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

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

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

4. Identification with the TPC Sebastian Neubert TPC Truncated mean Peaks are nice Gaussian (~98% of the events) How far does the tail extend? (1% level??) STT?? to be simulated  peak has to be multiplied by 10 5 -10 6

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

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

7. Momentum (GeV/c) Fraction of misidentified pions (DIRC) (ε electron =90%) Fraction of misidentified pions (EMC) (ε electron =80%) 0.52-3 10 -3 2.5 % 0.81.5 %<2 10 -4 1.012%<2 10 -4 1.527%<2 10 -4 Problems: reconstruction efficiency in the DIRC is only 66 % for electrons (limit on chi2 ? ) E deposit in ECAL for  ’s is completely stupid at certain energies (several dE/dx peaks, not at the right value,etc…) Results from the old PANDA software

8. 1000 MeV/c 800 MeV/c 1500 MeV/c 500 MeV/c Geant4 8.0 : LHEP LHEP_BERT LHEP_BIC 1.3% 3.5%  absorption  neutrons escaping SCX  p and  0   EMC Response to  + : 9x9 crystals ( 2x2x20 cm 3 ) e 1/3 in the dE/dx peak 2/3 have interacted

9. EMC Response to  - : 9x9 crystals ( 2x2x20 cm 3 ) Geant4 8.0 : LHEP LHEP_BERT LHEP_BIC 800 MeV/c 1000 MeV/c 1500 MeV/c 500 MeV/c e

10. More -- ++  - (pn)  nn  + (pn)  pp +n0p+n0p -p0n-p0n 5 GeV/c 0.5 GeV/c

11. GEANT4 validations LHEPLHEP-Bert BIC

12. Conclusion on the ECAL LHEP-Bertini cascade differs from the 2 other models: LHEP and LHEP-BIC LHEP-Bertini cascade differs from the 2 other models: LHEP and LHEP-BIC LHEP-Bertini model reproduces the experimental data (  0 production dominated by quasi-free SCX) LHEP-Bertini model reproduces the experimental data (  0 production dominated by quasi-free SCX) Misidentification of  is 0.3 to 4%, depending mostly on model Misidentification of  is 0.3 to 4%, depending mostly on model  + and  - differ substantially  + and  - differ substantially The 3 models fit together at 5 GeV/c! The 3 models fit together at 5 GeV/c!  need for an experimental comparison + workout of a method to ‘identify’  0 s  need for an experimental comparison + workout of a method to ‘identify’  0 s

13. How to recognize  showers ? Measuring the tranverse size of the E deposit Measuring the tranverse size of the E deposit –  min (  1,  2 ) is energy dependant At 150 MeV,  min =55°  big effect At 150 MeV,  min =55°  big effect At 500 MeV,  min =25°  measurable effect At 500 MeV,  min =25°  measurable effect At 1500 MeV,  min =8°  effect difficult to detect At 1500 MeV,  min =8°  effect difficult to detect –Charged  ’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. 0n0n 000n000n 00n00n  - + p  (k  0 ) + n  - kinetic energy (GeV)  0 production induced by charged  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 dE/dx: option TPC/ST (factor 2.5) but may be not the only relevant parameter  origin of « background » has to be understood DIRC: 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: ECAL: –understand the role of the  0 and investigate methods to separate it (cluster, etc…  simulation in Orsay) –conduct tests on a pion beam

16. 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?) Separating with TPC