Jet Measurements at RHIC M.L. Miller, MIT 1.The laboratory 2.Expectations 3.Measurements 4.Missing pieces 5.Conclusions
RHIC: A dedicated QCD machine QCD: ~95% of the bandwidth p+ p, d+Au, Au+Au (Cu+Cu next) Access to perturbative regime Runs I-4: 19, 63, 130, 200 GeV Run 5: commission 0.5 TeV p+p running “Mature performance” demonstrated Run 5 (November?): First “long” polarized p+p run Expect ~14 pb -1 STAR (SVT+TPC+EMC) 0 ≤ Φ ≤ 2π -1 ≤ η ≤ 2 PHENIX (DC+EMC+PID) 2 x |Φ| ≤ π/4 |η| ≤ 0.3 No hadron calorimetery!
Jet interests at RHIC (I): p+ p PHENIX –Well calibrated for leading π 0 STAR –Tevatron RunII jet algorithms –Ellis/Soper k T cluster –Midpoint cone with split/merge –20-30% jet energy resolution, calibration in progress 5<p T (jet)<25 GeV q+g dominates Expect ~14 pb -1 significant “Δg physics” from p+ p at RHIC run5
In QCD Medium Additional k T Significant energy loss? high p T suppression Sensitive to color properties of medium Jet Interests at RHIC (II): Au+Au Hard probe early time Calculable: pQCD Abundant at RHIC, LHC k T : “Radiative Corrections” pre- and post-scattering di-jet:
Moment Analysis of QCD Matter I. Vitev, nucl-th/ Induced Gluon Radiation ~collinear gluons in cone “Softened” fragmentation Gyulassy et al., nucl-th/
Jets and jet surrogates 1) Integral Distributions:, 2) Single Particle Spectra: d /dp T R AA, R dA 3) di-hadron correlations: dN/d( ) 4) Jet reconstruction: d /dE T, Frag. Func. (p+p, d+Au and peripheral Au+Au) trigger “Trigger” = 0 Adler et al., PRL90: (2003), STAR near-side away-side
Charged jet evolution at RHIC Thrust axis: direction of leading “charged” jet Study Σ p T, N ch vs. thrust axis Smooth transition to di-jet topology with increasing jet p T Agrees well with CDF charged jet study (see red points/curve) Soft physics of underlying p+p event under study at RHIC (but much to do!) Foundation for jet studies in Au+Au via leading charged particles STAR p T >200 MeV CDF p T >500 MeV MLM, CIPANP03 STAR Preliminary
But first, some jargon… peripheral (grazing shot) central (head-on) collision participants Centrality: event classes based on mid-rapidity multiplicity Preliminary s NN = 200 GeV Uncorrected Particle production scales with increasing “centrality”
Adams et al., Phys. Rev. Let. 91 (2003) Adler et al., PRL90: (2003), STAR 1/N trigger dN/d( ) Background subtracted di-hadron Final state jet quenching p+p 2-jets Peripheral Au+Au 2-jets Central Au+Au 1-jet! d+Au 2-jets Biased towards high-z hadron pairs not a sensitive measure of modified fragmentation 2 nd order correlations due to elliptic flow of entire event competing backgroundBut… Normalization applied potentially sensitive to large k T broadening
away toward syst. error Stiffer spectrum in cone indicative of jet fragmentation Similar slope in both systems Not absolutely normalized toward nucl-ex/ STAR Preliminary Towards a frag. function in Au+Au Study h ± p T distributions (p T >150 MeV) in toward, away region. Compare p+p to Au+Au Softened spectrum in both systems Au+Au softer than p+p Effect largest for most violent collisions away
hadron Getting quantitative: Jet profiles Reconstructed jetsdi-hadron Jet “width” Jet-coplanarity parton
j T, k T from p+p jets, di-jets STAR di-jet =2.3 ±1.1 GeV/c PHENIX di-h ± = 1.92 ± 0.1 GeV/c Reasonable agreement with previous di-jet measures Apanasevich et al.,PRD59, TPC+EMC reconstructed jets Good agreement between data and Pythia/Lund+Geant Mean value depends on p T of hadron p T >2 GeV/c, STAR di-jet =515±50 MeV/c p T >1 GeV/c PHENIX di-h ± = 510±10 MeV/c nucl-ex/
j T and k T in Au+Au from di-hadrons p+p d+Au pp (2.5 p Ttrigg 4.0) (1.0 p Tassoc 2.5) j T constant with centrality, consistent with p+p value k T increases ~30% from p+p to peripheral Au+Au consistent with PHENIX d+Au measure Strong centrality dependent k T broadening large final state radiation Perhaps most interpretable di-hadron measure at RHIC
What’s missing? Yields d 2 σ / dM dy (nb GeV -1 ) p+N h ± + h ± + X E CM =38.8 GeV -0.4<y<0.2 p Tpair <2 GeV/c normalized dσ / d cos(θ * ) cos(θ * ) p+N h ± + h ± + X E CM =38.8 GeV -0.25<y<0.1 p Tpair <2 GeV/c Lower energy di-hadron invariant mass spectra: NLO re-summation critical Strong scale dependence Do we understand the yields? di-jet/di-hadron M Inv and cos(θ * ) are critical next measures at RHIC hep-th/
Conclusions 2-particle correlations Robust jet probe from p+p to central Au+Au Partonic energy loss in dense QCD matter Evidence of softened fragmentation, increased multiplicity in jet in central Au+Au Large, centrality dependent k T Need to measure, compare di-jet, di-hadron yields to NLO QCD Reduce ambiguities Higher p T jets access to low-z fragments Possible with Run4 data on tape
Backup Slides
Some added complexity ΔΦ Δη ΔΦ Δη Central Au+Au Periph. Au+Au Correlation strength STAR Preliminary
PHENIX preliminary 1/ x E -4 to -5 CCOR (ISR) s = 63 GeV Nucl Phys B209 (1982) 1/ x E -5.3 Fragmentation from p+p di-hadrons Simple relation
k T, j T from p+p di-hadrons J. Rak, Wed. J. Rak, DNP03 di-hadron Statistical Errors Only near-sideaway-side
k T, j T from p+p di-hadrons Statistical Errors Only PHENIX preliminary |j Ty | = 359 11 MeV/c |k Ty | = 964 49 MeV/c PHENIX preliminary |j Ty | = 359 11 MeV/c |k Ty | = 964 49 MeV/c J. Rak, DNP03 Good agreement with previous measurements: PLB97 (1980)163 PRD 59 (1999) di-hadron
Disappearance of the away-side Disappearance (at mid-rapidity) is dominated by final state effect(s)! Jet Quenching Adler et al., PRL90: (2003), STAR 2 nd order correlations due to elliptic flow of entire event competing background p+p 2-jets Peripheral Au+Au 2-jets Central Au+Au 1-jet! d+Au 2-jets