An HBT Excitation Function: Experiment E895 at the AGS Mike Lisa, The Ohio State University Motivation Experiment E beam Systematics - data and RQMD –1D midrapidity and E866 –Bertsch-Pratt/Yano-Koonin parameterizations –x-p correlation, resonances, resolution effects 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 UniversityM. 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 CollegeJ. Kintner Harbin Institute (China)L. Huo, Y. Liu, W. Zhang Kent State UniveristyM. Justice, D. Keane, H. Liu, S. Panitkin, S. Wang, R. Witt Lawrence Livermore LabV. Cianciolo, R. Sotlz Ohio State UniversityA. 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 Lookout for signs of “anomalous” behavior in E beam systematics QGP threshold at AGS? take “condensed matter” approach especially look at low p T Thoroughly test existing transport models Bevalac experience-- easy to tune model with right mix of wrong physics at one energy Continue to establish baseline systematics how do signals change in “normal” RHI collision

Systematics/meta-analysis suggest approach to maximum AGS energy interesting... P. Braun-Munzinger and J. Stachel, NPA606, 320 (1996) B. Hong et al. (FOPI) Proceedings of International Workshop, Poiana Brasov, Romania (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

Proton sidewards flow excitation function Analysis by H. Liu no sharp behavior in sidewards flow E beam systematics powerful test of dynamical models some medium effects needed in addition to hadronic scattering

HBT systematics may also be QGP signature Rischke & Gyulassy NPA 608, 479 (1996) At too-high beam energy, increased timescale signal vanishes as the plasma explodes and cools quickly Prediction of 3D hydrodynamic model with phase transition without transition “”“” with transition cc ~ emission timescale

A Bevalac TPC meets an AGS beam... 2-year-old artist’s conceptionSingle 8 GeV event in TPC ~ 500k-1M Au+Au collisions measured at 2, 4, 6, and 8 AGeV continuous coverage with no low-pT threshold good PID ~ 1% momentum resolution lisa: after this comes the PID picture in portrait mode lisa: after this comes the PID picture in portrait mode

 - sample contaminated by e -   5% level moving PID definition up/down, “reasonable” relaxation of DCA cut, does not change HBT signal at higher energy, use of p T cut reduces contamination

Ideally, HBT gives a measure of source size x 1,p 1 x 2,p 2  2  ~ {exp(i x 1 p 1 ) exp(i x 2 p 2 ) + exp(i x 2 p 1 ) exp(i x 1 p 2 )}

Large acceptance  many  - But...phase space means most are at large Q Background (denominator) generated with standard event-mixing (15 previous) 4 GeV central single-particle acceptance effects eliminated

Finite 2-track resolution (hit merging) leads to suppression of correlation

Track merging/splitting effects removed by requiring >15 well- separated padrow crossings 2-track cut for real and mixed pairs removes low-Q suppression

Coulomb wave integration used for correction Gamow function overcorrects 5 fm  Gaussian spherical source assumed, based on results sensitive mainly to RMS applied pairwise used for both data and RQMD E877 uses identical correction; NA49 equivalent Gamow 5 fm  Kakija et al. (NA49) QM96 NPA 610, 248c (1996).

E895 correction roughly appropriate still overcorrects at smallest bin RQMD  - input:  - -  - correlation, then corrected ~ same as treating them as  0 ’s

2 GeV - fit with and without Coulomb

4 GeV - fit with and without Coulomb

6 GeV - fit with and without Coulomb

8 GeV - fit with and without Coulomb

~ logarithmic E beam  E beam M max  M max + 50 M  max  M  max + 15

Only  - used in HBT analysis Restrictive cuts  actual  - multiplicity higher

Systematics smooth Leads to E866 data with similar coverage RQMD with or without meanfield reproduces data at higher energies 2 GeV may be interesting with more statistics lisa: before this comes the 4- panel 1d HBT with fits and 4-panel HBT with RQMD (both in “portrait” file) lisa: before this comes the 4- panel 1d HBT with fits and 4-panel HBT with RQMD (both in “portrait” file)

Resolution from pixel-level simulations Multiple Coulomb Scattering dominates resolution for  ’s:  p j ~ % overall NOTE: data not corrected for Q-resolution model results smeared instead  p x does NOT depend on q x  ~ 10 MeV/c q-resolution

 1D fits not affected by resolution ( %)

However, not a lot of breathing room.... sensitivity very nonlinear

“Standard” Bertsch-Pratt coordinate system

Bertsch-Pratt parameters - what do they measure? Spatial RMS of source Can get temporal RMS Usually a small difference of large numbers emission duration longest at low p T 3-4 fm/c greatest seen so far with pions

Measuring size and lifetime with protons at low energy PRL (1993) lisa: this is just to show that lifetimes CAN be measured lisa: this is just to show that lifetimes CAN be measured

Q out -Q long correlations forward and backwards For present analysis at low p T, near y cm, R ol 2 usually consistent with 0 lisa: before this comes the similar plot from the NA49 thesis (in portrait-mode file) lisa: before this comes the similar plot from the NA49 thesis (in portrait-mode file)

3D HBT - 4, 6, 8 AGeV central collisions midrapidity Performed in y cm frame R out  R side R ol  0 Projections integrated over 30 MeV/c in other components

3D HBT Excitation Function at midrapidity

RQMD reproduces 3D HBT with or without meanfield

3D Excitation Function No jumps in any 3D parameter no large sensitivity to meanfield l parameter in RQMD fits somewhat unstable  large errors indicated

Momentum resolution more impt to 3D correlation functions included in all model comparisons

Long-lived resonance contribution in RQMD most impt at low pt and midrapidity

Any strong variations somewhere on phase space?  study/test HBT systematics in small chunks 10% most central collisions (not acceptance corrected) lisa: this has the FOUR low pt rapidity windows for the 4 GeV lisa: this has the FOUR low pt rapidity windows for the 4 GeV

Scanning rapidity with low p T 4 GeV central data lisa: this is the 4panel 4gev plot (fits) lisa: this is the 4panel 4gev plot (fits)

lisa: this is the 4panel 4gev plot (RQMD) lisa: this is the 4panel 4gev plot (RQMD) RQMD follows trends very well (with or without field)

4 GeV central collisions medium p T

Data vs RQMD - 4 GeV central medium p T

8 GeV central collisions low p T

Data vs RQMD - 8 GeV central low p T

8 GeV central collisions medium p T

Data vs RQMD - 8 GeV central medium p T

Particles output by RQMD Sources of  -        ’’

      ’’ Particles output by RQMD Sources of  -

Effect of manual decays

Position-Momentum correlations Rescattering, decays, decompression, lead to correlation between x and p Strength of correlation grows with p T Leads to smaller apparent source parameters in HBT measurements RQMD v2.3

Slightly stronger correlation with meanfield in RQMD Find  x-p vs p T independent of impact parameter

Explicit removal of x-p correlations RQMD x 1, p 1 x 2, p 2... Pratt CRAB code Scramble x 1, p 420 x 2, p (x i  x i, p i  p j ) pairs more spatially separated on average  reduced correlation weighting Exactly same points used  same bin-to-bin fluctuations

x-p correlations affect higher p T pairs

Dynamic  -emitting source Static (non-longitudinally expanding) source  Y source = 0 Boost-invariant expansion  Y source = Y 

timescale decreases slightly at higher energy (3-4 fm/c at SPS) locally spherical source with energy-independent scale

Summary HBT excitation function measured over large region of phase space present analysis restricted to low p T No surprising jumps in HBT systematics but would like more statistics at 2 AGeV Systematics consistent with measurements at max AGS energy standard hadronic model (RQMD) reproduces data well No large sensitivity to meanfield effects Flow effects affect fit radii at larger pT E895 low p T measurements sensitive to geometry MCS-dominated resolution reduces measured 3D radii by as much as 20% Bertsch-Pratt Rout ~ Rside decreases with energy due to resonances and resolution Yano-Koonin locally spherical with non-zero lifetime non-boost-invariant longitudinal flow of source seen

Reconstructed reaction plane flat in lab  Dispersions (and corrections) get large for 8 AGeV, where flow is small Plots by C. Pinkenburg Reaction plane reconstructed by method of Danielewicz/Odyniec

Systematics/meta-analysis suggest approach to maximum AGS energy interesting... P. Braun-Munzinger and J. Stachel, NPA606, 320 (1996) B. Hong et al. (FOPI) Proceedings of International Workshop, Poiana Brasov, Romania (1996)