Elena Bruna (Yale&INFN Torino) From yesterday Jet II: Full Jet Reconstruction Goal: set the Jet Energy Scale Different systematics to take into account (tracking,) Background fluctuations: the challenge Jet III: Results p+p and d+Au: reference/control measurements Broadening observed at RHIC Elena Bruna (Yale&INFN Torino) Today Jet III: Results p+p and d+Au: reference/control measurements Broadening observed at RHIC More on PHENIX vs STAR More quenching observables: di-jets, jet-hadron Jet IV: The Present: from RHIC to LHC Hard Probes at LHC vs RHIC Results on quenching at LHC Jet-finding in PHENIX Elena Bruna (Yale&INFN Torino) 3 CAVEAT: jet-finder based on unmodified jet-shapes veto against modified/quenched jets Anti-quenching biases! Jet-finding in PHENIX Elena Bruna (Yale&INFN Torino) 4 Step back: how does jet-finding work in PHENIX? Direct rejection of fake jets (i.e. jet by jet): May select specific jet fragmentation 1) Sum p T 2 inside a Gaussian kernel to obtain a discriminant: 2) Keep jets with g 0.1 > threshold Jet-finding based on a Gaussian kernel (=0.3, 0.4) Focuses on the core of the jet Are those jets that keep a Gaussian shape only minimally interacting? That would explain the suppressed R AA to the level of surface emission Jets in A+A: possible biases Elena Bruna (Yale&INFN Torino) 5 CAVEAT: jet-finder based on unmodified jet-shapes veto against modified/quenched jets Anti-quenching biases! p T cut to minimize background bias towards less-interacting jets Can we exploit the biases? Di-jet measurements Elena Bruna (Yale&INFN Torino) 6 EMC trigger Trigger jet Recoil jet Trigger jets are biased towards the surface. Recoil jets are exposed to a maximum path- length in the medium. Large energy loss expected. =6.5 GeV/c Anti-k T, R=0.4 Trigger Jet: p T,cut =2 GeV/c, p T (trig)>20 GeV/c Coincidence rate: how often I measure a recoil jet once the trigger jet is found di-jet coincidence rate 7 Elena Bruna (Yale&INFN Torino) Significant suppression in di-jet coincidence measurements broadening and/or absorption? STAR preliminary Recoil Jet: R=0.4, p T,cut =0.2 GeV/c Trigger Jet: p T,cut =2 GeV/c p T,cut on trigger jet: allows similar trigger jet population in p+p and Au+Au Recoil jets measured per trigger jet coincidence rate Broadening or absorption? Elena Bruna (Yale&INFN Torino) 8 p+p Au+Au Energy shift? Absorption? If broadening: Jet energy spread outside R p T Jet (R)

2.5 GeV/c STAR Preliminary 0-20% Au+Au STAR Preliminary 0-20% Au+Au STAR Preliminary 0-20% Au+Au Open symbols p+p Trigger jet: Anti-kt R=0.4, p t,cut >2 GeV/c, p t jet >20 GeV/c Significant broadening on the recoil side Observed modification of Fragmentation Function Remark: flat bkg subtraction by ZYAM - jet v 2 under investigation Jet-hadron correlations Elena Bruna (Yale&INFN Torino) 13 Significant (Gaussian) broadening of the away side. Broadening decreases with jet energy. Out-of-cone (R>0.4) energy ~ 6-9 GeV. in agreement with broadening scenario in di-jet analysis! Broadening Jet-hadron correlations Elena Bruna (Yale&INFN Torino) 14 Softening Softening of jet fragmentation Significant enhancement at low p T (p T 8 GeV 2) For fixed hadron p T, different parton energies are sampled at RHIC vs LHC ! Near side has higher p T parton than away side Fixed p Ttrig & p T assoc larger p T parton at LHC Keep in mind (1) and (2) when comparing di-hadron/di-jets at RHIC vs LHC Hard processes: from RHIC to LHC Elena Bruna (Yale&INFN Torino) 20 Large increase of jet x-section from RHIC to LHC! LHC: the hard probes factory Elena Bruna (Yale&INFN Torino) 21 LHC RHIC SPS (h + +h - )/2 00 17 GeV 200 GeV 5500 GeV=s LO p+p y=0 From RHIC to LHC: fireball hotter, denser, longer lifetime huge increase of hard probes! need high-p T triggers ! Elena Bruna (Yale&INFN Torino) 22 Simulation: PYTHIA Anti-kT, R=0.4 LHC: the hard probes factory jet cross section in p+p: RHIC vs LHC huge increase of hard probes! need high-p T triggers ! Cross-section falls with a smaller (power-law) exponent less sensitivity to the energy scale: important for background treatment Hard processes: from RHIC to LHC Elena Bruna (Yale&INFN Torino) 23 Different x T range: RHIC: 0.15 0.45 LHC: RHIC is quark dominated. LHC is gluon dominated N. Glover CTEQ, Rhodes, (2006) xTxT LHC detectors for Jet analysis Elena Bruna (Yale&INFN Torino) 24 tracking ECAL HCAL muon hadron PID counters lumi. Complimentary measurements: large acceptance for charged hadrons, leptons and neutral energy (ATLAS, CMS) Hadron PID in ALICE (| |