As a part of our program to study p−p collisions at Cosmotron energies, the differential cross sections for elastic scattering were measured at five laboratory angles between 2.3° and 17° for each incident energy. Total elastic cross sections obtained by integration are 21.4±1.4, 17.0±0.8, and 14.7±0.7 mb at 1.35, 2.1, and 2.9 BeV, respectively. The angular distribution as a function of the momentum transfer, exhibits a forward diffraction peak, the width of which shrinks slightly as the incident energy increases. The experimental results were fitted by simple optical model calculations and also compared with the predictions of the composite particle theory of Chew and Frautschi.
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Total (π+, p) and (p, p) cross sections in the momentum range 1.4 to 4.0 Bev/c are presented. These measurements, with an accuracy of approximately 2%, were made at the Berkeley Bevatron by using counter techniques. Pions were distinguished from protons by means of a gas-filled Čerenkov counter. The (π+, p) total cross section was found to be almost constant above 2.0 Bev/c at a value near 29 mb. The (p, p) cross section decreases gradually from 47.5 mb to 41.7 mb over the momentum range covered. Transmission measurements of π+-nucleus and p-nucleus cross sections in both good and poor geometry were made at 3.0 Bev/c. The results are compared with the predictions of the optical model. In contrast to most previous work at high energies, an essentially exact solution of the wave equation for a potential well with a diffuse edge was used. The values of the imaginary part of the optical potential that best fit the experimental data are in good agreement with the predicted values. No strong conclusion regarding the real part of the potential was possible. Absorption and total elastic scattering cross sections for Be, C, Al, and Cu are presented. The total elastic scattering cross sections from this experiment disagree with Wikner's for π−-nucleus scattering.
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The Brookhaven National Laboratory twenty-inch liquid hydrogen bubble chamber was exposed to a monoenergetic beam of 2.85-Bev protons, elastically scattered from a carbon target in the internal beam of the Cosmotron. All two-prong events, excluding strange particle events, have been studied by the Yale High-Energy Group. The remaining interactions have been studied by the Brookhaven Bubble Chamber Group. Elastic scattering was found to be mostly pure diffraction scattering at center-of-mass angles up to about thirty-five degrees. Some phase shift and/or tapering of the proton edge was required to fit the data at larger angles. No polarization effects in the proton-carbon scattering were observed using hydrogen as an analyzer of polarized protons. Nucleonic isobar formation in the T=32, J=32 state was found to account for a large part of single pion production. High-orbital angular-momentum states were found to be greatly favored in single pion production. The isobar model of Lindenbaum and Sternheimer gave good agreement with the observed nucleon and pion energy spectra. No polarization or alignment effects were observed for the isobar assumed in this model.
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An investigation of π−+p elastic scattering, made in a liquid propane bubble chamber, is reported. Identification of events is made on the basis of kinematics. The problem of contamination by pion scattering from protons bound in carbon is considered in some detail; it is shown that the latter requires a correction of only 4±2.5% of the total number of events. The angular distribution is presented. It shows a large diffraction peak at small angles and an approximately isotropic plateau over the backward hemisphere. The forward peak is fitted to a black-sphere diffraction pattern with a radius of (1.08±0.06)×10−13 cm. The total elastic cross section is found to be σe=10.1±0.80 mb.
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Transmission measurements in good and poor geometry have been performed at the Brookhaven Cosmotron to measure the total and absorption cross sections of several nuclei for neutrons in the Bev energy range. The neutrons are produced by bombarding a Be target with 2.2-Bev protons. The neutron detector requires the incident particle to pass an anticoincidence counter and produce in an aluminum radiator a charged particle that will traverse a fourfold scintillation telescope containing 6 in. of lead. Contribution of neutrons below 800 Mev are believed small. The angular distribution of neutrons from the target is sharply peaked forward with a half-width of 6°. The integral angular distributions of diffraction scattered neutrons from C, Cu, and Pb are measured by varying the detector geometry. The angular half-width of these distributions indicates a mean effective neutron energy of 1.4±0.2 Bev. The total cross sections σH and σD−σH are measured by attenuation differences in good geometry of CH2-C and D2O-H2O, with the result: σH=42.4±1.8 mb, σD−σH=42.2±1.8 mb. The cross sections of eight elements from Be to U are measured in good and poor geometry, and the following values of the total and absorption cross sections are deduced (in units of millibrans): Experimental errors are about 3 percent in σtotal and 5 percent in σabsorption. An interpretation of these cross sections is given in terms of optical model parameters for two extreme nuclear density distributions: uniform (radius R) and Gaussian [ρ=ρ0exp−(ra)2]. The absorption cross-section data are well fitted with R=1.28A13 or a=0.32+0.62A13 in units of 10−13 cm. A nuclear density distribution intermediate between uniform and Gaussian will make the present results consistent with the recent electromagnetic radii.
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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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