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Longitudinal Spin Program: Results and Plans

STAR. +. Longitudinal Spin Program: Results and Plans. For RHIC-Spin Collaboration. A.Bazilevsky Brookhaven National Laboratory For the PHENIX Collaboration. Gluon helicity distribution  G from A LL (Anti-)quark helicity distribution from A L of W. SPIN-Dubna-2011, Sep 20-24.

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Longitudinal Spin Program: Results and Plans

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  1. STAR + Longitudinal Spin Program: Results and Plans For RHIC-Spin Collaboration A.Bazilevsky Brookhaven National Laboratory For the PHENIX Collaboration • Gluon helicity distribution G from ALL • (Anti-)quark helicity distribution from AL of W SPIN-Dubna-2011, Sep 20-24

  2. From DIS to pp: (semi)DIS pp • Probes G: • Q2 dependence of quark PDFs • Photon-gluon fusion • (Anti-)quark flavor separation: • Through fragmentation processes • Probes G: • Directly from gg and qgscattering • (Anti-)quark flavor separation: • Through and Complimentary approaches

  3. RHIC as polarized proton collider Absolute Polarimeter (H jet) RHIC pC Polarimeters BRAHMS & now ANDY PHENIX STAR Siberian Snakes Longitudinal Spin Running in PHENIX/STAR Spin Rotators 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

  4. Measuring Asymmetries in a Collider • (N) Yield • 0, , ±, h±, , e,  etc. • (R) Relative Luminosity • (P) Polarization • RHIC Polarimeters(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

  5. STAR PHENIX and STAR PHENIX: High rate capability High granularity Good mass resolution and PID Limited acceptance Upgrades to wider acceptance, forward capabilities, inner tracking STAR: Large acceptance with azimuthal symmetry Good tracking and PID Central and forward calorimetry Upgrades to higher rate capabilities, inner and forward tracking

  6. charged particles neutron Local Polarimetry • Utilizes spin dependence of very forward neutron production discovered in RHIC Run-2002 (PLB650, 325) Zero Degree Calorimeter: <2.5 mrad Before Run11, STAR also used BBCs (3.3<|h|< 5.0) utilizing spin dependence of hadron production at high xF

  7. 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:

  8. 144 cm Relative Luminosity (PHENIX) 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)

  9. G • Polarized Gluon Distribution Measurements : • 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

  10. Unpol. Cross Section and pQCD in pp s=200 GeV PHENIX pp 0 X PRD76, 051106 STAR: ppjet X PRL 97, 252001 PHENIX pp X PRL 98, 012002 ||<0.35 ||<0.35 Good agreement between NLO pQCD calculations and data  pQCD can be used to extract spin dependent pdf’s from RHIC data.

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

  12. 20 10 ALL: jets pT(GeV) STAR Preliminary Run6 (s=200 GeV) Good discriminative power between calculations with different assumption for G

  13. 0 ALL The most abundant probe in PHENIX (triggering + identification capability) PHENIX Run5+6: PRL103, 012003 5 10 pT(GeV) 0pTwBG 2 GeV/c 20% 5 8% 10 5%

  14. From ALL(pT) to G Compare ALL(pT) data with calculated ALL(pT) for a variety of PRL103, 012003 (2009) 2(G) • From pQCD: • pT = 212 GeV/c  • xgluon = 0.02  0.3 Only weakly model dependent

  15. DSSV: Daniel de Florian Rodolfo Sassot Marco Stratmann Werner Vogelsang G: Global Fit • Phys. Rev. Lett. 101, 072001(2008) • First truly global analysis of all available polarized data including RHIC results • Uncertainty estimation: • 2=1 (optimistic) • 2/2=2% (conservative) • … Truth is in between RHIC data 2/2=2% A node?...

  16. + Run9 0 ALL : PHENIX Preliminary Run5 Run6 Run9 Tendency to positive G?

  17. Global Fit for +PHENIX Run9 0 ALL By S.Taneja et al (DIS2011) ala DSSV with slightly different uncertainty evaluation approach DSSV DSSV + PHENIX Run9 0 ALL No node … Uncertainties decreased A node at x~0.1 ?

  18. + Run9 0 ALL : STAR Preliminary • Run9: • 3-4 smaller stat. uncertainties than in Run6: • Trigger upgrade (improved eff.) • DAQ upgrade (increased rate, lower ET threshold) Run9 data will definitely have considerable impact on G global fit and its uncertainty

  19. Other probes •  • Analysis similar to 0 • Different flavor structure • Independent probe of G PHENIX PRD83,032001(2011) • ± • Preferred fragmentation u+ and d-; • u>0 and d<0 different qg contributions for +, 0, - •  access sign of G  

  20. Other probes ~80% • Direct Photon • Quark gluon scattering dominates • Direct sensitivity to size and sign of G • Need more P4L • Heavy Flavor • Production dominated by gluon gluon fusion • Measured via e+e-, +-, e, eX, X • Need more P4L

  21. Extend x-range  different s 0 at ||<0.35: xg distribution vspT bin s=62 GeV 2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c s=200 GeV  2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c s=500 GeV

  22. 0 at s=62 and 500 GeV:Unpolarized cross section s=62 GeV: PHENIX, PRD79, 012003 s=500 GeV: PHENIX Preliminary May need inclusion of NLL to NLO Data below NLO at =pTby (3015)%

  23. s=62 GeV 0: PHENIX, PRD79, 012003 • 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

  24. G: Path Forward • Limitations in current data: • Limited x-range covered • Weak sensitivity to the shape of G(x) • 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

  25. Get more data PHENIX pp 0 X : projections STAR pp jetX : projections

  26. Forward Calorimetry: PHENIX MPC • Muon Piston Calorimeter (MPC): PbWO4 • 3.1 < || < 3.9 • 2azimuth • Gives access to lower: x10-3 • Fully available from 2008 STAR: 0 forward rapidity PRL 97, 152302 MPC 0 500 GeV 300 pb-1 P=0.55 pQCD looks working even in forward rapidities

  27. STAR: di-jet ALL Constrains kinematics  shape of G(x) Run9 data ! Projections for s=500 GeV The same trend as from inclusive jets:  Slightly positive G? …

  28. PHENIX Silicon Vertex tracker (VTX & FVTX) VTX: available from 2011 FVTX: available from 2012 VTX barrel |h|<1.2 Q = c or b Q g g q g jet Q g q EMC and MPC: 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

  29. (Anti)quark flavor separation Mainly from SIDIS: Fragmentation functions to tag (anti)quark flavor DSSV: PRL 101, 072001 (2008) p+p W  (e/) +  • Parity violating W production: • Fixes quark helicity and flavor • No fragmentation involved • High Q2 (set by W mass) l+

  30. W: ALvsl • STAR • Central (barrel) region (We , ||<1) • First data from 2009: PRL106, 062002 (2011) • Forward (endcup) region (We , 1<||<2) : • Forward tracker upgrade, first data in 2012 • PHENIX • Central Arms (We , ||<0.35) • First data from 2009: PRL106, 062001 (2011) • Forward Arms (W , 1.2<||<2.4) : • Trigger upgraded, first data from 2011

  31. Central region: W  e from Run9 • Triggered by energy in EMCal • Momentum from energy in EMCal • Charge from tracking in B field STAR: |e|<1 PHENIX: |e|<0.35 e+ e- L=12 pb-1 L=8.6 pb-1 e+ e-

  32. Cross section Central region: W  e from Run9 P=0.39L=8.6/12 pb-1 in PHENIX/STAR PHENIX: PRL106, 062001 (2011) STAR: PRL106, 062002 (2011) STAR AL PHENIX AL e- e+ e- e+ Run11: larger sample with P~0.52

  33. First data collected in 2011: • L~15 pb-1 P~0.52 • Data being analyzed PHENIX Forward Arm: W    trigger eff. Raw yields with different triggers and cuts  trigger rejection Expected W yield PHENIX 2kHz Bandwidth More challenging than We at ~0

  34. W  l : Projections PHENIX: W PHENIX: We STAR: We

  35. Longer term upgrades • p+p: s=500 GeV  650 GeV • Will increase W production cross section twice • p+3He: s=432 GeV • Will allow full flavor separation for light quarks • Workshop “Opportunities for polarized He-3 in RHIC and EIC” at BNL, Sep 28-30, 2011

  36. 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&STAR continues producing results for different spin observables • Significant constraint on G for xg~0.02-0.03 from inclusive 0 and jet ALL at s=200 GeV • Other ALL measurements to be included in G global fit with different systematics and x-coverage • First AL results from Wein central rapidity at s=500 GeV from 2009 • First AL results from Win forward rapidity at s=500 GeV from 2011 coming soon • A major machine, PHENIX and STAR upgrades are under discussion • Machine: Polarized source upgrade and electron lenses in RHIC to increase L and P; s=500 GeV  650 GeV; polarized 3He • Experiments: considerably extended acceptance and improved capabilities in forward rapidity

  37. Backup

  38. 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 G is the main goal of longitudinal spin program at RHIC

  39. 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)

  40. … To polarized pp collider Utilizes strongly interacting probes g • Probes gluon directly • Higher energies  clean pQCD interpretation • 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

  41. PHENIX Detector in 2011 • Philosophy (initial design): • High rate capability & granularity • Good resolutions & particle ID • Sacrifice acceptance • p0, g, h • Electromagnetic Calorimeter: ||<0.35 • Muon Piston Calorimeter: 3.1<||<3.9 • p±, e,J/ye+e- : ||<0.35 • Drift, Pad Chambers, VTX (||<1) • Ring Imaging Cherenkov Counter, ToF • Electromagnetic Calorimeter • ,J/y+- : 1.2<||<2.4 • Muon Id/Muon Tracker • Relative Luminosity • Beam Beam Counter (BBC) • Zero Degree Calorimeter (ZDC) • Local Polarimetry – ZDC • Spin direction control

  42. 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?

  43. 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?

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

  45. RHIC Spin Measurements Check theory (pQCD) works Other exp. q g This exp. Theory p p Jet Extract polarized PDF from spin asymmetries using pQCD Other exp. This exp. Theory Jet Yield Spin Asymmetry Extract!

  46. From pT to xgluon 10-3 10-2 10-1 x • NLO pQCD: 0 pT=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

  47. 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 2 vs G)

  48. 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

  49. MPC: 0 cross section

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