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Three-Particle Azimuthal Correlations

Three-Particle Azimuthal Correlations. Jason Glyndwr Ulery 23 March 2007 High-pT Physics at LHC. Motivation. 4.0<P T Trig<6.0 GeV/c 0.15<P T Assoc<4.0 GeV/c. Jets are expected to be modified by the medium we create and therefore can be used to probe the medium.

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Three-Particle Azimuthal Correlations

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  1. Three-Particle Azimuthal Correlations Jason Glyndwr Ulery 23 March 2007 High-pT Physics at LHC

  2. Motivation 4.0<PTTrig<6.0 GeV/c 0.15<PTAssoc<4.0 GeV/c • Jets are expected to be modified by the medium we create and therefore can be used to probe the medium. • 2-Particle correlations show broadened or double humped away-side. • Mach-cone • Cerenkov gluon radiation • Jets deflected by radial flow or path length dependent energy loss. • Large angle gluon radiation • 3-particle correlations can distinguish conical emission from other mechanisms. Jason Glyndwr Ulery High-PT Physics at LHC

  3. Δ1 Three Three-Particle Analyses at RHIC STAR 2 Component Phenix Analysis STAR Cumulant Performed in - space =-Trigger Performed in 3-D space defined by trigger particle Performed in - space =Trigger- No assumptions about event composition 2 component approach 2 component approach Systematics due to flow normalization Systematics due to flow normalization Nontrivial interpretation of results Brief Look At This Analysis Look in Detail At This Analysis PHENIX Preliminary Covered in Previous Talk Δ2 Ulery IWCF’06 Ajitanand IWCF’06 Pruneau QM’06 Jason Glyndwr Ulery High-PT Physics at LHC

  4. Cumulant Method • 3 sets of combinatorial backgrounds consisting of 2-particle distribution times a flat single particle distribution. Pruneau QM’06 Jason Glyndwr Ulery High-PT Physics at LHC

  5. Cumulant Results 50-80% 10-30% 0-10% • Clear evidence of 3-particle correlation. • Results contain all 3-particle correlations; jet, flow and jetxflow. • Any additional interpretation requires invoking a model. • Non-possion fluctuations can leave residual 2-particle correlations. Pruneau QM’06 Jason Glyndwr Ulery High-PT Physics at LHC

  6. Trigger Δ1 Δ2 Δ1 2-Component Analysis Procedure • Trigger particle selected with transverse momentum 3<pT<4 GeV/c. • Look at Δ=Assoc-Trigger for all pairs of associated particles with 1<pT<2 GeV/c. • Plot Δ1 vs Δ2 for each pair of associated particles. • Particles are assumed to be jet-like or background. • Raw signal contains (Jet+Bkgd) x (Jet+Bkgd). • To obtain Jet x Jet we must subtract Bkgd x Bkgd and Jet x Bkgd (and Bkgd x Jet.) Δ2 Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  7. Jet x Background (Hard-Soft) • Top plot is 2-particle correlation. • Red is Jet + Background • Black is Background (from mixed events with v2 and v4 added) and blue is scaled background (such that Red - blue is zero around ±1.) • Mini panel is background subtracted signal. • Jet x Background term is created by folding 2-particle jet-like signal (mini panel) with 2-particle background. Δ Δ2 Ulery IWCF’06 Δ1 Jason Glyndwr Ulery High-PT Physics at LHC

  8. Background x Background (Soft-Soft) • Term is constructed by mixing a trigger particle from one event with pairs of background particles from an inclusive events of the same centrality. • Contains correlations between associated particles that are not associated with a trigger particle (including the flow between the 2 associated particles). Δ2 Δ1 Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  9. Δ2 Δ1 Δ2 Δ1 Flow • Soft-soft term contains from between the associated particles irrespective of the trigger. • Other flow terms must still be subtracted. • Top plot contains terms of v2Trigger*v2Associated. • Bottom plot contains terms of v4Trigger*v4Associated and v2*v2*v4 with v4 = 1.15*v22. • v2 is taken as average of reaction plane and 4-particle measurements. Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  10. Hard-Soft Plus Flow • Flow contributions from v2Trigger*v2Associated and v4Trigger*v4Associated cancel to first order. • Robust with respect to variations in flow. Δ2 Δ1 Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  11. - - = Background Subtraction Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  12. near near near Medium Medium Medium away away π away di-jets 0 π 0 deflected jets mach cone Conical Flow vs Deflected Jets Jason Glyndwr Ulery High-PT Physics at LHC

  13. Au+Au Central 0-12% Triggered pp d+Au Centrality Dependence Au+Au 50-80% Au+Au 30-50% Ulery IWCF’06 Au+Au 10-30% Au+Au 0-10% Jason Glyndwr Ulery High-PT Physics at LHC

  14. Projections d+Au Au+Au 10-30% Au+Au 0-12% (1+2)/2 Ulery IWCF’06 (1-2)/2 Jason Glyndwr Ulery High-PT Physics at LHC

  15. Angle from Fits • Fit of off-diagonal projections to Gaussians to extract conical emission angle. • Shaded errors are systematic and solid are statistical. • Fitting angle from different centralities to a constant give an angle of 1.47. Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  16. Centrality Dependence of the Signal Away Cone Cone + Deflected • Cone and cone + deflected at 1.45 radians from . • Positive conical emission signal seen in central Au+Au collisions. Average Signal in 0.7x0.7 Squares Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  17. Central Dependence of Differences Ulery QM’06 Poster Ulery Hard Probes ‘06 • Conical emission signal should give equal contribution on- and off-diagonal. • Difference is likely the contribution from deflected jets and/or large angle gluon radiation. On-diagonal – off-diagonal Jason Glyndwr Ulery High-PT Physics at LHC

  18. Au+Au 0-12% 3<pTTrig<4 GeV/c 0.5<pTAssoc<0.75 GeV/c 0.75<pTAssoc<1.0 GeV/c 1.0<pTAssoc<1.5 GeV/c 1.5<pTAssoc<2.0 GeV/c Associated PT Dependence • Mach cone signals should display no pT dependence of the angle. • Simple Cerenkov gluon radiation models predict decreasing angle with pT. Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  19. Angle from Fits • Angle consistent with flat or increasing with associated pT. • Inconsistent with current Cerenkov radiation model. • Predicts sharply decreasing angle with momentum. • Fitting points to a constant gives angles for 1.41 for ZDC triggered 0-12% Au+Au and 1.46 for 0-50% Au+Au from minimum bias. Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  20. Systematics • Major sources of systematic error are from the elliptic flow measurement and the normalization. • Off-diagonal signal robust with respect to variations in v2 and normalization. • Other sources include: • effect on the trigger particle flow from requiring a correlated particle (±20% on trigger particle v2) • uncertainty in the v4 parameterization • multiplicity bias effects on the soft-soft background Reaction Plane v2 4-Particle v2 Wide Normalization Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  21. Extreme Systematics No Jet Flow No v2Triggerv2Associated • No jet flow systematic has the jet not flowing with the medium. • No v2Triggerv2Associated has no subtraction of the v2 terms. • Signal persists even in these extreme cases. (1-2)/2 Ulery IWCF’06 Jason Glyndwr Ulery High-PT Physics at LHC

  22. Δ1 What Can Be Done at the LHC? PHENIX Preliminary Δ2 • Analyses similar to all 3 can be done at ALICE, ATLAS and CMS. • These experiments can additionally look at correlations with 4 or more particles. • ALICE can also look at 3-particle correlations with identified particles to look for differences in baryon and meson correlations. Ulery IWCF’06 Ajitanand IWCF’06 Pruneau QM’06 Jason Glyndwr Ulery High-PT Physics at LHC

  23. Summary • There are three different 3-particle analyses being done a RHIC. • Similar analyses could be done in the LHC experiments. • STAR two-component results show: • Away-side on-diagonal broadening in pp and d+Au consistent with kT broadening. • Off-diagonal signal seen in central Au+Au collisions consistent with Mach-cone. Jason Glyndwr Ulery High-PT Physics at LHC

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