1 strange and heavy quark probes of qcd matter at rhic huan zhong huang department of physics and...
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Strange and Heavy Quark Probes of QCD Matter at RHIC
Huan Zhong Huang
Department of Physics and Astronomy
University of California Los Angeles
Weihai, China 2004
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Outline
• Relativistic Heavy Ion Collider (RHIC) and Quark-Gluon Plasma (QGP)
• Intriguing New Experimental Phenomena at RHIC
• Strange and Heavy Quarks at RHIC
• Future Measurements
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STAR
Relativistic Heavy Ion Collider --- RHIC
Au+Au 200 GeV N-N CM energyPolarized p+p up to 500 GeV CM energy
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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
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Quark-Hadron Phase Transition
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New Phenomena at RHIC
1)High pT Particle Suppression and Disappearance of back-to-back Correlation
2)Saturation of Elliptic Flow v2
3)Hydrodynamic Flow of Bulk Matter
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Hard Scattering and Jet Quenching
back-to-back jets disappear
leading particle suppressed
Hard Scattering in p+p Parton Energy Loss in A+A
Reduction of high pT particlesDisappearance of back-to-back high pT particle correlations
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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
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Geometry of Nucleus-Nucleus Collisions
Number of Participants
Impact Parameter
Npart – No of participant nucleonsNbinary – No of binary nucleon-nucleon collisions cannot be directly measured at RHIC estimated from Woods-Saxon geometry
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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 --
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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 !
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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
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Saturation of Elliptic Flow v2
v2 saturation related to geometry of the emission sourcev2 non-zero at pT 5-6 GeV/c particle production source
not transparent to moderate pT particles
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Hydrodynamics Works at RHIC
Nucl-ex/0303001
Ideal hydrodynamic fluid the mean free path of the constituent partons ~ zero ! How?
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High Density Matter at RHIC
Experimental Evidences for High Density Matter:
1) High pT Suppression in Central Au+Au andDisappearance of back-to-back Correlations
2) Elliptic Flow v2 Saturation at Intermediate pT
3) Hydrodynamic Limit for Bulk Particle Production
Why not QGP yet?1) not directly sensitive to deconfinement 2-3) not consistent with parton transport picture, failed to describe the space-time correlation (HBT) hadronization scheme dependent
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Initial Energy Density EstimatePRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03)
PHOBOS
hminus:Central Au+Au <pT>=0.508GeV/cpp: 0.390GeV/c
Pseudo-rapidityWithin ||<0.5 the total transverse momentum created is 1.5x650x0.508 ~ 500 GeV from an initial transverse overlap area of R2 ~ 153 fm2 !
Energy density ~ 5-30 0 at early time =0.2-1 fm/c !
19.6 GeV
130 GeV200 GeV
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Strange and Heavy Quarks at RHIC
Strangeness Equilibration ?
Hadronization Scheme, in particular, for dense partonic matter ?
Signature for a deconfined matter?
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Particle Spectra
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Strange Baryon Production from Au+Au 200 GeV
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Strangeness Equilibration?
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Nuclear Modification Factors
Very distinct meson versus baryon dependence !PT scale for fragmentation ~ 5 GeV/c or above !
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Particle Dependence of v2
STAR
PHENIX
Baryon
Meson
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Salient Features at Inermediate pT
1)Why so many baryons versus mesons?
2)Why does elliptic v2 versus pT saturate ?
3)Why Rcp and v2 in two groups: Baryon and Meson ?
4)Why strange quark similar to light u/d quarks ?
Hadronization from bulk partonic matter – Constituent quark degrees of freedom Recombination/Coalescence scheme for hadron formation Surface emission
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Constituent Quark Degree of Freedom
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, Rafelski+Danos, Molnar+Voloshin …..)
Quark Recombination – (R.J. Fries et al, R. Hwa et al)
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Quark Cluster Formation from Strongly Interacting Partonic Matter
Volcanic mediate pT – Spatter (clumps)
Strangeness enhancement from QGP is most prominent in the region where particle formation from quark coalescence is dominant !
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Multi-Parton Dynamics for Bulk Matter Hadronization
Essential difference:Traditional fragmentation particle properties mostly determined by the leading quark !Emerging picture from RHIC data (RAA/RCP and v2) all
constituent quarks are almost equally important in determining particle properties !
v2 of hadron comes from v2 of all constituent quarks !
Are constituent quarks the effective degrees of freedom for bulk partonic matter hadronization ? How do we establish signatures for multi-parton dynamics, recombination model for example, where thermal constituent quarks or shower partons from jet production are both possible ?
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pT Scales and Physical Processes
RCPThree PT Regions:
-- Fragmentation
-- multi-parton dynamics (recombination or coalescence or …)
-- Hydrodynamics (constituent quarks ? parton dynamics from gluons to constituent quarks? )
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Future Perspectives
1) Quantitative Energy Loss of light/heavy Quarks
2) Where does the Energy Loss Go?
3) Strange and Charm Quark Dynamics from Bulk Matter
4) Fluctuations, Phase Transition and Critical Point
5) Initial Temperature of the Partonic System andIncoming Gluon Flux
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Heavy Quark in QCD Medium
• Heavy Quark energy loss in color medium !
-- dead cone effect (less than light quarks)• Charm enhancement from high temperature
gluonic matter (Tinit > 500 MeV)!
An Intriguing Scenario ?!
PT
RAA
1.0
Light hadrons
Open Charm
(pT scale)
Require direct open charm measurement !
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Energy Loss and Soft Particle Production
Leading hadrons
Medium
STAR PRELIMINARY
Fuqiang Wang’s work
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A Critical Test for Recombination
Duke Group, PLB 587, 73 (2004)
pT Scale !!
And Strange Quark Dynamics in Bulk Matter
STAR will make a measurement of and v2 from run-4 Au+Au data !
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Recombination DS/D0
PYTHIA Prediction
Charm quark recombines with a light (u,d,s) quark from a strangeness equilibrated partonic matter DS/D0 ~ 0.4-0.5 at intermediate pT !!!
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Fragmentation vs RecombinationFragmentation Function z = phadron/pparton < 1
Recombination Scheme phadron = pparton-1 + pparton-2 … Z >= 1
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Fragmentation Functions from e+e Collisions
Belle Data
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Charm Mesons from Hadronic Collisions
Charm meson pT ~ follow the NLO charm quark pT
-- add kT kick -- harder fragmentation ( func or recombination scheme)
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kT Kick? What about kL?
The xF distribution matches the NLO charm quark xF !
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The RHIC D meson pT ~ NLO charm quark too
NLO pQCD predictions are provided by R. Vogt, hep-ph/0203151
STAR Preliminary
But NLO QCD calculation fits CDF data within a factor of 2
Recombination mechanism for D formation ?!
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B Quark Cross Section at RHIC
The bottom quark production cross section at RHIC ?
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Summary
Formation of Dense Matter
Partonic Degrees of Freedom Important Hadronization of Bulk Partonic Matter Is Recombination Scheme Necessary?
If So, the Dense Matter Must Be Deconfined
Is It QGP?
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Discoveries from Unexpected Areas?!
RHIC -- Frontier for bulk partonic matter formation (quark clustering and rapid hadronization) -- 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……
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The End
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Two Particle Jet-like Correlations
Jet-like two particle correlations (e.g., trigger particle 4-6 GeV/c, associated particle 2-4 GeV/c) :
These correlations cannot be easily explained in terms of recombination/coalescence scenario !
But 1) the effect of resonances on the two particle correlations has not be adequately addressed 2) trigger biases – with two high pT particles the initial parton is considerably harder than if only one high pT particle
is produced. Fragmentation region pT > 5.5 GeV/c 3) low level two particle correlations in the soft region can be
accommodated in recombination/coalescence(wave induced correlation?)
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Charm and Bulk Matter
Volcanic low pT – Bulk matter flows
Does Charm Flow?
Thermalization of partonic matter -- charm elliptic flow v2 ! -- charm hadron chemistry !
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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…..
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RHIC Heavy Quark Physics Program
RHIC Exp Program from PHENIX and STAR:Au+Au data on charm and beauty ,Charm flow, J/ and Upsilon !
Detector Upgrade: PHENIX -- VTX STAR -- TOF and microVertex Detector (MVD) !
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Charm and Beauty reflect
QCD Properties of Matter
• Initial gluon flux and initial temperature of the gluon-dominated matter
• Transition temperature from partons to hadrons
• Color degree of freedom of the matter – definement
• Heavy Quark in the forward region -- CGC
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Chemical Freeze-out Conditions
Strangeness Enhancement Resonances
STARO PHENIX
Central Au+Au data can be described by thermal statistical model with Tch = 160 +- 10 MeV and quark chemical potential ~ 8-10 MeV !
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Kinetic Freeze-out Conditions
Final flow = partonic + hadronicSome particles () have less contributions from hadronic phase
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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!
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Data from d+Au collisions
No high pT suppression ! No disappearance of back-to-back correlations!
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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 !
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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
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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 !
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Multi-Parton Dynamics
KS – two quark coalescence– three quark coalescencefrom the partonic matter surface?!
V2/n versus pT/n indicatesquark matter anisotropy !!
Hadronization Scheme for Bulk Partonic Matter:
Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Rafelski+Danos, Molnar+Voloshin …..)
Quark Recombination – (R.J. Fries et al….)
STAR+PHENIX
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STAR
PHENIX
Particle Dependence of v2
Baryon
Meson
Why saturation at intermediate pT ?Why baryon and meson difference ?
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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
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Strangeness from Bulk Partonic Matter
Strangeness enhancement is most prominent at intermediate pT from quark coalescence in an equilibrated bulk matter !
RCP
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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.
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= 0 0.5 Infinite
Nuclear Collision Evolution Epoches
Chemical Freeze-out --- formation of hadrons
Kinetic Freeze-out --- Interaction ceases
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Dynamics between chemical and kinetic freeze-out
Torrieri and Rafelski Phys. Lett. B509 (2001) 23.
Particles form at the chemical freeze-out
Resonances decay and daughters rescatter and disappear.
Sensitive to time span between particle formation and kinetic freeze-out.
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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
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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/ ..........
KK
STAR Preliminary
KDD 00 KD
STAR Preliminary
STAR Preliminary
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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
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The UCLA Group
Faculty: Huan Zhong Huang and Charles WhittenStaff: Stephen Trentalange and Vahe GhazikhanianResearch Associate: Oleg Tsai and An TaiPost-doc: Joanna Kiryluk and Hui LongGraduate Students: Jeff Wood, Dylan Thein, Steve Guertin, Jingguo Ma, Johan Gonzalez,
Weijiang Dong and Hai JiangRecent Ph.D. Graduates on STAR physics:
Eugene Yamamoto (2001)Hui Long (2002)Yu Chen (2003)Paul Sorensen (2003)
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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>
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RHIC Spin Physics
At 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
Essential to measure photons, electrons and jets ! Electromagnetic Calorimeter: Lead/Plastic Scintillator sandwich, Shower Max Detector for electron/hadron
separation.Major Detector Construction at Wayne State
University and UCLA
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Salient Feature of Strong Interaction
Asymptotic Freedom: Quark Confinement:
庄子天下篇 ~ 300 B.C. 一尺之棰，日取其半，万世不竭
Take half from a foot long stick each day,You will never exhaust it in million years.
QCD q q
q qq q
Quark pairs can be produced from vacuumNo free quark can be observedMomentum Transfer
Co
up
lin
g S
tren
gth
Shorter distance
(GeV)
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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 !
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Building Blocks of Hadron World
Proton Neutron
(uud) (udd)
Mesons
(q-q)
Exotics
(qqqq-q,…)
Molecules
Atoms
Electrons
Strong interaction is due to color charges and mediated by gluons. Gluons carry color charges too.
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
Nucleus
Hyperons
(s…)
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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…..
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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
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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
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A Magnificent Collision in the Universe
Collision of two galaxies: the Antennae; Hubble Space Telescope