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Transverse Spin and RHIC Probing Transverse Spin in p+p Collisions

Transverse Spin and RHIC Probing Transverse Spin in p+p Collisions. OUTLINE Features of RHIC for polarized p+p collisions Transverse single spin effects in p+p collisions at  s =200 GeV Towards understanding forward p 0 cross sections Plans for the future. L.C. Bland

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Transverse Spin and RHIC Probing Transverse Spin in p+p Collisions

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  1. Transverse Spin and RHICProbing Transverse Spin in p+p Collisions • OUTLINE • Features of RHIC for polarized p+p collisions • Transverse single spin effects in p+p collisions at s=200 GeV • Towards understanding forward p0 cross sections • Plans for the future L.C. Bland Brookhaven National Laboratory Transverse Polarization in Hard Processes Como 7 September 2005

  2. Installed and commissioned during run 4 To be commissioned Installed/commissioned in run 5 • Developments for runs 2 (1/02), 3 (3/03  5/03) and 4 (4/04  5/03) • Helical dipole snake magnets • CNI polarimeters in RHIC,AGS •  fast feedback • b*=1m operataion • spin rotators  longitudinal polarization • polarized atomic hydrogen jet target L.C.Bland, Como

  3. RHIC Spin Physics Program • Direct measurement of polarized gluon distribution using • multiple probes • Direct measurement of anti-quark polarization using • parity violating production of W • Transverse spin: Transversity & transverse spin effects: • possible connections to orbital angular momentum? L.C.Bland, Como

  4. Calendar Summary for RHICRun-5 p+p Run • pp commissioning started on March 24, 2005 • pp Physics running, for longitudinal polarization, started on April 19, 2005 • 410 GeV Collider dev. & data, was May 31st to June 3rd • Transverse polarization was June 13th to June 16th • Run ended on June 24, 2005 L.C.Bland, Como

  5. RHIC Run-5 Performance (nb-1) Total for run ~ 9.2 pb-1 delivered ~ 3.1 pb-1 smpled (nb-1) Delivered STAR 2005 Longitudinal Goal Sampled L.C.Bland, Como

  6. PHENIX Detector • Philosophy: • High rate capability & granularity • Good mass resolution and particle ID • 0 reconstruction and • high pT photon trigger: • EMCal: ||<0.38, = • Granularity  = 0.010.01 • Minimum Bias trigger and Relative Luminosity: • Beam-Beam Counter (BBC): • 3.0<||<3.9, =2 L.C.Bland, Como

  7. L.C.Bland, Como

  8. STAR detector layout • TPC: -1.0 <  < 1.0 • FTPC: 2.8 <  < 3.8 • BBC : 2.2 <  < 5.0 • EEMC:1 <  < 2 • BEMC:0 <  < 1 • FPD: || ~ 4.0 & ~3.7 L.C.Bland, Como

  9. First AN Measurement at STARprototype FPD results STAR collaboration Phys. Rev. Lett. 92 (2004) 171801 Similar to result from E704 experiment (√s=20 GeV, 0.5 < pT < 2.0 GeV/c) Can be described by several models available as predictions: Sivers: spin and k correlation in parton distribution functions (initial state) Collins: spin and k correlation in fragmentation function (final state) Qiu and Sterman (initial state) / Koike (final state): twist-3 pQCD calculations, multi-parton correlations √s=200 GeV, <η> = 3.8 L.C.Bland, Como

  10. Deep inelastic scattering Why Consider Forward Physics at a Collider?Kinematics Hard scattering hadroproduction Can Bjorken x values be selected in hard scattering? • Assume: • Initial partons are collinear • Partonic interaction is elastic pT,1  pT,2  Studying pseudorapidity, h=-ln(tanq/2), dependence of particle production probes parton distributions at different Bjorken x values and involves different admixtures of gg, qg and qq’ subprocesses. L.C.Bland, Como

  11. p+p  p0+X, s = 200 GeV, h=0 Simple Kinematic Limits • Mid-rapidity particle detection: • h10 and <h2>0 •  xq  xg  xT = 2 pT / s • Large-rapidity particle detection: • h1>>h2 • xq  xT eh1 xF(Feynman x), and xg xF e-(h1+h2) NLO pQCD (Vogelsang) 1.0 0.8 0.6 0.4 0.2 0.0 qq fraction qg gg 0 10 20 30 pT,p(GeV/c)  Large rapidity particle production and correlations involving large rapidity particle probes low-x parton distributions using valence quarks L.C.Bland, Como

  12. STAR How can one infer the dynamics of particle production?Particle production and correlations near h0 in p+p collisions at s = 200 GeV Inclusive p0 cross section Two particle correlations (h) STAR, Phys. Rev. Lett. 90 (2003), nucl-ex/0210033 At √s = 200GeV and mid-rapidity, both NLO pQCD and PYTHIA explains p+p data well, down to pT~1GeV/c, consistent with partonic origin Do they work for forward rapidity? Phys. Rev. Lett. 91, 241803 (2003) hep-ex/0304038 L.C.Bland, Como

  13. <z> <xq> <xg> Forwardp0production in hadron collider Ep p0 p d EN qq qp p Au xgp xqp qg EN (collinear approx.) • Large rapidity p production (hp~4) probes asymmetric partonic collisions • Mostly high-x valence quark + low-x gluon • 0.3 < xq< 0.7 • 0.001< xg < 0.1 • <z> nearly constant and high 0.7 ~ 0.8 • Large-x quark polarization is known to be large from DIS • Directly couple to gluons = A probe of low x gluons NLO pQCD Jaeger,Stratmann,Vogelsang,Kretzer L.C.Bland, Como

  14. STAR xF and pT range of FPD data L.C.Bland, Como

  15. ppp0X cross sections at 200 GeV • The error bars are point-to-point systematic and statistical errors added in quadrature • The inclusive differential cross section for p0 production is consistent with NLO pQCD calculations at 3.3 < η < 4.0 • The data at low pT are more consistent with the Kretzer set of fragmentation functions, similar to what was observed by PHENIX for p0 production at midrapidity. D. Morozov (IHEP), XXXXth Rencontres de Moriond - QCD, March 12 - 19, 2005 NLO pQCD calculations by Vogelsang, et al. L.C.Bland, Como

  16. STAR -FPD Preliminary Cross Sections Similar to ISR analysis J. Singh, et al Nucl. Phys. B140 (1978) 189. L.C.Bland, Como

  17.  q g  q g g PYTHIA: a guide to the physics Subprocesses involved: Forward Inclusive Cross-Section: q+g g+g and q+g  q+g+g STAR FPD Soft processes • PYTHIA predictionagrees well with the inclusive 0 cross section at 3-4 • Dominant sources of large xF production from: • q + g  q + g (22) + X • q + g  q + g + g (23)+ X L.C.Bland, Como

  18. Definition: dσ↑(↓) – differential cross section of p0 then incoming proton has spin up(down) Two measurements: Single arm calorimeter: R – relative luminosity (by BBC) Pbeam – beam polarization Two arms (left-right) calorimeter: No relative luminosity needed Left π0, xF<0 π0, xF>0 p  p Right Single Spin AsymmetryDefinitions positive AN: more p0 going left to polarized beam L.C.Bland, Como

  19. Caveats: -RHIC CNI Absolute polarization still preliminary. -Result Averaged over azimuthal acceptance of detectors. -Positive XF (small angle scattering of the polarized proton). Run 2 Published Result. Run 3 Preliminary Result. -More Forward angles. -FPD Detectors. - ~0.25 pb-1 with Pbeam~27% Run 3 Preliminary Backward Angle Data. -No significant Asymmetry seen. (Presented at Spin 2004: hep-ex/0502040) L.C.Bland, Como

  20. Figure 3 Diagram showing the boundary between possible “phase” regions in the t=ln(1/x) vs ln Q2plane . New Physics at high gluon density • Shadowing. Gluons hidingbehind other gluons. Modificationof g(x) in nuclei. Modified distributionsneeded by codes that hope to calculateenergy density after heavy ion collision. • Saturation Physics. New phenomena associated with large gluon density. • Coherent gluon contributions. • Macroscopic gluon fields. • Higher twist effects. • “Color Glass Condensate” Edmond Iancu and Raju Venugopalan, review for Quark Gluon Plasma 3, R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/0303204]. L.C.Bland, Como

  21. y=0 As y grows Kharzeev, Kovchegov, and Tuchin, Phys. Rev. D 68 , 094013 (2003)  Dependence of RdAu G. Rakness (Penn State/BNL), XXXXth Rencontres de Moriond - QCD, March 12 - 19, 2005 See also J. Jalilian-Marian, Nucl. Phys. A739, 319 (2004) • From isospin considerations, p + p  h is expected to be suppressed relative to d + nucleon  h at large [Guzey, Strikman and Vogelsang, Phys. Lett. B 603, 173 (2004)] • Observe significant rapidity dependence similar to expectations from a “toy model” of RpA within the Color Glass Condensate framework. L.C.Bland, Como

  22. For 22 processes Log10(xGluon) TPC Barrel EMC FTPC FTPC FPD FPD Gluon Constraining the x-values probed in hadronic scattering Guzey, Strikman, and Vogelsang, Phys. Lett. B 603, 173 (2004). Log10(xGluon) Collinear partons: • x+ = pT/s (e+h1 + e+h2) • x = pT/s (eh1 + eh2) • FPD: ||  4.0 • TPC and Barrel EMC: || < 1.0 • Endcap EMC: 1.0 <  < 2.0 • FTPC: 2.8 <  < 3.8 CONCLUSION: Measure two particles in the final state to constrain the x-values probed L.C.Bland, Como

  23. Back-to-back Azimuthal Correlationswith large  Fit LCP normalized distributions and with Gaussian+constant Beam View Top View Trigger by forward   ] • E > 25 GeV •  4 ] Coicidence Probability [1/radian] Midrapidity h tracksin TPC • -0.75 < < +0.75 Leading Charged Particle(LCP) • pT > 0.5 GeV/c LCP S = Probability of “correlated” event under Gaussian B = Probability of “un-correlated” event under constant s = Width of Gaussian L.C.Bland, Como

  24. STAR STAR Preliminary STAR Preliminary PYTHIA (with detector effects) predicts • “S” grows with<xF> and <pT,> • “s” decrease with <xF> and <pT,> PYTHIA prediction agrees with p+p data Larger intrinsic kT required to fit data 25<E<35GeV 45<E<55GeV Statistical errors only L.C.Bland, Como

  25. Plans for the Future L.C.Bland, Como

  26. STAR Forward Meson Spectrometer • NSF Major Research Initiative (MRI) Proposal • submitted January 2005 • [hep-ex/0502040] L.C.Bland, Como

  27. FMS: 2.5<< 4.0 STAR detector layout with FMS TPC: -1.0 <  < 1.0 FTPC: 2.8 <  < 3.8 BBC : 2.2 <  < 5.0 EEMC:1 <  < 2 BEMC:-1 <  < 1 FPD: || ~ 4.0 & ~3.7 L.C.Bland, Como

  28. Three Highlighted Objectives In FMS Proposal(not exclusive) • A d(p)+Aup0p0+X measurement of the parton model gluon density distributions xg(x) in gold nucleifor0.001< x <0.1. For 0.01<x<0.1, this measurement tests the universality of the gluon distribution. • Characterization of correlated pion cross sections as a function of Q2 (pT2) to search for the onset of gluon saturation effects associated with macroscopic gluon fields. (again d-Au) • Measurements withtransversely polarized protonsthat are expected toresolve the origin of the large transverse spin asymmetriesin reactions for forward  production. (polarized pp) L.C.Bland, Como

  29. Frankfurt, Guzey and Strikman, J. Phys. G27 (2001) R23 [hep-ph/0010248]. • constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate. • span broad pseudorapidity range (-1<h<+4) for second hadron  span broad range of xgluon • provide sensitivity to higher pT for forward p0 reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in Df correlation. L.C.Bland, Como Pythia Simulation

  30. Disentangling Dynamics of Single Spin AsymmetriesSpin-dependent particle correlations Collins/Hepplemann mechanism requires transversity and spin-dependent fragmentation Sivers mechanism asymmetry is present for forward jet or g Large acceptance of FMS will enable disentangling dynamics of spin asymmetries L.C.Bland, Como

  31. New FMS Calorimeter Lead Glass From FNAL E831 804 cells of 5.8cm5.8cm60cm Schott F2 lead glass Loaded On a Rental Truck for Trip To BNL L.C.Bland, Como

  32. Run-5 FPD Run-7 FMS Run-6 FPD++ FPD++ Physics for Run6 We intend to stage a large version of the FPD to prove our ability to detect direct photons. L.C.Bland, Como

  33. How do we detect direct photons? Isolate photons by having sensitivity to partner in decay of known particles: π0 M=0.135 GeV BR=98.8% K0  π0π0   0.497 31%   0.547 39%  π0    0.782 8.9% Detailed simulations underway L.C.Bland, Como

  34. Where do decay partners go? m = p0(h) di-photon parameters zgg = |E1-E2|/(E1+E2) fgg = opening angle Mm = 0.135 GeV/c2 (p0) Mm=0.548 GeV/c2 (h) • Gain sensitivity to direct photons by making sure we have high probability to catch decay partners • This means we need dynamic range, because photon energies get low (~0.25 GeV), and sufficient area (typical opening angles few degrees at our h ranges). L.C.Bland, Como

  35. Sample decays on FPD++ With FPD++ module size and electronic dynamic range, have >95% probability of detecting second photon from p0 decay. L.C.Bland, Como

  36. Timeline for the Baseline RHIC Spin Program Ongoing progress on developing luminosity and polarization Research Plan for Spin Physics at RHIC (2/05) Program divides into 2 phases: • s=200 GeV with present detectors for gluon polarization (g) at higher x & transverse asymmetries; s=500 GeV with detector upgrades for g at lower x & W production L.C.Bland, Como

  37. Summary / Outlook • Large transverse single spin asymmetries are observed for large rapidity p0 production for polarized p+p collisions at s = 200 GeV • AN grows with increasing xF for xF>0.35 • AN is zero for negative xF • Large rapidity p0 cross sections for p+p collisions at s = 200 GeV is in agreement with NLO pQCD, unlike at lower s. Particle correlations are consistent with expectations of LO pQCD (+ parton showers). • Large rapidity p0 cross sections and particle correlations are suppressed in d+Au collisions at sNN=200 GeV, qualitatively consistent with parton saturation models. • Plan partial mapping of AN in xF-pT plane in RHIC run-5 • Propose increase in forward calorimetry in STAR to probe low-x gluon densities and establish dynamical origin of AN (complete upgrade by 10/06). L.C.Bland, Como

  38. Backups L.C.Bland, Como

  39. Towards establishing consistency between FPD (p0)/BRAHMS(h-) • Extrapolate xF dependence at pT=2.5 GeV/c to compare with BRAHMS h- data. Issues to consider: • <h> of BRAHMS data for 2.3<pT<2.9 GeV/c bin. From Fig. 1 of PRL 94 (2005) 032301 take <h>=3.07  <xF>=0.27 • p-/h- ratio? • Results appear consistent but have insufficient accuracy to establish p+pp-/p0 isospin effects L.C.Bland, Como

  40. Systematics Measurements utilizing independent calorimeters consistent within uncertainties • Systematics: • Normalization uncertainty = 16%: • position uncertainty (dominant) • Energy dependent uncertainty = 13% - 27%: • energy calibration to 1% (dominant) • background/bin migration correction • kinematical constraints L.C.Bland, Como

  41. FPD Detector and º reconstruction • robust di-photon reconstructions with FPD in d+Au collisions on deuteron beam side. • average number of photons reconstructed increases by 0.5 compared to p+p data. L.C.Bland, Como

  42. d+Au  p0+p0+X, pseudorapidity correlations with forward p0 HIJIING 1.381 Simulations • increased pT for forward p0 over run-3 results is expected to reduce the background in Df correlation • detection of p0 in interval -1<h<+1 correlated with forward p0 (3<h<4) is expected to probe 0.01<xgluon<0.1  provides a universality test of nuclear gluon distribution determined from DIS • detection of p0 in interval 1<h<4 correlated with forward p0 (3<h<4) is expected to probe 0.001<xgluon<0.01  smallest x range until eRHIC • at d+Au interaction rates achieved at the end of run-3 (Rint~30 kHz), expect 9,700200 (5,600140) p0-p0 coincident events that probe 0.001<xgluon<0.01 for “no shadowing” (“shadowing”) scenarios. L.C.Bland, Como

  43. STAR Forward Calorimetry Recent History and Plans • Prototype FPD proposal Dec 2000 • Approved March 2001 • Run 2 polarized proton data (published 2004 spin asymmetry and cross section) • FPD proposal June 2002 • Review July 2002 • Run 3 data pp dAu (Preliminary An Results) • FMS Proposal: Complete Forward EM Coverage(hep-ex/0502040). L.C.Bland, Como

  44. Students prepare cells at test Lab at BNL L.C.Bland, Como

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