Electron identification capabilities of the Electron identification capabilities of the CBMCBM experiment at FAIRexperiment at FAIR

S. LebedevS. Lebedev1,21,2, C. Höhne, C. Höhne11, G. Ososkov, G. Ososkov22

and the CBM collaborationand the CBM collaboration11 GSI, Darmstadt, Germany, GSI, Darmstadt, Germany, 22 JINR LIT, Dubna, Russia JINR LIT, Dubna, Russia e-mail: S.Lebedev@gsi.dee-mail: S.Lebedev@gsi.de

CBM experiment

ECALECAL

MVDMVD + +STSSTS

RICH or RICH or MUCHMUCH

TRDsTRDs TOFTOF

PSDPSD

CBM physics topics

The CBM RICH detector

Micro-Vertex Detector Micro-Vertex Detector (MVD)(MVD)determination of secondary verticesdetermination of secondary vertices

Silicon Tracking System Silicon Tracking System (STS) in dipole magnet(STS) in dipole magnettrack reconstruction and momentum track reconstruction and momentum determinationdetermination

Ring Imaging Cherenkov Ring Imaging Cherenkov (RICH)(RICH) electron identificationelectron identification

oror Muon identification Muon identification

system (MUCH)system (MUCH)moun identificationmoun identification

Transition Radiation Transition Radiation Detectors (TRDs)Detectors (TRDs) identification of electrons with momenta identification of electrons with momenta above 1.5 GeV/cabove 1.5 GeV/c

Time-of-flight (TOF) Time-of-flight (TOF) system system hadron identificationhadron identification

The RICH detector in CBM will serve for electron identification from lowest The RICH detector in CBM will serve for electron identification from lowest momenta up to 10-12 GeV/c needed for the study of the dielectronic decay momenta up to 10-12 GeV/c needed for the study of the dielectronic decay channel of vector mesonschannel of vector mesons and J/Psi. and J/Psi.

Typical event in the CBM RICH.Typical event in the CBM RICH.RICH hits (blue), track projections (brown).RICH hits (blue), track projections (brown).

RICH characteristics:RICH characteristics:• radiatorradiator NitrogenNitrogen, length 2.5 m, length 2.5 m• glass mirrorglass mirror of 3 mm thicknessof 3 mm thickness• photodetector Hamamatsu H8500photodetector Hamamatsu H8500 MAPMTMAPMT• aboutabout 22 hits/ electron ring.22 hits/ electron ring.

a)a) Sketch of the STS and the RICH Sketch of the STS and the RICH detector, track extrapolation and detector, track extrapolation and track projection onto the track projection onto the photodetector plane; photodetector plane;

b)b) sketch of RICH hits and found rings; sketch of RICH hits and found rings; c)c) ring-track matching.ring-track matching.

ElectronsElectrons

PionsPions

Radius versus momentum for reconstructedRadius versus momentum for reconstructed rings in central Au+Au collisions at 25 AGeV rings in central Au+Au collisions at 25 AGeV beambeam energy for UrQMD events. A 3energy for UrQMD events. A 3σσ band band

around the mean radiusaround the mean radius is indicated by the solid is indicated by the solid lines.lines.

Reconstruction in the CBM RICH detector

Simple procedure: Simple procedure: circular fitcircular fitImproved description: Improved description: non-linear ellipse fitnon-linear ellipse fit, as the , as the rings in the photodetector plane have a slight elliptic rings in the photodetector plane have a slight elliptic shape.shape.

Many overlapping rings -> algorithm based on Many overlapping rings -> algorithm based on Hough TransformHough Transform is used.is used.

Ring Ring recognitionrecognition

Ring fittingRing fitting

Parameters Parameters correctioncorrection

Ring-track Ring-track matchingmatching

Fake ring Fake ring rejectionrejection

Electron Electron identificationidentification

Ring-track matching is based on combining Ring-track matching is based on combining pairs with the smallest distance between pairs with the smallest distance between ring center and track extrapolation.ring center and track extrapolation.

The ring finder not only finds "true" rings but also "fake" rings by random The ring finder not only finds "true" rings but also "fake" rings by random

combinations of hits in the PMT plane. To reject fake rings an combinations of hits in the PMT plane. To reject fake rings an Artificial Artificial Neural Network (ANN) Neural Network (ANN) is used.is used.

Electron Identification in the TRD detector

Results

Finally, electronsFinally, electrons are chosen by a 3are chosen by a 3σσ cut around the mean electron cut around the mean electron radiusradius (minor half axes) (minor half axes).. As an alternative we investigate the possibility As an alternative we investigate the possibility

to use an to use an ANNANN..

Electron identification efficiency (Electron identification efficiency (left) left) and pion suppression factor (and pion suppression factor (rightright) for simulations of central) for simulations of central Au+Au Au+Au collisions at 25 AGeV beam energy (UrQMD).collisions at 25 AGeV beam energy (UrQMD).

The RICH detectorThe RICH detector alone yields a pion suppression factor of 500-1000alone yields a pion suppression factor of 500-1000 at an electron at an electron iidentification efficiency of 85% whiledentification efficiency of 85% while in combination with TRD and TOF a factor 10in combination with TRD and TOF a factor 1044 is is reached at 75% efficiencyreached at 75% efficiency..

The values of major and minor half axes strongly depend on The values of major and minor half axes strongly depend on

the position on the PMT plane. the position on the PMT plane. Parameter correction Parameter correction algorithmalgorithm was implemented. was implemented.

Electromagnetic Calorimeter (ECAL)Electromagnetic Calorimeter (ECAL)measurement of photon and neutral particlesmeasurement of photon and neutral particles

Projectile Spectator Detector (PSD)Projectile Spectator Detector (PSD) determination of the collision centralitydetermination of the collision centrality

The CBM TRD is intended for tracking and improved electron The CBM TRD is intended for tracking and improved electron identification for p > 1.5 GeV/c.identification for p > 1.5 GeV/c.

Sketch of the CBM setup with the TRD detectors Sketch of the CBM setup with the TRD detectors stations.stations.

TRD characteristics:TRD characteristics:• Each station consists of several identical Each station consists of several identical layers (by default 4) layers (by default 4) • PPad readout with coordinate resolution ad readout with coordinate resolution 0.03-0.05 cm across and 0.27-3.30.03-0.05 cm across and 0.27-3.3 cm along cm along the padthe pad

Tracking procedure is based on Kalman filter Tracking procedure is based on Kalman filter and track following methods (see A. Lebedev and track following methods (see A. Lebedev poster).poster).

Mean energy losses in 12 layers Mean energy losses in 12 layers for electron and pion.for electron and pion.

Using only cut on sum of energy losses is not Using only cut on sum of energy losses is not enough -> advanced algorithms were enough -> advanced algorithms were

implemented, which allow to reach a implemented, which allow to reach a pion pion suppression factor of 200 – 500 suppression factor of 200 – 500 for 90% for 90% electron efficiency.electron efficiency.3 methods of electron identification in TRD:3 methods of electron identification in TRD:• WWk,n k,n goodness-of-fit criteriongoodness-of-fit criterion• Artificial Neural Network (ANN)Artificial Neural Network (ANN)• Likelihood Ratio FunctionLikelihood Ratio Function

Energy loss, keV

Exploration of the QCD Exploration of the QCD phase diagram in regions of phase diagram in regions of high baryon densities and high baryon densities and moderate temperatures.moderate temperatures.

Physics TopicsPhysics Topics ObservablesObservables

In medium modifications In medium modifications of hadronsof hadrons , , , , ee++ee-- ((μμ++μμ--))

DD00, D, D±±, D, D±±ss, , cc

Strangeness in matterStrangeness in matter K,K, , , , , , ,

Indications of Indications of deconfinementdeconfinement

DD00, D, D±±

J/J/ΨΨ,,ΨΨ' ' ee++ee-- ((μμ++ μ μ--))

Critical pointCritical point Event by event fluctuationsEvent by event fluctuations

About 800 charged About 800 charged particles for central Au+Au particles for central Au+Au collision at a beam energy collision at a beam energy

of 25 AGeV for the CBM of 25 AGeV for the CBM acceptance. acceptance.