arXiv subjects
Publications and source records attributed to J. F. Gunion.
We outline several well-motivated models in which GUT boundary conditions for SUSY breaking are non-universal. The diverse phenomenological implications of the non-universality for SUSY discovery at LEP2, the Tevatron, the LHC and the NLC are sketched.
We update our earlier results regarding detection of $gg\to b\anti b h\to 4b$ ($h=h^0,H^0,A^0$) to incorporate the very high $b$-tagging efficiencies and purities that are now anticipated at the LHC. New results for the Tev$^*$ are given, and indicate substantial potential for these modes. The complementarity of the $H^0\to h^0h^0 \to 4b$ final state mode is illustrated for the LHC. The latest radiative corrections to the Higgs sector are incorporated.
We discuss the excellent prospects for a detailed study of a strongly interacting electroweak sector at a muon collider with c.m. energy $\rts\sim 4\tev$. For expected luminosity of $L=200-1000\fbi$ per year, $\mup\mum$ and $\mup\mup$ (or $\mum\mum$) collisions can be used to study longitudinal $\wp\wm$ and $\wp\wp$ (or $\wm\wm$) scattering with considerable precision. In particular, detailed measurements of the distribution in the $VV$ pair masses ($V=\wpm,Z$) will be possible. The shape and magnitude of these distributions will provide a powerful tool for determining the nature of strong gauge boson interactions. Event rates will be large enough that projection techniques can be used to directly isolate final states with different polarizations of the $V$'s and verify that the strong interaction cross section excess is mainly in the longitudinal-longitudinal mode.
Future muon colliders will have remarkable capability for revealing and studying physics beyond the Standard Model. A first muon collider with variable c.m.\ energy in the range $\sqrt s = 100$ to 500~GeV provides unique opportunities for discovery and factory-like production of Higgs bosons in the $s$-channel. For excellent (but achievable) machine energy resolution, the total width and $\mupmum$ coupling of a SM-like Higgs boson with mass $\lsim 2\mw$ (as particularly relevant to supersymmetric/GUT models) can be directly measured with substantial precision. Multiplication of measured branching ratios by the total width yields the corresponding couplings. As a result, the light CP-even SM-like Higgs of the minimal supersymmetric model can be distinguished from the Higgs of the minimal Standard Model over a larger portion of supersymmetric parameter space than otherwise possible. Scan discovery and detailed measurements of total widths and some partial widths of the heavier CP-even and CP-odd Higgs bosons of the minimal supersymmetric model are possible for Higgs masses up to the maximum $\rts$. The excellent energy resolution, absence of beamstrahlung and mild bremsstrahlung at the first muon collider would allow increased precision for the measurement of $\mt$ and $\mw$ via $t\anti t$ and $\wp\wm$ threshold studies. A multi-TeV $\mm$ collider would open up the realm of physics above the 1 TeV scale. Pair production of supersymmetric particles up to masses even higher than consistent with naturalness would be possible, guaranteeing that the heavier gauginos and possibly very massive squarks would be abundantly produced and that their properties could be studied. Very importantly, the multi-TeV collider would guarantee our ability to perform a detailed study of a strongly-interacting
The optimal procedure for extracting the coefficients of different components of a cross section which takes the form of unknown coefficients times functions of known kinematical form is developed. When applied to $\epem\to t\anti t+$Higgs production at $\rts=1\tev$ and integrated luminosity of $200\fbi$, we find that the $t\anti t\to$Higgs CP-even and CP-odd couplings and, to a lesser extent, the $ZZ\to$Higgs (CP-even) coupling can be extracted with reasonable errors, assuming the Higgs sector parameter choices yield a significant production rate. Indeed, the composition of a mixed-CP Higgs eigenstate can be determined with sufficient accuracy that a SM-like CP-even Higgs boson can be distinguished from a purely CP-odd Higgs boson at a high level of statistical significance, and vice versa.
We discuss the capabilities of future muon colliders to resolve important particle physics questions. A collider with c.m. energy $\sqrt s = 100$ to 500~GeV offers the unique opportunity to produce Higgs bosons in the $s$-channel and thereby measure the Higgs masses, total widths and several partial widths to high precision. At this same machine, $t\bar t$ and $W^+W^-$ threshold studies would yield superior precision in the determination of $m_t$ and $m_W$. A multi-TeV $μ^+μ^-$ collider would open up the realm of physics above the 1 TeV scale, allowing, for example, copious production of supersymmetric particles up to the highest anticipated masses or a detailed study of the strongly-interacting scenario of electroweak symmetry breaking.
Techniques and strategies for discovering and measuring the properties of Higgs bosons via $s$-channel production at a $μ^+μ^-$ collider, and the associated requirements for the machine and detector, are discussed in detail. The unique feature of $s$-channel production is that, with good energy resolution, the mass, total width and partial widths of a Higgs boson can be directly measured with remarkable accuracy in most cases. For the expected machine parameters and luminosity the Standard Model (SM) Higgs boson $\hsm$, with mass $\lsim 2\mw$, the light $\hl$ of the minimal supersymmetric Standard Model (MSSM), and the heavier MSSM Higgs bosons (the CP-odd $\ha$ and the CP-even $\hh$) can all be studied in the $s$-channel, with the heavier states accessible up to the maximal $\sqrt s$ over a large fraction of the MSSM parameter space. In addition, it may be possible to discover the $\ha$ and $\hh$ by running the collider at full energy and observing excess events in the bremsstrahlung tail at lower energy. The integrated luminosity, beam resolution and machine/detector features required to distinguish between the $\hsm$ and $\hl$ are delineated.
We review the search for the standard Higgs boson, the Higgs bosons of the supersymmetric standard model, and Higgs bosons from a variety of other models at present and future colliders.
We demonstrate that certain weighted moments of $t\anti t \h$ production can provide a determination of the CP nature of a light neutral Higgs boson produced and detected in this mode at the CERN LHC.
We demonstrate that detection of the heavier minimal supersymmetric model CP-even Higgs boson $H^0$ will be possible at the LHC via its $H^0\to h^0h^0\to 4b$ and/or $H^0\to A^0A^0\to 4b$ decay channels for significant portions of the $( m_{A^0},\tanβ)$ model parameter space. At low $ m_{A^0}$ ($\lsim 60\gev$), {\it both} the $H^0\to A^0A^0\to 4b$ and $H^0\to h^0h^0\to 4b$ modes yield a viable signal for most $\tanβ$ values; viability for the $h^0h^0$ channel extends up to $\mhh\sim 2\mt$ when the model parameter $\tanβ$ is not large. At the Tevatron, the $h^0h^0$ and $A^0A^0$ channels are both potentially viable at low $ m_{A^0}$ for sufficiently good $b$-tagging efficiency and purity.
The doubly charged Higgs bosons $Δ^{--}$ that are present in exotic Higgs representations can have lepton-number-violating couplings to $e^-e^-$. We discuss general constraints and phenomenology for the $Δ^{--}$ and demonstrate that extremely small values for the $e^-e^-\rightarrowΔ^{--}$ coupling (some 8 orders of magnitude smaller than the current limit) would produce observable signals for $Δ^{--}$ production in direct $s$-channel production at an $e^-e^-$ collider.
A brief overview of the physics capabilities of a $μ^+μ^-$ collider is given, with particular focus on special Higgs sector opportunities.
We investigate the phenomenology of minimal four-family MSSM supergravity theories containing an additional generation of heavy fermions along with their superpartners. We demand: gauge coupling constant unification at high energy scales; perturbative values for all Yukawa couplings for energy scales $\leq \mgut$; radiative electroweak symmetry breaking via renormalization group evolution; and a neutral LSP. The perturbative constraints imply a light fourth-family quark and lepton spectrum, and $\tanb\lsim 3$. The lightest CP-even Higgs mass is increased. Fourth-family Yukawa coupling contributions to the evolution of scalar masses lead to unexpected mass hierarchies; \eg\ the $\staupone$ is generally the lightest slepton and the lightest squark is the $\wt\bpr_1$. A significant lower bound is placed on the gluino mass by the requirement that the $\staupone$ not be the LSP. Sleptons of the first two families are much more massive compared to the LSP and other neutralinos and charginos than in the three-family models, and could easily lie beyond the reach of a $\sqrt s=500\gev$ $\epem$ collider. Relations between slepton masses and gaugino masses are shown to be very sensitive to the presence of a fourth generation. The most important near-future experimental probes of the four-family models are reviewed. A scenario with $\mt\sim\mw$ and $t\rta {\wt t_1}\cnone$ is shown to be inconsistent with universal soft-SUSY-breaking boundary conditions. Full four-family evolution of $α_s$ is shown to lead to a significant enhancement in inclusive jet and di-jet spectra at Tevatron energies when all sparticle masses are near their lower bounds.
We demonstrate that the detection of the SM and MSSM Higgs bosons will be possible at the LHC via $t\anti t b\anti b$ and $b\anti b b\anti b$ final state, provided $b$-tagging can be performed with good efficiency and purity.
We demonstrate that decay angle correlations in $\taum\taup$ and $t\anti t$ decay modes could allow a determination of whether or not a neutral Higgs boson is a CP eigenstate. Sensitivity of the correlations is illustrated in the case of the $\epem\rta Z \hn$ and $\mupmum\rta \hn$ production processes for a two-doublet Higgs model with CP-violating neutral sector. A very useful technique for minimizing `depolarization' factor suppressions of the correlations is introduced.
This working group report focuses on the physics potential of $μ^+μ^-$ colliders beyond what can be accomplished at linear $e^+e^-$ colliders and the LHC. Particularly interesting possibilities include (i)~$s$-channel resonance production to discover and study heavy Higgs bosons with $ZZ$ and $WW$ couplings that are suppressed or absent at tree-level (such as the $H$ and $A$ Higgs bosons of supersymmetric models), (ii)~study of the strongly interacting electroweak sector, where higher energies give larger signals, and (iii)~measurements of the masses and properties of heavy supersymmetric particles.
We demonstrate that decay angle correlations in $\taum\taup$ and $t\anti t$ decay modes could allow a determination of whether or not a neutral Higgs boson is a CP eigenstate. Sensitivity of the correlations is illustrated in the case of the $\epem\rta Z \hn$ and $\mupmum\rta \hn$ production processes for a two-doublet Higgs model with CP-violating neutral sector. A very useful technique for minimizing `depolarization-factor' suppressions of the correlations in the $t\anti t$ mode is introduced.
We demonstrate that simultaneous detection of two of the neutral Higgs bosons of the Minimal Supersymmetric Model will be possible at the LHC in the $b\anti b b\anti b$ final state, provided $\tanb$ is large and $b$-tagging can be performed with good efficiency and purity. This mode enhances the already established guarantee that there is no region of supersymmetric parameter space for which {\it none} of the Higgs bosons of the model can be seen at the LHC.