30 research outputs found
Colour Rearrangement for Dipole Showers
We present an algorithm to rearrange the colour chains of dipole showers in
the shower process according to the colour amplitudes of a simple matrix
element. We implement the procedure in the dipole shower of Herwig and show
comparisons to data.Comment: 4 pages, 6 figures, HERWIG-2018-01, LU-TP-18-01, MCnet-18-0
Higher Order Corrections to Multi Jet Final States at Colliders
The corrections to parton shower approximations with multiple leading order matrix elements and the inclusion of single next-to-leading order (NLO) corrections were investigated in the past. Here an algorithm was developed to merge multiple NLO corrections, without reducing the accuracy of the shower approximation or the NLO calculation. The effects of the NLO corrections are studied and direct comparisons to data are discussed. Improvements above and below the merging scale are observed
Improving the description of multiple interactions in Herwig
The modeling of multiple parton interactions in Monte Carlo event generators is a crucial part not only for the dressing of signal processes but also to describe data with a minimum bias on the event selection. Much work has and will be put into the theoretical framework and the numerical implementation of these models. In this contribution, we document various improvements of the multiple parton interaction model of Herwig 7 (Bellm et al. in Eur Phys J C76(4):196, 2016), that lead to an improved description of minimum bias and underlying event data
Improving the description of multiple interactions in Herwig
The modelling of multiple parton interactions in Monte Carlo event generators
is a crucial part not only for the dressing of signal processes but also to
describe data with a minimum bias on the event selection. Much work has and
will be put into the theoretical framework and the numerical implementation of
these models. In this contribution, we summarize various changes to the
machinery of multiparton interactions and related physics in the Monte Carlo
event generator Herwig 7.Comment: 9 pages, 7 figure
Parton color reconnection in Herwig 7 using a spacetime event topology
Herwig 7 is a general-purpose Monte Carlo generator of particle collisions
comprising both hard perturbative as well as soft phenomenological physics.
Herwig is therefore capable to describe the entire final state of hadronized
particles in a collision event. A spacetime topology of a parton system
entering hadronization is fully described and tested for the first time. A
combination of information from particles momenta and spacetime positions is
utilized to minimize a boost-invariant distance measure of the parton system.
We present a reasonable agreement of the model with a selection of experimental
data and conclude that spacetime event topology can be meaningfully used in the
further development.Comment: Contribution to: ICHEP 202
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
Jet cross sections at the LHC and the quest for higher precision
We perform a phenomenological study of plus jet, Higgs plus jet and
di-jet production at the Large Hadron Collider. We investigate in particular
the dependence of the leading jet cross section on the jet radius as a function
of the jet transverse momentum. Theoretical predictions are obtained using
perturbative QCD calculations at the next-to and next-to-next-to-leading order,
using a range of renormalization and factorization scales. The fixed order
predictions are compared to results obtained from matching next-to-leading
order calculations to parton showers. A study of the scale dependence as a
function of the jet radius is used to provide a better estimate of the scale
uncertainty for small jet sizes. The non-perturbative corrections as a function
of jet radius are estimated from different generators.Comment: 23 pages, 19 figure
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
Six Outbursts of Comet 46P/Wirtanen
Cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. However, cometary outbursts may arise from other processes that are not necessarily driven by volatiles. In order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. In that context, we present a study of mini-outbursts of comet 46P/Wirtanen. Six events are found in our long-term lightcurve of the comet around its perihelion passage in 2018. The apparent strengths range from −0.2 to −1.6 mag in a 5″ radius aperture and correspond to dust masses between ∼104 and 106 kg, but with large uncertainties due to the unknown grain size distributions. However, the nominal mass estimates are on the same order of magnitude as the mini-outbursts at comet 9P/Tempel 1 and 67P/Churyumov-Gerasimenko, events that were notably lacking at comet 103P/Hartley 2. We compare the frequency of outbursts at the four comets, and suggest that the surface of 46P has large-scale (∼10–100 m) roughness that is intermediate to that of 67P and 103P, if not similar to the latter. The strength of the outbursts appear to be correlated with time since the last event, but a physical interpretation with respect to solar insolation is lacking. We also examine Hubble Space Telescope images taken about two days following a near-perihelion outburst. No evidence for macroscopic ejecta was found in the image, with a limiting radius of about 2 m