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J. F. Gunion

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

At least 37 records · Page 2Linked to original sources
arXiv2002

New results for a photon-photon collider

We present new results from studies in progress on physics at a two-photon collider. We report on the sensitivity to top squark parameters of MSSM Higgs boson production in two-photon collisions; Higgs boson decay to two photons; radion production in models of warped extra dimensions; chargino pair production; sensitivity to the trilinear Higgs boson coupling; charged Higgs boson pair production; and we discuss the backgrounds produced by resolved photon-photon interactions.

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arXiv2002

The scalar sector of the Randall-Sundrum model

We derive the effective potential for the Standard Model Higgs-boson sector interacting with Kaluza-Klein excitations of the graviton ($h_μ^{νn}$) and the radion ($ϕ$) and show that {\it only} the Standard Model vacuum solution of $\partial V(h)/\partial h =0$ (h is the Higgs field) is allowed. We then consider the consequences of the curvature-scalar mixing xi R \Hhat^\dagger \Hhat$ (where $\Hhat$ is a Higgs doublet field on the visible brane), which causes the physical mass eigenstates h and $ϕ$ to be mixtures of the original Higgs and radion fields. First, we discuss the theoretical constraints on the allowed parameter space. Next, we give precise procedures for computing the h and $ϕ$ couplings given the {\it physical} eigenstate masses, mh and $\mphi$, xi and the new physics scales of the model. We show that LEP/LEP2 data implies that not both the h and $ϕ$ can be light. In the allowed region of parameter space, we examine numerically the couplings and branching ratios of the h and $ϕ$ for several cases with $\mh=120\gev$ and $\mphi\leq 300\gev$. The resulting prospects for detection of the h and $ϕ$ at the LHC, a future LC and a $\gam\gam$ collider are reviewed. For moderate $|ξ|$, both the anomalous $h\to gg$ coupling and (when $\mh>2\mphi$) the non-standard decay channel $h \to ϕϕ$ can substantially impact h discovery. Presence of the latter is a direct signature for non-zero xi. We find that $BR(h \to ϕϕ)$ as large as $30 ÷40 %$ is possible when $|ξ|$ is large. Conversely, if $\mphi>2\mh$ then $BR(ϕ\to hh)$ is generally large. The feasibility of experimentally measuring the anomalous gg and $\gam\gam$ couplings of the h and $ϕ$ is examined.

hep-ph↗
arXiv2002

The Precision of Higgs Boson Measurements and Their Implications

The prospects for a precise exploration of the properties of a single or many observed Higgs bosons at future accelerators are summarized, with particular emphasis on the abilities of a Linear Collider (LC). Some implications of these measurements for discerning new physics beyond the Standard Model (SM) are also discussed.

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arXiv2002

Establishing a No-Lose Theorem for NMSSM Higgs Boson Discovery at the LHC

We scan the parameter space of the NMSSM for the observability of at least one Higgs boson at the LHC with $300\fbi$ integrated luminosity, taking the present LEP2 constraints into account. We restrict the scan to those regions of parameter space for which Higgs boson decays to other Higgs bosons and/or supersymmetric particles are kinematically forbidden. We find that if $WW$-fusion detection modes for a light Higgs boson are not taken into account, then there are still significant regions in the scanned portion of the NMSSM parameter space where no Higgs boson can be observed at the $5σ$ level, despite the recent improvements in ATLAS and CMS procedures and techniques and even if we combine all non-fusion discovery channels. However, if the $WW$-fusion detection modes are included using the current theoretical study estimates, then we find that for all scanned points at least one of the NMSSM Higgs bosons will be detected. If the estimated $300\fbi$ significances for ATLAS and CMS are combined, one can also achieve $5σ$ signals after combining just the non-$WW$-fusion channels signals. We present the parameters of several particularly difficult points, and discuss the complementary roles played by different modes. We conclude that the LHC will discover at least one NMSSM Higgs boson unless there are large branching ratios for decays to SUSY particles and/or to other Higgs bosons.

hep-ph↗
arXiv2002

Determination of $\tanβ$ at a Future $e^+e^-$ Linear Collider

It is widely stated that the ratio of neutral Higgs field vacuum expectation values, $\tanb$, is one of the most difficult parameters to determine in either the Minimal Supersymmetric Standard Model (MSSM) or a general type-II Two-Higgs Doublet Model (2HDM). Assuming an energy and integrated luminosity of $\rts=500\gev$ and $\call=2000\fbi$, we show that a very accurate determination of $\tanb$ will often be possible using Higgs production rates and/or Higgs decays. Based on a TESLA simulation, and assuming no other light Higgs bosons and $100\leq m_A \leq 200\gev$, we find that the rate for the process $\epem\to b\anti b A \to b\anti b b\anti b$ provides an excellent determination of $\tanb$ at high $\tanb$. In the MSSM Higgs sector, the rate for $\epem\to b\anti b A+ b\anti b H \to b\anti b b\anti b$ ($\epem\to HA \to b\anti b b\anti b$) provides a good determination of $\tanb$ at high (low) $\tanb$, respectively, at moderate $m_A$ values. We also show that direct measurement of the average total width of the $H$ and $A$ in $\epem\to HA \to b\anti b b\anti b$ events provides an excellent determination of $\tanb$ at large $\tanb$.

hep-ph↗
arXiv2001

Physics of Higgs Factories

We outline the unique role of a muon collider as a Higgs factory for Higgs boson resonance production in the $s$-channel. Physics examples include: the precision measurements of the Higgs mass and total width, and the resulting ability to discriminate between the SM-like Higgs bosons of different models such as between a light SM Higgs boson and the light Higgs boson of the MSSM; the determination of the spin and coupling via the $h\to \tautau$ decay mode; differentiation of two nearly degenerate heavy Higgs bosons by an energy scan; and the ability to explore a general extended Higgs sector, possibly with CP-violating couplings. The muon collider Higgs factory could perform measurements that would be highly complementary to Higgs studies at the LHC and LC; it would be likely to play a very crucial role in fully understanding the Higgs sector.

hep-ph↗
arXiv2000

Do precision electroweak constraints guarantee $e^+e^-$ collider discovery of at least one Higgs boson of a two-Higgs-doublet model?

We consider a CP-conserving two-Higgs-doublet type II model with a light scalar or pseudoscalar neutral Higgs boson ($\h=\hl$ or $\h=\ha$) that has no $ZZ/WW$ coupling and, thus, cannot be detected in $\epem\to Z\h$ (Higgs-strahlung) or $ν\antiν\h$ (via $WW$ fusion). Despite sum rules which ensure that the light $\h$ must have significant $t\anti t$ or $b\anti b$ coupling, for a wedge of moderate $\tanb$, that becomes increasingly large as $\mh$ increases, the $\h$ can also escape discovery in both $b\anti b \h$ and $t\anti t \h$ production at a $\rts=500-800\gev$ $\epem$ collider (for expected luminosities). If the other Higgs bosons happen to be too heavy to be produced, then no Higgs boson would be detected. We demonstrate that, despite such high masses for the other Higgs bosons, only the low-$\tanb$ portion of the no-discovery wedges in $[\mh,\tanb]$ parameter space can be excluded due to failure to fit precision electroweak observables. In the $\tanb\gsim 1$ regions of the no-discovery wedges, we find that the 2HDM fit to precision electroweak observables has small $Δχ^2$ relative to the best minimal one-doublet SM fit.

hep-ph↗
arXiv2000

Search Strategies for Non-Standard Higgs Bosons at Future e^+e^- Colliders

Already in the simplest two-Higgs-doublet model with CP violation in the Higgs sector, the $3\times3$ mixing matrix for the neutral Higgs bosons can substantially modify their couplings, thereby endangering the ``classical'' Higgs search strategies. However, there are sum rules relating Yukawa and Higgs-Z couplings which ensure that the ZZ, $b\anti b$ and $t\anti t$ couplings of a given neutral 2HDM Higgs boson cannot all be simultaneously suppressed. This result implies that any single Higgs boson will be detectable at an e^+e^- collider if the Z+Higgs, $b\anti b+$Higgs {\it and} $t\anti t+$Higgs production channels are all kinematically accessible {\it and} if the integrated luminosity is sufficient. We explore, as a function of Higgs mass, the luminosity required to guarantee Higgs boson detection, and find that for moderate $\tanβ$ values the needed luminosity is unlikely to be available for all possible mixing scenarios. The additional difficulties for the case when the two-doublet Higgs sector is extended by adding one more singlet are summarized. Implications of the sum rules for Higgs discovery at the Tevatron and LHC are briefly discussed.

hep-ph↗
arXiv2000

Report of the Beyond the MSSM Subgroup for the Tevatron Run II SUSY/Higgs Workshop

There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal Supersymmetric Standard Model. In other cases, the parameters of the Lagrangian are unusual compared to commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.). The phenomenology of supersymmetry varies greatly between the different models. Correspondingly, particular aspects of the detectors assume greater or lesser importance. Detection of supersymmetry and the determination of all parameters may well depend upon having the widest possible view of supersymmetry phenomenology.

hep-ph↗
arXiv2000

How Valuable is Polarization at a Muon Collider? A Test Case: Determining the CP Nature of a Higgs Boson

We study the use of polarization asymmetries at a muon collider to determine the CP-even and CP-odd couplings of a Higgs boson to $μ^+mu^-$. We determine achievable accuracy as a function of beam polarization and luminosity. The appropriate techniques for dealing with the polarization precession are outlined. Strategies especially appropriate for a two-Higgs-doublet model (including the MSSM) are given. Our general conclusion is that polarization will be very useful, especially if the proton source is such that full luminosity in the storage ring can be retained even after imposing cuts on the originally accepted muons necessary for $P\gsim 0.4$ for each beam.

hep-ph↗
arXiv2000

Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario

The open light gluino window allows non-trivial higher twist gluino contributions to the proton wave function. Using a two-component model originally developed for charm hadroproduction, higher twist intrinsic gluino contributions to final state R-hadron formation are shown to enhance leading twist production in the forward $x_{F}$ region. We calculate R-hadron production at $p_{\rm{lab}}=800$ GeV in pp, pBe, and pCu interactions with light gluino masses of 1.2, 1.5, 3.5, and 5.0 GeV.

hep-ph↗
arXiv1999

The Lightest Pseudo-Goldstone Boson at Future e+e- Colliders

In a class of models of dynamical symmetry breaking not ruled out by the available data, the lightest neutral pseudo-Nambu-Goldstone boson P0 contains only down-type techniquarks and charged technileptons. Its mass scale is naturally determined by the b-quark and therefore it is likely to be light. As the presence of pseudo-Nambu-Goldstone bosons in models of dynamical symmetry breaking is a quite general feature, the search of the P0 at colliders is an interesting opportunity of putting limits on or discovering a dynamical electroweak symmetry breaking scenario. In this note we discuss the prospects for discovering and studying the P0 at future e+e- and gamma-gamma colliders.

hep-ph↗
arXiv1999

Detecting and Studying the Lightest Pseudo-Goldstone Boson at Future $pp$, $e^+e^-$ and $μ^+μ^-$ Colliders

For an attractive class of dynamical symmetry breaking (technicolor) models, the lightest neutral pseudo-Nambu-Goldstone boson ($\pzero$) contains only down-type techniquarks and charged technileptons. We discuss the prospects for discovering and studying the $\pzero$ of such models at the Tevatron and the LHC and at future $\epem$ and $\mupmum$ colliders. Depending upon the number of technicolors, $\ntc$, discovery of the $\pzero$ at the Tevatron and the LHC in the $gg\to\pzero\to\gam\gam$ mode could be possible over a wide range of mass. For $\ntc=4$, discovery of the $\pzero$ at an $\epem$ collider via the reaction $\epem\to\gam \pzero$ should be possible as long as $\mpzero$ is not near $\mz$. In the $\gam\gam$ collider mode of operation at an $\epem$ collider, the $\gam\gam\to\pzero\to b\anti b$ signal should be very robust if $\ntc=4$. For the minimal $\ntc=1$ case, detection of the $\pzero$ at the Tevatron and in $\epem$ collisions will be very difficult, and the precision of measurements at the LHC and the $\gam\gam$ collider decline markedly. A $\mupmum$ collider yields a $\pzero$ production rate that does not depend markedly upon $\ntc$. At a $\mupmum$ collider discovery of the $\pzero$ as an $s$-channel resonance should prove possible via scanning, even if it has not already been detected elsewhere. Once $\mpzero$ is precisely known, operation of the $\mupmum$ collider as a $\pzero$ factory will allow precision measurements of enough observables to determine the number of technicolors of the theory and (up to a discrete set of ambiguities) the fundamental parameters of the low-energy effective Lagrangian describing the Yukawa couplings of the $\pzero$.

hep-ph↗
arXiv1999

A study of SUSY signatures at the Tevatron in models with near mass degeneracy of the lightest chargino and neutralino

For some choices of soft SUSY-breaking parameters, the LSP is a stable neutralino $\cnone$, the NLSP is a chargino $\cpmone$ almost degenerate in mass with the LSP ($\dmchi\equiv\mcpmone-\mcnone\sim \mpi-$few GeV), and all other sparticles are relatively heavy. In this case, detection of sparticles in the usual, mSUGRA-motivated signals will be difficult, since the decay products in $\cpmone\to\cnone...$ will be very soft, and alternative signals must be considered. Here, we study the viability of signatures at the Tevatron based on highly-ionizing charged tracks, disappearing charged tracks, large impact parameters, missing transverse energy and a jet or a photon, and determine the mass reach of such signatures assuming that only the $\cpmone$ and $\cnone$ are light. We also consider the jet+$\etmiss$ and $γ+\etmiss$ signatures assuming that the gluino is also light with $\mgl\sim \mcpmone$. We find that the mass reach is critically dependent upon $\dmchi$ and $\mgl-\mcpmone$. If $\dmchi$ is sufficiently big that $cτ(\cpmone)\lsim$few cm and $\mgl$ is large, there is a significant possibility that the limits on $\mcpmone$ based on LEP2 data cannot be extended at the Tevatron. If $cτ(\cpmone)>$few cm, relatively background-free signals exist that will give a clear signal of $\cpmone$ production (for some range of $\mcpmone$) even if $\mgl$ is very large.

hep-ph↗
arXiv1999

Analysis of Narrow s-channel Resonances at Lepton Colliders

The procedures for studying a single narrow s-channel resonance or nearly degenerate resonances at a lepton collider, especially a muon collider, are discussed. In particular, we examine four methods for determining the parameters of a narrow s-channel resonance: scanning the resonance, measuring the convoluted cross section, measuring the Breit-Wigner area, and sitting on the resonance while varying the beam energy resolution. This latter procedure is new and appears to be potentially very powerful. Our focus is on computing the errors in resonance parameters resulting from uncertainty in the beam energy spread. Means for minimizing these errors are discussed. The discussion is applied to the examples of a light SM-Higgs, of the lightest pseudogoldstone boson of strong electroweak breaking, and of the two spin-1 resonances of the Degenerate BESS model (assuming that the beam energy spread is less than their mass splitting). We also examine the most effective procedures for nearly degenerate resonances, and apply these to the case of Degenerate BESS resonances with mass splitting of order the beam energy spread.

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