Abstract
We present an analysis of the role that the quark-gluon plasma (QGP) resolution length, the minimal distance by which two nearby colored charges in a jet must be separated such that they engage with the plasma independently, plays in understanding the modification of jet substructure due to interaction with QGP. The shorter the resolution length of QGP, the better its resolving power. We identify a set of observables that are sen- sitive to whether jets are quenched as if they are single energetic colored objects or whether the medium that quenches them has the ability to resolve the internal structure of the jet. Using the hybrid strong/weak coupling model, we find that although the ungroomed jet mass is not suitable for this purpose (because it is more sensitive to effects coming from particles reconstructed as a part of a jet that originate from the wake that the jet leaves in the plasma), groomed observables such as the number of Soft Drop splittings nSD, the momentum sharing fraction zg, or the groomed jet mass are particularly well-suited to discriminate the degree to which the QGP medium resolves substructure within a jet. In order to find the optimal grooming strategy, we explore different cuts in the Lund plane that allow for a clear identification of the regions of Soft Drop phase space that enhance the differences in the jet substructure between jets in vacuum and quenched jets. Comparison with present data seems to disfavor an “infinite resolution length”, which is to say the hypothesis that the medium interacts with the jet as if it were a single energetic colored object. Our analysis indicates that as the precision of experimental measurements of jet substructure observables and the control over uncertainties in their calculation improves, it will become possible to use comparisons like this to constrain the value of the resolution length of QGP, in addition to seeing how the substructure of jets is modified via their passage through it.
Highlights
Strongly interacting matter produced in ultrarelativistic heavy ion collisions
We present an analysis of the role that the quark-gluon plasma (QGP) resolution length, the minimal distance by which two nearby colored charges in a jet must be separated such that they engage with the plasma independently, plays in understanding the modification of jet substructure due to interaction with QGP
Our analysis indicates that as the precision of experimental measurements of jet substructure observables and the control over uncertainties in their calculation improves, it will become possible to use comparisons like this to constrain the value of the resolution length of QGP, in addition to seeing how the substructure of jets is modified via their passage through it
Summary
The hybrid strong/weak coupling model, introduced and extensively described in our earlier works refs. [11, 41,42,43,44], addresses the challenge of describing the interaction, and consequent modification, of jets that traverse QGP with which they are concurrently produced in heavy-ion collisions. The resolution length Lres, which for a strongly coupled medium must be related to the inverse of the local QGP temperature, sets the minimal transverse distance between partons in a shower such that they are seen as separate by QGP, meaning that they lose energy independently. Note that in perturbative analyses of multiple partonic sources traversing the medium [52,53,54,55], the resolution parameter can be related to the description of how a single parton loses energy; at strong coupling, no such connection between energy loss and the resolution length has been established and for this reason we shall take Lres to be a second, independent, free parameter of our hybrid model that should be determined via comparison between calculations and experimental measurements of observables that are sensitive to its value. The technical details of how these negative particle contribution are treated in our jet analyses can be found in appendix A
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