Transcript Slide 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
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.
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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.1
29:560-562,2004
15/March/2006
O. Kaczmarek, et al.,
Nucl.Phys.Proc.Suppl.129:560-562,2004
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Quarkonium at SPS
NA50 data:
“Anomalous”
suppression.
NA60 data:
Confirmation (with
smaller errors)
PHENIX at RHIC, see
Wei Xie next…
Satz, Digal, Fortunato (percolation)
Rapp, Grandchamp, Brown (diss. and recomb.)
Theory challenge
Capella, Ferreiro (comovers)
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.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?,
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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?
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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
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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
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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 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.
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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.
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 Trigger: L0 + L2
 Advantage:  mass is large
 Can use a simpler L0 trigger
 Require one BEMC towerwith
ET>3.5 GeV
T. Kollegger
 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
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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
STAR Preliminary
J. González
Dielectron Invariant Mass (GeV/c2)
EMC had smaller
acceptance
p ~ 1.5 GeV/c, borderline
for EMC PID
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 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!
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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.
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 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 Luminositylimited in a big way.
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Half field running, no BEMC-based
triggers.
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 Analysis in Au+Au
 Upper limit estimation:
+- ++
--
Npairs 8.4<m< 10.7 GeV 2
0
0
Npairs 10.7<m< 13.0
GeV
0
0
1
 90% C.L. : signal < 4.91
 B*ds/dy C.L. < 7.6 mb
T. Kollegger
 Acceptance increase will
help
 Factor ~ 4.
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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, p+p
Collected 1.7 M triggers
Simulation:
expected a sample of 6070 J/y’s in this test data
set.
Data:
P. Djawotho
Yield small, but
consistent with
simulations.
Ready for Run VI!
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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 p+p:
 Barrell EMC now fully installed
 |h|<1, full azimuth
 Increase by factor 4 over Run IV dielectron 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
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