the di-lepton physics program at star
DESCRIPTION
The di-lepton physics program at STAR. L ijuan Ruan for the STAR Collaboration ( Brookhaven National Laboratory ). Outline: Motivation and Introduction Recent results from STAR Future perspectives from STAR Conclusions and outlook. S. Bass. Probe the medium properties. - PowerPoint PPT PresentationTRANSCRIPT
06/01/2012 Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL) 1
The di-lepton physics program at STAR
Outline:• Motivation and Introduction • Recent results from STAR
• Future perspectives from STAR
• Conclusions and outlook
Lijuan Ruan for the STAR Collaboration (Brookhaven National Laboratory)
06/01/2012 Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL) 2
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
S.
Bas
sProbe the medium properties
H. van Hees and R. Rapp, Nucl.Phys.A806 (2008) 339; T. Renk and J. Ruppert, PRC77(2008)024907
In medium modification of vector mesons and thermal radiation: di-lepton continuum
NA60, PRL100(2008)022302NA60, Eur.Phys.J.C59(2009)607
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STAR detector: TPC & MRPC-TOF
A recent technology (TOF) ----Multi-gap Resistive Plate Chamber
1. Good timing resolution, (, K) < 1.6 GeV/c, proton < 3 GeV/c 2. Coverage: -0.9<<0.93. Coverage (72% y2009, 100% y2010)
Time Projection Chamber 1. Tracking2. Ionization energy loss (dE/dx): (, K) < 0.7 or > 3 GeV/c, proton < 1 or > 3 GeV/c 3. Coverage -1<<1
06/01/2012 4
STAR Time of Flight detector performance
STAR, PLB616(2005)8|1/-1|<0.03
STAR, PRL94(2005)062301
TOF PID: (, K) ~ 1.6, proton ~ 3 GeV/cSTAR Collaboration, PLB616(2005)8
TOF enables clean electron PID up to PT < 3 GeV/c. STAR Collaboration, PRL94(2005)062301 M. Shao et al., NIMA 558(2006)419
Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL)
200 GeV d+Au collisions
200 GeV d+Au collisions
Di-electron signal
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Di-electon signal: e+e- pairs from light flavor meson and heavy flavor decays (charmonia
and open charm correlation):
Pseudoscalar meson Dalitz decay: 0 , η, η' e+e-
Vector meson decays: 0 , , e+e-, 0 e+e- , ηe+e-
Heavy flavor decays: J/e+e- , ccbar e+e- X, bbbar e+e- X
Drell-Yan contribution
In Au+Au collisions, we search for
QGP thermal radiation at 1.1<Mee<3.0 GeV/c2 (intermediate mass range)
Vector meson in-medium modifications at Mee<1.1 GeV/c2 (low mass range)
Di-electron production in 200 GeV p+p
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cocktail simulation is consistent with
di-electron spectrum in p+p
collisions at 200 GeV
charm correlation contribution
dominates in the intermediate mass
region (1.1-2.9 GeV/c2)
Simulation: charm correlation
contribution is from PYTHIA .
STAR acceptance: |yee|<1, |ηe|<1, pT>0.2 GeV/c
J/
STAR Collaboration, arXiv:1204.1890.
Di-electron angular correlation in 200 GeV p+p
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Taking advantage of 2 azimuthal coverage, with better statistics
in future, we will do the angular correlations of di-leptons from
ccbar contribution.
STAR Collaboration, arXiv:1204.1890.
Di-electron spectra in 200 GeV Au+Au
06/01/2012 8Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL)
See J. Zhao’s talk for detail
Minbias (value ± stat ± sys) Central (value ± stat ± sys)
STAR1.53 ± 0.07 ± 0.41 (w/o ρ) 1.40 ± 0.06 ± 0.38 (w/ ρ)
1.72 ± 0.10 ± 0.50 (w/o ρ) 1.54 ± 0.09 ± 0.45 (w/ ρ)
possible enhancement factor in 0.15<Mee<0.75 Gev/c2
PHENIX results, see A. Drees’ talk.
J/ J/
0-80% Au+Au 0-10% Au+Au
06/01/2012 9Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL)
ee spectra in 200 GeV p+p and Au+Au
ωee measurements via di-lepton channel in p+p and Au+Au at STAR
ωee flow pattern is similar to light hadrons
Tsallis Blast-wave(TBW) fit:
<β>=0 in p+p,
<β>=0.47 in 0-80% AuAu.
Z.Tang et al., PRC79(2009)051901 STAR, QM2011, SQM2011
06/01/2012 10Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL)
ee spectra in 200 GeV Au+Au
The invariant yield of via di-lepton channel in Au+Au is consistent with that from hadronic decay channel.
STAR, SQM2011
STAR Preliminary
pT (GeV/c)
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Di-lepton elliptic flow
K. Dusling NPA839(2010)70
• Low pT direct photon elliptic flow measurement could provide direct constraints on QGP dynamics (η/s, T, t0…).
• Excess of direct photon yield over p+p and substantial positive v2 observed at
pT<4 GeV/c in central Au+Au, suggestive of significant contribution from the
hadronic sources at later stage. (H. v. Hees, C. Gale, R. Rapp, PRC84(2011)054906)
• Di-lepton v2 versus pT & Mll: probe the properties of the medium from hadron-gas
dominated to QGP dominated. (R. Chatterjee, D. K. Srivastava, U. Heinz, C. Gale, PRC75(2007)054909)
PHENIX, arXiv: 1105.4126PHENIX: PRL104 (2010)132301
v2 versus Mee at 200 GeV Au+Au
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A factor of 2 more minbias data from run11 are on disk.
STAR, SQM2011, DNP2011
STAR Preliminary
0-80% Au+Au at 200 GeV
13
To provide a comparison (blue) curve from simulation:1. Parameterize meson v2 results 2. Do the Dalitz decay simulation and obtain expected v2 of di-electrons pairs from 0 Dalitz decay. 3. This is consistent with our di-electrons v2 results.
To provide a comparison (blue) curve from simulation:• Assume η v2 same as KS • do the same Dalitz decay procedure
v2 of di-electrons from π0 and η Dalitz decay
STAR Preliminary
STAR Preliminary
0: PHENIX, PRC 80(2009)054907
06/01/2012 Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL)
STAR, SQM2011, DNP2011
0-80% Au+Au at 200 GeV
0-80% Au+Au at 200 GeV
The elliptic flow of ee pairs in the mass region is consistent with the result of KK within large errors
STAR preliminary
STAR preliminary
KK: STAR, PRL99(2007)112301
v2 of di-electrons at 0.5<Mee<1.1 GeV/c2
STAR, DNP2011
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0-80% Au+Au at 200 GeV 0-80% Au+Au at 200 GeV
Di-electron results in 39 GeV Au+Au
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Raw, efficiency correction to be done.
STAR, CPOD2011
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To the futureSTAR has started the di-lepton program with a bright future enabled by the
TOF upgrade :• Di-electron spectrum in 200 GeV p+p collisions: Cocktail simulation consistent with data
Charm correlation contribution dominates at intermediate mass
• Di-electron in 200 GeV Au+Au collisions: A possible low mass enhancement with respect to cocktail expectation
at Mee 0.15-0.75 GeV/c2
ee shows a similar flow velocity at freeze-out as light hadrons
yields are similar between di-leptonic decay and hadronic decay channel
Di-electron v2 from low to high mass measured
Towards the future: Differential measurements (Mee, pT, v2) are on-going
Energy dependence (19-200 GeV) can be systematically studied at STAR
Precise open charm measurements help study heavy flavor dynamics with HFT
e-µ correlation (spectrum and v2) to distinguish heavy flavor production from initial lepton pair production with MTD upgrade
The Heavy Flavor Tracker (HFT)
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10
20
30
-30
-10
-20
• The HFT puts 4 layers of Silicon around the vertex
• Provides ~20 m space point resolution on tracks
• Works at high rate (~ 800 Hz – 1K)
• Does topological reconstruction of open charm
• Will be ready for the 2014 run
The HFT – study heavy flavor dynamics
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RCP, v2, baryon/meson ratios:
heavy quark transport co-efficients, energy
loss mechanism, thermalization with medium.
To understand heavy quark dynamics in the
medium, constrain model inputs to calculate
di-leptons from heavy flavor correlation.
HFT CDR
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Concept of design of the STAR-MTD
Multi-gap Resistive Plate Chamber (MRPC):
gas detector, avalanche mode
A detector with long-MRPCs covers thewhole iron bars and leave the gaps in- between uncovered. Acceptance: 45% at ||<0.5
118 modules, 1416 readout strips, 2832 readoutchannels
Long-MRPC detector technology, electronics same as used in STAR-TOF
MTD
Measure charm correlation with MTD upgrade: ccbare+
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e correlation simulation with Muon Telescope Detector (MTD) at STAR fromccbar: S/B=2 (Meu>3 GeV/c2 and pT(e)<2 GeV/c) S/B=8 with electron pairing and tof association
MTD: construction has started in FY2011; project completion in FY2014
Z. Xu, BNL LDRD 07-007; L. Ruan et al., JPG36 (2009) 095001
R. Rapp, hep-ph/0010101
Simulation precision projection: ccbare+
06/01/2012 21Hard Probes 2012, May 27-June 1, Lijuan Ruan (BNL)
For FY2013, request three weeks Au+Au run at 200 GeV:
e-muon correlation measure charm correlation modification
Red: PYTHIA ccbareµBlack: de-correlated + energy loss
PYTHIA ccbareµwith electron and muon coincidence trigger
projection done with 43% MTD in place for 2013
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Di-lepton measurements at STAR
FY09/10/11 FY12/13 From FY14 on
Detector components
TPC+TOF+EMC TPC+TOF+EMC+MTD(p) TPC+TOF+EMC+MTD+HFT
Measurements J/ee, Upsilonee
J/ RAA, v2 vs. pT &Npart,
Upsilon RAA vs. Npart
di-electron continuum
di-electron spectra, v2 vs. pT
FY12 (10% MTD):
first proof-of-principle e-µ measurement
FY13 (43% MTD): J/µµ,
J/ RAA, v2 vs. pT & Npart,
e-µ mass and
BJ/XµµX
different Upsilon states RAA versus Npart, J/µµ RAA, v2
versus pT & Npart,
di-muon continuum,
e-µ spectra and v2
D v2 and RAA
Physics Color screening features, quarkonia production mechanisms,
vector meson in-medium modifications,
low mass enhancement, Intermediate mass
Better understanding of thermal radiation from QGP at intermediate mass and vector meson in-medium modifications
Measure thermal radiation from QGP at intermediate mass, vector meson in-medium modifications, color screening features
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Summary
• STAR has started the di-lepton program with a bright future enabled by the TOF upgrade :
Di-electron spectrum from low to high mass measured in 200 GeV p+p and Au+Au collisions
Di-electron v2 from low to high mass measured in 200 GeV Au+Au collisions
Energy dependence (19-200 GeV) can be nicely and systematically studied at STAR
Differential measurements (Mee, pT, v2) are on-going
• Future with the HFT and MTD:
Precise measurements on charmed hadrons help understand charm quark dynamics in the medium.
e-µ correlation (spectrum and v2) to directly measure heavy flavor correlation contribution to di-lepton continuum to access the QGP thermal radiation.
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Backup
Compared to theoretical calculations within STAR acceptance
Blue dotted: HG_mediumPink dotted: QGP
Solid lines: upper: cocktail + HG+QGP lower: cocktail
HG_med, QGP from R. Rapp (private communication)R. Rapp and J.Wambach, Adv. Nucl. Phys. 25, 1 (2000).
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Data sets for di-electron analyses
Run period Collision energy Beam species Detector
2009 200 GeV p+p TPC+TOF(72%)+EMC
2010 200 GeV Au+Au TPC+TOF+EMC
62 GeV Au+Au TPC+TOF+EMC
39 GeV Au+Au TPC+TOF+EMC
2011 200 GeV Au+Au TPC+TOF+EMC
27 GeV Au+Au TPC+TOF+EMC
19 GeV Au+Au TPC+TOF+EMC
large acceptance of the TOF system and low material budget * at mid-rapidity
* beam pipe (0.29% radiation length), beam pipe wrap (0.14%), air (0.17%), IFC (0.45%)
Electron identification capability
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|1/β-1|<0.03 |1/β-1/βexpected|<0.025
Clean electron identification obtained with TPC+TOF:Electron purity: 99% in p+p and 97% in minbias Au+Au
Hadron contamination contribution to di-lepton is insignificant and taken as
part of systematic uncertainties.
200 GeV p+p collisions
Di-electron signals in p+p and Au+Au
STAR preliminary
p+p @ 200 GeV
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Di-lepton background
Mixed-event normalized to like-sign within 0.4 - 1.5 GeV/c2
Cross-pair bg. can only be described by like-sign method.
For minimum bias events, we subtracted like-sign bg at Mee<0.4 GeV/c2, mixed-event bg subtraction was applied at Mee>0.4 GeV/c2.
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Di-lepton azimuthal angle distribution
Mixed-event normalized to like-sign within 0.4 - 1.5 GeV/c2
Cross-pair bg. can only be described by like-sign method.
For minimum bias events, we subtracted like-sign bg at Mee<0.4 GeV/c2, mixed-event bg subtraction was applied at Mee>0.4 GeV/c2.
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STAR preliminarySTAR preliminary
Di-lepton background
Mixed-event normalized to like-sign within 1 - 3 GeV/c2
Cross-pair bg. can only be described by like-sign method.
For minimum bias events, we subtracted like-sign bg at Mee<0.4 GeV/c2, mixed-event bg subtraction was applied at Mee>0.4 GeV/c2.
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Low mass enhancement
PHENIX PRC 81 (2010) 034911
Minbias (value ± stat ± sys) Central (value ± stat ± sys)
STAR1.53 ± 0.07 ± 0.41 (w/o ρ) 1.40 ± 0.06 ± 0.38 (w/ ρ)
1.72 ± 0.10 ± 0.50 (w/o ρ) 1.54 ± 0.09 ± 0.45 (w/ ρ)
PHENIX 4.7 ± 0.4 ± 1.5 7.6 ± 0.5 ± 1.3
Difference 2.0 σ 4.2 σ
Enhancement factor in 0.15<Mee<0.75 Gev/c2
Note: Acceptance difference etc.
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Systematic uncertainties
p+p: Au+Au:
STAR preliminary
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Reproduce PHENIX cocktail
• Reproduce the cocktail within PHENIX acceptance by our method.
• The momentum resolution are from STAR.
Scaled by all the yields from PHENIX paper[1], we can reproduce the PHENIX cocktail.
[1]. Phys. Rev. C 81, 034911 (2010).
STAR preliminary
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Check with acceptance difference
Scaled by same meson and charm yields.
Scaled by the acceptance difference
Difference at low mass is not from the simulation but from the measurements.
Cocktail in PHENIX acceptance
Cocktail in STAR acceptance
Acceptance difference:
STAR preliminary
STAR preliminary
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STAR data with PHENIX acceptance
STAR data with PHENIX acceptance cut
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v2 standard event-plane method
)(*)(*)()()(
2)(
22 MN
NvM
N
NMvMv
BS
Ss
BS
BBTotal
)(*)(*)()()(
2)(
22 MN
NvM
N
NMvMv
BS
Ss
BS
BBTotal
ν2Total is flow of unlike-sign pairs.
v2B(M) is flow of background calculated using the like-
sign or mixed events pairs.v2
S is flow of signal. NS is the signal number, NB is the background (like-sign) number. N(S+B) is unlike-sign number.
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Unlike-sign and background v2
)(*))(1(*)()()(
2)(
22 MN
NvM
N
NsMvMv
BS
Ss
BS
BTotal
Unlike-sign v2 Background v2 Signal/(Signal+Background)
Signal flow
STAR preliminary
STAR preliminary
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