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Kenneth N. Barish DSPIN 2013 October, 2013

The PHENIX Spin Program. Kenneth N. Barish DSPIN 2013 October, 2013. The Proton Spin Structure ( p+p ). Polarization experiments Helicity Valence quarks Gluon polarization (I) Sea quarks (II). gluon spin. momentum. valence + sea quark spin. quark & gluon orbital motion.

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Kenneth N. Barish DSPIN 2013 October, 2013

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  1. The PHENIX Spin Program Kenneth N. Barish DSPIN 2013 October, 2013

  2. The Proton Spin Structure (p+p) • Polarization experiments • Helicity • Valence quarks • Gluon polarization (I) • Sea quarks (II) gluon spin momentum valence + sea quark spin quark & gluon orbital motion DSSV: PRD80 034030,2009

  3. The Proton Spin Structure (p+p) • Polarization experiments • Helicity • Valence quarks • Gluon polarization (I) • Sea quarks (II) • Transversity • Transverse spin (III) gluon spin What is the connection to orbital angular momentum? momentum momentum valence + sea quark spin quark & gluon orbital motion

  4. The PHENIX Detector for Spin Physics • Philosophy : • High rate capability and granularity at cost of acceptance • Good mass resolution & particle ID • Trigger for rare events • p0/g/h detection (central and forward) • Electromagnetic Calorimeter, MPC • p+/p- (central) • Drift Chamber • Ring Imaging Cherenkov Counter • J/y (central and forward) • Muon Id/MuonTracker • Resistive Plate Chambers (RPC) • Relative Luminosity • Beam Beam Counter (BBC) • Zero Degree Calorimeter (ZDC) • Local Polarimetry - ZDC • Filters for “rare” events

  5. RHIC Polarized Proton Runs

  6. I. Gluon Polarization Robust measurement covering wide xg region through multiple channels: Each experimental channel (p0, g, etc) covers different ranges in xg, have different systematics, and in principle, uniquely contribute to a Global fit.

  7. Longitudinal Data

  8. Cross sections p0 Dg2 DgDq Dq2 PRD76:051106,2007 p0 (200 GeV) p0@ 200 GeV, h~0 NLO pQCD calculations are consistent with cross-section measurements

  9. Cross sections PRD76:051106,2007 p0 (200 GeV) p0 (62.4 GeV) p0 (500 GeV) NLO pQCD calculations are consistent with cross-section measurements

  10. Cross sections g (200 GeV) h (200 GeV) PRD83:032001,2011 PRD86:072008,2012 NLO pQCD calculations are consistent with cross-section measurements

  11. ALL of 0 at Ös=200GeV Run 5 Run 6 Run 9 RelLumi Systematic Uncert. Combined asymmetries consistent with DSSV, and also with 0 to O(10-3)

  12. Relative Luminosity Uncertainty • The central arm π0 ALL is systematics limited up to pT = 4 GeV/c • Relative luminosity systematic uncertainty 1.4 x 10-3 • Limits constraining power on ΔG. • Understanding and reducing this systematic will increase impact of PHENIX ALL results. • R = ratio of luminosity for same vs opposite sign helicitycrossings • Measure high statistics (scalars) from different detectors in different kinematic regions. • ZDC and BBC luminosities do not agree with each other at the 5-10% level • Addition of FVTX may help understand these residual effects and improve the significance of the data we have already taken.

  13. ALL of 0 at Ös=62.4GeV • Low FoM but good high-x coverage

  14. ALLπ+/- and ALLηMid-rapidity • Features: • Charged pare sensitive to the sign of ΔG • h provides a good test for strangeness fragmentation functions • Challenge: need more statistics

  15. DSSV++ ΔG From RHIC Data • DSSV++ includes RHIC Run 9 data. • Favors a positive gluon spin for 0.05<x<0.2. • Node is disfavored. • Large uncertainty at low x may hide large contribution to ΔG • Need forward rapidity to access low x • But ALL expected to be small there • Minimizing systematic top priority

  16. ALLe Mid-rapidity PRD87:012011,2013 Predictions for various values of |ΔG/G| compared with measurement • Consistent with 0 within errors • Features: • heavy quarks produced dominantly by gg interactions • Large mass of heavy quarks => pQCD reliable • Challenge:statistics

  17. p0 Pairs Mid-rapidity • Constrains event kinematics • need more Luminosity

  18. Forward Calorimetry: MPC • lower x10-3 Cluster (p0 dominant) ALL PT • On disk already: FOM 50x greater than Run 9, so new statistical error will be O(10-4) • Improved understanding of relative luminosity crucial

  19. II. Sea Quark Helicity • Features • High energy scale • Parity violating • Flavor conserving • Low rate Sea quark polarization have sizable uncertainties. DSSV: PRD81 094020 (2010)

  20. Measured W+ and W- Spectra (Mid-rapidity) e- e+ After all cuts, we have 25% background in the signal region for W+ After all cuts, we have 42% background in the signal region for W-

  21. W→e in Central Arms Errors currently too large to significantly constrain models Phys. Rev. Lett. 106, 062001 (2011) Cross section consistent with expectations from world’s data.

  22. Muon trigger upgrade RPC3 • Momentum selective trigger and timing to reject beam related backgrounds • Staged installation and commissioning to match beam luminosity requirements • Rejection power sufficient fit within 2kHz trigger bandwidth assigned. • Full sampling available p+p @ 500GeV delivered luminosity in Run 13. Run 13 2kHz Run 12

  23. W→mAnalysis Status • Run 11: L~15 pb-1 P~0.52 • Run 12: 30pb-1, P~0.55(S/N ~ 1/3)

  24. W→mAnalysis Status Run 13: >150pb-1recorded (expected improvement of S/BG ®1/1 due to FVTX not taken into account in plot)

  25. W→mAnalysis Status Run 13: >150pb-1 recorded (expected improvement of S/BG ®1/1 due to FVTX not taken into account in plot) From RHIC Spin whitepaper for the NSAC Subcommittee

  26. III. Transverse Spin (AN) • In (collinear) pQCD AN should scale like Asymmetries were expected to be very small.

  27. III. Transverse Spin (AN) • In (collinear) pQCD AN should scale like Asymmetries were expected to be very small. Z.Phys., C56, 181 (1992) IP Conf. Proc., vol. 915 (2007) PRL 101, 222001 (2008)

  28. III. Transverse Spin (AN) • Sizable forward non-zero asymmetries • Asymmetries consistent over an order of magnitude in s • Several theoretical frameworks to explain the results. Z.Phys., C56, 181 (1992) IP Conf. Proc., vol. 915 (2007) PRL 101, 222001 (2008)

  29. Transverse Spin Asymmetry Sources X. Ji, J.-W. Qiu, W. Vogelsang, F. Yuan, PRL 97, 082002 (2006) (III) Higher-twist effectsTwist-3 quark-gluon/gluon-gluon correlatorsExpectation: at large pT, AN ~ 1/pT So far, fall-off with pT has not been observed. (II) Sivers quark-distribution Correlation between proton-spin and intrinsic transverse quark momentum Graphic from Zhongbo Kang (I) Transversity quark distributionsand Collins fragmentation functionCorrelation between proton & quark spin + spin dependant fragmentation function Sivers distribution • Access to non-collinear PDFs • Needs orbital angular momentum of the quarks Quark transverse spin distribution Collins FF J. C. Collins, Nucl. Phys. B396, 161 (1993) D. Sivers, Phys. Rev. D 41, 83 (1990)

  30. Measurements Initial state interaction Sivers effect Hard Scattering Transversity Twist-3 Final state interaction Collins effect Transverse Asymmetries • Inclusive AN (central/forward) • Hadron Correlations (back-to-back) • Interference Fragmentation Functions • Photon AN (MPC-EX) • Jet correlations/structure (fsPHENIX) Upgrades Upgrade plans • Separation of Sivers & Collins and test TMD parton distribution factorization and universality

  31. Transverse Data

  32. AN: mid-rapidity0 and  • Little or no Asymmetries observed over a wide pTrange • Constrains gluon Sivers s=200 GeV Phys. Rev. D 74, 094011 • Partonic Cross Sections • quark-gluon dominated • gluon-gluon at low pT (Sivers) • quark-quark at large pT (Sivers+Collins)

  33. Forward p0 AN@ 62.4 GeV π0 process contribution=3.3, s=200 GeV Guzeyet al, PLB 603,173 (2004) • Significant asymmetries for xF>0 ~ p+/- (Brahms). • Quark-gluon is the dominant partonic component.

  34. Forward AN for EM Clusters MPC tower size 2.252 cm2 220 cm from vertex √s = 200 GeV Decay photon impact positions for low and high energy p0’s. EM Cluster contribution decay photon • Magnitude of forward asymmetries similar to E704 (19.4 GeV/c2) and STAR at (200GeV/c2) π0 η < 3.3 η > 3.3 direct photon xF xF

  35. pT Behavior decay photon π0 direct photon • A significant decrease of the asymmetry as expected from higher twist calculations is not apparent up to 4 GeV/c.

  36. Forward AN( ) PRD86 (2012) 051101 • Significant asymmetries observed for positive xF • Asymmetries consistent with PHENIX p0 measurements • Difference in fragmentation mass, strangeness, isospin

  37. AN forward neutrons • Þ Talk by Kiyoshi Tanida (Monday)

  38. AN : forward g (MPC-EX) • 8 layer Silicon minipad Tungsten sandwich pre-shower in front of lead-tungstate MPC electromagnetic calorimeter (3.1<|h|<3.8) • Reconstruct and reject p0mesons Þ enhances p0/g separation (up to >80GeV) • Spin Physics Motivation: • Sign mismatch between twist-3 quark gluon distribution functions Tq,F(x, x) extracted from RHIC (assuming no Collins) and moments of the Sivers function from SIDIS measurements. • The Collins fragmentation functions in the p+p measurements may be the reason. • AN of prompt photons (free of contribution from the Collins effect) can be used to verify this & check consistency of theory. • Timescale: Expected for Run 15. Gamberg and Kang

  39. IV. Future Prospects • High luminosity and polarization • 2013 500 GeVLongitudinal Run Analysis • Complete W measurements • Access DG to lower x • 200 GeV Transverse Running (2015) • Interference fragmentation functions • Back to back jets (Collins) • Recent Upgrades • W trigger • Central and forward Silicon • MPC electronics • MPC-EX • Future Major UpgradeÞtalk by Edward Kistenev • sPHENIX, forward sPHENIX?, ePHENIX

  40. Summary and Outlook • Gluon polarization • Significant constraints on Dg(x) for 0.02<x<0.3 • Higher energy and forward region => lower x • Flavor decomposed quark distribution via W • Low statistics central arm (e) and forward (m) measurements. High statistics to follow. • Upgrades will significantly extend physics capabilities • MPC-EX will enable forward AN measurements • A new Forward Spectrometer, will be able to understand large SSA, separating contributions from Sivers and Collins. • The sPHENIX forward would also be well matched with ePHENIX.

  41. Extra slides…

  42. Measuring ALL • Helicity Dependent Particle Yields • (Local) Polarimetry (ZDC) • Relative Luminosity (R=L++/L+-) – BBC (ZDC) • ALL ++ same helicity + opposite helicity

  43. PHENIX Forward Upgrade Program 2009, 2010 2011 2009, 2010 2011 RPC3 RPC3 FVTX 2010 Absorber RPC1 Mutrg

  44. Understanding Forward (Muon) Arm Backgrounds No Jacobian peak to help distinguish signal from background level PYTHIA W –→ – W +→ + Central arm (e±) PYTHIA + GEANT detector response Forward arm (μ±) Transverse Momentum [GeV/c] • Dominated background is from • misreconstructed low pT hadrons Backgrounds: • Muon BGs: Heavy flavor, quarkonia (“true” muons, momentum smeared to high pT) • Hadronic BGs (“fake”)

  45. Signal Extraction in Forward Arm Analysis Likelihood-based signal selection (2 steps): 1. Pre-selection: multivariate cut using likelihood ratio 2. S/B ratio extraction: unbinned maximum likelihood fitting Step 1. Multivariate cut for pre-selection Signal and BG distributions as function of W likeliness f : f > 0.92 Signal DCAr Distribution (16 < pT < 60 GeV/c) Data W Simulation

  46. Signal Extraction in Forward Arm Analysis Step 2. Unbinned maximum likelihood fitting S/B ratio was extracted minimizing likelihood function: pc(xi) – probability distribution functions extracted from simulation (W signal, muon BGs) and data (hadron BGs) using eta, dw23 (reduced azimuthal bending): dw23 distributions (16 < pT < 60 GeV/c, f > 0.02)

  47. S/B Ratio in Forward Arm 1D projections of the 2D unbinned maximum likelihood fit of dw23 (top) and rapidity η (bottom) 16 < pT < 60 GeV/c, f > 0.92 Extracted S/B ratios: Factor [0.5 – 2.0] range, as a conservative uncertainty of the S/B Extracted S/B ratios are used for the dilution factor

  48. Event kinematics at s = 200 GeV • Estimated with Pythia simulation package • Mid-rapidity:Low pT dominated bygluon gluon scattering • Forward-rapidity: High-x + Low-xscattering h h 48

  49. Forward AN for Clusters √s = 200 GeV MPC tower size 2.252 cm2 220 cm from vertex • Cluster contribution • decay photon • π0 • direct photon η < 3.3 η > 3.3 xF xF

  50. Interference Fragmentation fa IFF σ fb • IFF x transversity • input e+e- annihilationfew percent @ Belle • Forward direction

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