et Experiments at LHC (as opposed to Jet Physics at RHIC ) JET Collaboration Symposium Montreal June 2015
Heavy-ion jet results at LHC Dijet asymmetries Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at sqrt(s) = 2.76 TeV with the ATLAS Detector at the LHC (ATLAS; 1011.6182) Observation and studies of jet quenching in PbPb collisions at sqrt(s) =2.76TeV (CMS; 1102.1957) Jet momentum dependence of jet quenching in PbPb collisions at snn =2.76TeV (CMS; 1202.5022v2) Photon-jet asymmetries Studies of jet quenching using isolated- photon + jet correlations in PbPb and pp collisions at sqrt(s[nn]) = 2.76 TeV (CMS; 1205.0206) Single-jet suppression Measurement of the jet radius and transverse momentum dependence of inclusive jet suppression in lead-lead collisions at snn = 2.76 TeV with the ATLAS detector (ATLAS; 1208.1967v2) Measurement of charged jet suppression in Pb-Pb collisions at snn = 2.76 TeV (ALICE; 1311.0633) Measurement of jet suppression in central Pb Pb collisions at snn= 2.76 TeV (ALICE; 1502.01689v1.pdf) Jet structure Measurement of jet fragmentation into charged particles in pp and PbPb collisions at sqrt(s[nn]) = 2.76 TeV (CMS; 1205.5872) Modification of jet shapes in PbPb collisions at sqrt(s) = 2.76TeV (CMS; 1310.0878) Measurement of inclusive jet charged-particle fragmentation functions in Pb+Pb collisions at snn =2.76TeV with the ATLAS detector (ATLAS; 1406.2979v2) Measurement of jet fragmentation in PbPb and pp collisions at snn =2.76TeV (CMS;1406.0932v2) B-tagged jets Evidence of b-jet quenching in PbPb collisions at snn =2.76TeV (CMS;1312.4918) Jet-hadron correlations Measurement of jet quenching with semi-inclusive hadron-jet distributions in central Pb Pb collisions at snn = 2.76 TeV (ALICE; 1506.03984v1) Jets in ppb Studies of dijet transverse momentum balance and pseudorapidity distributions in ppb collisions at snn =5.02TeV (CMS; 1401.4433v2.pdf) Measurements of the Nuclear Modification Factor for Jets in Pb+Pb Collisions at snn = 2.76 TeV with the ATLAS Detector (ATLAS; 1411.2357v2) Centrality and rapidity dependence of inclusive jet production in snn = 5.02 TeV proton lead collisions with the ATLAS detector (ATLAS; 1412.4092v1) Measurement of charged jet production cross sections and nuclear modification in p Pb collisions at snn = 5.02 TeV (ALICE; 1503.00681v1) Measurement of dijet kt in p Pb collisions at snn = 5.02 TeV (ALICE; 1503.03050v1) Jet Experiments at LHC 2
et Experiments at LHC Some key results on jets in LHC HI collisions Some comments on what to expect from Run II Some comments on experiment/theory interactions
Jets as tools to characterize QGP Medium effects on jets allow extraction of QGP transport coefficients: q: ^ transverse momentum diffusion (radiative energy loss) e: ^ longitudinal drag (collisional energy loss) Jets as tools to manipulate QGP How does QGP respond to local energy deposition by jets? pqcd plasma AdS/CFT goo Jets as tools to understand QGP How does the strongly coupled liquid emerge from QCD? Jets probe QGP at different (controllable) length scales Scattering sensitive to quasi-particle nature of the medium Jet Experiments at LHC 4
LHC jet experiments (in heavy ion collisions) Jet measurement approach: Clustering with anti-kt algorithm Subtraction of event-by-event background energy estimate Jet energy corrections using pp calibration and MC correction factors Achieved good experimental control Reconstruction efficiency (close to 100%@50+ GeV) Jet energy scale (2-4% above 30 GeV) Resolution and UE fluctuations (~15%@100GeV) } This was not obvious a-priori; success enabled by nature of observed jet modifications Complementary approaches to reconstruction biases At low pt: efficiency vs fake jets Restrict measurement to high pt (CMS/ATLAS) Ensemble-based measurement with combinatorial correction (ALICE/STAR) For sufficiently high trigger pt, all away-side jets are found Jet Experiments at LHC 5
Jets in LHC Run-2 (and beyond) LHC schedule HI HI HI HI PbPb HI s = 5TeV HI Collision rate 20kHz Lint 3/nb s = 5.5TeV Collision rate 50kHz Lint 10/nb (run 2+3) + RHIC Compared to LHC Run1: x60 due to higher luminosity; x3 due to higher s Jet Experiments at LHC 6
Kinematic reach: Now and tomorrow (*) (*) Artist s impression RHIC today LHC today RHIC tomorrow LHC tomorrow RAA D mesons B mesons Hadrons Jets b Jets Dijets (pt,1) x+jet Z 0 +jets (pt Z ) γ+jets (pt γ ) Double b-tag (pt,1) Jet Experiments at LHC 7
Kinematic reach: Now and tomorrow (*) (*) Artist s impression RHIC today LHC today RHIC tomorrow LHC tomorrow RAA D mesons B mesons Hadrons Jets b Jets Dijets (pt,1) x+jet Ensemble-based measurements and x+hadron correlations add low pt reach Z 0 +jets (pt Z ) γ+jets (pt γ ) Double b-tag (pt,1) New observables; smaller uncertainties; broader pt reach RHIC+LHC overlap Jet Experiments at LHC 8
The importance of photon-jet correlations Using isolated photons to tag away-side jets determines initial parton energy to 15% determines initial direction of the parton tags parton to be a light quark 40 < pt γ < 50GeV 50 < pt γ < 60GeV 60 < pt γ < 80GeV pt γ > 80GeV jet pt > 30 GeV photon pt <50GeV: Spectrum of PbPb jets is suppressed vs pp Biased jet selection photon pt >80GeV: Spectrum of PbPb jets is shifted vs pp Unbiased jet selection Sufficiently high γ pt or sufficiently low jet pt yield unbiased selection of jets Jet Experiments at LHC 9
Extracting QGP transport coefficients Similar information from jet RAA, dijet asymmetries, γ-jet momentum shift ^ q determined with about 35% uncertainty Combined RHIC and LHC data: Test model consistency First hint of temperature dependence Quantitative extraction of e ^ awaits more precise heavy flavor data Jet Experiments at LHC 10
RAA now and in Run-2 R AA 1 0.9 0.8 0.7 0.6 0.5 ALICE, η < 0.8 ATLAS, η < 1.0 CMS, η < 1.0 PbPb 0-5%, 2.76 TeV pp, 2.76 TeV LHC Run-2?? 0.4 0.3 ATLAS; 1504.04337 0.2 0.1 0 20 40 60 80 100 120 140 16 Charged Particle p T (GeV/c) 200 250 Essential to not let systematic, quantitative exp/theo comparison go stale Add new Run-1 data Predict/prepare for Run-2 data 300 Jet Experiments at LHC 11
RAA for charged hadrons and jets ~ Agreement between CMS and ATLAS at high jet p T Agree with charged particle R AA at high p T ATLAS; 1504.04337 It would be nice to have low p T CMS data / ATLAS R AA with R=0.2 / ALICE high p T data Jet Experiments at LHC 12
The B s are coming Collisional energy loss Radiative energy loss This is what google thinks of dead cones Jet Experiments at LHC 13
Flavor/mass Flavor dependence: Dependence Yes, of Jet no, Quenching maybe? Pb+Pb b-jet D bà J/ψ π Qualitatively not too dissimilar wrt. expectations Quantitatively there are many subtleties Jet Experiments at LHC 14
Not all heavy quarks are created equal Gluon Splitting Contribution from Yen-Jie Lee RHIC users meeting HF studies: matched partons are not necessary heavy quarks! b jets D mesons Non-Prompt J/ψ ~30-40% ~40-50% ~20% Estimated from PYTHIA 6 Non-negligible for both jets and hadrons! Even more important for charm than for bottom at LHC energy! Jet Experiments at LHC 15
Flavor/mass dependence: Yes, no, maybe? from Yen-Jie Lee RHIC users meeting 0< η <0.5 2.0< η <2.5 Forward spectra are steeper (RAA smaller) But it s 85% quark jets! It might be good to look at a global analysis of all data relevant to q/g flavor dependence and mass dependence to verify some of the basic beliefs Jet Experiments at LHC 16 25
Energy flow and medium response Ma, Wang PRL 2011 Neufeld, Vitev PRC 2012 Do we have a medium, if there s no medium response? Experimental and theoretical challenges: Strength and angular structure of medium response unknown Jets are correlated with the complex e-by-e flow fields through quenching How to distinguish medium-response from modified jet branching? Jet Experiments at LHC 17
Jet-track correlations in CMS CMS dijet missing pt Enhancement of low-p T correlated yields at large angles to jet axis PbPb 0-30% A J > 0.22 Is this trivial jet-medium coupling or signature of modified QCD branching ( turbulent flow )? PbPb pp Jet-track correlations for leading/subleading jet Common interpretation with MPT analysis is highly non-trivial Need jet MC to translate one to the other Jet Experiments at LHC 18
Jet measurements as QGP microscope Jet Experiments at LHC 19
Jet measurements as QGP microscope Large angle inter-jet scattering pqcd plasma Angular and momentum structure of intra-jet parton cascade AdS/CFT goo D Eramo, Rajagopal, 12 updated calculation underway CMS γ+jet data STAR jet-hadron correlations (1506.03984v1) Need x10 better precision Kurkela, Wiedemann, arxiv:1407.0293 Differential (event-by-event) measurements may allow glimpse at QCD Rutherford scattering off QGP constituents Jet Experiments at LHC 20
We have observed medium modifications of jet momentum and angular structure Jet shapes Fragmentation functions RAA radius dependence Little change at small r, high p T Narrowing/depletion at intermediate r, p T ΔRecoil radius dependence Radius r Jet Experiments at LHC 21 Broadening/excess at large r, low p T (~2% of jet energy)
But there is a long road ahead Z = p Trk / p Jet Qualitative consistent results between CMS and ATLAS High p T particles CMS: PRC 90 (2014) 024908 ATLAS: PLB 739 (2014) 320-342 Low p T particles But: Experiment-comparison suggests that we do NOT YET have sufficient control over systematics necessary for our decadal program Jet Experiments at LHC 22
Jet structure in pp and PbPb Jewel Liliana Apolinario Lisbon HI jet workshop Jesse Thaler, Boost 2014 Q-Pythia Jet structure variables sensitive to (in-medium) shower evolution Critical effort in pp highest sensitivity searches (q/g and boosted object discrimination) Stability vs pp pileup is major issue Dani Pablos Lisbon HI jet workshop Convergence of AA and pp needs Jet Experiments at LHC 23
Summary Rich (overwhelming?) harvest of jet results from LHC Run-1 Theory/experiment dialogue is essential JET collaboration qhat extraction from RAA is paradigmatic Needs to be continuous process, not one and done (e.g. new RAA measurements) Complex questions will need global analyses (e.g. flavor dependence) Full MC essential for interpretation of complex measurements (e.g. jet-medium correlations) Step forward with LHC Run-2 may prove as big as LHC Run-1 Will experiment or theory lead? Jet Experiments at LHC 24