Quarkonium%20progress%20in%20STAR

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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

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Outline

• Motivation
• STAR capabilities
• Trigger
• ee-
• Triggered samples so far
• Run IV AuAu ?
• Run V pp J/y
• Prospects for Run VI and beyond.

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Why are we interested in quarkonia?

• Charmonium suppression longstanding QGP
  signature
• Original idea screening.
• lattice calculations confirm screening effects
• Nucl.Phys.Proc.Suppl.129560-562,2004

O. Kaczmarek, et al., Nucl.Phys.Proc.Suppl.129560
-562,2004
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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

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Binding Energy TD
Binding Energy Sequential Suppression.
State y(2s) cc(1p) J/y(1s)
Eb (GeV) 0.05 0.23 0.64
TD/TC 0.1-0.2 0.74 1.1
State ?(3s) cb(2p) ?(2s) cb(2p) ?(1s)
Eb (GeV) 0.2 0.3 0.54 0.67 1.1
TD/TC 0.75 0.83 1.1 1.13 2.31
Digal, Petreczky, Satz Phys.Rev.D64094015,2001 U
sing 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?,
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Lessons learned the hard way

• To connect with theory, we need a good systematic
  programme
• pp, AuAu, vs. cent. vs. vs
• Measure not just J/y.
• Excited states are needed for feeddown.
• Y states are a key, but
• Small cross section
• Mass resolution?

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What can STAR contribute?

• STAR was not built for di-leptons, but
• Large acceptance at mid-rapidity
• hlt1 , 0ltflt2p
• Pair acceptance single acceptance2
• Electron ID-capabilities
• TPC dE/dx
• EMC Egt1-2 GeV (full barrel in 2006)
• TOF plt2-3 GeV/c (only patch, full barrel in the
  future)
• Triggering capabilities on Barrel EMC
• Suitable for single electrons (proxy for open
  charm)
• (see J. Harriss 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
  AuAu

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Electron ID

• Combine detectors
• TPC dE/dx in a limited region
• Barrel EMC for pgt1 GeV/c
• TPCBEMC

P.Djawotho
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Electron Efficiency and Purity
P. Djawotho
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J/Y Topology Trigger Level-0

• 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.

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J/Y Software Trigger Level-2

• Looking for ee- 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 AuAu, but 30 cm in pp.
• Otherwise assume vtx at (0,0,0).
• Make tower cluster pairs, neglecting me
• m2inv ? 2E1E2(1-cos(q12))
• Issue decision in Tlt500 ms.

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Can it be used in AuAu?

• 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
• pp environment well matched for trigger
• AuAu must rely on a large dataset.

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? Trigger L0 L2

• Advantage ? mass is large
• Can use a simpler L0 trigger
• Require one BEMC towerwith ETgt3.5 GeV
• Use similar L2 algorithm
• Can trigger in pp and also in central AuAu!
• 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 AuAu
  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
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J/y in AuAu Run IV

• No triggering is possible, too much background.
• Search in the AuAu 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)
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? Trigger in AuAu Run IV

• L0 events with Etower gt 3.5 GeV.
• L2 events with cluster pair masses mgt7 GeV/c2.
• Trigger works!

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Trigger performance in AuAu

• 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 -gt Dp
• Additional triggers reducing ? trigger livetime.

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? Analysis in AuAu 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.
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? Analysis in AuAu

• Upper limit estimation
• 90 C.L. signal lt 4.91
• Bds/dy C.L. lt 7.6 mb
• Acceptance increase will help
• Factor 4.

- --
Npairs 8.4ltmlt 10.7 GeV 2 0 0
Npairs 10.7ltmlt 13.0 GeV 1 0 0
T. Kollegger
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Trigger performance in Run V
Energy (MeV)
Invariant mass (MeV/c2)

• Online monitoring of trigger information.
• Extremely fast turnaround.
• No need to wait for offline production to find if
  trigger is behaving as expected.

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Sample from Run V, pp

• Collected 1.7 M triggers
• Simulation
• expected a sample of 60-70 J/ys in this test
  data set.
• Data
• Yield small, but consistent with simulations.
• Ready for Run VI!

P. Djawotho
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Data and simulation comparison

• Width is consistent with our detector resolution.
• Mass is slightly lower than expected (2s)

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Future

• Run VI pp
• Barrell EMC now fully installed
• hlt1, 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.
• RD on possible muon trigger in hlt1, 60
  azimuth