Predictions for boson-jet observables and fragmentation function ratios from a hybrid strong/weak coupling model for jet quenching

Journal of High Energy Physics, Mar 2016

We have previously introduced a hybrid strong/weak coupling model for jet quenching in heavy ion collisions in which we describe the production and fragmentation of jets at weak coupling, using Pythia, and describe the rate at which each parton in the jet shower loses energy as it propagates through the strongly coupled plasma, dE/dx, using an expression computed holographically at strong coupling. The model has a single free parameter that we fit to a single experimental measurement. We then confront our model with experimental data on many other jet observables, focusing in this paper on boson-jet observables, finding that it provides a good description of present jet data. Next, we provide the predictions of our hybrid model for many measurements to come, including those for inclusive jet, dijet, photon-jet and Z-jet observables in heavy ion collisions with energy \( \sqrt{s}=5:02 \) ATeV coming soon at the LHC. As the statistical uncertainties on near-future measurements of photon-jet observables are expected to be much smaller than those in present data, with about an order of magnitude more photon-jet events expected, predictions for these observables are particularly important. We find that most of our pre- and post-dictions do not depend sensitively on the form we choose for the rate of energy loss dE/dx of the partons in the shower. This gives our predictions considerable robustness. To better discriminate between possible forms for the rate of energy loss, though, we must turn to intrajet observables. Here, we focus on ratios of fragmentation functions. We close with a suggestion for a particular ratio, between the fragmentation functions of inclusive and associated jets with the same kinematics in the same collisions, which is particularly sensitive to the x- and E-dependence of dE/dx, and hence may be used to learn which mechanism of parton energy loss best describes the quenching of jets.

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Predictions for boson-jet observables and fragmentation function ratios from a hybrid strong/weak coupling model for jet quenching

HJE Predictions for boson-jet observables and fragmentation function ratios from a hybrid strong/weak coupling model for jet quenching Jorge Casalderrey-Solana 0 1 3 7 8 Doga Can Gulhan 0 1 3 5 7 8 Jose Guilherme Milhano 0 1 2 3 6 7 8 Daniel Pablos 0 1 3 7 8 Krishna Rajagopal 0 1 3 4 5 7 8 0 Av. Rovisco Pais , P-1049-001 Lisboa , Portugal 1 Massachusetts Institute of Technology , MIT 2 Physics Department, Theory Unit , CERN 3 Mart i Franques 1 , 08028 Barcelona , Spain 4 Center for Theoretical Physics , MIT 5 Laboratory for Nuclear Science and Department of Physics 6 CENTRA, Instituto Superior Tecnico, Universidade de Lisboa 7 Cambridge , MA 02139 , U.S.A 8 CH-1211 Geneve 23 , Switzerland We have previously introduced a hybrid strong/weak coupling model for jet quenching in heavy ion collisions in which we describe the production and fragmentation of jets at weak coupling, using Pythia, and describe the rate at which each parton in the jet shower loses energy as it propagates through the strongly coupled plasma, dE=dx, using an expression computed holographically at strong coupling. The model has a single free parameter that we t to a single experimental measurement. We then confront our model with experimental data on many other jet observables, focusing in this paper on boson-jet observables, nding that it provides a good description of present jet data. Next, we provide the predictions of our hybrid model for many measurements to come, including those for inclusive jet, dijet, photon-jet and Z-jet observables in heavy ion collisions with s = 5:02 ATeV coming soon at the LHC. As the statistical uncertainties on near-future measurements of photon-jet observables are expected to be much smaller than energy p - those in present data, with about an order of magnitude more photon-jet events expected, predictions for these observables are particularly important. We nd that most of our preand post-dictions do not depend sensitively on the form we choose for the rate of energy loss dE=dx of the partons in the shower. This gives our predictions considerable robustness. To better discriminate between possible forms for the rate of energy loss, though, we must turn to intrajet observables. Here, we focus on ratios of fragmentation functions. We close with a suggestion for a particular ratio, between the fragmentation functions of inclusive and associated jets with the same kinematics in the same collisions, which is particularly sensitive to the x- and E-dependence of dE=dx, and hence may be used to learn which mechanism of parton energy loss best describes the quenching of jets. ArXiv ePrint: 1508.00815 4 5 2.1 2.2 2.3 2.4 3.1 3.2 3.3 4.1 4.2 1 Introduction 2 Description of the model and its implementation The hybrid model approach The e ects of ow on the rate of energy loss The e ects of ow on single-jet and dijet observables Species dependence of jet suppression Fragmentation functions Conclusions and outlook 3 Boson-jet correlations, including predictions for p s = 5:02 ATeV collisions and for Z-jet correlations 2:76 ATeV and predictions for p Z-jet observables: predictions for p s = 5:02 ATeV Generation and selection of Monte Carlo events Photon-jet observables: comparison with experimental results at p s = Fragmentation functions of the associated jets in photon-jet and Z-jet pairs Fragmentation functions of the associated jets in dijet pairs A Energy Loss in a boosted uid B Update on single-jet and dijet observables at p C Predictions for single-jet and dijet observables at p Model dependence of boson-jet correlations 1 Introduction The LHC has ushered in a new era in the exploration of the properties of matter under extreme conditions. By colliding Pb ions at center of mass energies in the multi-TeV regime, the LHC has provided us with droplets of the hottest matter ever produced in the laboratory and a diverse suite of copious high energy probes with which to explore the microscopic properties of the strongly coupled, liquid, quark-gluon plasma (QGP) discovered at RHIC [1{4]. For jet probes in particular, the results of the successful LHC Run 1 have shown that many of the properties of these fundamental QCD objects are substantially modi ed when the jets are produced in Pb-Pb collisions as compared to { 1 { when they are produced in p-p collisions [5{20]. These modi cations are results of the nal state interaction between the jets and the droplets of hot QCD matter formed in heavy ion collisions. As the principal underlying e ect is the energy loss su ered by each of the components of the jet showers on their way out of the hot matter, the various modi cations of jet properties observed in heavy ion collisions are referred to, in sum, as jet quenching. The phenomenon of jet quenching was rst discovered without reconstructing individual jets via the strong reduction in the number of intermediate-pT hadrons in heavy ion collisions at RHIC [21, 22]. Precisely because varied modi catio (...truncated)


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Jorge Casalderrey-Solana, Doga Can Gulhan. Predictions for boson-jet observables and fragmentation function ratios from a hybrid strong/weak coupling model for jet quenching, Journal of High Energy Physics, 2016, pp. 53, Volume 2016, Issue 3, DOI: 10.1007/JHEP03(2016)053