A Bidimensional Method for Particle Identification with the ALICE TRD

One of the main objectives of the Transition Radiation Detector (TRD) at LHC at CERN is to provide electron/pion identification for pt > 1GeV/c. The separation of electrons is based on ionization dE/dx and TR production and detection. We have improved the electron identification by better considering the contributions of ionization and TR production on the dE/dx measurements. The TRD detector design [1] enables up to 30 samples of dE/dx in one module. Due to reconstruction and tracking efficiency a robust estimator for dE/dx has to be introduced. The following effects can affect the dE/dx estimation: missing measurements, cluster sharing between tracks (high multiplicity environment) and drift velocity. The following estimator reflects these requierments: < dE/dx >t= 1/n ∗ ∑ t1 i=t0 wi ∗ dE/dxi, where t0 and t1 are defining slice integration limits of the dE/dxi measurements in one TRD module, n is the number of measurements in the slice and wi are weights reflecting cluster sharing and size. The limits t0 and t1 are 0 respectively 0.66 ∗ ntb for the measurements which contains mainly ionization contributions (dE/dxion) and 0.66 ∗ntb respectively ntb for those having also TR contribution (dE/dxtr). We are introducing here the calibration awareness by ntb = N ∗ vd/ν with N total number of time bins measured, vd the local drift velocity and ν the sampling frequency.