Experimental Results on Jets in Heavy Ion Collisions Yen-Jie Lee - PowerPoint PPT Presentation

Experimental Results on Jets in Heavy Ion Collisions Yen-Jie Lee Massachusetts Institute of Technology XLVII International Symposium on Multiparticle Dynamics 12 September, 2017 1 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Reconstruct the Quark Gluon Plasma QGP O(1m) O(10 27 m) O(10 -15 m) O(10 13 m) 2 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Prepare the Quark Soup Azimuthal anisotropy Particle Multiplicity • Early thermalization <1 fm/c • Collision impact parameter of the ions • Shear viscosity • Energy density of the medium • Fluctuation of v N coefficients from particle azimuthal correlation: Initial-state geometry fluctuation 3 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Beyond the Analysis of Debris • How does the strongly interacting medium emerge from an asymptotic free theory (QCD)? • Can we see quasi particles (quarks and gluons) and medium resonse in the Quark Gluon Plasma? 4 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Beyond the Analysis of Debris • How does the strongly interacting medium emerge from an asymptotic free theory (QCD)? • Can we see quasi particles (quarks and gluons) and medium resonse in the Quark Gluon Plasma? 5 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Hard Probes in Heavy Ion Collisions In medium parton energy loss Photons / Z  “ Jet quenching ” Photons, electroweak bosons (Bjorken, 1982) Quark Gluon Plasma Transport coefficient 𝑟 , stopping power dE/dx, 𝑒𝑂 𝑕 𝑒𝑧 , temperature 𝑈 … gluon density Jets and hadrons from High energy quarks and gluons Studies of the medium properties Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics 6

Parton Energy Loss Models • The main problem: we don’t know how to describe the interaction between the hard scattered parton and QGP (a multi-scale problem) • Two theoretical approaches: (neither of them are the full stories and both of them are effective descriptions in proper regimes) Holographic calculation Perturbative QCD Strong coupling limit Weak coupling limit Collisional Radiative AdS /CFT “drag force” energy loss energy loss CUJet3.0 CCNU JEWEL HYBRID Q-PYTHIA SCET G JETSCAPE 7 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet Quenching What is the mechanism of jet quenching? QGP 8 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet R AA up to p T ~ 1 TeV Can we capture all the quenched energy by jet reconstruction? Anti-k T R=0.4 Jet R AA in 2.76 and 5.02 TeV • Jet R AA < 1 : quenched energy goes out of the jet cone • Similar results from the STAR measurement on the h-jet at RHIC • Significant jet suppression at high p T (up to ~ 1 TeV !) • If the suppression is purely due to energy loss → Energy transported out of the cone is O(100) GeV! What is the fraction of parton energy going out of the jet cone? 9 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Absolute Energy Loss with Z+Jet at 5 TeV arXiv 1702.01060 PRL 119, 082301 (2017) Z Boson Jet Momentum conservation in the transverse direction Jet quenching (E-loss) pp pp PbPb PbPb 1 Jet / p T boson x=p T ~ 15% of the energy went out of the jet cone (R=0.3) 10 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Absolute Energy Loss with γ+Jet at 5 TeV ATLAS-CONF-2016-110 CMS-PAS-HIN-16-002 (2017) pp PbPb PbPb Photon Jet / p T γ x J γ =p T Jet 11 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Photon-Jet Data vs. Theoretical Predictions CMS-PAS-HIN-16-002 (2017) PbPb Photon p T 40-50 GeV/c 50-60 GeV/c 60-80 GeV/c • JEWEL: pQCD 2 to 2 scattering extrapolated to infrared region + recoil parton • LBT: pQCD Transport model with medium recoil and thermalization of the quenched energy • HYBRID Model: PYTHIA8 + AdS/CFT drag force (strong coupling) 12 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Search for Quasi-Particles in the QGP “QGP Rutherford experiment” Photon Jet PbPb Photon “Backscattering”? Jet No significant modification ATLAS-CONF-2016-110 QGP probed looks smooth 13 13 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics XLVII International Symposium on Multiparticle Dynamics

Hadron-Jet Angular Correlation Df No significant broadening QGP probed looks smooth 14 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet Quenching QGP Do gluons lose more energy than the quarks? If Yes: Gluon jet to quark jet ratio will decrease (Gluon jets are more suppressed) 15 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Charged Jet p T D (Dispersion) and Jet Girth Quark Gluon Quark Gluon Anti-k T R=0.2 40<p T <60 GeV PbPb PbPb • Jets in PbPb are more Quark-like ! (Gluon jets suppressed) 16 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet Longitudinal Structure Jet axis R D(z) = PbPb / pp ATLAS-CONF-2017-005 Δ r Projection to jet axis QGP • Fragmentation functions Ratio R D(z) between PbPb and pp collisions at 5 TeV • Enhancement at large z (high p T particles in jet): smaller gluon/quark ratio in PbPb • Weak or no dependence on the jet p T → If switch to γ -tagged jet (mainly quarks), will this enhancement go away? 17 Yen-Jie Lee 5th Heavy Ion Jet Workshop

Photon-Tagged Fragmentation Function Photon Jet • First γ -tagged fragmentation function! • Decrease the population of gluon jets: ~70% of the tagged jets are quark jets • Significant modification in PbPb with respect to pp reference is observed • No high z (or small ξ =ln(1/z) ) enhancement observed! 18 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet Quenching Do we see medium response? QGP 19 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Where does the Quenched Energy Go? Jet axis JHEP 01 (2016) 006 Subleading jet Δ QGP Leading jet • Quenched energy carried by • Average momentum of those particles are higher than that from medium debris → Not Completely Thermalized? 20 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet Transverse Structure Jet shapes in pp and PbPb at 5.02 TeV Jet axis pp PbPb Δ r Anti-k T R=0.4 3-4 GeV 1-2 GeV 0.7-1 GeV Ratio: PbPb/pp CMS-PAS-HIN-16-020 • Jet shapes and fragmentation functions in pp and PbPb collisions at 5 TeV • Sensitive to the possible medium response to hard probes and induced radiation 21 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Theoretical Interpretation of the excess SCET G JEWEL arXiv:1707.01539 CCNU Different explanation of the large angle arXiv:1701.07951 enhancement in jet shape measurement • SCET G : Splitting function (large angle radiation) • JEWEL & JETSCAPE: medium recoil parton • CCNU: recoil parton + hydro dynamical evolution • HYBRID: fully thermalized medium response HYBRID See talk from Ivan Vitev, Yasuki Tachibana, Abhijit Majumder 22 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Jet Quenching QGP Can we groom away the soft radiation? (focus on the hard jet core) Can jet quenching depends on the structure of parton shower? 23 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Groomed Jet Substructure with Soft Drop CMS: used two grooming settings with Δ R>0.1 cut subjet “Default” “Jet Core” From Yi Chen Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Groomed Jet Mass (z cut , β ) = (0.5,1.5) (z cut , β ) = (0.1,0.0) Δ R>0.1 Δ R>0.1 “Default” “Jet Core” 0-10% 0-10% Anti-k T R=0.4 CMS-PAS-HIN-16-024 • • Results with a “more aggressive grooming” Enhancement of large mass when looking • No significant modification of the “jet core” at a less aggressive grooming setting 25 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

Momentum Sharing of Subjets arXiv:1708.09429 One hard subjet Two hard subjets p T,2 p T,1 p T,1 p T,2 Z g small Z g ~ 0.5 • Quark and gluon Z g distributions are very similar in pp (z cut , β ) = (0.1,0.0) • Jets with two hard subjets (large Z g ) “relatively” more suppressed than jets with a single core (small Z g ) (Or small Z g is enhanced) 26 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics

CMS Groomed Jet Splitting Function arXiv:1708.09429 • JEWEL : enhancement of low Z g jets (due to medium recoil ) • SCET G : modification due to medium induced splitting function • HT & Coherent antenna BDMPS: Data prefer coherent energy loss • Measurement of r g and groomed R AA would help to separate models 27 Yen-Jie Lee XLVII International Symposium on Multiparticle Dynamics