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

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC2 Motivation 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. 4.0<P T Trig<6.0 GeV/c 0.15<P T Assoc<4.0 GeV/c

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC3 Three Three-Particle Analyses at RHIC ΔΔ STAR Cumulant Performed in  -  space  =  Trigger -  No assumptions about event composition Nontrivial interpretation of results Pruneau QM’06 Brief Look At This Analysis Phenix Analysis Performed in 3-D space defined by trigger particle 2 component approach Systematics due to flow normalization Ajitanand IWCF’06 Covered in Previous Talk STAR 2 Component Performed in  -  space  =  -  Trigger 2 component approach Systematics due to flow normalization Δ1Δ1 Ulery IWCF’06 Look in Detail At This Analysis PHENIX Preliminary

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC4 Cumulant Method 3 sets of combinatorial backgrounds consisting of 2-particle distribution times a flat single particle distribution. Pruneau QM’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC5 Cumulant Results 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’ %10-30%0-10%

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC6 2-Component Analysis Procedure Trigger particle selected with transverse momentum 3<p T <4 GeV/c. Look at Δ  =  Assoc -  Trigger for all pairs of associated particles with 1<p T <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1Δ1 ΔΔ Δ1Δ1 Trigger Δ2Δ2 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC7 Jet x Background (Hard-Soft) Top plot is 2-particle correlation. Red is Jet + Background Black is Background (from mixed events with v 2 and v 4 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 Δ1Δ1 Δ2Δ2 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC8 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1Δ1 Δ2Δ2 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC9 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 v 2 Trigger *v 2 Associated. Bottom plot contains terms of v 4 Trigger *v 4 Associated and v 2 *v 2 *v 4 with v 4 = 1.15*v 2 2. v 2 is taken as average of reaction plane and 4-particle measurements. Δ1Δ1 Δ1Δ1 Δ2Δ2 Δ2Δ2 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC10 Hard-Soft Plus Flow Flow contributions from v 2 Trigger *v 2 Associated and v 4 Trigger *v 4 Associated cancel to first order. Robust with respect to variations in flow. Δ1Δ1 ΔΔ Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC11 Background Subtraction - = - Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC12 Conical Flow vs Deflected Jets Medium away near deflected jets away near Medium mach cone Medium away near di-jets 0 0 π π

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC13 Au+Au Central 0-12% Triggered Centrality Dependence ppd+Au Au+Au 50-80% Au+Au 30-50% Au+Au 10-30% Au+Au 0-10% Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC14 Projections Au+Au 0-12%Au+Au 10-30%d+Au (  1 +  2 )/2 (  1 -  2 )/2 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC15 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 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC16 Centrality Dependence of the Signal 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 AwayCone + Deflected Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC17 Central Dependence of Differences 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 Ulery QM’06 Poster Ulery Hard Probes ‘06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC18 Associated P T Dependence Mach cone signals should display no p T dependence of the angle. Simple Cerenkov gluon radiation models predict decreasing angle with p T. 0.5<p T Assoc <0.75 GeV/c0.75<p T Assoc <1.0 GeV/c1.0<p T Assoc <1.5 GeV/c1.5<p T Assoc <2.0 GeV/c 3<p T Trig <4 GeV/cAu+Au 0-12% Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC19 Angle from Fits Angle consistent with flat or increasing with associated p T. 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

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC20 Systematics Major sources of systematic error are from the elliptic flow measurement and the normalization. Off-diagonal signal robust with respect to variations in v 2 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 v 2 4-Particle v 2 Wide Normalization Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC21 Extreme Systematics No jet flow systematic has the jet not flowing with the medium. No v 2 Trigger v 2 Associated has no subtraction of the v 2 terms. Signal persists even in these extreme cases. No Jet FlowNo v 2 Trigger v 2 Associated (  1 -  2 )/2 Ulery IWCF’06

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC22 What Can Be Done at the LHC? 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. Δ1Δ1 ΔΔ Ulery IWCF’06 Pruneau QM’06 Ajitanand IWCF’06 PHENIX Preliminary

23 March 2007Jason Glyndwr Ulery High-PT Physics at LHC23 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 k T broadening. Off-diagonal signal seen in central Au+Au collisions consistent with Mach-cone.