The Forward GEM Tracker of STAR at RHIC

TL;DR

The paper discusses the design and construction of a forward tracking system using triple GEM technology for the STAR experiment at RHIC, enabling charge sign reconstruction of W bosons to study proton spin structure.

Contribution

It introduces a new forward GEM tracker system with specific design features and demonstrates its high spatial resolution and efficiency through beam tests.

Findings

Achieved spatial resolution of 70 micrometers or better.

Demonstrated high efficiency of the GEM detectors.

Extended rapidity coverage for W boson charge sign identification.

Abstract

The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is in the process of designing and constructing a forward tracking system based on triple GEM technology. This upgrade is necessary to give STAR the capability to reconstruct and identify the charge sign of W bosons over an extended rapidity range through their leptonic decay mode into an electron (positron) and a neutrino. This will allow a detailed study of the flavor-separated spin structure of the proton in polarized p + p collisions uniquely available at RHIC. The Forward GEM Tracker FGT will consist of six triple GEM disks with an outer radius of ~39 cm and an inner radius of ~10.5 cm, arranged along the beam pipe, covering the pseudo-rapidity range from 1.0 to 2.0 over a wide range of collision vertices. The GEM foils will be produced by Tech-Etch, Inc. Beam tests with test detectors using 10 cm x 10 cm Tech-Etch GEM foils and a two dimensional orthogonal strip readout have demonstrated a spatial resolution of 70 um or better and high efficiency.