Two-particle correlations on transverse rapidity and the momentum dependence of angular correlation features in Au+Au collisions at = 200 GeV at STAR Elizabeth W. Oldag for the STAR Collaboration October 28, 2011

E. Oldag (UT Austin)- DNP MSU 2 Two-particle correlation measure Fill 2D histograms (x 1,x 2 ): e.g. (y t,y t ),(Φ Δ =Φ 1 -Φ 2,η Δ =η 1 -η 2 )… Fill 2D histograms (x 1,x 2 ): e.g. (y t,y t ),(Φ Δ =Φ 1 -Φ 2,η Δ =η 1 -η 2 )… Sibling Pairs Sibling Pairs Mixed Pairs Mixed Pairs Final Measure: Final Measure: Number of correlated pairs per final state particle Number of correlated pairs per final state particle Data Set: 2004 Au+Au Collisions at 200 GeV, ~11.5 Million Minimum Bias Events, p t >0.15 GeV/c, |η| 0.15 GeV/c, |η| < 1, full φ Normalized Ref Pairs: Total number of sibling to mixed pairs

E. Oldag (UT Austin)- DNP MSU 3 A For example For example Centrality (55-64%) Centrality (55-64%) No particle identification, y t is simply a useful logarithmic measure No particle identification, y t is simply a useful logarithmic measure Notice a peak or “bump” around 3 in y t (1.4 GeV/c) Notice a peak or “bump” around 3 in y t (1.4 GeV/c) (p t,p t )→(y t,y t ) ytyt ytyt ytyt ytyt ytyt ptpt ptpt ptpt ptpt ytyt p t (GeV/c)

E. Oldag (UT Austin)- DNP MSU 4 (y t, y t ) Correlations 200 GeV Au+Au *STAR Preliminary All pairs Charge Independent p t ≥ 0.15 GeV/c at (3,3) (1.4 GeV/c) persists through higher centralitiesPeak at (3,3) (1.4 GeV/c) persists through higher centralities

E. Oldag (UT Austin)- DNP MSU 5 Discussion of Transverse Rapidity Correlations Use (y t,y t ) correlations to test theories Semi-hard jet fragmentation (i.e. minijets) Glasma flux-tubes (see Lanny Ray’s talk later in this session) Peak around (y t,y t )=(3,3) (p t = 1.4 GeV/c) HIJING: Further evidence gathered by selecting pairs from distinct momentum regions and fitting with a well studied 11 parameter fit function [arXiv: ] Plots from M. Daugherity Jets Off Jets On ytyt ytyt ytyt ytyt

E. Oldag (UT Austin)- DNP MSU 6 (y t, y t ) Pair Selection and Fit Function Weighting factors are applied to each cut bin to accurately compare fit values η Δ Φ Δ ref   y t,1 y t,2     i ref ref,tot iref ytall ref N N    ,, 2D Fit

E. Oldag (UT Austin)- DNP MSU 7 Map back onto (y t,y t ) space the features of interest, for example: Volume of the 2D Gaussian The integral of the 2D Gaussian over a range of η Δ Amplitude of the dipole Prefactor applied in order to get the number of correlated pairs in an angular correlation feature, for pairs in a (y t,y t ) bin, per final state particle on y t Displaying Fit Results ytyt Volume = ytyt

E. Oldag (UT Austin)- DNP MSU 8 Total 2D Gaussian Volume *STAR Preliminary Peak is observed around (3,3) and remains at the same approximate location as the centrality increases

E. Oldag (UT Austin)- DNP MSU 9 2D Gaussian Volume by η Δ Region *STAR Preliminary Peak position does not soften in y t as the cut region moves towards the edge of the 2D Gaussian ηΔηΔ ΦΔΦΔ ηΔηΔ ΦΔΦΔ ηΔηΔ ΦΔΦΔ

E. Oldag (UT Austin)- DNP MSU 10Dipole *STAR Preliminary

E. Oldag (UT Austin)- DNP MSU 11 Conclusion The correlated pairs that contribute to the 2D Gaussian structure, hypothesized to be from minijets, have a momentum distribution peaked around (y t,1,y t,2 )=(3,3) (1.4 GeV/c). The extended correlation on η Δ, commonly referred to as the “ridge”, is not comprised of softer pairs relative to the center of the jet peak. The dipole (dijet away-side) does not soften with an increase in centrality. Currently working on repeating same cut scheme but with identified particles. Plan to study correlations of baryons vs. mesons and strange vs. non-strange particles.

E. Oldag (UT Austin)- DNP MSU 12 Backup p t integrated 2D Gaussian amplitude versus centrality arXiv: