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The Balance Function: Experimental Studies in STAR

The Balance Function: Experimental Studies in STAR. Marguerite Belt Tonjes, G.D. Westfall, A.M. Vander Molen, the STAR collaboration. STAR. S olenoidal T racker A t R HIC

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The Balance Function: Experimental Studies in STAR

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  1. The Balance Function:Experimental 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.

  3. Selecting Good Data • Use Au+Au 130GeV events from Year1 running, summer, 2000 • Physics events: • Central trigger • Minimum bias trigger • -75cm ≤ vertexz ≤ 75cm • -1cm ≤ vertexx ≤ 1cm, • -1cm ≤ vertexy ≤ 1cm

  4. Selecting good TPC tracks Collaboration-wide selection cuts • | h | < 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 > 0.52

  5. 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. PID

  6. PID cuts • ZPidp = ln( Imeas/Ihyp(p)) • Imeas = measured truncated mean for track • Ihyp(p) = expected ionization for p hypothesis • p: p≤0.7 GeV/c, and |ZPidp|≤0.2 • K: p≤0.8 GeV/c, |ZpidK|≤0.2, |ZPidp|>0.2, |ZPidp|>0.2 • P: p≤ 1 GeV/c, |ZPidp|≤0.2, |ZPidp|>0.2, |ZPidK|>0.2 • E: |ZPide|≤0.2, |ZPidp|>0.2, |ZPidK|>0.2, |ZPidp|>0.2

  7. 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-)|

  8. 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

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

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