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Status of Run 8 FMS w analysis

Status of Run 8 FMS w analysis. STAR. Andrew Gordon Analysis Meeting at MIT July 8, 2009. Outline. Run 8 inclusive pions. Data extraction for omegas and comparisons of GEANT and Data. Fast simulation and additional cuts. dAu comparisons and future work.

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Status of Run 8 FMS w analysis

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  1. Status of Run 8 FMS w analysis STAR Andrew Gordon Analysis Meeting at MIT July 8, 2009

  2. Outline Run 8 inclusive pions Data extraction for omegas and comparisons of GEANT and Data Fast simulation and additional cuts dAu comparisons and future work

  3. Inclusive pions can be simulated over nearly entire range Simulation is Pythia+GSTAR Trigger simulation: Includes simulation of high tower trigger using realistic gains to calculate ADCs per tower.

  4. PT dependence of Run 8 inclusive pions FMS data reaches PT ~ 6 GeV Mgg in bins of PT XF-PT locus of data Akio Ogawa, CIPANP 2009

  5. PT dependence of Run 8 AN Indications that AN persists to PT ~ 5 GeV. Positive XF Negative XF J.Drachenberg, Spin 2008, arXiv:0901.2763 Akio Ogawa, CIPANP 2009

  6. FMS acceptance allows azimuthal AN dependence to be measured and extends data to higher XF Run 8 data Run 8 data P(blue)=45.5±3.3% L~6.2 pb-1 in plot Anf(f) versus <cos φ> for positive (blue beam) and negative (yellow beam) XF AN as a function of xF integrated over the FMS acceptance. Important confirmation of previous data 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.

  7. North-half, view from the hall w  p0 g Run 9057004, Event 4474 Ep=16.7+6.3=23.0 GeV Eg=7.5 GeV Energy (GeV) Ew=30.5 GeV Mw=0.754 GeV/c2 -1 Nearly contiguous coverage for 2.5<h<4.0. Run 8 FMS Enhanced areal coverage of FMS… …allows new measurements Run 5 FPD

  8. Motivation to search for w signal Spin asymmetries: The w is spin-1. The Artru string fragmentation model predicts that a spin-1 particle should have opposite asymmetry from a scalar particle, if the observed asymmetries result from the Collins effect. Observing a negative asymmetry would provide strong evidence for the Collins effect. AN for w Mass shift in d+Au relative to p+p: The Run 8 data allows a comparison of p+p data with d+Au. Shifts in the mass or width of the w would provide evidence of the partial restoration of the chiral symmetry in a denser hadronic medium. Spectral shifts RdAu: Can compare results from this resonance to previous scalar particle measurements. Yield ratios References: Artru and Dzyzewski, hep-ph/9805463 Brown and Rho, PRL 66, 21 (1991) STAR collaboration, PRL 97, 152302 (2006)

  9. Cut set 1: Use BBC to require w photon neutral w decays accessible in the FMS through p0g (BR=9%) decay channel. Track photon associated with w decay back to small tiles of BBC and require fewer than 5 counts in BBC. Four west small tile BBC phototubes, zero suppressed MIP peaks ~ 18 counts Suppresses charged hadrons that looks like photons in FMS. Forces photons to be isolated from charged tracks. Removes many real events by requiring that the photon did not convert in material before BBC (below ~ 1 X0). Forces photons into inner tiles and thus lower PT. Kinematic cuts: Look at all clusters with E>3 GeV instead of 6. Look in window 30<E(triple)<35 and 2.0<PT(triple)<2.5 GeV

  10. Spin-sorted (on blue beam) mass distributions Left Right Large acceptance asymmetries Calibration did not use data in this low cluster energy region. Non-linear corrections need to be calculated. We need simulation in this region of phase space. There is a hint of a negative asymmetry

  11. Set 2: High PT w selection See A. Gordon, Moriond 2009 Proc., arXiv:0906.2332 Mass distribution of two clusters of the triplet associated with π0. Associate clusters with π0 and g: Choose π0 to be pair with mass closest to 0.135 GeV. Simulation indicates that this gives correct association for nearly all events. Run 8 data Require that M(π0) be within 0.1 GeV of 0.135 GeV. Look at all triples of clusters with E>6 GeV. Apply fiducial cuts of 1/2 cell from all module boundaries. • Kinematic cuts to reduce QCD background (real π0 decays with a third EM-rich hadronic cluster in the FMS): • PT(triplet)>2.5 GeV • E(triplet)>30 GeV • PT(photon cluster)>1.5 GeV • PT(π0)>1 GeV.

  12. Mass distribution of all triples Fit is gaussian + cubic polynomial  μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events PYTHIA(6.222)+GSTAR over- predicts low mass region and under-predicts high mass Df weighting improves comparison (see below) Significant (10s) wp0g signal seen in the data.

  13. Df Distribution too narrow in PYTHIA Df=difference in azimuth in STAR coordinates between p0 and g. Comparison of Df distribution for data and simulation Df distribution too narrow in simulation (compare black solid lines to blue dashed lines). Replacing GSTAR and trigger simulation with geometric acceptance only and using PYTHIA level quantities (red triangles) does not change distribution.

  14. CDF Tune A does not change distribution Df(p0g) for PYTHIA 6.2.22 Linear scale Default PYTHIA 6.2.22 tune PYTHIA quantities level only. PYTHIA 6.2.22 with “CDF Tune A” parameters Log scale PYTHIA quantities level only. Pythia 6.4.20 gave a narrower distribution with default tune and with 6.2.22 tune. Df(p0g)

  15. Conclusions on Df distribution PYTHIA Df distribution is tunable PYTHIA needs to be tuned in this kinematic region. One possibility is that the momentum components perpendicular to the thrust axis (JT) need better tuning in the forward region.

  16. Backgrounds from simulation Currently backgrounds are too high for a spin analysis. We do an association analysis with reconstruted clusters and Pythia particles for triples in the w mass region. We find that the three clusters are ~ 100% photons. Perhaps do not need slow GEANT simulation in this kinematic region. Looking at the mother of the w decay photon: ~ 55% of backgrounds have p0 mothers ~ 30% of backgrounds have h mothers · · · · p0 h Fake w · · h Fake w · · Fake w · or · · · p0 p0 p0 Isolation-type cuts might help reduce these backgrounds.

  17. Fast Simulation A fast simulation can help us tune the cuts and would also make it possible to greatly extend integrated luminosity of simulation. Resources for the Pythia+GSTAR simulation: We ran a Pythia “preselection” with ~ 3.5% pass rate. 83 nb-1 used ~ 100,000 hours of CPU and ~ 500 Gbytes By varying offline random seeds (for example, the smearing on the measured Z(BBC) vertex), we increased the sample size relatively easily by a factor of ~ 3. A bench-marked, fast simulation can greatly reduce the resources needed. With linux farm, ~ 1-2 pb-1 per day. Some of this increase is increased efficiency of a photons-only preselection.

  18. Ingredients for fast simulator Track all PYTHIA photons to face of FMS. Smear x-y position by 10th of cell size. Spread energy among cells based on transverse EM shower shape. After all photons have been accumulated, smear energy in each FMS tower: Currently using per tower s(E)/E = 15%/E + 2% Pass event to analysis code as if it were a normal GEANT event and use offline gain determinations to calculate ADCs and apply high tower trigger.

  19. Comparison of Fast simulator with GSTAR Mass of two photons associated with p0 in triple. Gaussian+cubic fits to peak region give Fast sim: μ=0.1372±0.0005 GeVσ=0.0219±0.0004 GeV Fast sim GSTAR GSTAR: μ=0.1344 GeVσ=0.0202 GeV Note: data tends to be wider. This is partly because large cell gains are less well determined.. M(gg) (GeV)

  20. Other variables to reduce backgrounds RISO=minimum transverse distance between extra clusters and the w decay photon Fast sim GSTAR Data To reduce background where w decay photon is really from a p0, search through all other fiducial photon clusters in the FMS and calculate nearest transverse distance. The peak below ~ 20 is from p0 decays. RISO(cm)

  21. Other variables to reduce backgrounds (cont) Mp=mass of extra cluster with each of the triple clusters closest to 0.135 GeV/c2 Fast sim Data For w decay g Instead of transverse distance, calculate the pair mass that is closest to the pion mass, of all the extra clusters in the event. For p0 photon 1 Do this for the w decay photon and also for the two photons from the identified w decay pion. For p0 photon 2 p0 peaks are evident in all three distributions Mp(with other clusters) (GeV/c2)

  22. Other variables to reduce backgrounds (cont) Mh=mass of extra cluster with each of the triple clusters closest to 0.548 GeV/c2 Fast sim Data RISO<25 cm For w decay g Look at mass closest to the h mass after applying a RISO<25 cm cut. RISO<25 cm For p0 photon 1 The h backgrounds are visible. RISO<25 cm Perhaps “isolation” type cuts be improved by looking at all energy in the FMS, instead of just fiducial, fitted clusters For p0 photon 2 Mh(with other clusters) (GeV/c2)

  23. Update on dAu data We have begun initial analysis of this data Gain calibrations with neutral pions complete Simulation needs to be generated PYTHIA may be adequate for deuteron side (where FMS sits) May need to also compare to HIJING For RdAu measurement: Use Hank Crawford’s scaler boards for luminosity tracking Attempt to reproduce Run 3 RdAu measurements (STAR collaboration, PRL 97, 152302 (2006)). p Extend to the w data.

  24. Conclusions A clear w signal is visible in the Run 8 p+p data. The fast simulator can be used to understand the high PT triple data. Additional cuts and better tuning on simulation can improve signal to background. To do Continue simulation development Tune the cuts. Analyze the dAu data.

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