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Characterization of the pion source at the AGS

Characterization of the pion source at the AGS. Motivation and Measurement Systematics of HBT in E895 Existing problems - failed consistency check Summary. Mike Lisa The Ohio State University. APS Meeting March 1999. E895 @ AGS. AGS. SPS. RHIC. AGS. SPS. RHIC. with transition.

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Characterization of the pion source at the AGS

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  1. Characterization of the pion source at the AGS • Motivation and Measurement • Systematics of HBT in E895 • Existing problems - failed consistency check • Summary Mike Lisa The Ohio State University APS Meeting March 1999

  2. E895 @ AGS

  3. AGS SPS RHIC AGS SPS RHIC with transition observable observable ec E E “e” ?? !! Motivation 2) watch for “anomolous” lifetimes/sizes(QGP@AGS?) 1) fully characterize HBT systematics as fctn of collision conditions: Ebeam, b, y, mT, frp 3D hydro model Rischke & Gyulassy NPA 608, 479 (1996) ~ emission timescale 3) test dynamical models that provide “hadronic baseline”: can they extrapolate to RHIC? Signatures may be subtle

  4. Mmax 180 (320) at 2 (8) AGeV • Npa M • dp/p  1% •  5% e- contamination

  5. 1D p- HBT Excitation Function Smooth evolution of source parameters

  6. Bertsch-Pratt projections at ycm for central collisions

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

  8. Bertsch-Pratt & Yano-Koonin Fits - central collisions at ycm • RQMD with or without • meanfield: • Ebeam dependence weaker than observed • At low energy... • Effective spatial extent underpredicted • Effective temporal extent overpredicted

  9. AGS: apparent size underpredicted SPS: p- size overpredicted Extrapolate to RHIC? NA44RQMD 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)

  10. y (fm) x (fm) y (fm) x (fm) • Well reproduced by RQMD • l increases w/ mT due to decreased contrib from L’s... • mT falloff in Rlong greatest • mT falloff in Rout least 8 AGeV mT dependence mT dependence sensitive to space-momentum correlations, flow

  11. y (fm) x (fm) y (fm) x (fm) • Well reproduced by RQMD • l increases w/ mT due to decreased contrib from L’s... • mT falloff in Rlong greatest • mT falloff in Rout least 8 AGeV pT dependence pT dependence sensitive to space-momentum correlations, flow

  12. 6 AGeV mT dependence“again CERN-type systematics”

  13. 6 AGeV pT dependence“again CERN-type systematics”

  14. 4 AGeV mT dependence

  15. 4 AGeV pT dependence

  16. 2 AGeV mT dependence

  17. 2 AGeV pT dependence

  18. Rapidity dependence Strongest at lower energy (ybeam = 0.904 for 2 AGeV) Asymmetry about ycm may indicate major problem!?! Spurious y-dependent effect = spurious Ebeam-dependent effect?

  19. Centrality dependence pT=0.1-0.8, y=ycm0.4 Ignoring shadowing, flow, lifetime... Overlap region RMS changes ~35% between b=2, b=7 Gentle Mch dependence: Transverse radii vary by 15-35% strongest variation at 2 AGeV

  20. 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 PRL see also JB 12.02

  21. Nonspherical source (w/ no physics)“b=7 fm”  RMSx=3.5 fm RMSy=6.0 fm

  22. RQMD (w/meanfield) prediction of effect at ycmb=4-9 fm (perfect frp resolution) • 0.5 fm difference consistent w/RQMD freezeout geometry • Rs and Ro oscillate against each other  3D HBT more sensitive than 1D Elliptic flow of baryons

  23. b = 7 x and y from RQMD

  24. 2 and 4 AGeV, b=4-7 fm: promising signal in Rside, but... 4 AGeV, y=ycm  0.4 pT = 0.05 - 0.8 MeV/c 2 AGeV, y=(ycm-0.5) - ybeam pT = 0.1-0.8 MeV/c

  25. 6 AGeV midrapidity - no signal so far...

  26. Transverse source size varies with viewing angle with respect to reaction plane in peripheral collisions Transverse size small when viewed at 90o reaction plane target projectile overlap region

  27. Modulation of x-p correlation with frpenhances geometric effectstronger flow effects out of plane reduce Rside further.Meanfield required at low energy to give squeeze-out in momentum spaceModulation decreases with beam energy

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