STAR Jet quenching overview Mateusz Ploskon Outline • Jet quenching and its measurements • Full jet reconstrucon in heavy‐ion collisions? • Recent measurements of jets at STAR/RHIC • Outlook M. Ploskon, TECHQM CERN July 2009 2 Jets in p+p and Au+Au Au+Au Collision Jet parton parton p+p collision Jet We use the jets to probe the medium! Nice idea… but there is a price to pay… M. Ploskon, TECHQM CERN July 2009 3 Finding jets? p+p Collision Au+Au Collision xy plane STAR TPC Event Display STAR M. Ploskon, TECHQM CERN July 2009 4 Jet quenching observaons in heavy‐ion collisions at RHIC Jet quenching: recoil jet suppression via leading hadron azimuthal correlaons trig 4< pT < 6 GeV/c Leading parcle assoc pT > 2 GeV/c Azimuthal Correlaon ~ 180 deg Strong modification of the recoil-jet indicates substantial partonic interaction within the medium M. Ploskon, TECHQM CERN July 2009 6 Di‐hadron correlaons with high‐pt associated hadrons Reaperance of the away side peak Most central at high‐assoc.‐pT: o similar suppression as in the inclusive spectra o unmodified shape Differenal measurement of jets w/o interacon ‐> limitaon of the LO probes High‐pT M. Ploskon, TECHQM CERN July 2009 7 From hadronic to energy flow observables o Single and di‐hadron triggered observables: o Approximate jet (axis etc.) o Single‐hadron and di‐hadron observables fold producon spectra with probability of partonic energy loss o Weak constrains on energy loss (upper and lower limits only) o Suffer from (geometrical?) bias towards non‐interacng jets Need for more differenal measurements to probe partonic energy loss Full jet reconstrucon M. Ploskon, TECHQM CERN July 2009 8 Full jet reconstrucon Fragmentaon Hard scaering Movaon and Strategy Physics of full jet reconstrucon in heavy ion collisions R Energy shi? Example: Measure energy flow into R=0.4 “cone” of radius R p+p Absorpon? Au+Au o Momentum conservaon o Jet reconstrucon: recover the full jet energy o Allow complete exploraon of Cross‐secon o Collision geometry Strong constrains rao AuAu/pp o Fragmentaon paerns for quenching models 1 o Compare Au+Au and p+p jet spectra o Caveat: inial state nuclear effects M. Ploskon, TECHQM CERN July 2009 10 Heavy Ion collisions and background characterizaon Single di‐jet event from a central Au+Au (STAR): ‐ Two jet peaks on top of the HI background (underlying event) Real Data Central assumpon: Signal and background can be factorized φ η φ o Main uncertainty: underlying event non‐uniformies induce uncertaines on background esmaon => jet energy resoluon o Extra handle: ulize mulple jet algorithms and their different sensivity to heavy‐ion background. M. Ploskon, TECHQM CERN July 2009 11 Background Background level in central Au+Au Single parameter sufficient to characterize the BG(?) BG non‐uniformies ‐> BG level fluctuaons ‐> Not necessarily Gaussian M. Ploskon, TECHQM CERN July 2009 12 Spectrum unfolding Background non‐uniformity (fluctuaons) and energy Pythia resoluon introduce pT‐ Pythia smeared smearing Pythia unfolded Correct via “unfolding”: inversion of full bin‐migraon unfolding matrix Check numerical stability of procedure using jet spectrum shape from PYTHIA Procedure is numerically stable Correcon depends crically on background model → main systemac uncertainty for Au+Au M. Ploskon, TECHQM CERN July 2009 13 Fake jet contaminaon/STAR “Fake” jets: signal in excess of background model from random associaon of uncorrelated so parcles (i.e. not due to hard scaering) “Fake” jet rate esmaon: • Central Au+Au dataset (real data) • Randomize azimuth of each charged parcle and calorimeter tower • Run jet finder • Remove leading parcle from each found jet STAR Preliminary • Re‐run jet finder M. Ploskon, TECHQM CERN July 2009 14 Fake jet contaminaon/STAR “Fake” jets: signal in excess of background model from random associaon of uncorrelated so parcles (i.e. not due to hard scaering) “Fake” jet rate esmaon: • Central Au+Au dataset (real data) • Randomize azimuth of each charged parcle and calorimeter tower • Run jet finder • Remove leading parcle from each found jet STAR Preliminary • Re‐run jet finder M. Ploskon, TECHQM CERN July 2009 15 Systemac correcons Trigger correcons: – p+p trigger bias correcon – p+p Jet patch trigger efficiency Parcle level correcons: – Detector effects: efficiency and pT resoluon – “Double* counng” of parcle energies • * electrons: ‐ double; hadrons: ‐ showering correcons • All towers matched to primary tracks are removed from the analysis Jet level correcons: • Spectrum shi: – Unobserved energy – TPC tracking efficiency • BEMC calibraon (dominant uncertainty in p+p) • Jet pT resoluon • Underlying event (dominant uncertainty in Au+Au) Full assessment of jet energy scale uncertaines Data driven correcon scheme • Weak model dependence: only for single‐parcle response, p+p trigger response • No dependence on quenching models M. Ploskon, TECHQM CERN July 2009 16 p+p trigger (coincidence) biases recorded Systemac correcons jet populaon – jet Et dependent Trigger correcons: correcon – p+p trigger bias correcon – p+p Jet patch trigger efficiency Offline vertex cuts ‐> x‐secon calculaon Parcle level correcons: – Detector effects: efficiency and pT resoluon Reacon trigger influencing jet spectra – “Double* counng” of parcle energies • * electrons: ‐ double; hadrons: ‐ showering correcons • All towers matched to primary tracks are removed from the analysis Jet level correcons: • Spectrum shi: – Unobserved energy – TPC tracking efficiency • BEMC calibraon (dominant uncertainty in p+p) • Jet pT resoluon • Underlying event (dominant uncertainty in Au+Au) Full assessment of jet energy scale uncertaines Data driven correcon scheme • Weak model dependence: only for single‐parcle response, p+p trigger response • No dependence on quenching models M. Ploskon, TECHQM CERN July 2009 17 Systemac correcons Jet patch trigger efficiency: Trigger correcons: Patch 1x1 (in pseudo‐rap. and azimuth) – p+p trigger bias correcon requesng ~7.5 GeV neutral energy (p+p – p+p Jet patch trigger efficiency only) Parcle level correcons: – Detector effects: efficiency and pT resoluon Large bias at low jet‐pt (x2 at 20 GeV/c), but – “Double* counng” of parcle energies persists up to 30 GeV/c • * electrons: ‐ double; hadrons: ‐ showering correcons • All towers matched to primary tracks are removed from the analysis Jet level correcons: • Spectrum shi: – Unobserved energy – TPC tracking efficiency • BEMC calibraon (dominant uncertainty in p+p) • Jet pT resoluon • Underlying event (dominant uncertainty in Au+Au) Full assessment of jet energy scale uncertaines Data driven correcon scheme • Weak model dependence: only for single‐parcle response, p+p trigger response • No dependence on quenching models M. Ploskon, TECHQM CERN July 2009 18 Systemac correcons Trigger correcons: – p+p trigger bias correcon ‐Relevant constant for EMCAL – p+p Jet patch trigger efficiency (response of calorimeter) Parcle level correcons: – Detector effects: efficiency and pT resoluon ‐Dead/hot tower correcons/ – “Double* counng” of parcle energies removal • * electrons: ‐ double; hadrons: ‐ showering correcons • All towers matched to primary tracks are removed from the analysis ‐High‐pt track quality/applicability Jet level correcons: • Spectrum shi: – Unobserved energy Calculate jet neutral energy fracon – TPC tracking efficiency • BEMC calibraon (dominant uncertainty in (NEF) p+p) and apply • Jet pT resoluon pT correcons according to the •fracon of carried jet energy by charge Underlying event (dominant uncertainty in Au+Au) parcles Full assessment of jet energy scale uncertaines ‐ Different efficiencies in p+p and Au+Au Data driven correcon scheme • Weak model dependence: only for single‐parcle response, p+p trigger response • No dependence on quenching models M. Ploskon, TECHQM CERN July 2009 19 Systemac correcons Trigger correcons: – p+p trigger bias correcon – p+p Jet patch trigger efficiency Several possibilies: Parcle level correcons: – Detector effects: efficiency and pT resoluon MIP, constant E‐fracon, – “Double* counng” of parcle energies complete removal of the • * electrons: ‐ double; hadrons: ‐ showering correcons “matched energy” • All towers matched to primary tracks are removed from the analysis Jet level correcons: Minimize the effect. • Spectrum shi: – Unobserved energy – TPC tracking efficiency • BEMC calibraon (dominant uncertainty in p+p) • Jet pT resoluon • Underlying event (dominant uncertainty in Au+Au) Full assessment of jet energy scale uncertaines Data driven correcon scheme • Weak model dependence: only for single‐parcle response, p+p trigger response • No dependence on quenching models M. Ploskon, TECHQM CERN July 2009 20 Systemac correcons Trigger correcons: – p+p trigger bias correcon – p+p Jet patch trigger efficiency Parcle level correcons: – Detector effects: efficiency and pT resoluon – “Double* counng” of parcle energies • * electrons: ‐ double; hadrons: ‐ showering correcons • All towers matched to primary tracks are removed from the analysis Jet level correcons: Energy scale correcon ‐> “Shi” • Spectrum shi: – Unobserved energy Esmate the unobserved jet energy and – TPC tracking efficiency apply “average” correcon • BEMC calibraon (dominant uncertainty in p+p) • Jet pT resoluon #neutron ~ #proton (?) • Underlying event (dominant uncertainty in Au+Au) Full assessment of jet energy scale uncertaines Data driven correcon scheme • Weak model dependence: only for single‐parcle response, p+p trigger response • No dependence on quenching models M. Ploskon, TECHQM CERN July 2009 21 Systemac correcons Trigger correcons: – p+p trigger bias correcon