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Energy Dependence of Minijet Structure in Au-Au Collisions at √sNN = 19-200 GeV

Explore the correlation measures in events of proton-proton to central Au-Au collisions at different GeV energies, revealing the evolution of minijet structure and pt correlations. Discover how energy and centrality influence the minijet correlation structure, providing insights into the colored medium in RHIC collisions.

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Energy Dependence of Minijet Structure in Au-Au Collisions at √sNN = 19-200 GeV

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  1. Energy dependence of minijet structure inAu-Au collisions at √sNN = 19 – 200 GeV STAR Collaboration DNP 04 Michael Daugherity Graduate Student - University of Texas

  2. Correlation Measures I ρsibling(p1,p2) Event 1 ρreference(p1,p2) Event 2 Normalize with the previous talk used Number Correlations ρ(p1,p2)= 2 particle density in momentum space Or, defining Δρ as a histogram, bin (a,b) can be written as: is a per-particle measure We calculate this as a function of (ηΔ = η1 –η2, ΦΔ= Φ1 – Φ2), separation in pseudorapidity and azimuth (axial momentum space) Daugherity – DNP 04 University of Texas

  3. centrality proton-proton 200 GeV • Correlation structure evolves smoothly from p-p to central Au-Au • Measure of minimum-bias jets (minijets) STAR Au-Au 62 GeV Number Correlations Peripheral ΦΔ ΦΔ ΦΔ ΦΔ ΦΔ ηΔ ηΔ ηΔ ηΔ ηΔ STAR Preliminary Central ΦΔ ΦΔ ΦΔ ΦΔ ΦΔ ηΔ ηΔ ηΔ ηΔ ηΔ Daugherity – DNP 04 University of Texas

  4. Correlation Measures II Above plots showed number correlations, we can also find correlations in pt Number Correlation pt Correlation STAR 130 GeV mid-central STAR Preliminary ηΔ ΦΔ We will discuss pt correlations where bin (a,b) is the pt covariance between particles with separation (ηΔ,ΦΔ) Daugherity – DNP 04 University of Texas

  5. Centrality Dependence of ptCorrelations centrality STAR 62 GeV pt Correlations 70-80% 55-65% 45-55% STAR Preliminary 35-25% 5-10% 0-5% Daugherity – DNP 04 University of Texas

  6. Energy Dependence of ptCorrelations Peripheral 19 GeV 62 GeV 130 GeV 200 GeV STAR Preliminary Mid-central 19 GeV 62 GeV 130 GeV 200 GeV Daugherity – DNP 04 University of Texas

  7. Isolating Minijet Structure Isolate “same-side” peak (ηΔ,ΦΔ≈ 0) by subtracting azimuth multipole components 62 GeV unsubtracted data 70-80% 45-55% 15-25% 62 GeV subtracted data same as above, but with cos(ΦΔ) and cos(2ΦΔ) components subtracted STAR Preliminary Daugherity – DNP 04 University of Texas

  8. Energy and Centrality Dependence of Minijets subtracted data 19 GeV 62 GeV 130 GeV 200 GeV Peripheral Mid-central STAR Preliminary Central

  9. Summary • Minijets (minimum-bias parton fragments) produce number and pt correlations in axial momentum space • Minijet structure is revealed with minimum bias by two-particle correlations formed with no trigger particle • pt correlations attributed to minijets are strongly energy and centrality dependent • Minijet correlation structure probes the colored medium produced in RHIC Au-Au collisions Daugherity – DNP 04 University of Texas

  10. Extra Slides Daugherity – DNP 04 University of Texas

  11. Extra Slide 1 – Direct Method for pt Correlations # of pairs Single Event ΦΔ Sum over events ηΔ b ΦΔ a ηΔ Find pt covariance between particles in bins a and b: Normalize to number of particles in bins a and b: Construct pt correlation for all bins (a,b): Daugherity – DNP 04 University of Texas

  12. Extra Slide 2 – Fluctuation Inversion “discrete integral” variance difference event-wise mean pt variance minus variance of inclusive reference distribution (see nucl-ex/0308033) pt correlation 2D binning function The pt correlation data were obtained with the fluctuation inversion method Fluctuation Inversion in a Nutshell: Calculate Δσ2pt:n then numerically invert to find pt correlations see hep-ph/0410180 and hep-ph/0410182 for details Daugherity – DNP 04 University of Texas

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