arXiv subjects

V. Barger

Publications and source records attributed to V. Barger.

At least 91 records · Page 5Linked to original sources

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

Cosmology and Hierarchy in Stabilized Warped Brane Models

We examine the cosmology and hierarchy of scales in models with branes immersed in a five-dimensional curved spacetime subject to radion stabilization. When the radion field is time-independent and the inter-brane spacing is stabilized, the universe can naturally find itself in the radiation-dominated epoch. This feature is independent of the form of the stabilizing potential. We recover the standard Friedmann equations without assuming a specific form for the bulk energy-momentum tensor. In the models considered, if the observable brane has positive tension, a solution to the hierarchy problem requires the presence of a negative tension brane somewhere in the bulk. We find that the string scale can be as low as the electroweak scale. In the situation of self-tuning branes where the bulk cosmological constant is set to zero, the brane tensions have hierarchical values. In the case of a polynomial stabilizing potential no new hierarchy is created.

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↗

arXiv2000

$\tanβ$ Determination From Heavy Higgs Boson Production at Linear Colliders

We study the production at future $e^+e^-$ linear colliders of the heavy neutral Higgs bosons $H$ and $A$ of the minimal supersymmetric standard model in association with top and bottom quarks. The cross sections have a strong dependence on the parameter $\tanβ$, and thus provide a good way to determine it. At a linear collider with $\sqrt s = 0.5-1$ TeV and expected integrated luminosities, we find significant sensitivities for determining $\tanβ$. In the Supergravity scenario, the sensitivity is particularly strong for $\tanβ> 10$, reaching a 15% or better measurement. In the general MSSM scenario, the interplay between the $4b$ and $4t$ channels results in a good determination for $\tanβ< 10$, while the sensitivity is weakened for higher values of $\tanβ$.

hep-ph↗

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

Phenomenology of a String-Inspired Supersymmetric Model with Inverted Scalar Mass Hierarchy

Supersymmetric (SUSY) models with heavy sfermions ($m_{\tilde{f}} \sim 10$ TeV) in the first two generations and the third generation sfermion masses below 1 TeV can solve the SUSY flavor and the CP problems as well as satisfy naturalness constraints. We study the phenomenology of a string-inspired scenario and compare it with the minimal supergravity unified model (mSUGRA). The SUSY trilepton signature at the upgraded Tevatron, the $b\to sγ$ branching fraction and the neutralino dark matter relic density in this model can differ significantly from the mSUGRA model.

hep-ph↗

arXiv2000

Overview of Neutrino Oscillation Physics

Recent evidence for neutrino oscillations has revolutionized the study of neutrino masses and mixing. This report gives an overview of what we are learning from the neutrino oscillation experiments, the prospects for the near term, and the bright future of neutrino mass studies.

hep-ph↗

arXiv2000

Neutrino Masses and Mixing at the Millennium

hep-ph↗

arXiv2000

Higgs Boson Decays to tau-pairs in the s-channel at a Muon Collider

We study the observability of the $\tautau$ decay mode of a Higgs boson produced in the $s$-channel at a muon collider. We find that the spin correlations of the $\tautau$ in $τ\to πν_τ, ρν_τ$ decays are discriminative between the Higgs boson signal and the Standard Model background. Observation of the predicted distinctive distribution can confirm the spin-0 nature of the Higgs resonance. The relative coupling strength of the Higgs boson to $b$ and $τ$ can also be experimentally determined.

hep-ph↗

arXiv2000

Atomic Parity Violation, Leptoquarks, and Contact Interactions

The recent measurement of atomic parity violation in cesium atoms shows a $2.3σ$ deviation from the standard model prediction. We show that such an effect can be explained by four-fermion contact interactions with specific chiralities or by scalar leptoquarks which couple to the left-handed quarks. For a coupling of electromagnetic strength, the leptoquark mass is inferred to be 1.1 to 1.3 TeV. We also show that these solutions are consistent with all other low-energy and high-energy neutral-current data.

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↗

arXiv2000

Report of the SUGRA Working Group for Run II of the Tevatron

We present an analysis of the discovery reach for supersymmetric particles at the upgraded Tevatron collider, assuming that SUSY breaking results in universal soft breaking parameters at the grand unification scale, and that the lightest supersymmetric particle is stable and neutral. We first present a review of the literature, including the issues of unification, renormalization group evolution of the supersymmetry breaking parameters and the effect of radiative corrections on the effective low energy couplings and masses of the theory. We consider the experimental bounds coming from direct searches and those arising indirectly from precision data, cosmology and the requirement of vacuum stability. The issues of flavor and CP-violation are also addressed. The main subject of this study is to update sparticle production cross sections, make improved estimates of backgrounds, delineate the discovery reach in the supergravity framework, and examine how this might vary when assumptions about universality of soft breaking parameters are relaxed. With 30 fb$^{-1}$ luminosity and one detector, charginos and neutralinos, as well as third generation squarks, can be seen if their masses are not larger than 200-250 GeV, while first and second generation squarks and gluinos can be discovered if their masses do not significantly exceed 400 GeV. We conclude that there are important and exciting physics opportunities at the Tevatron collider, which will be significantly enhanced by continued Tevatron operation beyond the first phase of Run II.

hep-ph↗

arXiv2000

Physics Potential of a Tevatron Tripler

We explore the capabilities for new physics discovery in proton-antiproton collisions at 5.4 TeV center-of-mass energy with luminosity $10^{33} cm^{-2} s^{-1}$ at a Tripler upgrade of the Tevatron collider. The prospects are robust for the usual Higgs boson and supersymmetry benchmarks. With an integrated luminosity of 40 fb$^{-1}$, discoveries at 5$σ$ could be made for a standard Higgs boson of mass $\alt 680$ GeV (600 GeV for 10 fb$^{-1}$), a lighter chargino of mass $\alt 380$ GeV, and an extra $Z$ boson of mass $\alt 2.6$ TeV; four-fermion contact interactions from new physics with scale $\alt 74$ TeV could be excluded at the 95% confidence level.

hep-ph↗

arXiv2000

Measuring CP Violating Phases at a Future Linear Collider

At a future Linear Collider one will be able to determine the masses of charginos and neutralinos and their pair production cross sections to high accuracies. We show how systematically including the cross sections into the analysis improves the measurement of the underlying mass parameters, including potential CP violating phases. In addition, we investigate how experimental errors will affect the determination of these parameters. We present a first estimate on the lower limit of observable small phases and on the accuracy in determining large phases.

hep-ph↗