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Theoretical predictions of jet observables in QCD matter

Final Report Summary - JETS IN QCD MATTER (Theoretical predictions of jet observables in QCD matter)

PROJECT OBJECTIVES: A new state of nuclear matter, called quark-gluon plasma (QGP), is predicted to be created at extreme energy densities. This new state consists of interacting quarks, antiquarks and gluons. One of the major goals of LHC (Large Hadron Collider) and RHIC (Relativistic Heavy Ion Collision) experiments is to create and explore QGP. The main goal of this proposal was to develop a realistic theoretical formalism for generating theoretical predictions that can be compared with the experimental data. Such comparison can both test our quantitative understanding of QGP and improve our qualitative understanding of the measurements.

WORK PERFORMED SO FAR: For reliable predictions of jet suppression at RHIC and LHC it is necessary to accurately compute the energy that jets lose due to interactions with QCD medium. As a starting point of the project, we improved the dynamical jet energy loss formalism - which the fellow previously developed - by consistently introducing finite magnetic mass and running coupling. We then integrated the improved formalism into a computational framework that can generate reliable predictions for jet suppression. The numerical procedure includes multi-gluon fluctuations, path-length fluctuations and most up-to-date jet production and fragmentation functions. We then generated comprehensive set of theoretical predictions for angular-averaged RAA, for both RHIC and LHC, all types of available probes (both light and heavy), and all centrality regions. Robust agreement of the dynamical energy loss formalism with the extensive RAA data, obtained by the same formalism, the same numerical procedure, the same parameter set and no free parameters, strongly suggests that the developed formalism can realistically model jet-medium interactions. We also provided clear predictions for the upcoming 5.02 TeV experiments at the LHC (just released preliminary experimental results indicate an excellent agreement with our predictions), as well as tested which energy loss mechanisms are numerically important for realistically describing the jet-medium interactions in the QCD matter.

We also used the developed computational procedure to analyze phenomena behind some intuitively surprising experimental data, as well as some fine resolution data. As an important result of our work, which the scientist in charge published in Physical Review Letters as a single author, we proposed an explanation for "heavy flavour puzzle at LHC". The puzzle considers unexpected experimental observations at LHC, which show the same suppression for charged hadrons and D mesons; this result may - contrary to pQCD expectations - suggest similar energy losses for light quarks and gluons in QCD medium. PI showed that this puzzle is a consequence of an unusual combination of the suppression and fragmentation patterns, so that it is not necessary to invoke the same energy loss for light partons.

MAIN RESULTS ACHIEVED SO FAR: The project resulted in 15 papers that are published in leading international journals (Phys. Rev. Lett., Phys. Lett. B, Phys. Rev. C, J Phys. G, Nucl. Phys. A), one paper accepted for publication (Nucl. Phys. A), one under revision in Phys. Lett. B and one submitted for publication in Phys. Rev. C; the fellow is both the first and the senior (corresponding) author on 16 of those papers. The results were also presented as invited and contributed talks at 9 major conferences in the field, as well as three invited seminars.

In addition to the scientific results stated above, the fellow became a member of four scientific international collaborations. She is also continuously providing predictions (by invitation) for the LHC and RHIC experiments. The fellow is currently in the process of promotion to Research Professor (a permanent position not subject to further re-elections). Her promotion is currently in the final stage of the election process, where the approval of the University is awaiting for the process to be finalized. For her research results upon return to Serbia, she just received a 2016. Institute of Physics Belgrade Annual Prize for Scientific Work.

The fellow also initiated her independent research group, and is currently mentoring two PhD students. Finally, in 2015., the fellow was a finalist of European Research Council (ERC) Starting grant. She has again applied this year - and is again a finalist - for ERC Consolidator grant. We therefore think that the fellow has successfully reintegrated as an independent researcher/group leader. Web site of the fellow is available at