Transcript RHIC PHENOMENOLOGY AS SEEN BY Wit Busza QCD in the RHIC Era

Wit Busza
QCD in the RHIC Era
UCSB, April 2002
RHIC PHENOMENOLOGY AS SEEN BY
The PHOBOS Collaboration
ARGONNE NATIONAL LABORATORY
BROOKHAVEN NATIONAL LABORATORY
INSTITUTE OF NUCLEAR PHYSICS, KRAKOW
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
NATIONAL CENTRAL UNIVERSITY, TAIWAN
UNIVERSITY OF ROCHESTER
UNIVERSITY OF ILLINOIS AT CHICAGO
UNIVERSITY OF MARYLAND
Birger Back, Alan Wuosmaa
Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen
Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis
Remsberg, Peter Steinberg, Andrei Sukhanov
Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski,
Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek,
Barbara Wosiek, Krzysztof Wozniak
Maarten Ballintijn, Wit Busza (Spokesperson), Patrick Decowski,
Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy,
Piotr Kulinich, Heinz Pernegger, Corey
Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep
Sarin, Stephen Steadman, George Stephans, Gerrit van
Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth,
Bolek Wyslouch
Willis Lin, ChiaMing Kuo
Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,
Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs
Russell Betts, Edmundo Garcia, Clive Halliwell, David Hofman,
Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter
Richard Bindel, Edmundo Garcia, Alice Mignerey
PHOBOS Detector
4p Multiplicity:
f
-5.4
-3.1
Two-arm Spectrometer:
0
+3.1
+5.4
h
Number of Participants
Participants Npart
pA:
Spectators
Npart=n+1
AA:
Estimating the Number of Participants
Model
•
Assumption:
– Multiplicity is monotonic with Npart
– Glauber model applicable
•
Nucleons maintain same crosssection
Charged Particle Multiplicity
130 GeV AuAu
200 GeV AuAu
Ntot = 4100 ±210
Ntot = 4960 ±250
0-6%cent
25-35%cent
45-55%cent
h
ISR data
s (GeV )
31 45 53
0-6%cent
63
20-24 15-19 10-14 5-9 2-4
Total observed multiplicity
24
130 GeV AuAu 200 GeV AuAu
1 d n
 n dh
h
W. Thome et al.,
Nucl. Phys. B129
(1977) 365.
25-35%cent
45-55%cent
h
Compilation of p-emulsion data
Limiting fragmentation in
pA, Ap and pp scattering
pA
pp
Ap
Collision Viewed in Rest Frame of One Projectile
UA5, Z.Phys.C33, 1 (1986)
Limiting Fragmentation is seen
Reduction of Target Fragments with Centrality ?
200 GeV AuAu
pA
From Barton et al
NA5 DeMarzo, et al (1984)
pA
pX
pi-X
XF
With one exception, the pp, pA and AA data in the fragmentation
region are consistent with the following picture:
1.
A “wall of gluons” strips the gluons from the target nucleons.
This process is independent of the energy of the incident nucleus.
2.
The number of remaining quarks is only weakly dependent on
the thickness of the incident nucleus.
3.
The quarks fragment into the particles detected in the
fragmentation region. Some rescattering occurs.
Au+Au & pp at 200 GeV
From Peter Steinberg
From W. Busza (1976)
Collision Viewed in Center of Mass Frame
Most central
RHIC : PHOBOS AuAu s = 200 GeV
RHIC : PHOBOS AuAu s = 130 GeV
SPS : EMU-13 PbPb s = 17 GeV
200 GeV AuAu
AuAu normalized to equivalent number
of participants
PRL 87 (2001)
h  1
h 1
45
p+p
Central Au+Au
fpp(s) =
(CDF/UA5)
 dN 

 ~ 1000
 dh  all
E ~ 1GeV
Total energy released ~2000GeV
Max. initial overlap volume
~ pR 2 (1 fm) ~ 200 fm3
3
At 200 GeV initial released energy density  10GeV / fm
Centrality Dependence of dN/deta
• Naïve expectations:
– Consider collision of two
“tubes of nucleons”
dN
dh
dN
N part / 2
dh
1
6 or 36?
1
1 or 6?
Note: N binary  N part / 2 n
n = Avg number of collision each
participant makes (~6 for central
AuAu)
Au+Au
& pp at
200atGeV
Au+Au
& pp
200 GeV
From Peter Steinberg
Azimuthal Angular Distributions
“head on” view of colliding nuclei
b (reaction plane)
y
f
x
Look at emission patterns using
Fourier expansion: extract V2
components from the fits.
dN/d(f YR ) = N0 (1 + 2V1cos (fYR) + 2V2cos (2(fYR)) + ... )
Centrality Dependence of v2
Preliminary
|h| < 1.0
sNN=130GeV
Hydrodynamic model
Preliminary
SPS
AGS
Systematic
error ~ 0.007
b
Peripheral Collisions
Normalized Paddle Signal
Central Collisions
b
V2 (elliptical flow) vs h
sNN= 130 GeV
V2
sNN= 17 GeV
PHOBOS Preliminary
STAR (PRL)
All Charged
Min. bias
PHOBOS Systematic
error ~ 0.007
h
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
SPS NA49 (QM99)
Pion (b<11fm)
0
1
2
• Averaged over centrality
• V2 drops for |h| > 1.5
• Dependence on h appears to be
different than at lower energy.
3
4
5
rapidity
6
Preliminary 200GeV AuAu
AuAu130 GeV Stat.
p
p
K
K
p
p
Syst.
 1.00  0.01  0.02
 0.91  0.07  0.06
 0.60  0.04  0.06
p
 1.025  0.006( stat )  0.020( sys )

p
K
 0.95  0.03( stat )  0.04( sys )

K
p
 0.74  0.02( stat )  0.03( sys )
p
Energy Dependence of Baryo-chemical potential mB
Nucl. Phy. A697: 902-912 (2002)
Baryon Stopping
From W.B and A.S.Goldhaber
•PHOBOS web-site: www.phobos.bnl.gov
•Published Physics Results
–Charged particle multiplicity near mid-rapidity in central Au+Au collisions
at 56 and 130 GeV
Phys. Rev. Lett. 85, 3100 (2000)
–Ratios of charged antiparticles-to-particles near mid-rapidity in Au+Au
collisions at 130 GeV
Phys. Rev. Lett. 87, 102301 (2001)
–Charged-particle pseudorapidity density distributions from Au+Au
collisions at 130 GeV
Phys. Rev. Lett. 87, 102303 (2001)
–Energy dependence of particle multiplicities near mid-rapidity in central
Au+Au collisions
Phys. Rev. Lett 88, 22302(2002)
–Centrality Dependence of Charged Particle Multiplicity at |h|<1 in Au+Au
Collisions at 130 GeV
Phys. Rev. C65, 031901(R)(2002)
–Centrality Dependence of Charged Particle Multiplicity at |h|<1 in Au+Au
Collisions at 130 and 200 GeV
Submitted to Phys. Rev. C (2002)
Conclusions based on PHOBOS Results
•
Central rapidity density increases approximately logarithmically with energy.
Why?
It is lower than most pre-RHIC predictions. Initial Energy Density > 10GeV/fm3
•
Eliptic Flow suggests high pressure is created.
dN/dn is boost invariant for +- 2 units of rapidity about zero, but not eliptic
flow. Why?
•
Fragmentation of incident states essentially as expected.
Rapidity distribution per participant for AuAu and p pbar have similar shape
over entire pseudo rapidity range. The former is approximately 1.3 times the
later. This scaling is not understood.
•
Many features of AuAu multiparticle production are well reproduced by
saturation model of Kharzeev et al.
•
No surprises in particle ratios.
•
To understand multiparticle production, need energy scan and species scan.