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Low- Q 2 Partons in p-p and Au-Au Collisions

Low- Q 2 Partons in p-p and Au-Au Collisions. Tom Trainor ISMD 2005 – Krom ěříž , CR August, 2005. Agenda. Survey of p-p correlations Fragment distributions on (y t , y t ) in p-p Fragment distributions in Au-Au Angular correlations on ( h D ,f D ) in p-p

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Low- Q 2 Partons in p-p and Au-Au Collisions

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  1. Low-Q2 Partons in p-p and Au-Au Collisions Tom Trainor ISMD 2005 – Kroměříž, CR August, 2005

  2. Agenda • Survey of p-p correlations • Fragment distributions on (yt,yt) in p-p • Fragment distributions in Au-Au • Angular correlations on (hD,fD) in p-p • Angular correlations in Au-Au • pt correlations in p-p and Au-Au QCD from the bottom up

  3. Low-Q2 Partons in p-p Collisions minijet fragments nch=10 √Dr nch Dr/√rref nch=1 1D 2D p-p 200 GeV subtract soft reference pt yt away side same side hadron pt ~ 0.5 GeV/c yt2 yt2 Dr/√rref 0.15 1 6 yt1 pt (GeV/c) string fragments parton fragments minimum-bias: no trigger condition

  4. Analysis Method (yt1,yt2) correlations (h1,h2,f1,f2) correlations (yt,h,f) hD=h1-h2 Dr/√rref Dr/√rref fD=f1-f2 joint autocorrelation on two difference variables in each 2D bin: k xS xD x2 e – bin size average over a on kth diagonal modified Pearson’s coefficient: normalized covariance density a number of correlated pairs ‘per particle’ x1 a+k k autocorrelations can be determined by pair counting or by inversion of fluctuation scale dependence

  5. p-p Correlations on (yt1,yt2) string and parton fragmentation: first two-particle fragment distributions SS AS (except OPAL on x ) LS – like sign US – unlike sign SS – same side string HBT parton Dr/√rref Dr/√rref same-side parton fragmentation restricted to US pairs AS – away side string parton parton away-side parton fragmentation is independent of charge combination Dr/√rref Dr/√rref 10.0 1.0 pt(GeV/c) 0.15

  6. p-p Correlations on (hD,fD) PF local charge and momentum conservation SF joint autocorrelation on two difference variables SF – string fragments LS – like sign US – unlike sign HBT string string fragmentation reflects local measure conservation Dr/√rref Dr/√rref PF – parton fragments parton parton parton away-side parton fragmentation is independent of charge combination HBT Dr/√rref Dr/√rref

  7. Single-particle Fragmentation – I fragmentation functions on logarithmic variables e-e fragmentation functions on transverse rapidity yt – systematic variation described by single model function LEP PETRA e-e xp =pt /Ejet p-p jets: 105, 225, 350, 625 GeV e-e jets: 14, 44, 91 GeV x = ln(1/xp) LEP sampling: not full data! OPAL – 91 GeV TASSO – 14 GeV transverse rapidity yt conventional CDF PRD 68 (2003) 012003 OPAL PLB 247 (1990) 617 Biebel, Nason and Webber hep-ph/0109282 617 ln(pt)

  8. Single-particle Fragmentation – II simple e-e systematics on transverse rapidity  two-particle fragment distribution fit: b distribution e-e upeak p = 2.9 q = 3.55 14, 44, 91 GeV u= slope = 0.41 A = 0.65 ~ independent ofyt,max e-e mode mode: nch and xpeak values from Bethke hep-ex/9812026 unidentified hadrons from unidentified partons

  9. Two-particle Fragment Distributions an approach derived from fragmentation functions one can sketch a two-particle minimum-bias fragment distribution starting with a surface from which fragmentation functions are conditional slices symmetrize the surface to represent fragment-fragment correlations compare to data: general features agree; string fragments appear at small yt construct a surface representing frag- mentation functions vs parton momentum Q/2 US – same side Dyt~x xp≡-ln(xp) nch ytD 4 3 Q/2 2 1 fragment rapidity yt,peak 1 10 STAR preliminary Q/2 (GeV) parton momentum conditional: trigger particle data

  10. Number Correlations on ytyt evolution of fragment distribution with Au-Au centrality 200 GeV p-p 200 GeV Au-Au same-side - US peripheral Dr/√rref Dr/√rref Dr/√rref STAR preliminary central RAA Dr/√rref Dr/√rref Dr/√rref

  11. Jet Morphology Relative to Thrust angular correlations hadron momenta jet thrust axis (parton momentum) z pt2 jth jtf p-p collision axis pt1 jt – transverse momentum relative to jet thrust axis y f x h parton kt jth Dr/√rref most-probable parton Q/2 at right is 1-2 GeV/c, comparable to the intrinsic parton kt jtf

  12. Symmetrized Angular Kinematics remove trigger-associated asymmetry jt scaling (not generally valid) pt1,2,f1,2 independent random variables symmetrize: trigger, associated  particles 1, 2 pt,1 pout f1 pt,part f2 pS /2 pt,2 J. Rak, J. Jia kinematic limit asymmetric: T. Trainor, J. Porter symmetric: remove the trigger/associated asymmetry

  13. Symmetrize | jtf | and | ktf | no small-angle approximation, similar fragment pt same for AS SS pt (GeV/c) pt (GeV/c) 0.15 1 6 0.15 1 6 ytD ytS ytD ytS yt2 yt2 fDAS Dyt Dyt fDSS yt1 yt1 autocorrelation (fD=f12) STAR preliminary

  14. Angular Correlation Measurements AS SS ytS sh sf jt scaling STAR preliminary SS - same side AS - away side sf ktf jth jtf large same-side (h,f) asymmetry

  15. Fragment Asymmetry about Thrust evolution with Q2of soft jet angular asymmetry previously unexplored region! two-particle fragmentation yt cut space ytS pQCD pQCD hi pt combinations determine Q2 of parton interaction jth jtf lo STAR preliminary lo hi no trigger particle • Small-Q2 partons down to 1 GeV are detectable • These softest jets are strongly elongated • in the azimuth f direction in p-p collisions softest jets ever! big non-perturbative effects small Q2 larger Q2 200 GeV p-p 1:1 aspect ratio

  16. Interpretation water drops vrel = 6 m/s contact plane z  hydrodynamics of parton collisions broadened in contact plane (f,pt), narrowed perpendicular to it (h) contact plane z  df dpt low-Q2 fragmentation

  17. Minijet Deformation on (h,f) in Au-Au fragmentation asymmetry reverses – p-p  Au-Au central HI low Q2 p-p h f 130 GeV Au-Au p-p HI peripheral widths sh h low Q2 p-p f minbias p-p Au-Au sf centrality 130 GeV Au-Au mid-central low Q2

  18. The Other kt Broadening interaction between intrinsic kt and momentum transfer q the alignment between parton kts and q determines whether relative azimuth or relative pt of fragments will broaden azimuth broadening pt broadening condition on (yt1,yt2) biases away-side azimuth broadening US yt2 Dr/√rref ytD ytS SS - intrajet kty,1+ kty,2 AS - interjet yt1 pt,part,1 pt,part,2 largest kt effects: small q/2, q/2 -q/2  pt,part,2 pt,part,1 STAR preliminary

  19.  pt  Fluctuations and pt Correlations partons and velocity correlations: how is pt distributed on (h,f)? full STAR acceptance 70-80% autocorrelation variance excess Dr/√rref f STAR preliminary  pt  fluctuations h 20-30% Dr/√rref subtract multipoles fluctuation inversion Dr/√rref centrality 0-5% fluctuation scaling • pt fluctuations invertible to • pt autocorrelations Dr/√rref T. A. Trainor, R. J. Porter and D. J Prindle, J. Phys. G: Nucl. Part. Phys. 31 (2005) 809-824; hep-ph/0410182

  20. Compare with p-p pt Autocorrelations p-p 200 GeV minbias p-p 200 GeV nch > 9 CI=LS+US STAR preliminary direct – from pair counting Hijing Au-Au 200 GeV Dr/√rref Dr/√rref 70-80% data Au-Au 200 GeV CD=LS–US Dr/√rref Dr/√rref Dr/√rref net-charge correlations from fluctuation inversion

  21. Model Fits peak amplitudes peak widths red shifts and blue shifts data fit hijing 20-30% fit peak B1 B3 hijing collision centrality Hijing does not predict strong h broadening or negative structure B2 Hijing 70-80% data - fit peak fit residuals quench off quench on 0-10% 0-10% negative structure is unanticipated – what is the origin?

  22. Recoil Response to Parton Stopping red shift: particle production may be from a recoiling source fit data low-x partons 20-30% model peak p-p pt autocorrelation parton fragments STAR preliminary Au-Au 200 GeV fit residuals data - model peak  recoil 80-90% ~ p-p 40-50% red shift bulk medium Au-Au ptautocorrelation STAR preliminary 20-30% 0-5% • Response of medium to minimum-bias parton stopping • Momentum transfer to medium • Velocity structure of medium • Medium recoil observed via same-side pt correlations

  23. Energy Dependence: SPS  RHIC full acceptance STAR CERES NPA 727 (2003) 97 STAR preliminary centrality dramatic increase of pt fluctuations with increasing sNN STAR ! Hijing CERES string structure in Hijing does not appear in Au-Au data

  24. Summary • Precision survey of p-p correlation structure • Model-independent access to low-Q2 partons • Hydrodynamic aspects of parton scattering? • The other kt broadening: pt asymmetry • Low-Q2 partons as Brownian probes of A-A • Dissipation: p-p fragment distributions modified in A-A • Non-pQCD p-p angular correlations modified in A-A • pt correlations: temperature/velocity structure of A-A • Strong disagreement with pQCD Hijing Monte Carlo • Recoil response of A-A bulk medium: viscosity  0

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