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

15/March/2006Manuel Calderón de la Barca 2Outline  Motivation  STAR capabilities  Trigger  e + e -  Triggered samples so far  Run IV Au+Au:   Run V p+p: J/   Prospects for Run VI and beyond.

15/March/2006Manuel 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.1 29: ,2004 O. Kaczmarek, et al., Nucl.Phys.Proc.Suppl.129: ,2004

15/March/2006Manuel Calderón de la Barca 4 Quarkonium at SPS  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 Satz, Digal, Fortunato (percolation) Rapp, Grandchamp, Brown (diss. and recomb.) Capella, Ferreiro (comovers)

15/March/2006Manuel Calderón de la Barca 5 Binding Energy & T D State  (2s)  c (1p) J/  (1s) E b (GeV) T D /T C State  (3s)  b (2p)  (2s)  b (2p)  (1s) E b (GeV) T D /T C Digal, Petreczky, Satz; Phys.Rev.D64:094015,2001 Using lattice free energy as potential. Binding Energy & Sequential Suppression. full quarkonium spectroscopy 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/ , recombination contribution?,

15/March/2006Manuel 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/ .  Excited states are needed for feeddown.  Y states are a key, but  Small cross section  Mass resolution?

15/March/2006Manuel Calderón de la Barca 7 What can STAR contribute?  STAR was not built for di-leptons, but…  Large acceptance at mid-rapidity  |  |<1, 0<  <2   Pair acceptance ~ single acceptance 2  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/  are rare,  triggering where possible  J/  in pp   in all systems (no signal without a trigger)  large dataset if triggering not possible: J/  in Au+Au

15/March/2006Manuel Calderón de la Barca 8 Electron ID  Combine detectors  TPC dE/dx in a limited region  Barrel EMC for p>1 GeV/c  TPC+BEMC 1.5<p< 5 GeV, |p/E-1|<1 P.Djawotho

15/March/2006Manuel Calderón de la Barca 9 Electron Efficiency and Purity P. Djawotho

15/March/2006Manuel Calderón de la Barca 10 J/  “Topology” Trigger: Level-0  Fast, T ≤1  s  Divide  into 6 sections  Find a tower above a threshold  Look in the 3 opposite sections in   If another tower above threshold, issue trigger. Real Data, p+p Run V

15/March/2006Manuel Calderón de la Barca 11 J/  Software Trigger: Level-2  Looking for e + e - pair  Approximate electron daughters with tower cluster  Use L0 tower cluster, combine with L2 clusters  Energy, Position  cos(  )  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 m e :  m 2 inv  2E 1 E 2 (1-cos(  12 ))  Issue decision in T<500  s. Real Data, p+p Run V

15/March/2006Manuel 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.

15/March/2006Manuel Calderón de la Barca 13  Trigger: L0 + L2  Advantage:  mass is large  Can use a simpler L0 trigger  Require one BEMC towerwith E T >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 T. Kollegger

15/March/2006Manuel Calderón de la Barca 14 J/  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 Dielectron Invariant Mass (GeV/c 2 ) STAR Preliminary J. González

15/March/2006Manuel Calderón de la Barca 15  Trigger in Au+Au Run IV  L0: events with E tower > 3.5 GeV.  L2: events with cluster pair masses m>7 GeV/c 2.  Trigger works!

15/March/2006Manuel 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+   Additional triggers reducing  trigger livetime.

15/March/2006Manuel Calderón de la Barca 17  Analysis in Au+Au run IV  Sampled 34.2  b -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.  1 st STAR measurement where we are Luminosity- limited in a big way. Half field running, no BEMC-based triggers.

15/March/2006Manuel Calderón de la Barca 18  Analysis in Au+Au  Upper limit estimation:  90% C.L. : signal < 4.91  B*d  /dy C.L. < 7.6  b  Acceptance increase will help  Factor ~ 4. T. Kollegger N pairs 8.4<m< 10.7 GeV 200 N pairs 10.7<m< 13.0 GeV 100

15/March/2006Manuel 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/c 2 )

15/March/2006Manuel Calderón de la Barca 20 Sample from Run V, p+p  Collected 1.7 M triggers  Simulation:  expected a sample of J/  ’s in this test data set.  Data:  Yield small, but consistent with simulations.  Ready for Run VI! P. Djawotho

15/March/2006Manuel Calderón de la Barca 21 Data and simulation comparison  Width is consistent with our detector resolution.  Mass is slightly lower than expected (2  )

15/March/2006Manuel Calderón de la Barca 22Future  Run VI p+p:  Barrell EMC now fully installed  |  |<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