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

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 @ AGS

Motivation1) fully characterize HBT systematics as fctn of collision conditions: Ebeam, b, y, mT, rp

3) test dynamical models that provide “hadronic baseline”: can they extrapolate to RHIC?

2) watch for “anomolous” lifetimes/sizes(QGP@AGS?)

E

obse

rvab

le AGS SPS RHIC

“”

withtransition

c

E

obse

rvab

le AGS SPS RHIC

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

~ emissiontimescale

Signaturesmay be subtle

• Mmax 180 (320) at 2 (8) AGeV• N M• p/p 1%• 5% e- contamination

1D - HBT Excitation Function

Smooth evolution of source parameters

Bertsch-Pratt projections at ycm for central collisions

Bertsch-Pratt projections at ycm for central collisionsdata and RQMD v2.3 with and without meanfield

Bertsch-Pratt & Yano-Koonin Fits - central collisions at ycm

RQMD with or withoutmeanfield:•Ebeam dependence weaker than observed

At low energy...•Effective spatial extent underpredicted

•Effective temporal extent overpredicted

AGS: apparent size underpredicted

SPS: - size overpredicted

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

Extrapolate to RHIC?

I.G. Bearden et al (NA44)PRC58, 1656 (1998)

D. Hardtke, Ph.D. thesis (1997)

• Well reproduced by RQMD

• increases w/ mT due to decreased contrib from ’s...

• mT falloff in Rlong greatest

• mT falloff in Rout least

x (fm)y

(fm

)y

(fm

)

x (fm)

8 AGeV mT dependence

mT dependence sensitive tospace-momentum correlations, flow

• Well reproduced by RQMD

• increases w/ mT due to decreased contrib from ’s...

• mT falloff in Rlong greatest

• mT falloff in Rout least

x (fm)y

(fm

)y

(fm

)

x (fm)

8 AGeV pT dependence

pT dependence sensitive tospace-momentum correlations, flow

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 mayindicate major problem!?!

Spurious y-dependent effect =

spurious Ebeam-dependent effect?

Centrality dependencepT=0.1-0.8, y=ycm0.4

Ignoring shadowing,flow, lifetime...

Overlap region RMSchanges ~35% betweenb=2, b=7

Gentle Mch dependence:Transverse radii varyby 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 PRLsee 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 rp resolution)

Elliptic flow of baryons

• 0.5 fm difference consistent w/RQMD freezeout geometry

• 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 0.4pT = 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

target projectile

overlap region

reactionplane

Transverse size small when viewed at 90o

Modulation of x-p correlation with rp

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