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Autocorrelations and Event Structure from STAR

Autocorrelations and Event Structure from STAR. Lanny Ray STAR Collaboration University of Texas at Austin June 21, 2005. Outline: Introduction – studying the medium in RHIC Au-Au collisions at low-to-intermediate p t via joint autocorrelations .

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Autocorrelations and Event Structure from STAR

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  1. Autocorrelations and Event Structure from STAR Lanny Ray STAR Collaboration University of Texas at Austin June 21, 2005 RHIC & AGS User's Meeting

  2. Outline: • Introduction – studying the medium in RHIC Au-Au collisions at low-to-intermediatept via joint autocorrelations. • p+p correlations as a reference for A+A • Charge-independent number correlations • Transverse momentum correlations • Conclusions RHIC & AGS User's Meeting

  3. B A ‘trigger’ ? fragmentation color energy loss Introduction: Why study correlations at low-to-intermediate pt? Df high pt process in A-A collision RAA A “jet quenching” & high gluon density B trigger/associated conditional distribution inclusive pt spectrum To learn about the nature of the medium we borrow techniques from 1905… RHIC & AGS User's Meeting

  4. what is the microscopic structure of matter? 1905 Brownian motion A. Einstein P. Langevin probe particle: 1) large enough to be observed 2) small enough to visibly experience medium dynamics velocity displacement At RHIC, low-Q2 scattered partons serve as the analogous “small” probe that may be affected by the constituents of the medium but are “big” enough to be observed via correlation structures. Of course, such probes are extended objects with internal structure. RHIC & AGS User's Meeting

  5. Autocorrelations How can we measure soft ptcorrelation structures which consist of only a few particles, with multiple instances per A-A collision event, when there is no basis for assigning a “trigger” particle? The autocorrelation, best known from time series analysis, integrates multiple instances of any repeated structure on h,f into a single, statistically significant structure on relative h1-h2 and f1-f2. Simulations of multiple, per event correlations from low-Q2 partons: Construct two-particle autocorrelations using all particle pairs No trigger particle RHIC & AGS User's Meeting

  6. Event 1 Sum the number of sibling pairs in each bin in (f1-f2) vs (h1-h2) for all events in all subsets Define the bin-by-bin ratio: Event 2 Azimuth angle f Similarly, sum the number of mixed-event pairs in each bin in (f1-f2) vs (h1-h2) for all events in all subsets Pseudorapidity h Constructing the Joint (2D) Autocorrelation Joint-Autocorrelation (2D) (on relative coordinates) fD = f1-f2 hD = h1-h2 beam axis Normalized Joint-Autocorrelation: RHIC & AGS User's Meeting

  7. ρsibling(p1,p2) Event 1 ρreference(p1,p2) Event 2 Constructing the Joint Autocorrelation per-particle ρ(p1,p2)= 2 particle density in momentum space Or, relating Δρ to a histogram, bin (a,b) can be written as: (where e is the bin size) is a per-particle measure Normalize with where bin (a,b) is on relative pseudorapidity and azimuth coordinates hD = (h1 - h2) and fD = (f1 - f2). RHIC & AGS User's Meeting

  8. Justification for the Joint Autocorrelations Au-Au at 130 GeV like sign unlike sign hD hS h1vsh2 t STAR preliminary fD fS f1vsf2 STAR preliminary Correlations on (x1,x2); use rotated coordinates (xD,xS ) along symmetry axes; structures are found to be invariant on xS (“stationary”); all structure retained on xD– a lossless projection. RHIC & AGS User's Meeting

  9. Jet-A proton parton-parton cm Jet-B NN cm A-A B-B h A-B B-A A-A B-B A-B B-A proton Number of pairs Number of pairs h1-h2 0 0 p fD=f1-f2 Example of Joint Autocorrelation: di-jets in p-p collisions p-p 200 GeV STAR preliminary sum over many events Additional jets, if random, add to these structures. RHIC & AGS User's Meeting

  10. STAR preliminary US LS AS SS 10.0 1.0 pt(GeV/c) 0.15 p+p correlations as a reference for A+A: Project the same-side and away-side joint autocorrelations onto transverse rapidity p-p at 200 GeV Two components: Longitudinal string and scattered parton fragmentation showing two-particle fragment distributions SS - same side AS - away side US LS STAR preliminary RHIC & AGS User's Meeting

  11. 200 GeV p-p joint autocorrelations on (hD,fD) a study in local charge and momentum conservation PF SF longitudinal string fragments: pt transverse parton fragments:  jt ,kt SF PF US LS US LS STAR preliminary CI=LS+US CI=LS+US RHIC & AGS User's Meeting

  12. pQCD pQCD jth jtf Fragment asymmetry about thrust axis – p-p at 200 GeV larger Q2 ytS STAR preliminary small Q2 jth jtf vary ytS slice STAR preliminary previously unexplored region! pQCD width at high pt Broader azimuthal width for soft “jets”; large non-perturbative effect. RHIC & AGS User's Meeting

  13. charge-ordering local momentum conservation pt,2 Semi-hard parton scattering “minijet” (min-bias) pt,1 Two-component model for high energy p-p collisions • Two-Component Model: • Longitudinal color string fragmentation – low pt particle production • Transverse semi-hard parton scattering and fragmentation (i.e. breakup into hadrons) • Local charge and momentum conservation Longitudinal string fragments, soft pt Joint autocorrelation measurements of minimum bias (no trigger), same- side jet-like structure in p-p collisions provides an observable, low-Q2 probe of the A-A medium. RHIC & AGS User's Meeting

  14. Charge-independent number correlations: All Charges Central h,fautocorrelations for 130 GeV Au-Au: (correlation amplitude per final state hadron) Features: peak at small relative angles cos(fD) – momentum conser- vation at low pt cos(2fD) - elliptic anisotropy J. Adams et al. (STAR), nucl-ex/0411003. Peripheral ~300k events 0.15 < pt<2 GeV/c |h|<1.3, full f=2p merging & HBT cuts applied RHIC & AGS User's Meeting

  15. h,fautocorrelations for 130 GeV Au-Au; subtract cos(fD) and cos(2fD) central • Notable Results: • Absence of away-side soft • string fragmentation structure • beginning in most peripheral bin. • Elongation along hD • Narrowing along fD J. Adams et al. (STAR), nucl-ex/0411003. p-p 200 GeV STAR preliminary peripheral RHIC & AGS User's Meeting

  16. Centrality dependence of same-side correlation structure widths amplitude & volume amplitude Correlation amplitude and volume per final state particle. Relative f,h widths reversed for central Au-Au compared p-p Linear amp. increase Factor 2.3 increase RHIC & AGS User's Meeting

  17. h,fcorrelations for 62 GeV Au-Au p-p 200 GeV STAR preliminary Correlation structure evolves smoothly from p-p to central Au-Au 0.15 < pt<2 GeV/c |h|<1.0, full f=2p merging & HBT cuts applied Peripheral ΦΔ ΦΔ ΦΔ ΦΔ ΦΔ ηΔ ηΔ ηΔ ηΔ ηΔ STAR Preliminary Central ΦΔ ΦΔ ΦΔ ΦΔ ΦΔ ηΔ ηΔ ηΔ ηΔ ηΔ RHIC & AGS User's Meeting

  18. min-bias Hijing Hijing-1.37 Au-Au 200 GeV with & without jet quenching; same-side peak widths increase (Liu, Prindle, Trainor hep-ph/0410180) Gluon bremsstrahlung/ medium dragging calculations: (Armesto, Salgado, Wiedemann, hep-ph/0405301) 100 GeV jet Possible interpretation… Au Soft, away-side recoil, cos(fD) minijet Au Interaction with longitudinally expanding color fluid drags pre-hadronic matter associated with semi-hard partonic scattering along pseudorapidity. RHIC & AGS User's Meeting

  19. Transverse momentum correlations: Number Correlation pt Correlation STAR 130 GeV mid-central STAR Preliminary ηΔ ΦΔ Here pt correlations for bin (a,b) is the pt covariance between particles with separation (ηΔ,ΦΔ) RHIC & AGS User's Meeting

  20. 1D b distribution b2 f b2 b1 local parent b1 h 1D projection ptautocorrelations access variations in effective temperature b(h,f) ptdistribution at point #1: beam axis Lévy distribution: Consider the possibility that the b’s are correlated in each event but the pattern of hot/cold or blue/red-shift spots changes from event-to-event. pt autocorrelations measure the relative size and intensity of repeated “hot/cold” patterns in the h,f distributions at RHIC. WMAP CMB survey One BIG event RHIC & AGS User's Meeting

  21. “discrete integral” variance difference event-wise mean ptvariance minus variance of inclusive reference distribution [see Phys. Rev. C (2005); nucl-ex/0308033] pt correlation 2D binning function Method used by STAR which allows measurement of normalization 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 RHIC & AGS User's Meeting

  22. Minijets: velocity/temperature correlation structures on (h,f) Strong elongation on h and new negative same-side structure fD hD  pt  Fluctuations and pt Correlations – 200 GeV Au-Au partons and velocity correlations fluctuation scale dependence 70-80% STAR preliminary autocorrelation 20-30% fluctuation inversion centrality subtract multipoles 0-5% RHIC & AGS User's Meeting STAR preliminary

  23. collision centrality Model Fits, Hijing and a New Feature amplitudes widths data fit 20-30% fit peak STAR preliminary data - fit peak fit residuals Hijing Au-Au 200 GeV 0-10% centrality recoil? Quench off & on RHIC & AGS User's Meeting

  24. Medium response to minimum-bias parton stopping Momentum transfer to medium Velocity structure of medium Medium recoil observed viasame-sideptcorrelations low-x partons recoil Au-Au 200 GeV parton fragments STAR preliminary STAR preliminary  blue shift red shift bulk medium pt autocorrelation Recoil Response to Parton Stopping RHIC & AGS User's Meeting

  25. Same-side Medium Recoil jet 200 GeV Au-Au p-p 200 GeV ~x4 80-90% ~ p-p recoil peripheral 45-55% STAR preliminary 20-30% 0-5% central RHIC & AGS User's Meeting

  26. SPS  RHIC full acceptance scale dependence STAR centrality CERES NPA727:97, 2003 STAR preliminary STAR dramatic increase of  pt fluctuations with increasing sNN Hijing CERES RHIC & AGS User's Meeting

  27. Conclusions: • Low-Q2 partons probe constituents of the medium; autocorrelations integrate multiple, per-event instances of a few correlated fragments. • The 2-component structure of p-p collisions is apparent; strong fragment angular asymmetry observed at low Q2. • Strong increase in same-side correlation width along h in Au-Au. • Evidence suggests medium recoils against low-Q2 partons. • Observations are consistent with a picture in which semi-hard parton scattering • transfers pt to the medium, inducing temperature/velocity fluctuations and recoil, • where correlated particles are carried by the longitudinally expanding medium. Evidence for a nonequilibrated, pt dissipative, viscous medium! RHIC & AGS User's Meeting

  28. The STAR Collaboration Brazil: Universidade de Sao Paulo China: IHEP – Beijing IMP - Lanzou IPP – Wuhan USTC SINR – Shanghai Tsinghua University Croatia: U. Zagreb Czech Republic: NPI – Prague Great Britain: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University University of Rajasthan Jammu University IIT - Bombay VECC – Kolcata The Netherlands: NIKHEF – Amsterdam Poland: Warsaw University of Tech. Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino Switzerland: Univ. Bern U.S. Laboratories: Argonne Berkeley Brookhaven U.S. Universities: UC Berkeley Cal Tech UC Davis UC Los Angeles Carnegie Mellon Creighton University Indiana University Kent State University MIT Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin U. of Washington Valparaiso U. Wayne State University Yale University RHIC & AGS User's Meeting

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