Transcript PPT

Overview of Experimental results
from RHIC
Y. Akiba (RIKEN Nishina Center)
ATHIC08
Tsukuba
October 13, 2008
QCD Phase Transition
• The colliding nuclei at RHIC energies would melt from protons and
neutrons into a collection of quarks and gluons
• A QCD phase transition that the universe last went through ~1ms after
the Big Bang
SB (T) 
2
30
(N bosons  7 /8 N fermions)T 4

Tc ~ 170 MeV;  ~ 1 GeV/fm3
This is the only phase transition that occurred in the early universe that can be
recreated in the lab
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The RHIC Experiments
RHIC
Approx 500 tracks result
from a Au+Au ion collision
RHIC runs (2001-2008)
Beam species:
p+p (polaized)
d+Au
Cu+Cu
Au+Au
Energy:
sNN1/2=200 GeV
Also @ 130 GeV
62 GeV
56 GeV
22 GeV
(10 GeV)
130 GeV
200 GeV
RHIC’s Two Major Discoveries
STAR PRL86,402 (2001)
Strong Elliptic flow
Agree with ideal hydrodynamics
Low viscosity/entropy (h/s)
PHENIX PRL88,022301(2002)
High pT suppression
Energy loss of quark/gluon
Very dense matter
Based on these two major discoveries and other evidence, RHIC
experiments concluded that that state of dense partonic matter is
formed in A+A collisions at RHIC
Highlights from more recent RHIC results
• Scaling of v2
• Suppression at higher pT (up to 20 GeV/c)
– Constraining model parameter from RAA
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Modification of jet-correlations
J/y suppression
Heavy quark suppression and flow
Dileptons and photons
Topics I don’t discuss due to time limitation
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Low pT hadron spectra
Hadron ratios and thermal model
Enhanced (anti-)baryons
multi-strange baryons
v1
• v2/v4 scaling
• c/b  m
• g-jet correlation
• HBT and source imaging
• And more…
Elliptic flow
v2
Scaling of v2 of hadrons
PRL98,162301(2007)
• More data on v2(pT) of hadrons are accumulated
• When v2/nq vs KET/nq (KET=transverse kinetic enery), all data points
are on a universal curve, suggesting that v2 developed in partonic stage
More on the scaling of v2: phi flow
PRL99, 052301 (2007)
Phi meson (small interaction cross section) also follows
the number of quark (nq) scaling.
v2 of Direct photon and J/y e+eDirect g v2 Min Bias Au+Au 200
GeV (Run 4)
PHENIX preliminary
Sign of direct g v2 (at high pT):
– Positive == parton emission quenched
– Negative == parton emission (Brems.)
enhanced
At high pT, photon v2 is consistent with zero
First ever at RHIC,
v2 - J/µ+µ- coming soon
J/Psi coalescence ?
High p T suppression
RAA
π0 pT spectra at √sNN = 200 GeV
RUN4 Au+Au arXiv:0801.4020 [nucl-ex]
RUN2 Au+Au PRL91,072301
RAA measurements now extends to 20 GeV/c
RAA of hadrons and direct photon (AuAu 200GeV)
A factor of ~5
suppression to
~20 GeV !
• A factor of ~5 suppression of 0 to ~20 GeV/c
• Ncoll scaling for direct g
• Same suppression pattern for 0 and h:
Consistent with parton energy loss and fragmentation in the vacuum
• Smaller suppression for the f meson for 2<pT<5 GeV/c
Quantitative analysis: contrain density parameters
Comparison with GRV model: dNg/dy=1400
PRC77,064907
RAA beam energy dependence (Cu+Cu)
 Cu+Cu 22,62,200 GeV (Run 5)
arXiv:0801.4555
Accepted in PRL
g
• Model calculations indicate quenching expected at sNN = 22 GeV,
but Cronin effect dominates
• Species dependence to probe space/time of suppression
Di-jet correlations
Dijet correlation
Recoil jet
Trigger
Back-to-back peak
due to di-jets is seen
in two particle correlation
Reconstruction of jets is
difficult in A+A @ RHIC
In central Au+Au collisions,
the peak in the far side
(Df ~ ) is suppressed,
consistent with energy loss
of the recoil jet.
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Modification of jet correlation
PRL97,052301 (2006)
Au+Au
• This is another big
surprise: two particle
of two high pT track
(jet correlation) is
modified in central
Au+Au collisions.
• Many theory attempts
to explain this effect
Origin of the modification of jets?
• An interesting interpretation of the modification is that it is Mach cone in the medium
• Scattered parton travels faster than the speed of sound in the medium, causing a shock-wave
• If this is the case, the opening angle can be related to the speed of sound in the medium…
More detailed study of jet correlation
D
m n  ( D   ) n
rms 
m2
kurtosis  m 4 / m 22
J (D ) 
G (D ) G (D    D)
G (D    D)
PRL98_232302
Reaction plane dependence of di-jet correlation
Shortest path length
longest path length
• Shape of the near-side peak is unchanged
• Far-side shape strongly depends on the angle from the reaction plane
o Stronger modification for longer pathlength in the dense matter
Conical emission?
Df*=

Dq*=

PHENIX Preliminary
Consistent with conical emission;
STAR, 0805.0622
3-particle correlation analysis shows that the
data is consistent with conical emission
More surprize: the Ridge?
Trigger Jet
STAR QM2006
Ridge
Bulk Medium
In QM2006, STAR shows that there is “Ridge”,
Enhancement in small Df and large Dh of leading particle
This is the latest surprise in jet correlation in Au+Au and becomes a hot topics
Is there “Ridge”? Apparently…
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In QM2008, both
PHENIX and PHOBOS
shows that they also
see “Ridge”
So far there is no
consensus on the origin
of this effect.
It is difficult to imagine
that information can
propagate for a wide
rapidity gap.
My Speculation:
Effect can be due to
non-linear correlation
between jets and v2?
Screening by the QGP
(An explicit test of deconfinement)
r -->
V(r)
V(r)
r -->
QCD potential at
T=0
QCD potential at
high T and
high density
Non-perturbative Vacuum
c
c
Perturbative Vacuum
If QGP is formed,
J/yproduction is
suppressed
c
c
Color Screening
In normal vacuum,
J/yparticle is formed
In QGP, J/yis destroyed
by color screening
J/y suppression in Au+Au
PRL98_172301
• High statistics measurement of
J/y in AuAu in wide rapidity
range
– Mid-rapidty J/y  ee
– Forward rapidty J/ymm
• Strong suppression of J/y is
observed
– Consistent with the prediction
that J/ys are destroyed in deconfined matter
• Surprisingly, the suppression is
stronger at forward rapidity than
in mid-rapidity
– J/y formation by recombination
of charm pairs in deconfined
matter?
• But…we need to look the
cold nuclear matter effect
J/y in d+Au: Cold Nuclear Matter effect
J/y RdAu 200 GeV
PRC77_024912
• Nuclear suppression factor RdAu of
J/y in d+Au is measured and
compared with models of CNM
• Result:
CNM = Shadowing(EKS)+Breakup
Breakup = 2.8 +1.7
-1.4 mb
• This is consistent with the J/y break
up cross section at lower energy
Breakup=4.2+/-0.5mb
• If Breakup is obtained separately in
forward and central region, larger
value is prefered in forward
As SQM participants are aware of it, PHENIX is revisiting
the systematic error in the break-up cross section.
J/y RAA Cu+Cu and Au+Au
J/y RAA 200 GeV
PRL101,12301(2008)
• Approx 2x more J/y in Cu+Cu sample
than Au+Au sample
– More precise Npart<100 info
• Curves show RAA prediction from ad
hoc CNM fit to RdAu separately at y=0
and y > 1.2
• CNM from RdAu fit describes
suppression well for Npart < 50.
RdAu constraints are not sufficient to
say if suppression beyond cold nuclear
matter is stronger at forward rapidity
New Au+Au data (x4 statistics) and
d+Au data (x30 statistics) obtained in
2007 and 2008 run can determine if
the suppression really stronger beyond
CNM in forward region.
Heavy quark (charm and bottom) probe
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D, B
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c, b quark
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Study medium effect in open
charm and bottom production
Ideally, D or B meson should
be measured, but for technical
reason most of the
measurement so far is done
through electron decay
channel.
From RAA and v2 of the
electrons from heavy quark
decays, the energy loss and
the flow of heavy quarks are
indirectly measured.
So far, ce and be are not
separated
Heavy flavor production in pp (base line)
Phys. Rev. Lett 97,252002 (2006)
• Single electrons from heavy
flavor (charm/bottom) decay are
measured and compared with
pQCD theory (FONLL)
• The new data extends the pT
reach to 9 GeV/c
• FONLL pQCD calculation agree
with the data
• c e dominant in low pT
be is expected to be dominant
in high pT
Large energy loss and flow of heavy quarks
RAA of b,c e
v2 of b,c e
Strong suppression of electron from c and b
Large elliptic flow of electrons from c and b!
Large energy loss of heavy quark
Heavy quark flows in the medium
• These results require very strong interaction between the dense matter and heavy quarks.
• Since the observed electron is mixture of ce (dominant) and be, we cannot determine the
suppression or flow of be.
• Theoretical expectation is that the medium-quark interaction becomes weaker for heavier
quark. Large energy loss and/or flow of b quark would be very interesting
Heavy flavor electron RAA and flow
 Two models describes strong
suppression and large v2
 Rapp and Van Hee
 Moore and Teaney
 From model comparison,
viscosity to entropy ratio h/s
can be estimated

DHQ × 2πT = 4 - 6
DHQ ~ 6 x h/(+p) = 6 x h/Ts
h/s ~ (4/3 – 2)/4
estimate of h/s is close
to the conjectured bound
1/4from AdS/CFT
 The
PRL98,172301 (2007)
Comparison with other estimates
R. Lacey et al.: PRL 98:092301, 2007
h / s  (1.1  0.2  1.2) / 4
H.-J. Drescher et al.: arXiv:0704.3553
S. Gavin and M. Abdel-Aziz:
PRL 97:162302, 2006
pTfluctuations STAR
v2 PHENIX
& STAR
v2 PHOBOS
h / s  (1.4  2.4) / 4
Estimates of h/s based on
flow and fluctuation data
indicate small value as well
close to conjectured limit
significantly below h/s of
helium (4h/s ~ 9)
conjectured quantum limit
h / s  (1.0  3.8) / 4
Bottom Measurement
p+p 200 GeV Charm and bottom extracted via e-h mass analysis
• Charm and bottom spectra are both by a factor  above FONLL pQCD
calculations (but within the uncertainty)
• STAR studied be/ce ratios in pp and obtained similar b/c ratios
Next steps in Heavy quark measurements
Higher statistics electron v2 measurement
minimum-bias
Run-4
PRELIMINARY
Run-7
b/c separation (so far only in pp)
Preliminary results
STAR and PHENIX
Rapp & van Hees,
PRC 71, 034907 (2005)
• Does b quark also have large energy loss
and/or flow? Recent data show large v2 at
high pT where be dominates
• Silicon vertex tracker now under construction
can answer this queston by separating be
and ce in Au+Au collisions.
Electromagentic probes (photon and lepton pairs)
e+
g*
g
e-
• Photons and lepton
pairs are cleanest
probes of the dense
matter formed at RHIC
• These probes has little
interaction with the
matter so they carry
information deep inside
of the matter
PHENIX low mass dielectrons
p+p NORMALIZED TO mee<100 MeV
low mass
w
f AuAu
intermediate
mass
J/y
y’
pp
submitted to Phys. Lett.B
arXiv: 0802.0050
pp and AuAu normalized to
p0 Dalitz region (~ same #
of particles)
submitted to Phys. Rev. Lett
arXiv:0706.3034
p+p: agree with the
expected background from
hadron decays
Au+Au: large Enhancement
in 0.15-0.75 GeV/c2
PT Dependence of Au+Au Mee
0 < pT < 8 GeV/c
0.7 < pT < 1.5 GeV/c
0 < pT < 0.7 GeV/c
1.5 < pT < 8 GeV/c
PHENIX Preliminary
• Low Mass excess is
a low pT
enhancement
– Huge excess at
lowest pT
– Excess reduced for
higher pT
This suggests that
the low mass
enhancement is from
later phase of the
reaction
  ee in later
hadronic gas phase?
Thermal(?) Photons from the hot matter
thermal:
e
 Eg /T
If the dense matter formed at RHIC
Thermailzed, it should emit
“thermal radiation”.
Decay photons (background)
hard:
1
pTn
The temperature of the matter can
directly measured from the
spectrum of thermal photon.
Measurement is difficult since the
expected signal is only 1/10 of
photons from hadron decays
Enhancement of almost real photon
arXiv:0804.4168
pp
Au+Au (MB)
1 < pT < 2 GeV
2 < pT < 3 GeV
3 < pT < 4 GeV
4 < pT < 5 GeV
Low mass e+e- pairs (m<300
MeV) for 1<pT<5 GeV/c
p+p:
• Good agreement of p+p data
and hadronic decay cocktail
• Small excess in p+p at large
mee and high pT
Au+Au:
• Clear enhancement visible
above for all pT
Determination of g* fraction, r
Direct g*/inclusive g* is determined by fitting the following
function for each pT bin.
f data mee   1  r  f cocktail mee   r  f direct mee 
Reminder : fdirect is given by Eq.(1) with S = 1.
r : direct g*/inclusive g*
 the mass spectrum follows the
expected 1/m behavior of photon
internal conversion
 Determine the fraction r of the
“direct photon” component from the fit
Fraction of direct photons
Au+Au (MB)
p+p
μ = 0.5pT
μ = 1.0pT
μ = 2.0pT
• Fraction r of direct
photons
p+p:
• Consistent with
NLO pQCD
• favors small μ
Au+Au:
• Clear excess above
pQCD
NLO pQCD calculation is provided by Werner Vogelsang
Direct photon in p+p, Au+Au
arXiv:0804.4168
exp + TAA scaled pp
Fit to pp
NLO pQCD (W. Vogelsang)
• The p+p data agrees with NLO
pQCD predictions
• For Au+Au there is a significant
low pT excess above scaled p+p
expectations
• Excess is exponential in shape
with inverse slope T~ 220MeV
• Thermal photons from
hydrodynamical models with
Tinit=300 – 600MeV at
t0=0.6-0.15fm/c
are qualitative agreement with
the data (see next)
Theory comparison
• Hydrodynamical models are
compared with the data
D.d’Enterria &D.Peressounko
T=590MeV, t0=0.15fm/c
S. Rasanen et al.
T=580MeV, t0=0.17fm/c
D. K. Srivastava
T=450-600MeV, t0=0.2fm/c
S. Turbide et al.
T=370MeV, t0=0.33fm/c
J. Alam et al.
T=300MeV, t0=0.5fm/c
• Hydrodynamical models are
in qualitative agreement with
the data
Thery compilation by D. d’Enterria and D. Peressounko
EPJC46, 451 (2006)
Summary
• Huge amount of data are accumulated from RHIC in the past 8
years
• Many interesting phenomena are observed
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Strong elliptic flow of light hadrons and heavy quarks
Strong suppression of high pT jets
Modification of jet correlation
Strong suppression of J/y
Energy loss and flow of heavy quarks
Enhanced production of lepton pairs and photons
• These observations are consistent with formation of thermalized,
high temperature, high density partonic fluid