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K. Whisnant

Publications and source records attributed to K. Whisnant.

At least 55 records · Page 3Linked to original sources
arXiv2000

Determination of the pattern of neutrino masses at a Neutrino Factory

We study the precision to which the sign of δm_{32}^2 can be determined at a neutrino factory, as a function of stored energies and baselines. This is done by simultaneously fitting the channels ν_μ\to ν_μ$, \barν_e \to \barν_μfrom μ^- decays and the channels \barν_μ\to \barν_μ, ν_e \to ν_μfrom μ^+ decays. We investigate the sensitivity reach in the parameter \sin^22θ_{13} to which one can determine the sign of δm_{32}^2 to 3 standard deviations as a function of the baseline length and magnitude of δm_{32}^2 with a 20 GeV muon storage ring. We find that for baselines longer than 2000 km, the sign of δm^2_{32} can be determined for \sin^22θ_{13} down to the 10^{-3} level with 10^{20} decays of 20 GeV muons.

hep-ph↗
arXiv2000

CPT-odd Resonances in Neutrino Oscillations

We consider the consequences for future neutrino factory experiments of small CPT-odd interactions in neutrino oscillations. The ν_μ\toν_μand \barν_μ\to\barν_μsurvival probabilities at a baseline L=732 km can test for CPT-odd contributions at orders of magnitude better sensitivity than present limits. Interference between the CPT-violating interaction and CPT-even mass terms in the Lagrangian can lead to a resonant enhancement of the oscillation amplitude. For oscillations in matter, a simultaneous enhancement of both neutrino and antineutrino oscillation amplitudes is possible.

hep-ph↗
arXiv2000

Long-Baseline Study of the Leading Neutrino Oscillation at a Neutrino Factory

Within the framework of three-flavor neutrino oscillations, we consider the physics potential of ν_e --> ν_μappearance and ν_μ--> ν_μsurvival measurements at a neutrino factory for a leading oscillation scale δm^2 ~ 3.5 \times 10^{-3} eV^2. Event rates are evaluated versus baseline and stored muon energy, and optimal values discussed. Over a sizeable region of oscillation parameter space, matter effects would enable the sign of δm^2 to be determined from a comparison of ν_e --> ν_μwith \barν_e --> \barν_μevent rates and energy distributions. It is important, therefore, that both positive and negative muons can be stored in the ring. Measurements of the ν_μ--> ν_μsurvival spectrum could determine the magnitude of δm^2 and the leading oscillation amplitude with a precision of O(1%--2%).

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

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

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

Probing anomalous top quark interactions at the Fermilab Tevatron Collider

We study the effects of dimension-six operators contributing to the $gt\bar t$ vertex in top quark pair production at the Tevatron collider. We derive both the limits from Run 1 data and the potential bounds from future runs (Run 2 and 3). Although the current constraints are not very strong, the future runs are quite effective in probing these operators. We investigate the possibility of disentangling different operators with the $t\bar t$ invariant mass distribution and the top quark polarization asymmetry. We also study the effects of a different set of operators contributing to single top production via the $Wt\bar b$ coupling. We derive the current and potential future bounds on these anomalous operators and find that the upgraded Tevatron can improve the existing constraints from $R_b$ for one of the operators.

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

Single Top Quark Production via FCNC Couplings at Hadron Colliders

We calculate single top-quark production at hadron colliders via the chromo-magnetic flavor-changing neutral current couplings $\bar tcg$ and $\bar tug$. We find that the strength for the anomalous $\bar tcg$ ($\bar tug$) coupling may be probed to $κ_c / Λ= 0.092 {TeV}^{-1}$ ($κ_u / Λ= 0.026 {TeV}^{-1}$) at the Tevatron with $2 {fb}^{-1}$ of data and $κ_c / Λ= 0.013 {TeV}^{-1}$ ($κ_u / Λ= 0.0061 {TeV}^{-1}$) at the LHC with $10 {fb}^{-1}$ of data. The two couplings may be distinguished by a comparision of the single top signal with the direct top and top decay signals for these couplings.

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↗
arXiv1997

Four-Way Neutrino Oscillations

We present a four-neutrino model with three active neutrinos and one sterile neutrino which naturally has maximal $ν_μ\toν_τ$ oscillations of atmospheric neutrinos and can explain the solar neutrino and LSND results. The model predicts $ν_e \to ν_τ$ and $ν_e \to ν_μ$ oscillations in long-baseline experiments with $L/E \gg 1$ km/GeV with amplitudes that are determined by the LSND oscillation amplitude and argument controlled by the atmospheric $δm^2$.

hep-ph↗
arXiv1997

Probing top quark decay into light stop in the supersymmetric standard model at the upgraded Tevatron

We investigate the possibility of observing the exotic decay mode of the top quark into the lightest stop ($\tilde t_1$) and neutralino ($\tildeχ^0_1$) in the minimal supersymmetric standard model with R-parity at the upgraded Tevatron. First we determine the allowed range for the branching fraction $B(t\to \tilde t_1 \tildeχ^0_1)$ in the region of parameter space allowed by the $R_b$ data and the CDF $eeγγ+{\large \not} E_T$ event, and then consider all possible backgrounds and investigate the possibility of observing this final state at the Tevatron. We find that this final state is unobservable at Run 1. However, Run 2 can provide significant information on this new decay mode of the top quark: either discover it, or establish a strong constraint on the masses of $\tilde t_1$ and $\tildeχ^0_1$ given approximately by $M_{\tilde χ^0_1} > M_{\tilde t_1} - 6$ GeV.

hep-ph↗
arXiv1997

Searching for an anomalous $\bar t q γ$ coupling via single top quark production at a $γγ$ collider

We investigate the potential of a high-energy $γγ$ collider to detect an anomalous $\bar t q γ$ coupling from observation of the reaction $γγ\to t\bar q$, $\bar t q$, where $q=c$ or $u$. We find that with $b$-tagging and suitable kinematic cuts this process should be observable if the anomalous coupling $κ/Λ$ is no less than about 0.05/TeV, where $Λ$ is the scale of new physics associated with the anomalous interaction. This improves upon the bound possible from observation of top decays at the Tevatron.

hep-ph↗