arXiv subjects

S. Dawson

Publications and source records attributed to S. Dawson.

105 records · Page 6Linked to original sources

arXiv1996

Electroweak Symmetry Breaking and Physics Beyond the Standard Model

In order to extend the Standard Model to TeV scale energies one must address two basic questions: (1) What is the complete description of the effective theory of fundamental particles at and below the electroweak scale? and (2) What is the dynamics responsible for electroweak symmetry breaking? The answers to these questions are crucial for addressing the third outstanding question of particle physics: What are the origins of the Standard Model parameters? We briefly summarize current theoretical approaches to answering these questions.

hep-ph↗

arXiv1996

QCD Corrections to SUSY Higgs Production: The Role of Squark Loops

We calculate the two-loop QCD corrections to the production of the neutral supersymmetric Higgs bosons via the gluon fusion mechanism at hadron colliders, including the contributions of squark loops. To a good approximation, these additional contributions lead to the same QCD corrections as in the case where only top and bottom quark loops are taken into account. The QCD corrections are large and increase the Higgs production cross sections significantly.

hep-ph↗

arXiv1995

Precision Measurements at a Muon Collider

We discuss the potential for making precision measurements of $M_W$ and $M_T$ at a muon collider and the motivations for each measurement. A comparison is made with the precision measurements expected at other facilities. The measurement of the top quark decay width is also discussed.

hep-ph↗

arXiv1995

Limits on Non-Standard Top Quark Couplings from Electroweak Measurements

We calculate the typical size of loop corrections to electroweak observables arising from non-standard $Z {\overline t } t$ and $W t b$ vertices. We use an effective Lagrangian formalism based on the electroweak gauge group $SU(2)_L\times U(1)_Y \rightarrow U(1)_{EM}$. Limits on the non-standard model top quark couplings from electroweak observables are presented and compared with previously obtained limits.

hep-ph↗

arXiv1995

Electroweak Symmetry Breaking and Beyond the Standard Model

This is a report of the Electroweak Symmetry Breaking and Beyond the Standard Model Working Group which was prepared for the Division of Particles and Fields Committee for Long Term Planning. We study the phenomenology of electroweak symmetry breaking and attempt to quantify the "physics reach" of present and future colliders. Our investigations encompass the Standard Model (with one doublet of Higgs scalars) and approaches to physics beyond the Standard Model. These include models of low energy supersymmetry, technicolor and other approaches to dynamical electroweak symmetry breaking, and a variety of extensions of the Standard Model with new particles and interactions ({\it e.g.}, non-minimal Higgs sectors, new gauge bosons and/or exotic fermions, {\it etc.}). Signals of new physics in precision measurements arising from virtual processes (which can result, for example, in ``anomalous'' couplings of Standard Model particles) are also considered. Finally, we examine experimental issues associated with the study of electroweak symmetry breaking and the search for new physics at present and future hadron and $e^+e^-$ colliders.

hep-ph↗

arXiv1995

Looking for CP Violation in W Production and Decay

We describe CP violating observables in resonant $W^\pm$ and $W^\pm$ plus one jet production at the Tevatron. We present simple examples of CP violating effective operators, consistent with the symmetries of the Standard Model, which would give rise to these observables. We find that CP violating effects coming from new physics at the $TeV$ scale could in principle be observable at the Tevatron with $10^6$ $W^\pm$ decays.

hep-ph↗

arXiv1994

Probing Anomalous Gauge Boson Couplings at LEP

We bound anomalous gauge boson couplings using LEP data for the $Z\rightarrow {\overline f} f$ partial widths. We use an effective field theory formalism to compute the one-loop corrections resulting from non-standard model three and four gauge boson vertices. We find that measurements at LEP constrain the three gauge boson couplings at a level comparable to that obtainable at LEPII.

hep-ph↗

arXiv1994

Bounds on $g_5^Z$ from Precision LEP Measurements

The parity violating but CP conserving anomalous three-gauge-boson coupling $g_5^Z$ induces a universal contribution to the left-handed coupling of the $Z$ boson to fermions. We find that the LEP measurements of the partial $Z$ widths and lepton forward-backward asymmetries are sufficiently precise to place a bound of order $|g_5^Z|$ less than $\sim~10\%$. This bound is significantly better than what can be obtained at present from rare $K$ and $B$ meson decays.

hep-ph↗

arXiv1994

Bounds on Anomalous Gauge Boson Couplings From Partial Z Widths at LEP

We place bounds on anomalous gauge boson couplings from LEP data with particular emphasis on those couplings which do not contribute to $Z$ decays at tree level. We use an effective field theory formalism to compute the one-loop corrections to the $Z\rightarrow {\overline f} f$ decay widths resulting from non-standard model three and four gauge boson vertices. We find that the precise measurements at LEP constrain the three gauge boson couplings at a level comparable to that obtainable at LEPII and LHC.

hep-ph↗

arXiv1994

Search for Anomalous Couplings at $eγ$ Colliders

We consider the possibility of observing deviations from the Standard Model gauge-boson self-couplings at future $eγ$ colliders. We concentrate on the process $e^-γ\rightarrow νW^- Z$, which is particularly sensitive to the parity violating coupling $g_5^Z$ at high energies. We find that a 2~TeV $e^+ e^-$ collider operating in the $e^- γ$ mode could reach a sensitivity of order $5\times 10^{-3}$ to $g_5^Z$.

hep-ph↗

arXiv1994

Signals For Parity Violation in the Electroweak Symmetry Breaking Sector

We consider the possibility of observing a parity violating but $CP$ conserving interaction in the symmetry breaking sector of the electroweak theory. We find that the best probe for such an interaction is a forward-backward asymmetry in $W^+W^-$ production from polarized $e^-_R e^+_L$ collisions. An observable asymmetry would be strong evidence against a custodial $SU(2)$ symmetry. We also discuss the effects of such an interaction in future $e^- γ$ colliders as well as in rare decays of $K$ and $B$ mesons.

hep-ph↗

arXiv1993

QCD Corrections to Higgs Boson Production: Non- Leading Terms in the Heavy Quark Limit

We compute analytic results for the QCD corrections to Higgs boson production via gluon fusion in hadronic collisions in the limit in which the top quark is much heavier than the Higgs boson. The first non-leading corrections of $Ø(α_s^3 \mh^2/m_t^2)$ are given and numerical results presented for both LHC and SSC energies. We confirm earlier numerical results showing that the dominant corrections have the same mass dependence as the Born cross section.

hep-ph↗

arXiv1993

$K_L \ra μ^\pm e^\mp ν\overlineν$ as background to $K_L \ra μ^\pm e^\mp$

We consider the process $K_L \ra μ^\pm e^\mp ν\overlineν$ at next to leading order in chiral perturbation theory. This process occurs in the standard model at second order in the weak interaction and constitutes a potential background in searches for new physics through the modes $K_L \ra μ^\pm e^\mp$. We find that the same cut, $M_{μe}>489$~MeV, used to remove the sequential decays $K_{l3}\ra π_{l2}$ pushes the $B(K_L \ra μ^\pm e^\mp ν\overlineν)$ to the $10^{-23}$ level, effectively removing it as a background.

hep-ph↗

arXiv1992

Effective Field Theory of Anomalous Gauge-Boson Couplings at High-Energy pp Colliders

We compute the effects of anomalous gauge-boson couplings at high-energy hadron colliders using next-to-leading order $SU(2) \times SU(2)$ chiral perturbation theory. By comparing the yields from the universal $p^2$ terms with those arising from new physics at order $p^4$, we estimate the sensitivity of the SSC and LHC to the indirect effects of electroweak symmetry breaking.

hep-ph↗

arXiv1992

Vector-Boson versus Gluon Fusion at Hadron Colliders

We use chiral perturbation theory to show that pseudo-Goldstone boson scattering and gluon fusion probe different aspects of electroweak symmetry breaking at hadron colliders. In particular, the physics responsible for unitarizing the lowest-order pseudo-Goldstone boson scattering amplitudes need not significantly affect the gluon fusion process. We first show this within the context of strict chiral perturbation theory, and then discuss it using the language of resonances.

hep-ph↗