STAR Barrel Electromagnetic Calorimeter Absolute Calibration Using "Minimum Ionizing Particles" from Collisions at RHIC

TL;DR

This paper presents a method for calibrating the STAR BEMC using minimum ionizing particles from RHIC collisions, achieving percent-level accuracy and enabling continuous gain monitoring without disrupting physics measurements.

Contribution

The paper introduces a calibration technique using MIP-hits that directly transfers test beam calibration to RHIC operations with minimal reliance on simulations.

Findings

Calibration accuracy reaches about 1%

Method allows continuous gain monitoring

Calibration process is efficient and minimally intrusive

Abstract

The procedure for the STAR Barrel Electromagnetic Calorimeter (BEMC) absolute calibrations, using penetrating charged particle hits (MIP-hits) from physics events at RHIC, is presented. Its systematic and statistical errors are evaluated. It is shown that, using this technique, the equalization and transfer of the absolute scale from the test beam can be done to a percent level accuracy in a reasonable amount of time for the entire STAR BEMC. MIP-hits would also be an effective tool for continuously monitoring the variations of the BEMC tower's gains, virtually without interference to STAR's main physics program. The method does not rely on simulations for anything other than geometric and some other small corrections, and also for estimations of the systematic errors. It directly transfers measured test beam responses to operations at RHIC.