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Stephen Parke

Publications and source records attributed to Stephen Parke.

At least 19 recordsLinked to original sources
arXiv2018

Constraints on the Solar $\Delta m^2$ using Daya Bay & RENO

We demonstrate that the currently running short baseline reactor experiments, especially Daya Bay, can put a significant upper bound on $\Delta m^2_{21}$. This novel approach to determining $\Delta m^2_{21}$ can be performed with the current data of both Daya Bay \& RENO and provides additional information on $\Delta m^2_{21}$ in a different $L/E$ range ($\sim$ 0.5 km/MeV) for an important consistency check on the 3 flavor massive neutrino paradigm. Upper limits by Daya Bay and RENO and a possible lower limit from Daya Bay, before the end of 2020, will be the only new information on this important quantity until the medium baseline reactor experiment, JUNO, gives a very precise measurement in the middle of the next decade. In this study $\theta_{12}$ value is fixed since its impact on the $\Delta m^2_{21}$ measurement is relatively small as discussed in the Appendix.

hep-ex↗
arXiv2018

Properties of the Top Quark

The top quark is the heaviest known elementary particle, and it is often seen as a window to search for new physics processes in particle physics. A large program to study the top-quark properties has been performed both at the Tevatron and LHC colliders by the D0, CDF, ATLAS and CMS experiments. The most recent results are discussed in this review.

hep-ex↗
arXiv2018

Theoretical Aspects of the Quantum Neutrino

In this summary of my talk I will review the following the following three theoretical aspects of the quantum neutrino: current status, why we need precision measurements and neutrino oscillations amplitudes.

hep-ph↗
arXiv2016

What is $\Delta m^2_{ee}$ ?

The current short baseline reactor experiments, Daya Bay and RENO (Double Chooz) have measured (or are capable of measuring) an effective $\Delta m^2$ associated with the atmospheric oscillation scale of 0.5 km/MeV in electron anti-neutrino disappearance. In this paper, I compare and contrast the different definitions of such an effective $\Delta m^2$ and argue that the simple, L/E independent, definition given by $\Delta m^2_{ee} \equiv \cos^2 \theta_{12} \Delta m^2_{31}+ \sin^2 \theta_{12} \Delta m^2_{32}$, i.e. "the $\nu_e$ weighted average of $\Delta m^2_{31}$ and $\Delta m^2_{32}$," is superior to all other definitions and is useful for both short baseline experiments mentioned above and for the future medium baseline experiments JUNO and RENO 50.

hep-ph↗
arXiv2015

Unitarity and the three flavour neutrino mixing matrix

Unitarity is a fundamental property of any theory required to ensure we work in a theoretically consistent framework. In comparison with the quark sector, experimental tests of unitarity for the 3x3 neutrino mixing matrix are considerably weaker. It must be remembered that the vast majority of our information on the neutrino mixing angles originates from $\overline{\nu}_e$ and $\nu_\mu$ disappearance experiments, with the assumption of unitarity being invoked to constrain the remaining elements. New physics can invalidate this assumption for the 3x3 subset and thus modify our precision measurements. We perform a reanalysis to see how global knowledge is altered when one refits oscillation results without assuming unitarity, and present $3 \sigma$ ranges for allowed $U_\text{PMNS}$ elements consistent with all observed phenomena. We calculate the bounds on the closure of the six neutrino unitarity triangles, with the closure of the $\nu_e \nu_\mu$ triangle being constrained to be $\leq$ 0.03, while the remaining triangles are significantly less constrained to be $\leq$ 0.1 - 0.2. Similarly for the row and column normalization, we find their deviation from unity is constrained to be $\leq$ 0.2 - 0.4, for four out of six such normalisations, while for the $\nu_\mu$ and $\nu_e$ row normalisation the deviations are constrained to be $\leq$ 0.07, all at the $3\sigma$ CL. We emphasise that there is significant room for new low energy physics, especially in the $\nu_\tau$ sector which very few current experiments constrain directly.

hep-ph↗
arXiv2008

Determination of the Neutrino Mass Hierarchy via the Phase of the Disappearance Oscillation Probability with a Monochromatic \barν_e Source

The neutrino mass hierarchy can be determined, in principle, by measuring a phase in the disappearance oscillation probability in vacuum, without relying on the matter effect, using a single channel. This phase is not the same for the normal and inverted neutrino mass spectra. In this paper, we give a complete description and physics understanding of the method. The key feature of the method is to detect advancement (normal) or retardation (inverted) of the phase of the atmospheric-scale oscillation relative to the solar-scale oscillation. We then show that this method can be realized with the recently proposed resonant $\barν_{e}$ absorption reaction enhanced by Mössbauer effect. The unique feature of this setup is the ultra-monochromaticity of the observed \barν_{e}'s. Because of this feature the phase advancement or retardation of atmospheric-scale neutrino oscillation is detectable after 20 or more oscillations if the source and the target are made sufficiently compact in size. A quantitative estimate of the sensitivity to mass hierarchy resolution is given. We have also examined how a possible continuation of such experiment can be carried out in order also to achieve high precision (few %) determination of the solar-scale oscillation parameters Δm^2_{21} and θ_{12}.

hep-ph↗
arXiv2007

Combining CPT-conjugate Neutrino channels at Fermilab

We explore an alternative strategy to determine the neutrino mass hierarchy by making use of possible future neutrino facilities at Fermilab. Here, we use CPT-conjugate neutrino channels, exploiting a nu_mu beam from the NuMI beamline and a barnu_e beam from a betabeam experimental setup. Both experiments are performed at approximately the same E/L. We present different possible accelerator scenarios for the betabeam neutrino setup and fluxes. This CPT-conjugate neutrino channel scenario can extract the neutrino mass hierarchy down to sin^2 (2 theta_13) \approx 0.02.

hep-ph↗
arXiv2007

CP Violation and Neutrino Oscillations

We review the basic mechanisms of neutrino mass generation and the corresponding structure of the lepton mixing matrix. We summarize the status of three-neutrino oscillation parameters as determined from current observations, using state-of-the-art solar and atmospheric neutrino fluxes, as well as latest experimental data as of September 2007. We also comment on recent attempts to account for these results and to understand flavour from first principles. We discuss extensively the prospects for probing the strength of CP violation in two near term accelerator neutrino oscillation experiments, T2K and NOvA, as well as possible extensions such as T2KK and a second large off-axis detector near the NOvA detector. We also briefly discuss the possibility of probing the effect of Majorana phases in future neutrinoless double beta decay searches and discuss other implications of leptonic CP violation such as leptogenesis. Finally we comment on the issue of robustness of the current oscillation interpretation and possible ways of probing for non-standard neutrino interactions in precision oscillation studies.

hep-ph↗
arXiv2006

NOvA and T2K: The race for the neutrino mass hierarchy

The determination of the ordering of the neutrino masses (the hierarchy) is probably a crucial prerequisite to understand the origin of lepton masses and mixings and to establish their relationship to the analogous properties in the quark sector. Here, we follow an alternative strategy to the usual neutrino--antineutrino comparison in long baseline neutrino oscillation experiments: we exploit the combination of the neutrino-only data from the NOvA and the T2K experiments by performing these two off-axis experiments at different distances but at the same $ /L$, where $ $ is the mean neutrino energy and $L$ is the baseline. This would require a minor adjustment to the proposed off-axis angle for one or both of the proposed experiments.

hep-ph↗
arXiv2006

Using Spin Correlations to Distinguish Zh from ZA at the International Linear Collider

We investigate how to exploit the spin information imparted to the Z boson in associated Higgs production at a future linear collider as an aid in distinguishing between CP-even and CP-odd Higgs bosons. We apply a generalized spin-basis analysis which allowsus to study the possibilities offered by non-traditional choices of spin projection axis. In particular, we find that the Z bosons produced in association with a CP-even Higgs via polarized collisions are in a single transverse spin-state (>90% purity) when we use the Zh-transverse basis, provided that the Z~bosons are not ultra-relativistic (speed <0.9c). This same basis applied to the associated production of a CP-odd Higgs yields Z's that are an approximately equal mixture of longitudinal and transverse polarizations. We present a decay angular distribution which could be used to distinguish between the CP-even and CP-odd cases. Finally, we make a few brief remarks about how this distribution would be affected if the Higgs boson turns out to not be a CP-eigenstate.

hep-ph↗
arXiv2006

What Fraction of Boron-8 Solar Neutrinos arrive at the Earth as a nu_2 mass eigenstate?

We calculate the fraction of B^8 solar neutrinos that arrive at the Earth as a nu_2 mass eigenstate as a function of the neutrino energy. Weighting this fraction with the B^8 neutrino energy spectrum and the energy dependence of the cross section for the charged current interaction on deuteron with a threshold on the kinetic energy of the recoil electrons of 5.5 MeV, we find that the integrated weighted fraction of nu_2's to be 91 \pm 2 % at the 95% CL. This energy weighting procedure corresponds to the charged current response of the Sudbury Neutrino Observatory (SNO). We have used SNO's current best fit values for the solar mass squared difference and the mixing angle, obtained by combining the data from all solar neutrino experiments and the reactor data from KamLAND. The uncertainty on the nu_2 fraction comes primarily from the uncertainty on the solar delta m^2 rather than from the uncertainty on the solar mixing angle or the Standard Solar Model. Similar results for the Super-Kamiokande experiment are also given. We extend this analysis to three neutrinos and discuss how to extract the modulus of the Maki-Nakagawa-Sakata mixing matrix element U_{e2} as well as place a lower bound on the electron number density in the solar B^8 neutrino production region.

hep-ph↗
arXiv2005

Physics Potential of the Fermilab NuMI beamline

We explore the physics potential of the NuMI beamline with a detector located 10 km off-axis at a distant site (810 km). We study the sensitivity to $\sin^2 2 θ_{13}$ and to the CP-violating parameter $\sin δ$ as well as the determination of the neutrino mass hierarchy by exploiting the $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ appearance channels. The results are illustrated for three different experimental setups to quantify the benefits of increased detector sizes, proton luminosities and $ν_e$ detection efficiencies.

hep-ph↗
arXiv2005

Another possible way to determine the Neutrino Mass Hierarchy

We show that by combining high precision measurements of the atmospheric delta m^2 in both the electron and muon neutrino (or anti-neutrino) disappearance channels one can determine the neutrino mass hierarchy. The required precision is a very challenging fraction of one per cent for both measurements. At even higher precision, sensitivity to the cosine of the CP violating phase is also possible. This method for determining the mass hierarchy of the neutrino sector does not depend on matter effects.

hep-ph↗
arXiv2004

Untangling CP Violation and the Mass Hierarchy in Long Baseline Experiments

In the overlap region, for the normal and inverted hierarchies, of the neutrino-antineutrino bi-probability space for $ν_μ\to ν_e$ appearance, we derive a simple identity between the solutions in the ($\sin^2 2θ_{13}$, $\sin δ$) plane for the different hierarchies. The parameter $\sin^2 2θ_{13}$ sets the scale of the $ν_μ\to ν_e$ appearance probabilities at the atmospheric $δm^2_{atm} \approx 2.4 \times 10^{-3}$ eV$^2$ whereas $\sin δ$ controls the amount of CP violation in the lepton sector. The identity between the solutions is that the difference in the values of $\sin δ$ for the two hierarchies equals twice the value of $\sqrt{\sin^2 2θ_{13}}$ divided by the {\it critical} value of $\sqrt{\sin^2 2θ_{13}}$. We apply this identity to the two proposed long baseline experiments, T2K and NO$ν$A, and we show how it can be used to provide a simple understanding of when and why fake solutions are excluded when two or more experiments are combined. The identity demonstrates the true complimentarity of T2K and NO$ν$A.

hep-ph↗
arXiv2003

Unified Graphical Summary of Neutrino Mixing Parameters

The neutrino mixing parameters are presented in a number of different ways by the various experiments, e.g. SuperKamiokande, K2K, SNO, KamLAND and Chooz and also by the Particle Data Group. In this paper, we argue that presenting the data in terms of $\sin^2 θ$, where $θ$ is the mixing angle appropriate for a given experiment has a direct physical interpretation. For current atmospheric, solar and reactor neutrino experiments, the $\sin^2 θ$'s are effectively the probability of finding a given flavor in a particular neutrino mass eigenstate. The given flavor and particular mass eigenstate varies from experiment to experiment, however, the use of $\sin^2 θ$ provides a unified picture of all the data. Using this unified picture we present a graphical way to represent these neutrino mixing parameters which includes the uncertainties. All of this is performed in the context of the present experimental status of three neutrino oscillations.

hep-ph↗
arXiv2003

Long Baseline Neutrino Oscillations: Parameter Degeneracies and JHF/NuMI Complementarity

A summary of the parameter degeneracy issue for long baseline neutrino oscillations is presented and how a sequence of measurements can be used to resolve all degeneracies. Next, a comparison of the JHF and NuMI Off-Axis proposals is made with emphasis on how both experiments running neutrinos can distinguish between the normal and inverted hierarchies provided the E/L of NuMI is less than or equal to the E/L of JHF. Due to the space limitations of this proceedings only an executive style summary can be presented here, but the references and transparencies of the talk contain the detailed arguments.

hep-ph↗