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Stephen Pate (for the PHENIX Collaboration) New Mexico State University

PHENIX Measurement of Parity -Violating Single Spin Asymmetry in W Production in p + p Collisions at 500 GeV. Stephen Pate (for the PHENIX Collaboration) New Mexico State University. DSSV Global Fit -- PRD80 (2009) 034030 [0904.3821].

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Stephen Pate (for the PHENIX Collaboration) New Mexico State University

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  1. PHENIX Measurement ofParity-Violating Single Spin Asymmetry in W Production in p+p Collisionsat 500 GeV Stephen Pate (for the PHENIX Collaboration) New Mexico State University Diffraction 2010

  2. DSSV Global Fit -- PRD80 (2009) 034030 [0904.3821] Over many years, the worldwide program of form factor measurements, inclusive deep-inelastic and semi-inclusive deep-inelastic scattering has made possible a definitive measurement of the polarized PDFs of the u and d quarks. But the contribution of the sea and gluons to the spin of the proton remains relatively unclear. Diffraction 2010

  3. PHENIX@RHIC is measuring asymmetries in W production that are sensitive to the light quark sea contribution to the proton spin. l+ PHENIX Muon Arm Rapidity PHENIX Central Arm Rapidity Diffraction 2010

  4. RHIC-PHENIX 2009 run STAR Siberian Snake pC and H-jet polarimeters Spin Rotators Siberian Snake • Run 09: First 500 GeV Run, March 17-April 13, 2009 • Machine development in parallel with physics running to increase luminosity, polarization • Integrated luminosity (with vertex cut) is Ldt=8.6 pb-1 • Polarization is <P>=0.39±0.04 (scale uncertainty) Diffraction 2010

  5. Polarization • Measured with two polarimeters • CNI polarimeter measurements available during run • H jet polarimeter provides absolute polarization • Measured residual polarization in real time after rotation at PHENIX P P Polarization measured by CNI polarimeters fill-by-fill Diffraction 2010

  6. PHENIX Central arm: We Fully efficient at 12 GeV • EMC 4x4 Tower Sum Trigger • ±30 cm vertex cut • High energy EM Calorimeter clusters matched to charged track • Loose timing cut to reduce cosmic ray bkg • Loose E/p cut e  Central Arm Acceptance : ||<0.35 in rapidity 2 arms covering  =  Diffraction 2010

  7. Effect of Cuts Clusters • Smooth spectrum of EMC clusters after removing bad towers Diffraction 2010

  8. Effect of Cuts Clusters Good track match • Smooth spectrum of EMC clusters after removing bad towers • Have a good track pointing to an EMC cluster Diffraction 2010

  9. Effect of Cuts Clusters Good track match TOF cut • Smooth spectrum of EMC clusters after removing bad towers • Have a good track pointing to an EMC cluster • Timing within start time of collision • Reduces out of time backgrounds (cosmics) by ~80% Diffraction 2010

  10. Effect of Cuts Clusters Good track match TOF cut E/p • Smooth spectrum of EMC clusters after removing bad towers • Have a good track pointing to an EMC cluster • Timing within start time of collision • Reduces out of time backgrounds (cosmics) by ~80% • E/P cut Diffraction 2010

  11. Signal and Background • QCD provides the most obvious background (W. Vogelsang) • Not shown here but very important • Cosmics and photons (from meson decays and direct), which can have accidental matches to tracks or conversions • c/b relatively small above 30 GeV, calculated at FONLL (MatteoCarciari) • Z/* background is estimated from PYTHIA (~1 count is expected in Run09). • We is also small Diffraction 2010

  12. Signal and Background Hadron spectrum suppressed by poor response of EMC to hadrons • QCD provides the most obvious background (W. Vogelsang) • Not shown here but very important • Cosmics and photons (from meson decays and direct), which can have accidental matches to tracks or conversions • c/b relatively small above 30 GeV, calculated at FONLL (MatteoCarciari) • Z/* background is estimated from PYTHIA (~1 count is expected in Run09). • We is also small Diffraction 2010

  13. Background subtracted spectra of positron and electron candidates Gray bands = range of background estimates. Compared to spectrum of W andZ decays from a NLO calculation [D. de Florian and W. Vogelsang, Phys. Rev. D81, 094020 (2010). P. M. Nadolsky and C. P. Yuan, Nucl. Phys. B666, 31 (2003)] These yields were used for cross section results. For the asymmetry measurement, additional cuts were applied to make the background contribution negligible. Diffraction 2010

  14. Isolation Cut – use fact that lepton from W decay is not from a jet E < 2GeV Sum up energy in a cone around electron/positron >80% of signal is kept (blue dashed line) Factor ~4 reduction in background Diffraction 2010

  15. Signal for Asymmetry Measurement After Isolation Cut Signal region is 30 < pT < 50 GeV/c Positrons: 42 signal events (background 1.7 ± 1.0) Electrons: 13 signal events (background 1.6 ± 1.0) Diffraction 2010

  16. Longitudinal spin asymmetry AL Parity-violating longitudinal single spin asymmetry • N+ = right-handed production of W • N- = left-handed production of W • P = Polarization • R = relative luminosities of the helicity states • D = dilution by background and Z0 Diffraction 2010

  17. Parity-violating Asymmetries In W Production in PHENIX Final Results for RHIC 2009 Run [arXiv:1009.0505] Likelihood function used to determine value and limits for AL (low statistics) Direct observation of parity-violation in W production. Diffraction 2010

  18. Muon Trigger Upgrade muTrnorth Existing Muon Arms: • muID(triggering) • muTr(tracking) • trigger rejection • ~ 200 - 500 muTrsouth muID south muID north Diffraction 2010

  19. Muon Trigger Upgrade muTrnorth Trigger idea: Reject low momen- tum muons Cut out-of-time beam background • Existing Muon Arms: • muID(triggering) • muTr (tracking) • trigger rejection • ~ 200 - 500 muTrsouth muID north muID south RPC3 RPC1(a,b) RPC3 muTr-trigger Upgrade: 1) muTr trigger electronics: muTr 1-3  send tracking info to level-1 trigger 2) RPC stations: RPC 1+3 tracking + timing info to level-1 trigger Diffraction 2010

  20. RPCs: trigger level timing Test assembly of RPC-3 half octant support structure at UIUC • Timing used in Run-9 to characterize background • RPC3-N installed for Run-10 • Commissioned & ready From collision or out going beam From beam background Diffraction 2010

  21. MUTRIG ready for physics in 2011 Run Station 1 Station 2 • Good efficiency for MIPs • MUTR.N installed for Run-9 • MUTR.s installed for Run-10 • ready to go Station 3 Minimum Ionizing Particle Diffraction 2010

  22. Expectation for uncertainties in parity-violating asymmetries in high-pTmuon production Assuming: 50 pb-1 50% polarization S/B = 0.3 Diffraction 2010

  23. Expectation for uncertainties in parity-violating asymmetries in high-pTmuon production Assuming: 50 pb-1 50% polarization S/B = 3.0 Diffraction 2010

  24. Expectation for uncertainties in parity-violating asymmetries in high-pTmuon production Assuming: 150 pb-1 50% polarization S/B = 3.0 Diffraction 2010

  25. Summary • PHENIX has observed a non-zero parity-violating asymmetry in W production in pp collisions at 500 GeV • Future measurements with greater precision will allow a measurement of the light quark sea contribution to the spin of the proton, using a technique complementary to that used in leptonic SIDIS Diffraction 2010

  26. Diffraction 2010

  27. Cross Sections forW Production in PHENIX Final Results for RHIC 2009 Run [arXiv:1009.0505] Diffraction 2010

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