1. Spin Physics with PHENIX (an overview, but mainly  G) Abhay Deshpande Stony Brook University RIKEN BNL Research Center PANIC’11 at MIT July 28, 2011

2. Outline  Introduction  Relativistic Heavy Ion Collide as a polarized p+p collider  A brief overview of the RHIC Spin program  Spin Physics with PHENIX  Recent measurements leading to  G: Impact & limitations  PHENIX spin measurements leading to  G in near future  The question of anti-quark polarization  Summary & outlook 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 2

3. Complementary techniques  Polarized DIS discovered and established the nucleon spin crisis: quarks carry a small fraction of nucleon’s spin. Do gluon carry the remaining spin? Previous talk by COMPASS experiment at CERN  Protons are mostly gluons. Why not explore the gluon’s contribution to the nucleon spin by colliding polarized protons? A complementary approach! 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 3 pDIS p+p

4. RHIC as a polarized Collider 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 4 Without Siberian snakes: sp = G  = 1.79 E/m  ~1000 depolarizing resonances With Siberian snakes (local 180  spin rotators): sp = ½  no first order resonances Two partial Siberian snakes (11  and 27  spin rotators) in AGS

5. The RHIC Spin Program  Determination of polarized gluon distribution via multiple probes ( , c-cbar,… production)  Measurement of double longitudinal spin asymmetry A LL  THIS TALK (for PHENIX) & C. Gagliardi (STAR)  Determination of anti-quark polarization using production and decay of W +/- [ maximal parity violation]  Measurement of single longitudinal spin asymmetry A L  TALKS BY E. Kistenev (PHENIX) & J. Balewski (STAR)  Systematic study of transverse spin phenomena & their connections to transverse momentum and spatial distribution of partons  Measurement of single transverse spin asymmetries A N  TALKS BY D. Kleinjan (PHENIX) and R. Fatemi (STAR) 7/28/11 5 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC

6. Probes available at RHIC 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 6 Luminosity Low High 500 GeV CM

7. 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 7 Measuring A LL in a collider (N) Yield (R) Relative Luminosity (P) Polarization Bunch spin configuration alternates every 106 ns Data for all bunch spin configurations are collected at the same time  Possibility for false asymmetries are greatly reduced Exquisite control over false asymmetries due to ultra fast rotations of the target and probe spin.

8.  G program at PHENIX 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 8

9. PHENIX in 2011 Design philosophy: high resolution in limited acceptance, high rate capability DAQ, excellent trigger and DAQ system  Central Arms (|  | < 0.35) Tracking: Drift, Pad Chambers EM Calorimetry:  x  ~ 0.01 x 0.01 Particle ID: RHIC, TOF Si VTX tracker (|  | < 1)  Forward arms: Mu trackers and identifier (1.2 <  < 2.4) Global detectors: Beam-Beam collisions counters, Zero Degree Calorimeters Muon Piston Calorimeter (3.1 <  < 3.9)  Online monitoring, calibration & fast production the data 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 9

10. Access to  G in p+p collisions:   f =  q, input from polarized DIS   G to be measured! 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 10 From ep (& pp) (HERA mostly) NLO pQCD From e+e- (& SIDIS,pp) pp  hX Spin dependence PDF

11.   s in PHENIX  Large cross section, predominantly g-g interactions  2-g photon invariant mass reconstructed using high p T photon triggers 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 11 Partonic contribution to  0  s=200GeV, |  |<0.35  0 p T w BG 2 20% 5 8% 10 5% p T (GeV/c) vs. % background under signal PRD 76, 051106 (2007)

12.  0 cross section & A LL ( CM: 200 GeV) 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 12 PRL 103, 012003 (2009) PRD 76, 051106 (2007)

13. Impact: Early studies by PHENIX 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 13 PRL 103, 012003 (2009) at  2 = 4 GeV 2

14.  0 cross section & A LL ( CM: 62.4 GeV)  Lower CM Energy: accesses higher x  No evidence of significant asymmetry,  Consistent within uncertainties with asymmetry measurements at 200 GeV 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 14 00 PRD 79, 012003 (2009)

15. Impact: Global analysis at NLO (I)  NLO pQCD + Data from RHIC ( p+p ), p DIS (inclusive & semi-inclusive)  RHIC ( p+p ): Included PHENIX  0 at 200 & 62.4 GeV CM and STAR inclusive jets 200 GeV (Run-6) 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 15 DSSV : PRL 101, 072001 (2008) RHIC

16. PHENIX  0 (2009, preliminary) 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 16 Dataset (%) (%) L analyzed (pb -1 ) FOM (P 4 L) Run550492.50.15 Run656576.50.66 Run95757141.5 Run5 Run6 Run9

17. Other measurements related to  G Most of these measurements “luminosity starved”. Current impact is limited, but are important complimentary measurements, anticipated to be impactful in the next few years 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 17

18. 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 18 PRD83,032001(2011) PHENIX Direct Photon PHENIX p+p   +X Un-polarized NLO cross-section calculations compare well with the measured cross sections, in all cases.

19. What’s next for  G investigations @ PHENIX? Substantial uncertainties in  G at low x, accessible by: Accessing a different event geometry Accessing a different event geometry Collisions at higher center of mass energy Collisions at higher center of mass energy 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 19

20. Asymmetric x 1 & x 2 :  The Muon Piston Calorimeter (MPC)  3.1 <  < 3.9, both  arms  EM showers:  For p T < 2 GeV (  0  2   For p T > 2 GeV merged cluster algorithm developed  PYTHIA indicates 80% events from  0 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 20 x1x1 x2x2 pT=0.5 GeV/c … pT=4 (ref.) |  |<0.35

21. PHENIX MPC  0 : X-section & A LL 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 21

22. Low x using p+p at 500 GeV CM Cross section measured A LL (  0 ) analysis in progress 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 22 X min dependance on CM Energy x min

23. Quark/Anti-Quark Spin: W Physics at RHIC   From DIS experiments, using   as the probe  Can not distinguish between quark and anti-quark’s contributions  Determined in semi-inclusive DIS (SIDIS) which employ fragmentation functions to tag quark & anti-quark flavors: resulting in large uncertainties 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 23 DSSV : PRL 101, 072001 (2008)

24. PHENIX W physics PHENIX accesses Q and Qbar via W production & its PV decay Needs identification of charge of the final state lepton  PHENIX measures electrons/positrons in the central arm & muons in forward arm  Measurement of cross section & comparison with Standard Model Calculation an essential first step 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 24

25. PHENIX p+p  W cross section 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 25 Details of W measurements & its decay in to electrons (and progress on doing the same with) muons: in the following talk by E. Kistenev PHENIX PRL 106, 062001 (2011)

26. Summary (mainly  G)  PHENIX has measured double longitudinal spin asymmetries for various final in polarized p+p collisions at 62.4, 200 & 500 GeV in CM  Results indicate small contribution from  G to the nucleon’s spin in the currently measured regions.  Low x access to  G being explored with forward detectors in PHENIX and by raising the collision energy  Future possible upgrade of RHIC including possible construction of eRHIC at BNL are aimed with such measurement (See M. Stratmann’s talk later today)  Other components to the nucleon’s spin budget (anti-quark’s spin contribution & orbital motion: transverse spin results) being discussed in this and other sessions. (Talks by R. Fatemi, D. Kleinjan, T. Horn) 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 26

27. Thanks 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 27

28. The nucleon spin puzzle  Polarized DIS explored  Attempts of measurement at low x, resulting in the discovery of the nucleon spin puzzle   G: the gluon’s contribution to the nucleon spin (the principle focus of this talk)  L Q+G : connected to the transverse motion and transverse momentum dependence of the partons 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 28

29. Impact: Global Analysis at NLO (II) 7/28/11 Abhay L. Deshpande, Nucleon spin studies with PHENIX at RHIC 29 DSSV : PRL 101, 072001 (2008)