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Quarkonium progress in STAR

This presentation by Manuel Calderón de la Barca Sánchez from UC Davis, delivered at the XXII Winter Workshop on Nuclear Dynamics, delves into the intricacies of quarkonium production and suppression in heavy ion collisions, focusing on STAR's capabilities and potential contributions to the understanding of quark-gluon plasma (QGP). It covers experimental approaches, including electron pair triggers, and highlights the importance of charmonium suppression as a signature of QGP formation. Future prospects for STAR analyses in Run VI are also discussed, emphasizing the need for systematic data collection and theoretical connections.

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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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