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

TL;DR

This paper presents a new method to improve high-pT hadron identification in the STAR TPC by calibrating dE/dx measurements using various particle decays and electron triggers, enhancing particle discrimination up to 15 GeV/c.

Contribution

The paper introduces a novel calibration technique for dE/dx in the STAR TPC that accounts for deviations from the Bichsel function, improving high-pT particle identification accuracy.

Findings

Deviations in dE/dx can be up to 0.4σ (~3%) in p+p collisions.

Deviations depend on βγ and are modeled by a specific function.

Calibration improves the accuracy of hadron spectra analysis up to 15 GeV/c.

Abstract

We derive a method to improve particle identification (PID) at high transverse momentum ($p_T$) using the relativistic rise of the ionization energy loss ($rdE/dx$) when charged particles traverse the Time Projection Chamber (TPC) at STAR. Electrons triggered and identified by the Barrel Electro-Magnetic Calorimeter (BEMC), pure protons and pions from $\Lambda\to p+\pi^{-}$ ($\bar{\Lambda}\to \bar{p}+\pi^{+}$), and $K^{0}_{S}\to\pi^{+}+\pi^{-}$ decays are used to obtain the $dE/dx$ value and its width at given $\beta\gamma=p/m$. We found that the deviation of the $dE/dx$ from the Bichsel function can be up to $0.4\sigma$ ($\sim3%$) in p+p collisions at $\sqrt{s_{NN}}=200$ GeV taken and subsequently calibrated in year 2005. The deviation is approximately a function of $\beta\gamma$ independent of particle species and can be described with a function of $f(x) = A+\frac{B}{C+x^{2}}$. The deviations obtained with this method are used to re-calibrate the data sample from p+p collision for physics analysis of identified hadron spectra and their correlations up to transverse momentum of 15 GeV/$c$. The ratio of $e^{-}/e^{+}$ (dominantly from $\gamma$-conversion) is also used to correct the residual asymmetry in the negative and positive charged hadrons due to momentun distortion in the STAR TPC.