star physics highlights huan zhong huang department of physics and astronomy university of...
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STAR Physics Highlights
Huan Zhong HuangDepartment of Physics and Astronomy
University of California Los Angeles
@ShanDong UniversityOct. 16-18, 2003
Outline
• Quark-Gluon Plasma (QGP) and Relativistic Heavy Ion Collider (RHIC)
• Salient Features of Particle Production at High, Intermediate and Low pT
• Spin Physics Program
• Outlook
Quark-Hadron Phase Transition
STAR
Relativistic Heavy Ion Collider --- RHIC
Au+Au 200 GeV N-N CM energyPolarized p+p up to 500 GeV CM energy
The STAR Collaboration: 49 Institutions, ~ 500 PeopleEngland:
University of BirminghamFrance:
Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes
Germany: Max Planck Institute – Munich University of Frankfurt
India:Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC
Netherlands:
NIKHEFPoland:
Warsaw University of TechnologyRussia:
MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvino
U.S. Labs: Argonne, Berkeley, and Brookhaven National Labs
U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale
Brazil: Universidade de Sao Paolo
China: IHEP - Beijing, IPP - Wuhan, USTC,Tsinghua, SINR, IMP Lanzhou
Croatia: Zagreb University
Czech Republic: Institute of Nuclear Physics
Ideas for QGP Signatures
Strangeness Production: (J.Rafelski and B. Muller PRL 48, 1066 (1982))
s-s quark pair production from gluon fusions in QGP leads to strangeness equilibration in QGP most prominent in strange hyperon production (and anti-particles).
Parton Energy Loss in a QCD Color Medium:(J.D. Bjorken Fermilab-pub-82-059 (1982) X.N. Wang and M. Gyulassy, PRL 68, 1480 (1992))
Quark/gluon
Quark/gluon dE/dx in color medium is large!
Ideas for QGP Signatures
Chiral Symmetry Restoration: T = 0, m(u,d,s) > 0 – Spontaneous symmetry breaking T> 150 MeV, m=0 – Chiral symmetry restored Mass, width and decay branching ratios of resonances may be different in dense medium .
QCD Color Screening: (T. Matsui and H. Satz, Phys. Lett. B178, 416 (1986))
A color charge in a color medium is screened similar to Debye screening in QED the melting of J/.
c c Charm quarks c-c may not bindInto J/ in high T QCD medium
The J/ yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050)
Nucleus-Nucleus Collisions and Volcanic Eruption
Volcanic high pT -- Strombolian eruption Volcanic mediate pT – Spatter (clumps)
Volcanic low pT – Bulk matter flows
Jet Quenching in QCD Color Matter
leading particle
qq q
q
q q
Mono-JetNo back-to-back jet correlationHigh pT yield suppresion
Tangential jets from surface Complete quenching
of di-jet events
leading particle
Contribute to surface emission pattern !!
Contribute to residual back-to-back particle correlation!
Disappearanceof back-to-back correlation !
Disappearance of back-to-back angular correlations
x
y ptrigpss
pos
Ptrig – pss same side correlation
Ptrig – pos opposite side corr.
ptrig> 4 GeV/c, pss pos 2<pT<ptrig
Naïve Expectation for Au+Au
ddp
Nd
collddpNd
TAA
T
pp
T
AA NpR 2
2
/)(
Use number of binary nucleon-nucleon collisions to gauge the colliding parton flux:
N-binary Scaling RAA or RCP = 1 simple superposition of independent nucleon-nucleon collisions !
Peripheralcoll
T
Centralcoll
TTCP
NddpNd
NddpNd
pR
]/[
]/[
)( 2
2
High pT particles are from hard scattering of partons --
Suppression of high pT particles
pT Spectra Au+Au and p+p
p+p
Au+Au 0-5%
RAA=(Au+Au)/[Nbinaryx(p+p)]
Strong high pT suppression by a factor of 4-5 in central Au+Au collisions !The suppression sets in gradually from peripheral to central Au+Au collisions !
Two Explanations for High pT Observations
Energy Loss: Particles lose energy while traversing high density medium after the hard scattering. Energy loss quenches back-to-back angular correlations. J. Bjorken, M. Gyulassy, X-N Wang et al….
Parton Saturation: The parton (gluon) structure function in the relevant region (saturation scale) is modified. Not enough partons available to produce high pT particles. Parton fusion produces mono-jet with no back-to-back angular correlations. D. Kharzeev, L. McLerran, R. Venugopalan et al…..
d+Au Collisions
Au+Au Geometry d+Au Geometry
d+Au collisions: Little energy loss from the dense medium created, But Parton saturation from Au nuclei persists!
Data from d+Au collisions
No high pT suppression ! No disappearance of back-to-back correlations!
High pT Phenomena at RHIC
Very dense matter has been created in central Au+Au collisions!
This dense matter is responsible for the disappearance of back-to-back correlation and the suppression of high pT particles !
Intermediate pT Region
Volcanic mediate pT – Spatter (clumps)
At RHIC intriguing experimental features: multi-quark clustering enhanced baryon over meson production strangeness equilibration increased multi-strange hypeons
Elliptic Flow Parameter v2
y
x
py
px
coordinate-space-anisotropy momentum-space-anisotropy
Initial/final conditions, dof, EOS
1i
Ritttt
))ψcos(i(2v1dydpp
dN
2π
1
dyddpp
dN
STAR
PHENIX
Particle Dependence of v2
Baryon
Meson
Why saturation at intermediate pT ?Why baryon and meson difference ?
Multi-Parton Dynamics
KS – two quark coalescence– three quark coalescence from the partonic matter surface?!
Particle v2 may be related to quark matter anisotropy !!
pT < 1 GeV/c may be affected by hydrodynamic flow !
Hadronization Scheme for Bulk Partonic Matter:
Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al,Molnar+Voloshin …..)
Quark Recombination – (R.J. Fries et al….)
STAR+PHENIX
Multi-strange Baryons Flow Too
Hydro calcs.: P. Huovinen et al., Phys. Lett. B503, 58(2001).
Nuclear Modification Factor RAA RCP
Multi-parton dynamics predict baryon yield increases with centrality FASTER than mesons! Yield ~ n and n>nK a feature not present in single parton fragmentation !
Multi-parton dynamics: coalescence, recombination and gluon junctions.
RCP
RCP=[yield/N-N]central
[yield/N-N]peripheral
Intermediate pT Dynamics
Multi-parton dynamics – clustering of quarks – could be responsible for -- increased baryon production -- strange baryon enhancement -- strong elliptic flow at intermediate pT !!!
Hadronization of bulk partonic matter -- different phenomenon from e+e- collisions !
Low pT Phenomenon at RHIC
Volcanic mediate pT – Spatter (clumps) Volcanic low pT – Bulk matter flows
Prominent features at low pT: bulk matter flows ! 1) Thermal statistical models can describe the
yield of most particles. 2) Particle pT spectra and elliptic flow v2 – hydrodynamics.
= 0 0.5 Infinite
Nuclear Collision Evolution Epoches
Chemical Freeze-out --- formation of hadrons
Kinetic Freeze-out --- Interaction ceases
Between Two Epoches: Resonance Physics
Au+Au 40% to 80%
1.2 pT 1.4 GeV/c
|y| 0.5
STAR Preliminary
K*0
*(1520)
STAR preliminary p+p at 200 GeV
, f, f00, , *(892), *(892), , , , , *(1385), *(1385), *(1520)*(1520)
ρ0
f0
K0S
ω K*0
f2
0 & f0
++
p+p
Kinetic Freeze-out Condition
Hydrodynamics-inspired model fit most particles decouple at T~ 100 MeV and expansion velocity ~ 0.55c !Some particles decouple at earlier time because of smaller coupling strength with the hadronic medium!
important messengers of partonic matter !
Messenger for Conditions at Phase Boundary
Particles with small hadronic rescattering cross sections can be used to probe phase boundary at the hadron formation: , , , D, J/ ..........
KKSTAR Preliminary
KDD 00 KD
STAR Preliminary
STAR Preliminary
Transition from Soft to Semi-Hard Dynamics
PT 1.5-4 GeV/c TOF PID Region !
Non-Trivial Dynamics at Intermediate pT
Enhanced Baryon Yield at Intermediate pT cannot be due to Cronin Effect Alone !
d+Au
Au+Au
STAR TOFr physics paper (see Jian Wu’s talk)
What has been learned
1)Evidence for high energy density matter produced in central Au+Au collisions – high pT particle suppression and disappearance of back-to-back correlations.
2)Multi-parton dynamics for particle formations – hadronization of bulk partonic matter.
3)Hydrodynamical behavior at low pT – collective partonic dynamics and thermal statistical description of particle production.
Discoveries from Unexpected Areas?!
RHIC -- Frontier for bulk partonic matter formation -- Factory for exotic particles/phenomena
Potential exotic particles/phenomena:penta-quark states (uudds, uudds!)
di-baryonsH – (, uuddss) [] (ssssss)
strange quark matter
meta-stable Parity/CP odd vacuum bubblesdisoriented chiral condensate……
Spin Physics Program
The Spin Structure of the Proton:
½ = ½ q + G + <L>
q up, down and strange quarksG gluonsL angular momentum of quarks and gluons
Experimentally: 1) total spin in quarks ~ 30% 2) sea quarks are polarized too 3) little info about the gluon polarization 4) even less know about <L> and how to measure <L>
RHIC Spin PhysicsAt RHIC we use polarized p+p collisions to study1) Gluon spin structure function q+gq+2) Sea quark spin structure function q+qW boson3) Quark transverse spin distribution
Syst. Uncer. = ±0.05
STAR FPD Preliminary DataAssuming AN(CNI)= 0.013
pT=1.1 - 2.5 GeV/c
s=200 GeV
p+ p 0 + X
A
N
0
0.2
0.4
-0.20 0.2 0.4 0.6 0.8 1.0
xF
First RHIC spin result onsingle spin asymmetry !
RHIC Physics Outlook
Heavy Ion Physics: 1) discovering the Quark Gluon Plasma 2) Properties of high density QCD matter 3) Chiral symmetry at high temperature and density 4) Search for exotic particles/phenomena at RHIC
RHIC Spin Physics Using Polarized p+p Collisions: 1) the gluon spin structure function major milestone to understand the spin of the proton! 2) sea quark spin structure function 3) quark transverse spin distribution
End of Talk
STAR Physics ApproachesEmphasis on Observables Sensitive to Early Partonic Stages:
1) High pT particles – Jet quenching? New baryon dynamics? 2) Particle fluctuations and large scale correlations – probe
conditions near phase boundary.3) Partonic collective flow observables especially for those particles
believed to have small hadronic re-scattering cross sections, D mesons and J/.
4) D meson production for initial gluon flux and structure function of nuclei.
5) J/ for possible color screening effect6) Direct and thermal photon production
Precision Measurements to Map Out Hadronic Evolution Dynamics
1) Resonances (,,f0, K*, , (1385) and(1520)) – Sensitive tohadronic evolution between chemical and kinetic freeze-out
2) Momentum-space-time relations at the kinetic freeze-out thrucorrelations of identical, non-identical pairs, and light clusters.
We need TOF upgrade !!
A Pictorial View of Micro-Bangs at RHIC
Thin PancakesLorentz =100
Nuclei pass thru each other
< 1 fm/c
Huge StretchTransverse ExpansionHigh Temperature (?!)
The Last Epoch:Final Freezeout--
Large Volume
Au+Au Head-on Collisions 40x1012 eV ~ 6 micro-Joule
Human Ear Sensitivity ~ 10-11 erg = 10-18 Joule
A very loud Bang, indeed, if E Sound……
Ultra-Peripheral Collision Physics
STAR Preliminary, 200 GeV Au+Au
dN
/dt
(GeV
2)-1
Data (w/ fit) No Interference Interference
t = pT2 (GeV2)
Au+Au at 200 GeV
1) Two indistinguishable possibilities: A photon from nucleus 1 scatters from 2 A photon from nucleus 2 scatters from 1
2) Negative parity – destructive inter. ~ |A1 - A2eip·b|2
- At y=0 =0[1-cos(pb)] - pT <<1/<b> - For 0 w/ XnXn <b> ~ 20 fm
- Clear signal of interference!Clear signal of interference!
Au beam as virtual photon source Strong Field QED and Spectroscopy
Strangeness from Bulk Partonic Matter
Strangeness enhancement is most prominent at intermediate pT from quark coalescence in an equilibrated bulk matter !
What More Measurements ?
• Experimentally determine the amount of jet energy loss? Where did the energy loss go (increase in soft particle emissions?)
• Is the experimental energy loss consistent with theoretical calculation of dE/dx from a QCD medium, not with a hadronic medium?
• Signatures of QCD deconfinement?• Peoperties of bulk partonic matter at the phase
boundary?
Practically we need Au+Au, Si+Si …… at several beam energies , , J/, open charm mesons, direct photons…..
y
Dynamical Origin of Elliptic Flow
STAR PreliminaryAu+Au 200 GeV
V2 in the high pT region: should large parton energy loss lead to surface emission pattern ?! Particle Dependence of v2 ?
Collective Pressure
High pressure gradientLarge expansion velocity
Small expansion velocity
pT dependent !
Surface Geometrical Phase Space
Surface Emission PatternHigh particle density
Low particle density
pT independent ! orpT dependence may comefrom surface thickness (pT)
x
Energy Scale and Phase Transition
Entity Energy Dimension Physics Bulk Property P/T
Atom 10’s eV 10-10 m Ionization e/Ion Plasma No
Nucleus 8 MeV 10-14 m Multifrag. Liquid-Gas Y(?)
QCD 200 MeV 10-15 m Deconfine. QGP Y(?)
EW 100 GeV 10-18 m P/CP Baryon Asymmetry Y(?)
GUT 1015-16 GeV Supersymmetry
TOE 1019 GeV Superstring
A Magnificent Collision in the Universe
Collision of two galaxies: the Antennae; Hubble Space Telescope
Quarks and Quantum ChromoDynamics
Baryon Density: = baryon number/volumenormal nucleus 0 ~ 0.15 /fm3 ~ 0.25x1015 g/cm3
Temperature, MeV ~ 1.16 x 1010 K10-6 second after the Big Bang T~200 MeV
Three family of quarks
Up Charm TopDown Strange Beauty
Strong interaction is due to color chargesColor Interaction mediated by gluons (EM by photons)Gluons carry color charges (photons electric neutral)
Ordinary Matter: proton (uud) and neutron (udd)