MRI Consortium: Development of a Forward Calorimetry Upgrade for the STAR Detector

Indiana University, Bloomington IN

Investigators

Abstract

Quantum Chromodynamics, or QCD, is considered a cornerstone of modern physics. As the fundamental theory of the nuclear force, it describes strongly interacting matter in terms of point-like quarks bound together via exchange of massless particles called gluons. Yet despite its remarkable success in explaining measurements carried out at the highest energies, a detailed understanding of low-energy phenomena, such as the internal structure of the protons and neutrons that make up 99% of the visible mass of the universes, remains elusive theoretically and must be gained through experiment. Over the last few decades, much progress has been made in this area, but not for the very low or very high energy constituents within the proton. This project will upgrade the STAR detector in order to make possible the study of proton-proton collision products at far-forward angles, a kinematic regime dominated by the scattering of high-momentum quarks on low-momentum gluons. This study will provide a unique opportunity to explore how the quarks, gluons, and their spins are distributed in space and momentum. Using the same techniques in proton-nucleus collisions will allow for a better understanding of how properties of protons and neutrons are modified in the nuclear environment. That in turn will improve the understanding of nucleus-nucleus collisions. The STAR forward upgrade is designed to explore QCD physics in the very high and low regions of partonic momentum fraction, a kinematic regime that has thus far remained inaccessible at RHIC. It will provide superior detection and reconstruction capabilities for neutral pions, photons, electrons, jets, and leading hadrons over the pseudo-rapidity range 2.5-4. To reduce costs and risk, much of the detector package will consist of previously used components. The electromagnetic calorimeter will use refurbished sampling Pb-scintillator blocks from PHENIX. The hadronic calorimeter will be a sandwich iron-scintillator plate sampling type, designed and prototyped with separate R&D funds. Both calorimeters will share the same cost-effective readout electronics, and will use SiPMs as photo-sensors, thereby allowing them to operate without shielding in high magnetic fields and high radiation environments, as will be encountered in this location. By design, the system is scalable and reconfigurable: the EMCal blocks are simply stacked vertically, while HCal "slabs" will be assembled in place. Integration into STAR will require only minimal modification of existing infrastructure. Based on detailed GEANT simulations, the Forward Calorimetry System (FCS) will have very good electromagnetic (10% / sqrt(E) + 3%) and hadronic (~50% / sqrt(E) + 10%) energy resolution. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.