dilepton and medium effect on particle properties
DESCRIPTION
Dilepton and medium effect on particle properties. Zhangbu Xu. Outline 共振态在 QGP 态下的性质 双轻子谱 探测方法. Medium Effect in Dense Nuclear Matter. Brown-Rho Scaling Broadening Low Mass Dilepton measuring properties. R. Rapp, et al. Last Call for RHIC Predictions - PowerPoint PPT PresentationTRANSCRIPT
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Zhangbu Xu, USTC 2009 lecture 1
Dilepton and medium effect on particle properties
Zhangbu Xu
Outline•共振态在 QGP 态下的性质
•双轻子谱•探测方法
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Zhangbu Xu, USTC 2009 lecture 2
Brown-Rho Scaling Broadening Low Mass Dilepton
measuring properties
Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260
• Chiral UA(1) symmetry restoration (J. Schaffner, D. Kharzeev, et al.)手征对称
Medium Effect in Dense Nuclear Matter
R. Rapp, et al
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Zhangbu Xu, USTC 2009 lecture 3
A little bit of historyWith the establishment of the hydrogen bubble-chamber, entirely new possibilities for research into high-energy physics present themselves. Results have already been apparent in the form of newly-discovered elementary particles. The first, very short-lived, so called, "resonance particle" was found in 1960. The Nobel Prize in Physics 1968
First time Invariant Mass was used (bump hunting)
(1952?)(1385) (1960)(892) (1961)(1405)
1411 (1967)
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Zhangbu Xu, USTC 2009 lecture 4
Measurement Technique 强子道的测量
• Mixed-event, Like-sign Background subtraction
• P-Wave Breit-Wigner function or Modified BW
ISRK*0 from p+p Collisions
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Zhangbu Xu, USTC 2009 lecture 5
All that Matters: X-section 作用截面
Different by 5
Rescattering>Regeneration at later stageChemical freeze-out
Kinetic freeze-out
K*
lost
K*
measured
K
K* K
K*
K*
K
K*
K K K*
measured
强子衰变道 : 散射 ( 大于 ) 再产生
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Zhangbu Xu, USTC 2009 lecture 6
重核子碰撞的时空演化 Stages in the collision
1. Pre-equilibriumHard parton scattering processes
2. EquilibrationAfter ≤ 1 fm/c partons materialise
and either hadronise or rescatter.
3. Thermal quark-gluon plasmaHydrodynamic expansion
4. Hadronization (phase transition)Quark coalescence + gluon
fragmentation … or … String fragmentation
5. Hadron gasHadrons continue to interact
6. Particle freeze-out Chemical freeze-out 化学冻结
粒子数不再变化 Thermal freeze-out 热冻结
不再有强相互作用
a) Without QGP b) With QGP
Hadron gas
Mixed phaseHadron gas
Parton formation and thermalisation.
Hadron formation.
t
z
, K, N, …, K, N, …
f
f
0 = h
(H)
(Q)
3.
4.
5.
6.
4.
6.
QGP
2.
1.
5.
A A
1.
0 = q
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Zhangbu Xu, USTC 2009 lecture 7
共振态有化学冻结吗 ?
Au+Au, p+p, Thermal Fit; Feed-down
STARPHENIX
Strangeness Enhancement Resonance Suppression
K. Schweda, O. Barannikova
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Zhangbu Xu, USTC 2009 lecture 8
Finite Interaction Cross Section Breakdown of Ideal fluid? Different Cross Section regeneration or rescattering ? Different Cross Section Flow at hadron stage
Resonance driven by Cross Section
Statistical and systematic errors added in quadrature
M. Bleicher et al. J. Phys. G 25 (1999) 1859
σ(Kπ)
σ(ππ)
K. Schweda, P. Fachini, C. Markert, H. Zhang
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Zhangbu Xu, USTC 2009 lecture 9
质量 or 重子 / 介子 ?
RCP flattens at intermediate pT
Two groups (2<pt<6GeV/c):
- ,K0s, K, K*, mesons
- p,, , baryons
Meson/Baryon Effect!
Collective velocity is not the only
scale
quark coalescence ?
介子共振态的特征 : 质量大
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Zhangbu Xu, USTC 2009 lecture 10
Quark Contents
K+K*? s+uK*?
Constituent Quark Scaling?
n=20.3
C. Nonaka, B. Muller et al. , Phys.Rev.C69:031902,2004
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Zhangbu Xu, USTC 2009 lecture 11
+ - Invariant Mass Distribution
2.1106 Au+Au minimum bias events and 4.7106 pp events
Breit-Wigner fixed width 0 = 150 MeV and f0 = 75 MeV fixed f0 masse 0.98 GeV (AuAu) and 0.96 GeV (pp)
0 mass = 0.698 ± 0.013 GeV (AuAu)
0 mass = 0.729 ± 0.006 GeV (pp)
AuAu 40% to 80%0.2 pT 0.9
GeV/c
|y| 0.5
0
f0
K0S
K*0
STAR Preliminary
STAR Preliminary
0
f0
K0S
K*0
0.2 pT 0.8 GeV/c
|y| 0.5
pp
Statistical error only Statistical error only
sNN = 200 GeV
P. Fachini (STAR)
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Zhangbu Xu, USTC 2009 lecture 12
<qq>, TQGP
The Lost Sword (Fable, 《呂氏春秋》 ~250B.C.)
RHIC
<qq>, TQGP
The SwordA+A CollisionsMoving Boat
Freeze-outFerry
HadronsMark
Detecting SignalsJumping into water
Chiral Symmetry Restoration e+e-, thermal Radiation g+ge+e-
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Zhangbu Xu, USTC 2009 lecture 13
Brown-Rho Scaling Rho Broadening Low Mass Dilepton
measuring properties
Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260
• Chiral UA(1) symmetry restoration (J. Schaffner, D. Kharzeev, et al.)
Medium Effect in Dense Nuclear Matter
R. Rapp, et al
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Zhangbu Xu, USTC 2009 lecture 14
How to Probe Early Stage?
Modification in medium
Decay quicklymatter exists 10-23s
Small or no FSIleptons, photons
Golden: J/
q
q
l
l
s
Small Branching Ratio(10-4), Low Production Rate
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Zhangbu Xu, USTC 2009 lecture 15
NA49 at SPS
A central Pb+Pb Collision1 cm slice centred on beam-axis
B = 1.5 T B = 1.1 T
NA49 Pb+Pb 158 GeV/A
s 17 GeV
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Zhangbu Xu, USTC 2009 lecture 16
-Production: Hadronic versus Leptonic Decay Channel
Different decay channels: NA49: -+
NA50: -+
Transverse momentum spectrum fit: 1/mTdn/dmT ~ exp(-
mT/T)
(NA49: 3.0<y<3.8)significant differences in
slopes and yields
Dieter Röhrich, QM02
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Zhangbu Xu, USTC 2009 lecture 17
Vector Meson at RHIC
AMPT: (l+l-)/(K+K-)=1.5 Experiments’ comparison
c=50fm
K
K
l+l-
K+K-
AMPT, STAR
Nucl-th/0202086
130GeV
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Zhangbu Xu, USTC 2009 lecture 18
The NA45 experiment
Ring Imaging Cherenkov (RICH)Radiator chosen to select electrons
Time Projection ChamberUsed for charged particle tracking
Nee
Nch ~10 5
th 32
95% of charged hadrons do not produced Cherenkov light
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Zhangbu Xu, USTC 2009 lecture 19
Dileptons at SPS
Conventional cocktail of particles Underpredicts dilepton production
Mass shifted??
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Zhangbu Xu, USTC 2009 lecture 20
The NA50/NA60 experimentNA50: di-muon spectrometerNote: absorber to remove all hadrons
muon spectrometer
absorber
ET E0
event selection
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Zhangbu Xu, USTC 2009 lecture 21S. Damjanovic, Quark Matter 2008 21
双轻子的质量和动量谱斜率Phys. Rev. Lett. 96 (2006) 162302
drop
-Teff rises in low mass region radial flow of a hadronic source- drop at M~1 GeV suggests partonic nature of equilibrated particles~thermal radiation? - note: yield goes like (dN ch /dy)2
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Zhangbu Xu, USTC 2009 lecture 22
PHENIX from Above
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Zhangbu Xu, USTC 2009 lecture 23
West Arm tracking:
DC,PC1, PC2, PC3 electron ID:
RICH, EMCal
Photons EMCal
East Arm tracking:
DC, PC1, TEC, PC3 hadron& electron ID:
RICH,TEC, TOF, EMC photons:
EMCal
PHENIX Setup
full heavy ion program and first spin physics including electron & muon pairs
South Arm tracking:
MuTr muon ID:
MuID
Other Detectors Vertex
& centrality: ZDC, BBC, MVD
accumulated ~200 106 Au-Au
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Zhangbu Xu, USTC 2009 lecture 24
Measured p+p Mee
Cocktail filtered in PHENIX acceptance
Charm, Bottom, DY contributions from PYTHIA
Excellent agreement!
arXiv:0802.0050
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Zhangbu Xu, USTC 2009 lecture 25
Au+Au Mee compared to Cocktail Data and Cocktail
absolutely normalized Cocktail normalized to
Au+Au measurements Except ccbar
Low mass excess 150 < Mee < 750 X 3.4±0.2(stat.)
±1.3(syst.)±0.7(model) Intermediate mass
agreement
arXiv:0706.3034
Thermal contribution perhaps if ccbar mass spectrum softened by rescatt.
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Zhangbu Xu, USTC 2009 lecture 26
PT Dependence of Au+Au Mee
Low Mass excess is a low pT enhancement Huge excess at
lowest pT
Late Phase info
0 < pT < 8 GeV/c 0 < pT < 0.7 GeV/c
0.7 < pT < 1.5 GeV/c 1.5 < pT < 8 GeV/c
PHENIX Preliminary Still significant at high pT
PHENIX Preliminary QM08
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Zhangbu Xu, USTC 2009 lecture 27
STAR UpgradesMRPC ToF barrel
BBCRPSD
PMD
F0S
FMS
EMC barrelEMC End Cap
- DAQ1000
- TPC FEE
- MTD
- Soft HFT: Si-pixels; IST: Si-strips; FGT: GEM-layers
Integrated Tracking Upgrades
finished
ongoing
MTD
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Zhangbu Xu, USTC 2009 lecture 28
STAR 的目标
To study: 1. vector meson production and in-medium effect 2. heavy Quarkonian production (suppression)
Measuring the dilepton →
Electrons may come from the following sources at low mass region:
γ conversionπ0 , η Dalitz decaysρ ω Φ vector meson decays
Focus on the dilepton spectra at low mass region
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Zhangbu Xu, USTC 2009 lecture 29
What STAR Can Do?
Future upgraded detectors:
Full TOF μVertex detector
Electrons PID Reject electrons not from primary vertex
(gamma conversion)
Simulation:
γ conversion and π0 , η Dalitz decay background
How can μVertex detector deal with γ conversion subtraction?
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Zhangbu Xu, USTC 2009 lecture 30
Electron IdentificationBefore, using TPC dE/dx only to separate electrons from hadrons is complicated
TOF detector lights up this study
|1/β-1|<0.03
With TOF PID cut, electron band can be separated from others readily!
A prototype TOF tray (TOFr) installed this year
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Zhangbu Xu, USTC 2009 lecture 31
DileptonAssume electrons can be identified with full TOF
Total bkgd: ~10-4/25MeV (ω) ~2∙10-5/25MeV (Φ)
Dalitz decay bkgd: ~5∙10-6/25MeV (ω) ~5∙10-7/25MeV (Φ)
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Zhangbu Xu, USTC 2009 lecture 32
Background Rejection
L.J.Ruan
Electrons from gamma conversion
Require TPC+SVT+μVertex
~98% electrons fromgamma conversion rejected
Dalitz decays become dominant sources!!!
Great thanks to Kai!
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Zhangbu Xu, USTC 2009 lecture 33
Upgraded TOF for dileptons
Detectors
TPC+TOF 20K 6K
Background: e+e-
HFT discriminates background
Need low mass detector
Statistics comparable to NA60
Charm background
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Zhangbu Xu, USTC 2009 lecture 34
强作用下的宇称破缺
Vacuum Engineering Big Bang
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Zhangbu Xu, USTC 2009 lecture 35D. Kharzeev, QM08
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Zhangbu Xu, USTC 2009 lecture 36
Conclusions
Vector Meson Resonances are sensitive tools to study new state of matter
An important physics program STAR will pursue
TOF+TPC+SVT+ μVertexSTAR RHIC II Upgrade