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
Jan 9, 2008 @IHEP
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Outline
• Formation of Dense Partonic Matter
• High pT and Heavy Quark Measurements
• Hadronization of Bulk Partonic Matter
• Searches for Exotic Particles and
Phenomenon
• Outlook
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Au + Au Collisions at RHIC
Central Event
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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
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?
Is there a noticeable difference in experimental
phenomenon related to quarks versus gluons?
What is the flavor dependence of energy loss?
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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 Charged hadrons
from heavy quark decays
STAR
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Heavy quark energy loss: Early Expectations
Heavy quark has less dE/dx due Y. Dokshitzer & D. Kharzeev PLB 519(2001)199
to suppression of small angle dP
s C F d 2 2
k dk
dP0
gluon radiation p (k 0 )
2 2 2 2
(1 0 / 2 ) 2
2
M k
“Dead Cone” effect 0
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?10
Radiative Energy Loss not Enough
Moore & Teaney, PRC 71, 064904 (2005)
Large collisional (not radiative) interactions also
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produce large suppression and v2
Does Charm Quark Flow Too ?
Reduce Experimental Uncertainties !!
Suppression in RAA Non-zero azimuthal anisotropy 122 !
v
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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B and D contributions compatible
Bottom quarks
may suffer
considerable
energy loss
in the dense
partonic medium
too !
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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.
Many recent studies:
H. Stoecker, nucl-th/0406018.
Muller, Ruppert, nucl-th/0507043.
F. Wang (STAR), QM’04 talk, nucl-ex/0404010.
Chaudhuri, Heinz, nucl-th/0503028.
Now published: STAR, PRL 95, 152301 (2005).
Y.G. Ma, et al. nucl-th/0601012. 15
Does Heavy Quark Energy Loss
Generate Mach Cone Emission?
Trigger on non-photonic electrons from
heavy quark decays --
AWAY
AWAY
SIDE
SIDE
NEAR
SIDE
Preliminary STAR data show a broadening peak at the away side !
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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 !
The mechanism for parton energy loss is yet to
be understood !
The nature for the broad peak on the away-side
requires more studies !
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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 18
Elliptic Flow Parameter v2
coordinate-space-anisotropy momentum-space-anisotropy
y
x
Initial/final conditions, dof, EOS
dN 1 dN
1 2v icos(i( ψR ))
p t dp t dyd 2π p t dp t dy i1 19
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
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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 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 ? 40
Spin Physics Program
The Spin Structure of the Proton:
½ = ½ SDq + DG +
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 and how to measure
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