arXiv subjects

W. Anthony Mann

Publications and source records attributed to W. Anthony Mann.

7 recordsLinked to original sources

arXiv2017

Decoherence, matter effect, neutrino hierarchy signature in long baseline experiments

Environmental decoherence of oscillating neutrinos of strength $Γ= (2.3 \pm 1.1) \times 10^{-23}$ GeV can explain how maximal $θ_{23}$ mixing observed at 295 km by T2K appears to be non-maximal at longer baselines. As shown recently by R. Oliveira, the MSW matter effect for neutrinos is altered by decoherence: In normal (inverted) mass hierarchy, a resonant enhancement of $ν_μ (\barν_μ) \rightarrow ν_{e} (\barν_{e})$ occurs for $6 < E_ν < 20$ GeV. Thus decoherence at the rated strength may be detectable as an excess of charged-current $ν_{e}$ events in the full $ν_μ$ exposures of MINOS+ and OPERA.

hep-ph↗

arXiv2017

Nonmaximal $θ_{23}$ mixing at NOvA from neutrino decoherence

In study of muon neutrino disappearance at 810 km, the NOvA experiment finds flavor mixing of the atmospheric sector to deviate from maximal ($\sin^2θ_{23} = 0.5$) by 2.6 $σ$. The result is in tension with the 295-km baseline measurements of T2K which are consistent with maximal mixing. We propose that $θ_{23}$ is in fact maximal, and that the disagreement is harbinger of environmentally-induced decoherence. The departure from maximal mixing can be accounted for by an energy-independent decoherence of strength $Γ= (2.3 \pm 1.1) \times 10^{-23}$ GeV.

hep-ph↗

arXiv2012

Transition probability of perturbative form for nu_mu -> nu_e oscillations in matter of constant density

We give a convenient expression for the appearance probability P(nu_mu -> nu_e) describing neutrino oscillations in matter of constant density, derived using textbook quantum mechanics stratagems. Our formulation retains the clarity of an expansion in alpha = Delta m_{21}^2/Delta m_{31}^2 exhibited by the popular Cervera et al. formula [Nucl. Phys. B 579, 17 (2000)] while enabling more accurate evaluation of oscillations over terrestrial baselines.

hep-ph↗

arXiv2012

Constraints for non-standard interaction epsilon_{e tau}V_e from nu_e appearance in MINOS and T2K

Event rates for nu_e and anti-nu_e appearance oscillations reported by the MINOS and T2K long baseline experiments are used to set constraints on the strength of the non-standard interaction epsilon_{e tau}V_e matter potential. The ranges allowed for the magnitude and phase of epsilon_{e tau} are delineated for scenarios wherein i) other non-standard interactions for neutrinos propagating through the terrestrial crust are negligible, and ii) the real-valued, flavor-diagonal couplings epsilon_{e e} and epsilon_{tau tau} are also operative. Our analysis makes use of accurate analytic forms for the nu_e amplitude A(nu_mu --> nu_e) describing neutrino oscillation in constant-density matter in the presence of epsilon_{e tau}, epsilon_{e e} and epsilon_{tau tau} non- standard interactions.

hep-ph↗

arXiv2010

Apparent multiple Delta m^2_32 in muon anti-neutrino and muon neutrino survival oscillations from non-standard interaction matter effect

Neutrinos propagating through matter may participate in forward coherent neutral-current-like scattering arising from non-standard interactions as well as from the Mikheyev-Smirnov-Wolfenstein matter potential $V_e$. We show that at fixed long baselines through matter of constant density, the non-standard interaction potential $ε_{μτ} V_e$ can contribute an additional term to the oscillation phase whose sign differs for $\anumu$ versus $\numu$ propagation in matter. Its presence can cause different apparent $Δm^2$ to be erroneously inferred on the basis of oscillations in vacuum, with values lying above (for $\anumu$) or below (for $\numu$) the actual $Δm^2_{32}$ for the case where $ε_{μτ}$ is predominantly real-valued and of sign opposite to $Δm_{32}^2$. An NSI scenario invoking only $\Re(ε_{μτ})$ is shown to be capable of accounting for a disparity recently reported between oscillation survival for $\anumu$ and $\numu$ fluxes measured at $735~\mathrm{km}$ by the MINOS experiment. Implications for mantle traversal by atmospheric neutrinos are examined. The NSI matter potential with non-maximal mixing could evade conventional atmospheric neutrino analyses which do not distinguish $\numu$ from $\anumu$ on an event-by-event basis.

hep-ph↗

arXiv2000

New results on atmospheric neutrinos from Soudan 2

Neutrino interactions recorded in a 5.1 fiducial kiloton-year exposure of the Soudan-2 iron tracking calorimeter are analyzed for effects of neutrino oscillations. Using contained single track and single shower events, we update our measurement of the atmospheric nu_mu/nu_e ratio-of-ratios and find R = 0.68 \pm 0.11 \pm 0.06. Assuming this anomalously low R-value is the result of nu_mu flavor disappearance via nu_mu to nu_tau oscillation, we select samples of charged current events which offer good resolution, event-by-event, for L/Enu reconstruction. Oscillation-weighted Monte Carlo events are fitted to these data events using a chisq function summed over bins of log(L/E_nu). The region allowed in the (sin^2 2θ, Δm^2) plane at 90% CL is obtained using the Feldman-Cousins procedure: 0.46 < sin^2 2θ< 1.0 and 2.2x10^-4 < Δm^2 < 2.2x10^-2 ev^2. A small but relatively energetic sample of partially contained nu_mu events has also been isolated. Their distribution in log(L/E_vis) relative to null oscillation Monte Carlo is compatible with nu_mu to nu_tau oscillation scenarios within the parameter region allowed by our contained events.

hep-ex↗

arXiv1999

Atmospheric Neutrinos and the Oscillations Bonanza

New observations with atmospheric neutrinos from the underground experiments SuperKamiokande, Soudan 2, and MACRO, together with earlier results from Kamiokande and IMB, are reviewed. The most recent observations reconfirm aspects of atmospheric flavor content and of zenith angle distributions which appear anomalous in the context of null oscillations. The anomalous trends, exhibited with high statistics in both sub-GeV and multi-GeV data of the SuperKamiokande water Cherenkov experiment, occur also in event samples recorded by the tracking calorimeters. The data are well-described by disappearence of nu_mu flavor neutrinos arising in oscillations with dominant two-state mixing, for which there exists a parameter region allowed by all experiments. In a new analysis by SuperKamiokande, nu_mu -> nu_tau is favored over nu_mu -> nu_s as the dominant oscillation based upon absence of oscillation suppression from matter effects at high energies. The possibility for sub-dominant nu_mu -> nu_e oscillations in atmospheric neutrinos which arises with three-flavor mixing, is reviewed, and intriguing possibilities for amplification of this oscillation by terrestrial matter-induced resonances are discussed. Developments and future measurements which will enhance our knowledge of the atmospheric neutrino fluxes are briefly noted.

hep-ex↗