arXiv subjects
Publications and source records attributed to M. A. Doncheski.
We study the effects of virtual leptoquark exchange on charged current and neutral current processes at HERA, on di-lepton production at the Tevatron, and on quark pair production at LEP II. We present the areas of parameter space that can be excluded at these colliders by searching for deviations from Standard Model expectations.
We examine the spin-dependence of standard model Higgs boson production at large transverse momentum via the processes $gg \rightarrow gH^0$, $qg \rightarrow qH^0$, and $q\overline{q} \rightarrow gH^0$. The partonic level spin-spin asymmetries ($\hat{a}_{LL}$) for these processes are large at SSC/LHC energies.
We study the effects of virtual leptoquarks on charged current and neutral current processes at the $ep$ collider HERA. We present the areas of parameter space that can be excluded at HERA by searching for deviations from Standard Model expectations. The best results are obtained by examining the ratio of neutral current to charged current cross sections, $R=σ_{NC}/σ_{CC}$, where, with $200\inpb$ of integrated luminosity for unpolarized $e^-$ and $e^+$ beams, HERA can search for leptoquarks with masses up to $\sim 800\gev$, with leptoquark coupling strengths of order $α_{em}$.
We study the prospects of testing the $WWγ$ vertex in $e^- p\toνγX$ and $e^+ p\toνγX$ at HERA and LEP/LHC. Destructive interference effects between the Standard Model and the anomalous contributions to the amplitude severely limit the sensitivity of both processes to non-standard $WWγ$ couplings. Sensitivity limits for the anomalous $WWγ$ couplings $κ$ and $λ$ at HERA and LEP/LHC are derived, taking into account experimental cuts and uncertainties, and the form factor behaviour of nonstandard couplings. These limits are found to be significantly weaker than those which can be expected from other collider processes within the next few years. At HERA, they are comparable to bounds obtained from $S$-matrix unitarity.