Electron identification capabilities of the Electron identification capabilities of the CBM CBM experiment at FAIR experiment at FAIR S. Lebedev S. Lebedev 1,2 1,2 , C. Höhne , C. Höhne 1 1 , G. Ososkov , G. Ososkov 2 2 and the CBM collaboration and the CBM collaboration 1 1 GSI, Darmstadt, Germany, GSI, Darmstadt, Germany, 2 2 JINR LIT, Dubna, Russia JINR LIT, Dubna, Russia e-mail: [email protected] e-mail: [email protected] CBM experiment ECAL ECAL MVD MVD + + STS STS RICH or RICH or MUCH MUCH TRDs TRDs TOF TOF PSD PSD CBM physics topics The CBM RICH detector Micro-Vertex Detector Micro-Vertex Detector (MVD) (MVD) determination of secondary vertices determination of secondary vertices Silicon Tracking System Silicon Tracking System (STS) in dipole magnet (STS) in dipole magnet track reconstruction and momentum track reconstruction and momentum determination determination Ring Imaging Cherenkov Ring Imaging Cherenkov (RICH) (RICH) electron identification electron identification or or Muon identification Muon identification system (MUCH) system (MUCH) moun identification moun identification Transition Radiation Transition Radiation Detectors (TRDs) Detectors (TRDs) identification of electrons with momenta identification of electrons with momenta above 1.5 GeV/c above 1.5 GeV/c Time-of-flight (TOF) Time-of-flight (TOF) system system hadron identification hadron 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 channel momenta up to 10-12 GeV/c needed for the study of the dielectronic decay channel of vector mesons 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: • radiator radiator Nitrogen Nitrogen , length 2.5 m , length 2.5 m • glass mirror glass mirror of 3 mm thickness of 3 mm thickness • photodetector Hamamatsu H8500 photodetector Hamamatsu H8500 MAPMT MAPMT • about about 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. Electrons Electrons Pions Pions Radius versus momentum for reconstructed Radius versus momentum for reconstructed rings in central Au+Au collisions at 25 AGeV rings in central Au+Au collisions at 25 AGeV beam beam energy for UrQMD events. A 3 energy for UrQMD events. A 3 σ σ band band around the mean radius around 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 fit circular fit Improved description: Improved description: non-linear ellipse fit non-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 Transform Hough Transform is is used. used. Ring recognition Ring recognition Ring fitting Ring fitting Parameters Parameters correction correction Ring-track Ring-track matching matching Fake ring Fake ring rejection rejection Electron Electron identification identification 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, electrons Finally, electrons are chosen by a 3 are chosen by a 3 σ σ cut around the mean electron cut around the mean electron radius radius (minor half axes) (minor half axes) . . As an alternative we investigate the possibility to use As an alternative we investigate the possibility to use an an ANN ANN . . Electron identification efficiency ( Electron identification efficiency ( left) left) and pion suppression factor ( and pion suppression factor ( right right ) 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 detector The RICH detector alone yields a pion suppression factor of 500-1000 alone yields a pion suppression factor of 500-1000 at an electron at an electron i i dentification efficiency of 85% while dentification efficiency of 85% while in combination with TRD and TOF a factor 10 in combination with TRD and TOF a factor 10 4 is is reached at 75% efficiency reached 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 algorithm algorithm was implemented. was implemented. Electromagnetic Calorimeter (ECAL) Electromagnetic Calorimeter (ECAL) measurement of photon and neutral particles measurement of photon and neutral particles Projectile Spectator Detector (PSD) Projectile Spectator Detector (PSD) determination of the collision centrality determination 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) • P P ad readout with coordinate resolution ad readout with coordinate resolution 0.03-0.05 cm across and 0.27-3.3 0.03-0.05 cm across and 0.27-3.3 cm along cm along the pad the 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: • W W k,n k,n goodness-of-fit criterion goodness-of-fit criterion • Artificial Neural Network (ANN) Artificial Neural Network (ANN) • Likelihood Ratio Function Likelihood 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 Topics Physics Topics Observables Observables In medium modifications In medium modifications of hadrons of hadrons , , , , e e + + e e - - ( ( μ μ + μ μ - ) ) D D 0 , D , D ± , D , D ± s , , c Strangeness in matter Strangeness in matter K, K, , , , , , , Indications of Indications of deconfinement deconfinement D D 0 , D , D ± J/ J/ Ψ Ψ , , Ψ Ψ ' ' e e + e e - ( ( μ μ + μ μ - ) ) Critical point Critical point Event by event fluctuations Event 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.