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V. Barger

Publications and source records attributed to V. Barger.

At least 163 records · Page 9Linked to original sources
arXiv1994

Z Plus Four Jets Production in Hadronic Collisions

We present first results of $Z+4$ jet cross sections at the Tevatron $p\bar p$ collider with heavy quark flavor identification. The $Z + 4$ jet channel is of particular interest as a normalizer for the $W +4$ jet background to top quark signals, as a background to a possible $t\to cZ$ flavor-changing neutral-current (FCNC) decay signal, and as a background to missing-$p_T$ signals from gluino pairs. We also calculate the different heavy flavor contributions to $W+4$ jet production. The MADGRAPH program is used to generate all leading order subprocess helicity amplitudes. We present Monte Carlo studies with separation and acceptance criteria suitable for the Tevatron experimental analyses.

hep-ph↗
arXiv1994

Calculation of Z Plus Four Jet Production at the Tevatron

We present the first calculation of $Z+4$ jet production with heavy quark flavor identification at the Tevatron $p\bar p$ collider. The $Z + 4$ jet channel is especially interesting as a normalizer for the $W +4$ jet background to top quark signals, as a background to a possible $t\to cZ$ flavor-changing neutral-current (FCNC) decay signal, and as a background to missing-$p_T$ signals from gluino pairs. We also calculate the contributions to $W+4$ jet production from all the different heavy-flavor final states. The MADGRAPH program is used to generate all leading order subprocess helicity amplitudes. We present Monte Carlo results with separation and acceptance criteria suitable for the Tevatron experimental analyses. The dependence of the cross sections on experimental cuts and the theoretical ambiguities due to the scale dependence are discussed. The predicted ($W+4$ jet)/($Z+4$ jet) ratio is insensitive to most of these choices.

hep-ph↗
arXiv1994

Constraints on SUSY-GUT unification from $b\to sγ$ decay

The top-quark Yukawa infrared fixed-point solution of the renormalization group equations, with minimal supersymmetry and GUT unification, defines a low-energy spectrum of supersymmetric particle masses in terms of a few GUT-scale parameters assuming universal boundary conditions. We give predictions in this model for the inclusive $b\to sγ$ branching fraction and investigate the impact of non-universal scalar mass boundary conditions. We find our results do not depend significantly on the value of the GUT-scale trilinear coupling $A^G$. The small $\tan β$ region favors predictions for the inclusive $b\to sγ$ branching fraction close to that of the Standard Model value. Nevertheless forthcoming experimental results can eliminate some regions of the GUT parameter space.

hep-ph↗
arXiv1994

Multilepton SUSY signals from R-parity violation at the Tevatron

The expected trilepton signals from $p \bar p \to χ^\pm_1χ^0_2 \to (χ^0_1\ell^\pmν) (χ^0_1\ell'^+\ell'^-) $ will be converted into hadronically quiet multilepton signals, if the two final $χ^0_1$ have leptonic $R$-parity-violating (RPV) decays $χ^0_1 \to \ell \ell' ν$. We make illustrative calculations of the acceptance for these spectacular RPV signals, and point out that distinctive multilepton signals are possible even when the $R$-conserving trilepton signals are blocked by the ``spoiler mode" $χ^0_2 \to h^0 χ^0_1$. Other channels such as $p\bar p\to χ_1^\pm χ_2^0 \to (χ_1^0\ell^\pmν) (χ_1^0νν)$, $p\bar p\to χ_1^\pm χ_1^0 \to (χ_1^0\ellν)χ_1^0$ and $p\bar p\toχ_1^+χ_1^-\to(χ_1^0\ell^+ν)(χ_1^0\ell'^-ν)$ can also give quiet multileptons from RPV. We investigate these signals in the context of supersymmetric models with radiative electroweak symmetry breaking, using examples in the low-$\tanβ$ $λ_t$ fixed-point region.

hep-ph↗
arXiv1994

Singlet quarks beyond the top at the Tevatron?

The first evidence for the top quark at the Tevatron may indicate a cross section higher than the QCD expectation. We consider the possibility that isosinglet heavy quarks may be contributing to the signal and discuss ways of testing this possibility. For example, a charge $\case2/3$ singlet quark, approximately degenerate and mixing with the top quark, would effectively double the standard top signals. A charge $-\case1/3$ singlet quark mixing with the bottom quark would not affect top signals but would generate excess $Z+{}$multijet events with a $b$-tag.

hep-ph↗
arXiv1994

Supergravity Solutions in the Low-$\tanβ$ $ λ_t$ Fixed Point Region

There has been much discussion in the literature about applying the radiative electroweak symmetry breaking (EWSB) requirement to GUT models with supergravity. We motivate and discuss the application of the EWSB requirement to the low $\tanβ$ fixed-point region and describe the solutions we find.

hep-ph↗
arXiv1994

Production of Weak Bosons and Higgs Bosons at e-e- Colliders

We present calculations of cross sections for single $W^-$ and $Z$ production and $W^-W^-, W^-Z, W^-γ, ZZ$, and $W^+W^-$ pair production within the Standard Model at $e^-e^-$ linear colliders. We evaluate Standard-Model Higgs boson production in the channels $e^-e^- \to e^-e^- H$, $e^-νW^- H$, and $e^-e^- ZH$. We also illustrate the enhancements in the $W^-W^-$ cross section that would result from a strongly-interacting Higgs sector or from a $H^{--}$ resonance in a Higgs doublet + triplet model.

hep-ph↗
arXiv1994

Implications of Supersymmetric Grand Unification

Unification of the interactions of the Standard Model is possible in its simplest supersymmetric extension. The implications of the $λ_t$ fixed-point solution on the top mass and on Higgs phenomenology is discussed. Expected correlations between the masses of various supersymmetric particles are detailed.

hep-ph↗
arXiv1993

Single-Lepton Top Signals with a b-Tag at the Tevatron

Events with a leptonic W-decay plus jets should contain top-quark signals, but a QCD W+jets background must be separated. We compare transverse W-momentum, jet multiplicity, and b-tagging separation criteria, and find that the main background after tagging comes from mistagging. We illustrate how to extract the mass m_t via event reconstructions and how to confirm signal purity by lepton angular distributions.

hep-ph↗
arXiv1993

Natural Conservation of R Parity in Supersymmetry

Since baryon number B and lepton number L are no longer automatically conserved once the standard model is extended to include supersymmetry, the usually assumed conservation of R parity is an imposed condition. For a more satisfactory realization of supersymmetry, we propose here a new model which conserves R automatically. It is unifiable under SO(14) and has exotic fermions at the 100 GeV scale. One important result is the enhancement of the Higgs-boson decay rates into two gluons and into two photons by factors of 25 and 15 respectively.

hep-ph↗
arXiv1993

Heavy Charged Higgs Signals at the LHC

We discuss the viability of $gb \to tH \to ttb$ charged-Higgs signals at the proposed LHC $pp$ supercollider, in the decay channel $tt \to (bq \bar q')(b \ell ν)$. Here one top quark decays hadronically and one semileptonically, with all three $b$-quarks giving flavor-tagged jets. The principal backgrounds come from $ttg,ttq,ttc$ and $ttb$ continuum production, with possible mis-tagging of $g,q$ and $c$. We conclude that significant signals can be separated from these backgrounds, for limited but interesting ranges of the parameters $m_{H\pm}$ and $\tanβ$, with the LHC energy and luminosity.

hep-ph↗
arXiv1993

The Supersymmetric Particle Spectrum

We examine the spectrum of supersymmetric particles predicted by grand unified theoretical (GUT) models where the electroweak symmetry breaking is accomplished radiatively. We evolve the soft supersymmetry breaking parameters according to the renormalization group equations (RGE). The minimization of the Higgs potential is conveniently described by means of tadpole diagrams. We present complete one-loop expressions for these minimization conditions, including contributions from the matter and the gauge sectors. We concentrate on the low $\tan β$ fixed point region (that provides a natural explanation of a large top quark mass) for which we find solutions to the RGE satisfying both experimental bounds and fine-tuning criteria. We also find that the constraint from the consideration of the lightest supersymmetric particle as the dark matter of the universe is accommodated in much of parameter space where the lightest neutralino is predominantly gaugino. The supersymmetric mass spectrum displays correlations that are model-independent over much of the GUT parameter space.

hep-ph↗
arXiv1993

Yukawa Coupling Evolution In SUSY GUTS

The scaling behavior and fixed points in the evolution of fermion Yukawa couplings and mixing angles are discussed. The relevance of fixed points in determining the top quark mass is described.

hep-ph↗
arXiv1993

RGE Results for Supersymmetric GUTS

The scaling behavior of gauge couplings and fermion Yukawa couplings in the minimal supersymmetric model is discussed. The relevance of the top quark Yukawa coupling fixed point in establishing the top quark mass is described. The evolution of mixing angles is presented.

hep-ph↗
arXiv1993

Collider Physics 1993

These lectures survey the present situation and future prospects in selected areas of particle physics phenomenology: (1) the top quark, (2) the Higgs boson in the Standard Model, (3) strong $WW$ scattering, (4) supersymmetry, (5) the Higgs sector in minimal supersymmetry, and (6) low-energy constraints on supersymmetry.

hep-ph↗
arXiv1993

Supersymmetry with Grand Unification

Supersymmetry (SUSY) has many well known attractions, especially in the context of Grand Unified Theories (GUTs). SUSY stabilizes scalar mass corrections (the hierarchy problem), greatly reduces the number of free parameters, facilitates gauge coupling unification, and provides a plausible candidate for cosmological dark matter. In this conference report we survey some recent examples of progress in SUSY-GUT applications.

hep-ph↗
arXiv1993

Event shape criteria for single-lepton top signals

Single-lepton plus jets signals from $t\bar t$ production at hadron colliders generally give more spherically symmetrical events than the principal backgrounds from $W$ production. We show that sphericity and aplanarity criteria, applied to lepton plus neutrino plus four jet final states at the Fermilab Tevatron $p\bar p$ collider, help to discriminate; they can be used either to validate an eventual top signal or simply to reduce background. An alternative circularity criterion in the transverse plane is less successful.

hep-ph↗