CBM experiment

1. CBM experiment Reconstruction in the CBM RICH detector The CBM RICH detector Results Electron Identification in the TRD detector CBM physics topics ECAL TOF TRDs RICH or MUCH MVD +STS PSD Electrons Pions Electron identification capabilities of the CBMexperiment at FAIRS. Lebedev1,2, C. Höhne1, G. Ososkov2and the CBM collaboration1 GSI, Darmstadt, Germany, 2 JINR LIT, Dubna, Russia e-mail: S.Lebedev@gsi.de Exploration of the QCD phase diagram in regions of high baryon densities and moderate temperatures. • Micro-Vertex Detector (MVD)determination of secondary vertices • Silicon Tracking System (STS) in dipole magnettrack reconstruction and momentum determination • Ring Imaging Cherenkov (RICH)electron identification or • Muon identification system (MUCH)moun identification • Transition Radiation Detectors (TRDs)identification of electrons with momenta above 1.5 GeV/c • Time-of-flight (TOF) system hadron identification About 800 charged particles for central Au+Au collision at a beam energy of 25 AGeV for the CBM acceptance. • Electromagnetic Calorimeter (ECAL)measurement of photon and neutral particles • Projectile Spectator Detector (PSD) determination of the collision centrality • Sketch of the STS and the RICH detector, track extrapolation and track projection onto the photodetector plane; • sketch of RICH hits and found rings; • ring-track matching. 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 of vector mesonsand J/Psi. • RICH characteristics: • radiatorNitrogen, length 2.5 m • glass mirrorof 3 mm thickness • photodetector Hamamatsu H8500MAPMT • about22 hits/ electron ring. Ring recognition Many overlapping rings -> algorithm based on Hough Transform is used. Simple procedure: circular fit Improved description: non-linear ellipse fit, as the rings in the photodetector plane have a slight elliptic shape. Ring fitting Parameters correction The values of major and minor half axes strongly depend on the position on the PMT plane. Parameter correction algorithm was implemented. Radius versus momentum for reconstructedrings in central Au+Au collisions at 25 AGeV beamenergy for UrQMD events. A 3σ band around the mean radiusis indicated by the solid lines. Ring-track matching Ring-track matching is based on combining pairs with the smallest distance between ring center and track extrapolation. Typical event in the CBM RICH. RICH hits (blue), track projections (brown). 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 Artificial Neural Network (ANN) is used. Fake ring rejection The CBM TRD is intended for tracking and improved electron identification for p > 1.5 GeV/c. Electron identification Finally, electronsare chosen by a 3σ cut around the mean electronradius (minor half axes). As an alternative we investigate the possibility to use an ANN. • TRD characteristics: • Each station consists of several identical layers (by default 4) • Pad readout with coordinate resolution 0.03-0.05 cm across and 0.27-3.3 cm along the pad Sketch of the CBM setup with the TRD detectors stations. Tracking procedure is based on Kalman filter and track following methods (see A. Lebedev poster). • Using only cut on sum of energy losses is not enough -> advanced algorithms were implemented, which allow to reach a pion suppression factor of 200 – 500 for 90% electron efficiency. • 3 methods of electron identification in TRD: • Wk,n goodness-of-fit criterion • Artificial Neural Network (ANN) • Likelihood Ratio Function Electron identification efficiency (left) and pion suppression factor (right) for simulations of centralAu+Au collisions at 25 AGeV beam energy (UrQMD). Energy loss, keV Mean energy losses in 12 layers for electron and pion. The RICH detectoralone yields a pion suppression factor of 500-1000at an electron identification efficiency of 85% whilein combination with TRD and TOF a factor 104 isreached at 75% efficiency.