Transcript Search for a new state of matter – the Quark

Recent Results from RHIC
Huan Zhong Huang
黄焕中
Department of Physics and Astronomy
University of California Los Angeles
Department of Engineering Physics
Tsinghua University
Mar 23, 2008 @CCAST
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Outline
• High pT and Heavy Quark Measurements
• Hadronization of Bulk Partonic Matter
• Outlook
2
Hard Scattering and Jet Quenching
leading particle suppressed
back-to-back jets disappear
Hard Scattering in p+p
Parton Energy Loss in A+A
Reduction of high pT particles
Disappearance of back-to-back high pT particle 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 !
Is the energy loss due to parton or hadron stage?
What is the flavor dependence of energy loss?
Particle emission pattern associated with E Loss?
4
The Suppression is the Same for p0
and h – parton level effect
No suppression for direct photons – photons do not participant !
5
No Significant Difference Between
Heavy Quark Meson and Light Quark Mesons
Non-photonic electrons
from heavy quark decays
Charged hadrons
STAR
6
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
dP 
 sCF d
k2 dk2
dP0

2
2 2 2
p
 (k    0 )
(1   02 /  2 ) 2
0 
M
k
,  
E

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? 7
Radiative Energy Loss not Enough
Moore & Teaney, PRC 71, 064904 (2005)
Large collisional (not radiative) interactions also
produce large suppression and v2
8
Does Charm Quark Flow Too ?
Reduce Experimental Uncertainties !!
Suppression in RAA  Non-zero azimuthal anisotropy v92 !
B and D contributions compatible
Bottom quarks
may suffer
considerable
energy loss
in the dense
partonic medium
too !
10
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. 11
Mach cone in QCD vs. N=4 SYM
r
x gz ( x)
mD2 T
r
x  ( x)
mD2 T
Energy Density
Energy Flux
u = 0.99955 c
R.B. Neufeld
(preliminary)
u = 0.75 c
Chesler & Yaffe
arXiv:0712.0050
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In order to discriminate Mach-cone from deflected jets,
one needs three-particle correlation.
0
1
near
Df2
p
2
1
Medium
away
mach cone
2
2
0
0
p
Df1
0
p
Df1
0
near
1
Df2
p
Medium
2
away 1 2
deflected jets
0
13
Conic Emission in 3-hadron Correlations
Au+Au 0-12%
Au+Au 0-12%
(Df1-Df2)/2
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Angle predictions:
• Mach-cone:
Angle independent of associated pT
• Cerenkov gluon radiation:
Angle decreases with associated pT
Cone angle (radians)
Mach cone or Cerenkov gluons?
Central Au+Au results consistent
with Mach cone emission
D12
Au+Au 0-12%
STAR Preliminary
pT
(GeV/c)
Naive calc. of time averaged
velocity of sound in medium:
cs
v parton
 cosθM  , v parton  c
Cone angle ~ 1.36 radians
cs = 0.2c ??!
(Df1-Df2)/2
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Reaction Plane Dependence
STAR
3<pTtrig<4GeV/c & 1.0<pTasso<1.5GeV/c 20-60%
Df = fassociate - ftrigger (rad)
STAR—Aogi Feng (CCNU)
At low pT region, study the medium response to jets
- Away side (medium side): single  double peaks
- Near side (jet side): amplitude reduced
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Does Heavy Quark Energy Loss
Generate Mach Cone Emission?
Gang Wang (UCLA)
Trigger on non-photonic electrons from
heavy quark decays -200 GeV Cu+Cu
AWAY
SIDE
NEAR
SIDE
Pythia result
Preliminary STAR data show a broadening peak at the away side !
17
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 !
There is a conic emission of particles when
partons lose energy in medium, but the nature
of the conic emission yet to be determined! 18
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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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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Strangeness from Bulk Partonic Matter
RCP

X
Constituent Quark Number Scaling
-- Hadronization through quark clustering
W
-- Effective DOF – constituent quarks
quasi-hadrons at Tc ?
Lattice QCD picture?
fss
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Jinhui Chen et al (SINAP)
W and f production from coalescence
STAR
Preliminary
Au+Au@200GeV
At intermediate pT W (sss) and f
(ss) should be dominated by
bulk thermal quark
coalescence – no jet
contribution
(Hwa and Yang PRC 75, 054904 (2007))
Cu+Cu@200Gev
It appears that thermal quark
coalescences dominate the
particle production below pT
4 GeV/c, for both central
Au+Au and Cu+Cu collisions
pT (GeV/c) Xiaobin Wang (Tsinghua U.) -- W
Jinhui Chen (SINAP) -- f
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Parton PT Distributions at Hadronization
If baryons of pT are mostly formed from
coalescence of partons at pT/3 and
mesons of pT are mostly formed from
coalescence of partons at pT/2
W( pT / 3)
s
f ( pT / 2)
X( pT / 3)
d
f ( pT / 2)
W and f particles have no decay feeddown contribution !
X decay contribution is small
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These particles have small hadronic rescattering cross sections
Strange and down quark distributions
s distribution harder
than d distribution
perhaps related to
higher s quark mass
in partonic evolution
Independent Test –
f/s should be consistent
with s quark distribution
Yes !
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Jinhui Chen et al (SINAP/UCLA)
Test on s/d Quark Ratios
s/d quark ratios
= W/X
= X/
yes! but with large
uncertainties due
to decay feeddown
corrections in 
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Debye Screening of Color Charge
-- quarkonium melting in QGP
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/y.
c
c
Charm quarks c-c may not bind
Into J/y in high T QCD medium
The J/y yield may be increased due to charm quark coalescence at
the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050)
J/y, y’ and cc will melt in high temperature Quark-Gluon Plasma !
The melting temperatures for y’ and cc are lower !
J/y may not melt until the temperature is higher than 2Tc ?! 26
J/y is suppressed, but
the physical mechanism is not clear !
The suppression
at forward
rapidity seems
to be larger than
at mid-rapidity !
Note parton
density should
be higher at
mid-rapidity.
The pT, rapidity and Npart dependence of
J/y production cannot be explained yet!
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Suppression + Regeneration
Zhuang, Pengfei et al, Phys. Rev. Lett. 97:232301,2006
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J/y non-suppression at high pT
Two Component Approach: X. Zhao and R. Rapp, hep-ph/07122407
Zebo Tang (USTC)
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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 !
---- Evidence for Deconfinement !!!
Hadronization of bulk partonic matter -different phenomenon from e+e- collisions !
J/y suppression and regeneration –
More accurate experimental data and elliptic flow of J/y !
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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
FY2008 Run – d+Au until mid-Feb
4 weeks of p+p
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End of Talk
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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
Elliptic Flow Parameter v2
coordinate-space-anisotropy

momentum-space-anisotropy
y
x
Initial/final conditions, dof, EOS
dN
1
dN 


1  2vicos(i(  ψR ))

pt dpt dyd 2π pt dpt dy  i1
 35
Constituent Quark Scaling
STAR
Baryon
Meson
PHENIX
Constituent (n) Quark Scaling
-- Meson n=2 and Baryon n=3 grouping
Saturation of v2 at Intermediate pT
36
No Significant Difference Between
Quarks and Gluons at High pT
Baryons more likely from gluon fragmentations in the pQCD region
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Charm Quark in Dynamical Model (AMPT)
Large scattering cross sections needed !
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s and d quark distributions physical
AMPT model using
string-melting
and coalescence
can fit v2
but fails pT spec
Using our s-d quark
distribution AMPT
can fit pT spec
-- Early evolution
important in
determining quark
distributions!
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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.
40
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>
42
B and D contributions to electrons
Experimental
measurement of
B and D
contributions to
non-photonic
electrons !
Direct measurement
of D and B mesons
43