What Happened in China ?
Dec 21, 2015
What Happened in China ?
Gluons can begin to fuse with high enough gluon density. Saturation will limit parton production
Final state charged particle yields per collision limited?
Gluon Saturation?
Gluon Saturation does not appear to set in for peripheral collisions Cannot yet rule out Eskola’s saturation for central collisions Kharzeev’s initial-state saturation picture is consistent with data
Eskola, Kajantie, and Tuominen: hep-ph/0009246Kharzeev, Nandi: nucl-th/0012025
r/gggPhys. Rev. Lett. 86, 3500 (2001)
Energy density
02j
TB
dE
R
1
c dy
1
Bjorken formula for energy density in terms of measured transverse energy assuming a thermalized system at time
PHENIX: Central Au-Au yields
6.88 fm(hard sphere radius)
Time to thermalize the system (~ 1.0 - 0.2 fm/c?)
Phys. Rev. Lett. 87, 52301 (2001)
2%
26T39
y 0
dE578 GeV 1.19 0.01
dy
Is the energy density high enough?The PHENIX EMCal measures transverse energy
For the most central events:Bjorken~ 4.6-23 GeV/fm3
critical~ 0.6-1.8 GeV/fm3
Lattice phase transition:
Energy deposition is certainly adequate, but does it create a thermalized new phase of matter while crit?
Roughly 1.5 to 2 times higher than previous experiments if assume same formation time
Latticec
Bj~ 4.6 GeV/fm3
J. Nagle
Bj~ 23.0 GeV/fm3
thermalization time?
Comparison with pp baselineCentral
Peripheral
Peripheral
consistent with NN scaled by number of collisions
Central
below scaled NN spectrum
larger deficit than unidentified hadrons
Scaled NN
ratio’s with pp and peripheralcentral binary central
AApp
/Yield NR
Yield
central binary central
peripheral binary peripheral
/
/
Yield N
Yield N
h
h
AAR
Cen
tral
/per
iph
eral
PT PT
00
Complications• “Ordinary” Nuclear effects:
Cronin Effect and PT broadening Nuclear shadowing of gluon structure functions
Issues:Does the parton fragment inside the medium?Particle composition is a strong function of pT
Other unknown effects?
q
q
Year-1 High PT ConclusionsCentral collision data shows significant suppression relative to prediction without energy loss.
Indicates a novel effect: Indicates a novel effect: deviation from point like deviation from point like scalingscaling
It is consistent with parton energy loss , but too early to make definitive conclusion.A systematic study including pA and higher PT reach is needed. Stay tuned …
“Other” Year-1 PHENIX results
HBT
Electrons
Gamma Distribution Calculation
Centrality:
0-5%
PHENIX Preliminary
<Pt> (GeV/c)
Fluctuations
5.9 0.47.9 1.1 6.2 .5
= 0.49 .07
Elliptic Flow
PHENIX PreliminaryPHENIX Preliminary
BRAHMS acceptance 00 & 01
FFS
BFS
• N=dE /<dE>• P(0)/P(n1)• Background corr.due to
secondaries (37-50%)• Consistency between 4
independent. detector systems
• 65 AGeV+65 AGeV: N(ch)d= 4050±300• Central 0-5% dN(ch)/d (=0) =550• FWHM of distribution
= 7.6 0.7
0-5%
10-20%
20-30%
30-40%
40-50%
5-10%
600
BRAHMS Subm. Phys. Lett. B 7/2001.
Charged Particle Mult. at 130 GeV
BRAHMS. Subm. Phys Lett. B. 2001
SPS
dNch/d for100 AGeV+ 100 AGeV
• 100 AGeV + 100 AGeV AU+AU
N(ch)d= 5100±300• Central 0-6% dN(ch)/d (=0) =61050• FWHM of distribution = 7.9 1.0
BRAHMS 200AGEV
Hard and Soft vs.High Density QCD @ 200 AGeV
• Kharzeev and Levin (nucl-th/0108006)
• Soft-Hard:
dN/d=(1-X) npp <Npart>/2
+ X npp <Ncoll>
<Ncoll>=1049, <Npart>=339, npp=2.43 =>dN/d=668 (with X=0.9)
• High Density QCD-saturation:
dN/dy =
f( Npart, Qs2, ,QCD,s,y)
with =0.3 from HERA data
=> dN/d=620
(using dN/d=549 at s=130GeV)
(
(
(
)
)
)
Total production of charged particles
• 130 AGeV• 4000 charged part. observed• Nch 23.5 pr. part. pair• cf. Nch 17 in p+p at s=130GeV
• 35-40% increase over p+p
Syst
BRAHMS
200 AGeV
200 AGeV 5100 charged part.
observed Nch 30 pr. part. pair cf. Nch 20 in p+p at
s=200GeV 50% increase over p+p
Bjorken limit reached for Au+Au s= 130AGeV?
ISR R803
s=23
s=63
BRAHMS
PRL sept. 2001
p-bar/p ratio:Centrality dependence
BRAHMS 2k
How consistent are the models?
Summary
RESULTS: 100+100
• Nch (0-5%) 5100
• dN/d (y=0) 625. FWHM 7.8
• N(ch) 30 pr. participant-pair
• dN/d (y=0) 3.6 pr. part. Pair
• p-pbar/p 0.48±0.05 (y=2)
0.99±0.01(stat) (y=3)
RESULTS: 65+65• Nch (0-5%) 4000• dN/d (y=0) 550. FWHM 7.6• N(ch) 23 pr. participant-pair• dN/d (y=0) 3 pr. part. Pair
• AntiMeson/Meson close to unity
• p-bar/ p vs y shows increased but still incomplete transparency
• Midrapidity Plateau?• y =0,0.7,2 : pbar/p 0.64, 0.66, 0.41
(±0.05 ± 0.06)• Weak pt and centrality dependence• Bjorken limit not reached• Models inconsistent with data
Energy Dependence at =0Errors are dominated by systematics
AGS/SPS points extracted by measured dN/dy and <mT>
New data at 200 GeV shows a continuous logarithmic rise at midrapidity
fpp(s) =
Ratio of dN/d at 200 & 130 GeV 90% Confidence Level
Pseudo-rapidity Distributions• Using Octagon and Ring
subdetectors• Measure out to ||<5.4• Corrections
– Acceptance– Occupancy– Backgrounds (from MC)
• Systematic errors– 10% near =0– Higher near rings
Back
grou
nd C
orr.
HIJING Simulation
PRL 87 (2001) forthcoming
Centrality Dependence vs.
• Total charged multiplicity is about 4200 ± 420 for central events
• At high 3-4 multiplicity starts to decrease as a function of Npart
• Similar feature seen in pA collisions
PRL 87 (2001) forthcoming
Comparison to pp and models
Peripheral
Central
Scaled UA5 data
HIJINGAMPT
(rescattering)
Ybeam
(Y130/Y200)dN/d = fpp(s)
PRL 87 (2001) forthcoming
DeMarzo et al, 1984
Systematic error not shown
Change in dN/d with energy
• UA5 looked for ‘limiting fragmentation’ by plotting dN/d with - Ybeam
• We can do the same thing with the PHOBOS data– agreement for AA in the fragmentation region
200 GeV
130 GeV
UA5 200 GeV(NSD)
UA5, Z.Phys.C33, 1 (1986)
Saturation model fits to 130 Data
m2=2Qsm, pT=Qs, ~.3 extracted from HERA F2 data
Kharzeev & Levin, nucl-th/0108006, input from Golec-Biernat & Wüsthoff (1999)
42/
2
2
2
222
11
ln
sinh
cosh
ys
QCD
ysy
opart
TT
es
Qy
eQe
s
scN
ypm
y
d
dN
Azimuthal Asymmetry at =0
• 130 GeV data from PHOBOS • Correct for occupancy, resolution
of reaction plane estimate• Good agreement with hydro
calcuations for central events (and STAR…)
• X = cos(ni), Y = sin(ni) n = atan(Y/X) v2 = <cos 2(2)>
• At midrapidity, using “SymOct”• Account for detector response
using “weighting matrix”.
Padsin
Pads in z
Asymmetry vs. Multiplicity
• Compare– Flow for mid-central
events – Multiplicity per participant
pair for central events (only 10% variation down to Npart=100)
• Flow (for more peripheral events) seems to scale with particle density
• 200 GeV data should be interesting!– Saturation or scaling?
PRELIMINARY
Asymmetry vs. Rapidity
Systematic Error ~ .007
Preliminary Results – final results coming soon!
dy dp p
dN
p m
p
d dp p
dN
T T T
T
T T2 2
) cosh (
cosh
P. Kolb, Utah proc.
Results on particle ratios
• Measured near midrapidity – 0 < y <1 (species-dependent)
• Final results submitted to PRL (Apr. 2001)
• Consistent within systematic errors with results presented at QM2001 (Jan. 2001)
• Smaller systematic errors (10% 6%)
.)(06.0.)(04.060.0
.)(06.0.)(07.091.0
.)(02.0.)(01.000.1
syststat
syststat
syststat
p
p
K
K
Conclusions
• Systematics of charged particle production have been explored by the PHOBOS experiment– Energy – multiplicity rises approximately logarithmically– Centrality – data shows simple interpolation between pp and central AA– Rapidity – scaling with Npart changes in fragmentation region – Azimuthal – elliptic flow appears to scale with multiplicity– Particle ratios are reaching zero net baryon number, small B
• Broad features of particle production are consistent with soft nature of strong interactions– pp and pA collisions are very instructive
• Theoretical models are assimilating new data– None simultaneously describe full set of systematics!
Energy dependence of v2
Logarithmic rise
Statistical models• Braun-Munzinger et al. (hep-ph/0106066)
- Follows curve for <E>/<N> = 1 GeV at freezeout
- Usesphenomenologicalparameterization:
B(s)1.27 GeV
(1 s /(4.3 GeV)) J. Cleymans & K. Redlich,PRL 81 (1998) 5284
Strangeness production
Lines of constant S where:
<E>/<N> = 1 GeV
I. Increase instrange/non-strangeparticle ratios
II. Maximum isreached
III. Ratios decrease(Strange baryonsaffected more stronglythan strange mesons)Braun-Munzinger et al.
hep-ph/0106066
Implications for ratios
s (GeV)
(PRELIMINARY)
STAR 130 GeV14% central (
(PRELIMINARY)
STAR 130 GeV14% central (
(*0.2)
Braun-Munzinger et al.hep-ph/0106066
Mid-rapidity ratios
Sensitivity to multi-strange baryons
T (MeV)
Rat
ios
Braun-Munzinger et al.hep-ph/0105229
Thermal fit resultsin T = 174 MeV
Model getsK/ correct,but misseson ratios!!!
Statistical errors only
+/h-
(Preliminary)
STAR 130 GeV14% central data
-/K- (7% central)
Stat. model 200 GeV predictions
Becattini et al.PRC 64 (2001) 024901
B(s) 1.27 GeV(1 s /(4.3 GeV))
s (GeV) B(MeV)
130 40.7
200 26.7
Use parameterization:
Predicts~0.8
(Preliminary)
STAR 130 GeV minbias data
(CAUTION! Really for 4 ratios)
Statistical errors only
Anti-lambda/lambda
Ratio ~ 0.76 +/- 0.02 (stat) 130 GeVRatio ~ 0.75
minbias
GeV/c2
-> p -
GeV/c2
-> p +
Preliminary STAR200 GeV minbias data
Uncorrected for absorption,which may be as much as afew percent effect.
Ratios at midrapidity, averaged over experimental acceptance in pt
Stat. Model Predictions Revisited
Becattini et al.PRC 64 (2001) 024901
B(s) 1.27 GeV(1 s /(4.3 GeV))
s (GeV) B(MeV)
130 40.7
200 26.7
Use parameterization:
(Preliminary)
STAR 130 GeV Data
(CAUTION! Really for 4 ratios) Pretty close to prediction!
(Preliminary)
STAR 200 GeV minbias data
Statistical errors only
Conclusions• Statistical model fits do well with most
particle/antiparticle ratios. • Statistical model fits do not reproduce /meson
ratios very well.– It will be interesting to see how fits in the picture.
• Quark coalescence model roughly reproduces particle ratios well.– Losing sensitivity to particle/antiparticle ratios as we
approach B=0.
• We are still not in a net baryon free region atsqrt(sNN) = 200 GeV - and perhaps still a long ways away?