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J. M. Butterworth

Publications and source records attributed to J. M. Butterworth.

54 records · Page 3Linked to original sources
arXiv2004

QCD uncertainties at the LHC and the implications of HERA

Strong interaction physics will be ubiquitous at the Large Hadron Collider since the colliding beams consist of confined quarks and gluons. Although the main purpose of the LHC is to study the mechanism of electroweak symmetry breaking and to search for physics beyond the Standard Model, to maximise the precision and sensitivity of such anaylses it is necessary to understand in detail various perturbative, semi-perturbative and non-perturbative QCD effects. Many of these effects have been extensively studied at HERA and will be studied further at HERA II. We discuss the impact of the knowledge thus gained on physics at the LHC.

hep-ph↗
arXiv2002

JetWeb: A WWW Interface and Database for Monte Carlo Tuning and Validation

A World Wide Web interface to a Monte Carlo validation and tuning facility is described. The aim of the package is to allow rapid and reproducible comparisons to be made between detailed measurements at high-energy physics colliders and general physics simulation packages. The package includes a relational database, a Java servlet query and display facility, and clean interfaces to simulation packages and their parameters.

hep-ph↗
arXiv2002

KtJet: A C++ implementation of the Kt clustering algorithm

A C++ implementation of the Kt jet algorithm for high energy particle collisions is presented. The time performance of this implementation is comparable to the widely used Fortran implementation. Identical algorithmic functionality is provided, with a clean and intuitive user interface and additional recombination schemes. A short description of the algorithm and examples of its use are given.

hep-ph↗
arXiv2002

Snowmass 2001: Jet Energy Flow Project

Conventional cone jet algorithms arose from heuristic considerations of LO hard scattering coupled to independent showering. These algorithms implicitly assume that the final states of individual events can be mapped onto a unique set of jets that are in turn associated with a unique set of underlying hard scattering partons. Thus each final state hadron is assigned to a unique underlying parton. The Jet Energy Flow (JEF) analysis described here does not make such assumptions. The final states of individual events are instead described in terms of flow distributions of hadronic energy. Quantities of physical interest are constructed from the energy flow distribution summed over all events. The resulting analysis is less sensitive to higher order perturbative corrections and the impact of showering and hadronization than the standard cone algorithms.

hep-ph↗
arXiv2002

WW scattering at the LHC

A detailed study is presented of elastic WW scattering in the scenario that there are no new particles discovered prior to the commissioning of the LHC. We work within the framework of the electroweak chiral lagrangian and two different unitarisation protocols are investigated. Signals and backgrounds are simulated to the final-state-particle level. A new technique for identifying the hadronically decaying W is developed, which is more generally applicable to massive particles which decay to jets where the separation of the jets is small. The effect of different assumptions about the underlying event is also studied. We conclude that the channel WW -> jj+l+nu may contain scalar and/or vector resonances which could be measurable after 100 fb^(-1) of LHC data.

hep-ph↗
arXiv1999

Structure of the Photon

An overview of the current data and phenomenology on the structure of the photon and an outline of some opportunities available in the medium term future.

hep-ex↗
arXiv1999

A Global Study of Photon-Induced Jet Production

We present results of a global tuning of general purpose Monte Carlo models to published measurements of photon-proton -> jets at HERA and photon-photon -> jets at LEP and TRISTAN. The principle free parameters in the tuning are the simulation of the underlying event and the choice of photon structure. Several combinations of models are ruled out by the data. Some consequences of the tuned models at a future linear collider are discussed.

hep-ph↗
arXiv1998

Charm `in' the Photon

Some recent ZEUS results on the photoproduction of open charm and possible implications for photon structure are discussed.

hep-ex↗
arXiv1997

Photoproduction Processes in Polarized ep - Collisions at HERA

We study various conceivable photoproduction reactions in a polarized ep collider mode of HERA with respect to their sensitivity to the proton's polarized gluon distribution. A special emphasis is put on the `resolved' part of the cross sections which in principle opens the possibility to determine for the first time also the completely unknown parton content of longitudinally polarized photons. In the very promising case of dijet production we also investigate the impact of parton showering, hadronization and jet finding on the parton level results.

hep-ph↗
arXiv1997

Jet Photoproduction

The status of HERA data on jet photoproduction is reviewed, and some suggestions and prospects for further work are given.

hep-ex↗
arXiv1996

High p_T Charm Photoproduction

The expected rates for charm-tagged jet photoproduction are evaluated for a number of tagging procedures, and some of the physics potential is discussed. Charm in jets is tagged using $D^*$'s, $μ$'s, or tracks from secondary vertices which might be identified in a microvertex detector. We find high expected event rates, leading to the possibility of placing strong constraints on the kinematics of charm production and on the gluon content of the proton and the charm content of the photon.

hep-ph↗
arXiv1996

Rapidity Gaps Between Jets

An excess of events with a rapidity gap between jets, over what would be expected from non-diffractive processes, has been observed at HERA. A process based on a perturbative QCD calculation of colour singlet exchange has been added to HERWIG. With this addition, HERWIG is able to describe the number of events with a gap between jets over the number without a gap. This gap fraction is predicted to rise at large rapidity intervals between jets which would only be visible if the detector coverage were increased.

hep-ph↗
arXiv1996

Matching Experimental and Theoretical Jet Definitions for Photoproduction at HERA

Predictions from a new next-to-leading order (NLO) calculation for direct and resolved photoproduction of one and two jets are compared to simulated HERA data. We propose a method to match experimental and theoretical jet definitions and observe a reduced dependence on jet definitions and hadronization corrections at larger transverse energies. From the irreducible uncertainty, we estimate the maximum benefit that can be obtained from increased luminosity to constrain the structure of the photon and the proton.

hep-ph↗
arXiv1996

Multiparton Interactions in Photoproduction at HERA

The high energy photoproduction of jets is being observed at the ep collider, HERA. It may be that the HERA centre-of-mass energy is sufficiently large that the production of more than one pair of jets per ep collision becomes possible, owing to the large number density of the probed gluons. We construct a Monte Carlo model of such multiparton interactions and study their effects on a wide range of physical observables. The conclusion is that multiple interactions could have very significant effects upon the photoproduction final state and that this would for example make extractions of the gluon density in the photon rather difficult. Total rates for the production of many (i.e. > 2) jets could provide direct evidence for the presence of multiple interactions, although parton showering and hadronization significantly affect low transverse energy jets.

hep-ph↗
arXiv1996

Multiple Hard Parton Interactions at HERA

At HERA, the large flux of almost real photons accompanying the electron beam leads to the copious photoproduction of jets. Regions of small momentum fractions $x$ of the incoming particles are explored, where the density of partons is high. As a result, the probability for more than one hard partonic scattering occurring in a single $γp$ collision could become significant. It is well known that this effect modifies the contribution of jets (minijets) to the total cross section. We discuss the latest HERA data on the total $γp$ cross section in this context. The possible effects of multiple hard interactions on event shapes and jet cross sections at HERA have been studied using Monte Carlo programs. We review some of the available results, which in general indicate that the effects of multiple interactions should be significant and may already be manifest in the existing HERA data.

hep-ph↗
arXiv1995

Multiple Hard Interactions in Gamma-Gamma and Gamma-P Physics at LEP and HERA

At $e^+e^-$ and $ep$ colliders, the large fluxes of almost on-shell photons accompanying the lepton beams lead to the photoproduction of jets. As the centre-of-mass energy is increased, regions of smaller $x$ in the parton densities are explored and these are regions of high parton density. As a result, the probability for more than one hard partonic scattering occurring in a single $γγ$ or $γp$ collision can become significant. This effect has been simulated using an eikonal prescription combined with the HERWIG Monte Carlo program. The possible effects of multiple hard interactions on event shapes and jet cross sections have been studied in this framework at a range of energies relevant to HERA and LEPII. The results indicate that the effects could be significant.

hep-ph↗
arXiv1995

Photon Structure, as seen at HERA

At HERA, the electron-proton collider at DESY, Hamburg, the large flux of almost on-shell photons accompanying the lepton beam is being used to shed new light on the structure of the photon. Recent results are reviewed and discussed, with emphasis on those aspects of the photon's nature which should be understandable using perturbative QCD.

hep-ex↗