D. McDonald

The STAR Vertex Position Detector

Abstract The 2×3 channel pseudo Vertex Position Detector (pVPD) in the STAR experiment at RHIC has been upgraded to a 2×19 channel detector in the same acceptance, called the Vertex Position Detector (VPD). This detector is fully integrated into the STAR trigger system and provides the primary input to the minimum-bias trigger in Au+Au collisions. The information from the detector is used both in the STAR Level-0 trigger and offline to measure the location of the primary collision vertex along the beam pipe and the event “start time” needed by other fast-timing detectors in STAR. The offline timing resolution of single detector channels in full-energy Au+Au collisions is ~100xa0ps, resulting in a start time resolution of a few tens of picoseconds and a resolution on the primary vertex location of ~1xa0cm.

Suppression of Y production in d+Au and Au+Au collisions at √SNN=200 GeV

We report measurements of Υ meson production in p + p, d + Au, and Au + Au collisions using the STAR ndetector at RHIC. We compare the Υ yield to the measured cross section in p + p collisions in order to nquantify any modifications of the yield in cold nuclear matter using d+Au data and in hot nuclear matter nusing Au+Au data separated into three centrality classes. Our p+ p measurement is based on three times nthe statistics of our previous result. We obtain a nuclear modification factor for Υ (1S + 2S + 3S) in the nrapidity range |y| < 1 in d + Au collisions of RdAu = 0.79 ± 0.24(stat.) ± 0.03(syst.) ± 0.10(p + p syst.). nA comparison with models including shadowing and initial state parton energy loss indicates the npresence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au + Au ncollisions, we measure a nuclear modification factor of R A A = 0.49 ± 0.1(stat.) ± 0.02(syst.) ± 0.06(p + p syst.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are nconsistent with complete suppression of excited-state Υ mesons in Au + Au collisions. The additional nsuppression in Au + Au is consistent with the level expected in model calculations that include the npresence of a hot, deconfined Quark–Gluon Plasma. However, understanding the suppression seen in nd + Au is still needed before any definitive statements about the nature of the suppression in Au + Au ncan be made