Lisa - Quark Matter 991 Beam Energy Evolution of HBT Sytematics at the AGS Mike Lisa, The Ohio State...

Lisa - Quark Matter 99

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Beam Energy Evolution of HBT Sytematics at the AGS

Mike Lisa, The Ohio State Universityfor 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 rp

• Summary

2 Lisa - Quark Matter 99

HBT Excitation Function at AGS - Motivation

Characterize source geometry and dynamics as function ofEbeam, mT, y, rp

Watch for “anomalous” lifetimes/sizes (QGP@AGS?)

Test dynamical models that provide “hadronic baseline” - can they extrapolate to RHIC?

“”

withtransition

c

3D hydro modelRischke & GyulassyNPA 608, 479 (1996)

Eob

serv

able AGS SPS RHIC

Signatures of new physics may be subtle

E

obse

rvab

le AGS SPS RHIC


Measurement with the EOS TPC

Up to ~350 particles/event (60 -) measured over large phase space

Good reaction plane resolution

p/p 3% (dominated by MCS)

5% e- contamination in -

Posters by D. Cebra & C. Pinkenburg Talk by G. Rai in Thurs. plenary session


The E895 - HBT Analysis

Iterative correction for p (typical increase in fit parameters by ~ 8%)

2-track cut eliminates track merging limits analysis to low pT (< 0.4 GeV/c)

Full Coulomb-wave (= 5 fm) Coulomb correction employed

Analyze in frame fixed at ycm

Event-mixing with rp selection:

mix only events with “same” rp

Statistical uncertainties shown. Systematic errors of same order.

Passage of a track “kills” an area ~ (1 cm)2

on padrow merging

128 padrows

beam


1-D Correlation Function Excitation Function at ycm

Smooth evolution of 1-D fit parameters with E


Bertsch-Pratt projections(11% T ycm0.35 pT = 0.1-0.3 MeV/c)


Evolution of the BP and YKP fit parameters

Increased production of long-lived --emitters fall in

Strong evolution of Rs (R) with beam energy

Hadronic model with or without meanfield underpredicts (apparent) geometric size at low beam energy


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?


mT dependence at ycm for 2 AGeV central collisions

Dynamics (timescale/flow) radii drop with mT

- from decays at low mT increases with mT

x (fm)

y (f

m)


mT dependence at ycm for 6 AGeV central collisions

At higher beam energy, RS falls more steeply


Evolution of mT dependence (y=ycm0.5)

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


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


Testing the model at the SPS

For -...

Model underpredicts apparent size below 10 AGeV...

overpredicts size at 158 AGeV

Extrapolation to RHIC???

NA44 RQMD

Rout 4.88 0.21 6.96 0.14

Rside 4.45 0.32 6.23 0.20

Rlong 6.03 0.35 7.94 0.21

I.G. Bearden et al (NA44)PRC58, 1656 (1998)D. Hardtke, Ph.D. thesis (1997)


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


Longitudinal flow from cross-term and yso:

Rapidity dependence of Bertsch-Pratt Rol

2 and Yano-Koonin yso sensitive to longitudinal flow

2 AGeV: little longitudinal flow

8 AGeV: non-boost-invariant flow


Centrality Dependence of the Correlations

suppressed for central collisions due to increased production of ,

Gentle fall of sideward radii as size of overlap region falls

b=27 fm: ~ 35% reduction in RMS


Viewing the pion source in its natural frame

b0 collisions anisotropy in momentum space (elliptic flow)

Also visible in coordinate space?

P. Danielewicz et al,PRL 81, 2438 (1998)Also see E895 ellipticflow poster

toy example


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


Evolution of HBT @ AGS - Summary

E895 has measured systematics of - interferometry at 2-8 AGeV no anomalous behaviour suggestive of QGP formation apparent sideward radius (and ) 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 Rol

2, 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


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(rp) (including dispersion corrections) - phasespace density as a function of p


HBT with respect to the Reaction Plane - RQMD

(perfect r.p. resolution)

oscillation - elliptical flow?

Rout oscillates against Rside, with similar magnitude

Oscillation strength roughly constant with Ebeam

Rlong: ?


Bertsch-Pratt projections - data and RQMD(11% T ycm0.35 pT = 0.1-0.3 MeV/c)


Typical 1- Error contours for BP fits

Primary correlation is the familiar correlation between and radii

Large acceptance no strong correlations between radii

Cross-term uncorrelated with any other parameter


- Acceptance

Lisa - Quark Matter 991 Beam Energy Evolution of HBT Sytematics at the AGS Mike Lisa, The Ohio State...

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