Measurement of Upsilon production cross section in dAu

Measurement of Upsilon production cross section in d+Au collisions at √s. NN=200 Ge. V Anthony Kesich STAR Collaboration University of California, Davis Summer Quarkonium Workshop June 13, 2011

Quarkonia as a Temperature Probe A. Mocsy, BNL Quarkonia Workshop, June 2011 • Quarkonia suppression is a proposed signature of QGP formation • Degree of suppression is a probe of initial QGP temperature • Need d+Au measurements to constrain cold nuclear matter effects • e. g. Shadowing, Cronin effect Slide

STAR Detector Time Projection Chamber • Gas Ionization Tracker • Used for e. ID • Full coverage in φ • |η|<1 No Silicon Tracker! Reduces EM material budget from 0. 06 to 0. 01 radiation lengths. Removed in Run 8 and beyond. Electromagnetic Calorimeter • Fast detector • Used for triggering and e. ID • Full coverage in φ • |η|<1 Slide

Upsilon Trigger • Called every time we see a high energy tower (>4. 2 Ge. V) • Looks for an associated high energy cluster • Required opening angle larger than 90° • Cuts on reconstructed mass • Only looks at the electromagnetic calorimeters E 1 Cluster L 0 Trigger Tower p+p q E 2 Cluster Data Slide

e. ID via Energy Loss • Identify electrons via energy loss in the TPC • Some contamination from hadrons • Contamination is less at higher momenta Slide

Track Matching and E/p • We can reject out-of-time tracks by matching to the EMC • EMC is a fast detector as opposed to the TPC • Once matched, we can compute E/p for the track • “Over-cut” on d. E/dx to get a more pure sample (but smaller) • Due to their low mass, electrons will have E/p ≈ 1 • Some variation from 1 due to background and E loss Slide

Observed Upsilon Signal n n n Signal + Background unlike-sign electron pairs Background like-sign electron pairs (1 S+2 S+3 S) total yield: integrated from 7 to 11 Ge. V from background-subtracted me+e- distribution n n Raw Yield: 172 +/- 20 (stat. ) Strong signal (8σ significance) Slide

Efficiencies = acc× L 0+L 2× 2(TPC reco)× 2 (e. ID cut) × mass acc 0. 34± 0. 025 L 0+L 2 0. 71± 0. 05 2(TPC reco) 0. 72± 0. 07 2(e. ID cut) 0. 87± 0. 04 mass 0. 96± 0. 04 0. 15± 0. 02 • • • acc is the efficiency of EMC detector and the geometrical acceptance L 0+L 2 is the efficiency trigger system (TPC reco) is efficiency of e reco in TPC mass is efficiency of mass cut (e. ID cut) is efficiency of e. ID cuts Slide

Upsilon d+Au Cross Section N 172 ± 20 0. 15 ± 0. 02 Ldt 32 nb-1 dy 1. 0 σ=35 ± 4(stat. ) ± 5(syst. ) nb Slide

Nuclear Modification Factor • Measure of suppression vs. binary scaled pp collisions • Rd. Au=1 means no net cold nuclear effects • Rd. Au=0 is full suppression • σpp=42 mb, σd. Au=2. 2 b • From Glauber model: <Nbin>=7. 5± 0. 4 • pp Y->ee mid-rapidity cross section: 114± 38± 24 pb • PRD 82 012004 (2010) • Rd. Au=0. 78± 0. 28(stat. )± 0. 20(syst. ) • Note: Doesn’t include background like Drell-Yan Slide

Summary and Outlook • Run 8 d+Au greatly increased our available data in a low material environment • Measured Rd. Au=0. 78± 0. 28(stat. )± 0. 20(syst. ) – Consistent with minimal cold nuclear matter shadowing • Additional statistics (∼× 3) in Run 9 pp 200 Ge. V will further shrink the Rd. Au uncertainty Slide

Back-ups Summer Quarkonia Workshop, June 2011 Slide

Summer Quarkonia Workshop, June 2011 Slide

With SVT Without SVT Summer Quarkonia Workshop, June 2011 Slide