Advanced digitization and cluster finding in MUCH

1. Advanced digitization and cluster finding in MUCH Evgeny Kryshen (PNPI) Vladimir Nikulin (PNPI) Mikhail Ryzhinskiy (SPbSPU) 11th CBM Collaboration Meeting, February 27, 2008 Supported from INTAS project 05-103-7484

2. Digitization algorithm Primary electrons: Number of primary electrons is generated according to Landau distribution (MPV and sigma taken from HEED) MPV and sigma are calculated for electrons, muons and protons. For other particle types we use mass scaling. Secondary electrons: Exponential gas gain distribution with mean value of 104 sec. electrons/prim. electron Charge thresholds: Maximal charge for muon track: 4x105 electrons/pad For 256 channel ADC one has 1.5x103 electrons/channel Factors not taken into account: Transverse diffusion of primary electrons is not accounted for Cluster nature of primary electrons Electronic noise is not accounted for 11th Collaboration Meeting, February 27, 2008

3. Charge distribution Mean charge: 3.6∙105 (In average 36 primary electrons) • Factors contributing to the charge dispersion: • Particle type • Particle energy • Track length variation • Number of “primary” electrons generated according to Landau distribution with a given MPV and sigma (dependent on Particle energy and type) • Gas gain fluctuations in accordance with exponential distribution with mean value of 10000 11th Collaboration Meeting, February 27, 2008

4. Energy dependence of the charge X axis – decimal logarithm of track energy measured in MeV Y axis – charge generated by track (number of secondary electrons) The sharp cut-off at Log E equal to 0 ( or equivalently 1 MeV) is due to the geant3 minimum energy cut 11th Collaboration Meeting, February 27, 2008

5. Energy dependence of the charge • Solid lines correspond to MPV energy dependencies built in the simulation (MPV curve is proportional to Bethe-Bloch in the first approximation) • These plots demonstrate the consistency of the simulation • Electrons are most sensitive to 1 MeV cut-off • Detailed studies of the electron cut-off dependency are desired Charge vs energy distributions for different particle types: 11th Collaboration Meeting, February 27, 2008

6. Charge vs. track length • Sensitive gap of the detectors is 3 mm • Difference in the track length is caused by the track slope • The large track length is usually caused by secondaries • Track lengths smaller than 3 mm are due to edge effects • Mean length for electrons: 4.5 mm • Mean length for protons: 3.5 mm 11th Collaboration Meeting, February 27, 2008

7. Clustering Q Qmax Qthr Primary cluster Hit coordinates: Hit errors: Qthr(Qmax) = 0.1Qmax pads 11th Collaboration Meeting, February 27, 2008

8. Cluster statistics • Mean number of generated MC points contributing to one cluster: 1.16 • Mean number of fired pads in one cluster: 2.33 • Mean number of reconstructed hits produced in one cluster: 1.02 11th Collaboration Meeting, February 27, 2008

9. Hit finding results inactive pads fired pads traces from MC tracks reconstructed hits –  3000 MC points/event 11th Collaboration Meeting, February 27, 2008

10. Fake hits 0.3% Fake hits – number of reconstructed hits is larger than the number of tracks which formed the cluster 11th Collaboration Meeting, February 27, 2008

11. Lost hits Lost hits – number of reconstructed hits is less than the number of tracks which formed the cluster 10.1% Conclusion: the naive hit finding algorithm should be improved 11th Collaboration Meeting, February 27, 2008

12. MUCH hit pulls • “True” position of the point – center of IN and OUT positions of the track at the sensitive gap • At the moment, a simple model has been used – the minimum pad size in the corresponding cluster is considered as a hit position uncertainty (divided by square root of 12) • For the estimation of pulls, we consider the hits at the first layer of the first station which are uniquely assigned to the MC point. • No bias • Sigma ~ 0.6 – 0.7 • Pull distributions are close to Gaussian shape, but hit uncertainties are systematically overestimated • Can be used in tracking algorithms but still error assignment requires detailed study • Central region: pad size 2.3 mm, which corresponds to sigma=680 m 11th Collaboration Meeting, February 27, 2008

13. Future plans • Study the influence of charge thresholds on cluster formation and hit finding • Develop an appropriate model for hit uncertainties • Develop advanced hit finder • Study the impact of realistic hit finding on muon hit reconstruction • Compare tracking performance for the ideal hitproducer and the real one • Play with digitization schemes – study the impact on hit production and tracking – optimization of segmentation and the number of channels • Introduce electronics noise (typical noise in “good” readout electronics ~ 1000 electrons) • Study the influence of additional secondary tracks (plugin by D.Bertini), compare with FLUKA, study energy dependence of FLUKA vs GEANT3 • Study GEM vsMicromegas • Study the influence of number of ADC channels on hit finding • Simulation parameter tuning according to beam test results 11th Collaboration Meeting, February 27, 2008