arXiv subjects

P. M. Zerwas

Publications and source records attributed to P. M. Zerwas.

At least 91 records · Page 5Linked to original sources

arXiv1997

Pair production of scalar leptoquarks at the Tevatron

We present the cross section for pair production of scalar leptoquarks $LQ$ in $p\bar{p}$ collisions, $p+\bar{p} \to LQ + \bar{LQ} + X$, at the Fermilab Tevatron in next-to-leading order QCD. Including the higher-order corrections stabilizes the theoretical prediction and increases the size of the cross section for renormalization/factorization scales close to the mass of the leptoquarks. This leads to an increase of the lower bound on the mass of scalar leptoquarks by up to 15 GeV with respect to earlier analyses.

hep-ph↗

arXiv1997

Supersymmetry with R-Parity Breaking: Contact Interactions and Resonance Formation in Leptonic Processes at LEP2

In supersymmetric theories with R-parity breaking, trilinear couplings of two leptons to scalar sleptons are possible. In electron-positron collisions such interactions would manifest themselves through contact terms in Bhabha scattering and in annihilation to mu or tau pair Interpreting the high x, high Q2 DIS HERA events as charm squark production with squark masses of order 200 GeV, the formation of tau sneutrinos with a mass in the range close to the LEP2 energy or even in reach, is an exciting speculation which can be investigated in the coming LEP2 runs with energies close to 200 GeV.

hep-ph↗

arXiv1997

Formation and Decay of Scalar Leptoquarks/Squarks in ep collisions

The cross sections for the formation of scalar resonances, leptoquarks or squarks, in electron/positron-proton collisions at HERA are presented including next-to-leading order QCD corrections. Depending mildly on the mass of the resonances, the K-factors increase the production cross sections by up to 30% if the target quarks are valence quarks. The QCD corrections to the partial decay widths of leptoquarks/squarks to leptons and quarks are small. The electron spectrum in the decays is softened nevertheless by perturbative gluon radiation at a level of 3.4 GeV for a leptoquark/squark mass of 200 GeV.

hep-ph↗

arXiv1997

Leptoquark/Squark Interpretation of HERA Events: Virtual Effects in e+e- Annihilation to Hadrons

In reference to the recently observed high Q^2, large x events in deep-inelastic positron-proton scattering at HERA, various leptoquark and supersymmetric scenarios are discussed. We study the impact of virtual leptoquark or R-parity breaking squark exchange as well as generic contact interaction on the production of quark-antiquark pairs in $e^+e^-$ annihilation, in particular at LEP2.

hep-ph↗

arXiv1997

Decays of W Bosons to Charginos and Neutralinos

The region of the supersymmetry parameter space, in which charginos decay predominantly into sneutrinos and leptons: chi+ -> \tildeν + l+, is not excluded experimentally for small mass differences between charginos and sneutrinos. The decay sneutrinos are invisible in R-parity conserving theories since they are either the lightest supersymmetric particles or they decay primarily into the channel: neutrino + lightest neutralino. If the energy of the decay leptons is so small that they escape detection, chargino events e+e- -> chi+chi- in e+e- collisions remain invisible, eroding the excluded chargino mass range at LEP. This region of the supersymmetry parameter space can partly be covered by searching for single W events in e+e- -> W+W-$, with one W boson decaying to leptons or quark jets, but the second W boson decaying to (undetected) charginos and neutralinos.

hep-ph↗

arXiv1996

Squark and Gluino Production at Hadron Colliders

We have determined the theoretical predictions for the cross-sections of squark and gluino production at $\ppb$ and $pp$ colliders (Tevatron and LHC) in next-to-leading order of supersymmetric QCD. By reducing the dependence on the renormalization/factorization scale considerably, the theoretically predicted values for the cross-sections are much more stable if these higher-order corrections are implemented. If squarks and gluinos are discovered, this improved stability translates into a reduced error on the masses, as extracted experimentally from the size of the production cross-sections. The cross-sections increase significantly if the next-to-leading order corrections are included at a renormalization/factorization scale near the average mass of the produced massive particles. This rise results in improved lower bounds on squark and gluino masses. By contrast, the shape of the transverse-momentum and rapidity distributions remains nearly unchanged when the next-to-leading order corrections are included.

hep-ph↗

arXiv1996

Stop decays in SUSY-QCD

The partial widths are determined for stop decays to top quarks and gluinos, and gluino decays to stop particles and top quarks (depending on the masses of the particles involved). The widths are calculated including one-loop SUSY-QCD corrections. The radiative corrections for these strong-interaction decays are compared with the SUSY-QCD corrections for electroweak stop decays to quarks and neutralinos/charginos and top-quark decays to stops and neutralinos.

hep-ph↗

arXiv1996

Heavy SUSY Higgs Bosons at $e^+e^-$ Linear Colliders

The production mechanisms and decay modes of the heavy neutral and charged Higgs bosons in the Minimal Supersymmetric Standard Model are investigated at future $e^+ e^-$ colliders in the TeV energy regime. We generate supersymmetric particle spectra by requiring the MSSM Higgs potential to produce correct radiative electroweak symmetry breaking, and we assume a common scalar mass $m_0$, gaugino mass $m_{1/2}$ and trilinear coupling $A$, as well as gauge and Yukawa coupling unification at the Grand Unification scale. Particular emphasis is put on the low $\tb$ solution in this scenario where decays of the Higgs bosons to Standard Model particles compete with decays to supersymmetric charginos/neutralinos as well as sfermions. In the high $\tb$ case, the supersymmetric spectrum is either too heavy or the supersymmetric decay modes are suppressed, since the Higgs bosons decay almost exclusively into $b$ and $τ$ pairs. The main production mechanisms for the heavy Higgs particles are the associated $AH$ production and $H^+H^-$ pair production with cross sections of the order of a few fb.

hep-ph↗

arXiv1996

Anomalous couplings in the Higgs-strahlung process

The angular distributions in the Higgs-strahlung process $e^+e^-\to HZ\to H\bar f f$ are uniquely determined in the Standard Model. We study how these predictions are modified if non-standard couplings are present in the $ZZH$ vertex, as well as lepton-boson contact terms. We restrict ourselves to the set of operators which are singlets under standard $SU_3\times SU_2\times U_1$ transformations, CP conserving, dimension 6, helicity conserving, and custodial $SU_2$ conserving.

hep-ph↗

arXiv1996

SUSY Decays of Higgs Particles

Among the possible decay modes of Higgs particles into supersymmetric states, neutralino and chargino decays play a prominent rôle. The experimental opportunities of observing such decay modes at LEP2 and at future e+e- linear colliders are analyzed within the frame of the Minimal Supersymmetric extension of the Standard Model. For heavy Higgs particles, the chargino/neutralino decay modes can be very important, while only a small window is open for the lightest CP-even Higgs particle. If charginos/neutralinos are found at LEP2, such decay modes can be searched for in a small area of the parameter space, and invisible decays may reduce the exclusion limits of the lightest CP-even Higgs particle slightly; if charginos/neutralinos are not found at LEP2 in direct searches, the Higgs search will not be affected by the SUSY particle sector.

hep-ph↗

arXiv1996

Pair Production of Neutral Higgs Particles in Gluon--Gluon Collisions

Pair production processes of neutral Higgs particles will allow us to study the trilinear Higgs couplings at future high--energy colliders. Several mechanisms give rise to multi--Higgs final states in hadron interactions. In the present paper we investigate Higgs pair production in gluon--gluon collisions. After recapitulating pair production in the Standard Model, the analysis of the cross sections is carried out in detail for the neutral Higgs particles in the minimal supersymmetric extension.

hep-ph↗

arXiv1996

SUSY-QCD Decays of Squarks and Gluinos

The partial widths are determined for squark decays to gluinos and quarks, and gluino decays to squarks and quarks, respectively. The widths are calculated including one-loop SUSY-QCD corrections. The corrections amount to $+$30\% to $+$50\% for squark decays and $-$10\% to $+$10\% for gluino decays. We have derived the results in the \DR ~and \MS ~renormalization schemes, and we have demonstrated explicitly that the one-loop effective $qqg$ and $q\sq\gl$ couplings are equal in the limit of exact supersymmetry.

hep-ph↗

arXiv1996

Multiple Production of MSSM Neutral Higgs Bosons at High--Energy $e^+e^-$ Colliders

The cross sections for the multiple production of the lightest neutral Higgs boson at high--energy $e^+ e^-$ colliders are presented in the framework of the Minimal Supersymmetric extension of the Standard Model (MSSM). We consider production through Higgs--strahlung, associated production of the scalar and the pseudoscalar bosons, and the fusion mechanisms for which we will use the effective longitudinal vector--boson approximation. These cross sections allow one to determine trilinear Higgs couplings $λ_{Hhh}$ and $λ_{hhh}$, which are theoretically predicted by the Higgs potential.

hep-ph↗

arXiv1995

Two- and Three-Body Decay Modes of SUSY Higgs Particles

We summarize the dominant decay modes of the neutral and charged Higgs bosons in the Minimal Supersymmetric extension of the Standard Model. While two--body decays are in general dominating, the branching ratios for three--body decays of the heavy scalar, pseudoscalar and charged Higgs bosons can be large below the thresholds if top quarks, $W/Z$ bosons or heavy scalar bosons are involved. Analytical expressions have been derived for the partial decay widths and the physical implications of these decay modes are discussed.

hep-ph↗

arXiv1995

QCD Corrections to Hadronic Higgs Decays

We present an update of the branching ratios for Higgs decays in the Standard Model and the Minimal Supersymmetric extension of the Standard Model. In particular, the decays of the Higgs particles to quark and gluon jets are analyzed and the spread in the theoretical predictions due to uncertainties of the quark masses and the QCD coupling is discussed.

hep-ph↗

arXiv1995

Gluino-Pair Production at the Tevatron

The next-to-leading order QCD corrections to the production of gluino pairs at the Tevatron are presented in this paper. Similar to the production of squark-antisquark pairs, the dependence of the cross section on the renormalization/factorization scale is reduced considerably by including the higher-order corrections. The cross section increases with respect to the lowest-order calculation which, in previous experimental analyses, had been evaluated at the scale of the invariant energy of the partonic subprocesses.

hep-ph↗

arXiv1995

HIGGS BOSON PRODUCTION AT THE LHC

Gluon fusion is the main production mechanism for Higgs particles at the LHC. We present the QCD corrections to the fusion cross sections for the Higgs boson in the Standard Model, and for the neutral Higgs bosons in the minimal supersymmetric extension of the Standard Model. The QCD corrections are in general large and they increase the cross sections significantly. In two steps preceding the calculation of the production processes, we determine the QCD radiative corrections to Higgs decays into two photons and gluons.

hep-ph↗

arXiv1995

Hadronic Coupling Constants in Lattice QCD

We calculate the hadronic coupling constants $g_{NNπ}$ and $g_{ρππ}$ in QCD, including dynamical quarks in the framework of staggered fermions in the lattice approach. For the nucleon--pion coupling we obtain $g_{NNπ} = 13.8 \pm 5.8$, to be compared with the experimental value $13.13 \pm 0.07$. The $ρππ$ coupling has been analysed for two different sets of operators with the averaged result $g_{ρππ} = 4.2 \pm 1.9$ which is to be compared with the experimental value $6.06 \pm 0.01$.

hep-lat↗