The production of π∘ mesons in the reaction γ+p→π∘+p is investigated as a function of the incident γ-ray energy in the region from 200 Mev to 300 Mev. For the π∘ emitted at approximately 90° laboratory angle, the differential cross section can be represented by (dσπ∘dΩ)π2=C(K−145)1.9±0.4, where K= energy of incident γ-ray in Mev. The approximate threshold for the reaction is 145 Mev. The ratio of the cross section at 60° laboratory angle to that at 90° laboratory angle, for γ-rays between 250 Mev and 300 Mev, is 1.45±0.25.
No description provided.
The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive $\pi ^0$ and $\eta $ photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the $\gamma p \rightarrow \pi ^0 p$ and $\gamma p \rightarrow \eta p$ reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the $\eta n$ system at $W = 1.68\ \textrm{GeV}$. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the $S_{11}(1535)$ and $S_{11}(1650)$ resonances within the $S_{11}$-partial wave.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \pi^0 p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma n \to \pi^0 n$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \eta p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
<jats:title>Abstract</jats:title> <jats:p> The existence of three distinct neutrino flavours, <jats:italic>ν</jats:italic> <jats:sub>e</jats:sub> , <jats:italic>ν</jats:italic> <jats:sub>μ</jats:sub> and <jats:italic>ν</jats:italic> <jats:sub>τ</jats:sub> , is a central tenet of the Standard Model of particle physics <jats:sup>1,2</jats:sup> . Quantum-mechanical interference can allow a neutrino of one initial flavour to be detected sometime later as a different flavour, a process called neutrino oscillation. Several anomalous observations inconsistent with this three-flavour picture have motivated the hypothesis that an additional neutrino state exists, which does not interact directly with matter, termed as ‘sterile’ neutrino, <jats:italic>ν</jats:italic> <jats:sub>s</jats:sub> (refs. <jats:sup>3–9</jats:sup> ). This includes anomalous observations from the Liquid Scintillator Neutrino Detector (LSND) <jats:sup>3</jats:sup> experiment and Mini-Booster Neutrino Experiment (MiniBooNE) <jats:sup>4,5</jats:sup> , consistent with <jats:italic>ν</jats:italic> <jats:sub>μ</jats:sub> → <jats:italic>ν</jats:italic> <jats:sub>e</jats:sub> transitions at a distance inconsistent with the three-neutrino picture. Here we use data obtained from the MicroBooNE liquid-argon time projection chamber <jats:sup>10</jats:sup> in two accelerator neutrino beams to exclude the single light sterile neutrino interpretation of the LSND and MiniBooNE anomalies at the 95% confidence level (CL). Moreover, we rule out a notable portion of the parameter space that could explain the gallium anomaly <jats:sup>6–8</jats:sup> . This is one of the first measurements to use two accelerator neutrino beams to break a degeneracy between <jats:italic>ν</jats:italic> <jats:sub>e</jats:sub> appearance and disappearance, which would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for either <jats:italic>ν</jats:italic> <jats:sub>μ</jats:sub> → <jats:italic>ν</jats:italic> <jats:sub>e</jats:sub> flavour transitions or <jats:italic>ν</jats:italic> <jats:sub>e</jats:sub> disappearance that would indicate non-standard flavour oscillations. Our results indicate that previous anomalous observations consistent with <jats:italic>ν</jats:italic> <jats:sub>μ</jats:sub> → <jats:italic>ν</jats:italic> <jats:sub>e</jats:sub> transitions cannot be explained by introducing a single sterile neutrino state. </jats:p>
14 observation channels used in this analysis. The first 7 channels correspond to the BNB, while the last 7 channels correspond to the NuMI beam. Each set of seven channels is split by reconstructed event type as well as containment in the detector, fully contained (FC) or partially contained (PC). The seven channels in order are $\nu_e$CC FC, $\nu_e$CC PC, $\nu_\mu$CC FC, $\nu_\mu$CC PC, $\nu_\mu$CC $\pi^0$ FC, $\nu_\mu$CC $\pi^0$ PC, and NC $\pi^0$. Each channel contains 25 bins from 0 to 2500 MeV of reconstructed neutrino energy, with an additional overflow bin.
Four $\nu_e$CC observation channels, after constraints from 10 $\nu_\mu$CC and NC $\pi^0$ channels. The four channels in order are BNB $\nu_e$CC FC, BNB $\nu_e$CC PC, NuMI $\nu_e$CC FC, and NuMI $\nu_e$CC PC. Each channel contains 25 bins from 0 to 2500 MeV of reconstructed neutrino energy, with an additional overflow bin.
14 channel covariance matrix showing uncertainties and correlations between bins due to flux uncertainties, cross-section uncertainties, hadron reinteraction uncertainties, detector systematic uncertainties, Monte-Carlo statistical uncertainties, and dirt (outside cryostat) uncertainties. Data statistical uncertainties have not been included, but they can be calculated with the Combined Neyman-Pearson (CNP) method. Each channel contains 25 bins from 0 to 2500 MeV of reconstructed neutrino energy, with an additional overflow bin.
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