Characterization of the pion source at the AGS
Mike Lisa
The Ohio State University
•Motivation and Measurement
•Systematics of HBT in E895
•Existing problems - failed consistency check
•Summary
APS Meeting March 1999
E895 @ AGS
Lawrence Berkeley Lab
D. Best, T. Case, K. Crowe, D. Olson, G. Rai, H.-G. Ritter,
L. Schroeder, J. Symons, T. Wienold
Brookhaven National Lab
S. Gushue, N. Stone
Carnegie Mellon University M. Kaplan, Z. Milosevich, J. Whitfield
Columbia University
I. Chemakin, B. Cole, H. Hiejima, X. Yang, Y. Zhang
U.C. Davis
P. Brady, B. Caskey, D. Cebra, J. Chance, J. Draper, M. Heffner,
J. Romero, L. Wood
St. Mary’s College
J. Kintner
Harbin Institute (China)
L. Huo, Y. Liu, W. Zhang
Kent State Univeristy
M. Justice, D. Keane, H. Liu, S. Panitkin, S. Wang, R. Witt
Lawrence Livermore Lab
V. Cianciolo, R. Sotlz
Ohio State University
A. Das, M. Lisa, R. Wells
University of Auckland (NZ) D. Krofcheck
Purdue University
M. Gilkes, A. Hirsch, E. Hjort, N. Porile, R. Scharenberg, B.
Srivastava
S.U.N.Y. Stony Brook
N.N. Ajitanand, J. Alexander, P. Chung, R. Lacey, J. Lauret, E.
LeBras, B. McGrath, C. Pinkenburg
Motivation
1) fully characterize HBT systematics as fctn of collision conditions: Ebeam, b, y, mT, frp
2) watch for “anomolous” lifetimes/sizes(QGP@AGS?)
3D hydro model
~ emission
timescale
with
transition
ec
Rischke & Gyulassy
NPA 608, 479 (1996)
“e”
AGS
SPS
RHIC
E
observable
Signatures
may be subtle
observable
3) test dynamical models that provide “hadronic baseline”: can they extrapolate to RHIC?
AGS
SPS
RHIC
E
• Mmax  180 (320) at 2 (8) AGeV
• Np a M
• dp/p  1%
•  5% e- contamination
1D p- HBT Excitation Function
Smooth evolution of source parameters
Bertsch-Pratt projections at ycm for central collisions
Bertsch-Pratt projections at ycm for central collisions
data and RQMD v2.3 with and without meanfield
Bertsch-Pratt & Yano-Koonin Fits - central collisions at ycm
RQMD with or without
meanfield:
• Ebeam dependence
weaker than observed
At low energy...
• Effective spatial extent
underpredicted
• Effective temporal
extent overpredicted
AGS:
apparent size underpredicted
SPS: p- size overpredicted
Extrapolate to RHIC?
I.G. Bearden et al (NA44)
PRC58, 1656 (1998)
D. Hardtke, Ph.D. thesis (1997)
Rout
Rside
Rlong
NA44
4.88  0.21
4.45  0.32
6.03  0.35
RQMD
6.96  0.14
6.23  0.20
7.94  0.21
mT dependence
sensitive to
space-momentum
correlations, flow
y (fm)
• Well reproduced by RQMD
• l increases w/ mT due to
decreased contrib from L’s...
• mT falloff in Rlong greatest
• mT falloff in Rout least
x (fm)
y (fm)
8 AGeV mT dependence
x (fm)
pT dependence
sensitive to
space-momentum
correlations, flow
y (fm)
• Well reproduced by RQMD
• l increases w/ mT due to
decreased contrib from L’s...
• mT falloff in Rlong greatest
• mT falloff in Rout least
x (fm)
y (fm)
8 AGeV pT dependence
x (fm)
6 AGeV mT dependence
“again CERN-type systematics”
6 AGeV pT dependence
“again CERN-type systematics”
4 AGeV mT dependence
4 AGeV pT dependence
2 AGeV mT dependence
2 AGeV pT dependence
Rapidity dependence
Strongest at lower energy
(ybeam = 0.904 for 2 AGeV)
Asymmetry about ycm may
indicate major problem!?!
Spurious y-dependent effect
=
spurious Ebeam-dependent effect?
Centrality dependence
pT=0.1-0.8, y=ycm0.4
Ignoring shadowing,
flow, lifetime...
Overlap region RMS
changes ~35% between
b=2, b=7
Gentle Mch dependence:
Transverse radii vary
by 15-35%
strongest variation at 2 AGeV
b  0  anisotropy in
momentum space (elliptic
flow)
visible in coordinate
space??
P. Danielewicz et al,
PRL 81, 2438 (1998)
C. Pinkenburg et al (E895),
submitted to PRL
see also JB 12.02
Nonspherical source (w/ no physics)
“b=7 fm”  RMSx=3.5 fm RMSy=6.0 fm
RQMD (w/meanfield) prediction of effect at ycm
b=4-9 fm (perfect frp resolution)
• 0.5 fm difference consistent w/RQMD
freezeout geometry
Elliptic flow of baryons
• Rs and Ro oscillate against each other 
3D HBT more sensitive than 1D
b = 7 x and y from RQMD
2 and 4 AGeV, b=4-7 fm: promising signal in Rside, but...
2 AGeV, y=(ycm-0.5) - ybeam
pT = 0.1-0.8 MeV/c
4 AGeV, y=ycm  0.4
pT = 0.05 - 0.8 MeV/c
6 AGeV midrapidity
- no signal so far...
Transverse source size varies with viewing angle
with respect to reaction plane in peripheral collisions
Transverse size small
when viewed at 90o
reaction
plane
target
projectile
overlap region
Modulation of x-p
correlation with frp
enhances geometric
effect
stronger flow effects
out of plane reduce
Rside further.
Meanfield required at
low energy to give
squeeze-out in
momentum space
Modulation decreases
with beam energy