1 May 27, 2005 Comparison tower A data and Montecarlo OVERVIEW Comparison of MC (EM- v 4r060302p18 ) and tower A data using the “baseline” run (Run ) “Some” differences, especially for tracker related variables Investigation: possible causes of discrepancy This is not a systematic study Sara Cutini - Gino Tosti INFN-PG Francesco Longo INFN-TS

2 May 27, 2005 Kalman’s variables Tkr1KalThetaMS represents the angle of multiple scattering calculated using the kalman filter. Muon selection: 1 reconstructed track, 36 tracker clusters, reconstructed energy in the Cal between 50MeV and 150MeV pink: MC, black: the real data The MC mean value (0.005rad) is nearly half value respect to the real data

3 May 27, 2005 Kalman’s variables Tkr1KalEne represents the track energy calculated using the kalman filter. This variable goes like 1/ , where  is the MS angle, Indeed the MC variable peaks at twice the value of the real data Why do we have this difference? For two towers? Let’s see.

4 May 27, 2005 Kalman’s variables for TwoTowers Let’s see the same variables for two towers data, after the muons selection. We have the same result. MC (EM-v4r060302p23): pink Run ( ): black

5 May 27, 2005 Kalman’s variables for Two Towers data We note this peak and we tried to understand where this peak comes from but we need more time to study it.

6 May 27, 2005 Possible causes of the Problems Problem generated by an underestimation of multiple scattering in the Montecarlo? We generated some events with the new version of Geant that seems to reproduce well the theoretical MS. See this link pdfhttp://www-glast.slac.stanford.edu/software/AnaGroup/burnett/Background%20status-25-april- 05.pdf But the problem persists… Problem is the MC Kalman filter? It uses the deposited energy in the Cal to extrapolate the energy of the track and its MS’s angle. But: it uses as default particle the electrons But also the data have been processed using the same option, and changing this option is not useful.

7 May 27, 2005 Input Flux?? The last hypothesis that we tested is that the input flux is not well modeling real data In the /flux/v…/xml/surface_library.xml we have 3 different options available. The pink one is the official MC. The blue one is the flux reproduced by the Caprice data. The green one the Hiro flux (Analytical Spectrum)

8 May 27, 2005 Caprice Flux We generated 3M events with the Caprice energy spectrum, looking at the same Kalman’s variables we note a “small” improvement. Let’s see… The Caprice’s peak is lower then the previous MC and the tail follows the real data. Blue Caprice MC. Pink Official MC. Black the real data

9 May 27, 2005 Hiro Flux We tried also the spectrum provided by Hiro but the result is very similar to the Caprice spectrum. Green Hiro MC. Pink Official MC. Black the real data But the problem persists!!

10 May 27, 2005 Low Flux We have looked only to the low energy part of the official Montecarlo: a flat spectrum energy below 1 GeV Red Low MC. Pink Official MC. Black the real data The multiple scattering angle is still not well reproduced.

11 May 27, 2005 Digi Variables Look at the digi data. Some differences also in the digi variables We used the Svac Ntuple, using the “tot[tower][layer][view][end]”. This plots represent the Time Over Threshold for one layer in both view. This could be due to a digitization problem, so we generated some events with a different digitization algorithm (the Bari’s digitization). But: that doesn’t change the distribution. (Thanks Anders!)

12 May 27, 2005 Conclusions We don’t understand why we have this difference and we need to figure out where the problem comes from We checked also other variables from the Merit and Svac Ntuple: e.g. Hits multiplicity, Cal variables, reconstructed direction… but we don’t find considerable differences. The problem could be generated by Wrong input flux? Multiple Scattering? Kalman filter which maybe works in two different ways for the real data and MC? Digitization problem? Help us to understand!!!

13 May 27, 2005 Backup slide Let see the ratio between the run histogram and the MC histograms. In black: run/Mc official In blue: run/Mc caprice In green: run/Mc hiro In pink: run/Mc low