SN0619 : A Proposal for STAR Inner TPC Sector Upgrade (iTPC)

Author(s):STAR Collaboration
Date:Feb. 18, 2015
File(s): STAR_iTPC_proposal_06_09_2015.pdf delta-y-rt.pdf Summary_September14th_iTPC_final.pdf
Abstract: We propose to upgrade the inner sectors of the STAR TPC to increase the segmentation on the inner padplane and to renew the inner sector wires. The upgrade will provide better momentum resolution, better dE/dx resolution, and most importantly it will provide improved acceptance at high rapidity to |η| < 1.7 compared to the current TPC configuration of |η| < ~1.0. In this proposal, we demonstrate that acceptance at high rapidity is a crucial part of STAR’s future as we contemplate forward physics topics such as pA, eA and the proposed Phase-II of the Beam Energy Scan program. Unlike the outer TPC sectors, the current inner TPC pad row geometry does not provide hermetic coverage at all radii. The inner pads are 11.5 mm tall yet the spacing between rows is variable but always greater than 5 cm, resulting in “missing rows”. Therefore, only 20% of the path length of a charged particles path traversing an inner sector of the TPC is sampled by the current padplane and electronics readout. With this proposal, we would like to increase the path length coverage in the inner sectors to 100%.
Future measurements, motivated by several open physics questions, will be greatly enhanced by the upgraded performance of the iTPC. Searching for a possible critical point in the QCD phase diagram is one of the major scientific tasks in heavy ion physics. The critical point, if it exists and can be identified, would provide a landmark in the phase diagram and guide further experimental and theoretical studies of QCD matter under a wide range of conditions. The ability of RHIC to scan a wide range of beam energies and beam species provides a unique opportunity for the exploration of the phase diagram. RHIC has completed Phase-I of the beam energy scan program (BES-I) with center-of-mass beam energies of 39, 27, 19.6, 14.5, 11.5 and 7.7 GeV. The STAR BES Phase-II (BES-II) White Paper sets out the physics case for an in-depth study of energies below 20 GeV with typically 20 times the statistics as in the same energy region in BES-I. Thus the enhanced measurement capabilities of STAR after the iTPC upgrade are a vital part of the new BES-II effort. The iTPC upgrade extends the rapidity coverage by 50%, a major benefit for many analyses, especially fluctuations (Kurtosis) and baryon v1 measurements; it improves the 2nd-order event-plane resolution away from mid-rapidity by a factor of 2, greatly enhancing all elliptic flow measurements; and in the area of dielectron measurements it reduces hadron contamination from a dominant source of uncertainty (20%) down by an order of magnitude, much less than the expected statistical uncertainty (10%).
Keywords:TPC Upgrade, Beam Energy Scan, Critical Point Search