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Spin Physics Progress with the STAR Detector at RHIC

STAR. Spin Physics Progress with the STAR Detector at RHIC. Spin related hardware improvements to STAR Important constraints on D G along the way – jets and p 0 s Sivers Functions from jets at mid-rapidity. J. Sowinski. for the. Collaboration. Detector. Lum. Monitor

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Spin Physics Progress with the STAR Detector at RHIC

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  1. STAR Spin Physics Progress with the STAR Detector at RHIC • Spin related hardware improvements to STAR • Important constraints on DG along the way – jets and p0s • Sivers Functions from jets at mid-rapidity J. Sowinski for the Collaboration

  2. Detector Lum. Monitor Local Polarim. Barrel EM Calorimeter -1<η< 1 STAR Triggering Beam-Beam Counters See talk by J. Kiryluk 2.2<|η|< 5 h = - ln(tan(q/2) =0 = -1 =2 Triggering Endcap EM Calorimeter Forward Pion Detector 1<η< 2 -4.1<η< -3.3 Time Projection Chamber -1.6<η< 1.6 Solenoidal Magnetic Field 5kG 2003 2004 2005 Tracking

  3. Endcap ElectroMagnetic Calorimeter • 1/3 Towers • All Towers . 1/3 SMD • Fully Instr. • Pb Scintillator sampling calorimeter – 21 rad. lengths • 720 Towers give EM energy • Shower Max. Detector for p0/g discrimination • Pre- and post-shower det’s for e/h discrimination • 9,792 channels read out • High Tower and Jet Patch triggers

  4. SMD profiles for a 9 GeV 0 candidate V U 7 cm [200 GeV p+p (2003)] 8 cm Online tower-only 0 reconstruction, 200 GeV Au+Au Charged tracks matched to fired EEMC towers for a 62 GeV Au+Au event. 2004 Data MIPs ~ 0.3GeV g All events Mixed events Difference Inv. Mass

  5. Barrel ElectroMagnetic Calorimeter One module = 40 towers 24 modules FY02 60 modules FY03 90 modules FY04 All modules (plan all elect.)FY05 • Scinti. + Pb sandwich sampling EMC • 4800 projective towers (2p in f, -1<h <1) • Shower Max Detector-gas detector-18K strips • Pre Shower Detector (first 2 layers) • High tower trigger & 1x1 (η, φ) jet trigger #120 – the last one! August 2004 pT>3GeV

  6. STAR The Proton Spin Structure - DG Orb. Ang. Mom. unknown Sz=½=½+G+ Lzq+ Lzg Gluon polarization poorly determined Quark pol. well known from DIS But only a small fraction of p helicity SMC Analysis, PRD 58, 112002 (1998) First Moments at Q02=1 GeV2: (MS) = 0.19 ± 0.05 ± 0.04 (AB) = 0.38 G(AB) = 0.99 (just one example of many) — + 0.03 + 0.03 + 0.03  0.03  0.02  0.05 + 1.17 + 0.42 + 1.43 0.31  0.22  0.45 DG is accessible and a high priority at RHIC and STAR!

  7. g STAR DG via partonic scattering from a gluon Know from DIS g-jet coinc.rare Measure • Dominant reaction mechanism • Experimentally clean reaction mechanism • Large a • But jet and p0 rates are sufficient to give significant DG const. in 2005 data ^ A ~ P3P3a g part LL LL pQCD Jets and p0s “DG” Prefer Heavy flavorrare ^ LL

  8. STAR Sees and reconstructs jets Large solid angle is crucial 1.0 Inclusive Jets :LO W. Vogelsang Leads to small but significant ALL in 2005 0.8 qg 0.6 0.4 Fraction gg qq (~1/10 of these stats from 2004 currently being processed) But signal is mixture of multiple partonic subprocesses 0.2 0.0 0 5 10 15 20 25 30 pT (GeV)

  9. Polarized Proton Operation at RHIC Year 2002 ~2007 s = 200 GeV Improving L and Pol. Spin flipper T/L Division To be decided Transverse/Longitudinal Spin running • 2002 2003 2004 2005 2006 2007 • L (s-1cm-2) 0.5x1030 2x10303x10308x1030 17x1030 48x1030 • Int. L(pb-1) (T/L) 0.3/0.00.5/0.4 0.5/0.4 4/7 28 86 • Pol. 0.2 0.3 0.40 0.45 0.65 0.70

  10. dDsab dDs Simulation ~1/3 of the jet energy is EM Use EM cals for triggering jets p0s carry ~same physics Jager, Stratmann, Vogelsang NLO pQCD calculations hep-ph/0404057 -1<h<1 -1<h<1 BEMC EEMC 1<h<2 EEM/Ejet Significant const. on DG expected in 2005 data (~1/10 stats. from ’04 being analyzed) (error bar estimates too small pT<6 GeV) • Only STAR can track vs. h – EMCs+FPD • Different partonic contributions • Large h small x

  11. Compton scattering dominates competing qq gg mechanism STAR Quark – Gluon Compton Scatteringp 1 p Direct g1Jet Eventually gives best determ. of Dg(x) for existing experiments. HERMES: PRL 84, 2584 (2000) SMC:PRD70, 012002(2004) fraction Will get started in 2005 & 2006 but need L of 2007+ and 500 GeV for g(x) Source: F.H. Heinsius, DIS 2004 xg pT Simulated full data set • Coinc.g– jet relatively clean exp. signature • Eg, hg and hjet determine xq, xg,q • Allows extraction of Dg(x) ^

  12. Jet For given parton at some x kTL=kTR STAR Jet Analyzing Powers at Mid-Rapidity Do processes invoked in forward scattering show up at large angles? STAR Collab. Phys. Rev. Lett. 92 (2004) 171801 Measure See A. Ogawa talk on fwd p0s D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004) 094025 Sivers Function – Initial state correlation between kT and spin

  13. sf= 0.236 0.026 0.03 0.05 STAR Partonic kT from Dijet Analysis Sivers Effect Prediction T. Henry, Quark Matter 2004, J. Phys. G 4.1 x 10 -4 D. Boer and W. Vogelsang, Phys.Rev. D 69 (2004) 094025 8 < pT1,2 < 12 GeV |η1,2 | < 1 AN df kT = <kT>2 = ET sin (sf) ET = 13.0 6 0.7sys GeV Trigger Jet STAR agrees well with World Data on Partonic kT df kT distribution • Curves are for various gluonic Sivers functions • Connection to partonic orbital angular momentum • Suppressed by Sudakov effect kT S

  14. STAR Conclusions(Beginnings;-) • RHIC will provide increasing L and P • STAR EM calorimeters complete • Triggering • Large solid angle EM coverage • See poster on future upgrades • Important constraints on DG expected in ‘05 • p0s • Jets • Direct gs – longer term • Investigations of transverse spin effects

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