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Gluon polarization and jet production at STAR

Gluon polarization and jet production at STAR. Pibero Djawotho for the STAR Collaboration Texas A&M University 30 September 2010 17:00-17:30. The proton spin sum rule. Quark polarization ΔΣ≈ 0.3 from polarized deep inelastic scattering

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Gluon polarization and jet production at STAR

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  1. Gluon polarization and jet production at STAR Pibero Djawotho for the STAR Collaboration Texas A&M University 30 September 2010 17:00-17:30

  2. The proton spin sum rule • Quark polarization ΔΣ≈0.3 from polarized deep inelastic scattering • Gluon polarization (ΔG), orbital angular momenta of quarks (Lq) and gluons (Lg) poorly constrained • A primary charge of RHIC spin physics  map Δg(x) Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  3. f: polarized parton distribution functions 10 20 30 pT(GeV) Polarized pp collisions at RHIC Partonic fractions in jet production at 200 GeV For most RHIC kinematics, gg and qg dominate, making ALL for jets sensitive to gluon polarization. 0 Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  4. RHIC pC Polarimeters Absolute Polarimeter (H jet) BRAHMS PHOBOS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin flipper Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake Pol. H- Source Helical Partial Siberian Snake LINAC BOOSTER AGS Internal Polarimeter AGS 200 MeV Polarimeter AGS pC Polarimeters Strong Helical AGS Snake Rf Dipole RHIC: The World’s First Polarized Hadron Collider • Spin varies from rf bucket to rf bucket (9.4 MHz) • Spin pattern changes from fill to fill • Spin rotators provide choice of spin orientation • Billions of spin reversals during a fill with little if any depolarization Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  5. The STAR detector E-M Calorimeter Projection           Chamber Time of    Flight Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  6. Jet reconstruction in STAR Data jets MC jets • Midpoint cone algorithm • (Adapted from Tevatron II - hep-ex/0005012) • Seed energy = 0.5 GeV • Cone radius in - • R=0.4 with 0.2 <  < 0.8 (till 2005) • R=0.7 with -0.7 <  < 0.9(since ‘06) • Splitting/merging fraction f=0.5 GEANT Detector Particle PYTHIA Use PYTHIA + GEANT to quantify detector response Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  7. Run 3 & 4 inclusive jets cross section PRL 97 (2006) 252001 • Jet reconstruction at STAR well understood • Agreement with NLO pQCD over 7 decades Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  8. 2005 Inclusive ALLjets Analysis • 2 pb-1 after run selection • <PBPY> ≈ 0.25 • 2.38 M events (post-cuts), 50% from newly commissioned Jet Patch (1×1 rad) trigger • Jet cone radius = 0.4 • 0.1 < Neutral Energy Fraction < 0.8 • 0.2 < Jet Detector  < 0.8 Neutral Energy Fraction Data well described by MC Dominated byJet Reconstruction&Trigger Bias: • Jet reconstruction bias: ~25% jet resolution and steeply falling jet pT distribution causes measured pT to average 20% larger than true pT • Trigger bias : each trigger samples the sub-processes (qq/qg/gg) differently Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  9. STAR 2005 inclusive jets ALL Model calculations from: Jager et al, PRD 70, 034010 PRL 100, 232003 (2008) 200 GeV 0.2 < η < 0.8 Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  10. Additional ALL predictions for 2005 Many predictions for ALL have been proposed at various times Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  11. Run 6 data • Improved FOM • Luminosity : 2  4.7 pb-1 • Polarization: 50%  60% (online polarization) • Barrel EMC  coverage: [0,1]  [-1,1] • In addition • Jet Cone Radius: 0.4  0.7 • -0.7 < jet axis < 0.9 • Neutral Energy Fraction < 0.85 • Increased trigger thresholds • Inclusion of Endcap EMC towers • Improved tracking at large || • Shielding from backgrounds Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  12. preliminary preliminary Run 6 inclusive jets cross section • Jet cone radius = 0.7 • Higher precision and reach to higher pT relative to ’03-’04 results • Data well described by NLO pQCD+Hadronization+Underlying Event • Hadronization+Underlying event corrections significant at low jet pT Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  13. Jet ALL reconstruction and trigger bias for 2006 data Step 1: Use PYTHIA+GEANT to estimate the pT shift from detector jets to particle jets Step 2: Simulate the difference in ALL between particle and detector jets for various gluon polarization scenarios Particle jets Shifted detector jets Detector jets • Maximum deviation determines ALL systematic Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  14. Run 6 inclusive jets ALL GRSV curves with cone radius 0.7 and -0.7 <  < 0.9 200 GeV -0.7 <  < 0.9 • Using jet patch trigger (× = 1×1 patch of towers) only • Statistical uncertainties are 3-4 times smaller than 2005 in high pT region (pT>13 GeV/c) Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  15. The first global NLO analysis to include inclusive DIS, SIDIS, and RHIC pp data on an equal footing Finds a node in the gluon distribution near x ~ 0.1, but with the opposite phase from GS-C DSSV – First Global Analysis with Polarized Jets de Florian et al., PRL 101 (2008) 072001 STAR Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  16.  = -1.0 -0.6 0 +0.4 +1.0 +1.4 +2.0  = 1 preliminary Run 9 jet patch trigger upgrades • Overlapping jet patches and lower ET threshold increase efficiency and reduce trigger bias: • JP1 (~5.4 GeV, prescaled) ~130M events on tape • JP2 (~7.3 GeV) ~84M events on tape • Compare to Run 6: JP (~8.5 GeV) ~4.2M events on tape • Remove beam-beam counter coincidence requirement: • Trigger more efficiently at high jet pT • Measure non-collision background • Increased rate enabled by DAQ1000: • Run 6: recorded ~40 Hz with 40% deadtime • Run 9: recorded several 100 Hz with <5% deadtime Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  17. preliminary preliminary Run 9 jet patch trigger upgrades Two analyses of the same Run 9 data subset: Run 9 setup Run 6 setup • Overlapping jet patches in η • Collisions at different z-vertex locations provide an even more uniform acceptance for particle jet η • Two adjacent jet patches in φ at half nominal jet patch ET threshold combined to fill in φ gaps • Gaps in φ softened 37% increase in jet acceptance due to Run 9 improvements in jet patch trigger over Run 6 Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  18. BEMC tower TPC track Improvements in jet reconstruction • EMCs are ~1 strong interaction length thick • Many charged hadrons deposit MIP • Others shower and may deposit sizeable fraction when passing through Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  19. Improvements in jet reconstruction • Run 6 treatment: Subtract MIP from EMC tower when charge track passes through • Allows to see EM energy emitted very close to charge track • Makes reconstruction susceptible to fluctuations in charge hadron showering • Major contribution when jet energies are larger at detector level than particle level • Run 9 treatment: Subtract total charged track momentum from EMC tower when passing through • Reduces ability to see EM energy emitted close to charge track • Significantly reduces response to fluctuations from charge hadron showering • Reduces average difference between jet energies at the detector and particle level Improves overall jet energy resolution 23% to ~18% Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  20. Trigger and reconstruction bias Error bars show RMS of the distributions • 100% hadronic subtraction scheme: • Smaller mean and RMS pT shift • Better jet pTresolution Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  21. STAR pp→jet+X projected sensitivity to ALL • Anticipated sensitivity for 50 pb-1 with 60% polarization • Only sampled ⅓ of the hoped for Figure-of-Merit Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  22. Run 9 inclusive jets ALL projected statistics • Projected statistical precision of ~0.001 in many jet pT bins • Run 9 statistical errors on jet ALL comparable to systematic errors  control of trigger and reconstruction bias and relative luminosity systematics paramount (work in progress) Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

  23. Summary • STAR inclusive jets cross section from 2006 is in good agreement with NLO pQCD calculations when hadronization and underlying event effects are included • STAR inclusive jets ALL from 2006 imposes stringent constraints on theoretical models of gluon polarization in the proton • STAR inclusive jets ALL plays significant role when combined with DIS, SIDIS and RHIC data into NLO global analyses • Projected statistical precision of 2009 STAR inclusive jets ALL is factor of ~3 better than 2006 data Pibero Djawotho - SPIN2010 - Δg(x) and jet production at STAR

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