Jets at RHIC Kirill Filimonov Lawrence Berkeley National

Jets at RHIC Kirill Filimonov Lawrence Berkeley National Laboratory s. NN = 200 Ge. V

What is a jet? Jet: A localized collection of hadrons which come from a fragmenting parton Parton distribution Functions c a Hard-scattering cross-section Fragmentation Function d High p. T (> ~2. 0 Ge. V/c) hadron production in pp collisions: Provides a well calibrated probe b

High p. T Particle Production in A+A (According to p. QCD…) Parton Distribution Functions Intrinsic k. T , Cronin Effect Shadowing, EMC Effect Hard-scattering cross-section c Partonic Energy Loss a Fragmentation Function b d

Suppresion is due to the final state

High pt Spectra 0’s in Au+Au up to 15 Ge. V/c! NEW

Cronin enhancement C. Klein-Boesing Cronin Enhancement vanishes at high p. T

Perturbative QCD in Au+Au Prompt ’s in Au+Au up to 12 Ge. V/c J. Frantz Prompt ’s scale with Nbinary

High pt Spectra D’s in d-Au up to 11 Ge. V/c! A. Tai

Opening Act from Tom Hemmick: • Jet fragmentation in pp and d-Au: j. T, k. T • v 2 at high p. T in Au. Au and di-hadron correlations w. r. t. reaction plane • Baryon/meson ratios and RCP, flavour-tagged correlations • High p. T/low p. T di-hadron correlations

1. pp, d. Au: Calibration of jets at RHIC

Jet Fragmentation “shape” parton hadron parton di-hadron Jet “width” Jet-coplanarity Reconstructed jets

Full jet reconstruction in pp, d. Au T. Henry (STAR) pt > 0. 6 pt STAR Preliminary Et Jt s = 200 Ge. V pp Min. Bias: ET Corrected <Et> = 11. 3 ± 0. 7 sys Ge. V pt > 2. 0 pp Min. Bias pythia-GEANT Jt in Ge. V/c Agree within 4% Jet “Width” (RMS Jt): ET pt>0. 6: 490 ± 50 sys Me. V/c pt>2. 0: 615 ± 60 sys Me. V/c

Di-Jet Reconstruction Trigger Jet TPC only Determines first thrust axis parton hadron 0. 03 f=0. 23± 0. 02± 0. 05 Raw Per Event Yield STAR Preliminary 0 0 parton Away Jet TPC only Determines second thrust axis • Dijet high tower corrected <Et>= 13. 0 ± 0. 7(sys) Ge. V kt=2. 3± 0. 4 ± 0. 67 1. 11 Ge. V/c p+p s = 200 Ge. V No correction for <z> needed! 2 T. Henry

Di-hadron correlations n Fragmentation function unknown: extract kt*<z>, or infer <z> from the data di-hadron J. Rak PHENIX • Jt=615± 60 sys Me. V/c • kt=2. 3± 0. 4± 0. 67 1. 11 Ge. V/c n n Jt=636± 20 Me. V/c kt=1. 7± 0. 1 Ge. V/c ó STAR

Extracting nuclear k. T from d. Au 1. 4 * 10 -3 STAR Raw Per Event Yield R=. 35 Cdf s = 200 Ge. V p+p d+Au 0 0 T. Henry Df=0. 22 ± 0. 02 ±. 06 Df=0. 31 ± 0. 05 ±. 06 Nuclear kt = 2. 8± 1. 2± 1. 0 Ge. V/c f (radians) 2

Extracting nuclear k. T from d. Au J. Rak STAR

2. Au+Au: Azimuthal dependencies at high p. T

Azimuthal anisotropy v 2 at high p. T A. Tang M. Kaneta v 2{2} phenix preliminary }nucl-ex/0305013 v 2{RP} STAR Preliminary all charged v 2{4} Vertical bar : stat. error curves, Gray Box : sys. error The data point : at <p. T> in the bin Finite azimuthal anisotropy to the highest measured p. T v 2 for p. T=3 -6 Ge. V/c exceeds the maximum values from surface emission: quark coalescence? Need reliable v 2 for p. T>7 Ge. V/c to test jet quenching

Azimuthal correlation in Au. Au, d. Au and pp S. Voloshin: - multiplicity (or Nbinary) independent quantity - compare azimuthal correlations in different systems A. Tang STAR Preliminary Strong real collective motion in Au+Au

Di-jet tomography: Predictions X. N. Wang Out-plane In-plane Path length dependence of energy loss leads to IAA( )

Correlations w. r. t. reaction plane STAR (A. Tang) p. Ttrigger=4 -6 Ge. V/c, 2<p. Tassociated<p. Ttrigger, | |<1 /4 3 /4 y x -3 /4 Flow pattern is shifted by /2: J. Bielcikova, S. Esumi, KF, S. Voloshin, and J. P. Wurm, nucl-ex/0311007, to appear in PRC(R). - /4

Di-hardron tomography p. Ttrig=4. 0 -6. 0 Ge. V/c, | |<1. 0 2. 0<p. Tassoc<p. Ttrig=2. 5 -4. 0 Ge. V/c, | |<0. 35 1. 0<p. Tassoc<2. 5 Ge. V/c STARpreliminary Preliminary STAR color scheme: in-plane out-of-plane 20 -60% W. Holzmann A. Tang Back-to-back suppression depends on the reaction plane orientation: energy loss dependence on the path length

3. Unraveling flavor of jets

Baryon/Meson Ratios F. Matathias M. Lamont Baryon/meson ratio “anomalous” for p. T<6 -7 Ge. V/c

Identified particle RCP Baryon/meson effect! Coalecence for p. T=2 -6 Ge. V/c? v 2 says yes…

A. Sickles p. Ttrig =2. 5 -4 Ge. V/c p. Tassoc=1. 7 -2. 5 Ge. V/c 1/Ntrigger*d. N/d(∆ Φ) Flavor-tagged correlations M. Lamont STAR Au+Au 5% 1/Ntriggerd. N/d(∆Φ) Fig. 3 ∆Φ (radians) p. Ttrig > 2. 5 Ge. V/c <p. Tassoc< p. Ttrig Note pt-range: right in the baryon/meson “anomaly” Fig. 5 ∆Φ (radians)

Identified particle angular distributions A. Sickles M. Lamont, Y. Guo p. Ttrig =2. 5 -4 Ge. V/c p. Tassoc=1. 7 -2. 5 Ge. V/c Nsame Nback p. Ttrig > 2. 5 Ge. V/c <p. Tassoc< p. Ttrig Nsame Nback Trigger PT STAR preliminary Trigger PT So Why More To far, test would associated more the Λ coalescence, questions andparticles anti-Λthan be choose ondifferent? answers… the away p. Ttrig(baryon)=3/2*p side for trigger. Ttrig baryons? (meson)

4. Search for the lost energy

Medium Modification of FF X. N. Wang, Phys. Lett. B 579: 299 -308, 2004 • Softening of fragmentation function due to energy loss • Enhancement of soft hadrons from emitted gluons at low z

Di-hadron correlations at “all” p. T’s Jet-like structures RMS s f (1/Ntrig(1/N ) d. N/d( ) trig) STAR Preliminary f) (1/Nd. N/d( trig) d. N/d( f) • Trigger on leading particle p. T=4 -6 Ge. V/c, | |<0. 75 F. Wang • Associate “all” particles (p. T=0. 15 -4. 0 Ge. V/c, | |<1. 1) • Form , correlation in pp, Au+Au STAR Preliminary • Background from mixed events. 0. 15<p T<4 Ge. V/c Au+Au top 5% bkgd subt. • Au+Au: v 2 modulation on background. p+p Au+Au top 5% f near Signal background

p. T distributions on near and away side Near side: syst. error Away side: energy from initial parton seems to be converted to lower p. T particles Overall enhancement from pp to AA Away Trigger bias in Au+Au? Coalescence effects at 4 Ge. V? reminiscent of energy loss predictions What about other explanations? Do we really know if it is a jet on away side?

Momentum conservation A thermal fluctuated large p. T particle (or a mono-jet) would produce an away side excess due to momentum conservation. Borghini et al. PRC 62, 034902 (2000): (1/Ntrig) d. N/d( f) p+p Fit to near side: const. + gaussian + Borghini-cos(fixed) p+p Au+Au 5% stat. mom. conserv. Borghini et al. f STAR, PRL 90, 082302 (2003) Au+Au 5% assoc. particle p. T (Ge. V/c) f free fit stat. mom. conserv. Borghini et al. f STAR Preliminary: Ying Guo poster stat. mom. conserv. Borghini et al. f cos strength per particle STAR Preliminary (1/Ntrig) d. N/d( f) (1/Ntrig) d. N/d( f) cos strength per particle STAR, PRL 90, 082302 Fit (2003) STAR Preliminary: Ying Guo poster to near side: const. + gaussian + Borghini-cos(fixed) f free fit stat. mom. conserv. Borghini et al. f f trigger particle p. T (Ge. V/c) • near side is mostly a. No jet, punch-through and initially no mono-jet mid-rapidity. for 6 < pat. Ttrig < 10 Ge. V/c. • the final state away excess has a similar shape to a stat. distr. from momentum conservation. the away side excess approaches equilibration with the medium, consistent with the p T spectra results.

Broadening of di-hadron correlations Trigger and associated particles: (2. 5 p. Ttrigg 4. 0) (1. 0 p. Tassoc 2. 5) J. Rak PHENIX Most likely consistent with STAR, easy to check!

Summary Inclusive spectra: • very nice confirmation of R(d. Au)~1>6 -8 Ge. V • at higher p. T most likely be boring (according to I. Vitev & Co) Jet calibration: Finalize analysis, get solid numbers on k. Tvac, k. Tnucl v 2 at high p. T: It’d better start going down with p. T! Di-jets with respect to reaction plane: • Test d. E/dx(L)-dependence soon Jet chemistry: flavor-tagged correlations • Potentially extremely interesting! More statistics is needed… • More methods to disentangle jets and flow to come soon. . . Search for lost energy: Very promising • Higher trigger p. T! Low z-region (not necessarily low p. T) • Medium reaction to fast parton & thermalization Be at labforbythe Monday anddiscussions!!! take data!!! Thanks data and