Transcript Document 7316035

Recent* Results from A+A Collisions
at RHIC
Paul Stankus, ORNL
First colliding
nuclear beams
First accelerator
designed for
high-energy
heavy ions
* Recent = July ‘02,
“Quark Matter” in
Nantes, France
Goal
To persuade (some of) you that pQCD in A+A collisions
at RHIC could be a very rich and interesting field:
Exotic initial state effects
Exotic collision effects
Exotic final state effects
Many channels, processes and probes
Dramatic data available now! with much
more to follow
Exotic (p & non-p)QCD effects
Initial State:
High density
of partons at low
and modest x;
Unusual shadowing?
“Colored Glass
Condensate”?
Collision Overlap:
Multiple scattering
of partons; large
kT smearing?
Very high density
of gluons; Classical
color fields?
Final State:
Hard-scattered
products exit
through excited
medium;
Medium Effects?
Is fragmentation
modified?
Our Original Motivation
p
p
We can measure a full
palette of hard-scattering
products:
q: fast color triplet
• To use hard scattering products
as probes to measure the
properties of dense, highly
excited QCD matter (what you
would call final-state-effects)
• We originally conceived of
hard-scattering products as
“calibrated sources” created
within HI collisions (we have
since learned better!)
Induced
gluon
radiation?
g: fast color octet
Q: slow color triplet
QQbar: slow color
singlet/octet
Energy
Loss?
Dissociation?
Virtual photon: colorless
Real photon: colorless
Unknown Medium
Controls
Jet Prelude: Why is this hard?
• Cannot look at “true”, traditional calorimetric jets; soft particle
energy density dET/dhdf ~ 100 GeV/unit-radian
• Next best thing: leading particles = high-PT hadrons, and also
high-PT pairs, either same side (leading and next-leading) or
opposite side (leading and opposite leading)
• Ambiguity between hadrons from jet fragmentation source and
hadrons from multi-collisional/”thermal” source, even out to
several GeV/c (and beyond?)
• Model “thermal” source: hadron gas with temperature,
chemical (ie flavor) equilibration, baryon density and overall
flow velocity in radial direction
Thermal Model can fit hadron spectra out to at
least 4 GeV/c -- do you believe it?
T.P., nucl-th/
0207012
• spectra of pions and
(anti)protons
• description by
hydrodynamical source
– perfect description possible
Tch = 172 ± 2 MeV
mB = 37 ± 4 MeV
Tkin = 123 ± 6 MeV
< bT > = 0.45 ± 0.02
T. Peitzman
History of High-Energy A+A Beams
• BNL-AGS: mid 80’s, early 90’s
O+A, Si+A 15 AGeV/c s1/2NN ~ 6 GeV
Au+A
11 AGeV/c s1/2NN ~ 5 GeV
• CERN-SPS: mid 80’s, early 90’s
O+A, S+A 200 AGeV/c s1/2NN ~ 20 GeV
Pb+A
160 AGeV/c s1/2NN ~ 17 GeV
• BNL-RHIC: early 00’s
Au+Au
s1/2NN ~ 130 GeV
Au+Au, p+p
s1/2NN ~ 200 GeV
Finally: enough energy for copious hard scattering processes!
Nomenclature: Centrality
Describe classes of events by
percentile of impact parameter
distribution:
40 mbarn
Peripheral; 60%-80%
<NCollisions> = 20 +- 5
Characterize A+A collision
intuitively in Glauber model:
Here NParticipant = 4
NCollision = 3
<NColl> = <TAB> sN+N inel
Central; 0%-10%
<NCollisions> = 850 +- 20
Quantifying Nuclear Effects
R
R = seA(x,Q2)/A sep(x,Q2) General DIS
1
x
Shadowing, EMC, etc.
RA = spA(PT)/A spp(PT) Hadron PT spectra
RA
1
PT
Cronin effect
a
spA(xF)
= Aa
spp(xF) eg DY, J/Y
1
xF
Absorption, initial state energy loss
R AA (p T )
 N binary (d 2s pp /dp Tdh/s pp inelastic )


1/Nevents d 2 N AA /dp Tdh
A+A hadrons
(This space available!)
?
RHIC Year-1 High-PT Hadrons
Charged and neutral
hadron spectra out to
pT~4-5 GeV/c
Nominally expect
production through
hard scattering, scale
spectra from N+N by
number of binary
collisions
Peripheral reasonably well
reproduced; but central
significantly below
binary scaling
Last Year’s Big News
Observe:
RHIC spectra fall below
binary scaling at all pT
for central events
Previous highest energy A+A
collisions exceed binary
scaling (Cronin
expectation)
Suspect: scattered parton
interaction in dense
medium; but must keep
an open mind
“The cover of the Rolling Stone”
(Almost) No one reads
PRL on paper these days.
Cover artists thought the
graph looked better
without numbers on the
axes.
(We were pleased
nonetheless.)
Charged Hadron
T.Peitzman
Spectra
200 GeV results
from all experiments
J. Klay, STAR
Parallel Saturday
C. Jorgensen, BRAHMS
Parallel Saturday
J. Jia, PHENIX
Parallel Saturday
Preliminary sNN = 200
GeV
Preliminary sNN = 200 GeV
C. Roland,
PHOBOS
Parallel Saturday
J.Klay
RAA Comparison to pT = 6 GeV/c
130 GeV nucl-ex/0206011
Preliminary sNN = 200 GeV
Preliminary sNN = 200 GeV
Similar Suppression in all centralities at 200 GeV
J.Klay
Central/Peripheral Comparison
Preliminary sNN = 200 GeV
0.5
0.5
At 130 GeV, the
suppression
increases up to pT
= 6 GeV/c.
With higher pT
data from 200
GeV, we see that
the suppression
has saturated at
pT ~6 GeV/c
 130 GeV
•
200 GeV
High pt suppression at 130 GeV
J.Jia
PHENIX (nucl-ex/0207010)
130GeV
• Detailed pT and
centrality dependence
– Peripheral RAA  1
– Central RAA saturates
~ 0.6 at pt >2GeV/C
Consistent with STAR(nucl-ex/0206011)
J.Jia
Ratio central/peripheral
colored bracket represent the systematic error.
thick black line is uncertainty of the scaling factor from N. collisions
• Lower ratio for
200 GeV
– more suppression
or change in
proton yield?
• Similar shape for
130 and 200 GeV
– increase to 2
GeV/c
– decrease to 4
GeV/c
Charged particle pT spectra from 200 GeV
pT >2 GeV/c,
decrease of
inverse slope
 suppression
h+ + hJ.Jia
pT <2 GeV/c, increase of inverse slope  flow
Comparison with NN references I
Calculate RAA: divide data by NN references
• RAA for peripheral collisions
– ~ 0.75 ± 0.3 for pT>2GeV/c
– consistent with 1
• RAA for central collisions
– similar to 130 GeV
– significantly below 1
– 200 GeV below 130 GeV data
– ~ 0.2 ± 0.08 from 4 to 8 GeV/c
Shaded band is syst. error from NN
Common syst. Scaling error
J.Jia
S.Mioduszewski
PHENIX Overview
• Most of central arms
used to measure the
pion spectrum
• Powerful cross-checks
of results
Au  Au
s NN  200 GeV
Comparison with
UA1 Fitting
PHENIX Preliminary
H. Torii
• UA1 data are only up to
6GeV/c and extrapolated
to higher pT
• The extrapolation is below
our data at high pT
Now have pp data to use
as important reference for
Au+Au collision and jet
quenching measurement.
Normalization systematic error
30% is not included here.
UA1 data
extrapolation
pT dependent systematic error
Comparison with
QCD Calculation
PHENIX Preliminary
• NLO pQCD calculation
– CTEQ5M pdf
– Potter-Kniehl-Kramer
fragmentation function
– m = pT/2, pT, 2pT
• Consistent with data within
the scale dependence.
H. Torii
Normalization systematic error
30% is not included here.
pT dependent systematic error
Nuclear Modification Factor
 N binary (d 2s pp /dp Tdh/s pp inelastic )
R AA (p T ) 

1/Nevents d 2 N AA /dp Tdh
S.Mioduszewski
D. d’Enterria talk
Yield central /  N binary  central
Yield pp
 Effect of nuclear
medium on yields
SPS – “Cronin” effect
RHIC - suppression
Our own measure of the
p+p spectrum reduces
the uncertainty!
PHENIX Preliminary
binary scaling
Suppression in Inclusive Photons
S.Mioduszewski
Photons (primarily
from 0 decays)
also show
suppression
 Not an artifact of
extraction of 0
peak yield
Yield central /  N binary  central
Yield peripheral /  N binary  peripheral
Klaus Reygers talk
Hadron Species Ratios in Run-1
(Anti)Baryon/pion
ratios rise well
above values in
p+p
Suspect radial
hydrodynamical flow
boosting baryons
while mesons are
suppressed; but
Similar effect seen in
p+A/p+p (Cronin);
Could potentially be a
modification to the
fragmentation process
T.Sakaguchi
pbar/ and p/
• pbar/ , p/ ratios
– pT<2GeV, pbar/-, p/+
– pT>1GeV, use 0 with -, +
• Point-by-Point Errors
include point-by-point
statistics+systematic errors
• Bands: pT independent
systematic errors
• Decreasing at much more
high pT?
pbar/pi
p/pi
By Takao Sakaguchi at Quark Matter 2002, July 18-24 at Nantes, France
Comparison with Year-1 Data
• Data Compared to Year-1
• Both Year-1 and Year-2 are consistent within systematic errors
•Another hint.
–More  rather
than protons?
By Takao Sakaguchi at Quark Matter 2002, July 18-24 at Nantes, France
T.Sakaguchi
Particle Composition at high pT
0/(h++h-)/2 ratio ~ 0.5 up to 9 GeV/c
 do protons continue to make up a large fraction
of charged
hadron yield?
S.Mioduszewski
Interlude: “Elliptic Flow”
f
b
dN/df ~ 1  2 v2 cos(2f)
-
+
The impact parameter vector
defines the “reaction plane
direction” in non-central collisions.
Low PT particles “feel” this
geometry and show a quadrupole
distribution relative to the event
plane direction.
Event plane directions were first
measured with recoiling beam
fragments, but can also be derived
from low-PT f distributions
How to sense geometry
Hard-scattered partons travel
through early medium; modification?
High-Pt
hadrons
Identical pair
correlations reveal
space-time geometry
Br?
Fragmentation
Pressure gradients lead
to collective motion
Heavy flavor quark endures;
Is there medium interaction?
Thermal production?
Difference in pressure gradients
can lead to anisotropic motion
Comparison v2 (pT) with models (130
GeV)
K.Filimonov
Adler et al., nucl-ex/0206006
• qualitative agreement with “jet-quenching” scenario
K.Filimonov
v2(pT) up to 12 GeV/c
• Statistical errors only
• Finite v2 up to 12 GeV/c
in mid-peripheral bin
Sources of azimuthal correlations
STAR Preliminary
Au+Au @ 200 GeV/c
0-5% most central
4<pT(trig)<6 GeV/c
2<pT(assoc.)<pT(trig)
• Au+Au
– flow
• p+p and Au+Au
collisions:
– dijets
– momentum
conservation
– jets
– resonances
D.Hardtke
All h
Small h
Relative Charge Dependence
Strong dynamical
charge correlations in
jet fragmentation 
Compare ++ and -charged azimuthal
correlations to +azimuthal correlations
System
(+-)/(++ & --)
p+p
2.7+-0.6
0-10% Au+Au
2.4+-0.6
Jetset
2.6+-0.7
STAR Preliminary @ 200 GeV/c
0-10% most central Au+Au
p+p minimum bias
4<pT(trig)<6 GeV/c
2<pT(assoc.)<pT(trig)
|h|<0.5 - |h|>0.5 (scaled)
Au+Au
0<|h|<1.4
p+p
Same particle production mechanism for pT>4 GeV/c in pp
and central Au+Au
D.Hardtke
Excess Above Flat Background, p-p
1/Ntrig dN/df
PHENIX Preliminary
PHENIX Preliminary
0.6-1 GeV
1- 2 GeV
f
f
PHENIX Preliminary
1/Ntrig dN/dh
PHENIX Preliminary
PHENIX Preliminary
2- 4 GeV
f
PHENIX Preliminary
0.6-1 GeV
1- 2 GeV
h
h
2- 4 GeV
•Data points (black) are background subtracted and
acceptance corrected.
M.Chiu
•Blue is the PYTHIA curve * apythia * <>
h
Excess from Flat Bkg, Au-Au
M.Chiu
black = associated charged particles, green = mixed, purple = subtracted
PHENIX Preliminary
2-4 GeV
40-60% Central
PHENIX Preliminary
2-4 GeV
0-10% Central
•In AuAu collisions there is a statistically significant excess from a
flat distribution at all centralities and all pt bins.
•So what is that excess? Try both PYTHIA only and also PYTHIA +
elliptic flow contribution.
PHENIX Preliminary
PHENIX Preliminary
PHENIX Preliminary
0.3-0.6 GeV
0.6-1 GeV
1- 2 GeV
20-40% Cent
PHENIX Preliminary
2- 4 GeV
vchvtrig
1/Ntrig dN/df
Fitting Pythia + 2vchvtrigcos(2f),
M.Chiu
pt dependence
apythia
•For lower pt, ambiguity between the contribution from the
elliptic flow component and the jet-like component.
•At higher pt (2 GeV and above), the jet-like component
dominates over any elliptic flow component.
Peripheral Au+Au data vs. pp+flow
C2 (Au  Au)  C2 ( p  p)  A * (1 2v 22 cos(2f ))

D.Hardtke
Central Au+Au data vs. pp+flow
C2 (Au  Au)  C2 ( p  p)  A * (1 2v 22 cos(2f ))

D.Hardtke
Ratio vs. # participants
D.Hardtke
C.Roland
Npart Scaling at high pT
PHOBOS Preliminary
Ncoll-scaling
Normalized to yield
at Npart = 65
Npart scaling describes data at pT 4.25 GeV/c
Central/Semi-peripheral collision at y2
C.Jorgensen
y=2.2
• Indicates suppression of high pT pions at y2.
• Sets in at lower pT (compared to y=0)?
Separation of non-photonic e±: cocktail method
g conversion
0  gee
h  gee, 30
w  ee, 0ee
PYTHIA
f  ee, hee
direct g
(J. Alam et al. PRC 63(2001)021901)
r  ee
h’  gee
R.Averbeck
Energy dependence of charm
R.Averbeck
production
PHENIX: PRL 88(2002)192303
NLO pQCD (M. Mangano et al.,
NPB405(1993)507)
PHENIX
PYTHIA
ISR
R.Averbeck
Centrality dependence at 200 GeV
A.Frawley
Same
plots
but now
on Spectrum
a linear scale.
p-pas previously
ee Invariant
Mass
This analysis
NJ/Y = 24 + 6 (stat) + 4 (sys)
Bds/dy = 52 + 13 (stat) + 18 (sys) nb
All triggers
A.Frawley
pp mm Invariant Mass Spectrum
1.2 < y < 1.7 NJ/Y = 26 + 6 + 2.6 (sys) B ds/dy = 49 + 22%
+ 29% (sys) nb
1.7 < y < 2.2 NJ/Y = 10 + 4 + 1.0 (sys) B ds/dy = 23 + 37%
+ 29% (sys) nb
Gaussian and
PYTHIA shape fits
give essentially the
same integral.
A.Frawley
The quoted result is
the average of the
two fits.
s (pp->J/Y) = 3.8 + 0.6 (stat) +
1.3 (sys) mb
* See J.F. Amundson et al.,
Phys. Lett. B 390 (1997) 323.
Au-Au
ee Invariant Mass Spectra
NJ/Y = 10.8 + 3.2 (stat) + 3.8 - 2.8 (sys)
A.Frawley
NJ/Y = 5.9 + 2.4 (stat) + 0.7 (sys)
Are our data
consistent with
binary scaling?
A confidence level
of 16% says that a
truly flat
distribution would
produce a fit as poor
as this in 16% of
cases.
So it probably
trends down with
increasing Npart, but
don't bet the farm!
A.Frawley
Scorecard
• Jets/High-PT hadrons: Lots of action! Singles yields,
spectra, composition do not agree with pQCD
expectations, while high-PT pair correlations are a mixed
bag. And this is only the beginning!
• Open charm and J/Y seem to agree with Pythia
predictions, but statistics are limited.
• Lots more to come! From existing data: direct photons,
more detailed pair correlations; in later years Y’, Y, DY,
g+jet, double direct photons; plus p+A/d+A; etc.etc….
• Plenty for any theorist to work with! And many
fundamental QCD issues potentially involved.