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
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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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