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 0 Transverse Single Spin Asymmetries at High x F in p  +p Collisions in

 0 Transverse Single Spin Asymmetries at High x F in p  +p Collisions in. Mickey Chiu. SPIN2010 Sep 30, 2010. A Brief Motivation. E704. Polarization data has often been the graveyar compass-0.25.gif d of fashionable theories.

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 0 Transverse Single Spin Asymmetries at High x F in p  +p Collisions in

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  1. 0 Transverse Single Spin Asymmetries at High xF in p+p Collisions in Mickey Chiu SPIN2010 Sep 30, 2010

  2. A Brief Motivation E704 Polarization data has often been the graveyarcompass-0.25.gifd of fashionable theories. If theorists had their way, they might just ban such measurements altogether out of self-protection. J.D. Bjorken St. Croix, 1987

  3. PHENIX at RHIC Spin MPC STAR • Central Arm Tracking || < 0.35, xF ~ 0 • Drift Chamber (DC) • momentum measurement • Pad Chambers (PC) • pattern recognition, 3d space point • Time Expansion Chamber (TEC) • additional resolution at high pt • Central Arm Calorimetry • PbGl and PbSc • Very Fine Granularity • Tower x ~ 0.01x0.01 • Trigger • Central Arm Particle Id • RICH • electron/hadron separation • TOF • /K/p identification • Global Detectors (Luminosity,Trigger) • BBC 3.0 < || < 3.9 • Quartz Cherenkov Radiators • ZDC/SMD (Local Polarimeter) • Forward Hadron Calorimeter • Forward Calorimetry3.1 < || < 3.7 • MPC • PbWO4 Crystal • Forward Muon Arms 1.2 < || < 2.4 PHENIX Transversely Polarized p+p Data Set

  4. PHENIX Muon Piston Calorimeter Upgrade PbWO4 Density 8.28 g/cm3 Size 2.2x2.2x18 cm3 Length 20 X0, 0.92  Weight 721.3 g SOUTH Moliere radius 2.0 cm Radiation Length 0.89 cm Interaction Length 22.4 cm Light Yield ~10 p.e./MeV @ 25 C Temp. Coefficient -2% / C Radiation Hardness 1000 Gy Main Emission Lines 420-440, 500 nm Refractive Index 2.16 Small cylindrical hole in Muon Magnet Piston, Radius 22.5 cm and Depth 43.1 cm

  5. Measuring 0’s with the MPC Clustering: • Groups towers together above an energy theshold • Fit energy and position of incident photon If two photons are separated by ~1 tower, they are reconstructed as a single cluster. Physics Impact: Photon merging effects prevent two-photon 0 analysis: for Epi0>20 GeV (pT>2 GeV/c) • At √s = 62 GeV 20 GeV  0.65 xF:Two-photon0 analysis • At √s = 200 GeV 20 GeV  0.20 xF for two-photon pi0 analysis Use merged Single clusters as proxy for pi0 Yields dominated by 0’s but subject to backgrounds Decay photon impact positions for lowand high energy 0’s

  6. Muon Piston Calorimeter Performance MIP Peak • 62.4 GeV Energy scale set by MIP • In noisy towers, used tower spectrum • Shower Reconstruction Using Shower Shape Fits All Pairs Mixed Events Background subtracted • Photon Pair Cuts (pi0 62 GeV) • Pair Energy > 8 GeV • Asymmetry |E1-E2|/|E1+E2| < 0.6 • Noisy Towers in Run06 (up to 25% of MPC) were excluded • Cluster Cuts (200 GeV) • Energy > 25 GeV • Fiducial Radial Cuts to avoid edges • Only ~4/416 noisy towers excluded in Run08 • Width ~ 20 MeV at 62.4 GeV, but improved by factor two in Run08 using pi0 tower by tower calibration • LED Monitoring for gain stability

  7. Transverse Single Spin Asymmetries Left Right where p is the 4-momentum of a particle (hadron, jet, photon, etc...) Definition: Experimentally, there are a variety of (~equivalent) ways this can be measured. 1. Yield difference between up/down proton in a single detector This is susceptible to Rel. Luminosity differences 2. Or, take the left-right difference between 2 detectors This is susceptible to detector Relative Acceptance differences 3. Or, take the cross geometric mean (square-root formula) Mostly insensitive to Relative Luminosity and Detector Acceptance differences

  8. 0AN at High xF, s=62.4 GeV p+p0+X at s=62.4 GeV/c2 p+p0+X at s=62.4 GeV/c2 3.0<<4.0 • Large asymmetries at forward xF • Valence quark effect? • xF, pT, s, and  dependence provide quantitative tests for theories • Complementary to other data, ie, Brahms , which allows flavor study

  9. Forward AN Cluster at s=200 GeV GeV/c GeV/c Fraction of clusters PLB 603,173 (2004) η<3.3 η<3.3 Decay photonπ0Direct photon Eta>3.3 xF xF process contribution to 0, =3.3, s=200 GeV

  10. Forward AN Cluster at s=200 GeV Fraction of clusters Decay photonπ0Direct photon

  11. pT Dependence Fraction of clusters pT Decay photonπ0Direct photon So far, 1/pT has not been observed in proton-proton collisions Figure of Merit:This analysis: 1.1 pb-1Projected 2012+2013: 66. pb-1Errors shrink by factor of 8.In addition, triggering system is being upgraded now.Greater efficiency pT=0  AN=0 pT large, AN ~ 1/pT Low pT (TMD regime) Graphic from Zhongbo Kang

  12. Isospin Dependence (“Collins”) Transversity PDF Sivers PDF (Preliminary) + (ud) 0 (uu+dd) - (du) TransversityCollins: • Sign of AN seems consistent with sign of tranversity • However, transversity larger for u, but AN is larger for + • Collins is symmetric between + and - so it doesn’t contribute to difference • 0 not average of + and - • What is 0 Collins? Might be 0 (Belle’s sees isospin symmetry in )

  13. Isospin Dependence (“Sivers”) Transversity PDF Sivers PDF (Preliminary) + (ud) 0 (uu+dd) - (du) Sivers: • Sign also consistent with Sivers • Again, Sivers larger for u, but AN is larger for + • Is AN(0) ~ 2AN(+) + AN(-) • Factorization/Universality breaks down???

  14. PYTHIA 6.214 Studies Ongoing u d g u d g • TuneA, CKIN(3)=2, describes 0 x-section well • Extrapolation from known Sivers or Transversity/Collins depends on <z> and x versus s • Want to know outgoing jet type (Collins) • Same as incoming (Sivers) • Soft vs Hard: @pT = 1 GeV, ~50/50 • @pT = 2 GeV, ~90% • +: ~100%u, -: 50/50 d/u, 0: 25/75 d/u

  15. s Dependence of 0 AN (Preliminary) • No strong dependence on s from 19.4 to 200 GeV • Spread probably due to different acceptance in pseudorapidity and/or pT • If purely Sivers, should have a strong s dependence? • xF ~ <z>Pjet/PL ~ x so maybe xF just scales it out. • Collinstransversity should also depend on s through <z> and x dependence?

  16. s Dependence of  AN + AN (%)‏ - • Features: •  AN(xF) are opposite in sign and symmetric in magnitude until s = 62.4 GeV • xF intercept (where xF0) seems to saturate at ~0.2, but is ~0.5 at s=6.6 GeV • Maximum measured asymmetry the same (accident of where statistics runs out?)

  17. NLO pQCD FWD 0Cross-section Bourrely and Soffer, Eur.Phys.J.C36:371-374,2004 • Cross-sections generally better described at mid-rapidity and at higher s • NLL calculations are very promising for intermediate to lower s • PHENIX s=62.4 GeV y=0 0 cross-section, arXiv:0810.0701 • Understanding lower pT AN important for understanding AN at higher s • More remarkable because AN(xF) are qualitatively similar across all s

  18. Summary • Single Transverse Spin Asymmetries of hadrons from p+p collisions is still not understood, after over 20 years • Data coming from SIDIS (Hermes, Compass, JLab), and e+e- (Belle) helps tremendously • Test of extrapolation from transversities/Sivers measured by other experiments and applied to hadron-hadron collisions • Does universality hold in hadron-hadron collisions? • Future prospects from the MPC in PHENIX •  asymmetries, extending flavor dependence (D. Kleinjan’s talk Tuesday) • Possibility of more differentiating measurements? • back-to-back di-hadron angular asymmetry • Correlations with very forward neutrons • Direct photons at very high pT (>6 GeV)?? • Etc… • More 200 GeV transverse data, possibly in Runs 12 and 13 • SSA in transversely polarized proton collisions might add information on proton structure, but are beset by theoretical difficulties • Transversity extracted/applied to p+p collisions • TMD factorization/universality breakdown in p+ph+X • Transition from Sivers to twist-3 description • Information on magnitude of color Lorentz force in the proton? • Orbital angular momentum? • While GPD’s may be cleanest way to OAM, strongest asymmetries are in p+p, and are what started the field of transverse spin physics

  19. Backup Slides

  20. Transverse Proton Spin Physics E704 Polarized parton distribution functions quark helicity distribution – known gluonhelicity distribution – poorly known transversity distribution – unknown Naïve LO, Leading Twist, pQCD Result Helicity violation term due to finite quark masses

  21. Transverse Proton Spin Physics • Various possible explanations have been proposed to explain these asymmetries • Transversity x Spin-dep fragmentation (e.g., Collins effect or IFF), • Intrinsic-kT in proton (Transverse Momentum Dep Functions) , • Eg, Sivers Function • Perturbative LO Twist-3 Calculations (Qiu-Sterman, Efremov, Koike) • These calculations have been related to the Sivers function • Or some combination of the above • Caveat: The theory is still being actively worked out • A Unified picture for single transverse-spin asymmetries in hard processes, • Ji, Qiu, Vogelsang, Yuan PRL97:082002,2006 Anim. courtesy J. Kruhwel, JLAB

  22. Kinematic Cuts and AN Phys.Rev.D74:114013,2006. eta<3.5 eta>3.5 • Mean AN is measured to be lower for pT>1, even though mean xF is higher for this pT bin, and higher xF implies higher asymmetry • This implies that AN is dropping with pt for a given xF slice • The  cut, for a given xF slice, splits that slice into high pt and low pt, with the lower eta selecting higher pt • This implies that AN at lower  should be smaller, consistent with predictions of PRD74:114013 • However, at 62.4 GeV the pT are low (pQCD invalid?) • Cross-section is being analyzed now

  23. RHIC Forward Pion AN at 62.4 GeV BRAHMS PRL 101, 042001 E704, 19.4 GeV, PLB261, (1991) 201 PHENIX Preliminary • Brahms Spectrometer at “2.3” and “3.0” setting  <> = 3.44, comparable to PHENIX all eta • Qualitatively similar behavior to E704 data: pi0 is positive and between pi+ and pi-, and roughly similar magnitude: AN(pi+)/AN(pi0) ~ 25-50% • Flavor dependence of identified pion asymmetries can help to distinguish between effects • Kouvaris, Qiu, Vogelsang, Yuan, PRD74:114013, 2006 • Twist-3 calculation for pions for pion  exactly at 3.3 • Derived from fits to E704 data at s=19.4 GeV and then extrapolated to 62.4 and 200 GeV

  24. Carry Out Steps Analogous to QCD Analysis of Unpolarized Distributions (ii) Extract Distributions from SIDIS and e+e- Predict proton-proton observables Transversity PDF Sivers PDF Disagreement between theory and experiment. Theoretical analysis: Umberto D’Alesio and collaborators, PKU/RBRC Transverse Spin Physics WorkshopExperimental data: STAR Collaboration PRL 101, 222001 (2008) Phys.Rev.D75:054032,2007,Nucl.Phys.Proc.Suppl.191:98-107,2009

  25. Comparison to 0 at s = 200 GeV/c2 <3.5 PHENIX 62 GeV Preliminary >3.5 STAR arxiv:0801.2990v1, p+p0 @ s=200 GeV, accepted by PRL • At higher , the scaling with s is stronger? • The  dependence is switched when going from 62 to 200 GeV?

  26. Sivers n from Back2Back Analysis MPC 0  Cent h,0 Boer and Vogelsang, Phys.Rev.D69:094025,2004, hep-ph/0312320 Bomhof,Mulders,Vogelsang,Yuan, PRD75:074019,2007 • Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the  distribution of back-to-back jets • Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets • Important analysis to decouple the effects in single inclusive AN * See also Feng Wei’s talk in previous session

  27. Particle Fractions of Single Clusters • Generate simulated proton-proton collision (Pythia)Pick Pythia configuration using detailed comparison of measured cross-sections at RHIC • Propagate proton-proton collision products through realistic detector response simulation (GEANT3) • Produce simulated data files using realistic detector resolution/smearing • Contributions: • Electromagnetic • Merged pi0’s • Direct photons • Decay photons (η, etc) • Hadronic: (+/-, K+/-, etc.) small

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