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

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  [-10°,10°]  [140,-140°]  [10°,22°]  [22°, 140°] régions

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 -

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

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

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

Momentum (GeV/c) Fraction of misidentified pions (DIRC) (ε electron =90%) Fraction of misidentified pions (EMC) (ε electron =80%) % %< %< %< 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

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

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

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

GEANT4 validations LHEPLHEP-Bert BIC

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

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

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 !!

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

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