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V. Barger

Publications and source records attributed to V. Barger.

At least 109 records · Page 6Linked to original sources
arXiv1999

Trilepton Signature of Minimal Supergravity at the Upgraded Tevatron

The prospects for detecting trilepton events ($\ell = e$ or $μ$) from chargino-neutralino ($χ^\pm_1 χ^0_2$) associated production are investigated for the upgraded Fermilab Tevatron Collider in the context of the minimal supergravity model (mSUGRA). In some regions of parameter space, $χ^\pm_1$ and $χ^0_2$ decay dominantly into final states with $τ$ leptons and the contributions from $τ-$leptonic decays enhance the trilepton signal substantially when soft cuts on lepton transverse momenta are used. Additional sources of the mSUGRA trilepton signal and dominant irreducible backgrounds are discussed. The dilepton ($\ell^+\ell^-$) invariant mass distribution near the endpoint is considered as a test of mSUGRA mass relations. Discovery contours for $p\bar{p} \to 3\ell +X$ at 2 TeV with an integrated luminosity of 2 fb$^{-1}$ to 30 fb$^{-1}$ are presented in the mSUGRA parameter space of $(m_0,m_{1/2})$ for several choices of $\tanβ$.

hep-ph↗
arXiv1999

Neutrino Decay and Atmospheric Neutrinos

We reconsider neutrino decay as an explanation for atmospheric neutrino observations. We show that if the mass-difference relevant to the two mixed states ν_μand ν_τis very small (< 10^{-4} eV^2), then a very good fit to the observations can be obtained with decay of a component of ν_μto a sterile neutrino and a Majoron. We discuss how the K2K and MINOS long-baseline experiments can distinguish the decay and oscillation scenarios.

hep-ph↗
arXiv1999

Long Baseline Neutrino Physics with a Muon Storage Ring Neutrino Source

We examine the physics capabilities of known flavor neutrino beams from intense muon sources. We find that long-baseline neutrino experiments based on such beams can provide precise measurements of neutrino oscillation mass and mixing parameters. Furthermore, they can test whether the dominant atmospheric neutrino oscillations are ν_μ--> ν_τand/or ν_μ--> ν_s, determine the ν_μ--> ν_e content of atmospheric neutrino oscillations, and measure ν_e --> ν_τappearance. Depending on the oscillation parameters, they may be able to detect Earth matter and CP violation effects and to determine the ordering of some of the mass eigenstates.

hep-ph↗
arXiv1999

Astrophysical Constraints on Large Extra Dimensions

In the Kaluza-Klein (KK) scenario with n large extra dimensions where gravity propagates in the 4+n dimensional bulk of spacetime while gauge and matter fields are confined to a four dimensional subspace, the light graviton KK modes can be produced in the Sun, red giants and supernovae. We study the energy-loss rates through photon-photon annihilation, electron-positron annihilation, gravi-Compton-Primakoff scattering, gravi-bremsstrahlung and nucleon-nucleon bremsstrahlung, and derive lower limits to the string scale M_S. The most stringent lower limit obtained from SN1987A leads to $M_S> 30 - 130$ TeV (2.1-9.2 TeV) for the case of two (three) large extra dimensions.

hep-ph↗
arXiv1999

Majorana Neutrino Masses from Neutrinoless Double Beta Decay and Cosmology

When three Majorana neutrinos describe the solar and atmospheric neutrino data via oscillations, a nonzero measurement of neutrinoless double beta ($0νββ$) decay can determine the sum of neutrino masses $\sum m_ν$ if the solar solution has small-angle mixing, and place a lower bound on $\sum m_ν$ for large-angle solar mixing. If in addition a nonzero $\sum m_ν$ is deduced from cosmology, the neutrino mass spectrum may be uniquely specified for some ranges of neutrino parameters. For $\sum m_ν> 0.75$ eV, the small-angle solar solution is excluded by the current upper limit on neutrinoless double beta decay. In models with maximal solar mixing the $CP$ phases of the neutrinos may be strongly constrained by stringent upper bounds on $0νββ$ decay.

hep-ph↗
arXiv1999

Seasonal and Energy Dependence of Solar Neutrino Vacuum Oscillations

We make a global vacuum neutrino oscillation analysis of solar neutrino data, including the seasonal and energy dependence of the recent Super-Kamiokande 708-day results. The best fit parameters for ν_e oscillations to an active neutrino are δm^2 = 4.42\times10^{-10} eV^2, \sin^2 2θ= 0.93. The allowed mixing angle region is consistent with bi-maximal mixing of three neutrinos. Oscillations to a sterile neutrino are disfavored. Allowing an enhanced hep neutrino flux does not significantly alter the oscillation parameters.

hep-ph↗
arXiv1999

The Pattern of Neutrino Masses and How to Determine It

Our knowledge of the neutrino sector of the Standard Model has recently undergone a revolution. Deficits of the atmospheric muon neutrino flux and the solar electron neutrino flux compared to their predicted values can be understood in terms of neutrino oscillations and we can therefore infer that neutrinos have non-degenerate masses. Additional but somewhat less secure evidence for \barν_μ\to \barν_e and ν_μ\toν_e oscillations has been found in the LSND accelerator experiment. Because these experiments have widely different L/E_νranges (\approx 10 to 10^4 km/GeV for atmospheric, \approx 10^{11} for solar, and \approx 1 for LSND), the mass-squared differences required to explain the phenomena must be distinct. Given the observations, an important next step is to deduce the pattern of neutrino masses and mixings. Such studies depend on the number of neutrinos. The invisible width of the Z-boson measured in LEP experiments gives N_ν= 2.993\pm 0.011, consistent with the usual ν_e, ν_μand ν_τ"active" neutrinos. But there may also be right-handed "sterile" neutrinos with no weak interactions. Only the observation of oscillations of the active neutrinos to sterile neutrinos can test for their existence. In the following, we first discuss the atmospheric and solar neutrino data in a 3-neutrino framework and then later generalize our considerations to include the LSND data with oscillations of four neutrinos.

hep-ph↗
arXiv1999

Global Three-Neutrino Vacuum Oscillation fits to the Solar and Atmospheric Anomalies

We determine the three-neutrino mixing and mass parameters that are allowed by the solar and atmospheric neutrino data when vacuum oscillations are responsible for both phenomena. The global fit does not appreciably change the allowed regions for the parameters obtained from effective two-neutrino fits. We discuss how measurements of the solar electron energy spectrum below 6.5 GeV in Super-Kamiokande and seasonal variations in the Super-Kamiokande, $^{71}$Ga, and BOREXINO experiments can distinguish the different solar vacuum solutions.

hep-ph↗
arXiv1999

Neutrino Mixing, CP/T Violation and Textures in Four-Neutrino Models

We examine the prospects for determining the neutrino mixing matrix and for observing CP and T violation in neutrino oscillations in four-neutrino models. We focus on a general class of four-neutrino models with two pairs of nearly degenerate mass eigenstates separated by approximately 1 eV, which can describe the solar, atmospheric and LSND neutrino data. We present a general parametrization of these models and discuss in detail the determination of the mixing parameters and the mass matrix texture from current and future neutrino data in the case where $ν_e$ and $ν_μ$ each mix primarily with one other neutrino. We find that measurable CP/T violation in long-baseline experiments, with amplitude at the level of the LSND signal, is possible given current experimental constraints. Also, additional oscillation effects in short- and long-baseline experiments may be measurable in many cases. We point out that, given separate scales for the mass-squared differences of the solar and atmospheric oscillations, observable CP/T violation effects in neutrino oscillations signals the existence of a sterile neutrino. We examine several textures of the neutrino mass matrix and determine which textures can have measurable CP/T violation in neutrino oscillations in long-baseline experiments. We also briefly discuss some possible origins of the neutrino mass terms in straightforward extensions of the Standard Model.

hep-ph↗
arXiv1998

Inferred 4.4 eV Upper Limits on the Muon- and Tau-Neutrino Masses

By combining experimental constraints from atmospheric and solar neutrino oscillations and the tritium beta decay endpoint, we infer upper limits of 4.4 eV on the $ν_μ$ and $ν_τ$ masses, if the universe consists of three neutrinos. For hierarchical mass spectra $m_3 \gg m_1, m_2$ or $m_3 \simeq m_2 \gg m_1$ we infer that $m_{ν_α} \lsim 0.08$ eV for $α= e, μ, τ$. In a four neutrino universe, and assuming neutrino oscillations also account for the LSND experimental results, $m_{ν_α} \lsim 5.4$ eV. We also obtain lower limits on the masses.

hep-ph↗
arXiv1998

Four-Neutrino Oscillations

Models with three active neutrinos and one sterile neutrino can naturally account for maximal oscillations of atmospheric neutrinos, explain the solar neutrino deficit, and accommodate the results of the LSND experiment. The models predict either $ν_e\toν_τ$ or $ν_e\toν_s$ oscillations in long-baseline experiments with the atmospheric $δm^2$ scale and amplitude determined by the LSND oscillations.

hep-ph↗
arXiv1998

Generalized Neutrino Mixing from the Atmospheric Anomaly

We determine the neutrino mixing and mass parameters that are allowed by the Super-Kamiokande atmospheric neutrino data in a three-neutrino model with one mass-squared difference contributing to the oscillations. We find that although $ν_μ\toν_τ$ oscillations are favored, $ν_μ\to ν_e$ oscillations with amplitude as large as 0.18 are allowed even after accounting for the limit from the CHOOZ reactor experiment. The range of allowed parameters permit observable $ν_μ\leftrightarrowν_e$ and $ν_e\toν_τ$ oscillations in future long-baseline experiments.

hep-ph↗
arXiv1998

Bi-Maximal Mixing of Three Neutrinos

We show that if the solar and atmospheric data are both described by maximal vacuum oscillations at the relevant mass scales then there exists a unique mixing matrix for three neutrino flavors. The solution necessarily conserves CP and automatically implies that there is no disappearance of atmospheric $ν_e$, consistent with indications from the Super-Kamiokande experiment. We also investigate the consequences for three-neutrino mixing if the solar and atmospheric oscillations exhibit mixing that is large but not maximal. For non-maximal mixing $ν_e\leftrightarrowν_τ$ and $ν_e\leftrightarrowν_μ$ oscillations are predicted that may be observable in future long-baseline experiments.

hep-ph↗
arXiv1998

Variations on Four-Neutrino Oscillations

We make a model-independent analysis of all available data that indicate neutrino oscillations. Using probability diagrams, we confirm that a mass spectrum with two nearly degenerate pairs of neutrinos separated by a mass gap of $\simeq1$ eV is preferred over a spectrum with one mass eigenstate separated from the others. We derive some new relations among the four-neutrino mixing matrix elements. We design four-neutrino mass matrices with three active neutrinos and one sterile neutrino that naturally incorporate maximal oscillations of atmospheric $ν_μ$ and explain the solar neutrino and LSND results. The models allow either a large or small angle MSW or vacuum oscillation description of the solar neutrino deficit. The models predict (i) oscillations of either $ν_e \to ν_τ$ or $ν_e \toν_s$ in long-baseline experiments at $L/E \gg 1$ km/GeV, with amplitude determined by the LSND oscillation amplitude and argument given by the atmospheric $δm^2$, and (ii) the equality of the $ν_e$ disappearance probability, the $ν_μ$ disappearance probability, and the LSND $ν_μ\toν_e$ appearance probability in short-baseline experiments.

hep-ph↗
arXiv1998

Trilepton Signal of Minimal Supergravity at the Tevatron Including $τ$-lepton Contributions

The trilepton signal with missing transverse energy ($3\ell+\notE_T$, with $\ell = e$ or $μ$) from chargino-neutralino ($χ^\pm_1 χ^0_2$) associated production and decays is studied for the upgraded Fermilab Tevatron Collider with 2 TeV center of mass energy and integrated luminosity of 2 fb$^{-1}$ (MI) to 20 fb$^{-1}$ (TeV33). In some regions of parameter space in the minimal supergravity model, $χ^\pm_1$ and $χ^0_2$ decay dominantly into final states with $τ$ leptons via real or virtual $\tildeτ_1$ sleptons. The contributions from $τ-$leptonic decays increase the trilepton signal from $χ^\pm_1 χ^0_2$ by at least a factor of two when soft but realistic cuts on lepton transverse momenta are used. With the Main Injector, a trilepton signal can be detected at $\tanβ\equiv v_2/v_1 \sim 3$ for universal masses $m_{1/2}, m_0 \alt$ 200 GeV.

hep-ph↗
arXiv1998

Overview of Physics at a Muon Collider

Muon colliders offer special opportunities to discover and study new physics. With the high intensity source of muons at the front end, orders of magnitude improvements would be realized in searches for rare muon processes, in deep inelastic muon and neutrino scattering experiments, and in long-baseline neutrino oscillation experiments. At a 100 to 500 GeV muon collider, neutral Higgs boson (or techni-particle) masses, widths and couplings could be precisely measured via s-channel production. Also, threshold cross-section studies of W+ W-, t t-bar, Zh and supersymmetric particle pairs would precisely determine the corrresponding masses and test supersymmetric radiative corrections. At the high energy frontier a 3 to 4 TeV muon collider is ideally suited for the study of scalar supersymmetric particles and extra Z-bosons or strong WW scattering.

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