Jet Quenching at RHIC and LHC Oliver Busch University of Tsukuba Heidelberg University 1 • Nuclear modification factor • Event plane dependence • Semi-inclusive jet-hadron yields • Jet shapes, subjets, jet mass • Identified jet fragmentation 2 • Nuclear modification factor • Event plane dependence • Semi-inclusive jet-hadron yields • Jet shapes, subjets, jet mass • Identified jet fragmentation selection strongly biased towards: • light flavour jet results • LHC • ALICE 3 Hadron nuclear modification factor • high-pT hadron suppression both at RHIC and LHC • hadron observable biased towards leading fragment → study the effect for fully reconstructed jets • theory: energy loss ⊗ leading hadron fragmentation → parton shower ⊗ energy loss ⊗ hadronisation PHENIX, Nucl Part. Phys 38 (2011) 124016 CMS, JHEP 04 (2017) 039 4 Underlying event • jet reconstruction in heavy-ion collisions : difficult due to the high underlying event background not related to hard scattering • correct spectra for background fluctuations and detector effects • not possible down to lowest jet pT • fake jets jet area ~ 0.5 (R = 0.4) central peripheral 5 Experimental aspects / differences • jet reconstruction: • EM + hadron calorimeter based (ATLAS) • charged track + EMCal based (STAR + ALICE) • particle flow (CMS) • fake jet rejection: • constituent pT cuts • leading constituent bias / track jet matching • di-jet (hadron-jet) coincidence • subtraction • …. • consistently applied to the reference, but may introduce physics bias • background subtraction: • median density from clusters (ALICE, STAR) • iterative geometrical (ATLAS, CMS) • corrections: for detector effects (efficiency, resolution) and background fluctuations (resolution-like) • typical: full corrections to particle level • sometimes: detector and/or background effects applied to a reference 6 complementarity of LHC experiments • ALICE: ‘charged’ jets from charged particle tracking + ‘full’ jets from tracking + em. Calorimeter • ATLAS/CMS: em. + hadronic calorimetry (+tracking) • complementary jet pT reach, ALICE typically lower constituent pT cutoff CMS, PRD 87 (2012) 112002 ALICE, Phys. Lett. B 722 (2013) 262 7 Jet nuclear modification factor: ATLAS • ATLAS jet RAA at √sNN = 2.76 TeV, R = 0.4 • strong suppression observed, similar to hadron RAA → parton energy not recovered inside jet cone • stronger suppression for more central events • weak pT dependence ATLAS, PRL 114, 072302 • JEWEL and YaJEM jet quenching models reproduce suppression Jet nuclear modification factor: ALICE • ALICE full jet RAA at √sNN = 2.76 TeV, R = 0.2 Phys.Lett. B746 (2015) 1 const,ch Cluster lead, ch • pT > 150 MeV, E > 300 MeV, pT > 5 GeV/c JEWEL: PLB 735 (2014) • maybe hint for weak pT dependence YaJEM:PRC 88 (2013) 014905 • JEWEL and YaJEM jet quenching models reproduce suppression 9 Jet nuclear modification factor: CMS • CMS jet RAA at √sNN = 2.76 TeV, R = 0.2, 0.3, 0.4 • constituent pT > 150 MeV/c, fake jet spectrum from ‘background events’ subtracted • no significant R dependence for pT > 70 GeV/c CMS, nucl-ex/1609.05383 10 Angular dependence • R dependence sensitive to broadening of transverse jet profile • ATLAS RCP double ratio: R dependence seen, in particular for low pT and high R • not observed in ALICE (but small R difference) ATLAS, PLB 719 (2013) 220 ALICE, JHEP 03 (2014) 013 11 Rapidity dependence • expect stronger energy loss for gluons than for quarks • ATLAS: no significant rapidity dependence of RAA, despite change in q/g • balanced by parton spectral slope, y-dependence of energy density ? • role of fluctuations / biases ? ATLAS, PRL 114, 072302 12 √s depencence ALICE, HP 2016 • comparison of different √s constrains energy density dependence • no significant difference • increased energy loss compensated by flatter parton spectrum ? ATLAS, QM 2017 13 Jet Azimuthal Anisotropy 14 Local background subtraction • ALICE jet v2: event plane from forward/backward V0 scintillators • account for flow-modulation of background via event-by-event fit and subtraction of local background density • unfolding to account for ) 200 background fluctuations : c Pb-Pb sNN = 2.76 TeV ALICE separately for spectra Single event in- and out-of-plane 150 ) (GeV/ ϕ ( ch ρ 100 50 0.15 < p < 5 GeV/c, |η | < 0.9 T, track track ρ (ϕ) ρ (1+2v cos(2[ϕ-Ψ ])) ch 0 2 EP, 2 ρ ρ (1+2v cos(3[ϕ-Ψ ])) 0 0 0 3 EP, 3 0123456 ϕ (rad) Phys. Lett. B753 (2016) 511 \ 15 Charged jet v2: results nd ch jet • quantify azimuthal asymmetry via 2 Fourier harmonic v2 ch jet • central collisions: 1.5 - 2 sigma from v2 = 0 → consistent with 0, but maybe hint for effect of initial density fluctuations ? ch jet • non-zero v2 in semi-central collisions 0-5% 30-50% ALICE ch jet ALICE v ch jet 0-5%, Stat unc. v 30-50%, Stat unc. 0.2 2 0.2 2 |>0.9 } |>0.9 } Pb-Pb s = 2.76 TeV Pb-Pb s = 2.76 TeV Syst unc. (shape) NN Syst unc. (shape) NN η η Syst (correlated) R = 0.2 anti-k , |η |<0.7 R = 0.2 anti-k , |η |<0.7 ∆ ∆ Syst (correlated) T T jet Syst unc. (correlated) jet Syst unc. (correlated) {EP, | {EP, | 0.1 0.1 ch jet 2 ch jet 2 v v 0 0 (a) p > 0.15 GeV/c, p > 3 GeV/c (b) p > 0.15 GeV/c, p > 3 GeV/c T, track T, lead T, track T, lead 20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 100 pch jet (GeV/c) pch jet (GeV/c) T T Phys. Lett. B753 (2016) 511 16 Comparison to previous results • ALICE + CMS single particles, ATLAS full jets : different energy scales ! CMS, PRL 109 (2012) 022 • non-zero v2 up to high pT ATLAS, PRL 111 (2013) 152 ALICE, Phys. Lett. B753 (2016) 511 ALICE, Phys. Lett. B719 (2013) 18 jet 2 ALICE ch jet jet 2 ALICE ch jet v v2 0-5%, Stat unc. v v 0.3 Pb-Pb s = 2.76 TeV 2 30-50%, Stat unc. , NN 0.3 Pb-Pb s = 2.76 TeV Syst unc. (shape) , NN Syst unc. (shape) R = 0.2 anti-k T, |η |<0.7 R = 0.2 anti-k , |η |<0.7 jet Syst unc. (correlated) T jet part 2 Syst unc. (correlated) part 2 calo jet calo jet v ATLAS v 5-10% v 2 ATLAS v 2 30-50% part 0.2 CMS v {|∆η|>3} 0-10% 0.2 part 2 CMS v 2 {|∆η|>3} 30-50% part part ALICE v 2 {|∆η|>2} 0-5% ALICE v 2 {|∆η|>2} 30-50% 0.1 0.1 0 0 p > 0.15 GeV/c, p > 3 GeV/c p > 0.15 GeV/c, p > 3 GeV/c (a) T, track T, lead (b) T, track T, lead 0 50 100 150 0 50 100 150 part jet p part, p jet (GeV/c) p , p (GeV/c) T T T T 17 Comparison to JEWEL • good agreement with JEWEL in semi-central collisions • clear indication of path-length dependence of energy loss • caveat: no transverse expansion in JEWEL ch jet ch jet v 30-50%, JEWEL ALICE v 0-5%, JEWEL ALICE 2 ch jet 2 2 ch jet 2 0.2 ch jet v ch jet v 30-50%, Stat unc. 0.2 v 2 Pb-Pb sNN = 2.76 TeV v 2 0-5%, Stat unc. Pb-Pb sNN = 2.76 TeV R = 0.2 anti-k , |η |<0.7 Syst unc. (shape) R = 0.2 anti-k T, |η |<0.7 Syst unc. (shape) T jet jet Syst unc. (correlated) Syst unc. (correlated) 0.1 0.1 0 0 lead (a) p > 0.15 GeV/c, p > 3 GeV/c lead T, track T (b) p > 0.15 GeV/c, p > 3 GeV/c T, track T 20 30 40 50 60 70 80 90 100 ch jet 20 30 40 50 60 70 80 90 100 p (GeV/c) ch jet T p (GeV/c) T Phys. Lett. B753 (2016) 511 18 Semi-Inclusive Hadron-Jet Distributions 19 Hadron triggered recoil jets • charged jets recoiling from charged hadron • hadron biased towards surface • Δrecoil: difference between hadron trigger pT classes • further fake jet removal ALICE, JHEP 09 (2015) 170 20 ΔIAA • Δrecoil divided by PYTHIA reference: significant suppression observed • subtraction technique allows for large R up to 0.5 with constituent pT > 0.150 GeV/c, no leading constituent bias ALICE, JHEP 09 (2015) 170 21 ΔIAA: R dependence • R dependence as expected for vacuum fragmentation (PYTHIA) • no medium-induced broadening observed for recoil jets ALICE, JHEP 09 (2015) 170 22 Medium-induced acoplanarity ? • Δφ hadron-jet: potentially sensitive to large-angle scattering • data compared to embedded PYTHIA reference • no significant effect within present uncertainties ALICE, JHEP 09 (2015) 170 23 Recoil jets at RHIC • STAR charged jets, mixed event background subtraction • ICP(central-peripheral): jet suppression observed • estimate E-loss through spectral ‘shift’ ΔE : energy transported out-of-cone smaller at RHIC than LHC STAR, nucl-ex/1702.01108 24 Recoil jets at RHIC: R dependence • no evidence of broadening STAR, nucl-ex/1702.01108 25 Intrajet Observables and Subjets 26 Jet shapes • radial moment ‘girth’ g, longitudinal dispersion pTD, difference leading - subleading pT LeSub • shapes in pp collisions at 7 TeV: - constrain QCD calculations of small-R jets (‘microjets’: M. Dasgupta, F. Dreyer, G. Salam, G. Soyez hep-ph/1602.01110) - validate MC simulations • shapes in Pb-Pb probe of quenching of low-pT jets: characterise fragment distributions and are sensitive to medium induced changes of intra-jet momentum flow • ‘event-by-event’ measure, sensitive to fluctuations • infrared (& collinear) safe 27 Jet shapes in Pb-Pb jet • R=0.2, 40 < pT < 60 GeV/c, no leading constituent cut, fully corrected to charged particle level • g shifted to smaller values compared to PYTHIA reference → indicates more collimated jet core 30 g ALICE Preliminary Pb-Pb sNN = 2.76 TeV 25 Anti-k T charged jets, R = 0.2 dN/d ALICE Data 40 < pjet,ch < 60 GeV/c T Shape uncertainty jets 20 Correlated uncertainty PYTHIA Perugia 11 1/N 15 10 5 0 0 0.02 0.04 0.06 0.08 0.1 0.12 g ALI−PREL−101580 28 • larger pTD in Pb-Pb compared to PYTHIA → indicates fewer constituents in quenched jets (or ‘less democratic’ splitting) • LeSub in Pb-Pb in good agreement with Pb-Pb: → hardest splittings likely unaffected 6 0.2 D ALICE Preliminary ALICE Preliminary T Pb-Pb s = 2.76 TeV 0.18 Pb-Pb s = 2.76 TeV p NN NN 5 Anti-k charged jets, R = 0.2 Anti-k T charged jets,