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PHENIX G Program: Results and Plans

PHENIX G Program: Results and Plans. A.Bazilevsky Brookhaven National Laboratory For the PHENIX Collaboration. SPIN-Praha-2010, Jul 18-24. Proton Spin. Proton Spin. (anti)quark spin. Gluon spin. Parton Orbital Momentum. 1988 EMC (CERN):  is small  Proton Spin Crisis

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PHENIX G Program: Results and Plans

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  1. PHENIX G Program: Results and Plans A.Bazilevsky Brookhaven National Laboratory For the PHENIX Collaboration SPIN-Praha-2010, Jul 18-24

  2. Proton Spin Proton Spin (anti)quark spin Gluon spin Parton Orbital Momentum 1988 EMC (CERN):  is small  Proton Spin Crisis From recent fits: ~1/4 (PRL101:072001,2008) Gluons carry ~1/2 of the proton momentum  Natural candidate to carry proton spin Determination of Gis the main goal of longitudinal spin program at RHIC

  3. From DIS … • Inclusive polarized DIS • Only information about input and scattered lepton (e, ) is recorded • x and Q2 reconstructed from kinematics • Do not have direct access to gluon • Probe it through scaling violation (Q2 dependence of quark PDFs) - with poor precision currently • Semi-inclusive polarized DIS • Probe gluon through photon-gluon fusion process. • Record heavy mesons (fragmented from heavy quarks) • + Theoretically clean (high energy scale established by quark heavy mass) • –Background, low statistics • Record light mesons (fragmented from light quarks) • + High statistics • – Large background and low energy scale (problematic theoretical interpretation)

  4. … To polarized pp collider Utilizes strongly interacting probes g • Probes gluon directly • Higher energies  clean pQCDinterpretation • Polarized Gluon Distribution Measurements (G): • Use a variety of probes with variety of kinematics • Access to different gluon momentum fraction x • Different systematics • Use different beam energies • Access to different gluon momentum fraction x

  5. Polarized PDF q = u,d,s … Proton spin Quark spin helicity(longitudinal spin) distribution Dq(x,Q2)= Quarks unpolariseddistribution q(x,Q2) = helicity(longitudinal spin) distribution Dg(x,Q2)= Gluons unpolariseddistribution g(x,Q2) =

  6. Double longitudinal spin asymmetry ALL is sensitive to G Probing G in pol. pp collisions pp  hX

  7. BRAHMS & PP2PP (p) PHENIX (p) STAR (p) RHIC as polarized proton collider Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes Spin Rotators Longitudinal Spin Running in PHENIX 2  1011 Pol. Protons / Bunch e = 20 p mm mrad Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles

  8. Measuring ALL • (N) Yield • 0, , ±, h±, , e,  etc. • (R) Relative Luminosity • (P) Polarization • RHIC Polarimeter (at 12 o’clock) • Local Polarimeters(in experiments) • Bunch spin configuration alternates every 106 ns, at RHIC • Data for all bunch spin configurations are collected at the same time •  Possibility for false asymmetries are greatly reduced

  9. PHENIX Detector • Philosophy (initial design): • High rate capability & granularity • Good mass resolution & particle ID • Sacrifice acceptance • p0, g, h • Electromagnetic Calorimeter • p±, e,J/ye+e- • Drift Chamber • Ring Imaging Cherenkov Counter • Electromagnetic Calorimeter • ,J/y+- • Muon Id/Muon Tracker • Relative Luminosity • Beam Beam Counter (BBC) • Zero Degree Calorimeter (ZDC) • Local Polarimetry– ZDC • Spin direction control

  10. charged particles neutron PHENIX Local Polarimeter • Utilizes spin dependence of very forward neutron production discovered in RHIC Run-2002 (PLB650, 325) Zero Degree Calorimeter: <2.5 mrad

  11. PHENIX Local Polarimeter Asymmetry vs  Measures transverse polarization PT , Separately PX and PY Longitudinal component: P – from CNI polarimeters Vertical Radial Longitudinal Vertical f~ ±p/2 Radial  f~ 0 Longitudinal  no asymmetry 0 /2 -/2 Longitudinal spin runs:

  12. 144 cm Relative Luminosity Beam-Beam Counters (BBC) • Two arrays of 64 elements, each a quartz Cherenkov radiator with PMT • Δη = ±(3.1 to 3.9), Δφ = 2π • Cross checked with ZDC: • <2.5 mrad (>6) • Different physics signal, different kinematic region • ALL of BBC relative to ZDC is ~0 • Results: • R ~ (25)10-4  ALL ~ (37)10-4(for P~0.6)

  13. Unpol. Cross Section and pQCD in pp s=200 GeV ||<0.35 0: PRD76, 051106 (2007) pp X: PRL 98, 012002 Good agreement between NLO pQCD calculations and data pQCDcan be used to extract spin dependent pdf’s from RHIC data.

  14. From soft to hard PRD76, 051106 (2007) • Exponent (e-pT) describes our pion cross section data perfectly well at pT<1 GeV/c (dominated by soft physics): • =5.560.02 (GeV/c)-1 • 2/NDF=6.2/3 • Assume that exponent describes soft physics contribution also at higher pTs  soft physics contribution at pT>2 GeV/c is <10% exponential fit pT>2 GeV/c – hard scale?

  15. From soft to hard PRD76, 051106 (2007) xT scaling: Running (Q2) Evolution of PDF and FF Higher order effects Etc.  n=n(xT,Ös) 10-2 10-1 xT • Soft region: n(xT) increase with xT • If ~exp(-pT) • Hard region: n(xT) decrease with xT • Stronger scale breaking at lower pT 2 GeV/c at Ös=62 GeV pT~2 GeV/c – transition from soft to hard scale?

  16. 0 ALL The most abundant probe in PHENIX (triggering + identification capability) PRL103, 012003 (2009) 5 10 pT(GeV) 0pTwBG 2 GeV/c 20% 5 8% 10 5%

  17. From pT to xgluon 10-3 10-2 10-1 x • NLO pQCD: 0pT=212 GeV/c  xgluon=0.020.3 • GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon=01 ) • Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins • These data is not much sensitive to variation of G(xgluon) within our x range • Any quantitative analysis should assume some G(xgluon) shape

  18. From ALL to G (with GRSV) Generate g(x) curves for different (with DIS refit) Calculate ALL for each G Compare ALL data to curves (produce 2vs G)

  19. G: theoretical uncertainties • Parameterization (g(x) shape) choice • Vary g’(x) =g(x) for best fit, and generate many ALL • Get 2 profile • At 2=9 (~3), consistent constraint: • -0.7 < G[0.02,0.3] < 0.5  Our data are primarily sensitive to the size of G[0.02,0.3]. Theoretical Scale Dependence: • Vary theoretical scale : • =2pT, pT, pT/2  0.1 shift for positive constraint  Larger shift for negative constraint

  20. Other probes ± • Preferred fragmentation u+ and d-; • u>0 and d<0 different qg contributions for +, 0, -  access sign of G  • Analysis similar to 0 • Different flavor structure • Independent probe of G  

  21. Other probes ~80% Direct Photon • Quark gluon scattering dominates • Direct sensitivity to size and sign of G • Need more P2L Heavy Flavor • Production dominated by gluon gluon fusion • Measured via e+e-, +-, e, eX, X • Need more P2L

  22. Extend to higher x at s = 62.4 GeV Extend to lower x at s = 500 GeV Extend x-range  different s present (0) x-range s = 200 GeV

  23. 0 at s=62 and 500 GeV:Unpolarized cross section s=62 GeV: PRD79, 012003 (2009) s=500 GeV: PHENIX Preliminary May need inclusion of NLL to NLO Data below NLO at =pTby (3015)%

  24. 0 s=62 GeV • Very limited data sample (0.04 pb-1, compared 2.5 pb-1 from Run2005 s=200 GeV) • Clear statistical improvement at larger x; extends the range to higher x (0.06<x< 0.4) • Overlap with 200 GeV ALL provides measurements at the same x but different scale (pT) • s=500 ALL results will be available soon (from Run2009 with L~10 pb-1 and P=0.4) Charged hadrons

  25. Daniel de Florian Rodolfo Sassot Marco Stratmann Werner Vogelsang G: Global Fit • PRL101, 072001(2008) • First truly global analysis of polarized DIS, SIDIS and pp results • PHENIX s = 200 and 62 GeV0data used • RHIC data significantly constrain G in range 0.05<x<0.2 • Other data will be incorporated into the fit G~0 in the probed x-range Very large uncertainty at lower x

  26. G: Path Forward • Improve precision of current measurements • Get more data • Extend xg-range • Move to forward rapidities • Constrain kinematics: map G vsxg • More exclusive channels: pp  + jet and pp jet + jet

  27. Get more data A factor of 3-4 reduction in stat. errors expected in next s=200 GeV RHIC Run (2013?) PHENIX 0: projections

  28. Forward Calorimetry • Muon Piston Calorimeter (MPC): PbWO4 • 3.1 < || < 3.7 • 2 azimuth • Fully available from 2008 • 2009 ALL data being analyzed • FOCAL: Tungsten absorber with silicon pad readout • 1<  <3 • 2 azimuth • 24 X0 deep • Available by 2013 (?)

  29. Silicon Vertex tracker (VTX & FVTX) Available in 2011/12 VTX barrel |h|<1.2 Q = c or b Q g g q g jet Q g q FOCAL: pT and photon VTX: jet Rejects hadronic background c/b separated measurements FVTX endcaps 1.2<|h|<2.7 mini strips May be luminosity (and polarization) hungry

  30. Summary • RHIC is the world’s first and the only facility which provides collisions of high energy polarized protons • Allows to directly use strongly interacting probes (parton collisions) • High s  NLO pQCD is applicable • PHENIX inclusive 0ALLdata offer a significance constraint on G in the xgrange ~0.020.3 • G ~ 0 in this xg range • Other PHENIX ALL data are available • , ±, h± - will be included in the G constraint (and global fit) • , e, , J/ - need more P4L • Extending xg coverage is crucial • Other channels from high luminosity and polarization • Different s

  31. Backup

  32. xT scaling s=200/62 GeV s=500/200 GeV

  33. x  pT qg gg pT=2-2.5 GeV/c Up Down Glue pT=4-5 GeV/c pT=9-12 GeV/c

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