Transcript STAR Charmonium - Istituto Nazionale di Fisica Nucleare

Quarkonium Physics with
STAR
Mauro Cosentino
(University of Sao Paulo/BNL)
Why Quarkonia ?
– Key Idea: Melting in the plasma
• Suppression of states is determined by TC and their binding
energy
• Color screening  Deconfinement
• QCD thermometer  Properties of QGP
Using F1: S. Digal, P. Petreczky, H. Satz, Phys. Lett. B514 (2001) 57
Using V1: C.-Y. Wong, hep-ph/0408020
Is the sequential suppression pattern the smoking gun?
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The STAR Detector
TPC: || < 1, 0 <  < 2
ToF: -1 <  < 0,  = 0.1
EMC: || < 1, 0 <  < 2
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 
Golden Decay Mode : QQ  e e
Typical electron p
range for:
J/y: 1-3 GeV/c
: > 3.5 GeV/c
Need:
Electron ID
Hadron Rejection
Trigger
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Electron ID
• Works from p=0.5-10 GeV/c
• TPC: dE/dx for p > 0.5 GeV/c
– Electrons can be discriminated
well from hadrons up to 8
GeV/c
– Allows to determine the
remaining hadron
contamination after EMC
K
p
d

ToF
EMC
electrons
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Electron ID at medium-pT
•
• Downside: only patch
(/30 -0.5<<0)
ToF
• Future (2008): full barrel
– Cut at |1/–1| < 0.03
(2, ||<1.0)
– clean e± identification with TPC- • will enable J/y physics
(also trigger in AA)
ToF up to 2.5 GeV/c
TPC – particle energy loss
• pT < 2 GeV/c so far
EMC+TPC only not
p
K
sufficient
e

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Electron ID at high-pT
• EMC
• Towers energy & TPC
momentum → p/E≈1 for
electrons
• SMD: hadrons and
electrons have different
shower shapes
hadrons
electrons
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J/y Trigger
•
•
•
•
Level-0 (topology):
Fast: t ≤ 1ms
Φ divided in 6 sections
Find a tower above
threshold (E > 1.2 GeV)
Look for other towers
above threshold on the 3
opposite sections
•
•
•
•
•
•
•
Level-2 (software):
Full EMC tower data available
Towers clustering → Ee
CTB matching (veto photons)
Vertex: BBC resolution ~6cm
for Au+Au, 30cm for p+p
Invariant mass assuming
straight tracks: m2inv 
2E1E2[1-cos(q12)]
Trigger for minv > 2.5 GeV/c2
Decision is taking up to 500ms
This J/y trigger setup is efficient
only for p+p
L0 rate: ~100 Hz
L2 rate: ~ 1 Hz
Au+Au will require ToF upgrade
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 Trigger Implementation
• L0 Trigger
– Simple single high tower
trigger ET>3.5 GeV
• L2 Trigger
– Use similar L2 to J/y
• Very efficient > 80%
• Large rejection power
– 100 at L0
– 100 at L2
• Luminosity limited
• Works in p+p and central
Au+Au
• Exploit full STAR
acceptance, 2 & ||<1
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Results J/y
Au+Au@200GeV (Run IV)
• Just a faint signal
• For efficient J/y trigger, full
barrel ToF is needed
p+p@200GeV (Run V)
• trigger commissioning (~1.7M
events)
• Results compatible with
expectations
Run VI (this year): expect S =500-1000 (work in progress)
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Results 
•Cannot resolve different S states
 (1S+2S+3S)  e+e-
Au+Au (Run IV):
• comissioning run
•½ EMC
•Several technical issues
•upper limit only
p+p (Run VI):
•Expect significant signal
trigger
threshold
No N+++N-subtracted
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Future & Rates
• Upgrades:
• DAQ1000: high data taking rate, no trigger dead time
• ToF full barrel: → J/y PID and trigger (g veto)
• RHIC-II: e-cooling, 40  nominal luminosity
Signal
RHIC Exp.
Obtained
RHIC-I
(>2008)
RHIC-II
RHIC-II /
R2D
LHC /
ALICE+
J/y →e+e
J/y →mm
PHENIX
~80
~7000
3,300
29,000
45,000
395,000
4,300,000
4,300,000
9,500
740,000
 → e+e → mm
STAR
PHENIX
-
830
80
11,200
1,040
39,000
39,000
2,600
8,400
B→J/y→e+e
B→J/y→mm
PHENIX
-
40
420
570
5,700
67,000
67,000
N/A
N/A
cc→e+e g
cc→m+m g
PHENIX
-
220
8,600
2,900*
117,000*
670,000
670,000
N/A
N/A
~0.4×106
(S/B~1/60
0)
30,000**
30,000**
N/A
8000
D→K
STAR
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Summary & Conclusion
• Quarkonia trigger tested successfully
• J/y
– Expect moderate sample in p+p and Au+Au
compared to PHENIX
• Require ToF upgrade
• 
– Large acceptance & clean trigger
– Strength of STAR’s quarkonium program
• Also:
– J/y at forward rapidities -> FPD & FMS (upgrade)
– Testing m detectors (re-use CTB, magnet=absorber)
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Quarkonia in STAR
Slowly getting started with J/y:
• Signal in 200 GeV p+p from 2005
• Tested and working trigger in p+p
• No trigger for AuAu until full ToF in 2009
• Much more from 2006 in the works…
• Also signal in Au+Au with TPC only
• Large hadron contamination
• Need full EMC
STAR Preliminary
J/ye+e- p+p √s=200 GeV
STAR Preliminary
J/ye+e- Au+Au √sNN=200 GeV
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 in STAR
• Cannot resolve different S
states  (1S+2S+3S) 
e+e• STAR
– Large acceptance (|| < 1,
full EMC)
– PID for electrons (EMC,
TPC)
– Trigger
• Very efficient > 80%
– Luminosity
limited
trigger
threshold
No N+++N-subtracted
STAR Preliminary
Scaling from Au+Au to
elementary: a=1
• First look in 2004:
½ EMC, little
statistics
• 90% C.L.: signal <
4.91
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Electron ID in STAR – EMC
1. TPC: dE/dx for p > 1.5 GeV/c
• Only primary tracks
(reduces effective radiation
length)
• Electrons can be discriminated
well from hadrons up to 8 GeV/c
• Allows to determine the remaining
hadron contamination after EMC
2. EMC:
a) Tower E ⇒ p/E~1 for eb) Shower Max Detector
• Hadrons/Electron shower
develop different shape
• Use # hits cuts
85-90% purity of electrons
(pT dependent)
h discrimination power ~ 103-104
hadrons
electrons
Electron Identification
• Association of TPC and BEMC information
– TPC gives dE/dx and momentum (p)
– BEMC gives the energy (E)
– Selected particles are within specifics dE/dx and p/E ranges.
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Why Quarkonia?
• J/y would “melt” in QGP due to screening of static potential
between heavy quarks:
–
Matsui and Satz, Phys. Lett. B 178 (1986) 416
• Recent developments shows that the dissociation
temperature for heavy quarkonia states are considerably
higher than first supposed
Using F1: S. Digal, P. Petreczky, H. Satz, Phys. Lett. B514 (2001) 57
Using V1: C.-Y. Wong, hep-ph/0408020
• Feed down from excited states could account for observed
suppression
[Matsui and Satz, Phys. Lett. B 178 (1986) 416]
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Achieving our Goals
A complete understanding of suppression
requires a broad range of systematic studies
– p+p, Au+Au, vs. centrality, vs. √s
– Measurement of J/y and excited states
– Measurement of  and excited states
• small cross-section  high luminosity  trigger
• good mass resolution to resolve 1S, 2S, 3S states
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STAR Contribution
• Large Acceptance at Mid-Rapidity
– ||<1, 0<<2
– Pair acceptance~(single acceptance)2
• Electron identification capabilities
– TPC dE/dx
– EMC E>1-2 GeV (operating full barrel)
– TOF p<2-3 GeV/c
• Trigger capabilities on Barrel EMC
– Suitable for single electron (see F. Laue’s talk)
– Suitable for di-electrons(?)
• Heavy-Quarkonia states are rare
– : efficient trigger for all systems
– J/y: trigger in p+p only, need large min. bias. dataset in Au+Au
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Efficiency and Purity of the Id
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J/y Trigger Level-0 (topology)
• Fast: t ≤ 1ms
• Φ divided in 6 sections
• Find a tower above
threshold
• Look for other towers
above threshold on the
3 opposite sections
• If signal above
threshold found, issue
trigger
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J/y Trigger Level-2 (software)
• Looks for e+e- pairs
• Towers above threshold→
“seeds” → clusters
• CTB matching (veto photons)
• cos(q12) obtained from clusters
and vertex positions
• Vertex: BBC resolution ~6cm
for Au+Au, 30cm for p+p
• Pairing clusters and neglecting
me: m2inv  2E1E2[1-cos(q12)]
• Decision is taking up to 500ms
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Applicability of the trigger J/y
• Au+Au:
– Only peripheral events
have good rejection
– Most of J/y yield is on
central events (98% of
signal on top 60% central)
– So, J/y trigger not suitable
for Au+Au
– Alternative is large min.
bias dataset
• J/y trigger efficient only
for p+p
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 trigger: L0 + L2
•  large mass
– Simpler L0, requiring one
single tower with ET>3.5
GeV
– Use similar L2 algo
– Can trigger p+p and central
Au+Au events
• Rare triggers go to
“express stream”
processing
• But… very low production
rate
– Less than 100 expected for
full Run IV Au+Au dataset
– Actually, only a few
achieved, for several
reasons
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J/y in Au+Au (Run IV)
• No trigger due to
high background
• Dataset:
Au+Au@200
GeV
• Just a faint signal
• For efficient J/y
trigger, full barrel
ToF is needed
(just patch in
Run IV)
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 trigger in Au+Au
• →e+e- channel
• L0: events with Etower> 3.5
GeV
• L2: events with pair mass
> 7 GeV/c2
• High efficiency (80%)
• Needs full BEMC for that
(only ½ in RunIV)
• Little statistics
trigger
threshold
No N+++N-subtracted
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 Analysis for Au+Au: Upper Limit
Scaling from Au+Au to elementary: a=1
•
•
•
90% C.L.: signal < 4.91
B*ds/dy C.L. < 7.6 mb
Acceptance increase will help (Factor ~4)
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Run V data sample (p+p)
• 1.7M events
• Simulation: yield
of 60-70 J/y
• Data: yield small
but consistent with
simulation
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Data  Simulation
• Width consistent with detector resolution
• Mass slightly lower than simulation (2s)
• Left tail in simulation due to bremsstrahlung in material
at r < 50 cm (beam pipe, SVT, SSD, air, TPC field cage)
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Run VI p+p (just finished)
• Barrel EMC full installed
• L2 widely used (jets, dijets,…)
• Both triggers are on (J/y and )
• p+p@200GeV just ended
– ~3.3M J/y triggered events taken (~800J/y)
– ~1.9M  triggered events taken (~80 )
• Most of events not reconstructed yet
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Future perspectives
• Completed Run VI with sufficient dataset to
measure J/y cross-section
• J/y trigger also deployed for p+p @ 62.4 GeV
• Medium-Term Upgrades:
– ToF (full barrel)
– Heavy Flavor Tracker (HFT)
– See next talk (Tony Frawley)
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ToF Upgrade
MRPC Time of Flight Barrel in STAR
23,000 channels covering TPC & Barrel Calorimeter
Construction FY 06 – FY 08
Will allow to deploy J/y trigger in Au+Au
Coincidence: ToF slat + EMC tower
substantially reduces photon background
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Origin of J/y suppression on SPS
F. Karsch, D. Kharzeev, H. Satz, hep-ph/0512239
Assume:
1.
NJ/y(observed) = 0.6 NJ/y + 0.4 Ncc
(compatible w Hera-B data)
2.
J/y doesn’t melt
3.
cc dissociation = y’ dissociation
Right or wrong, it shows how important
the missing cc measurement is!
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EXTRA: trigger pre-calibration for
BEMC
• Online energy
resolution
~ 17%/√E
• Offline energy
resolution
~ 14 %/√E
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J/y in Au+Au (Run IV)
dE/dx
• No trigger due to high background
• Dataset: Au+Au@200 GeV (Minbias)
• Invariant mass spectra from dE/dx
selection (skiping hadron bands)
• Subtracted spectrum shows a 3.5s
signicance peak arount J/y mass
Johan Gonzalez, SQM2006
J/ψe+e-
p (GeV/c)
(BR = 5.93%)
Zoom
Same event
Mixed event
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Invariant mass spectra vs. centrality
• Number of J/y in each
centrality class is determined
by bin counting
Johan Gonzalez, SQM2006
• Gaussian fits (widths are
held fixed to the value seen
in minbias events) are used
to estimate systematics
• Signal in the 0-20% bin is
rather weak, so only an
upper limit is quoted
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Centrality dependence of scaled J/y yields
• The Nbin-scaled yields
are plotted vs number of
participants
Johan Gonzalez, SQM2006
• Bars indicate statistical
uncertainties and the
bands indicate the
systematic uncertainties
• An upper limit is quoted
for the most central bin
Binary Scaling (black line and grey band) Determined from PHENIX
data (nucl-ex/0507032)
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Centrality dependence of scaled J/y yields
•
Statistical Hadronization[1]
calculations are shown for
various values of the differential
ccbar cross section
•
The model appears to
overpredict the scaled J/ψ yields
(~Ncc2) for most values of the
ccbar cross section
•
However, it should be noted that
the uncertainties in the
measured[2,3] c-cbar cross
sections are rather large at this
time.
[1] A. Andronic et al., Phys.Lett. B571 (2003) 36-44
[2] PHENIX, Phys.Rev.Lett. 96 (2006) 032001
[3] STAR, Phys. Rev. Lett. 94 (2005) 062301
pQCD x-section from:Cacciari, Nason,
Vogt, PRL 95 (2005) 122001
Johan Gonzalez, SQM2006
Statistical Hadronization Synopsis:
Complete screening of primordial J/ψ’s
J/ψ’s regenerated at chemical freezout from
thermalized c-cbars
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 trigger in Au+Au
• L0: events with Etower> 3.5 GeV
• L2: events with pair mass > 7 GeV/c2
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Trigger performance in Au+Au
• 4-20 M events sampled
per day
• Variation on daily
samples sizes due to
several STAR goals
• Other triggers reduced
the  trigger livetime
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 Analysis for Au+Au
• 34.2 mb-1 sampled
– 200M+ mb events
scanned with  trigger
– Only 50M off-line
– Small dataset processed
• Only 3 signal counts (no
BG) observed
Half field running, no BEMC-based
triggers.
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Trigger performance in Run V
Energy (MeV)
Invariant mass (MeV/c2)
Online monitoring of the trigger:
• Extremely fast turnaround
• No need for offline production to check the trigger
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Trigger performance for Run VI
Trigger monitoring shows consistency with Run V tests
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Run VI data analysis
• Only a few hundred k
events, for both
triggers, are reconstruct
so far
• Besides limited statistcs
is available data seem
promissing
• ~270k  trigger events
were enough to give a
hint of signal
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 Preliminary analysis
• Subtracted
invariant mass
spectrum
• 270k events
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