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Stephen J. Parke

Publications and source records attributed to Stephen J. Parke.

At least 37 records · Page 2Linked to original sources
arXiv2019

Compact Perturbative Expressions for Oscillations with Sterile Neutrinos in Matter

We extend a simple and compact method for calculating the three flavor neutrino oscillation probabilities in uniform matter density to schemes with sterile neutrinos, with favorable features inherited. The only constraint of the extended method is that the scale of the matter potential is not significantly larger than the atmospheric $Δm^2$, which is satisfied by all the running and proposed accelerator oscillation experiments. Degeneracy of the zeroth order eigensystem around solar and atmospheric resonances are resolved. Corrections to the zeroth order results are restricted to no larger than the ratio of the solar to the atmospheric $Δm^2$. The zeroth order expressions are exact in vacuum because all the higher order corrections vanish when the matter potential is set zero. Also because all the corrections are continuous functions of matter potential, the zeroth order precision is much better than $Δm^2_\odot/Δm^2_\text{atm}$ for weak matter effect. Numerical tests are presented to verify the theoretical predictions of the exceptional features. Moreover, possible applications of the method in experiments to check the existence of sterile neutrinos are discussed.

hep-ph↗
arXiv2019

Simple and Precise Factorization of the Jarlskog Invariant for Neutrino Oscillations in Matter

For neutrino propagation in matter, we show that the Jarlskog invariant, which controls the size of true CP violation in neutrino oscillation appearance experiments, factorizes into three pieces: the vacuum Jarlskog invariant times two simple two-flavor matter resonance factors that control the matter effects for the solar and atmospheric resonances independently. If the solar effective matter potential and the atmospheric effective $Δm^2$ are chosen carefully for these two resonance factors, then the fractional corrections to this factorization are an impressive 0.04\% or smaller. We also show that the inverse of the square of the Jarlskog in matter ($1/\hat{J}^2$) is a fourth order polynomial in the matter potential which guarantees that it can be factored into two quadratics which immediately implies the functional form of our approximate, factorized expression.

hep-ph↗
arXiv2019

Constraint on the solar $Δm^2$ using 4,000 days of short baseline reactor neutrino data

There is a well known 2$σ$ tension in the measurements of the solar $Δm^2$ between KamLAND and SNO/Super-KamioKANDE. Precise determination of the solar $Δm^2$ is especially important in connection with current and future long baseline CP violation measurements. Reference \cite{Seo:2018rrb} points out that currently running short baseline reactor neutrino experiments, Daya Bay and RENO, can also constrain solar $Δm^2$ value as demonstrated by a GLoBES simulation with a limited systematic uncertainty consideration. In this work, the publicly available data, from Daya Bay (1,958 days) and RENO (2,200 days) are used to constrain the solar $Δm^2$. Verification of our method through $Δm^2_{ee}$ and $\sin^2 θ_{13}$ measurements is discussed in Appendix A. Using this verified method, reasonable constraints on the solar $Δm^2$ are obtained using above Daya Bay and RENO data, both individually and combined. We find that the combined data of Daya Bay and RENO set an upper limit on the solar $Δm^2$ of 18 $\times 10^{-5}$ eV$^2$ at the 95% C.L., including both systematic and statistical uncertainties. This constraint is slightly more than twice the KamLAND value. As this combined result is still statistics limited, even though driven by Daya Bay data, the constraint will improve with the additional running of this experiment.

hep-ex↗
arXiv2019

Scalar Non-Standard Interactions in Neutrino Oscillation

The scalar nonstandard interactions (NSI) can also introduce matter effect for neutrino oscillation in a medium. Especially the recent Borexino data prefers nonzero scalar NSI, $η_{ee} = - 0.16$. In contrast to the conventional vector NSI, the scalar type contributes as a correction to the neutrino mass matrix rather than the matter potential. Consequently, the scalar matter effect is energy independent while the vector one scales linearly with neutrino energy. This leads to significantly different phenomenological consequences in reactor, solar, atmospheric, and accelerator neutrino oscillations. A synergy of different types of experiments, especially those with matter density variation, is necessary to identify the scalar NSI and guarantee the measurement of CP violation at accelerator experiments.

hep-ph↗
arXiv2019

Matter density profile effects on neutrino oscillations at T2HK and T2HKK

This project aims to explore the effects that changes in a matter density profile could have on neutrino oscillations, and whether these could potentially be seen by the future Hyper-Kamiokande experiment (T2HK). The analysis is extended to include the possibility of having a second detector in Korea (T2HKK).

hep-ph↗
arXiv2019

Sub-GeV Atmospheric Neutrinos and CP-Violation in DUNE

We propose to use the unique event topology and reconstruction capabilities of liquid argon time projection chambers to study sub-GeV atmospheric neutrinos. The detection of low energy recoiled protons in DUNE allows for a determination of the leptonic $CP$-violating phase independent from the accelerator neutrino measurement. Our findings indicate that this analysis can exclude several values of $δ_{CP}$ beyond the $3σ$ level. Moreover, the determination of the sub-GeV atmospheric neutrino flux will have important consequences in the detection of diffuse supernova neutrinos and in dark matter experiments.

hep-ph↗
arXiv2019

Neutrino oscillation probabilities through the looking glass

In this paper we review different expansions for neutrino oscillation probabilities in matter in the context of long-baseline neutrino experiments. We examine the accuracy and computational efficiency of different exact and approximate expressions. We find that many of the expressions used in the literature are not precise enough for the next generation of long-baseline experiments, but several of them are while maintaining comparable simplicity. The results of this paper can be used as guidance to both phenomenologists and experimentalists when implementing the various oscillation expressions into their analysis tools.

hep-ph↗
arXiv2018

The Effective $Δm^2_{ee}$ in Matter

In this paper we generalize the concept of an effective $Δm^2_{ee}$ for $ν_e/\barν_e$ disappearance experiments, which has been extensively used by the short baseline reactor experiments, to include the effects of propagation through matter for longer baseline $ν_e/\barν_e$ disappearance experiments. This generalization is a trivial, linear combination of the neutrino mass squared eigenvalues in matter and thus is not a simple extension of the usually vacuum expression, although, as it must, it reduces to the correct expression in the vacuum limit. We also demonstrated that the effective $Δm^2_{ee}$ in matter is very useful conceptually and numerically for understanding the form of the neutrino mass squared eigenstates in matter and hence for calculating the matter oscillation probabilities. Finally we analytically estimate the precision of this two-flavor approach and numerically verify that it is precise at the sub-percent level.

hep-ph↗
arXiv2018

Rotations Versus Perturbative Expansions for Calculating Neutrino Oscillation Probabilities in Matter

We further develop a simple and compact technique for calculating the three flavor neutrino oscillation probabilities in uniform matter density. By performing additional rotations instead of implementing a perturbative expansion we significantly decrease the scale of the perturbing Hamiltonian and therefore improve the accuracy of zeroth order. We explore the relationship between implementing additional rotations and that of performing a perturbative expansion. Based on our analysis, independent of the size of the matter potential, we find that the first order perturbation expansion can be replaced by two additional rotations and a second order perturbative expansion can be replaced by one more rotation. Numerical tests have been applied and all the exceptional features of our analysis have been verified.

hep-ph↗
arXiv2018

Matter Density Profile Shape Effects at DUNE

Quantum mechanical interactions between neutrinos and matter along the path of propagation, the Wolfenstein matter effect, are of particular importance for the upcoming long-baseline neutrino oscillation experiments, specifically the Deep Underground Neutrino Experiment (DUNE). Here, we explore specifically what about the matter density profile can be measured by DUNE, considering both the shape and normalization of the profile between the neutrinos' origin and detection. Additionally, we explore the capability of a perturbative method for calculating neutrino oscillation probabilities and whether this method is suitable for DUNE. We also briefly quantitatively explore the ability of DUNE to measure the Earth's matter density, and the impact of performing this measurement on measuring standard neutrino oscillation parameters.

hep-ph↗
arXiv2018

Compact Perturbative Expressions for Neutrino Oscillations in Matter: II

In this paper we rewrite the neutrino mixing angles and mass squared differences in matter given, in our original paper, in a notation that is more conventional for the reader. Replacing the usual neutrino mixing angles and mass squared differences in the expressions for the vacuum oscillation probabilities with these matter mixing angles and mass squared differences gives an excellent approximation to the oscillation probabilities in matter. Comparisons for T2K, NOvA, T2HKK and DUNE are also given for neutrinos and anti-neutrinos, disappearance and appearance channels, normal ordering and inverted ordering.

hep-ph↗
arXiv2018

Analytic Neutrino Oscillation Probabilities in Matter: Revisited

We summarize our recent paper on neutrino oscillation probabilities in matter, explaining the importance, relevance and need for simple, highly accurate approximations to the neutrino oscillation probabilities in matter. Simple expressions for the neutrino mixing angles and mass squared differences in matter are given in an Appendix. Using these in the vacuum oscillation probabilities instead of the vacuum values, gives an excellent approximation to the oscillation probabilities in matter.

hep-ph↗
arXiv2017

DUNE sensitivities to the mixing between sterile and tau neutrinos

Light sterile neutrinos can be probed in a number of ways, including electroweak decays, cosmology and neutrino oscillation experiments. At long-baseline experiments, the neutral-current data is directly sensitive to the presence of light sterile neutrinos: once the active neutrinos have oscillated into a sterile state, a depletion in the neutral-current data sample is expected since they do not interact with the $Z$ boson. This channel offers a direct avenue to probe the mixing between a sterile neutrino and the tau neutrino, which remains largely unconstrained by current data. In this work, we study the potential of the DUNE experiment to constrain the mixing angle which parametrizes this mixing, $θ_{34}$, through the observation of neutral-current events at the far detector. We find that DUNE will be able to improve significantly over current constraints thanks to its large statistics and excellent discrimination between neutral- and charged-current events.

hep-ph↗
arXiv2016

Compact Perturbative Expressions For Neutrino Oscillations in Matter

We further develop and extend a recent perturbative framework for neutrino oscillations in uniform matter density so that the resulting oscillation probabilities are accurate for the complete matter potential versus baseline divided by neutrino energy plane. This extension also gives the exact oscillation probabilities in vacuum for all values of baseline divided by neutrino energy. The expansion parameter used is related to the ratio of the solar to the atmospheric $Δm^2$ scales but with a unique choice of the atmospheric $Δm^2$ such that certain first-order effects are taken into account in the zeroth-order Hamiltonian. Using a mixing matrix formulation, this framework has the exceptional feature that the neutrino oscillation probability in matter has the same structure as in vacuum, to all orders in the expansion parameter. It also contains all orders in the matter potential and $\sinθ_{13}$. It facilitates immediate physical interpretation of the analytic results, and makes the expressions for the neutrino oscillation probabilities extremely compact and very accurate even at zeroth order in our perturbative expansion. The first and second order results are also given which improve the precision by approximately two or more orders of magnitude per perturbative order.

hep-ph↗
arXiv2014

Interplay between Appearance and Disappearance Channels for Precision Measurements of $θ_{23}$ and $δ$

We discuss how the CP violating phase $δ$ and the mixing angle $θ_{23}$ can be measured precisely in an environment where there are strong correlations between them. This is achieved by paying special attention to the mutual roles and the interplay between the appearance and the disappearance channels in long-baseline neutrino oscillation experiments. We analyze and clarify the general structure of the $θ_{23} - θ_{13} - δ$ degeneracy for both the appearance and disappearance channels in a more complete fashion than what has previously been discussed in the literature. A full understanding of this degeneracy is of vital importance if $θ_{23}$ is close to maximal mixing. The relative importance between the appearance and disappearance channels depends upon the particular setup and how close to maximal mixing Nature has chosen the value for $θ_{23}$. For facilities that operate with a narrow band beam or a wide band beam centered on the first oscillation extremum, the contribution of the disappearance channel depends critically on the systematic uncertainties assumed for this channel. Whereas for facilities that operate at energies above the first oscillation extremum or at the second oscillation extremum the appearance channels dominate. On the other hand, for $δ$ we find that the disappearance channel usually improves the sensitivity, modestly for facilities around the first oscillation extremum and more significantly for facilities operating at an energy above the first oscillation extremum, especially near $δ\sim \pm π/2$.

hep-ph↗
arXiv2013

Correlated, Precision Measurements of θ_{23} and $δ$ using only the Electron Neutrino Appearance Experiments

Precision measurement of the leptonic CP violating phase $δ$ will suffer from the, then surviving, large uncertainty of sin^2 θ_{23} of 10-20% in the experimentally interesting region near maximal mixing of θ_{23}. We advocate a new method for determination of both θ_{23} and $δ$ at the same time using only the ν_e and \barν_e appearance channels, and show that sin^2 θ_{23} can be determined automatically with much higher accuracy, approximately a factor of six, than \sin δ. In this method, we identify a new degeneracy for the simultaneous determination of θ_{23} and δ, the θ_{23} intrinsic degeneracy, which must be resolved in order to achieve precision measurement of these two parameters. Spectral information around the vacuum oscillation maxima is shown to be the best way to resolve this degeneracy.

hep-ph↗