arXiv subjects
Publications and source records attributed to S. Dawson.
We discuss associated production of a Higgs boson with a pair of $t {\bar t}$ quarks at a future high energy $e^+e^-$ collider. The process $e^+e^-\to t {\bar t}h$ is particularly sensitive to the presence of new physics and we consider the MSSM and models with extra dimensions at the $TeV$ scale as examples.
Any consideration of future physics facilities must be made in the context of the Tevatron and the LHC. I discuss some examples of physics results which could emerge from these machines and the resulting questions which would remain for a high energy $e^+e^-$ collider. Particular attention is paid to the electroweak symmetry breaking sector. If a light Higgs boson exists, it will be observed at the LHC and the role of any later accelerator will be to map out the Higg's boson mass and couplings and then determine the space of possible models. If there is no light Higgs boson, then some effects of a strongly interacting electroweak symmetry breaking sector will be observed at the LHC and I discuss the role of a high energy linear collider in exploring this scenario.
We investigate the inclusive production of a Higgs boson with a pair of heavy quarks (t-tbar b-bbar), in e^+e^- collisions at high energies, sqrt(s)=500 GeV and sqrt(s)=1 TeV. We consider both the Standard Model and the supersymmetric case. In both cases O(alpha_s) QCD corrections are included. The associated production of a Higgs boson with a t-tbar pair is extremely sensitive to the top-Higgs Yukawa coupling and may allow the precision measurement of this coupling. In some regions of the supersymmetric parameter space the associated production of a Higgs boson with a b-bbar pair receives large resonant contributions and can have a significant rate.
We investigate the inclusive production of the Higgs boson with a heavy quark pair, $t {\bar t}$ or $b {\bar b}$, in e^+e^- collisions at high energy. The ${\cal O}(α_s)$ QCD corrections are included.
We investigate the inclusive production of the Higgs bosons of the minimal supersymmetric model with a heavy quark pair, ($t {\bar t}$ and $b {\bar b}$), in e^+e^- collisions at high energies, $\sqrt{s}=500 GeV$ and $\sqrt{s}=1 TeV$. The ${\cal O}(α_s)$ QCD radiative corrections are included and the dependence of the production rates on the parameters of the MSSM is explored. The associated production of a Higgs boson with a $b {\bar b}$ pair receives large resonant contributions and can have a significant rate.
An introduction to the physics of electroweak symmetry breaking is given. We discuss Higgs boson production in $e^+e^-$ and hadronic collisions and survey search techniques at present and future accelerators. Indirect limits on the Higgs boson mass from triviality arguments, vacuum stability, and precision electroweak measurements are presented. An effective Lagrangian, valid when there is no low mass Higgs boson, is used to discuss the physics of a strongly interacting electroweak symmetry breaking sector. Finally, the Higgs bosons of the minimal supersymmetric model are considered, along with the resulting differences in phenomenology from the Standard Model.
The calculation of the next-to-leading order QCD corrections to the production of a neutral Higgs-boson pair is briefly summarized. The dominant production mechanism is gluon fusion via top-quark loops, so that the QCD corrections can be considered, to good approximation, in the limit of a heavy top-quark mass.
Neutral Higgs-boson pair production provides the possibility of studying the trilinear Higgs couplings at future high-energy colliders. We present the QCD corrections to the gluon-initiated processes in the limit of a heavy top quark in the loops and the Drell-Yan-like pair production of scalar and pseudoscalar Higgs particles. The pp cross sections are discussed for LHC energies within the Standard Model and its minimal supersymmetric extension. The QCD corrections are large, enhancing the total cross sections significantly.
An introduction to the minimal supersymmetric standard model is presented. We emphasize phenomenological motivations for this model, along with examples of experimental tests. Particular attention is paid to the Higgs sector of the theory.
We compute QCD corrections to the processes $e^+e^-\to t \bar t h^0$ and $pp\to t \bar t h^0$ by treating the Higgs boson as a parton which radiates off a heavy quark. This approximatiion is valid in the limits $M_h<<M_t$ and $M_h, M_t<<\sqrt{s}$. The corrections increase the rate for $pp\to t \bar t h^0$ at the LHC by a factor of 1.2 to 1.5 over the lowest order rate for an intermediate mass Higgs boson, $M_h < 180 GeV$. The QCD corrections are small for $e^+e^-\to t \bar t h^0$ at $\sqrt{s}=1 TeV$.
It is possible to place constraints on non-Standard-Model gauge-boson self-couplings and other new physics by studying their one-loop contributions to precisely measured observables. We extend previous analyses which constrain such nonstandard couplings, and we present the results in a compact and transparent form. Particular attention is given to comparing results for the light-Higgs scenario, where nonstandard effects are parameterized by an effective Lagrangian with a linear realization of the electroweak symmetry breaking sector, and the heavy-Higgs/strongly interacting scenario, described by the electroweak chiral Lagrangian. The constraints on nonstandard gauge-boson self-couplings which are obtained from a global analysis of low-energy data and LEP/SLC measurements on the Z pole are updated and improved from previous studies. Replaced version: tables and figures of Section VIb recalculated. There were roundoff problems, especially in Fig. 8. Text unchanged.
We consider the phenomenology of the Standard Model intermediate mass Higgs boson, $71 GeV < M_h < 2 M_W$. The motivation for a Higgs boson in this mass region is emphasized. The branching ratios for the Higgs boson, including electroweak and QCD radiative corrections, are presented, along with production cross sections for $e^+e^-, μ^+μ^-, γγ$, and hadronic interactions. Search strategies are surveyed briefly.
Introductory lectures on the phenomenology of the minimal supersymmetric Standard Model. The emphasis is on general signatures for supersymmetry and on the motivation for constructing supersymmetric models. These lectures are intended for experimental graduate students.
Despite many experimental verifications of the correctness of our basic understanding of QCD, there remain numerous open questions in strong interaction physics and we focus on the role of future colliders in addressing these questions. We discuss possible advances in the measurement of $α_s$, in the study of parton distribution functions, and in the understanding of low $x$ physics at present colliders and potential new facilities. We also touch briefly on the role of spin physics in advancing our understanding of QCD.
The measurement of anomalous gauge boson self couplings is reviewed for a variety of present and planned accelerators. Sensitivities are compared for these accelerators using models based on the effective Lagrangian approach. The sensitivities described here are for measurement of generic parameters kappa_v, lambda_v, etc., defined in the text. Pre-LHC measurements will not probe these couplings to precision better than O(1/10). The LHC should be sensitive to better than O(1/100), while a future NLC should achieve sensitivity of O(1/1000) to O(1/10000) for center of mass energies ranging from 0.5 to 1.5 TeV.
We explore the capability of a 500 or 1000 GeV $e^+e^-$ linear collider to measure anomalous quartic gauge boson couplings. In the framework of a non-linear effective Lagrangian with a custodial $SU)2)$ symmetry, there are only two next-to-leading order operators which contribute to quartic, but not to two- and three- gauge boson interactions. The limits on the coefficients of these operators from present and future $e^+e^-$ colliders are compared with those available from other sources.
We study the capability of a $2 TeV$ $p\overline{p}$ collider with an integrated luminosity of $10 fb^{-1}$ to study CP violation in the processes $p \bar{p} \ra W^\pm γ$ and $p \bar{p} \ra Z γ$. We assume the existence of new CP violating interactions beyond the standard model which we describe with an effective Lagrangian. We find that the study of CP-odd observables would allow this machine to place bounds on CP violating anomalous couplings similar to the bounds that the same machine can place on $\cp$ conserving anomalous couplings. For example it could place the bound $|\tildeκ_γ|<0.1$ at the 95% confidence level.
I summarize some of the highlights of the 1996 DPF meeting, paying particular attention to new measurements of the $W$, $Z$, and top quark masses. Precision electroweak measurements from LEP are discussed with emphasis on recent measurements of $R_b$ and values of the coupling constants $α(M_Z^2)$ and $α_s(M_Z^2)$ are presented. Taken as a whole, the data are in spectacular agreement with the predictions of the Standard Model.