Transcript Beam Energy Evolution of HBT Sytematics at the AGS Mike Lisa, The Ohio State University for the E895 Collaboration N.N.

Beam Energy Evolution of HBT Sytematics at the AGS
Mike Lisa, The Ohio State University
for the E895 Collaboration
N.N. Ajitanand, J. Alexander, D. Best, P. Brady, T. Case, B. Caskey, D. Cebra,
J. Chance, I. Chemakin, P. Chung, V. Cianciolo, B. Cole, K. Crowe, A. Das,
J. Draper, S. Gushue, M. Gilkes, M. Heffner, H. Hiejima, A. Hirsch, E. Hjort,
L. Huo, M. Justice, M. Kaplan, J. Klay, D. Keane, J. Kintner, D. Krofcheck,
R. Lacey, J. Lauret, E. LeBras, M. Lisa, H. Liu, Y. Liu, B. McGrath, Z. Milosevich,
D. Olson, S. Panitkin, C. Pinkenburg N. Porile, G. Rai, H.-G. Ritter, J. Romero,
R. Scharenberg, L. Schroeder, R. Sotlz, B. Srivastava, N. Stone, J. Symons, S. Wang,
R. Wells, J. Whitfield,T. Wienold, R. Witt, L. Wood, X. Yang, Y. Zhang, W. Zhang
Auckland - BNL - CMU - Columbia - UC Davis - Harbin - KSU - LBL - LLNL St. Mary’s College - OSU - Purdue - Stony Brook
• Motivation and Measurement
• Correlation Systematics at Intermediate AGS energy
• Ebeam Centrality y mT frp
• Summary
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HBT Excitation Function at AGS - Motivation
3D hydro model
Characterize p source
geometry and dynamics
as function of
Ebeam, mT, y, frp
Rischke & Gyulassy
NPA 608, 479 (1996)
with
transition
Watch for “anomalous”
lifetimes/sizes
(QGP@AGS?)
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“e”
AGS
SPS
RHIC
E
observable
Signatures of new physics may be subtle
observable
Test dynamical models
that provide “hadronic
baseline” - can they
extrapolate to RHIC?
ec
AGS
SPS
RHIC
E
Measurement with the EOS TPC
Up to ~350 particles/event (60 p-)
measured over large phase space
Good reaction plane resolution
dp/p  3% (dominated by MCS)
 5% e- contamination in p-
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Posters by D. Cebra & C. Pinkenburg
Talk by G. Rai in Thurs. plenary session
The E895 p- HBT Analysis
Iterative correction for dp (typical
increase in fit parameters by ~ 8%)
Passage of a
track “kills” an
area ~ (1 cm)2
on padrow
 merging
2-track cut eliminates track merging
limits analysis to low pT (< 0.4 GeV/c)
Full Coulomb-wave (s= 5 fm)
Coulomb correction employed
Analyze in frame fixed at ycm
Event-mixing with frpp selection:
mix only events with “same” frp
beam
Statistical uncertainties shown.
Systematic errors of same order.
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128 padrows
1-D Correlation Function Excitation Function at ycm
Smooth evolution of 1-D fit parameters with E
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Bertsch-Pratt projections
(11% sT ycm0.35
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pT = 0.1-0.3 MeV/c)
Evolution of the BP and YKP fit parameters
Increased production of longlived p--emitters  fall in l
Strong evolution of Rs (R)
with beam energy
Hadronic model with or without
meanfield underpredicts
(apparent) geometric size at
low beam energy
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Evolution of (apparent) Shape: Oblate to Prolate
Transition from oblate to
prolate shape at AGS connects
Bevalac observations to SPS
Transition in character of
flow/expansion:
transverse  longitudinal?
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y (fm)
mT dependence at ycm for 2 AGeV central collisions
x (fm)
Dynamics (timescale/flow)
 radii drop with mT
p- from decays at low mT
 l increases with mT
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mT dependence at ycm for 6 AGeV central collisions
At higher beam energy,
RS falls more steeply
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Evolution of mT dependence (y=ycm0.5)
magnitude of RO(mT) falls
with Ebeam.
Decline of RS with Ebeam
driven primarily by increased
falloff with mT at high energy.
RL(mT) roughly constant as
function of Ebeam
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Evolution of systematics - data and model
Observed evolution of
systematics not reproduced
by model
Dynamics driving RS(mT)
may not depend on collision
energy within RQMD
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Testing the model at the SPS
For p-...
Model underpredicts apparent
size below 10 AGeV...
overpredicts size at 158 AGeV
Extrapolation to RHIC???
I.G. Bearden et al (NA44)
PRC58, 1656 (1998)
D. Hardtke, Ph.D. thesis (1997)
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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
Rapidity dependence
Rather flat dependence of fit
parameters near ycm
Near beam rapidity (0.9, 1.4),
radii begin to fall off when
analyzed in Au+Au c.m. frame
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Longitudinal flow from cross-term and yso:
Rapidity dependence of
Bertsch-Pratt Rol2 and
Yano-Koonin yso sensitive to
longitudinal flow
2 AGeV: little longitudinal flow
8 AGeV: non-boost-invariant
flow
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Centrality Dependence of the Correlations
l suppressed for central
collisions due to increased
production of L, h...
Gentle fall of sideward radii as
size of overlap region falls
b=27 fm: ~ 35% reduction in RMS
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Viewing the pion source in its natural frame
P. Danielewicz et al,
PRL 81, 2438 (1998)
Also see E895 elliptic
flow poster
b0 collisions  anisotropy in
momentum space (elliptic flow)
Also visible in coordinate space?
toy example
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HBT with respect to the Reaction Plane - data
b  4 - 9 fm
Small but significant oscillation
observed in sideward radius
Consistent with naïve
geometrical view, and RQMD
Reduced strength of oscillation
in Rout may give information on
lifetime or effective opaqueness
Uncorrected for r.p. resolution
cuts not identical
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Evolution of HBT @ AGS - Summary
E895 has measured systematics of p- interferometry at 2-8 AGeV
 no anomalous behaviour suggestive of QGP formation
 apparent sideward radius (and l) fall with E
 mT-dependence of RS weak at low Ebeam: less flow?
 evolution from oblate (Bevalac-like) toward prolate (SPS-like) source
 y-dependence of Rol2, ysoYKP  little longitudinal flow at 2 AGeV
 gentle centrality dependence - no surprises
The Next Frontier - Imaging the source in its natural frame
 ~0.5 fm oscillation of RS observed at low Ebeam - less at higher energy
 detailed study of source in natural frame may give info on opacity/lifetime
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Evolution of HBT @ AGS - Summary II
Excitation Function - powerful tool to test/tune understanding
of “normal” physics in R.H.I.C.
RQMD does not reproduce evolution in detail
 underpredicts transverse size below ~10 AGeV - overpredicts size above
 incorrect evolution of x-p correlation?
 correct outward radius an artifact of effective emission timescale?
 little (relevant) evolution of dynamics in AGS range
Plans
 detailed analysis of HBT(frp) (including dispersion corrections)
 p- phasespace density as a function of p
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HBT with respect to the Reaction Plane - RQMD
(perfect r.p. resolution)
l oscillation - L elliptical flow?
Rout oscillates against Rside,
with similar magnitude
Oscillation strength roughly
constant with Ebeam
Rlong: ?
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Bertsch-Pratt projections - data and RQMD
(11% sT ycm0.35
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pT = 0.1-0.3 MeV/c)
Typical 1-s Error contours for BP fits
Primary correlation is the
familiar correlation between l
and radii
Large acceptance  no
strong correlations between
radii
Cross-term uncorrelated with
any other parameter
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p- Acceptance
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