Miranda, O. G., Tortola, M., & Valle, J. W. F. (2016). New Ambiguity in Probing CP Violation in Neutrino Oscillations. Phys. Rev. Lett., 117(6), 061804–5pp.
Abstract: If neutrinos get mass via the seesaw mechanism the mixing matrix describing neutrino oscillations can be effectively nonunitary. We show that in this case the neutrino appearance probabilities involve a new CP phase phi associated with nonunitarity. This leads to an ambiguity in extracting the “standard” three-neutrino phase delta(CP), which can survive even after neutrino and antineutrino channels are combined. Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of delta(CP).
|
MiniBooNE Collaboration(Aguilar-Arevalo, A. A. et al), & Sorel, M. (2010). Event Excess in the MiniBooNE Search for (nu)over-bar(mu) -> (nu)over-bar(e) Oscillations. Phys. Rev. Lett., 105(18), 181801–5pp.
Abstract: The MiniBooNE experiment at Fermilab reports results from a search for (nu) over bar (mu) -> (nu) over bar (e) oscillations, using a data sample corresponding to 5.66 x 10(20) protons on target. An excess of 20.9 +/- 14.0 events is observed in the energy range 475 < E-nu(QE) < 1250 MeV, which, when constrained by the observed <(nu)over bar>(mu) events, has a probability for consistency with the background-only hypothesis of 0.5%. On the other hand, fitting for (nu) over bar (mu) -> (nu) over bar (e) oscillations, the best-fit point has chi(2) probability of 8.7%. The data are consistent with (nu) over bar (mu) -> (nu) over bar (e) oscillations in the 0.1 to 1.0 eV(2) Delta m(2) range and with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory.
|
Mena, O., Palomares-Ruiz, S., & Vincent, A. C. (2014). Flavor Composition of the High-Energy Neutrino Events in IceCube. Phys. Rev. Lett., 113(9), 091103–5pp.
Abstract: The IceCube experiment has recently reported the observation of 28 high-energy (> 30 TeV) neutrino events, separated into 21 showers and 7 muon tracks, consistent with an extraterrestrial origin. In this Letter, we compute the compatibility of such an observation with possible combinations of neutrino flavors with relative proportion (alpha(e:)alpha(mu):alpha tau)(circle plus). Although the 7: 21 track-to-shower ratio is naively favored for the canonical (1:1:1)(circle plus) at Earth, this is not true once the atmospheric muon and neutrino backgrounds are properly accounted for. We find that, for an astrophysical neutrino E-2 energy spectrum, (1:1:1)(circle plus). at Earth is disfavored at 81% C. L. If this proportion does not change, 6 more years of data would be needed to exclude (1:1:1)(circle plus) at Earth at 3 sigma C.L. Indeed, with the recently released 3-yr data, that flavor composition is excluded at 92% C. L. The best fit is obtained for (1:0:0)(circle plus). at Earth, which cannot be achieved from any flavor ratio at sources with averaged oscillations during propagation. If confirmed, this result would suggest either a misunderstanding of the expected background events or a misidentification of tracks as showers, or even more compellingly, some exotic physics which deviates from the standard scenario.
|
Matsubara, H. et al, & Rubio, B. (2015). Nonquenched Isoscalar Spin-M1 Excitations in sd-Shell Nuclei. Phys. Rev. Lett., 115(10), 102501–6pp.
Abstract: Differential cross sections of isoscalar and isovector spin-M1 (0(+) -> 1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E-p = 295 MeV on Mg-24, Si-28, S-32, and Ar-36 at 0 degrees-14 degrees. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E-x = 16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.
|
Martinez Torres, A., & Oset, E. (2010). Novel Interpretation of the “Theta(+)(1540) Pentaquark” Peak. Phys. Rev. Lett., 105(9), 092001–4pp.
Abstract: We use a theoretical model of the gamma d --> K+K- np reaction adapted to the experiment done at LEPS where a peak was observed and associated with the Theta(+)(1540) pentaquark. The study shows that the method used in the experiment to assign momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed K(+)n invariant mass in the region of the claimed Theta(+)(1540), such that the remaining strength seen for the experimental peak is compatible with a fluctuation of 2 sigma significance.
|
