Improving the dE/dxdE/dx calibration of the STAR TPC for the high-pTpT hadron identification

We derive a method to improve particle identification (PID) at high transverse momentum (pTpT) using the relativistic rise of the ionization energy loss (dE/dxdE/dx) when charged particles traverse the Time Projection Chamber (TPC) at STAR. Electrons triggered and identified by the Barrel Electro-Magnetic Calorimeter (BEMC), pure protons (anti-protons) and pions from ΛΛ (Λ¯), and KS0 decays are used to obtain the dE/dxdE/dx value and its width at given βγ=p/mβγ=p/m. We found that the deviation of the dE/dxdE/dx from the Bichsel function can be up to 0.4σ0.4σ (∼3%∼3%) in p+pp+p collisions at sNN=200GeV taken and subsequently calibrated in year 2005. The deviation is approximately a function of βγβγ independent of particle species and can be described with the function f(x)=A+B/(C+x2)f(x)=A+B/(C+x2). The deviations obtained with this method are used in the data sample from p+pp+p collision for physics analysis of identified hadron spectra and their correlations up to transverse momentum of 15 GeV/c  . The ratio of e−/e+e−/e+ (dominantly from γγ-conversion) is also used to correct for the residual momentum distortion in the STAR TPC.