arXiv subjects
Publications and source records attributed to P. M. Zerwas.
We present the distributions for gluon radiation off stop-antistop particles produced in $e^+e^-$ annihilation: $e^+e^- \to \tilde t \bar{\tilde t} g$. For high energies the splitting functions of the fragmentation processes $\tilde t \to \tilde t g$ and $g \to \tilde t \bar{\tilde t}$ are derived; they are universal and apply also to high-energy stop particles produced at hadron colliders.
We have determined the QCD corrections to the production of squark-antisquark pairs in $p\bar p$ collisions at the Tevatron. If the next-to-leading order corrections are taken into account, the renormalization/factorization scale dependence of the theoretical prediction for the cross section is reduced considerably. The higher order corrections increase the production cross section at the Tevatron by about a factor two if we compare the next-to-leading order prediction at a scale near the squark mass with the lowest order prediction for which, in the experimental analyses, the scale was identified with the invariant energy of the parton subprocess. This results in a rise of the experimental lower bound on the squark mass from the Tevatron by about $20$ GeV.
The measurement of the forward-backward asymmetries of heavy quarks provides one of the most precise determinations of $\sin^2θ_W$ in $Z$ decays. We discuss in detail the one--loop QCD radiative corrections to these asymmetries. Results are given for single heavy--quark jet asymmetries and asymmetries of the thrust axis, as well as for heavy--quark two--jet final states.}
Inelastic photoproduction of $J/ψ$ particles at high energies is one of the processes to determine the gluon distribution in the nucleon. We have calculated the QCD radiative corrections to the color-singlet model of this reaction. They are large at moderate photon energies, but decrease with increasing energies. The cross section and the $J/ψ$ energy spectrum are compared with the available fixed-target photoproduction data and predictions are given for the HERA energy range.
Leptons, quarks and gauge bosons are assumed to be pointlike particles in the Standard Model. Stringent bounds on the radii of quarks and leptons and their weak anomalous magnetic moments can be derived from the high-precision measurements at LEP and SLC. We find a model-independent bound of $R\lsim 10^{-17}cm$ for quark and lepton radii. HERA will provide complementary information on the electromagnetic static properties of the quarks and the parameters of the charged quark currents.
Leptoquarks can be produced in pairs by gluon--gluon fusion and quark--antiquark annihilation at hadron colliders. While HERA is the proper machine for single production of $(eu)$ and $(ed)$ type leptoquarks, the flavor species of ($μu$), ($μd$) and ($τu$), ($τd$) type leptoquarks can be produced at hadron colliders very efficiently. Besides exploiting gluon-quark collisions, leptoquarks can also be produced singly by colliding the quarks in one proton beam with leptons $e,μ,τ$ generated by splitting photons which are radiated off the quarks in the other proton beam. For Yukawa couplings of the size $α$ leptoquark masses up to about 300~GeV can be generated at the Tevatron while the LHC can produce leptoquarks with masses up to about 3~TeV. [Leptoquarks involving heavy quarks can be produced singly at a lower rate, determined by the heavy flavor flux in the proton beam.]
We analyze the prospects of measuring the parity of Higgs particles in the Standard Model and its supersymmetric extensions. Higgs decays are discussed in this context as well as production processes including, in particular, the fusion of Higgs particles in linearly polarized photon--photon collisions.
Non--strongly interacting supersymmetric particles -- sleptons, charginos, neutral\-inos, and charged Higgs bosons -- are difficult to detect at the Large Hadron Collider. We therefore examine the possibility of producing particles of this type in virtual $γγ$ collisions at the LHC. Since photons can be emitted from protons which do not break up in the radiation process, very clean events can be generated, compensating to some extent for the small event numbers. Higher rates are expected, at the expense of stray hadrons, for events in which one or two protons break up.
We report on calculations of the hadronic coupling constants $g_{ρππ}$ and $g_{nnπ}$ based on lattice QCD with four flavors of dynamical staggered fermions. By computing 2--point and 3--point Green's functions we have been able to determine these coupling constants ab initio from QCD; the results are compatible with the experimental values.
We elaborate on the production of the Standard Model Higgs particle at high-energy $e^+e^-$ colliders through the reaction $e^+e^- \rightarrow ZH$. Particular emphasis is put on the intermediate mass range. In addition to the signal we discuss in detail the background processes. Angular distributions which are sensitive to the spin and parity of the Higgs particle are analyzed.
Two--photon decays of Higgs bosons are important channels for the search of these particles in the intermediate mass range at the $pp$ colliders LHC and SSC. Dynamical aspects of the Higgs coupling to two photons can also be studied by means of the $γγ$ fusion of Higgs particles at high--energy e$^+$e$^-$ linear colliders. Extending earlier analyses which had been restricted to the Standard Model, we present in this note the QCD radiative corrections to the $γγ$ decay widths of scalar and pseudoscalar Higgs particles in multi--doublet extensions of the Higgs sector, as realized for instance in supersymmetric theories.