Search

We study the production of the Higgs boson in association with a single top quark at hadron colliders. The cross sections for the three production processes (t-channel, s-channel, and W-associated) at both the Tevatron and the LHC are presented. We investigate the possibility of detecting a signal for the largest of these processes, the t-channel process at the LHC, via the Higgs decay into b b-bar. The QCD backgrounds are large and difficult to curb, hindering the extraction of the signal. Extensions of our analysis to the production of supersymmetric Higgs bosons are also addressed. The cross section is enhanced for large values of tangent beta, increasing the prospects for extracting a signal., Comment: 22 pages, 13 figures

We present a calculation of two photon radiation in W and Z boson production in hadronic collisions, based on the complete matrix elements for the processes q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma, including finite charged lepton masses. In order to achieve stable numerical results over the full phase space, multiconfiguration Monte Carlo techniques are used to map the peaks in the differential cross section. Numerical results are presented for the Fermilab Tevatron., Comment: Revtex, 28 pages, 3 figures

Top quark events in hadron collisions often contain additional hadronic jets from gluon bremsstrahlung off the quarks and gluons in the hard subprocesses. Such extra jets must be taken into account in attempts to reconstruct the momentum of the top quark from those of its decay products. We have performed a complete calculation of gluon radiation in top production and decay at the Fermilab Tevatron including hadronically decaying W bosons. In this talk we discuss the effect of gluon radiation on the reconstructed mass of the top quark, using various top mass reconstruction scenarios. Implications for the LHC are briefly discussed., Comment: 5 pages including 4 figures, LaTeX, uses ltwol.sty, talk given by LHO at ICHEP98, Vancouver, B.C., July 23-29, 1998

Radiation of gluons gives rise to extra jets in top quark events that can lead to complications in event reconstruction and mass measurement. I review recent results for gluon radiation in top quark production and decay, and discuss their implications for top quark physics., 3 pages latex including 2 figs; usues sprocl.sty (included) Talk presented by L. Orr at DPF96, Minneapolis, MN, Aug. 1996

Understanding the pattern of gluon radiation in $t \bar t$ production and decay processes is important for making an accurate determination of the top mass from the momenta of its decay products. The larger energy of the LHC $pp$ collider boosts the top cross section by a factor of 100 compared to that at the Tevatron, but it also increases the amount of additional gluon radiation. We calculate the cross section for gluon radiation in top production and decay at the LHC. The distributions of this radiation are presented and the exact matrix-element results are compared with results from the HERWIG parton-shower Monte Carlo., 16 pages including 7 figures, plain LaTeX; minor corrections to text; results unchanged

We consider single-top-quark production via the weak process $q\bar q to t\bar b$ at hadron colliders. This process may provide the best measurement of the magnitude of the Cabbibo-Kobayashi-Maskawa matrix element $V_{tb}$. We show that a signal can potentially be observed at the Fermilab Tevatron with 3 $fb^{-1}$ of integrated luminosity. In contrast, the signal is masked at the CERN Large Hadron Collider by top-quark pair production and single-top-quark production via $W$-gluon fusion., Comment: 12 pages latex + 5 uuencoded figures

Understanding the pattern of gluon radiation in $t \bar t$ production processes is important for making an accurate determination of the top mass from the measurement of its decay products. In a recent paper we showed that the exact matrix element and parton shower (HERWIG) calculations gave very different results for the distribution of gluon jets in $t \bar t$ production at the Tevatron $p \bar p$ collider. By repeating the calculation for the simpler $e^+e^- \to b \bar b W^+W^-g$ process, we reveal even more dramatic differences between the two approaches. We conclude that there are significant differences in gluon radiation between HERWIG and the matrix element calculation in regions of phase space where one would expect agreement., Comment: 5 pages + 4 uunecoded postscript figures

We consider single-top-quark production via the weak process $q\bar q to t\bar b$ at hadron colliders. This process may provide the best measurement of the magnitude of the Cabbibo-Kobayashi-Maskawa matrix element $V_{tb}$. We show that a signal can potentially be observed at the Fermilab Tevatron with 3 $fb^{-1}$ of integrated luminosity. In contrast, the signal is masked at the CERN Large Hadron Collider by top-quark pair production and single-top-quark production via $W$-gluon fusion., 12 pages latex + 5 uuencoded figures

We present a complete calculation of the matrix elements for the processes $q \bar q, gg \to b W^+ \bar b W^- g$ and $qg \to b W^+ \bar b W^- q$ which are relevant for the study of events with an additional jet in $t \bar t$ production at the Tevatron $p \bar p $ collider. Our calculation includes (i) the contributions from gluons emitted during the top production and decay stages and the interference between these, and (ii) the complete set of Feynman diagrams corresponding to both resonant and non-resonant top production. We study the distribution in phase space of the additional parton jet and make comparisons with previous studies based on the soft-gluon approximation and with results from parton-shower Monte Carlo simulations. The implications for top mass measurements are briefly discussed., Comment: 12 pages, latex, 9 uuencoded postscript figures

We examine the structure of the underlying event in neutral Higgs production at the Superconducting-Supercollider (SSC). Gaps, regions of rapidity containing no soft particle production, can provide a clean signature for $W$ boson fusion to the heavy Higgs. We first examine the physical basis of gap production and estimate the survival probability of gaps in the minijet model. Then, using PYTHIA, and HERWIG we compare gap events to $W$ pair production from top decay and $q\bar{q}$ fusion. We find that, if experimental problems can be overcome, gaps should provide a small, but clean, signal for heavy Higgs production at the SSC., 24 Latex pages 5 postscript figures available upon request MAD/PH/76 BA-93-31

We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5_aMC@NLO, capable of handling all these computations -- parton-level fixed order, shower-matched, merged -- in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV $e^+e^-$ collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way., 158 pages, 27 figures; a few references have been added