SN0625 : RHIC Beam Use Request for runs 16 and 17

Author(s):the STAR Collaboration
Date:May. 19, 2015
File(s): STAR_BUR_Run1617_v18.pdf
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.

STAR’s top scientific priority is to capitalize on the existing investments in the Heavy Flavor Tracker (HFT) and Muon Telescope Detector (MTD) in run 16. The HFT and MTD were installed prior to run 14 and successfully operated in runs 14 and 15. We request 13 weeks of Au+Au collsions at √sNN = 200 GeV in run 16 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 16 data will allow for measurements of each of the three Upsilon states. The heavy flavor and quarkonium programs are of high priority for fulfilling STAR’s scientific program with the HFT and MTD upgrades before Phase II of the Beam Energy Scan (BES II).
STAR’s second highest scientific priority is the first significant measurement of the sign change of the Sivers’ function, when compared to the value measured in SIDIS, and evolution effects in transverse momentum distributions through measurements of single spin asymmetries in W+/-, Z, direct photon and Drell-Yan production 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 scientific priority is to clarify the interpretation of the observed signatures of the chiral magnetic effect, chiral magnetic wave and chiral vortical effect by making measurements that disentangle signal from background v2 effects. We request a 3 week run each for Ruthenium-96 (Ru+Ru) and Zirconium-96 (Zr+Zr) collisions in run 17. 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 reduces the flow background dramatically, and will greatly advance our understanding of the chiral magnetic effect, which has fundamental impact beyond the field of high-temperature QCD. The availability of the Ru-96 source precludes running this program as part of run 16 and uncertainty remains also for run 17. If this source cannot be secured in time, STAR proposes the 22-cryoweek scenario in Table 1-2. In the case that only 15 cryoweeks are available in run 17, STAR proposes the scenario given in Table 1-3.
Our next scientific priority is to take data at beam energies that are lower than the nominal energies, but are not part of STAR’s proposed Beam-Energy-Scan Phase-II program. 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, inclusive jet measurements are possible with minimum-bias data in Au+Au collisions. We have recently extended the measurement to Au+Au at 62 GeV 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.
The STAR Collaboration presents in this BUR five compelling and prioritized scientific programs for the 2016 and 2017 RHIC runs, prior to the start of BES-II. Taking into account uncertainty in the availability of the Ru-96 source, the duration of run 17 and the optimal detector opeartion, we propose three running scenarios (Tables 1-1 through 1-3). In each scenario, the data requirements for STAR’s two top priority scientific goals will be met. In no scenario can all the data needs for all programs be met in runs 16 and 17, and STAR may thus propose to return to the data taking for these programs concurrent with that for BES-II. In this BUR we furthermore discuss the highlights from the scientific publications, on-going analyses and detector performance from recent runs. We also outline the planned upgrades in the next few years in preparation for Run 17 and the Beam Energy Scan II.
Keywords:Beam Use Request, heavy-ion, Spin, STAR physics