290 research outputs found
QCD Jets and Parton Showers
I discuss the calculation of QCD jet rates in e+e- annihilation as a testing
ground for parton shower simulations and jet finding algorithms.Comment: 13 pages, 5 figures, contribution to Proceedings of Gribov-80
Memorial Workshop on Quantum Chromodynamic and Beyond, ICTP, Trieste, Italy,
26-28 May, 201
Two-loop enhancement factor for 1/Q corrections to event shapes in deep inelastic scattering
We compute the two-loop enhancement factors for our earlier one-loop
calculations of leading (1/Q) power corrections to the mean values of some
event shape variables in deep inelastic lepton scattering. The enhancement is
found to be equal to the universal ``Milan factor'' for those shape variables
considered, provided the one-loop calculation is performed in a particular way.
As a result, the phenomenology of power corrections to DIS event shapes remains
largely unaffected.Comment: 15 pages, 1 figure, uses JHEP.cls. This revised version corrects an
error in the calculation of the enhancement factor. The main conclusions
remain unchange
The MC@NLO 2.2 Event Generator
This is the user's manual of MC@NLO 2.2. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of Higgs bosons, single vector bosons, vector boson pairs, and
heavy quark-antiquark pairs. This document is self-contained, but we emphasise
the main differences with respect to previous versions.Comment: 17 pages, no figures. Version 2 has more details on some features.
Program available at http://www.hep.phy.cam.ac.uk/theory/webber/MCatNLO
Jet Rates at Small x to Single-Logarithmic Accuracy
We present predictions of jet rates in deep inelastic scattering at small x
to leading-logarithmic order in x, including all sub-leading logarithms of
Q^2/m_R^2 where m_R is the transverse momentum scale at which jets are
resolved. We give explicit results for up to three jets, and a perturbative
expansion for multi-jet rates and jet multiplicities.Comment: 16 pages, 4 figure
The MC@NLO 3.4 Event Generator
This is the user's manual of MC@NLO 3.4. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy
quark pairs, single top, single top in association with a W, lepton pairs, and
Higgs bosons in association with a W or Z. Spin correlations are included for
all processes except ZZ and WZ production. This document is self-contained, but
we emphasise the main differences with respect to previous versions.Comment: 30 page
Multiplicity of (Mini-)Jets at Small x
We derive closed expressions for the mean and variance of the (mini-)jet
multiplicity distribution in hard scattering processes at low x. Here
(mini-)jets are defined as those due to initial-state radiation of gluons with
transverse momenta greater than some resolution scale m_R, where Lambda^2 <<
m_R^2 << Q^2, Lambda being the intrinsic QCD scale and Q the momentum transfer
scale of the hard scattering. Our results are valid to leading order in
log(1/x) but include all sub-leading logarithms of Q^2/m_R^2. As an
illustration, we predict the mini-jet multiplicity in Higgs boson production at
the Large Hadron Collider.Comment: 14 pages, 5 figure
Polarization Effects in Standard Model Parton Distributions at Very High Energies
We update the earlier work of Refs. arXiv:1703.08562 and arXiv:1712.07147 on
parton distribution functions in the full Standard Model to include gauge boson
polarization, non-zero input electroweak boson PDFs and next-to-leading-order
resummation of large logarithms.Comment: 24 pages, 7 Figures. arXiv admin note: text overlap with
arXiv:1703.08562, arXiv:1806.1015
Limits on Electroweak Instanton-Induced Processes with Multiple Boson Production
Recently, the CMS collaboration has reported their search for electroweak
instanton-like processes with anomalous violation assuming multi-fermion
but zero-boson final states. On the other hand, many theoretical studies
suggest that anomalous processes may have an observably large production
rate only if their final state contains a large number of electroweak gauge
bosons. In this paper, we compare collider signatures of zero- and multi-boson
events of anomalous violation at the LHC and derive an upper limit on the
cross-section for the multi-boson process by recasting the CMS analysis.Comment: 14 pages, 6 figures; JHEP version with typographic errors fixe
Standard Model Parton Distributions at Very High Energies
We compute the leading-order evolution of parton distribution functions for
all the Standard Model fermions and bosons up to energy scales far above the
electroweak scale, where electroweak symmetry is restored. Our results include
the 52 PDFs of the unpolarized proton, evolving according to the SU(3), SU(2),
U(1), mixed SU(2) x U(1) and Yukawa interactions. We illustrate the numerical
effects on parton distributions at large energies, and show that this can lead
to important corrections to parton luminosities at a future 100 TeV collider.Comment: 30 pages, 7 figures. Improved treatment of input PDFs at 100 GeV.
Adjusted plotting style to show features more clearly. Main results and
conclusions unchange
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