During the first reporting period of the project, despite the relevant impact that the COVID19 had in a normal development of the activities, we have made important progress in several items of the proposed research
- Modelling of the interaction of the jet with the QCD medium. One of the long-standing open problems in jet quenching phenomenology was to pin-down, at the same time, the relevance of the multiple scatterings that the quarks and the gluons suffer with the medium and the complete treatment of the corresponding cross sections, including the perturbative tails, responsible for large angle scatterings. YoctoLHC has produced important progress in this subject with: i) the first phenomenological analysis of experimental data with the complete resummation, showing that the inconsistencies previously found between data and theory disappear with this resummation; ii) a new method to compute the spectra of radiated gluons including this resummation with efficient numerical implementation; iii) progress on a new improved opacity expansion that is a good approximation to the whole problem for dense enough media and with the advantage of a better analytical control.
- Effect of the hydrodynamical flow on the jet. The medium produced in the high-energy heavy ion collisions is not static and the velocity fields modify the gluon radiation properties in ways that could be experimentally measured. Should this effect be large enough, a new powerful tool to directly sccess the velocity fields in the medium would be available. In this first months, a formalism was developed to rigorously include these velocity fields in the medium-induced gluon radiation, the building-block of jet quenching
- The evolution equations for jet quenching. Once the building-block for radiation is known, the next step is to understand how this building block has to be iterated, this is known as an evolution equation, or in jet quenching jargon, also a rate equation. YoctoLHC has also studied the effect of different hydrodynamical scenarios in the rate equations, finding that the final result is sensitive to these scenarios and that de differences cannot be accommodated by widely-employed scaling between them. Also, the correction to this equations due to color coherence was computed.
- Color correlations in the initial state, the 3-D structure of the proton and nuclei. The three-dimentional structure of the protons and nuclei is one of the hot topics in QCD at present and extremely relevant for the YoctoLHC physics as it provides the initial conditions that we propose to measure with jet observables.
- Identifying the presence of jets and characterize them in collisions at the LHC require developing sophisticated search algorithms. Different variables and techniques for the clustering of the particles into jets maybe more sensitive to the physics under scrutiny than other. So, devising the right observables is one of the main goals of the project. During this first reporting period, time-like variables have been explored. These time-like variables promise to be more efficient in catching the different snapshots in the evolution of the system at the initial times.
