1,529 research outputs found

    On the degeneracies of the mass-squared differences for three-neutrino oscillations

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    Using an algebraic formulation, we explore two well-known degeneracies involving the mass-squared differences for three-neutrino oscillations assuming CP symmetry is conserved. For vacuum oscillation, we derive the expression for the mixing angles that permit invariance under the interchange of two mass-squared differences. This symmetry is most easily expressed in terms of an ascending mass order. This can be used to reduce the parameter space by one half in the absence of the MSW effect. For oscillations in matter, we derive within our formalism the known approximate degeneracy between the standard and inverted mass hierarchies in the limit of vanishing θ13\theta_{13}. This is done with a mass ordering that permits the map Δ31Δ31\Delta_{31} \mapsto -\Delta_{31}. Our techniques allow us to translate mixing angles in this mass order convention into their values for the ascending order convention. Using this dictionary, we demonstrate that the vacuum symmetry and the approximate symmetry invoked for oscillations in matter are distinctly different.Comment: 5 pages, revised manuscrip

    Vacuum-UV negative photoion spectroscopy of CH3F, CH3Cl and CH3Br

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    Using tunable vacuum-UV radiation from a synchrotron, negative ions are detected by quadrupolar mass spectrometry following photoexcitation of three gaseous halogenated methanes CH3_3X (X = F,Cl,Br). The anions X^-, H^-, CX^-, CHX^- and CH2_2X^- are observed, and their ion yields recorded in the range 8-35 eV. The anions show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation, generically described as AB + hvv \rightarrow A^- + B+^+ (+ neutrals). Absolute cross sections for ion-pair formation are obtained by calibrating the signal intensities with those of F^- from both SF6_6 and CF4_4. The cross sections for formation of X^- + CH3_3+^+ are much greater than for formation of CH2_2X^- + H+^+. In common with many quadrupoles, the spectra of mm/zz 1 (H^-) anions show contributions from all anions, and only for CH3_3Br is it possible to perform the necessary subtraction to obtain the true H^- spectrum. The anion cross sections are normalised to vacuum-UV absorption cross sections to obtain quantum yields for their production. The appearance energies of X^- and CH2_2X^- are used to calculate upper limits to 298 K bond dissociation energies for Do^o (H3_3C-X) and Do^o (XH2_2C-H) which are consistent with literature values. The spectra suggest that most of the anions are formed indirectly by crossing of Rydberg states of the parent molecule onto an ion-pair continuum. The one exception is the lowest-energy peak of F^- from CH3_3F at 13.4 eV, where its width and lack of structure suggest it may correspond to a direct ion-pair transition

    On detecting CP violation in a single neutrino oscillation channel at very long baselines

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    We propose a way of detecting CP violation in a single neutrino oscillation channel at very long baselines (on the order of several thousands of kilometers), given precise knowledge of the smallest mass-squared difference. It is shown that CP violation can be characterized by a shift in L/EL/E of the peak oscillation in the νe\nu_e--νμ\nu_\mu appearance channel, both in vacuum and in matter. In fact, matter effects enhance the shift at a fixed energy. We consider the case in which sub-GeV neutrinos are measured with varying baseline and also the case of a fixed baseline. For the varied baseline, accurate knowledge of the absolute neutrino flux would not be necessary; however, neutrinos must be distinguishable from antineutrinos. For the fixed baseline, it is shown that CP violation can be distinguished if the mixing angle θ13\theta_{13} were known.Comment: 8 pages, 9 figures; minor typos correcte

    Measuring the mass of a sterile neutrino with a very short baseline reactor experiment

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    An analysis of the world's neutrino oscillation data, including sterile neutrinos, (M. Sorel, C. M. Conrad, and M. H. Shaevitz, Phys. Rev. D 70, 073004) found a peak in the allowed region at a mass-squared difference Δm20.9\Delta m^2 \cong 0.9 eV2^2. We trace its origin to harmonic oscillations in the electron survival probability PeeP_{ee} as a function of L/E, the ratio of baseline to neutrino energy, as measured in the near detector of the Bugey experiment. We find a second occurrence for Δm21.9\Delta m^2 \cong 1.9 eV2^2. We point out that the phenomenon of harmonic oscillations of PeeP_{ee} as a function of L/E, as seen in the Bugey experiment, can be used to measure the mass-squared difference associated with a sterile neutrino in the range from a fraction of an eV2^2 to several eV2^2 (compatible with that indicated by the LSND experiment), as well as measure the amount of electron-sterile neutrino mixing. We observe that the experiment is independent, to lowest order, of the size of the reactor and suggest the possibility of a small reactor with a detector sitting at a very short baseline.Comment: 4 pages, 2 figure

    Calculating error bars for neutrino mixing parameters

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    One goal of contemporary particle physics is to determine the mixing angles and mass-squared differences that constitute the phenomenological constants that describe neutrino oscillations. Of great interest are not only the best fit values of these constants but also their errors. Some of the neutrino oscillation data is statistically poor and cannot be treated by normal (Gaussian) statistics. To extract confidence intervals when the statistics are not normal, one should not utilize the value for chisquare versus confidence level taken from normal statistics. Instead, we propose that one should use the normalized likelihood function as a probability distribution; the relationship between the correct chisquare and a given confidence level can be computed by integrating over the likelihood function. This allows for a definition of confidence level independent of the functional form of the !2 function; it is particularly useful for cases in which the minimum of the !2 function is near a boundary. We present two pedagogic examples and find that the proposed method yields confidence intervals that can differ significantly from those obtained by using the value of chisquare from normal statistics. For example, we find that for the first data release of the T2K experiment the probability that chisquare is not zero, as defined by the maximum confidence level at which the value of zero is not allowed, is 92%. Using the value of chisquare at zero and assigning a confidence level from normal statistics, a common practice, gives the over estimation of 99.5%.Comment: 9 pages, 6 figure