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Recent PHENIX Spin Results

Astrid Morreale University of California at Riverside On behalf of the collaboration. Recent PHENIX Spin Results. WWND, April 12, 2008. Outline. About polarized RHIC, PHENIX The Proton Spin Structure via Asymmetries

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Recent PHENIX Spin Results

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  1. Astrid Morreale University of California at Riverside On behalf of the collaboration Recent PHENIX Spin Results WWND, April 12, 2008

  2. Outline • About polarized RHIC, PHENIX • The Proton Spin Structure via Asymmetries • Recent PHENIX results from polarized proton running (longitudinal, transverse if time permits) • Summary

  3. RHIC Acceleration of polarized protons between 25 and 250 GeV Up to 120 Bunches with 2*1011 protons (100ns apart) Polarization up to 70% http://www-nh.scphys.kyoto-u.ac.jp/SPIN2006/SciPro/pres/plenary/MeiBai.ppt

  4. Polarimetry “CNI”-Polarimeter measures left-right asymmetries in elastic pC collisions Provides fast relative polarization measurement Scan polarization over x and y range of the beam scattered proton polarized beam Carbon target recoil Carbon Forward scattered proton Year [GeV] Luminosity [pb-1] (recorded) Polarization [%] 2003 * 200 0.35 27 proton beam 2004 * 200 0.12 40 2005 * 200 3.4 49 proton target 2006 * 200 7.5 55 2006 * 62.4 0.08 48 • “Jet” Polarimeter measures left-right asymmetries in elastic pp collisions • Uses the known polarization of H atoms from Atomic Beam Source • Absolute measurement • Integrating over beam profile • Run 6: total syst. polarization uncertainty PBPY/(PBPY)=8.4%

  5. The PHENIX Detector for Spin Physics Central Detector Acceptance: (||x : • High efficiency  trigger • detection • Electromagnetic Calorimeter: PbSc + PbGl,  < |0.35|,  = 2 x 90 •  ,e+/e- • Drift Chamber • Ring Imaging Čerenkov Detector(RICH) • Muon Arms (forward kinematics (~1.1<|  |<2.4): • J • Muon ID/Muon Tracker () •  • Electromagnetic Calorimeter (MPC) • Global Detectors: • Relative Luminosity • Beam-Beam Counter (BBC) • Zero-Degree Calorimeter (ZDC) • Local Polarimetry - ZDC

  6. Intrinsic Spin Violates our intuition: How can an elementary particle such as thee¯be point like and have perpetual angular momentum.? The Protonalso violates our intuition. The Proton is composed of quarks, gluons and anti quarks. We should expect the proton's spin to be predominately carried by its 3 valence quarks 6

  7. That nucleon has a large anomalous magnetic moment proves that this is not a fundamental spin1/2 Dirac particle. Within the nucleon: Quarks, gluons and their angular momentum caused by their high speed motion within the nucleon are contributors to the Nucleon's spin.

  8. Contributions to the Proton's Spin Quarks and Gluons carry about 50%(each) of the longitudinal momentum What about Spin? Valence Quarks (QPM) ~30% (QCD) Gluons, Sea Quarks: ~>, =, <0? Orbital Angular Momentum ~?

  9. The Spin Structure of the Proton Longitudinal Spin Sum Rule: W-production (pp) Exclusive processes (DVCS,etc) Double Spin Asymmetries (pp,SIDIS) Transverse Spin Sum Rule? ΔG, Δq=are the probabilities of finding a parton with spin parallel or anti parallel to the spin of the nucleon. Sivers effect?? Chiral-odd Fragmentation functions (Collins,IFF,L)

  10. Accessing g with Asymmetries I Hard subprocess asymmetries (LO) Increasing x, pT

  11. Asymmetries For our g program the tools are measurements of helicity cross section asymmetries ALL • (N) Yield • (R) Relative Luminosity • BBC vs ZDC • (P) Polarization • RHIC Polarimeter (at 12 o’clock) • Local Polarimeters (SMD&ZDC) 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

  12. Asymmetries Accessing g: Inclusive channels ALL(ppAX) measurable at Phenix 0: wide pT range, mixture with ggX dominant at low pT , similar to 0 , different FF’s. , mixture sensitive to qgqX at high pT Multiparticle clusters (parts of jets), correlated with 0, Direct photons: pT range 6-20+ GeV/c, dominated by qgq J/, , e (ggcc) Lz : Current kT, , DL, AN,UT, T measurements at Phenix AN π0/π/h, J/forward neutrons DLL Anti-Λ Spin Transfer kT azimuthal di-h correlations

  13. 0 cross section measurement Agreement between data and pQCD theory Shows that pQCD and unpolarized PDFs determined in DIS can describe pp data Choice of fragmentation function crucial (dominated by gluon fragmentation) Scale uncertainty still large at lower pT<5 GeV PHENIX: 0 mid-rapidity, 200GeV hep-ex-0704.3599

  14. 0 Asymmetries Measured asymmetries for pp0X from Run 5 ,Run 6 Run3,4,5: PRL 93, 202002; PRD 73, 091102; hep-ex-0704.3599 Initial state parton configurations contributing to unpolarized cross section (Fractions) W. Vogelsang et al. • Dominated by gg for pT<3, qg for 3<pT<10 GeV/c • Asymmetry of combinatorial background estimated from sidebands and subtracted

  15. Information from 0 Asymmetries Maximum scenarios ruled out -> Constrain of g(x) Inclusive 0 ALL cannot access g(x) directly Only sensitive to an average over a wide x range No conclusions about moment of g(x) possible without a model for its shape vs. xT=2pT/S • More (indirect) information from varying cms energies • Higher (500 GeV)  lower x • Smaller (62 GeV)  higher x (and larger scale uncertainty)

  16. Fraction of pion production +,- Asymmetries Charged pions above 5 GeV/c identified with RICH. At higher pT, qg interactions become dominant: qg term. ALL becomes significant allowing access to the sign of G • New set from M. Stratmann et al. is the first to use charged separated  data from SIDIS for fragmentation functions

  17. Information from +,- Asymmetries • Inclusive +,-,0 ALL has access to sign g(x) directly • “Model independent” conclusion possible once enough data is available.

  18.  • Recent preliminary extraction of fragmentation functions, • Eta has (slightly) enhanced sensitivity to gg (when compared to the 0) Observation of difference in asymmetries could help disentangle the contributions from the different quarks and the gluons.

  19.  Asymmetries Dominated by qg Compton: - Small uncertainty from FFs - Better access to sign of G (qG) -Clean “Golden Channel” :-) -Luminosity Hungry :-(

  20. Information from e+,- Asymmetries xG(x) prompt photon cceX bbeX J/ • Provide access different x range • Thresholds • J/range (forward arms) • Prompt: no fragmentation z=1 • Rare channels with large background • Need more luminosity

  21. G(x) Global Analysis • Results from various channels combined into single results for G(x) • Correlations with other PDFs for each channel properly accounted • Every single channel result is usually smeared over x  global analysis can do deconvolution (map of G vs x) based on various channel results • NLO pQCD framework can be used • Global analysis framework already exist for pol. DIS data and being developed to include RHIC pp data, by different groups Now Run5-Final and Run6-Preliminary 0 data are available and has joined this effort

  22. G(x) Global AnalysisLatest Results -Flavor dependence of the sea -SU3 symmetry breaking?. “We also find that the SIDIS data give rise to a Robust pattern for the sea polarizations, clearly deviating from SU(3) symmetry, which awaits further clarification from the upcoming W boson Program at RHIC” Global Analysis of Helicity Parton Densities and Their Uncertainties (de Florian, Sassot, Stratmann and Wogelsang) ArXiv:0804.0422 (April 2008)

  23. G(x) Global AnalysisLatest Results -A first demonstration that p-p data can be included in a consistent way in a NLO pQCD calculation. -RHIC data set significantly constraints on the gluon helicity distribution -”Inclusion of theoretical uncertainties and the treatment of experimental ones should and will be improved” ArXiv:0804.0422 (April 2008)

  24. Transverse Spin hep-ex/0507073 (hep-ex/0507073) (Sivers effect) transversely asymmetric kt quark distributions (Collins effect) spin-dependent fragmentation functions (Twist-3) quark gluon field Interference

  25. Transverse Spin Mid-rapidity AN of 0 and h for y~0at s=200GeV AN : h+/h- PRL 95, 202001 (2005) p+p0+X at s=200 GeV/c2 PLB 603,173 (2004) process contribution to 0, =0, s=200 GeV • AN is 0 within 1%  interesting contrast with forward  • Mid-rapidity data at small pT sensitive to gluons, constrains magnitude of gluon Sivers function (Anselmino et al., PRD 74, 2006) • What happens if qq sets in (valence quarks) at high pT?

  26. PLB 603,173 (2004) Transverse Spin 0 AN at large xF p+p0+X at s=62.4 GeV 3.0<<4.0 p+p0+X at s=62.4 GeV process contribution to 0, =3.3, s=200 GeV Asymmetry seen in yellow beam (positive xF), but not in blue (negative xF) Large asymmetries at forward xF  Valence quark effect? xF, pT, s, and  dependence provide quantitative tests for theories

  27. Transverse Spin AN of J/ at s=200GeV Sensitive to gluon Sivers as produced through g-g fusion Charm theory prediction is available How does J/production affect prediction?

  28. Transverse Spin Other asymmetries at s=200GeV Results for <kT2> Results for <jT2> Run 5 charged particles neutron • Strange quark Components via Spin Transfer • In PHENIX the Self-analyzing decay channel (anti-Λ) has been found to be sensitive to the polarization of the anti-strange sea of the nucleon (See: hep-ph/0511061) • Probing Orbital angular Momentum with kT Asymmetries (See: Phys. Rev. D 74, 072002 (2006) • Neutron asymmetries. (See:AIP Conf.Proc.915:689-692,2007)

  29. Summary PHENIX is well suited to the study of spin physics with a wide variety of probes. Inclusive 0 data for ALL has reached statistical significance to constrain ΔG in a limited x-range (~0.02-0.3). Need more statistics (RHIC running time) to explore different (rare) channels for Different gluon kinematics Different mixtures of subprocesses Global Analysis of many channels together with DIS, SIDIS data will give us a more accurate picture of g(x) Upcoming W program will give more information about quarks PHENIX has an upgrade program that will give us the triggers and vertex information that we need for precise future measurements of G, q and new physics at higher luminosity and energy

  30. We Think That We Understand the Concept of “Rotational Motion“ THANK YOU For Listening ...but how does it workout at scales of about one fermi?(Marco Stratman. Lectures on the Longitudinal Spin Structure of the Nucleon, Wako, Japan) We Should Measure it and find out!!

  31. Extras

  32. Sivers effect: Initial state of the polarized nucleon Phys Rev D41 (1990) 83; Phys Rev D43 (1991) 261 x is longitudinal momentum fraction. Top view Quark transverse momentum in transversely polarized proton. Front view

  33. Collins Heppelmann effect:Final state of fragmentation hadrons Nucl Phys B396 (1993) 161, Nucl Phys B420 (1994) 565 Example: Polarization of struck quark which fragments to hadrons.

  34. Sivers effect and/or Collins- Heppelmann effect? Theoretical approaches to explain huge SSAs: • Siverseffect ( is connected to quark orbital angular momentum). • Collinseffect (Analyzer of transversity q). • Twist3 effect which is related to both initial and final states. Relation of Twist3 to Sivers effect is introduced. Relevance of Twist3 and Sivers effect is studied. PRL97, 082002 (2006) PRD73, 094017 (2006)

  35. Collins function: analyzer of “Transversity” Transversity: “with” : Probability to observe parton whose pol. vector is “with” or “against” the proton pol. vector with the renormalization scale . • q(x,) has not been measured experimentally. • Lattice QCD calculates the first moments of q(x,) for u,d, s quarks and the sum at 2=2 GeV2. “against”

  36. Relative Luminosity Use BBCs at 1.5 m from the interaction point to measure bunch-by-bunch luminosity Li=Ni/(Efficiency) , Eff.=const.=22.9mb9.7% Use independent measurement from ZDCs (18m) to check for intrinsic luminosity asymmetry For Run 6 (200 GeV): ALL(BBC-ZDC)=3.81.6*10-4 (>2 standard deviations) ALL=5.4*10-4 Sizeable asymmetry compared to stat. error of low pT data Can be instrumental or physics effect  need to find out

  37. 0 cross section and soft Physics Exponent (e-pT) describes pion cross section 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 pT soft physics contribution at pT>2 GeV/c is <10% PHENIX: 0 mid-rapidity, 200GeV hep-ex-0704.3599 PHENIX: hep-ex-0704.3599

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