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Quarkonium progress in STAR

Quarkonium progress in STAR. Manuel Calder ón de la Barca S ánchez UC Davis Heavy Flavor Working Group, STAR; XXII Winter Workshop on Nuclear Dynamics La Jolla, CA 15/March/2006. Outline. Motivation STAR capabilities Trigger e + e - Triggered samples so far Run IV Au+Au: 

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Quarkonium progress in STAR

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  1. Quarkonium progress in STAR Manuel Calderón de la Barca Sánchez UC Davis Heavy Flavor Working Group, STAR; XXII Winter Workshop on Nuclear Dynamics La Jolla, CA 15/March/2006

  2. Outline • Motivation • STAR capabilities • Trigger • e+e- • Triggered samples so far • Run IV Au+Au:  • Run V p+p: J/y • Prospects for Run VI and beyond. Manuel Calderón de la Barca

  3. Why are we interested in quarkonia? • Charmonium suppression: longstanding QGP signature • Original idea: screening. • lattice calculations confirm screening effects • Nucl.Phys.Proc.Suppl.129:560-562,2004 O. Kaczmarek, et al., Nucl.Phys.Proc.Suppl.129:560-562,2004 Manuel Calderón de la Barca

  4. Quarkonium at SPS Satz, Digal, Fortunato (percolation) Rapp, Grandchamp, Brown (diss. and recomb.) Capella, Ferreiro (comovers) • NA50 data: “Anomalous” suppression. • NA60 data: Confirmation (with smaller errors) • PHENIX at RHIC, see Wei Xie next… • Theory challenge • Description of SPS and RHIC data Manuel Calderón de la Barca

  5. Binding Energy & TD Binding Energy & Sequential Suppression. Digal, Petreczky, Satz; Phys.Rev.D64:094015,2001 Using lattice free energy as potential. The premise: A full quarkonium spectroscopy can help address the question of deconfinement; ~ direct connection to first principles LQCD. Reality Check: Uncertainties in the calculations (~factor 2), free energy vs. internal energy potential models vs. spectral functions Gluons breaking up J/y, recombination contribution?, Manuel Calderón de la Barca

  6. Lessons learned the hard way • To connect with theory, we need a good systematic programme: • p+p, Au+Au, vs. cent. vs. √s • Measure not just J/y. • Excited states are needed for feeddown. • Y states are a key, but • Small cross section • Mass resolution? Manuel Calderón de la Barca

  7. What can STAR contribute? • STAR was not built for di-leptons, but… • Large acceptance at mid-rapidity • |h|<1 , 0<f<2p • Pair acceptance ~ single acceptance2 • Electron ID-capabilities • TPC dE/dx • EMC E>1-2 GeV (full barrel in 2006) • TOF p<2-3 GeV/c (only patch, full barrel in the future) • Triggering capabilities on Barrel EMC • Suitable for single electrons (proxy for open charm) • (see J. Harris’s talk tomorrow afternoon) • Suitable for di-electrons? • J/y, are rare, • triggering where possible • J/y in pp •  in all systems (no signal without a trigger) • large dataset if triggering not possible: J/y in Au+Au Manuel Calderón de la Barca

  8. Electron ID 1.5<p< 5 GeV, |p/E-1|<1 • Combine detectors • TPC dE/dx in a limited region • Barrel EMC for p>1 GeV/c • TPC+BEMC P.Djawotho Manuel Calderón de la Barca

  9. Electron Efficiency and Purity P. Djawotho Manuel Calderón de la Barca

  10. J/Y “Topology” Trigger: Level-0 Real Data, p+p Run V • Fast, T ≤1ms • Divide f into 6 sections • Find a tower above a threshold • Look in the 3 opposite sections in f • If another tower above threshold, issue trigger. Manuel Calderón de la Barca

  11. J/Y Software Trigger: Level-2 Real Data, p+p Run V • Looking for e+e- pair • Approximate electron daughters with tower cluster • Use L0 tower cluster, combine with L2 clusters • Energy, Position  cos(q) • Vertex from trigger detectors timing • BBC Resolution ~ 6 cm in Au+Au, but 30 cm in p+p. • Otherwise assume vtx at (0,0,0). • Make tower cluster pairs, neglecting me: • m2inv  2E1E2(1-cos(q12)) • Issue decision in T<500 ms. Manuel Calderón de la Barca

  12. Can it be used in Au+Au? • High rejection only for peripheral events. • Most signal in central events. • 98% of the yield is in top 60% central. • There is no free lunch… • p+p: environment well matched for trigger • Au+Au: must rely on a large dataset. Manuel Calderón de la Barca

  13.  Trigger: L0 + L2 T. Kollegger • Advantage:  mass is large • Can use a simpler L0 trigger • Require one BEMC towerwith ET>3.5 GeV • Use similar L2 algorithm • Can trigger in p+p and also in central Au+Au! • Rare triggers can go to “express stream” processing. • Very quick turnaround time. • Disadvantage: production rate is tiny! • Expected less than 100 in the full Run IV Au+Au dataset. • Reality, got only a few counts due to many compounded effects • Smaller acceptance • Less running time • BEMC miscalibration • Some detectors not ready for L2 in Run IV Manuel Calderón de la Barca

  14. J/y in Au+Au Run IV • No triggering is possible, too much background. • Search in the Au+Au dataset of Run IV • Signal? Hints so far… • Analysis using TPC alone • EMC had smaller acceptance • p ~ 1.5 GeV/c, borderline for EMC PID STAR Preliminary J. González Dielectron Invariant Mass (GeV/c2) Manuel Calderón de la Barca

  15.  Trigger in Au+Au Run IV • L0: events with Etower > 3.5 GeV. • L2: events with cluster pair masses m>7 GeV/c2. • Trigger works! Manuel Calderón de la Barca

  16. Trigger performance in Au+Au • Events sampled per day • 4-20 M per day • Variations due to need to meet other STAR goals • Half-field running • Part of heavy-flavor progam: D* -> D+p • Additional triggers reducing  trigger livetime. Manuel Calderón de la Barca

  17.  Analysis in Au+Au run IV • Sampled 34.2 mb-1 • More than 200 M minimum bias events scanned with Upsilon trigger. • Comparison w/ offline • ~50 M minimum bias events. • Small dataset processed • Only 3 signal counts (with no background counts) were observed. • 1st STAR measurement where we are Luminosity-limited in a big way. Half field running, no BEMC-based triggers. Manuel Calderón de la Barca

  18.  Analysis in Au+Au • Upper limit estimation: • 90% C.L. : signal < 4.91 • B*ds/dy C.L. < 7.6 mb • Acceptance increase will help • Factor ~ 4. T. Kollegger Manuel Calderón de la Barca

  19. Trigger performance in Run V • Online monitoring of trigger information. • Extremely fast turnaround. • No need to wait for offline production to find if trigger is behaving as expected. Energy (MeV) Invariant mass (MeV/c2) Manuel Calderón de la Barca

  20. Sample from Run V, p+p • Collected 1.7 M triggers • Simulation: • expected a sample of 60-70 J/y’s in this test data set. • Data: • Yield small, but consistent with simulations. • Ready for Run VI! P. Djawotho Manuel Calderón de la Barca

  21. Data and simulation comparison • Width is consistent with our detector resolution. • Mass is slightly lower than expected (2s) Manuel Calderón de la Barca

  22. Future • Run VI p+p: • Barrell EMC now fully installed • |h|<1, full azimuth • Increase by factor 4 over Run IV di-electron acceptance. • L2 trigger has proved to work • Will be heavily used in Run VI (jets, dijets) • Longer term upgrades • Improve vertex knowledge at L0 • ~1 cm resolution using upgrade to pVPD used in TOF • Additional PID capabilities by full barrel TOF (2009) • TOF also allows a better background rejection. • R&D on possible muon trigger in |h|<1, 60% azimuth Manuel Calderón de la Barca

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