LAT Newsletter contributions from Beam Test Team
Issue 10, march 2008
Joint report with C&A on the C&A-SciOps workshop
Issue 9 - submitted december 25 (DRAFT)
Simulation highlights
- BT simulations were successfully ported to the Pipeline II environment by Johan; this ensures a consistent platform with other LAT simulations for data generation, archival and storage, which will allow efficient use of the BT data well after launch. A number of test simulations are now available from the data catalog, and any new simulation will be generated using Pipeline II.
- the H4 line simulation was double-checked and updated by Francesco as to extend the simulation up to the last bending magnet in the line. No significant difference was found in the energy distribution
- a comprehensive comparison with EGS5 from David showed very good agreement with Geant4
- scaling variables: we started looking into ways for scaling the MC data to match our data; Johan explored the consequences of changing CAL calibration constants, Luca scaled the ntuple variables and started looking at consequences of the scaling in the event classification, Carmelo showed the consequences of changing the incoming beam energy by the measured discrepancy. We will have further discussions on this topic in the CA-SO workshop in Bari, and plan to agree on a way to implement this
Analysis highlights
- bad position measurements in the CAL were studied by Philippe and Sasha; a possible explanation for these could be event pile-up, but it requires some more analysis to be confirmed
- TKR cuts are being revised in the light of the new variables introduced for the neutral energy events
- LAC thresholds behave in a different way in data and simulation : potentially due to pedestal drift, issue is under investigation
Issue 8 - submitted december 4 (DRAFT)
The status of the beam test analysis was summarized in the last collaboration meeting in the session devoted to illustrate all the source of systematics that can impact our science anlysis. The focus was on clarifying which results are complete and solid and what are the open issues which we still have to address. It is clear that the current difference in the calorimeter variables (see below) is a concern and calls for a final effort for being solved. In parallel, we should constrain that into a quantitative statement on the resulting systematic error on the energy measurement, and a similar approach should be pursued for the TKR variables.
Below are some details of the recent progress.
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- pass5 variables from the current event classification analysis are added to the Merit Tuple and replace old pass4 variables; this allow a subsystem specific data-MC comparison for the relevant variables for background rejection
- vertex variables in the tuples are modified to describe also neutral energy events; this requires a thorough check of the usual TKR cuts that were used so far in the TKR analysis, and in particular Tkr1 variables should replace Vtx variables for analysis of all charged tracks
- list of golden runs : we are adding some new reference runs after we discovered that many of the runs we used are showing a weird structure in the TkrYdir_vs_TkrY correlation plot as a consequence of a large dead area in plane 35 of Tower 2 that the beam crossed and noisy strips around that area
- a pressure scan in the cerenkov detectors along the SPS H4 line was performed as a quick way to simulate effects of different material along the line
- the high energy SPS runs (E>5GeV) were re-simulated with the correct pressure (0.1bar) and gas (He) in the cerenkov detectors along the H4 line0.1bar) and gas (He) in the cerenkov detectors along the H4 line
- along with moving to v71215p0, synchronized with GR v12r15, Beamtest MC software is going to be updated to run on the pipeline II, in particular to use the new standard ways to store data on xroots and access them via the data catalog.
Analysis highlights:
- geant4-EGS5 comparison: a full first check was documented by David Paneque, and shows a reassuring agreement for both the longitudinal and transverse EM shower shape, at least for a simple CAL geometry with no gaps
- but we heard that Babar had seen similar EM shower shape issues between their beam test Data and GEANT4 MC
- studies with extra material along the beamline : the average energy overestimation between data and MC is about 7%, but it is higher for the first layers of the calorimeter than for the last; this seems to indicate that the showers start earlier in the data than in the MC, tracing extra material along the beamline that is not described in the simulation. We have tested this idea by simulating different pressures in the Cherenkov and looking for the amount of extra-material that could account for the current disagreement between data and MC. When considering most of the SPS configurations, we find that 10% of radiation length would help, though it doesn't solve the discrepancy for all configurations and only 5% of radiation length seems necessary for the tracker variables
- a preliminary comparison of the pass5 variables performed within Insightful Miner for a specific run shows that these are fairly well reproduced in the MC, except for the calorimeter related variables. This is certainly due to the transverse size of the showers which is larger in the data than in the MC.
- the PSF with tagged photons was recomputed and shown to agree with the full bremsstrahlung analysis when using the same cuts
- TKR hits and cluster summary: a different behaviour with photons wrt electrons was observed after the simulation/reprocessing with the current BTRelease (v7r11117p1); while electrons show the usual lower number of hits and cluster in the MC, photons have now a larger number of hits; the analysis must be repeated with updated cuts. Scans along X and Y show a negligible dependence of the discrepancy with the position
- high energy electrons : an initial stab at modifying CAL variables to match the data was tested in the context of an event classification study to tag high energy electrons, and it was shown that the effect of the current discprepancy, mostly from the CalTransRms variable, on the algorithm that separated electrons from hadrons is non-negligible
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