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K. Whisnant

Publications and source records attributed to K. Whisnant.

At least 37 records · Page 2Linked to original sources
arXiv2002

Measuring CP violation and mass ordering in joint long baseline experiments with superbeams

We propose to measure the CP phase $δ_{\rm CP}$, the magnitude of the neutrino mixing matrix element $|U_{e3}|$ and the sign of the atmopheric scale mass--squared difference $Δ{\rm m}^2_{31}$ with a superbeam by the joint analysis of two different long baseline neutrino oscillation experiments. One is a long baseline experiment (LBL) at 300 km and the other is a very long baseline (VLBL) experiment at 2100 km. We take the neutrino source to be the approved high intensity proton synchrotron, HIPA. The neutrino beam for the LBL is the 2-degree off-axis superbeam and for the VLBL, a narrow band superbeam. Taking into account all possible errors, we evaluate the event rates required and the sensitivities that can be attained for the determination of $δ_{\rm CP}$ and the sign of $Δm^2_{31}$. We arrive at a representative scenario for a reasonably precise probe of this part of the neutrino physics.

hep-ph↗
arXiv2002

Off--axis Beams and Detector Clusters: Resolving Neutrino Parameter Degeneracies

There are three parameter degeneracies inherent in the three--neutrino analysis of long--baseline neutrino experiments. We develop a systematic method for determining whether or not a set of measurements in neutrino oscillation appearance experiments with approximately monoenergetic beams can completely resolve these ambiguities. We then use this method to identify experimental scenarios in which the parameter degeneracies may be efficiently resolved. Generally speaking, with two appearance measurements degeneracies can occur over wide areas of the $(δ,θ_{13})$ parameter space; with three measurements they occur along lines in the parameter space and with four measurements they occur only at isolated points. If two detectors are placed at the same distance from the source but at different locations with respect to the main axis of the beam (a detector cluster), each detector will measure neutrinos at different energies. Then one run with neutrinos and one run with antineutrinos will give the four independent measurements that in principle can resolve all of the parameter degeneracies if $\sin^22θ_{13} \geq 0.002$. We also examine scenarios with detector clusters using only neutrino beams. Without detector clusters, the measurement of neutrinos and antineutrinos at a short distance and only neutrinos at a longer distance may also work.

hep-ph↗
arXiv2002

Imprint of SNO neutral current data on the solar neutrino problem

We perform a global analysis in the framework of two active neutrino oscillations of all solar neutrino data, including the recent SNO day and night spectra (comprised of the charged current (CC), elastic scattering (ES) and neutral current (NC) events), the Super-Kamiokande (SK) day and night spectra (from 1496 days) and the updated SAGE results. We find that the Large Mixing Angle (LMA) solution is selected at the 99% C.L.; the best-fit parameters are Δm^2=5.6 \times 10^{-5} eV^2 and θ=32^{\circ}. No solutions with θ\geq π/4 are allowed at the 5σC.L. Oscillations to a pure sterile state are excluded at 5.3σ, but a sizeable sterile neutrino component could still be present in the solar flux.

hep-ph↗
arXiv2001

Breaking Eight-fold Degeneracies in Neutrino CP Violation, Mixing, and Mass Hierarchy

We identify three independent two-fold parameter degeneracies (δ, θ_{13}), sgn(δm^2_{31}) and (θ_{23}, π/2-θ_{23}) inherent in the usual three-neutrino analysis of long-baseline neutrino experiments, which can lead to as much as an eight-fold degeneracy in the determination of the oscillation parameters. We discuss the implications these degeneracies have for detecting CP violation and present criteria for breaking them. A superbeam facility with a baseline at least as long as the distance between Fermilab and Homestake (1290 km) and a narrow band beam with energy tuned so that the measurements are performed at the first oscillation peak can resolve all the ambiguities other than the (θ_{23}, π/2-θ_{23}) ambiguity (which can be resolved at a neutrino factory) and a residual (δ, π-δ) ambiguity. However, whether or not CP violation occurs in the neutrino sector can be ascertained independently of the latter two ambiguities. The (δ,π-δ) ambiguity can be eliminated by performing a second measurement to which only the \cosδterms contribute. The hierarchy of mass eigenstates can be determined at other oscillation peaks only in the most optimistic conditions, making it necessary to use the first oscillation maximum. We show that the degeneracies may severely compromise the ability of the proposed SuperJHF-HyperKamiokande experiment to establish CP violation. In our calculations we use approximate analytic expressions for oscillation probabilitites that agree with numerical solutions with a realistic Earth density profile.

hep-ph↗
arXiv2001

Probing neutrino oscillations jointly in long and very long baseline experiments

We examine the prospects of making a joint analysis of neutrino oscillation at two baselines with neutrino superbeams. Assuming narrow band superbeams and a 100 kt water Cerenkov calorimeter, we calculate the event rates and sensitivities to the matter effect, the signs of the neutrino mass differences, the CP phase and the mixing angle θ_{13}. Taking into account all possible experimental errors under general consideration, we explored the optimum cases of narrow band beam to measure the matter effect and the CP violation effect at all baselines up to 3000 km. We then focus on two specific baselines, a long baseline of 300 km and a very long baseline of 2100 km, and analyze their joint capabilities. We found that the joint analysis can offer extra leverage to resolve some of the ambiguities that are associated with the measurement at a single baseline.

hep-ph↗
arXiv2001

Unknowns after the SNO Charged-Current Measurement

We perform a model-independent analysis of solar neutrino flux rates including the recent charged-current measurement at the Sudbury Neutrino Observatory (SNO). We derive a universal sum rule involving SNO and SuperKamiokande rates, and show that the SNO neutral-current measurement can not fix the fraction of solar $ν_e$ oscillating to sterile neutrinos. The large uncertainty in the SSM $^8$B flux impedes a determination of the sterile neutrino fraction.

hep-ph↗
arXiv2001

Neutrino Superbeam Scenarios at the Peak

We discuss options for U.S. long baseline neutrino experiments using upgraded conventional neutrino beams, assuming $L/E_ν$ is chosen to be near the peak of the leading oscillation. We find that for L = 1290 km (FNAL-Homestake) or 1770 km (FNAL-Carlsbad, or BNL-Soudan) it is possible to simultaneously have good $\sin^22θ_{13}$ reach and sgn($δm^2_{31}$) determination, and possibly sizeable $τ$ rates and some $δ$ sensitivity.

hep-ph↗
arXiv2001

Piecing the Solar Neutrino Puzzle Together at SNO

We perform an oscillation parameter-independent analysis of solar neutrino flux measurements from which we predict the charged-current rate at SNO relative to Standard Solar Model to be $R_{SNO}^{CC}=0.35^{+0.16}_{-0.09} (0.46^{+0.13}_{-0.11})$ for oscillations to active (sterile) neutrinos. By alternately considering the $^8$B flux normalization fixed and free, we find that the flux measured by Super-Kamiokande (SK) not being a result of oscillations is strongly disfavored for oscillations to active neutrinos. SNO will determine the best-fit value of the $^8$B flux normalization $β$ (equal to the neutral-current rate), without recourse to neutral-current measurements, from the derived relation $β=R_{SNO}^{NC}=5.85 R_{SK} - 4.85 R_{SNO}^{CC}$. Using a simple parameterization of the fraction of high, intermediate, and low energy solar neutrinos starting above resonance, we reproduce the results of global analyses to good accuracy; we find that the LMA solution with a normal mass hierarchy is clearly favored. With $β$ free, our analysis for oscillations to active neutrinos gives $R_{SNO}^{NC}=β=1.34 \pm 0.34$, which corresponds to $R_{SNO}^{CC}=0.28\pm 0.07$.

hep-ph↗
arXiv2001

Exploring Neutrino Oscillations with Superbeams

We consider the medium- and long-baseline oscillation physics capabilities of intense muon-neutrino and muon-antineutrino beams produced using future upgraded megawatt-scale high-energy proton beams. In particular we consider the potential of these conventional neutrino ``superbeams'' for observing ν_μ\toν_e oscillations, determining the hierarchy of neutrino mass eigenstates, and measuring CP-violation in the lepton sector. The physics capabilities of superbeams are explored as a function of the beam energy, baseline, and the detector parameters. The trade-offs between very large detectors with poor background rejection and smaller detectors with excellent background rejection are illustrated. We find that it may be possible to observe ν_μ\toν_e oscillations with a superbeam provided that the amplitude parameter \sin^2 2θ_{13} is larger than a few \times 10^{-3}. If \sin^2 2θ_{13} is of order 10^{-2} or larger, then the neutrino mass hierarchy can be determined in long-baseline experiments, and if in addition the large mixing angle MSW solution describes the solar neutrino deficit then there is a small region of parameter space within which maximal CP-violation in the lepton sector would be observable in a low-energy medium-baseline experiment. We explicitly consider massive water Cherenkov and liquid argon detectors at superbeams with neutrino energies ranging from 1 GeV to 15 GeV, and baselines from 295 km to 9300 km. Finally, we compare the oscillation physics prospects at superbeams with the corresponding prospects at neutrino factories. The sensitivity at a neutrino factory to CP violation and the neutrino mass hierarchy extends to values of the amplitude parameter \sin^2 2θ_{13} that are one to two orders of magnitude lower than at a superbeam.

hep-ph↗
arXiv2001

Probing R-violating top quark decays at the NLC

We examine the possibility of observing exotic top quark decays via $R$-Parity violating SUSY interactions in $e^+e^-$ collisions at $\sqrt{s = 500 GeV$. We present cross-sections for $t\bar t$ production followed by the subsequent decay of either the $t$ or $\overline{t}$ via the $R$-Parity violating interaction while the other undergoes the SM decay. We discuss kinematic cuts that allow the exotic SUSY decays to be detected over standard model backgrounds. Discovery limits for $R$-Parity violating couplings in the top sector are presented assuming an integrated luminosity of $100 fb^{-1}$.

hep-ph↗
arXiv2001

Earth Regeneration of Solar Neutrinos at SNO and Super-Kamiokande

We analyze the 1258-day Super-Kamiokande day and night solar neutrino energy spectra with various $χ^2$ definitions. The best-fit lies in the LMA region at $(Δm^2, tan^2 θ)=(5.01\times 10^{-5} eV^2, 0.60)$, independently of whether systematic errors are included in the $χ^2$-definition. We compare the exclusion and allowed regions from the different definitions and choose the most suitable definition to predict the regions from SNO at the end of three years of data accumulation. We first work under the assumption that Super-Kamiokande sees a flux-suppressed flat energy spectrum. Then, we consider the possibility of each one of the three MSW regions being the solution to the solar neutrino problem. We find that the exclusion and allowed regions for the flat spectrum hypothesis and the LMA and LOW solutions are alike. In three years, we expect SNO to find very similar regions to that obtained by Super-Kamiokande. We evaluate whether the zenith angle distribution at SNO with optimum binning will add anything to the analysis of the day and night spectra; for comparison, we show the results of our analysis of the 1258-day zenith angle distribution from Super-Kamiokande, for which the best-fit parameters are $(Δm^2, tan^2 θ)=(5.01\times 10^{-5} eV^2, 0.56)$.

hep-ph↗
arXiv2000

Physics at a Neutrino Factory

In response to the growing interest in building a Neutrino Factory to produce high intensity beams of electron- and muon-neutrinos and antineutrinos, in October 1999 the Fermilab Directorate initiated two six-month studies. The first study, organized by N. Holtkamp and D. Finley, was to investigate the technical feasibility of an intense neutrino source based on a muon storage ring. This design study has produced a report in which the basic conclusion is that a Neutrino Factory is technically feasible, although it requires an aggressive R&D program. The second study, which is the subject of this report, was to explore the physics potential of a Neutrino Factory as a function of the muon beam energy and intensity, and for oscillation physics, the potential as a function of baseline.

hep-ex↗
arXiv2000

Fate of the Sterile Neutrino

In light of recent Super-Kamiokande data and global fits that seem to exclude both pure ν_μ\to ν_s oscillations of atmospheric neutrinos and pure ν_e \to ν_s oscillations of solar neutrinos (where ν_s is a sterile neutrino), we reconsider four-neutrino models to explain the LSND, atmospheric, and solar neutrino oscillation indications. We argue that the solar data, with the exception of the ^{37}Cl results, are suggestive of ν_e \to ν_s oscillations that average to a probability of approximately 1/2. In this interpretation, with two pairs of nearly degenerate mass eigenstates separated by order 1 eV, the day-night asymmetry, seasonal dependence, and energy dependence for ^8B neutrinos should be small. Alternatively, we find that four-neutrino models with one mass eigenstate widely separated from the others (and with small sterile mixings to active neutrinos) may now be acceptable in light of recently updated LSND results; the ^{37}Cl data can be accommodated in this model. For each scenario, we present simple four-neutrino mixing matrices that fit the stated criterion and discuss future tests.

hep-ph↗
arXiv2000

Probing R-violating top quark decays at hadron colliders

We examine the possibility of observing exotic top quark decays via R-violating SUSY interactions at the Fermilab Tevatron and CERN LHC. We present cross-sections for $t\bar t$ production followed by the subsequent decay of either $t$ or $\bar t$ via the R-violating interaction while the other undergoes the SM decay. With suitable kinematic cuts, we find that the exotic decays can possibly be detected over standard model backgrounds at the future runs of the Tevatron and LHC, but not at Run 1 of the Tevatron due to limited statistics. Discovery limits for R-Violating couplings in the top sector are presented.

hep-ph↗
arXiv2000

Neutrino Oscillations at an Entry-Level Neutrino Factory and Beyond

We consider the parameters of an entry-level neutrino factory designed to make the first observation of nu_e -> nu_mu oscillations, measure the corresponding amplitude sin^2 2theta_{13}, and determine the sign of the atmospheric-scale delta m_{32}^2 via matter effects. A 50 kt detector, a stored muon energy E_mu geq 20 GeV and 10^{19} muon decays would enable these goals to be met provided sin^2 2theta_{13} > 0.01. The determination of the sign of delta m_{32}^2 also requires a baseline L geq 2000 km. An upgraded neutrino factory with O(10^{20}) decays would enable the first observation of nu_e -> nu_tau oscillations. With O(10^{21}) decays the effects of a large CP-phase could be measured in the case of the large angle matter oscillation solution to the solar neutrino anomaly. Our analysis includes a family of three-neutrino models that can account for the atmospheric and solar neutrino oscillation indications.

hep-ph↗
arXiv2000

Short-Baseline Neutrino Oscillations at a Neutrino Factory

Within the framework of three-neutrino and four-neutrino scenarios that can describe the results of the LSND experiment, we consider the capabilities of short baseline neutrino oscillation experiments at a neutrino factory. We find that, when short baseline ($L \alt 100$ km) neutrino factory measurements are used together with other accelerator-based oscillation results, the complete three-neutrino parameter space can best be determined by measuring the rate of $ν_e \to ν_τ$ oscillations, and measuring CP violation with either $ν_e \to ν_μ$ or $ν_μ\to ν_τ$ oscillations (including the corresponding antineutrino channels). With measurements of CP violation in both $ν_e \to ν_μ$ and $ν_μ\to ν_τ$ it may be possible to distinguish between the three- and four-neutrino cases.

hep-ph↗
arXiv2000

Neutrino Mixing Schemes

A revolution in our understanding of the neutrino sector is underway, driven by observations that are interpreted in terms of changes in neutrino flavors as they propagate. Since neutrino oscillations occur only if neutrinos are massive, these phenomena indicate physics beyond the Standard Model. With the present evidence for oscillations from atmospheric, solar and accelerator data, we are already able to begin to make strong inferences about the mass spectrum and mixings of neutrinos. Theoretical efforts to achieve a synthesis have produced a variety of models with differing testable consequences. A combination of particle physics, nuclear physics and astrophysics is needed for a full determination of the fundamental properties of neutrinos. This article reviews what has been achieved thus far and the future prospects for understanding the nature of neutrino masses and mixing.

hep-ph↗