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

• Answer the question of the Answer the question of the feasibility of p_bar p feasibility of p_bar p e e++ee--

• Which discrimination power do we Which discrimination power do we need (competition between need (competition between ++-- and and ee++ee--)?)?

• Which tools do we have? Which tools do we have?

• Evaluate the discrimination power Evaluate the discrimination power of PANDA for electrons against of PANDA for electrons against pionspions

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

• KinematicsKinematics no way (10 MeV/c no way (10 MeV/c only)only)

• dE/dxdE/dx TPC or ST TPC or ST

• DIRCDIRC simulations with simulations with PANDA softwarePANDA software

• ECALECAL simulations with simulations with PANDA software and ‘local’ GEANT4PANDA software and ‘local’ GEANT4

What are the tools to What are the tools to separate separate ++-- from e from e++ee--

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 105-106

Pion/electron discrimination in DIRC : Pion/electron discrimination in DIRC : kinematicskinematics

a

A

a

45.110.7063.5970.963π- 0.5

47.160.680980.1.000e- 0.5

a

0.680

0.683

0.680

0.687

0.680

0.690

cos(θ)=1/(n)

47.162940.1.000e- 1.5

46.9310.7910.996π- 1.5

47.161960.1.000e- 1.

46.647.1940.990π- 1.

47.161570.1.000e- 0.8

46.365.7550.985π- 0.8

Θ (deg) =p/mp(Gev/c)

a

A

a

45.110.7063.5970.963π- 0.5

47.160.680980.1.000e- 0.5

a

0.680

0.683

0.680

0.687

0.680

0.690

cos(θ)=1/(n)

47.162940.1.000e- 1.5

46.9310.7910.996π- 1.5

47.161960.1.000e- 1.

46.647.1940.990π- 1.

47.161570.1.000e- 0.8

46.365.7550.985π- 0.8

Θ (deg) =p/mp(Gev/c)

DIRC resolutionafter track matchingσ~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)(εelectron=90%)

Fraction of misidentified pions (EMC) (εelectron=80%)

0.5 2-3 10-3 2.5 %

0.8 1.5 % <2 10-4

1.0 12% <2 10-4

1.5 27% <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

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 cm3)

e

1/3 in the dE/dx peak

2/3 have interacted

EMC Response to -: 9x9 crystals (2x2x20 cm3)Geant4 8.0 : LHEP LHEP_BERT LHEP_BIC

800 MeV/c

1000 MeV/c 1500 MeV/c

500 MeV/c

e

MoreMore

-

+

-

(pn)nn

+

(pn)pp+n0p

-p0n

5 GeV/c

0.5 GeV/c

GEANT4 GEANT4 validationvalidationss

LHEP LHEP-Bert

BIC

Conclusion on the Conclusion on the ECALECAL

• LHEP-Bertini cascade differs from the LHEP-Bertini cascade differs from the 2 other models: LHEP and LHEP-BIC2 other models: LHEP and LHEP-BIC

• LHEP-Bertini model reproduces the LHEP-Bertini model reproduces the experimental data (experimental data (00 production production dominated by quasi-free SCX) dominated by quasi-free SCX)

• Misidentification of Misidentification of is 0.3 to 4%, is 0.3 to 4%, depending mostly on modeldepending mostly on model

• ++ and and -- differ substantially differ substantially• The 3 models fit together at 5 GeV/c! The 3 models fit together at 5 GeV/c! • need for an experimental need for an experimental

comparison + workout of a method to comparison + workout of a method to ‘identify’ ‘identify’ 00ss

How to recognizeHow to recognize showers showers ??

• Measuring the tranverse size of the E Measuring the tranverse size of the E depositdeposit– minmin((11,,22) is energy dependant) is energy dependant

•At 150 MeV, At 150 MeV, minmin=55° =55° big effect big effect

•At 500 MeV, At 500 MeV, minmin=25° =25° measurable effect measurable effect

•At 1500 MeV, At 1500 MeV, minmin=8° =8° effect difficult to effect difficult to detectdetect

– Charged Charged ’s enter in cristals with a non ’s enter in cristals with a non zero angle which is both angle and zero angle which is both angle and momentum dependant (up to 22° at 500 momentum dependant (up to 22° at 500 MeV/c)MeV/c)

– Depth dependanceDepth dependance

0n

000n

00n

- + p (k0) + 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 !!

ConclusioConclusionsns

• dE/dx: option TPC/ST (factor 2.5) but may be dE/dx: option TPC/ST (factor 2.5) but may be not the only relevant parameter not the only relevant parameter origin of origin of « background » has to be understood« background » has to be understood

• DIRC:DIRC:– Barrel region: useful only at momenta < 1 GeV/cBarrel region: useful only at momenta < 1 GeV/c– Forward DIRC similar to Barrel DIRC Forward DIRC similar to Barrel DIRC no hope (E no hope (E

>> 3 GeV)>> 3 GeV)– RICH at forward angle (not yet investigated)RICH at forward angle (not yet investigated)

• ECAL: ECAL: – understand the role of the understand the role of the 00 and investigate and investigate

methods to separate it (cluster, etc… methods to separate it (cluster, etc… simulation in Orsay)simulation in Orsay)

– conduct tests on a pion beamconduct tests on a pion beam

e

e

dE/dx projections- for (1.50.1) GeV/c- for (2.00.1) GeV/c

Identifying e with TPC seems possiblePMID still to evaluate in details (1%?, less?)

Separating with TPC