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Publication
Modification of Jet Substructure in Heavy Ion Collisions as a Probe of the Resolution Length of Quark-Gluon Plasma
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Advisor(s)
Abstract(s)
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. We identify a set of observables that are sensitive 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 $n_{\rm SD}$, the
momentum sharing fraction $z_g$, 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
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.