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First spin results with PHENIX in RHIC Run-2 p+p collisions

This presentation outlines the spin physics research conducted at RHIC, focusing on the results obtained with the PHENIX detector in Run-2 p+p collisions (2001-2002). It covers topics such as cross sections, single-spin asymmetries, and future plans for studying spin structure and polarized proton collisions. The talk provides insights into the experimental setup, detectors used, and key findings related to polarized proton collisions in high-energy environments. The analysis includes cross-section measurements, muon detection, and interpretations of data within the context of perturbative QCD and theoretical models. The talk also explores the potential applications of spin physics beyond the standard model and the significance of single-spin asymmetries in understanding quark-gluon correlations. Overall, the results contribute to the growing body of knowledge in the field of spin physics at RHIC.

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First spin results with PHENIX in RHIC Run-2 p+p collisions

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  1. First spin results with PHENIX in RHIC Run-2 p+p collisions Hiroki Sato, Kyoto Univ./RIKEN DIS’03, St. Petersburg, Russia April 24, 2003

  2. Outline • Spin Physics at RHIC • Results with the PHENIX detector in Run-2 (2001-2002) p+p collisions • Cross sections • Single spin asymmetries (AN) • Future plan

  3. Spin Physics at RHIC Polarized p+p collisionsat high energy (50 < s < 500 GeV) enable us to study • Spin structure of the nucleon • Direct measurementof polarized gluon distributionG(x) • Flavor sensitive measurement of polarized anti-quark distribution q(x) • Parity violating spin symmetries for physics beyond standard model

  4. Relativistic Heavy-Ion Collider

  5. Polarizedproton collider RHIC RHIC pC Polarimeters BRAHMS & PP2PP PHOBOS Absolute Polarimeter (H jet) “Local” Polarimeters Yellow beam Blue beam RHIC PHENIX +-+-+-+- ++--++-- STAR Siberian Snakes 60 or 120 bunches Spin Rotators Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 75% polarization AGS AGS Internal Polarimeter Rf Dipoles 200 MeV Polarimeter Illustrated by Thomas Roser

  6. RHIC Run-2 p+p condition First polarized p+p collisions has achieved at s = 200 GeV • <PB>Yellow ~ 0.17, <PB>Blue ~ 0.14 • Transversely polarized protons  measurements of AN (left-right asymmetries) with various channels • Lint ~ 150nb-1 (triggered data) with PHENIX

  7. The PHENIX Detector • e, , h (Central Arms) • || < 0.35,  =  • pT> 0.2 GeV/c •  (Muon Arms) • 1.2 < || < 2.4,  = 2 • ptot> 2 GeV/c • Interaction-trigger and vertex Detectors • Beam-Beam Counters (3.0 < || < 3.9) • Zero-Degree Calorimeters (|| > 6.2) • Normalization Trigger Counters (1.1 < || < 2.8)

  8. The Beam-Beam Counters (BBC) • Cherenkov radiators (Quartz) each mounted on a PMT • Sensitive to charged particles with  > 0.7 • Cover 3.0 < || < 3.9 with a full azimuth • Primary trigger counter for p+p minimum bias (inelastic) events with ~50% efficiency • Used as a luminosity monitor • Determine event z-vertex positions (resolution ~2 cm for p+p  good enough for J/) 96 PMTs in each arm

  9. Central Arms • Tracking • Pad Chambers (PC1/2/3) • Drift Chambers (DC) • PID and Triggering • Ring Imaging CHerenkov detector (RICH) • Electro-Magnetic Calorimeter (EMCal, PbSc/PbGl) • Both West and East Arms were operational in Run-2 || < 0.35 Beam pipe  =  Cross section of the PHENIX Central Arms

  10. Muon Arms • Detect muons with ptot> 2 GeV/c,-1.2 >  > -2.2 (South Arm) or 1.2 <  < 2.4 (North Arm) • Muon Tracking Chamber (MuTr) • Measure momentum of muons with cathode-readout strip chambers at 3 stations inside Muon Magnet • Muon Identifier (MuID) • /µ separation with 5-layer sandwich of chambers (Iarocci tubes) and steel • Trigger muons • South Muon Arm was successfully operated first time during Run-2 MuID Muon Magnet MuTr

  11. Cross sections • Cross section measurements are important as the baseline for both heavy-ion and spin physics at RHIC • Test against perturbative QCD • Results of high-pT0(pT<13 GeV/c) and J/ will be shown here

  12. p+p 0X cross sections PHENIX Preliminary • Up to much higher pT compared to UA1 (pT<6 GeV/c) • NLO pQCD calculation • CTEQ5M pdf • Potter-Kniehl-Kramer fragmentation function •  = pT/2, pT, 2pT • Consistent with data within the scale dependence. Normalization error of 30% not shown. pT dependent systematic error

  13. p+p,s=200GeV e+e- µ+µ- Phys. Lett. B390,323 (1997) p+p  J/X cross sections Rapidity Fit gives Br (J/l+l-) (p+pJ/X) = 226  36 (stat.)  79 (syst.) nb  (p+pJ/X) = 3.8  0.6 (stat.)  1.3 (syst.) µb • Our result is consistent with s scaling from lower energy results

  14. Single-spin asymmetries (AN) FNAL E704 • Motivated by large AN measured by the FNAL-E704 experiment at high-xF at s = 19.4 GeV • Origin has not well understood theoretically • Quark-gluon correlation (higher-twist)? • L ? • Application for high-energy polarized proton polarimetry s=23.5 GeV PT=0.5~2 GeV/c

  15. ANfrom RHIC s=200 GeV Kinematical Coverage p0 (at high XF ) +10 ~ +20% XF 0.2 0.4 0.6 0.8 PT Charged ~0.5% FNAL-E704 s=20 GeV p+, p - (at high XF ) +10 ~ +30% STAR TPC PHENIX MUON PHENIX CENTRAL STAR FPD FNAL E704 STAR BBC PHENIX BBC pp2pp Neutron -10% g ~0% p0 <3% 0o CAL 0 1 2 3 4 5 Rapidity Work in progress! Results expected soon This talk

  16. BBC Asymmetries PHENIX preliminary R L AF = 1.3±1.8 AB = 1.2±1.8 ×10-3 assuming AN (RHIC pol.) = 0.0132 (backward) (forward) Results are consistent with 0

  17. Very-Forward  and n • Introduced as a polarized proton polarimeter at interaction region (thus called “Local” polarimeter) • Measure very-forward (||>6.5) photon and neutrons with low pT (pT<0.3 GeV/c) • In Run-2, installed in IP-12 region. In Run-3, installed also in IP-8 (PHENIX)

  18. Photon and 0 asymmetry • AN is Consistent with 0

  19. Neutron asymmetry • Unexpectedly large asymmetry has found -> No theoretical explanation so far • EM-Cal results and H-Cal results are consistent

  20. Neutron asymmetry phi dependence Very clear azimuthal asymmetry

  21. RHIC/Spin Present and Future • Run-3 (2003, just started!) • s = 200 GeV, 3pb-1 • pB ~ 40% • ALL for 0 and charged hadrons -> G(x) • Run-4 (2003-2004) • s = 200 GeV, 30pb-1 • pB ~ 50% • ALL for heavy flavors (single leptons, e, J/) -> G(x) • Run-5 and later • s = 500 GeV • PB ~ 70% • ALL for Direct photons -> G(x) • AL for W bosons-> q(x)

  22. Summary • In Run-2, RHIC has successfully accomplished transversely polarized p+p collisions at s = 200 GeV and PHENIX has accumulated Lint ~ 150nb-1 • Cross sections for high-pT 0 and J/ are consistent with pQCD predictions • Preliminary results of AN measurements are presented • Unexpectedly large asymmetry (AN~0.12) for neutron production at very-forward rapidity

  23. m p Single Muons Event vertex distribution containing  Asymmetric z-vertex distribution indicate /K  is dominant in inclusive single-muon yield Accepted range for single muon analysis ANof p/K can be obtained using single muons z [cm] MuTr Absorber Analysis is work in progress Beam Beam BBC Cu Fe

  24. Triggers Minimum-bias EMCal (low thres.) EMCal (high thres.) 1M 100k 3k Charged particle yield in Central Arm 3pT bins,0.8-2GeV/c, 2-4GeV/c, 4-6GeV/c Number of min-bias triggers　＝　31×106 Nch Both Arms Both charges pT [GeV/c]

  25. .6 4-6GeV/c 2-4GeV/c .4 0.8-2GeV/c AN(uncorr.) .2 0 -.2 -.4 -.6  Acceptance correction（０．８８） Raw asymmetry of each fill polarization （～１５％） Charged-hadron Asymmetries Work on progress! • Not corrected with • Trigger bias • Background dilution

  26. Qiu-Sterman model Muon Plus Pion Expected Error Bar (stat only) Minus <Xf> Pt(m)/Pt(p) Pt [GeV] 1 0.6 Expected AN by Single Muons <Xf>~0.04@Pt~1.5GeV • P(m) carries most of original P(p) • A_N(m) should be similar to A_N(p) • Xf(m) ~ 0.9 Xf(p)

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