Summary of the 2007 EHE workshop
a) IC-22 status
Carsten gave an introduction presentation on
the verification plots. The detection probability
against downgoing muon tracks is defined and calculated
in each of the DOMs. This is to compare to a nominal value
extracted from the "template of Good Run" and you make a judgment
of whether this run is good or bad. In Carsten's feeling,
most of RUN with data taken for longer than 4 hours are good.
Teresa introduced us to the work by Jon Dumm
where there are many plots of comparison between Corsika
("low energy" ~ TeV) data and the EHE filtered data.
It appears that there is a significant discrepancy between them,
especially at the deep layer of the IC-22 volume.
A straightforward interpretation is that the deep ice should be
much more cleaner than the simulation assumes. Then mystery
is that, why the standard candle real data looks dimmer than
the simulation data. See (b) below.
The EHE level1 filter is behind the schedule. Because we need
to take close look at the data as much and soon as possible,
we decided to generate it by ourselves until the "official" level1
data is released. Keiichi figured out the filtering way
and wrote a simple module to do this job. The file size
is around 3 Gbyte/day.
Paolo introduced a good piece of work by Sweden
to show a clear Cherenkov cylinder profile of hit timing
in the AMANDA bright events. This would be nice to be introduced
in the first guess geometrical reconstruction in order to possibly
improve the zenith angle resolution, which is a key in
EHE neutrino search.
(b) Standard candle.
Mina showed her first preliminary results of the comparison
between the data and simulation with the updated romeo.
The simulation still gave many more photons
than the real data. This discrepancy seems to have
distance dependences : For DOMs far away (>150 m)
the agreement gets better.
Aya showed her analysis concerning event total sum
of NPE and string 40 where the candle is located,
thus, making dominant contributions to the total NPE:
The systematic difference i.e., Data/MC is around 0.7
for the IC-9 readout configuration, 0.5 for the full bin
(c) Muon bundle modeling.
Shigeru gave a summary on what we have done for modeling
the background in IC-9 analysis and showed a significant
discrepancy between data and Corsika-QGSJET01. Teresa
gave a nice presentation on the present status of the different
hadronic interaction models. SYBYL featuring the complete
Feynman scaling is now producing more muons. Needs cautions
for QGSJET II because of the wrong cross sections but
it implemented the prompt muon production somehow.
Discussions on how we can study the prompt muons were made,
like looking at the horizontal events, but we seemed to agree
that this is nothing easy.
The plot was presented to show that simulating single
EHE muon gives more fluctuated NPE distribution than simulating bundle
with same energy in total, which leads to conservative estimates
on number of background events. You might to need simulate
the bundle, however, if your analysis is advanced to use
info recorded in each of DOMs, because then the spatial distribution
of muons in a bundle could matter. It was pointed out
that you can use Corsika events but with changing the flux weights
following the empirical model obtained from the data.
(d) Simulation issues
Related to (c) above, we need high energy Corsika sample.
Because of the limitation of CPU power and memory size,
we need to introduce threshold energy of muons in a bundle
and of cascades along muons in ice. The muon threshold energy
of 1 TeV would be the best compromise according to the Aya's trial.
Setting the threshold energy of the cascade was done in
level of the hit constructor in the 9-string analysis.
Keiichi will commit the Brutus trunk
to add this capability. Paolo will e-mail (he did already)
to Alex about the regular hit constructor.
Paolo will talk to Xianwu and begin the feasibility study
using the Southern cluster.
There may be a need to simulate EHE events with layered ice.
It requires some trick like binning the geometry.
Keiichi and Paolo discussed their technical details.
(e) Effective area comparison with that obtained by the diffuse analysis
Kotoyo (for the diffuse analysis) and Shigeru calculated
the IC-9 neutrino effective area of muons with up-going geometry
obtained by the diffuse analysis cut and the EHE cut, respectively,
and compared them each other. The diffuse area is larger below
20 PeV. The EHE area is a factor of two larger at 50 PeV.
The "paraboloid sigma zenith" cut (level 5) may play a role
to make this difference, according to Kotoyo's guess.