Recent Spin and FMS Results at STAR Andrew Gordon Brookhaven National Laboratory Moriond-QCD March...

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Recent Spin and FMS Results at STAR rew Gordon okhaven National Laboratory iond-QCD ch 14-21, 2009 STAR STAR

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Recent Spin and FMS Results at STAR Andrew Gordon Brookhaven National Laboratory Moriond-QCD March 14-21, 2009 STAR Slide 2 2 s=200 GeV 1) Longitudinal spin program at STAR Strong constraint on the size of g from RHIC data for 0.05 10 but rising P T dependence is not predicted by the same fits Data broken out in X F bins X F >0.4 B.I. Abelev et al. (STAR) PRL 101 (2008) 222001 Slide 11 11 A N versus for positive (blue beam) and negative (yellow beam) X F A N as a function of x F integrated over the FMS acceptance. Plots from Nikola Poljak, for STAR collaboration, Spin-dependent Forward Particle Correlations in p+p Collisions at s = 200 GeV, hep-ex/0901.2828, to be published as Spin 2008 conference proceedings. FMS Acceptance allows azimuthal dependence to be measured Run 8 data Important confirmation of previous data L~6.2 pb -1 in plot P(blue)=45.53.3% Slide 12 12 Jet-like events in the FMS can potentially allow integration over fragmentation products to measure Sivers effect. Inclusive 0 asymmetries can not distinguish these. Collins effect: asymmetry in fragmentation Sivers effect: asymmetry from initial state K T - spin correlations Jet-shape distribution of energy within jet-like objects in the FMS as a function of distance from the jet axis. Caveat for Run 8: FMS data was acquired with a high tower trigger, which creates a bias towards jets that derive from a small number of high-z initial fragments Plot from hep-ex/0901.2828. STAR Preliminary Simulation and Data agree well for jet-like events Slide 13 13 STAR 2006 PRELIMINARY Heavier mesons also accessible at high X F Di-photons in FPD with E(pair)>40 GeV No center cut (requirement that two-photon system point at middle of an FPD module) With center cut and Z 15 Look at all triplets of clusters with E>6 GeV. Apply fiducial cuts of 1/2 cell from all module boundaries Associate two of clusters with 0 from the decay and one with Choose 0 to be pair with mass closest to 0.135 GeV, and photon from decay to be the third cluster. A fast, photons-only simulation indicates that this produces the correct identification for nearly 100% of 0 decays M( 0 clusters) (GeV/c 2 ) Run 8 data STAR Preliminary All cuts applied (see below) Require that M( 0 ) be within 0.1 GeV of 0.135 GeV. Selection Pair mass for all triples Kinematic cuts to reduce QCD background (real 0 decays with a third EM-rich hadronic cluster in the FMS): P T (triplet)>2.5 GeV E(triplet)>30 GeV P T (photon cluster)>1.5 GeV P T ( 0 )>1 GeV. Slide 16 16 Run 8 data Pythia+GEANT (background only) (simulation generation ongoing) STAR Preliminary Mass distribution of all triples For this plot simulation is background only Fit is gaussian + cubic polynomial =0.7840.008 GeV =0.0870.009 GeV Scale=1339135 Events Significant (10 ) 0 signal seen in the data. Comparison to Run 8 dAu data may be interesting. Slide 17 17 Conclusions Large-acceptance FMS is online jet-like events hold the promise of a direct measurement of the Sivers effect. Data should allow asymmetry measurements beyond inclusive 0 s Outlook Run 9 (running now) should allow STAR to extend constraints on G and also to begin W measurements. Possibility of future direct- A N measurements with FMS. Possibility of future Drell-Yan A N with FMS. Run 8 measurements of A N vs P T for inclusive s at high X F. Run 8 pp and dAu comparisons. Slide 18 18 End Slide 19 19 Kinematic cuts to reduce QCD background (real 0 decays with a third EM-rich hadronic cluster in the FMS): P T (triplet)>2.5 GeV E(triplet)>30 GeV P T (photon cluster)>1.5 GeV P T ( 0 )>1 GeV. STAR Preliminary Comparison of data (black) to simulation (red) Run 8 data Pythia+GEANT Run 8 data Pythia+GEANT Slide 20 20 Can use large asymmetries to measure (relative) bunch-by- bunch polarization STAR BBC Inner tiles cover ~3.5< Slide 21 21 } { East-West Coincidence Bunch Crossing (7-bits) { Scaler Boards } 24-bit word is histogrammed every clock cycle Inner tiles of BBC accumulated every clock cycle Discriminated phototube outputs Slide 22 22 Inclusive Jets Phys. Rev. Lett. 97 (2006) 252001 Smeared x-range for jets at a few p T s Jets at each p T are a different mix of subprocesses