1,372 research outputs found
Resummation of transverse energy in vector boson and Higgs boson production at hadron colliders
We compute the resummed hadronic transverse energy (E_T) distribution due to
initial-state QCD radiation in vector boson and Higgs boson production at
hadron colliders. The resummed exponent, parton distributions and coefficient
functions are treated consistently to next-to-leading order. The results are
matched to fixed-order calculations at large E_T and compared with
parton-shower Monte Carlo predictions at Tevatron and LHC energies.Comment: 24 pages, 15 figure
Higgs Physics: Theory
I review the theoretical aspects of the physics of Higgs bosons, focusing on
the elements that are relevant for the production and detection at present
hadron colliders. After briefly summarizing the basics of electroweak symmetry
breaking in the Standard Model, I discuss Higgs production at the LHC and at
the Tevatron, with some focus on the main production mechanism, the gluon-gluon
fusion process, and summarize the main Higgs decay modes and the experimental
detection channels. I then briefly survey the case of the minimal
supersymmetric extension of the Standard Model. In a last section, I review the
prospects for determining the fundamental properties of the Higgs particles
once they have been experimentally observed.Comment: 21 pages, 15 figures. Talk given at the XXV International Symposium
on Lepton Photon Interactions at High Energies (Lepton Photon 11), 22-27
August 2011, Mumbai, Indi
New Physics Signals in Longitudinal Gauge Boson Scattering at the LHC
We introduce a novel technique designed to look for signatures of new physics
in vector boson fusion processes at the TeV scale. This functions by measuring
the polarization of the vector bosons to determine the relative longitudinal to
transverse production. In studying this ratio we can directly probe the high
energy E^2-growth of longitudinal vector boson scattering amplitudes
characteristic of models with non-Standard Model (SM) interactions. We will
focus on studying models parameterized by an effective Lagrangian that include
a light Higgs with non-SM couplings arising from TeV scale new physics
associated with the electroweak symmetry breaking, although our technique can
be used in more general scenarios. We will show that this technique is stable
against the large uncertainties that can result from variations in the
factorization scale, improving upon previous studies that measure cross section
alone
Next-to-leading order QCD corrections to Higgs boson production in association with a photon via weak-boson fusion at the LHC
Higgs boson production in association with a hard central photon and two
forward tagging jets is expected to provide valuable information on Higgs boson
couplings in a range where it is difficult to disentangle weak-boson fusion
processes from large QCD backgrounds. We present next-to-leading order QCD
corrections to Higgs production in association with a photon via weak-boson
fusion at a hadron collider in the form of a flexible parton-level Monte Carlo
program. The QCD corrections to integrated cross sections are found to be small
for experimentally relevant selection cuts, while the shape of kinematic
distributions can be distorted by up to 20% in some regions of phase space.
Residual scale uncertainties at next-to-leading order are at the few-percent
level.Comment: 17 pages, 7 figures, 1 tabl
Vector boson pair production at the LHC
We present phenomenological results for vector boson pair production at the
LHC, obtained using the parton-level next-to-leading order program MCFM. We
include the implementation of a new process in the code, pp -> \gamma\gamma,
and important updates to existing processes. We incorporate fragmentation
contributions in order to allow for the experimental isolation of photons in
\gamma\gamma, W\gamma, and Z\gamma production and also account for gluon-gluon
initial state contributions for all relevant processes. We present results for
a variety of phenomenological scenarios, at the current operating energy of
\sqrt{s} = 7 TeV and for the ultimate machine goal, \sqrt{s} = 14 TeV. We
investigate the impact of our predictions on several important distributions
that enter into searches for new physics at the LHC.Comment: 35 pages, 14 figure
Multiple Parton Interactions in Z+jets production at the LHC. A comparison of factorized and non--factorized double parton distribution functions
We examine the contribution of Multiple Parton Interactions to Z+n-jets
production at the LHC, n=2,3,4, where the Z boson is assumed to decay
leptonically. We compare the results obtained with the correlated GS09 double
parton distribution function with those obtained with two instances of fully
factorized single parton distribution functions: MSTW2008LO and CTEQ6LO. It
appears quite feasible to measure the MPI contribution to Z+2/3/4 jets already
in the first phase of the LHC with a total luminosity of one inverse femtobarn
at 7 TeV. If as expected the trigger threshold for single photons is around 80
GeV, Z+2-jets production may well turn out to be more easily observable than
the gamma+3-jets channel. The MPI cross section is dominated by relatively soft
events with two jets balancing in transverse momentum.Comment: 15 pages, 3 plot
Composite Octet Searches with Jet Substructure
Many new physics models with strongly interacting sectors predict a mass
hierarchy between the lightest vector meson and the lightest pseudoscalar
mesons. We examine the power of jet substructure tools to extend the 7 TeV LHC
sensitivity to these new states for the case of QCD octet mesons, considering
both two gluon and two b-jet decay modes for the pseudoscalar mesons. We
develop both a simple dijet search using only the jet mass and a more
sophisticated jet substructure analysis, both of which can discover the
composite octets in a dijet-like signature. The reach depends on the mass
hierarchy between the vector and pseudoscalar mesons. We find that for the
pseudoscalar-to-vector meson mass ratio below approximately 0.2 the simple jet
mass analysis provides the best discovery limit; for a ratio between 0.2 and
the QCD-like value of 0.3, the sophisticated jet substructure analysis has the
best discovery potential; for a ratio above approximately 0.3, the standard
four-jet analysis is more suitable.Comment: 21 pages, 8 figure
The Spin Structure of the Nucleon
We present an overview of recent experimental and theoretical advances in our
understanding of the spin structure of protons and neutrons.Comment: 84 pages, 29 figure
The dependence of dijet production on photon virtuality in ep collisions at HERA
The dependence of dijet production on the virtuality of the exchanged photon,
Q^2, has been studied by measuring dijet cross sections in the range 0 < Q^2 <
2000 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of
38.6 pb^-1.
Dijet cross sections were measured for jets with transverse energy E_T^jet >
7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame
in the range -3 < eta^jet <0. The variable xg^obs, a measure of the photon
momentum entering the hard process, was used to enhance the sensitivity of the
measurement to the photon structure. The Q^2 dependence of the ratio of low- to
high-xg^obs events was measured.
Next-to-leading-order QCD predictions were found to generally underestimate
the low-xg^obs contribution relative to that at high xg^obs. Monte Carlo models
based on leading-logarithmic parton-showers, using a partonic structure for the
photon which falls smoothly with increasing Q^2, provide a qualitative
description of the data.Comment: 35 pages, 6 eps figures, submitted to Eur.Phys.J.
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