ALICE Week, 14.09.2004
Response function for the ITS PID
B.Batyunya, S. Zaporozhets
JINR, Dubna
• Outlook
• Comparison of the default (AliRoot) response functions
with the ones extracted from the fit procedure.
• Conclusion
Default response functions:
-- The mean dE/dx is calculated from Bethe-Bloch formula.
-- dE/dx resolution is 15% of the mean value.
-- The rates of the particles are fixed (K/  = 0.12, p/ = 0.06)
Fitted response functions:
-- The dE/dx mean values and resolutions, and the particel
rates were obtained from the gaussian fit procedure for
narrow momentum intervals.
Default-Corrected response functions:
-- The fixed particle rates were substituted by the fitted ones.
The simulation has been done using 250 HIJING events in the
frame of v4-Release AliRoot.
Signal-momentum plot for 200 HIJING events
Probability cuts
Signal fit at momentum 375-400 MeV/c.
-- The fake track influence is seen for kaons and protons.
-- Maximum probability method was used for the particle selection.
-- The long pion tail is the most reason of the kaon contamination.
Total signal and components at momentum 525-550 MeV/c.
Signal fit at 375-400 MeV/c.
Signal fit at 500-550 MeV/c
dE/dx resolution dependencies.
Particle concentration ratios as function of momentum.
Pions efficiencies and contaminations.
-- Very small dependence from the response function type is seen.
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Kaons efficiencies and contaminations.
-- The contamination is 2 - 1.5 times smaller for the
fitted response functions at p < 0.4 GeV/c.
Protons efficiencies and contaminations.
-- Some improvement is seen for the fitted response functions
at p > 0.95 GeV/c.
35 HIJING events
HEAD AliRoot
Efficiencies and contaminations for kaons
with the default responce functions.
Conclusions.
-- Influence of the response function type is very small for the
pion selection.
-- The contamination to kaons is 1.5 - 2 times smaller for the fitted
response functions at p < 0.4 GeV/c
-- The proton efficiency is visibly larger for the fitted response
functions at p > 0.95 GeV/c.