Beam Test LAT NewsLetter Report - Issue 4 - submitted 31 may

Luca Latronico
May 31 2007

The Calibration Unit worldwide tour was successfully concluded in the beginning of April, when the module was sent to SLAC and handed off to ISOC-SO that will turn it into a test bed to for studying flight hardware response to flight software.
This was the last step of a successfull series of CU operations carried on by the beam test team since its first integration just about one year ago .
We are happy to deliver such a valuable instrument to the ISOC, and completion of data analysis is now our only target.

On this ground, three main activites were pursued during the last month:

  • re-evaluation of data-MC discrepancies after the last data reprocess and updates to the simulation
  • completion of the standalone single-tower simulation and comparison with our standard Gleam MC
  • systematic exploration of available hadronic physics lists

The most recent changes to our simulation/reconstruction package (BTRelease) include the adjacent crystal cross-talk correction for the calorimeter energy measurement, two alternative Tracker digitization algorithms with description of charge sharing and large signal induced cross-talks, and a correct use of the tracker calibration database.
These last improvements did not significantly improve the data/MC agreement in the CAL energy and in the number of tracker hits, but provided a very accurate description of the measured ToT distribution.

The standalone Geant4 simulation was completed with a realistic tracker tray honeycomb description, as opposed to a density-averaged homogeneuous material. No effect was observed in the total number of hits and in the EM shower development, which is also very similar to the one produced by Gleam. Our conclusions are that Gleam and a standalone Geant4 simulation generate similar EM shower profiles, and a more realistic tray description does not solve either the CAL energy or TKR hits discrepancy.

A more complete survey of the available hadronic physics list in Geant4 was performed, and the currently best results are obtained with the Bertini model up tp 10GeV, and the QGSP libraries above 20GeV. Mor models are being studied now