Laying the groundwork at the AGS: Recent results from E895 Mike Lisa, for the E895 Collaboration

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Laying the groundwork at the AGSRecent results
from E895Mike Lisa, for the E895 Collaboration
N.N. Ajitanand, J. Alexander, D. Best, P. Brady,
T. Case, B. Caskey, D. Cebra, J. Chance, P.
Chung, 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, 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 - St.
Marys College - OSU - Purdue - Stony Brook
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Reminder why AGS is (still) interesting
before E895
spp

• sets baseline systematicsyour systematics
  deviate from what?
• the other extreme condition - maximum baryon
  density
• probe medium bulk effects
• transition region for bulk properties

Fy
v2
?b?
T
Ebeam
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This talk

• Not a final wrap-up of E895, which is still
  alive. Since QM99
• PRL 83 1295 (1999) Transition from out-of-plane
  to in-plane elliptic flow
• PRL 84 2798 (2000) Bombarding energy dependence
  of p- HBT at the AGS
• PRL 84 5488 (2000) Sideward flow in AuAu
  collisions at 2-8 AGeV
• PRL 85 940 (2000) Anti-flow of K0 mesons in 6
  AGeV AuAu collisions
• PLB 496 1 (2000) Azimuthal dependence of pion
  interferometry
• PRL accepted (2000) L flow in 2-6AGeV AuAu
  collisions

• Published E895 flow
• Beyond proton flow - collective flow of strange
  particles
• Geometrical dependence of flow
• HBT Beyond Rp 5 fm
• geometric aspects of collective flow
• 6D phasespace density
• ?-p correlations
• Summary

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Measurement with the EOS TPC

• Up to 350 particles/event measured over large
  phase space
• Good reaction plane resolution
• ?p/p ? 3 (dominated by MCS)

Grandfather of STAR TPC
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Mike Lisa make bigger fonts!!!!
The Four Fundamental Corners of E895
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Reminder from QM99 Proton Flow
sideward flow
elliptic flow

• Transition region for flow mapped
• F drops as resonances dominate
• Strong sensitivity to medium contributions to
  pressure
• No single parameterization reproduces flow
  details
• No sudden drops in pressure (flow) signaling
  phase transition

Momentum space
PRL 83 1295 (1999) PRL 84 5488 (2000)
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Beyond protons...
neural networks identify decays of neutral
strange particles
L production excitation function
?L?
Minv (GeV/c2)
see talk of Chris Pinkenburg today
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L flow

• positive L flow
• decreases with Eb (more than p)
• RQMD (without L potential) underpredicts effect
• probe L potential at high r (complements
  hypernuclei studies) ? astrophysical models

2 AGeV
4 AGeV
? px ? (GeV/c)
quark counting
6 AGeV
y/ycm
see talk of Chris Pinkenburg today
PRL accepted (2000)
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K0S (anti-)flow

• Surprise strong antiflow
• grows with collision energy

see talk of Chris Pinkenburg today
PRL 85 940 (2000)
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proton elliptic flow - varying the geometry
0
-.02
min-bias flow measurements do not constrain
models ? geometry provides another handle on
flow increasing spatial asymmetry produces
larger signal Can HBT give geometrical
information on flow??
2 AGeV
-.04
D
.02
4 AGeV
0
v2
-.02
6 AGeV
.01
-.01
2
4
6
8
0
b (fm)
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HBT probing freeze-out space-time structure I -
Cylindrical sources
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HBT probing freeze-out space-time structure II -
Collisions at b?0
side
y
K?

• Source in b-fixed system (x,y,z)
• Space/time entangled in pair system (xO,xS,xL)

out
f
x
b
(several terms vanish _at_ pT y 0)
U. Wiedemann, PRC 57, 266 (1998) MAL, U. Heinz,
U. Wiedemann PLB 489, 287 (2000) See Poster by U.
Heinz
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First-order information in HBT(f)
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Data p- correlation functionsAu(4 AGeV)Au,
b?4-8 fm
2D projections
1D projections, f45
C(q)
out
side
long
lines projections of 3D Gaussian fit

• 6 components to radius tensor i, j o,s,l

E895, PLB 496 1 (2000)
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Cross-term radii Rol, Ros, Rsl quantify tilts
in correlation functions
? fit results to correlation functions
Mike Lisa thicker lines!!! bigger symbols!! have
2 GeV handy
Lines Simultaneous fit to HBT radii to extract
underlying geometry
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Images of p--emitting sources (scaled x1014)
Mike Lisa 1 fm 1/4
2 AGeV
4 AGeV
6 AGeV
Large, positive tilt angles
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Opposing average tilts in p, x and the physics of
p flow

• p antiflow (negative tilt in p-space)
• x-space tilt in positive direction
• ? non-hydro nature of p flow

B. Caskey
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Tomography in 6 Dimensions
Flow analysis and HBT relative to the reaction
plane allow a complete characterization of the
final state in phase space, get space-momentum
correlations
6 dimensional Tomography of proton flow
6 AGeV
Momentum Space (Flow)
Coordinate Space (HBT)
pz
py
px
Tiny flow angle
positive v2
px
Large tilt
Out-of-plane
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More on position - momentum space
relationshipthe phasespace density

• f occupation of 6-D position?momentum cell,
  volume h3
• determines magnitude of multi-particle
  correlations (lasers)
• provides a test of thermalization/consistency

T determines number of p, as well as spectral
shape
G. Bertsch, PRL 72 2349 (94) D. Ferenc et al, PL
B457 347 (99)

• observation _at_ SPS, AGS Universal p freeze-out
  density
• breaks down at lower energies?

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Measured phasespace densities

• non-universal growth of ?f? with collision energy
• flt1 ? no condensate

midrapidity central collisions
preliminary
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Measured phasespace densities

• non-universal growth of ?f? with collision energy
• flt1 ? no condensate
• low-pT saturation of ?f? as Ebeam ? 8 AGeV
• same occupancy as STAR!

midrapidity central collisions
preliminary
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Measured phasespace densities

• non-universal growth of ?f? with collision energy
• flt1 ? no condensate
• low-pT saturation of ?f? as Ebeam ? 8 AGeV
• same occupancy as STAR!
• Rough agreement with thermal Bose-Einstein
• high-pT excess _at_ high Eb

midrapidity central collisions
preliminary
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Measured phasespace densities

• non-universal growth of ?f? with collision energy
• flt1 ? no condensate
• low-pT saturation of ?f? as Ebeam ? 8 AGeV
• same occupancy as STAR!
• Rough agreement with thermal Bose-Einstein
• high-pT excess _at_ high Eb
• Better description by inclusion of radial
  flowB. Tomasik, Ph.D. thesis
• Substantial experimental theoretical
  uncertainties

midrapidity central collisions
preliminary
also see poster of D. Cebra
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Baryon correlations

• pp correlations Ebeam independent
• another handle on baryon source?

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Another E895 first L-p correlation function

• positive correlation observed
• qualitatively different shape than expected from
  Urbana p-L potential
• ? input to the particle physics
• work in progress

1.4
1.0
C(k)
0.6
1.4
1.0
0.6
100
80
60
40
20
0
k (MeV/c)
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Summary I

• continuing to push the envelope
• directed and elliptic flow excitation function
• continue input to bulk parameterization
• strange particle flow
• positive L flow
• does not scale with proton flow (naïve 2/3 rule
  broken)
• L potential important to describe flow
• strong antiflow of K0s
• strong, repulsive vector potential indicated
• Varying geometry (impact parameter) another
  handle
• increased x asymmetry ? larger p asymmetry

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Summary II

• azimuthally-sensitive p- HBT
• almond-shaped source, ( entrance-channel
  geometry)
• large positive spatial tilt angles
• non-hydro nature of p flow
• coordinate-space structure of proton flow
• 6-D p phasespace density
• non-universal growth of ltfgt with energy
• saturation to universal behaviour at 8 AGeV
• after 8 AGeV, increased p yield pushed to high
  pT ?flow
• first p-L signal observed
• significant positive correlation
• inconsistent with shape expected by Urbana
  potential

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More E895 _at_ QM01

• Production Collective Behaviour of Strange
  Particles Parallel session today Chris
  Pinkenburg
• p Phasespace Density Source Charge
  Density P063 Dan Cebra
• Directed, Elliptic, Radial, Longitudinal
  Flow P069 Jenn Klay
• Azimuthally-sensitive HBT and the Tilt of the p
  Source P018 Ulrich Heinz

honorary E895 member
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Pion and proton elliptic flow

• Ellitpic flow of both positive and negative pions
  follows the trends of the protons

W. Caskey, DNP98