Virtual photoproduction of J/ ψ mesons has been measured for 280 GeV muon iron interactions in an iron/scintillator calorimeter target. The J/ψ's were identified by their decay into muon pairs. 315 events were observed, about half of which were elastic. The t , Q 2 and v distributions of these elastic events are presented. The v dependence is measured between 40 and 180 Mev and compared with lower energy photoproduction results. The Q 2 dependence is compared with the predictions of the vector dominance model.
TPRIME DISTRIBUTION OF ELASTIC J/PSI EVENTS FOR ALL Q2 AND NU WITH 280 GEV MUON BEAM.
NORMALIZED Q**2 DISTRIBUTION OF ELASTIC J/PSI EVENTS FOR ALL NU AND T WITH 280 GEV MUON BEAM.
EXTRAPOLATION OF Q**2 AND T DEPENDENCE TO CALCULATE D(SIG)/DT AT Q**2=0 AND T=0 FOR ELASTIC J/PSI PHOTOPRODUCTION PER NUCLEON.
Results are presented on the charge exchange reaction\(\bar pp \to \bar nn\) and\(\bar np\) annihilations from bubble chamber exposures to antiproton beam of momenta 700 and 760 MeV/c. The differential cross section of\(\bar pp \to \bar nn\) shows a forward spike followed by a clear dip bump structure. Total annihilation cross section of\(\bar np\) for average\(\bar n\) momentum of 700 MeV/c has been evaluated to be 55.4±2.2 mb. The multiplicity, Feynmanx andpT2 distributions for inclusive charged pions in\(\bar pp\) and\(\bar np\) annihilations are found to be similar. The emission of charged pions from\(\bar np\) annihilations are found to be consistent with thermodynamic models with temperature ∼110 MeV.
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We have measured elastic scattering of 5 and 6 GeV photons on hydrogen and deuterium in the angular range 10–50 mrad. On hydrogen we observe a forward diffraction peak with a slope of 8.5 (GeV/ c ) −2 . The extrapolated forward cross sections in units μ b/(GeV/ c ) 2 are 0.82 ± 0.04 at 5 GeV and 0.79 ± 0.04 at 6 GeV. They are consistent with the calculated amplitudes obtained from total cross section measurements via the optical theorem and dispersion relations assuming negligible contributions of spin-dependent amplitudes. Deuterium cross sections show a transition from coherent scattering at low | t | to incoherent scattering at higher | t |. They indicate that the isovector exchange amplitude a 1 is very small compared to the isoscalar a 0 . We obtain |a 1 | 2 /|a 0 +a 1 | 2 =0.13±0.09 , Re (a 0 a ∗ 1 )/|a 0 +a 1 | 2 =0.0±0.03, at 5 GeV , |a 1 | 2 /|a 0 +a 1 | 2 =−0.12±0.15 , Re (a 0 a ∗ 1 )/|a 0 +a 1 | 2 =0.10±0.04, at 6 GeV .
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Results are presented concerning K − d and K − n elastic scattering at an incident momentum of 4.5 GeV/ c . The high-energy Glauber formalism has been used in analyzing the data in which the nucleon scattering amplitudes are parameterized and employing the spherical and quadrupole deuteron form factors. An impulse approximation analysis of the K − n differential scattering cross section fitted to a single exponential of the form d σ /d t ) 0 e Bt , leads to the result (d σ /d t ) 0 = 21.3 + mn ; 5.5 mb/(GeV/ c ) 2 and B = 6.9 + mn ; 0.5 (GeV/ c ) −2 . A global fit has been made to existing K + mn; N two-body scattering data at this energy in order to determine the scattering amplitudes. It was found that the K − n and K − p elastic amplitudes are dominantly imaginary with a relatively small contribution from spin-flip amplitudes. The slopes of the differential elastic cross sections for K − n and K − p are nearly equal, as are those for K + n and K + p. However, the value of the slope for K + is smaller than that for K − at this energy.
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Cross sections for γd and γn interactions and photoproduction of ϱ 0 and ω are studied at 4.3 GeV, using a linearly polarized photon beam in a deuterium bubble chamber. We find that σ T (γ n ) ⋍ σ T (γ p ) within about 5% and that the γn average charge multiplicity is lower than γp by 0.42±0.09. About 4000 ϱ 0 events and 70 coherent ω events are observed. We present total and differential cross sections for both xoherent and incoherent ϱ 0 production on deuterium, as well as decay angular distributions and density-matrix elements. We find that the t -channel isospin-one exchange amplitude in γ N → ϱ 0 N (e.g. A 2 exchange) is at most 5–13% of the dominant isoscalar amplituds. The ϱ 0 production mechanism is dominantly s -channel helicity-conserving (SHC) on both neutrons and protons. We find that relative to the SHC amplitudes, the single and double helicity-flip amplitudes at the γϱ 0 vertex are of the order of 10–15% for | t | > 0.25 GeV 2 , and have the same sign on both nucleons. This shows that helicity-flip is mainly due to isoscalar exchanges. The ratio of ω to ϱ 0 coherent forward cross sections is found to be 0.16±0.04. The natural-parity exchange part of γ N → ω N is strongly dominated by isoscalar exchanges, and the magnitude of the isovector-exchange is consistent with zero.
TOPOLOGICAL CROSS SECTIONS AND AVERAGE CHARGE MULTIPLICITIES GIVEN IN TABLE 1.
The proton form factors GE(q2) and GM(q2) are determined at q2 = 75fm−2.
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At the Bonn 2.5 GeV synchrotron the differential photoproduction cross section d σ /d t of φ mesons has been measured at a photon energy of 2.0 GeV at fibe different t values between 0.23 < | t | < 0.73 (GeV/ c ) 2 . The φ meson was detected by magnetic momentum analysis of both charged decay K mesons and by a time of flight and angle measurement of the coincident recoil proton. We found an exponential behaviour for the t dependence of the cross section. The measured slope of the exponential decrease was b = (4.01 ± 0.23) (GeV/ c −2 . This result, combined with previous measurements at higher energies, implies that the slope of the pomeron trajectory is compatible with zero. In addition the experiment yielded a value of the φ mass, m φ = (1019.4 ± 0.8) MeV and a value of the φ width, Γ = (4.4 ± 0.4) MeV.
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We have measured the p p differential elastic cross section at 8 momenta from 353 to 578 MeV/ c , determining, for each momentum, the ratio ρ of the real to imaginary parts of the elastic forward amplitude, the slope b of the elastic cross section and the total p p cross section σ. Our results are compared with previous experimental results and with theoretical predictions.
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Numerical values supplied by M. Cresti.
We present experimental results on K + d interactions from 865 to 1585 MeV/ c incident beam momentum. We report measurements of several K + d partial cross sections and calculate most of the others using relations derived from isospin conservation and data from other experiments. The most striking feature of the cross section data is the abrupt rise of the total single-pion-production cross section near 1000 MeV/ c . We extract isospin-0 KN partial cross sections and find a rapid quasi-two-body reaction KN → K ∗ N . As in the case of the isospin-1 K + N system, it appears that the structure around 1200 MeV/ c in the total cross section for the isospin-0 K ∗ N system is well reconstructed by the sum of three smoothly varying channel cross sections σ 0 (KN), σ 0 (KN π ) and σ 0 (KN ππ ). We study thereaction KN → K ∗ N near threshold and find that the production and decay angular distributions can be interpreted in terms of t -channel phenomena, specifically a superposition of ω, ϱ, and π exchange. As is true of the isospin-1 KΔ and K ∗ N final states, the isospin-0 K ∗ N state has a behavior near threshold which is not very different from its behavior at much higher energy.
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The photoproduction of the ψ(3100) meson from a beryllium target has been measured using an 11.8-GeV bremsstrahlung beam. The energy and angular dependence of the measured spectra may be obtained from an elastic nucleon cross section of the form dσdt=(1.01±0.20)exp[(1.25±0.20)t] nb/GeV2. This cross section is exceedingly small in comparison with those of the other vector mesons.
ELECTRON PAIR PRODUCTION FROM BERYLLIUM TARGET. ELASTIC CROSS SECTION VALUE ALLOWS FOR SYSTEMATIC UNCERTAINTIES AND POSSIBLE INELASTIC CONTRIBUTIONS. -TMIN = 0.41 GEV**2.
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