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J. F. Gunion

Publications and source records attributed to J. F. Gunion.

At least 55 records · Page 3Linked to original sources
arXiv1999

A New Technique for Determining the Properties of a Narrow $s$-channel Resonance at a Muon Collider

We explore an alternative to the usual procedure of scanning for determining the properties of a narrow $s$-channel resonance. By varying the beam energy resolution while sitting on the resonance peak, the width and branching ratios of the resonance can be determined. The statistical accuracy achieved is superior to that of the usual scan procedure in the case of a light SM-like Higgs boson with $\mh>130\gev$ or for the lightest pseudogoldstone boson of a strong electroweak breaking model if $\mpzero>150\gev$.

hep-ph↗
arXiv1999

A Non-Standard String/SUSY Scenario and its Phenomenological Implications

We investigate the phenomenology of an orbifold string model in which supersymmetry breaking is dominated by the overall `size' modulus field and all matter fields are in the untwisted sector. The possibly close degeneracy of the lightest neutralino and chargino and the possibly small splitting between the gluino and chargino/LSP mass imply that discovery of supersymmetry at future colliders could be more challenging than anticipated. Specialized search strategies and particular detector features could play an important role. For preferred model parameter choices, the phenomenology of dark matter in the universe is significantly modified.

hep-ph↗
arXiv1999

Searching for Invisible and Almost Invisible Particles at e^+e^- Colliders

We explore the techniques, cross sections and expected signal significance for detecting invisible and almost invisible particles at LEP2 and the NLC by means of a hard photon tag. Examples from supersymmetry include the lightest chargino and second lightest neutralino when their masses are nearly the same as that of the lightest neutralino (the LSP), and invisibly decaying sneutrinos. The importance of particular features of the detectors is discussed, instrumentation for vetoing a fast e^+ or e^- in the beam hole being especially crucial.

hep-ph↗
arXiv1999

Finding the CP-Violating Higgs Bosons at e^+e^- Colliders

We discuss a general two-Higgs-doublet model with CP violation in the Higgs sector. In general, the three neutral Higgs fields of the model all mix and the resulting physical Higgs bosons have no definite CP properties. We derive a new sum rule relating Yukawa and Higgs-Z couplings which implies that a neutral Higgs boson cannot escape detection at an e^+e^- collider if it is kinematically accessible in Z+Higgs, $b\anti b+$Higgs and $t\anti t+$Higgs production, irrespective of the mixing angles and the masses of the other neutral Higgs bosons. We also discuss modifications of the sum rules and their phenomenological consequences in the case when the two-doublet Higgs sector is extended by adding one or more singlets.

hep-ph↗
arXiv1998

Selected Low-Energy Supersymmetry Phenomenology Topics

I review selected topics in supersymmetry, including: effects of non-universality, high $\tanb$ and phases on SUSY signals; a heavy gluino as the LSP; gauge-mediated SUSY signals involving delayed decays; R-parity violation and the very worst case for SUSY discovery; some topics regarding Higgs bosons in supersymmetry; and doubly-charged Higgs and higgsinos in supersymmetric left-right symmetric models. I emphasize scenarios in which detectionof supersymmetric particles and/or the SUSY Higgs bosons might require special experimental and/or analysis techniques.

hep-ph↗
arXiv1998

A Heavy Gluino as the Lightest Supersymmetric Particle

We consider the possibility that the lightest supersymmetric particle is a heavy gluino. After discussing models in which this is the case, we demonstrate that the gluino-LSP could evade cosmological and other constraints by virtue of having a very small relic density. We then consider how neutral and charged hadrons containing a gluino will behave in a detector, demonstrating that there is generally substantial apparent missing momentum associated with a produced gluino-LSP. We next investigate limits on a (heavy) gluino-LSP deriving from LEP, LEP2 and RunI Tevatron experimental searches for excess events in the jets plus missing momentum channel and for stable heavily-ionizing charged particles. The range of gluino mass that can be excluded depends upon the path length of the gluino in the detector, the amount of energy it deposits in each hadronic collision, and the probability for the gluino to fragment to a pseudo-stable charged hadron after a given hadronic collision. We explore how the range of excluded gluino mass depends upon these ingredients, concluding that for non-extreme cases the range $3\gev\lsim\mgl\lsim 130-150\gev$ can be excluded at 95% CL based on currently available OPAL and CDF analyses. We find that RunII at the Tevatron can extend the excluded region (or discover the gluino) up to $\mgl\sim 160-180\gev$. For completeness, we also analyze the case where the gluino is the NLSP (as possible in gauge-mediated supersymmetry breaking) decaying via gluino -> g + gravitino. We find that the Tevatron RunI data excludes $\mgl\leq 240$ GeV. Finally, we discuss application of the procedures developed for the heavy gluino-LSP to searches for other stable strongly interacting particles, such as a stable heavy quark.

hep-ph↗
arXiv1998

Determining the relative size of the CP-even and CP-odd Higgs Boson Couplings to a Fermion at the LHC

We demonstrate that the relative size of the CP-even and CP-odd couplings of a Higgs boson to $t\anti t$ can be determined at the LHC at a level that is very useful in discriminating between models, provided that a Higgs signal can be observed at a reasonable $S/\sqrt B$ level in the $t\anti t\h$ (with $\h\toγγ$ or $b\anti b)$ channels. In particular, the CP-even nature of a SM-like Higgs boson's coupling to $t\anti t$ can be confirmed with very substantial statistical significance using the $t\anti t \h$ ($\h\to γγ$) production/decay mode. The key to achieving good discrimination between models is to make full use of the difference in the final state distributions for different ratios of the CP-even to CP-odd couplings. For our analysis, we employ the very convenient and simple optimal analysis procedures derived previously.

hep-ph↗
arXiv1998

A No-Lose Theorem for Higgs Searches at a Future Linear Collider

Assuming perturbativity up to a high energy scale $\sim 10^{16}$ GeV, we demonstrate that a future $e^+e^-$ linear collider operating at $\sqrt{s} =$ 500 GeV with $\int{\cal L}=$ 500 fb$^{-1}$ per year (such as the recently proposed TESLA facility) will detect a Higgs boson signal regardless of the complexity of the Higgs sector and of how the Higgs bosons decay.

hep-ph↗
arXiv1998

Determining the Coupling of a Higgs Boson to $ZZ$ at Linear Colliders

We demonstrate that, at a 500 GeV e+e- collider, inclusion of the $ZZ$-fusion process for production of a light standard-model-like Higgs boson can substantially increase the precision with which the $ZZh$ coupling can be determined (using the model-independent recoil mass technique) as compared to employing only $Zh$ associated production.

hep-ph↗
arXiv1998

Probing Exotic Higgs Sectors in $\ell^-\ell^-$ Collisions

I review extended Higgs sectors and constraints thereon arising from $ρ=1$, gauge-coupling unification and $b\to s\gam$. The couplings and decays of the Higgs boson eigenstates are outlined for triplet representations. Direct experimental probes of exotic Higgs bosons are reviewed with a focus on the important role that would be played by an $e^-e^-$ or $μ^-μ^-$ collider.

hep-ph↗
arXiv1998

Physics at a Muon Collider

I discuss the exciting prospects for exploring a wide range of new physics at a low-energy muon collider.

hep-ph↗
arXiv1998

Probing Gauge-Mediated Supersymmetry Breaking Models at the Tevatron via Delayed Decays of the Lightest Neutralino

We quantitatively explore, in the context of the D0 detector at the Tevatron, three very different techniques for observing delayed decays of the lightest neutralino of a simple gauge-mediated supersymmetry breaking (GMSB) model to photon plus gravitino. It is demonstrated that the delayed-decay signals considered can greatly increase the region of general GMSB parameter space for which supersymmetry can be detected. In the simple class of models considered, the combination of standard supersymmetry signals and delayed-decay signals potentially yields at least one viable signal for nearly all of the theoretically favored parameter space. The importance, for delayed-decay signal detection, of particular detector features and of building a simple photon detector on the roof of the D0 detector building is studied.

hep-ph↗
arXiv1998

A Strong Electroweak Sector at Future mu^+ mu^- Colliders

We discuss the prospects for detecting at a muon collider the massive new vector resonances V and light pseudo-Nambu-Goldstone bosons P of a typical strongly interacting electroweak sector (as represented by the BESS model). Expected sensitivities to V's at a high energy collider are evaluated and the excellent prospects for discovering P's via scanning at a low energy collider are delineated.

hep-ph↗
arXiv1997

R-Parity Violation and Sneutrino Resonances at Muon Colliders

In supersymmetric models with R-parity violating interactions, sneutrinos may be produced as $s$-channel resonances at $μ^+ μ^-$ colliders. We demonstrate that, for R-parity violating couplings as low as $10^{-4}$, sneutrinos can be discovered and their couplings measured to high accuracy. The excellent beam energy resolution of muon colliders is found to be especially useful for studying such resonances in certain cases.

hep-ph↗