The RHIC Beam Energy Scan Phase II: Physics and Upgrades

TL;DR

RHIC's Beam Energy Scan Phase II aims to precisely explore the QCD phase diagram's high baryon chemical potential region through upgraded detectors and increased statistics, seeking critical point signatures and phase transition evidence.

Contribution

This paper details the planned upgrades and physics goals of RHIC's BES Phase II, enhancing measurement precision in the intermediate-to-high  region of the QCD phase diagram.

Findings

Enhanced statistics with electron cooling upgrade.

Improved detector acceptance for key measurements.

Potential identification of the QCD critical point.

Abstract

The exploration of the QCD phase diagram has been one of the main drivers of contemporary nuclear physics. The Relativistic Heavy Ion Collider (RHIC) at BNL is uniquely suited for this task through its Beam Energy Scan (BES) program which allowed for a large range in baryon chemical potential $\mu_B$ as was successfully demonstrated after the completion of Phase 1 in 2014. Phase 2 of the BES at RHIC is scheduled to start in 2019 and will explore with precision measurements the intermediate-to-high $\mu_B$ region of the QCD phase diagram, five energies $\sqrt{s_{NN}}$ from 7.7 to 19.6 GeV in collider mode and eight energies $\sqrt{s{_{NN}}}$ from 3.0 to 7.7 GeV in fixed-target mode. Some of the key measurements are: the net-protons kurtosis that could pinpoint the position of a critical point, the directed flow that might prove a softening of the EOS, and the chiral restoration in the dielectron channel. These measurements will be possible with an order of magnitude better statistics provided by the electron cooling upgrade of RHIC and with the detector upgrades planned to improve STAR's acceptance. These proceedings review the BES Phase-2 program and the physics opportunities enabled by these upgrades.