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Spin Physics Results from RHIC

STAR. Spin Physics Results from RHIC. M. Grosse Perdekamp, UIUC. International Workshop on Hadron Structure and Spectroscopy CRNS, Paris April 4 th -6 th , 2011 . AnDY. pp2pp. Spin Physics Results from RHIC. Preliminaries: Facility Status QCD & PDFs vs Data

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Spin Physics Results from RHIC

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  1. STAR Spin Physics Results from RHIC M. Grosse Perdekamp, UIUC International Workshop on Hadron Structure and Spectroscopy CRNS, Paris April 4th -6th , 2011  AnDY pp2pp

  2. Spin Physics Results from RHIC Preliminaries: Facility Status QCD & PDFs vs Data Gluon spin distribution Inclusive hadron and jet results QCD analysis Low x & x-dependence with di-jets and rapidity separated di-hadrons W-production in polarized p-p First results from pp  W  eν Transverse Spin Inclusive AN Channels isolating Collins or Sivers effects  Drell Yan measurements in Akio Owaga’s talk

  3. RHIC Status: Running Polarized p-p at √s= 500 GeV through 4-8/15 First full length 500 GeV run P ~ 45 % (max above 50%) goal is P ~ 50% L ~ 5 x 1031 cm-2s-1 goal is L ~ 10 x 1031 cm-2s-1 o AnDY commissioned successfully o muon-W trigger in PHENIX in operation o ∫Ldt ~ 40% of planned, due to major hardware failure in cryo-system (repaired). 4 RHIC fills, last week of March impact from 3rd collision point Luminosity in Relative Unites Time in Store [days]

  4. NLO pQCD Cross Sections vs RHIC data for Different √s and Rapidity Intervals √s = 200 GeV √s = 62.4 GeV o PHENIX π0, η = 0 -------- NLO pQCD ∆ PHENIX π0, η = 0 ∙ Brahms π+ ,η = 2.95 ⌷ STAR π0 ,η = 3.7 - - - - - NLO pQCD pT [GeV] pT [GeV] See analysis in De Florian, Vogelsang, Wagner PRD 76,094021 (2007) and Bourrely and Soffer Eur.Phys.J.C36:371-374 (2004) Good agreement between inclusive hadron cross sections from RHIC data and pQCD calculations !

  5. (I) Gluon Spin Distribution Inclusive hadron and jet results QCD analysis Low x & x-dependence with di-jets and rapidity separated di-hadrons

  6. ALL for Inclusive Hadrons & Jets at mid-Rapidity η ~ 0 : constrain ΔG(x) at 0.05 < x < 0.2 ALL for neutral pions and jets vs DSSV de Florian, Sassot, Stratmann, Vogelsang PRD 80:034030,2009 x-range for ALLπ0 in 3 pT bins Courtesy Swadhin Taneja, Stony Brook other channels in STAR and PHENIX: eta, charged hadrons, ALL(“charm”) at mid-rapidity ALL(J/ψ) for η~ 2.

  7. ΔG(x) from DSSV Global QCD Analysis 0.2 ΔGtrunc[0.05,0.2] = ∫ ΔG(x) dx = 0.005 0.05 +0.051 -0.058 -0.058 -0.058 -0.058 de Florian, Sassot, Stratmann, Vogelsang PRD 80:034030,2009 x ΔG(x) • ΔGtrunc[0.05,0.2] ≈ 0 since node at x≈0.1 • Data constrains only truncated first moment of ΔG(x) in x-interval [0.05,0.2], but not functional form at low or high x • ΔGtrunc in large-x region constrained to be small by requirement that ΔG(x) ≤ G(x); at Q2=10 GeV2: ΔGtrunc[0.3,1.0] ≤ 0.03 • At small x, ΔG(x) can differ from DSSV beyond errors without violating funda-mental constraints RHIC Range Small-x x≤0.05 Large-x x≥0.2 0.05<x<0.2

  8. Next steps: ALL for di-jets in STAR resolve xq, xg projections for 500 GeV and ∫Ldt = 300 pb-1 P=70% • o Information on x1 and x2, forward jets • give access to • lower x ! • o Courtesy STAR De Florian, Frixione, Signer and Vogelsang NPB 539 (1999) 455 and PC for present calc.

  9. Extending ΔG(x) to Lowest x with Forward di-Jets or High pT di-Hadrons E.g. back-to-back neutral pion pairs in the PHENIX forward EMC forward EMC (3.1<|η|<3.9) Central Arm (|η|<0.35) back-to-back: selects di-jets Jet -1 (π0, pT,1) Trigger particle, pT,1 dφ Back-to-back hadrons: trigger (pT,1) and associate (pT,2<pT,1) in separate jets: large forward boost Jet 2 (π0, pT,2) x1 >> x2 Associate particle, pT,2 • 500M PYTHIA events ≈ 0.014 pb-1 , only hard • QCD processes, soft processes eliminated by • pT cuts (study by Cameron McKinney, UIUC) enhances q-g fraction to ~ 60%

  10. Selecting x2 with pT Cuts: x2 Decreases and q-g Fraction Increases with Magnitude of pT cut x2 x1 log x di-hadron pT cuts and resulting <x2> pT,1>1.0 GeV/c, pT,2>0.5 GeV/c <x2> ≈ 0.014 pT,1>2.0 GeV/c, pT,2>1.0 GeV/c <x2> ≈ 7.2*10-3 pT,1>3.0 GeV/c, pT,2>1.5 GeV/c <x2> ≈ 4.8*10-3

  11. Projected ALL(π0) in MPC for different ΔG(x) at low x for ∫Ldt = 300 pb-1, √s = 500 GeV (RHIC W program, 2011 to 2015) Increasing Δgtrunc [10-4,0.05] ΔGtrunc= -.2 ΔGtrunc= -.1 ΔGtrunc= -.5 pT,1>3 GeV, pT,2 > 1.5 GeV error bars are statistical only ΔGtrunc [10-4,0.05] = -0.1 will be observable

  12. First Forward EMC ALL , Run 2009 at √s=200 GeV and Projections for Run 2011, √s=500 GeV ALL forward EMC clusters run 2009 ALL forward clusters, projected 2011 DSSV-MAX PYTHIA GSC NLO DSSV NLO First step towards acquisition of large integrated luminosity for ΔG(x) at small x !

  13. (II) W-production in polarized p-p pp  W  eν first results pp  W  μν look at ongoing run

  14. Quark and Anti-Quark Helicity Distributions from Inclusive ALe,μin W-Production De Florian at Berkely RSC meeting Nov, 2009 • Large Q2, knowledge of FFs not needed • pQCD analysis of inclusive lepton AL • DSSV analyzed MC data of 200 pb-1 and 800 pb-1 from STAR and PHENIX • Significant improvement of knowledge with 200 pb-1 First exploratory run at √s=500 GeV in 2009 P ~ 35% ∫Ldt ~ 9 pb-1

  15. STAR, run 2009, √s= 500 GeV: Parity Violating AL in p+p  high pT e Phys.Rev.Lett. 106 (2011) 062002 Jacobian Peak for e- and e+ AL for e- and e+ Not yet (!) sensitive to quark and anti-quark helicity distributions

  16. W-Cross Sections for p-p: PHENIX & ATLAS Phys.Rev.Lett. 106 (2011) 062001 arXiv:1012.5382 [hep-ex] Consistent with NNLO QCD

  17. News from Present p-p Run at √s = 500 GeV PHENIX Muon Trigger Installed & Operating muTr trigger electronics(JSPS) First full length 500 GeV run P ~ 45 % (max above 50%) goal is P ~ 50% L ~ 5 x 1031 cm-2s-1 goal is L ~ 10 x 1031 cm-2s-1 o AnDY commissioned succesfully o muon/W trigger in PHENIX in operation o ∫Ldt ~ 40% of planned, due to major hardware failure in cryo system (repaired). RPCs in Urbana (NSF) RPCs in PHENIX (NSF) FPGA based level-1 trigger processors

  18. PHENIX Muon Trigger Performance muTracker trigger efficiencies RPC-Inner Ring Efficiency problems to be solved: RPC-gas -> mixture & pressure differentials timing -> RPC south is 1 beam clock late Taking data with muTr part of trigger in run 2011, use RPC offline for background rejection

  19. First Look at Data from Fast Production (Ralf Seidl) Arbitrary normalization

  20. (III) Transverse Spin Inclusive AN Collins or Sivers effects

  21. AN in Very Forward Neutron Productionusing the Zero Degree Calorimeter neutron • Large negative SSA observed for xF>0 • Diffractive physics • Highly useful as local polarimeter for PHENIX

  22. At Hard Scale: AN 0 , QCD Test !?

  23. Experiment: Sizeable SSA Observed over Large Range of Scales ! Experiment: AN >> 10-4 for 4 GeV < √s < 200 GeV for charged pions ! ZGS √s=4.7 GeV AGS √s=6.5 GeV FNAL √s = 20 GeV RHIC √s = 200 GeV π+ π- Soft effects due to QCD dynamics in hadrons remain relevant up to scales where pQCD can be used to describe the scattering process! from Christine Aidala, Spin 2008 and Don Crabb & Alan Krisch in then Spin 2008 Summary, CERN Courier, 6-2009

  24. AN vs xF almost unchanged for √s=19.4, 62.4 and 200 GeV

  25. Origin of Large SSA for Hard Scattering -- Two Solutions: Final State vs Initial State (I) “Transversity” quark-distributions and Collins fragmentation Correlation between proton- und quark-spin and spin dependent fragmentation STAR, PRL-92:171801, 2004 Quark transverse spin distribution Collins FF (II) Sivers quark-distribution+ Correlation between proton-spin and transverse quark momentum First measurement at RHIC √s = 200 GeV (III) Initial or final state twist-3+ Qiu/Sterman and Koike + unified picture: Ji, Qiu, Vogelsang and Yuan in PRL-97:082002, 2006 Sivers distribution

  26. BRAHMS: AN for Charged Pions vs pT and xF at √s=62.4 GeV and √s=200 GeV √s=62.4 GeV AN increases with xF (valence quarks) AN increases with pT ? Limited pT range! 0.8 pT<1.0 GeV/c 0.5 pT<0.6 GeV/c 0.6 pT<0.8 GeV/c 1.0 pT<1.2 GeV/c 0.4<pT<0.6 GeV/c 200 GeV √s=200 GeV 0.5<pT<0.75 GeV/c 1.0<pT<1.25 GeV/c 1.25<pT<1.5 GeV/c 1.5<pT<2.0 GeV/c 2.0<pT<2.5 GeV/c

  27. STAR Run 2008: pT Dependence of AN at √s=200 GeV Ogawa at CIPANP 2009 Consistent with zero for all pT Positive xF Negative xF Decrease as ~1/pT expected is not observed. AN constant from pT>2.5 GeV. Need more statistics to extend measurement to pT > 4 GeV !

  28. Expectations for AN with PHENIX MPC and Transverse Spin Running in 2012 or 2013 Red: Zhong-Bo Kang possible pT dependence if all even orders of twist expansion contribute Blue: pT dependence if sub-leading twist dominates

  29. BRAHMS: AN for Charged Pions , Kaons and Protons at √s=200 GeV p p K Large AN for K-  significant Sivers asymmetries for sea quarks ?! Large AN for anti-Proton unexplained.

  30. Another Surprise: AN for Eta Mesons larger than for Pions ! STAR STAR arXiv:0905.2840 (Heppelmann, DIS08) AN(η) > AN(π0) for 0.55 < xF < 0.75 Possibly large effects in the fragmentation for eta-mesons?

  31. Understanding of AN in terms of Collins and Sivers Effect: Work in Progress! Future goal: Extract Sivers and transversity quark distributions from global anlaysis to all SIDIS, pp and e+e- data! Present work: Extract Sivers + transversity from SIDIS and e+e- and predict AN in pp BRAHMS π+,- STAR π0 Global analysis of SIDIS & e+e- Anselmino, Boglione, D’Alesio, Kotzinian, Murgia, Prokudin, Turk Phys. Rev. D75:05032,2007 AN calculation from D’Alesio, 2008 Presently: Poor agreement with many problems to solve! Universality, evolution, pdf and fragmentation functions not sufficiently known. For example, note the impact of un-polarized FFs thick line DSS thin line Kretzer

  32. Measurements to Isolate Different Mechanisms o Transversity & Collins o Sivers

  33. Ideas for Measurements of Transversity Observables at RHIC Drell Yan: Required luminosity not available at RHIC. Spin dependent Lambda-FF unknown. Measure Λ-FF in e+e- ? Collins effect in jets; possible in STAR ?  hadron ID at high p, z- and ϕ-resolution ? Di-hadron intereference fragmentation function. IFF data available from e+e- Belle !

  34. Interference Fragmentation –IFF- for Di-Hadrons at Mid-Rapidity in PHENIX • AUT compatible ~0 with • present statistics • Dilution from gg processes! • Future: • Update with more statistics • from runs 2012 and 2013 • extend measurements in the • forward direction for smaller • g-g process fraction and • large x ! With 2012 & 2013 statistics

  35. IFF Measurement in e+e- at BELLE PHENIX & STAR collaborators have joined Belle: BNL-Illinois-Indiana-RBRC-RIKEN electron Artru and Collins, Z. Phys. C69, 277 (1996) Boer, Jakob, and Radici, PRD67, 094003 (2003) ϕpair-1 ϕpair-2 θ q1 q2 quark-1 spin quark-2 spin zpair-1 zpair-1 z1,2 relative pion-pair momenta positron

  36. Belle IFF- Asymmetries vsHadron Pair Momentum Fraction zi BNL-Illinois-Indiana-RBRC-RIKEN Preliminary Preliminary Preliminary a12 Preliminary Preliminary Preliminary to be published this month … 9x9 z1 z2 binning Preliminary Preliminary Preliminary z1

  37. Ideas for Measurements of Sivers Observables at RHIC Precision measurement of AN at mid-rapidity. Back-to-back correlations for jets. AN for heavy flavor. significant improve- ments from upgrades: forward calorimeters + silicon vertex detectors New Experiment: AnDY AN for inclusive jets. AN for direct photons. AN in jet-photon production. AN in Drell Yan.

  38. AN from p0 and h+/- at Central Rapidity Anselmino et al, Phys. Rev. D 74 094011 Process Contribution to 0, η=0, s=200 GeV PRL 95, 202001 (2005) Constrain gluon Sivers effect using PHENIX 2002 p0 data !

  39. AN from p0 Update • pT range extended from 5 to 12 GeV/c • Results consistent with previous PHENIX analysis • Statistical uncertainties reduced by more than factor of 30

  40. Impact of 2006 + 2008 Data Sets Sea quark Sivers maximized + Gluon Sivers function 0.02 < xSampled < 0.08 Gluon Sivers parameterized to 1 sigma of data Naïve expected impact of new data. u + d quarks Sivers w. no gluon or sea quark contribution.Low pT pi0 at mid-rapidity is not sensitive to valence quark Sivers function Maximized Gluon Sivers functionViolates <kT> of partons = 0 Theoretical analysis to be carried out.

  41. y z x proton spin Di-jet pT AN in Di-Jet Production in STAR STAR: PRL-99:142003,2007 Di-jet pT 180º parton Gluon radiation Di-jet AN consistent with 0 Additional kT kick to jet axis from Sivers effect  Boer & Vogelsang, PRD 69, 094025 (2004)

  42. Summary o Gluon Spin contribution constraint for 0.05 < x < 0.2 use di-jet and di-hadron measurements to probe x-dependence ΔG(x) and forward jet production to reach low x, x~0.001. o W-program has started with electrons (STAR & PHENIX) and muons (PHENIX). Luminosity accumulation will take 3-4 runs. o Precision data on AN are available. Exciting new Drell Yan experiment at IP2: AnDY (see Akio Ogawa’s talk). Initial measurements to isolate Collins -and Sivers- asymmetries. Much improvement from detector upgrades and increased statistics.

  43. Backup

  44. STAR Run 2006: pT Dependence of AN at √s=200 GeV PRL 101,222001 For given η strong correlation between xF and pT: AN(pT) integrated over xF AN(pT, xF) AN increases with pT up to pT ~ 3 GeV/c -- Models: AN ~ 1/pT

  45. PHENIX: AN vs XFfor p0’s at √s=62.4 GeV AN = 0 for xF < 0 no sizeable asymmetries at small x! Larger forward asymmetries at higher pseudo-rapidity, η ? Limited by statistics and correlations between xF, pT and η !

  46. Sivers Effect in Heavy Flavor Production Gluon Sivers=Max Measurement for m- Gluon Sivers=0 Calculations for D mesons Anselmino et al, PRD 70, 074025 (2004) • Heavy flavor production gives sensitivity to gluon Sivers effect . • Significant improvement with vertex detector upgrades. • Work needed to connect theory and experimental observable.

  47. A RHIC and US-Japan Contribution to Transverse Spin Analysis: Measurement of the Collins Effect in e+e- Annihilation into Quarks at Belle BNL-Illinois-RBRC-RIKEN Measurement of the Collins effect in e+e- at Belle: Belle Collins asymmetries & global fit electron e++e- π++ π- + X ~ Collins(z1) x Collins (z2) q1 q2 quark-1 spin quark-2 spin Collins FF extracted from Belle data. positron

  48. Collins Effect in Quark Fragmentation J.C. Collins, Nucl. Phys. B396, 161(1993) q Collins Effect: Fragmentation of a transversely polarized quark q into spin-less hadron h carries an azimuthal dependence:

  49. General Form of Fragmentation Functions Number density for finding hadron h from a transversely polarized quark, q: unpolarized FF Collins FF

  50. IFF- a12 vs Invariant Mass 8x8 m1 m2 binning Preliminary Preliminary Preliminary a12 Preliminary Preliminary Preliminary Systematic errors shown. a12 increases with m1 and m2 reaches |a12 | ~ 0.1 at large mi. Preliminary Preliminary m1 [GeV/c2] 50

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