Transcript Search for a new state of matter – the Quark

Evidence for Multi-parton Dynamics in
Hadronization of Bulk Partonic Matter at RHIC
Huan Zhong Huang (黄焕中)
Department of Physics and Astronomy
University of California Los Angeles
Department of Engineering Physics
Tsinghua University
7th Annual Conference of Chinese High
Energy Physics Society
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Outline
• Relativistic Heavy Ion Collider (RHIC) and
Quark-Gluon Plasma (QGP)
• Fragmentation Scheme
• Hadronization of Bulk Partonic Matter
• Recent Results of High pT Probes
• Outlook
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Relativistic Heavy Ion Collider --- RHIC
STAR
Au+Au 200 GeV N-N CM energy
Polarized p+p up to 500 GeV CM energy
3
Quark-Hadron Phase Transition
4
Au + Au Collisions at RHIC
Central Event
5
STAR
(real-time Level 3)
Nucleus-Nucleus Collisions and Volcanic Eruption
Volcanic high pT -- Strombolian eruption
Volcanic mediate pT – Spatter (clumps)
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Volcanic low pT – Bulk matter flows
The Field & Feynman picture of cascade fragmentation
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Kretzer@ISMD04
Baryon Production from pQCD
e+e-jet fragmentation from SLD
p
p
K
p
K
p
Normal Fragmentation Cannot Produce the Large Baryon Yield 8
Too Many Baryons at Intermediate pT
9
Elliptic Flow Parameter v2
coordinate-space-anisotropy

momentum-space-anisotropy
y
x
Initial/final conditions, dof, EOS
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Elliptic Flow: ultra-cold Fermi-Gas
• Li-atoms released from an optical trap exhibit
elliptic flow analogous to what is observed in ultrarelativistic heavy-ion collisions
 Elliptic flow is a general feature of strongly
interacting systems!
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Elliptic Flow v2
PRL 92 (2004) 052302; PRL 91 (2003) 182301
Hydro calculations
break-down at higher
pT (as expected).
How is v2 established
at pT above 2 GeV/c?
Why is baryon v2
larger than meson
v2?
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Constituent Quark Degree of Freedom
Hadronization Scheme for
Bulk Partonic Matter:
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 !
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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Constituent Quark Scaling
Constituent (n) Quark Scaling
-- Meson n=2 and Baryon n=3 grouping
Some deviation due to internal hadron structure
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Nuclear Modification Factor
N-binary Scaling 
RAA or RCP = 1
simple superposition of
independent N-N collisions !
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Strangeness from Bulk Partonic Matter
RCP

X
W
f
Constituent Quark Number Scaling
-- Hadronization through quark clustering
-- Effective DOF – constituent quarks
quasi-hadrons at Tc ?
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Lattice QCD picture?
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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pT Scales and Physical Processes
RCP
Three PT Regions:
-- Fragmentation
-- multi-parton dynamics
(recombination or
coalescence or …)
-- Hydrodynamics
(constituent quarks ?
parton dynamics
from gluons to
constituent quarks? )
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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 !
The fact that in order to explain the v2 of hadrons
individual constituent quarks (n=2-meson,3-baryon) must
have a collective elliptic flow v2 and the hadron v2 is the
sum of quark v2  Strong Evidence for Deconfiement !
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Recombination+Fragmentation Model
basic assumptions:
• at low pt, the quarks and antiquark spectrum is thermal and they
recombine into hadrons locally “at an instant”:
qq  M
qqq  B
 features of the parton spectrum are shifted to higher pt in the
hadron spectrum
• at high pt, the parton spectrum is given by a pQCD power law,
partons suffer jet energy loss and hadrons are formed via
fragmentation of quarks and gluons
• shape of parton spectrum
determines if recombination is more
effective than fragmentation
• baryons are shifted to higher pt
than mesons, for same quark
distribution
 understand behavior of baryons!20
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 !
Is the energy loss due to parton or hadron stage?
Is there a noticeable difference in experimental
phenomenon related to quarks versus gluons?
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The Suppression is the Same for p0
and h – parton level effect
No suppression for direct photons – photons do not participant !
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No Significant Difference Between
Quarks and Gluons at High pT
Baryons more likely from gluon fragmentations in the pQCD region
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No Significant Difference Between
Heavy Quark Meson and Light Quark Mesons
Non-photonic electrons
from heavy quark decays
Charged hadrons
STAR
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Heavy quark energy loss: Early Expectations
Heavy quark has less dE/dx due
to suppression of small angle
gluon radiation
“Dead Cone” effect
Y. Dokshitzer & D. Kharzeev PLB 519(2001)199
M. Djordjevic, et. al. PRL 94(2005)112301
J. Adams et. al, PRL 91(2003)072304
Radiative energy loss of heavy
quarks and light quarks
--- Probe the medium property !
What went wrong?25
B and D contributions to electrons
Experimental
measurement of
B and D
contributions to
non-photonic
electrons !
Direct measurement
of D and B mesons
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Poor (Wo)Man’s Approach to Measure B/D
Contributions to Electrons – e-h correlations
PYTHIA Simulations of e-h correlations from p+p
B
D
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X. Lin hep-ph/0602067
STAR preliminary data motivated sonic-boom prediction
pTtrig=4-6 GeV/c, pTassoc=0.15-4 GeV/c
Casalderrey-Solana, Shuryak, Teaney,
hep-ph/0411315
Actually sonic-boom was first predicted
in the 70’s by the Frankfurt school.
F. Wang (STAR), QM’04 talk, nucl-ex/0404010.
Now published: STAR, PRL 95, 152301 (2005).
Many recent studies:
H. Stoecker, nucl-th/0406018.
Muller, Ruppert, nucl-th/0507043.
Chaudhuri, Heinz, nucl-th/0503028.
Y.G. Ma, et al. nucl-th/0601012. 28
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 !
The mechanism for parton energy loss is yet to
be understood !
The nature for the broad peak on the away-side
requires more studies (Mach cone or not) !
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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-baryons
H – (-, uuddss)
[W-W] (ssssss)
strange quark matter
meta-stable Parity/CP odd vacuum bubbles
disoriented chiral condensate
……
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RHIC – Exotic Particle Factory
STAR – Exciting Physics Program
A full TOF upgrade will greatly enhance STAR’s capability !!
Chinese STAR Group
SINAP
Tsinghua University
USTC
CCNU, Wuhan
IMP, Lan Zhou
IHEP
Construction to be finished by 2008
Full installation in 2009
Full Barrel TOF Using MRPC
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RHIC Physics Outlook
Heavy Ion Physics:
1) Properties of high density QCD matter
2) Chiral symmetry at high temperature and density
3) Search for exotic particles/phenomena at RHIC
4) Search for critical point (low energy scan)
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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End of Talk
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Experimental Statistical and Systematic Errors
c-cbar production CS
PHENIX
0.92+-0.15+-0.54 mb
0.567+-0.057+-0.224 mb
STAR
1.4+-0.2+-0.4 mb
Errors taken seriously
High pT region does
not contribute to total
CS much. Difference
between STAR and
PHENIX has to be
resolved !!
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B does not seem dominant at pT 4.5 GeV/c
Preliminary STAR Data
Xiaoyan Lin – STAR presentation at Hard Probe 2006
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Intriguing Situation Regarding Pentaquark States
pK+ and pK- from 18.4 M d+Au at 200 GeV
Background – Combinatorial and Correlated Pairs
D++
M (GeV/c2)
M (GeV/c2)
Statistical significance ~ 4s
Intriguing ! Not conclusive yet !
Another long d+Au run will resolve this uncertainty !
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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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Radiative Energy Loss not Enough
Moore & Teaney, PRC 71, 064904 (2005)
Large collisional (not radiative) interactions also
produce large suppression and v2
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Charm Quark in Dynamical Model (AMPT)
Large scattering cross sections needed !
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Nuclear Modification Factor RAA RCP
RCP
[yield/N-N]central
RCP=
[yield/N-N]peripheral
Multi-parton dynamics predict
baryon yield increases with
centrality FASTER than
mesons!
Yield ~ rn and n>nK 
a feature not present in single
parton fragmentation !
Multi-parton dynamics:
coalescence,
recombination and
gluon junctions.
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Particle Dependence of v2
STAR
Baryon
Meson
PHENIX
Why saturation at intermediate pT ?
Why baryon and meson difference ?
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Spin Physics Program
The Spin Structure of the Proton:
½ = ½ SDq + DG + <L>
q  up, down and strange quarks
G  gluons
L  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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