554 research outputs found
A Comparison of Predictions for SM Higgs Boson Production at the LHC
This paper describes a comparison of most of the available predictions for
the cross section and transverse momentum distribution for a 125 GeV mass Higgs
at the LHC, including those from the PYTHIA and HERWIG parton shower Monte
Carlos and from four resummation calculations.Comment: 7 pages, submitted to proceedings of the Workshop on Physics at TeV
Colliders, Les Houches 200
NNLO QCD + NLO EW with Matrix+OpenLoops: precise predictions for vector-boson pair production
We present the first combination of NNLO QCD and NLO EW corrections for vector-boson pair production at the LHC. We consider all final states with two, three and four charged leptons, including resonant and non-resonant diagrams, spin correlations and off-shell effects. Detailed predictions are discussed for three representative channels corresponding to W+W−, W±Z and Z Z production. Both QCD and EW corrections are very significant, and the details of their combination can play a crucial role to achieve the level of precision demanded by experimental analyses. In this context we point out nontrivial issues that arise at large transverse momenta, where the EW corrections are strongly enhanced by Sudakov logarithms and the QCD corrections can feature so-called giant K -factors. Our calculations have been carried out in the Matrix+OpenLoops framework and can be extended to the production of an arbitrary colour singlet in hadronic collisions, provided that the required two-loop QCD amplitudes are available. Combined NNLO QCD and NLO EW predictions for the full set of massive diboson processes will be made publicly available in the next release of Matrix and will be instrumental in advancing precision diboson studies and new-physics searches at the LHC and future hadron colliders
BSM W W production with a jet veto
We consider the impact on W W production of the unique dimension-six operator coupling gluons to the Higgs field. In order to study this process, we have to appropriately model the effect of a veto on additional jets. This requires the resummation of large logarithms of the ratio of the maximum jet transverse momentum and the invariant mass of the W boson pair. We have performed such resummation at the appropriate accuracy for the Standard Model (SM) background and for a signal beyond the SM (BSM), and devised a simple method to interface jet-veto resummations with fixed-order event generators. This resulted in the fast numerical code MCFM-RE, the Resummation Edition of the fixed-order code MCFM. We compared our resummed predictions with parton-shower event generators and assessed the size of effects, such as limited detector acceptances, hadronisation and the underlying event, that were not included in our resummation. We have then used the code to compare the sensitivity of W W and Z Z production at the HL-LHC to the considered higher-dimension operator. We have found that W W can provide complementary sensitivity with respect to Z Z, provided one is able to control theory uncertainties at the percent-level. Our method is general and can be applied to the production of any colour singlet, both within and beyond the SM
Diffractive Photoproduction in the Framework of Fracture Functions
Recent data on diffractive photoproduction of dijets are analyzed within the
framework of fracture functions and paying special attention to the
consequences of the use of different rapidity gap definitions in order to
identify diffractive events. Although these effects are found to be
significant, it is shown that once they are properly taken into account, a very
precise agreement between diffractive DIS and diffractive dijet photoproduction
emerges without any significant hint of hard factorization breaking.Comment: 13 pages, 4 figures. To appear in Phys.Rev.
Multiscale Techniques for the Detection of Precipitation Using Thermal IR Satellite Images
Cut Vertices and Semi-Inclusive Deep Inelastic Processes
Cut vertices, a generalization of matrix elements of local operators, are
revisited, and an expansion in terms of minimally subtracted cut vertices is
formulated. An extension of the formalism to deal with semi-inclusive deep
inelastic processes in the target fragmentation region is explicitly
constructed. The problem of factorization is discussed in detail.Comment: LaTex2e, 24 pages including 17 postscript figure
Event Generators for High-Energy Physics Experiments
We provide an overview of the status of Monte-Carlo event generators for high-energy particle physics. Guided by the experimental needs and requirements, we highlight areas of active development, and opportunities for future improvements. Particular emphasis is given to physics models and algorithms that are employed across a variety of experiments. These common themes in event generator development lead to a more comprehensive understanding of physics at the highest energies and intensities, and allow models to be tested against a wealth of data that have been accumulated over the past decades. A cohesive approach to event generator development will allow these models to be further improved and systematic uncertainties to be reduced, directly contributing to future experimental success. Event generators are part of a much larger ecosystem of computational tools. They typically involve a number of unknown model parameters that must be tuned to experimental data, while maintaining the integrity of the underlying physics models. Making both these data, and the analyses with which they have been obtained accessible to future users is an essential aspect of open science and data preservation. It ensures the consistency of physics models across a variety of experiments
Soft-gluon effects in WW production at hadron colliders
We consider QCD radiative corrections to WW pair production in hadron
collisions. We perform a calculation that consistently combines next-to-leading
order predictions with soft-gluon resummation valid at small transverse momenta
ptWW of the WW pair. We present results for the ptWW distribution at the LHC up
to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect
of resummation on the charged-lepton distributions. Soft-gluon effects are
typically mild, but they can be strongly enhanced when hard cuts are applied.
The relevant distributions are generally well described by the MC@NLO event
generator.Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW
transverse-mass distribution. Results unchange
New vector bosons in the electroweak sector: a renormalizable model with decoupling
A linear realization of a model of dynamical electroweak symmetry breaking
describing additional heavy vector bosons is proposed. The model is a SU(2)_L x
U(1) x SU(2)_L' x SU(2)_R' gauge theory, breaking at some high scale u to
SU(2)_weak x U(1)_Y and breaking again in the standard way at the electroweak
scale v to U(1)_(em). The model is renormalizable and reproduces the Standard
Model in the limit u\to infinity. This decoupling property is shown to hold
also at the level of radiative corrections by computing, in particular, the
epsilon parameters.Comment: 39 pages, 16 Figures, Late
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