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Some remarks on (mis)identification: separation of pions from electrons

Some remarks on (mis)identification: separation of pions from electrons. Answer the question of the feasibility of p_bar p  e + e - Which discrimination power do we need (competition between p + p - and e + e - )? Which tools do we have?

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Some remarks on (mis)identification: separation of pions from electrons

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  1. Some remarks on (mis)identification: separation of pions from electrons • Answer the question of the feasibility of p_bar p  e+e- • Which discrimination power do we need (competition between p+p- and e+e-)? • Which tools do we have? • Evaluate the discrimination power of PANDA for electrons against pions

  2. Detection and idenfication in the different regions  [-10°,10°] 1 régions 2  [10°,22°] 3  [22°, 140°] 4  [140,-140°] Q²=22.3 (GeV/c)² cos(cm) Both e- et e+ are detected Part. 1 Part. 2

  3. What are the tools to separate p+p- from e+e- • Kinematics  no way (10 MeV/c only) • dE/dx  TPC or ST • DIRC  simulations with PANDA software • ECAL  simulations with PANDA software and ‘local’ GEANT4

  4. TPC Identification with the TPC p peak has to be multiplied by 105-106 • Truncated mean • Peaks are nice Gaussian (~98% of the events) • How far does the tail extend? (1% level??) • STT?? to be simulated Sebastian Neubert

  5. Pion/electron discrimination in DIRC : kinematics DIRC resolution after track matching σ~2.5 mrd (0.15 deg)

  6. Reconstructed mass with the Barrel DIRC (old PANDA software) 800 MeV/c 0.5 GeV/c 0.8 GeV/c π p e 1000 MeV/c 1500 MeV/c 1.0 GeV/c 1.5 GeV/c

  7. Results from the old PANDA software • Problems: • reconstruction efficiency in the DIRC is only 66 % for electrons (limit on chi2 ? ) • E deposit in ECAL for p’s is completely stupid at certain energies (several dE/dx peaks, not at the right value,etc…)

  8. EMC Response to +: 9x9 crystals (2x2x20 cm3) Geant4 8.0 :LHEP LHEP_BERTLHEP_BIC 500 MeV/c 800 MeV/c 1.3% 3.5% e p absorption  neutrons escaping SCX  p and p0  gg 1500 MeV/c 1000 MeV/c 2/3 have interacted 1/3 in the dE/dx peak

  9. 500 MeV/c 800 MeV/c e 1000 MeV/c 1500 MeV/c EMC Response to -: 9x9 crystals (2x2x20 cm3) Geant4 8.0:LHEP LHEP_BERT LHEP_BIC

  10. 0.5 GeV/c More p+ 5 GeV/c p+(pn)pp p+np0p p- p-(pn)nn p-pp0n

  11. LHEP LHEP-Bert BIC GEANT4 validations

  12. Conclusion on the ECAL • LHEP-Bertini cascade differs from the 2 other models: LHEP and LHEP-BIC • LHEP-Bertini model reproduces the experimental data (p0 production dominated by quasi-free SCX) • Misidentification of p is 0.3 to 4%, depending mostly on model • p+ and p- differ substantially • The 3 models fit together at 5 GeV/c! •  need for an experimental comparison + workout of a method to ‘identify’ p0s

  13. How to recognize p showers ? • Measuring the tranverse size of the E deposit • qmin(g1,g2) is energy dependant • At 150 MeV, qmin=55°  big effect • At 500 MeV, qmin=25°  measurable effect • At 1500 MeV, qmin=8°  effect difficult to detect • Charged p’s enter in cristals with a non zero angle which is both angle and momentum dependant (up to 22° at 500 MeV/c) • Depth dependance

  14. p- +p  (kp0) + n p0n p0p0p0n p0p0n p- kinetic energy (GeV) p0 production induced by charged p on proton Around 1 Gev/c, the probability for a SXC amounts to a few percent !!

  15. Conclusions • dE/dx: option TPC/ST (factor 2.5) but may be not the only relevant parameter  origin of « background » has to be understood • DIRC: • Barrel region: useful only at momenta < 1 GeV/c • Forward DIRC similar to Barrel DIRC  no hope (E >> 3 GeV) • RICH at forward angle (not yet investigated) • ECAL: • understand the role of the p0 and investigate methods to separate it (cluster, etc…  simulation in Orsay) • conduct tests on a pion beam

  16. Separating with TPC e e dE/dx projections - for (1.50.1) GeV/c - for (2.00.1) GeV/c Identifying e with TPC seems possible PMID still to evaluate in details (1%?, less?)

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