J.F. Gunion

The Snowmass points and slopes: Benchmarks for SUSY searches

Abstract. The ”Snowmass Points and Slopes” (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 ”Snowmass Workshop on the Future of Particle Physics” as a consensus based on different existing proposals.

Diffractive leptoproduction of vector mesons in QCD

We demonstrate that the distinctive features of the forward differential cross section of diffractive leptoproduction of a vector meson can be legitimately calculated in perturbative QCD in terms of the light-cone [ital q[bar q]] wave function of the vector meson and the gluon distribution of the target. In particular, we calculate the [ital Q][sup 2] and nuclear dependence of the diffractive leptoproduction of vector mesons and estimate the cross section. The production of longitudinally polarized vector mesons by longitudinally polarized virtual photons is predicted to be the dominant component, yielding a cross section behaving as [ital Q][sup [minus]6]. The nuclear dependence of the diffractive cross sections, which follows from a factorization theorem in perturbative QCD, provides important tests of color transparency as well as constraints on the shadowing of the gluon structure functions and the longitudinal structure functions of nuclei.

Global fit to Higgs signal strengths and couplings and implications for extended Higgs sectors

The most recent LHC data have provided a considerable improvement in the precision with which various Higgs production and decay channels have been measured. Using all available public results from ATLAS, CMS and the Tevatron, we derive for each final state the combined confidence level contours for the signal strengths in the (gluon fusion + ttH associated production) versus (vector boson fusion + VH associated production) space. These “combined signal strength ellipses” can be used in a simple, generic way to constrain a very wide class of New Physics models in which the couplings of the Higgs boson deviate from the Standard Model prediction. Here, we use them to constrain the reduced couplings of the Higgs boson to up-quarks, down-quarks/leptons and vector boson pairs. We also consider New Physics contributions to the loop-induced gluon-gluon and photon-photon couplings of the Higgs, as well as invisible/unseen decays. Finally, we apply our fits to some simple models with an extended Higgs sector, in particular to Two-Higgs-Doublet models of Type I and Type II, the Inert Doublet model, and the Georgi–Machacek triplet Higgs model.

CERN LHC analysis of the strongly interacting WW system: Gold-plated modes.

We study the gold-plated purely leptonic signal and background rates at the CERN LHC for the {ital ZZ}, {ital W}{sup +}{ital W}{sup {minus}}, {ital W}{sup {plus_minus}}{ital Z}, and {ital W}{sup {plus_minus}}{ital W}{sup {plus_minus}} final states associated with strongly interacting electroweak symmetry breaking. We work at an energy of {radical}{ital s} =14 TeV, and develop a combination of back-to-back leptonic, central-jet-vetoing, and forward-jet-tagging cuts that suppresses the standard-model backgrounds. We find that the LHC with an annual luminosity of 100 fb{sup {minus}1} will achieve a reasonably good sensitivity to the physics of strongly interacting electroweak symmetry breaking.

Using back scattered laser beams to detect CP violation in the neutral Higgs sector

Abstract We demonstrate that the ability to polarize the photons produced by back-scattering laser beams at a TeV scale linear e + e − collider could make it possible to determine whether or not a neutral Higgs boson produced in photon-photon collisions is a CP eigenstate. The relative utility of different types of polarization is discussed. Asymmetries that are only non-zero if the Higgs boson is a CP mixture are defined, and their magnitudes illustrated for a two-doublet Higgs model with CP -violating neutral sector.

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 CERN {ital e}{sup +}{ital e}{sup {minus}} collider LEP2 and the NLC (next linear {ital e}{sup +}{ital e}{sup {minus}} collider) 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 (lightest supersymmetric particle)], and invisibly decaying sneutrinos. The importance of particular features of the detectors is discussed. {copyright} {ital 1996 The American Physical Society.}

Short distance counting rules for low pT fragmentation

Abstract Recent experimental data provides evidence in favor of a model in which hadronic collisions are initiated by a factorizing mechanism, such as gluon exchange. We propose that fast fragments resulting from such collisions arise via quantum chromodynamics diagrams in which the required quarks and/or antiquark are produced in “point-like” fashion; these can be shown to be the leading diagrams as x , the momentum fraction of the secondary hadron, approaches 1. We obtain good agreement with the observed power law behaviors, dN / dx ∼ (1 − x ) n , of single particle low p T spectra.

Using decay angle correlations to detect CP violation in the neutral Higgs sector

Abstract We demonstrate that decay angle correlations in τ−τ+ and tt 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 e+e− → ZH and μ+μ− → H 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 tt mode is introduced.

Determining the {ital t{bar t}} and {ital ZZ} Couplings of a Neutral Higgs Boson of Arbitrary {ital CP} Nature at the Next Linear Collider

The optimal procedure for extracting the coefficients of different components of an observable which takes the form of unknown coefficients times functions of known form is developed. When applied to {ital e}{sup +}{ital e}{sup {minus}}{r_arrow}{ital t{bar t}}+ Higgs production at {radical}{ital s}=1 TeV and integrated luminosity times efficiency of 50 fb{sup {minus}1}, we find that the {ital t{bar t}}{r_arrow} Higgs {ital CP}-even and {ital CP}-odd couplings and, to a lesser extent, the {ital ZZ}{r_arrow}Higgs ({ital CP}-even) coupling can be extracted with reasonable errors, assuming the Higgs sector parameter choices yield a significant production rate. The composition of a mixed-{ital CP} Higgs eigenstate can be determined with sufficient accuracy that a standard-model-like {ital CP}-even Higgs boson can be distinguished from a purely {ital CP}-odd Higgs boson at a high level of statistical significance, and vice versa. {copyright} {ital 1996 The American Physical Society.}

Detecting the tb decays of a charged Higgs boson at a hadron supercollider

Abstract We demonstrate that detection of a charged Higgs boson decaying via H ± → tb will be possible at the LHC in gg → H − bt events, provided the H + → tb coupling, m t ≲ 100 GeV, and reasonably effecient and pure b -tagging can be performed.