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Spin Physics at PHENIX

Spin Physics at PHENIX. Douglas Fields University of New Mexico For the PHENIX Collaboration. Outline. Brief Motivation Polarized Proton Program at RHIC PHENIX Capabilities Central Forward PHENIX Present and Upcoming Results Double-Longitudinal Spin Asymmetries

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Spin Physics at PHENIX

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  1. Spin Physics at PHENIX Douglas Fields University of New Mexico For the PHENIX Collaboration

  2. Outline • Brief Motivation • Polarized Proton Program at RHIC • PHENIX Capabilities • Central • Forward • PHENIX Present and Upcoming Results • Double-Longitudinal Spin Asymmetries • Single-Longitudinal Spin Asymmetries • Transverse Spin Asymmetries • Future of PHENIX • Summary Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  3. 2D Fourier transform Motivation - Parton Distributions Slide stolen from CédricLorcé’sTransversity 2011 talk. Transverse Longitudinal PDFs TMDs DIS e.g. SIDIS Alessandro’s « elephant » FFs GPDs GTMDs elastic scattering e.g. DVCS ??? [Burkardt (2000,2003)] TDs IPDs Wigner distributions [Miller (2007)] [Carlson, Vanderhaeghen (2008)] [Alexandrou et al. (2009,2010)] [C.L., Pasquini, Vanderhaeghen (2011)] [C.L., Pasquini (2011)]

  4. Motivation - Moments • I won’t foray into the debate on spin decomposition. • Suffice to say that the proton is very complicated theoretically (or at least computationally) and is difficult to explore experimentally. • The best approach then, is to attempt to measure everything possible, and let the results lead the theorists to sort it all out. • The PHENIX experiment can contribute to: • The knowledge of ΔG through the double-longitudinal asymmetries in various channels. • The understanding of ΔΣ(antiquark) through single-longitudinal parity violating asymmetries in W production. • The understanding of δq and L (OAM) through single-transverse asymmetries and through other means. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  5. PDFs from Asymmetries • Example: • Choose channel with high statistics: p + p → π0 + X • Complicated mixture of amplitudes, changes as a function of kinematics. • How does one extract ΔG from the experimentally determined: • Requires calculational techniques based on factorization. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  6. Factorization Δ Δfa,b=polarized quark and gluon distribution functions Dhf=fragmentation function for Δ Δ Partonic cross section from pQCD Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  7. Factorization • A final state that can be produced from q-g or g-g scattering will contain Δg in its factorization • Factorization allows a global analysis to input a measured ALL to extract Δg(x). • Will need some evidence that factorization works. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  8. RHIC pC Polarimeters Absolute Polarimeter (H jet) BRAHMS & PP2PP PHOBOS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin flipper Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS Internal Polarimeter AGS pC Polarimeters Rf Dipole Strong AGS Snake RHIC Spin Douglas Fields, University of New Mexico, for the PHENIX Collaboration The polarized pp program at RHIC is a tremendously complicated project and its operation should be considered a great technical achievement. There have been issues that have frustrated us as consumers of luminosity, but we have managed to get close to our goals.

  9. RHIC Spin • Polarized p+pSqrt(s) collisions at 62.4 GeV, 200 GeV and 500 GeV • Recent Spin Runs: • 2009: first 500 GeV polarized running (longitudinal) • 2011, 2012: 510 GeV polarized running (longitudinal and transverse). • 2013: 510 GeV polarized running (longitudinal only) Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  10. PHENIX Experiment Douglas Fields, University of New Mexico, for the PHENIX Collaboration Began as a shotgun marriage of several collaborations, but has become a fruitful multi-purpose experiment. Central spectrometers focus on electrons and photons. Forward spectrometers focus on muons. Specialty in triggering for rare physics.

  11. PHENIX Central Spectrometers • 2 arms: |η|<0.35, each  = /2 • Electromagnetic Calorimeter (EMCal: PbSc, PbGl) with fine segmentation Δφ x Δη~0.01 x 0.01: triggering • Drift Chamber (DC) and Pad Chamber (PC): tracking charged tracks and charge separation • VTX detector (commissioned in 2011) g g p0 Good photon trigger => Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  12. PHENIX Central Spectrometers • 2 arms: |η|<0.35, each  = /2 • Electromagnetic Calorimeter (EMCal: PbSc, PbGl) with fine segmentation Δφ x Δη~0.01 x 0.01: triggering • Drift Chamber (DC) and Pad Chamber (PC): tracking charged tracks and charge separation • VTX detector (commissioned in 2011) e Good electron trigger => Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  13. PHENIX Forward Spectrometers • 1.2 < η < 2.4 (North) -2.2 < η <-1.2 (South),  = 2 • Muon Tracker (MuTr): tracking, triggering • Muon Identifier (MuID): particle ID, triggering • Resistive Plate Chamber (RPC): particle ID, triggering • FVTX silicon tracker for opening angle determination, track matching, displaced vertex and isolation cuts J/Ψ m+ m- Good di-muon trigger => Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  14. PHENIX Forward Spectrometers • 1.2 < η < 2.4 (North) -2.2 < η <-1.2 (South),  = 2 • Muon Tracker (MuTr): tracking, triggering • Muon Identifier (MuID): particle ID, triggering • Resistive Plate Chamber (RPC): particle ID, triggering • FVTX silicon tracker for opening angle determination, track matching, displaced vertex and isolation cuts W m Good high p muon trigger => Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  15. ALLπ0 Mid-rapidity • The most abundant probe at PHENIX, triggered using electromagnetic calorimeter • π0 → γγ BR ~ 98.8 % • Well developed method over the years • Sensitive to gluon polarization in leading order • Reconstruct invariant mass from photons in calorimeter and identify pion counts • Combinatorial background determined from sidebands • Asymmetry is corrected for background √s = 200 GeV Partonic contributions Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  16. Cross-sections 200 GeV, h, mid-rapidity 500 GeV, π0, mid-rapidity 200 GeV, π0, mid-rapidity Douglas Fields, University of New Mexico, for the PHENIX Collaboration NLO (or better) cross sections show good agreement to measured values, giving confidence in partonic cross-section determination for asymmetries.

  17. ALLπ0 Mid-rapidity • PHENIX has published data from 200 GeV 2005 and 2006 runs, and has preliminary from the 2009 run and the combined data. • The 500 GeV 2012 and 2013 runs will be forthcoming. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  18. Relative Luminosity • However, the central arm π0 ALL is systematics limited up to pT = 4 GeV/c • Limits constraining power on ΔG. • Understanding/reducing this systematic will increase impact of PHENIX ALL results. RelLumi Systematic Uncert. 1.4 x 10-3 Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  19. ALLπ+/- and ALLηMid-rapidity • While these channels are currently statistics limited, with the new, higher statistics data set coming, they can provide sensitivity to: • Charged pions are sensitive to the sign of ΔG • Eta provides a good test for s fragmentation functions Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  20. From ALL to G (with GRSV model) Generate g(x) curves for different (with DIS refit) Compare ALL data to curves (produce 2vs G) arXiv:0810.0694 Calculate ALL for each G Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  21. DSSV++ ΔG From RHIC Data • Very large uncertainty at lower x which may bring ΔG to big value • Need forward rapidity • But ALL expected to be small there • Minimizing systematic top priority Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  22. Bjorken-x sensitivity at Forward Rapidity <xg>~0.001 for π0- π0 <xg>~0.01 for π0 Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  23. MPC Cluster ALL • Since, at these very forward rapidities, the two photons from the π0s merge, we can, instead, look at clusters as π0 surrogates. • Cluster composition is dominated by them (~80%). Cluster Decomposition Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  24. Forward Di-Hadrons • MPC electronics upgrade has been functional for Runs 12 and 13 • Now have ability to trigger on di-hadrons • At 500 GeV, this gives gluon-x sensitivity at the 10-3 scale • Would (will) be very exciting to make a big dent here… Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  25. max signal expected Challenging Measurement at Low-x Relative Luminosity Syst Error History • The asymmetry is expected to be O(10-4) in the forward measurements • The relative luminosity uncertainty is O(10-3) • Statistical uncertainty for run9 is O(10-3) • On disk already: FOM 50x greater than run9, so new stat error will be O(10-4) • To better constrain ΔG at low-x, the relative luminosity must improve, but historically is has worsened (multiple collisions). Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  26. Relative Luminosity Currently, the collaboration is working diligently to reduce the uncertainty on the relative luminosity. Our approach is to measure high statistics (scalars) from several different detectors in different kinematic regions. In the past, we have only had information from the BBC and the ZDC. Residual effects (vertex profile, multiple collisions, residual asymmetries, etc.) have been difficult to sort at the 10-4level. We now have a FVTX scaler which is sensitive to multiple collisions and the vertex profile in a way which should help to understand these residual effects and reduce the relative luminosity uncertainty. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  27. Impact on ΔΣ DSSV Global Analysis: Phys. Rev. D 80, 034030 (2009) Sea anti-quark polarization not well constrained in polarized SIDIS SIDIS results depend on large-uncertainty fragmentation functions Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  28. W Production PHENIX exploits maximal-parity violation in W ± boson production in longitudinally polarized p+p collisions • No fragmentation involved - Ws detected through their leptonic decay channels • Ws couple directly to the quarks and antiquarks of interest • Due to parity violation, perfect quark/antiquark helicityseparation: only left-handed quarks and right-handed anti-quarks are selected Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  29. W Production Parity Violating Longitudinal Single-Spin Asymmetry: • For : and probed Flipping the spin orientation of one of the colliding protons and averaging over another : • For : and probed Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  30. Simulated Impact Phys. Rev. D 81, 094020 (2010) DSSV global analysis DSSV global analysis + simulated 200 pb−1 W ±AL at proton-proton collisions in RHIC Significant impact for reducing uncertainties Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  31. W± in PHENIX Central |η|<0.35 • Detect high energy e± : • Trigger: EMCal 4x4 Tower Sum (fully efficient above 12 GeV) • High energy EMCal clusters matched to charged tracks in DC for charge determination(Δϕ < 0.01 rad) e  • Isolation cut is the main background reducer: Relative isolation cut: removes >10 in background dominated region (10-20 GeV); signal region (30-50 GeV) is relatively untouched: W signal: Jacobian peak at ~MW /2 e+ ~MW /2 Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  32. W± in PHENIX Central • 30-50 GeV/c – Signal Region • 10-20 GeV/c – Background Dominated • Background estimation: • Fit region 10 to 69 GeV/c with a power law • Fit region 20 to 50 GeV/c with a power law + Jacobian peak (simulation) e+ e- • After cuts, 25% background in signal region for W+42% background in signal region for W- Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  33. Forward rapidity W± Measurements 1.2 < η < 2.4 (North) -2.2 < η <-1.2 (South) PHENIX Forward Upgrade Program Fully upgraded in 2012: new upgrades provide trigger rejection to reject low-p muons • High‐pT trigger including RPC: small bending in magnetic field + timing (BBC/RPC) • Trigger on straight-line tracks through the whole muon arm • Muon Tracker (MuTr): tracking, triggering • Muon Identifier (MuID): particle ID, triggering • Resistive Plate Chamber (RPC): particle ID, triggering • Forward Vertex Detector (FVTX) RPC3  Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  34. Run 2012 W±AL Beam combined asymmetries for forward and the mid-rapidity results • Boxes are systematic uncertainties from background • Run 2012 Beam Polarization uncertainty P/P = 3.4% (not shown) • With the upcoming analysis of the recent high statistics run will we be able to reduce the current uncertainties on Δq. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  35. Run 2013 and Expectation of PHENIX W Program Including Run 2013 data (~63% of luminosity goal), total luminosity ~200 pb-1 in the 30 cm vertex. 2013: BBC<30cm Luminosity pb-1 • Analyzing fast production data. • Run 2013 production has already begun. 2012: BBC<30cm 2011: BBC<30cm Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  36. Expected S/B Improvement using FVTX • FVTX was operational in Run 2012 • Much better performance (95% alive) in Run 2013 FVTX covers 1.2 < |η| < 2.4, 2π in φ Muon Arms + FVTX W Detection • FVTX is expected to improve analysis power by: • Precise vertexdetermination • Better Tracking: FVTX – MuTr track matching (can suppress decay-in-flight background). FVTX First evaluation using two observables above: S/B improved by factor 2 Expected better improvement when implementing the new multi-vertex finder and isolation cone cut! FVTX FVTX-VTX Track VTX MuTr Matching Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  37. Transverse Physics Collins mechanism:Transversity (quark polarization) * Spin-dependence in the jet fragmentation Sivers mechanism:Correlation between nucleon spin and parton kT Phys Rev D41 (1990) 83; 43 (1991) 261 NuclPhys B396 (1993) 161 • A good example of an emergent phenomena in physics is transverse asymmetries in high energy scattering. • Linked to: • Orbital Angular Momentum • Gauge link Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  38. Recent PHENIX Transverse Spin Runs Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  39. BBC hits neutron neutron Forward Neutron AN arXiv:1209.3283 Single pion exchange? Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  40. charged particles neutron neutron Forward Neutron AN Forward asymmetry AN = 0.0610.010(stat)0.004(syst) Backward asymmetry AN = 0.0060.011(stat)0.004(syst) Interaction trigger with charged particles in beam-beam counter (ZDCBBC trigger) Forward asymmetry AN = 0.0750.004(stat)0.004(syst) Backward asymmetry AN = 0.0080.005(stat)0.004(syst) Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  41. Mid-rapidity 0 andη So far, all mid-rapidity transverse asymmetries are consistent with zero. {x, Q2} dependence under investigation. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  42. MPC: Forward-rapidity 0 andη γ1 3.1 < |η| < 3.9 θ π, η γ2 Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  43. p+pη0+X at s=200 GeV/c2 MPC: 0 and η AN, s=62.4, 200 GeV Within uncertainties, and given some differences in kinematics, PHENIX data are in agreement with STAR and E704 measurements. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  44. Access Higher pT: EM Clusters PHENIX Preliminary EM clusters STAR 2γ method PHENIX inclusive cluster preliminary STAR pi0 data from:PRL101 (2008) AN vspT, s=200 GeV Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  45. J/ψAN • A new test of QCD factorization and role of spin in particle production • Expect much improved measurements from future high stat runs @RHIC. • FVTX detector significantly improves resolution and reduces background. Run 06+08+12 AN =0 Color Octet AN ≠ 0 Color singlet Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  46. kT Asymmetry Phys. Rev. D 74, 072002 (2006) o- h±azimuthal correlation The PHENIX central arms provide a good o trigger. Using those large data sets, we can measure azimuthal angular distribution w.r.t. the azimuth of associated (charged) particle. The strong same and awayside peaks in p-p collisions indicate di-jet origin from hard scattering partons. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  47. kT Asymmetry Like Helicity kPR kTR Un-like Helicity kPR kTR Douglas Fields, University of New Mexico, for the PHENIX Collaboration We became interested in a paper (MengTa-Chung et al. Phys. Rev. D 1989) describing a method to investigate orbital angular momentum in longitudinally polarized proton-antiproton collisions leading to Drell-Yan pairs. Possibility to probe the Wigner functions (correlations between position and transverse momentum)! With our di-hadron jet techniques, we applied this to determine if there are any effects in polarized proton-proton collisions.

  48. kT Asymmetry • Interpretation: • The small asymmetry in jT verifies our assumption that the third term is suppressed. • The second term may be constrained from current knowledge of the π0 ALL. • The first term can be related in the “Meng conjecture” to partonic transverse momentum: where cij give the initial state weights and Wij give the impact parameter weighting. Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  49. Future Forward Di-muon Drell-Yan ANStudy fundamentally important test of QCD factorization and gauge-link RHIC 1-year running projection • Drell-Yan AN accesses quark Sivers effect (f1T⊥) in proton • f1T⊥ expected to reverse in sign from SIDIS to DY. DOE milestone HP13 ~2016 Semi-inclusive DIS (SIDIS) Drell-Yan Douglas Fields, University of New Mexico, for the PHENIX Collaboration

  50. Future s/ePHENIX Douglas Fields, University of New Mexico, for the PHENIX Collaboration

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