BUR15 Executive Summary

The STAR Collaboration makes the following two-year beam-use proposal, in order to achieve its spin and relativistic heavy ion physics goals on a timescale consistent with intense international interest and competition in these areas, as well as to utilize RHIC beams effectively, taking full advantage of recent improvements in machine and detector capability.

Table 1 1: Scenario I-A: 22 cryoweeks for Run 17 with Isobar sources (Zr, Ru)

STAR’s top priority is to capitalize on the successful installation and operation of the Heavy Flavor Tracker (HFT) and Muon Telescope Detector (MTD) in runs 14 and 15. We request 13 weeks of Au+Au collsions at √s = 200 GeV to collect rare triggers for Upsilon states, gamma-jet correlations, B-->J/Psi and J/Psi production, as well as 2 billion minbias events for Lambda_c and differential studies of charm flow and correlations. The combination of the run 14 and run 16 will allow for measurements of each of the three Upsilon states. The heavy flavor and quarkonium program must be completed to fulfill STAR’s scientific program with the newly HFT and MTD upgrades before BES-II.

STAR’s second priority is to make the first significant measurement of the Sivers sign change and non-perturbative evolution effects in transverse momentum distributions via reconstruction of W+-, Z, direct photon and Drell-Yan single spin asymmetries in transversely polarized √s = 500 GeV p+p collisions. The sign change measurement is a fundamental test of QCD and is being pursued by other experiments, making a timely measurement imperative.

STAR’s third priority is to clarify the interpretation of the observed signatures of the chiral magnetic, wave and vortical effect by making measurements that disentangle signal from background v2 effects. We request a 3 week run each for Ruthinuium (Ru+Ru) and Zirconium (Zr+Zr) collisions. This choice of nuclei is ideal as it allows for a variation in magnetic field at a maximum of 10%, while keeping nearly all other parameters the same. This decisive measurement of the ratio of charge separation in the isobar while reducing the flow background to minimum will greatly advance our understanding of the chiral magnetic effect and has fundamental impact beyond the field of high-temperature QCD.  

Table 1 2: Scenario I-B: 22 cryoweeks for Run 17 for the case where the Ru-96 source cannot be procured. 

Our next priority is to take data at lower beam energies. There are two programs in our requests in this category:
a) Au+Au collisions at 62 GeV for measurements of inclusive jets and charm spectrum at low energy.
With newly developed analysis techniques, an inclusive jet measurement is possible with minimum-bias data in Au+Au collisions. We have recently extended the measurement to Au+Au at 62GeV with limited statistics from run 10. We request 4 (5) weeks of Au+Au collisions at this energy for an inclusive jet RCP measurement. This will also provide a measurement of D0 spectrum from HFT.
b) d+Au and p+p collisions at low energies for study of onset of high-pt hadron nuclear modification due to jet quenching.
STAR has produced a systematic measurement of RCP of inclusive hadrons as a function of momentum from all the beam energies taken at RHIC. The data has shown a systematic increase of RCP from less than unity to significantly above unity when the beam energy varies from top energy of 200 GeV to 7.7 GeV. A combination of d+Au collisions and p+p collisions at energies where RCP is around unity will help us address the onset of final-state hadron suppression.

Table 1 3: Scenario II: 15 cryoweeks for Run 17 (assume Isobar sources not possible in run16)

In this beam use request the STAR Collaboration presents five compelling scientific programs for the upcoming RHIC runs 16 and 17. We discuss the highlights from the scientific publications, on-going analyses and detector performance from recent runs. We have also outlined the planned upgrades in the next few years in preparation for the Beam Energy Scan II.