The Balance Function: Experimental Studies in STAR

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The Balance Function: Experimental Studies in STAR

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The Balance Function: Experimental Studies in STAR Marguerite Belt Tonjes, G.D. Westfall, A.M. Vander Molen, the STAR collaboration Selecting Good Data Use Au+Au ... – PowerPoint PPT presentation

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Title: The Balance Function: Experimental Studies in STAR


1
The Balance FunctionExperimental Studies in STAR
  • Marguerite Belt Tonjes,
  • G.D. Westfall, A.M. Vander Molen, the STAR
    collaboration

2
STAR
  • Solenoidal Tracker At RHIC
  • large acceptance detector with near 4? coverage,
    study hadrons, jets, event-by-event, high pt
    particles, strangeness.

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4
Selecting Good Data
  • Use AuAu 130GeV events from Year1 running,
    summer, 2000
  • Physics events
  • Central trigger
  • Minimum bias trigger
  • -75cm vertexz 75cm
  • -1cm vertexx 1cm,
  • -1cm vertexy 1cm

5
Selecting good TPC tracks
  • Collaboration-wide selection cuts
  • h lt 1.3
  • 0.1 GeV/c pt 2 GeV/c
  • DCA 1 cm (distance of closest approach to the
    primary vertex ? choose tracks from the vertex)
  • Fit points 15
  • Fit points/possible points gt 0.52

6
PID
  • Compare measured dE/dx with Bethe-Bloch
    calculation of dE/dx for p, K, p, and e.
  • Particles within 2s of predicted ionization are
    tagged.

7
PID cuts
  • ZPidp ln( Imeas/Ihyp(p))
  • Imeas measured truncated mean for track
  • Ihyp(p) expected ionization for p hypothesis
  • p p0.7 GeV/c, and ZPidp0.2
  • K p0.8 GeV/c, ZpidK0.2, ZPidpgt0.2,
    ZPidpgt0.2
  • P p 1 GeV/c, ZPidp0.2, ZPidpgt0.2,
    ZPidKgt0.2
  • E ZPide0.2, ZPidpgt0.2, ZPidKgt0.2,
    ZPidpgt0.2

8
Calculating the Balance Function
  • For p pairs
  • B 1/2 D - /N D- /N- - D/N - D- -/N-
  • D- Histogram of y(p) - y(p-) , for all
    possible pairs within an event. This histogram is
    summed over all events.
  • For charged particle pairs, we sum over all
    charged particle pairs.
  • D- Histogram of h(particle)-h(particle-)

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12
Conclusions and future analysis
  • More statistics are needed, and are being
    analyzed
  • We see no difference between central and
    peripheral events in HIJING
  • Need to study beam pipe/detector effects for
    simulations
  • Study pt sensitivity
  • Look at pp simulations

13
Thanks to
  • Gary Westfall, Skip Vander Molen, Scott Pratt for
    much discussion of the analysis
  • The STAR Collaboration
  • DOE
  • NSF
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