E895 Excitation Functions at the AGS
Mike Lisa, The Ohio State University
• E895 Motivation and Measurement
• Excitation functions
•
•
•
•
sidewards flow
elliptic flow
strangeness
HBT
• Summary
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
E895 mission - continuation of EOS mission
map out energy dependence of “all” physics variables
as a function of energy
Large acceptance device with good PID to characterize each event
Hope to answer:
• Is there a sign of anomolous behavior in data as Ebeam varied (or
is systematics smooth)?
• Hydro suggests a “condensed matter” type of QGP search
• Do medium effects matter @ AGS?
• Bevalac experience -- one point is not enough to tell
• Can we constrain parametrization of medium effects in models?
~ 500k - 1M Au+Au collisions measured at 2, 4, 6, 8 AGeV
with full coverage
Good PID by
ionization in gas
Momentum resolution
~ 1%
Systematics/meta-analysis suggest approach
to maximum AGS energy interesting...
B. Hong et al. (FOPI)
Proceedings of International Workshop,
Poiana Brasov, Romania (1996)
P. Braun-Munzinger and J. Stachel,
NPA606, 320 (1996)
Perhaps some signals only apparent near threshold
D. Rischke, NPA 610, c88 (1996)
Magnitude, position,
(existence?) of deviations
due to phase transistion
unclear
 concentrate on data
systematics
Reaction plane
reconstructed by method
of Danielewicz/Odyniec
Reconstructed
reaction plane 
flat in lab
Dispersions (and
corrections) get
large for 8 AGeV,
where flow is small
Plots by C. Pinkenburg
Flow correction
1) grows
2) depends on algorithm
when flow gets small
Analysis by C. Pinkenburg, N.N. Ajitanand
Proton sidewards flow excitation function
Analysis by H. Liu
• no sharp behavior in sidewards flow
• Ebeam systematics powerful test of dynamical models
• some medium effects needed in addition to hadronic scattering
Elliptic flow - measure of in/out of plane emission
Elliptic flow sensitive
to competition between
timescales in collision
At Bevalac and MSU energies,
elliptic flow (squeeze-out)
provided most sensitivity to EoS
Max AGS energy (E877):
emission is in-plane
P. Danielewicz et al.,
nucl-th/9803047
Elliptic flow below (and above?) 10 AGeV
sensitive to medium effects
BUU P. Danielewicz et al.,
nucl-th/9803047
RQMD v2.3
Elliptic flow below (and above?) 10 AGeV
sensitive to medium effects
BUU P. Danielewicz et al.,
nucl-th/9803047
RQMD v2.3
Excitation function
of elliptic flow
Sideflow- peaking at 0 (180)
at y>ycm (y<ycm)
Elliptic flow - second order
moment clearest at ycm
vanishes near 4 AGeV
• no obvious sharp
behavior in data
• maybe something
more subtle…
softening of EoS
around 4 AGeV???
Analysis by C. Pinkenburg
Neutral strange mesons and baryons
3-5% reconstruction efficiency
*** put mass peaks here ***
Analyses by P. Chung and D. Best. Plots by P. Chung
Strangeness excitation functions - no sharp structure
TAPS e
Nag K+
KAOS K+
FOPI K+
KAOS KFOPI KE895 K0
Analysis by P. Chung
K0 flow (medium bias events)
May provide sensitivity
to strange scalar and
vector potentials
p- HBT - a proposed QGP threshold signature
“ec”
“e”
Rischke & Gyulassy
NPA 608, 479 (1996)
At energies much above theshold, increased timescale signal
vanishes as the plasma explodes and cools quickly
Singles coverage for pions
pT cut at 100 MeV/c helps remove e- contamination
Q resolution ~ 10 MeV/c
(better when refitting track with
primary vertex)
Track merging/splitting effects
removed by requiring >15 wellseparated padrow crossings
NOTE: finite Q resolution not
corrected for in present results
All processed events
(~8% data taken,
50% for 4 GeV)
- no cuts
Only p- used in HBT
analysis
Restrictive cuts 
actual p- multiplicity
higher
“top 10% sT”
y = ycm  0.25
1D HBT excitation function - Central Au+Au, midrapidity
1D HBT
parameters show
no sharp anomoly
Some systematics to come...
3D HBT - 4 AGeV
central collisions
midrapidity
c2/n = 5797/6694
 = 0.57  0.04
Rol = 0.5  2 Rout = 5.23  0.31
C(q out , q side , q long ) 
2
2
2
2
1    exp(  R out
 q out
 R side
 q side
2
2
 R long
 q long
Rside = 5.31  0.27
2
 2R ol
 q out  q long )
Performed in ycm frame
• Rout Rside
• Rol  0
Rlong = 4.41  0.27
3D HBT - 4 AGeV
central collisions
forward rapidity
c2/n = 5337 / 6694
 = 0.59  0.03
Rol = 3.4  1.3
Rout = 5.45  0.21
C(q out , q side , q long ) 
2
2
2
2
1    exp(  R out
 q out
 R side
 q side
2
2
 R long
 q long
Rside = 4.47  0.14
2
 2R ol
 q out  q long )
Performed in ycm frame
• Rout Rside
• Rol > 0
Rlong = 4.73  0.18
Summary
• No drastic signatures of transition in AGS
energy range
– sideflow, elliptic flow, strangeness, HBT
• Medium effects impt. at AGS
• collective motion excitation function
provides true challenge to models’
parametrization of medium effects (or lack
thereof)
– models tuned to reproduce data at one energy
often fail elsewhere