8 research outputs found
LPM effect as the origin of the jet fragmentation scaling in heavy ion collisions
We address a recent puzzling result from the LHC: the jet fragmentation
functions measured in and collisions appear very similar in spite
of a large medium-induced energy loss (we will call this "jet fragmentation
scaling", JFS). To model the real-time non-perturbative effects in the
propagation of a high energy jet through the strongly coupled QCD matter, we
adopt an effective dimensionally reduced description in terms of the
quasi-Abelian Schwinger theory. This theory is exactly soluble at any value of
the coupling and shares with QCD the properties of dynamical generation of
"mesons" with a finite mass and the screening of "quark" charge that are
crucial for describing the transition of the jet into hadrons. We find that
this approach describes quite well the vacuum jet fragmentation in
annihilation at at jet energies in the range of the LHC heavy ion
measurements ( is the ratio of hadron and jet momenta). In QCD medium, we
find that the JFS is reproduced if the mean free path of the jet is
short, fm, which is in accord with the small shear viscosity
inferred from the measurements of the collective flow. The JFS holds since at
short mean free path the quantum interference (analogous to the
Landau-Pomeranchuk-Migdal effect in QED) causes the produced mesons to have low
momenta , where GeV is the typical meson mass.
Meanwhile the induced jet energy loss at short mean free path is much larger
than naively expected in string models.Comment: 4 pages, 4 figure
Herwig 7.1 Release Note
A new release of the Monte Carlo event generator Herwig (version 7.1) is now
available. This version introduces a number of improvements, notably: multi-jet
merging with the dipole shower at LO and NLO QCD; a new model for soft
interactions and diffraction; improvements to mass effects and top decays in
the dipole shower, as well as a new tune of the hadronisation parameters.Comment: 7 pages, 7 figures. Herwig is available from
https://herwig.hepforge.org
Herwig 7.2 release note
A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements over the major version 7.0, notably: multi-jet merging with the dipole shower at LO and NLO QCD; spin correlations in both the dipole and angular-ordered parton showers; an improved choice of evolution variable in the angular-ordered parton shower; improvements to mass effects and top decays in the dipole shower, improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour reconnection; improvements to strangeness production; as well as a new tune of the hadronisation parameters and support for generic Lorentz structures in BSM models. This article illustrates new features of versions 7.1 and 7.2
Herwig 7.2 release note
A new release of the Monte Carlo event generator Herwig (version 7.2) is now available. This version introduces a number of improvements over the major version 7.0, notably: multi-jet merging with the dipole shower at LO and NLO QCD; spin correlations in both the dipole and angular-ordered parton showers; an improved choice of evolution variable in the angular-ordered parton shower; improvements to mass effects and top decays in the dipole shower, improvements to the simulation of multiple-parton interactions, including diffractive processes; a new model for baryonic colour reconnection; improvements to strangeness production; as well as a new tune of the hadronisation parameters and support for generic Lorentz structures in BSM models. This article illustrates new features of versions 7.1 and 7.2