In the ALICE spectrometer, in order to expand the physics capabilities of EMCal by enabling back-to-back correlation measurements, a large acceptance Electromagnetic Calorimeter positioned opposite to and down EMCal (DCal) is under study.
Thus the aim of the proposed JRA is to perform an extensive study of jet quenching in heavy ion collisions by:

  • a combination of inclusive and correlation measurements enabled by large acceptance Electromagnetic Calorimeters EMCal and DCal;
  • a synergy of technological and conceptual innovations for jet trigger and jet reconstruction;
  • a new theoretical formalism and Monte Carlo modelization for the jet quenching.

 Description of work and role of partners

The proposed JRA consists of three tasks; the description of the working tasks and their sharing between participants is detailed in the following.

Task1: Trigger development
The INFN-LNF team will work on the development inherent to the HLT. For high energies expected in 2013 with the higher luminosity collisions at LHC, cluster deconvolution based on track parameters becomes fundamental.
More specifically, online clusterizer algorithm must be developed to maximize reconstruction efficiency for the wide range of correlation studies possible with the EMCAL+DCAL. For this particular aim, different algorithms with a NxN clusterizer where N=3,5 will be studied.

Task2: Theoretical model developments and modelization in Monte Carlo
The INFN-LNF team will be in charge for the study of hadronization corrections to the jet spectrum and on their dependence on jet algorithm, hadronization models and resolution R. Hadronization effects grow inversely proportional to the jet resolution R and dominates over other contributions (pileup and perturbative radiation) al low R. Jet algorithms are differently sensitive to hadronization effects.
The Monte Carlo event generator, developed by USC, which incorporates quenching effects, q-PYTHIA, accounts for radiative processes only. Other contributions need to be studied to properly modeling the quenching and the profile of the jets. In particular, for what concerns the theoretical aspects, the activity of USC team will aim for: i) medium-modified color reconnections, ii) inclusion of elastic scattering, ii) role of the different ordering variables.
The INFN-LNF team in collaboration with the USC will also work on the implementation of the in-medium color
flow in the q-PYTHIA Monte Carlo. The change on the color flow has direct impact on hadronization and the hadron composition of the jet.

Task3: Di-Jet and γ-jet reconstruction in heavy ion collisions
LNF is in charge to study the combination (reconstruction algorithms, subtraction algorithms) for the case of EMCal+DCal/EMCAL. Specifically, it will be quantified the improvement in the jet energy resolution in the case of full di-Jet with respect to single jet reconstruction.
The INFN-CT team will be in charge for the study of the hadrochemical composition in hadron-jet and di-jet events and jet-resonance correlation in heavy ion collisions. This study in di-Jet and in hadron-jet events will be extremely important to better characterize the matter created in heavy ion collision. In particular, the analysis of identified hadrons can be extended to include identified hadronic resonances. Based on their lifetimes, which range from a few fm/c to tens fm/c, these strongly decaying states are particularly sensitive to the evolution, lifetime and properties of the partonic medium. Algorithms and analysis procedures to study the hadrochemical composition of di-jet events in Pb-Pb will be developed by the Catania team.
CNRS/IN2P3/SUBATHEC&IPHC teams will be in charge to study how to improve the jet energy calibration using correlated events such as di-jets, π0-jet and γ-jet events in both elementary and heavy ion collisions. The configurations EMCal/EMCal+DCal will be compared in order to confront single inclusive measurements such as full jet reconstruction with correlated measurements such as di-jet reconstruction.
γ-jet events allow for a complete calibration of the jet energy. However these events are statistically suppressed at large jet energies. The combination of both EMCal and DCal calorimeters will improve the statistics for such measurement by almost a factor of two making γ-jet the optimal probe for the jet quenching. For this task SUBATHEC&IPHC teams will concentrate on the way particles are distributed inside the jet and on how the energy is redistributed in the dense medium.
USC team will be in charge for studying:
i) jets induced by light and heavy partons. Theoretical models have been successful in describing the suppression for light hadrons, while problems persist for heavy flavors. These latter are the best for determining the jet energy and consequently the best for determining the medium effects on the fragmentation function; for maximizing the medium effects on the jet shapes; and for maximizing the medium effects on the correlations between leading and sub-leading particles. Because of this, the case of heavy-quarks needs to be specially studied.
ii) photon production and correlations. The formalism used to compute the medium-induced gluon radiation will be used to compute the medium-induced photon emission as well as the correlations of two photons and photon-jet.
USC will be in charge for the theoretical development of these effects and for studying their impact on the jet

The HadronPhysics3 project is supported by the European Union
under the 7th Framework Capacities Programme in the area of Research Infrastructures (RI).