Differential cross sections for the elastic scattering of negative kaons on protons are presented for 19 momenta between 1.732 GeV/ c and 2.466 GeV/ c . The general features of the cross sections are discussed.
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The differential cross sections for π−p elastic scattering over the angular range 155° to 177° in the center of mass have been measured at 33 incident-pion momenta in the range 600 to 1280 MeV/c. Angular distributions are presented. The extrapolated differential cross sections at 180° show considerable structure, in particular a dip near 1150 MeV/c. In general the near-180° cross sections do not agree with existing phase shift solutions above 1000 MeV/c
INTERPOLATED DATA.
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Excitation functions of proton-proton elastic scattering cross sections have been measured in narrow steps for projectile momenta pp (energies Tp) from 1100 to 3300MeV/c (500 to 2500 MeV) in the angular range 35°≤Θc.m.≤90° with a detector providing ΔΘc.m.≈1.4° resolution. Measurements have been performed continuously during projectile acceleration in the cooler synchrotron COSY with an internal CH2 fiber target, taking particular care to monitor luminosity as a function of Tp. The advantages of this experimental technique are demonstrated, and the excitation functions obtained are compared to existing cross section data. No evidence for narrow structures was found.
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The backward angular distributions obtained in an experiment at the Zero Gradient Synchrotron of Argonne National Laboratory were used to systematically study the energy dependence of the 180° differential cross section for π+p elastic scattering in the center-of-mass energy region from 2159 to 3487 MeV. At each of 38 incident pion momenta between 2.0 and 6.0 GeV/c, a focusing spectrometer and scintillation counter hodoscopes were used to obtain differential cross sections for typically five pion scattering angles from 141° to 173° in the laboratory. Values for dσdΩ at 180° were then obtained by extrapolation. A resonance model and an interference model were used to perform fits to the energy dependence of dσdΩ (180°). Both models led to good fits to our data and yielded values for the masses, widths, parities, and the product of spin and elasticity for the Δ(2200), Δ(2420), Δ(2850), and Δ(3230) resonances. Our data confirm the existence of the Δ(3230) and require the negative-parity Δ(2200).
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Differential cross sections are presented for pion-proton elastic scattering in the angular range −0.6≳cosθc.m.≳−0.98 at 15 incident π+ momenta from 2.18−5.25 GeVc. The angular distributions rise steeply near 180° at all momenta. For laboratory momenta ≳2.75 GeVc they show a minimum at u≈−0.17 (GeVc)2 and a broad maximum near u≈−0.6 (GeVc)2. When the data are plotted versus s, for fixed u, a strong signal from the Δ(2420) resonance is observed. The data are compared with a direct-channel resonance model and with a Regge model which considers the exchange of the Nα, Nγ, and Δδ Regge trajectories. The qualitative success of both the direct-channel resonance model and the Regge model lends support to the concept of duality.
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pp-elastic differential cross sections are reported at 492 MeV from 40° to 90°, and at 576, 642, 728, and 793 MeV from 75° to 90° c.m., with an absolute accuracy of less than 1%. These data, obtained with polyethylene targets, agree with recent measurements at the same energies obtained with a liquid-hydrogen target. © 1996 The American Physical Society.
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Absolute pp-elastic-differential cross sections were measured at incident energies 492, 576, 642, 728, and 793 MeV from about 30° to 90° c.m. The total uncertainty was determined to be less than 1%, made possible by particle counting for beam normalization and extensive cross-checks of systematic effects. These new data are consistent with previous data above 600 MeV but have uncertainties about a factor of 10 smaller. Near 500 MeV these data are consistent with 90° data from TRIUMF, but differ significantly from similar data from PSI; the cause of this discrepancy is discussed.
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We have measured the differential cross section for π−p elastic scattering at 180° in steps of 0.10 GeV/c or less in the region P0=1.6 to 5.3 GeV/c. We detected elastic scattering events, from protons in a liquid H2 target, with a double spectrometer consisting of magnets and scintillation counters in coincidence. The incident π− beam was counted by scintillation counters. The cross section was found to have considerable structure. This may be interpreted as interference between the resonant amplitudes and the nonresonant or background amplitude. Very strong destructive interference occurs around P0=2.15 GeV/c, where the cross section drops almost two orders of magnitude in passing through the N*(2190). Another interesting feature of the data is a large narrow peak in the cross section at P0=5.12 GeV/c, providing firm evidence for the existence of a nucleon resonance with a mass of 3245±10 MeV. This N*(3245) has a full width of less than 35 MeV, which is about 1% of its mass. From this experiment we were able to determine the parity and the quantity χ(J+12) for each N* resonance, where χ is the elasticity and J is the spin of the resonance.
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Differential cross sections for p−p elastic scattering are presented with scattering angles in the center-of-mass system greater than 35° to 50°. The data were obtained at incident laboratory momenta 0.857, 1.091, 1.210, 1.374, 1.405, and 1.501 GeV/c. This spans the region of the onset of Δ(1236) production and where a possible spin-singlet D-wave resonance is indicated in an analysis of earlier data.
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The differential elastic scattering cross sections for negative pions on ; protons were measured at incident momenta of 1.51, 2.01, and 2.53 Bev/c with ; emphasis on the angular region outside the diffraction peak. The purpose of the ; experiment was to examine the behavior of the largeangle differential elastic ; cross section as a function of energy from the energy of the highest known ; resonance in the pion-nucleon system into the region where the total. cross ; sections appear to be approaching an asymptotic value. The experiment was ; performed at the Bevatron, using a luminescent chamber system to photograph the ; tracks of the scattered pion and the recoil proton from a liquid hydrogen target. ; A total of 2412 elastic scatterings were analyzed at 1.51 Bev/c, 1300 events at ; 2.01 Bev/c, and 1080 events at 2.53 Bev/c. From the existing data it may be ; noted that the backward bump, which has a maximum height of 2.1 mb/sr at 900 Mev ; and 1.1 mb/sr at 1020 Mev, is down to 0.4 mb/sr at 1.51 Bev/c (1.37 Bev), and is ; not present at 2.01 or 2.53 Bev/c. The angular distributions behind the ; diffraction peak at 2.01 and 2.53 Bev/c are rougly constant, decreasing from 0.18 ; mb/sr at 2.01 Bev/c to 0.125 mb/sr at 2.53 Bev/c. Although the data can be taken ; to suggest some oscillatory structure in this region, they are not inconsistent ; with an isotropic distribution that might be interpreted as evidence for an S-; wave scattering behind the diffraction peak. Large-Angle Elastic Scattering of Negative Pions by Protons at 1.51, 2.01, and 2.53 Bev/c.
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We present a series of numerical and statistical techniques for interpolating and combining ("amalgamating") data from meson-nucleon scattering experiments. These techniques have been extensively applied to πp elastic and charge-exchange differential-cross-section and polarization data in the resonance region. The amalgamation is done by fitting a momentum- and angle-dependent interpolating surface to the data over a moderately narrow momentum range, typically ∼150 MeV/c, using the interpolating surface to shift data in a narrower central momentum region into fixed angular bins at a predetermined central momentum, and then statistically combining the data in each bin. The fitting procedure takes into account normalization errors, momentum calibration errors, momentum resolution, electromagnetic corrections, threshold structure, and inconsistencies among the data. The full covariance matrix of the amalgamated data is calculated, including contributions of statistical error, systematic error, and interpolation error. Techniques are presented for extracting from the covariance matrix information on the collective statistical fluctuations which correlate the errors of the amalgamated data. These fluctuations are described in terms of "correlation vectors" which facilitate the use of the amalgamated data as input for resonance-region phenomenology.
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The differential cross-section for π - -p elastic scattering over the angular range 125° to 178° center of mass has been measured between 1.28 and 3.0 GeV/ c . Considerable structure is found and is discussed in terms of direct channel resonances.
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Large-angle π±p elastic-scattering cross sections, measured between 2 and 9 GeV/c in fine intervals of incident momentum and scattering angle, are used to search for cross-section fluctuations occurring for small changes in the center-of-mass energy as suggested by Ericson and Mayer-Kuckuck and by Frautschi. Significant fluctuations are observed.
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Polarization and differential cross-section data for elastic scattering of positive pions on protons between 0.82 and 2.74 GeV/ c are presented. A dip in the polarization, at constant u ≈ −0.65 GeV 2 , is observed. The data are compared with published phase-shift analyses.
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New high-statistics measurements of π + p elastic scattering differential cross sections are presented at 30 momentum points between 1.282 and 2.472 GeV/ c , covering most of the angular distribution outside the forward diffractive peak. These data show significant disagreements at some momenta with previous high-statistics experiments and with current partial wave analyses.
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Differential cross sections for π+p elastic scattering in the momentum region 1.2 to 2.3 GeV/c are presented for the center-of-mass angular range 0.9>cosθ>−0.9. Typically, 50 000 events were obtained at each of 16 momenta using magnetostrictive-readout wire spark chambers to detect the particles scattered from a liquid hydrogen target. The results are compared to those of the CERN-71 phase-shift analysis. The well-known dips at t≅−0.7 (GeV/c)2 and at u′=−0.2 (GeV/c)2 are observed. In addition, structure is seen at constant u′=−1.3 (GeV/c)2. The results of a pion attenuation study in iron are also presented.
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We measured elastic-scattering angular distributions for π++p scattering at 1.5, 2.0, and 2.5 BeV/c using spark chambers to detect scattered pions and protons. A bump that decreases in amplitude with increasing momentum is observed in the backward hemisphere in the 1.5- and 2.0-BeV/c distributions, but is not observed in the 2.5-BeV/c distributions. It appears reasonable to attribute this phenomenon to the 1.45-BeV/c resonance observed in the π++p total cross section. The data are compared with π−+p data and are found to support the theoretical prediction that the scattering cross sections for both charge states should become equal at high energies. We fit the angular distributions with a power series in cosθ*, and compare the extrapolated values for the scattering cross section in the backward direction with the calculation of the neutron-exchange pole contribution to the cross section. The "elementary" neutron-pole term contribution is calculated to be 90 mb/sr at 2.0 BeV/c, in violent disagreement with the extrapolated value, ≈0.5 mb/sr.
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New data on the K−p elastic and charge exchange reactions are presented in the K− momentum range between 1.934 GeV/c and 2.516 GeV/c. A conventional energy-dependent partial-wave analysis covering the widerPK- range from 1.6 GeV/c to 2.516 GeV/c is presented together with a p.w.a. in which the duality ands-helicity conservation ideas are explicitly imposed in the fits. Finally the new Y*’s observed in this experiment are classified inSU3 multiplets.
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pp interactions at 11 momenta in the range 0.9 to 2.0 GeV/ c have been studied. The elastic angular distributions, covering the c.m. angular range 22°–90°, agree in general with Hoshizaki's phase-shift analysis which shows the looping 1 D in and 3 F 3 amplitudes in the Argand diagram. About 80% of pn π + events come from the n Δ ++ state at all momenta above 1.2 GeV/ c . The behavior of the density matrix elements of the Δ ++ show no momentum or angular dependence. A large fraction of pp π 0 events also come from the p Δ + state at all momenta above 1.2 GeV/ c . The behavior of the Δ + density matrix elements is similar to that for the case of Δ ++ .
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Proton-proton elastic differential cross sections have been measured for incident laboratory momenta of 600-1800 MeVc and c.m. angles of 5°-90°. The data span, in a single experiment, the intermediate energy region from isotropic differential cross sections at lower energies to the development of a clear diffraction peak at higher energies. Parameters for phenomenological formulations derived from the experimental results are presented.
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We report on an experiment to obtain differential cross sections for K+p elastic scattering in the vicinity of the possible exotic baryon, the Z1*(1900). The differential cross sections are based on typically 70 000 selected events in the angular region −0.9≤cosθc.m.≤0.9 at each of 22 momenta from 0.865 to 2.125 GeV/c. The data are intended for use in partial-wave analysis to search for the Z1*.
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