Periodic Reporting for period 1 - JQ4LHC (Jet quenching for heavy-ion collisions at the LHC)
Periodo di rendicontazione: 2021-09-01 al 2023-08-31
Due to the extremely short lifetime of the QGP produced in heavy-ion colliders, it is not possible to use external probes to probe its dynamics. Fortunately, as in proton-proton collisions, high transverse momentum scatterings can occur in heavy-ion collisions, resulting in highly-energy parton pairs moving in opposite directions. In a p-p collision, each parton emits gluons at small angles ultimately fragmenting into a collimated spray of hadrons, which we refer to as a jet. In heavy-ion collisions, the partons within the jets traverse the QGP, interacting with it through the strong force. Such interactions induce modifications in heavy-ion jets compared to p-p jets.This phenomenon, known as jet quenching, is an excellent tool for probing and characterizing the properties of the QGP.
Describing heavy-ion jets and their interactions with the QGP poses significant technical challenges. Consequently, current jet quenching Monte Carlo approaches include a fair amount on modeling, making it difficult to drawing definitive conclusions about the QGP dynamics. JQ4LHC implements a bottom-up semi-analytical framework for jet quenching based on perturbative calculations in QCD, tailored for phenomenological applications. This framework aims to offer an alternative perspective to Monte Carlo approaches, serving as a complementary method in the study of jet quenching phenomena.
The theory of jet quenching usually neglects the propagation of the jets during the stages of the system prior to the formation of the QGP, known as initial stages. JQ4LHC extended this theoretical framework to account for the propagation of the initial high-energy parton through these initial stages.
Furthermore, JQ4LHC has delved into the dynamics of color coherence, a phenomenon anticipated to significantly impact the fragmentation and evolution of heavy-ion jets within the QGP. A new set of jet observables, known as energy correlators, were proposed, showcasing their potential to isolate the long-sough-after color coherence dynamics.
This formalism was also generalized to encompass the propagation of the hard parton in the initial stages, accounting from extra gluon emissions that occur before the formation of the QGP. Then, the impact of these additional emissions on the description of a pair of jet quenching observables was assessed. The results confirmed the crucial role of the treatment of jet quenching during the initial stages, not only for correctly describing these observables but also for determining the jet quenching parameter's extracted value.
To address the color coherence dynamics, JQ4LHC introduced the energy correlator approach to heavy-ion physics. This innovative strategy consists of examining the angular correlations between the energy deposited by the particles within the jets in the detectors, instead of reconstructing the full jet branching. By deriving and computing the two-point energy correlator within a heavy-ion jet in perturbative QCD, JQ4LHC has shown the potential of this observable to isolate the dynamics of color coherence.
These outcomes have been disseminated through scientific articles, including four published peer-reviewed papers, and two preprints currently undergoing review. Additionally, these findings were presented in various international conferences and workshops, contributing to the broader dissemination of this research across the scientific community.
Specifically, JQ4LHC has achieved the following advancements beyond the sate of the art:
- The first complete evaluation of the BDMPS-Z framework with multiple scatterings without the use of the Harmonic Oscillator approximation in dynamically evolving media.
- The incorporation of the emitter's propagation and corresponding radiation in the stages before the formation of the QGP.
- The introduction and calculation of the two-point energy correlator of heavy-ion jets.
with the following impact:
- Significantly advancing our knowledge and understanding of the medium-induced radiation process, which is the main contribution to the energy loss experienced by jets when traversing a colored medium
- Introducing a completely novel tool, energy correlators, to study jet substructure in heavy-ion collisions.
Given the fundamental and theoretical nature of the project, its primary focus is on advancing knowledge. As such, no other immediate socio-economic implications are anticipated in the short term.