that the size of physics data (nogeometry, calibration, detector information) in 2008 is similar to that with IC22 as long as the same NPE
region is considered, in the following this value is used for the filtered data volume estimation in 2008.
The NPE distributions of this sample is shown on the left in Fig.2 and integrated number of events above
threshold log NPE is shown on the right-hand side. It can be seen in the plots that a bias from Nchfilter condition become visible below log NPE ∼ 2.6. To estimate event rate in 2008 without Nch filter
bias, correction factors will be applied on the Nch filtered sample below log NPEthres = 2.6. Assuming
the high NPE event rate behavior continues down to the log NPE ∼2.0, the correction factors at log
NPEthres = 2.0, 2.2, 2.4, 2.6 are estimated to be x30, x10, x3 and x1.1 respectively and the same factor
is used in the case for the other number of strings.

Event Rate [Hz]10-1

10-2-310

10-4-5102345log (NPE)
10

Figure 3: Event rate as function of log NPE. Colors indicate different numbers of strings used to calculate
the total NPE. Colors for 22, 20, 18, 15, 13, 11 and 9 strings are black, red, light green, blue, pink, light
blue and green respectively.

2440

3.5

Integrated Event Rate [Hz]Integrated Event Rate [Hz]

1.2
10.8
0.60.4

30
2520
15

2

2.5

3

3.5log (NPE)
104thres

4.5

505

3
2.5
2
1.5
10.5
0

10-0.550.20

Integrated Event Rate [Hz]35-151015202530

35

401015202530

3540

45

Number of strings

45

Number of strings

Figure 4: Integrated event rate as function of thresholdlog NPE and number of strings. Nch filter bias correction
is applied on the right plot. Colors on the left indicate
different numbers of strings used to calculate the total NPE
as in Fig. 3 and on the right indicate different threshold log
NPE. Colors on the right is log NPEthres of 2.0, 2.2, 2.4,2.6, 2.8, 3.0, 3.2 are yellow, light green, blue, red, pink,light blue and green. Black are events which passed Nchfilter.

Figure 5: The integrated event rate asfunction of number of strings as theright plot in Fig. 4 but now focusing on
the higher log NPEthres . Colors on theright is log NPEthres of 2.4, 2.6, 2.8, 3.0,
3.2 are blue, red, pink, light blue andgreen. Black are events which passed
Nch filter. Extrapolation of the data
points to 40 strings gives an approximate event rate with IC40.

In Fig. 3, the event rates per second are shown for different number of strings indicated by different
colors from 9 strings to 22 strings. The rates for N string < 22 are obtained by applying the string number
reduction to the IC22 data and Nch filter is re-applied. No Nch bias correction is applied in the plot.
Given on the left in Fig. 4 is the integrated event rate as functions of threshold log NPE for each string
numbers. Shown on the right is also the integrated event rate but now as functions of number of strings
for different threshold log NPE indicated by different colors and the Nch filter bias correction factor isapplied. The 40 strings event rates can be inferred from the plot on the right in Fig. 4 and Fig. 5 (thesame plots with different axis range) by extrapolating total event rate values from N string ≤ 22 to 40strings, as it can be seen in the plot that the expected event rates show approximately linearly increase
with the number of strings. This gives an estimation that threshold log NPE value of 2.6 gives ∼3.0 Hz
with 40 strings while Nch > 80 filter will yield ∼3.8 Hz of event rate in 2008. EHE PWG propose to use
threshold log NPE value of 2.6 for the 2008 EHE filtering conditon, i.e. All events with log 10 NPE above
2.6 will be transfered to North. This ∼2.2 Hz event rate can be converted to expected data size of 4.37
GB per day as summarized in Table 1.

Filtering Condition
Threshold log10 NPE > 2.6 (proposed)
Threshold Nch > 80 (old)IC40 Event Rate [Hz]3.0
3.8

IC40 Data Size [GB/day]
5.9
7.55

Table 1: Expected data volume per day (in *.i3.gz format).

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Example Filter Module and Python script and CPU

Projects used in this filter are1) Portia
http://code.icecube.wisc.edu/svn/projects/portia/trunk r41017 or afterand 2) EHEFilter3http://code.icecube.wisc.edu/svn/sandbox/ishi-work/EHEFilter
An example script can be found at
http://code.icecube.wisc.edu/svn/sandbox/ishi-work/EHEFilter/resources/scripts/ExampleScript EHEFilter08.py
Time used to run this script is compared with the time used for simple Nch filter, e.g.,
http://code.icecube.wisc.edu/svn/sandbox/ishi-work/EHEFilter/resources/scripts/ExampleScript NchFilter08.py
Time consumed by Nch filter is xxx sec, time used by portia plus NPE filter is yyy sec.

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AppendixA

The NPE calculation and The Baseline Estimation

The filtering variable proposed to use in this request is NPE calculated using the PORTIA project(http://code.icecube.wisc.edu/svn/projects/portia) in which NPE is defined as total integrated charge
divided by a SPE charge. The only ambiguity may come from the baseline determination as there is noperfect baseline estimation method yet exists for every type of signals.
In the PORTIA project, there is a set of option to choose how to decide baseline. The most appropriate
method for EHE analysis has been studied using the standard candle sample [3], channel-by-channel basis
and summarized as eheoptimized option in the PORTIA.
Here the observation and the option are summarized.
For ATWD, it has been observed that waveforms with small pulses (contains a few PEs), iteration
methods work the best as known from hardware people. However this would not work for waveforms
with a large number of PEs. In this case the average of first 2 bins are the best, generally. However forthis option we can not avoid the possibility that the effect from a random photon or external effect (e.g.
previous events).
Considering these situation, baseline estimation for ATWD with eheoptimized option would do:
1. Take the first 2 bin average.
2. if the value is smaller than -1mV, larger than 2mV, consider the baseline as 0mV.
3. Then calculate NPE.
4. If the obtained the first 2 bin average is between -1mV and 2mV and NPE value is less than 20,
calculate the best baseline with the iteration method.
Also note that the systematic error due to the baseline mis-identification by 1mV from ATWD in total
number of pe by NPEerror = ± 1(mV)*3.3(ns)*128(bin)/43(ohm)/1.6(pC) = ±6.1pe per DOM.
Similarly for FADC, baseline estimation with eheoptimized option would do:
1. Use the average of the first 3 bins.
2. If the value is not within ±0.5 mV, then assume that baseline is at 0mV to avoid strangely triggeredpulses.
For FADC it need to be reminded that because of large undershoots, we count value only above baseline
to get integrated charge, while for ATWD, we use both positive and negative entry with an assumptionthat if we have correct baseline and we don’t have any pulse in it, we get zero integrated charge.
The systematic error due to the baseline mis-identification by 1mV from FADC in total number of PE
are estimated as, NPEerror = ± 1(mV)*25(ns)*256(bin)/43(ohm)/1.6(pC) = ±93pe per DOM.

References[1] the Cosmic-Ray working group, Cosmic Ray Filter Request for 2008[2] the Exotic Physics working group,[3] http://www.ppl.phys.chiba-u.jp/∼aya/SC/

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