Differential cross sections for the reaction π−p→π0n were measured at nine incident-pion kinetic energies in the interval from 500 to 1300 MeV. The negative pion beam from the bevatron was focused on a liquidhydrogen target completely surrounded by a cubic array of six steel-plate spark chambers. The spark chambers were triggered on events with neutral final states. Charge-exchange events were identified from the one-shower and two-shower events in the spark-chamber pictures. By the Monte Carlo technique, the π0 distributions were calculated from the bisector distributions of the two-shower π0 events together with the observed γ-ray distributions of the one-shower π0 events. These π0 distributions were fitted with both Legendre-polynomial expansions and power-series expansions by the method of least squares. The extrapolated forward differential cross sections are in good agreement with the dispersion calculations. The Legendre coefficients for the differential cross sections in isospin state T=12 were obtained by combining our results with available data on π±p elastic scattering. In the light of existing phase-shift solutions, the behavior of these coefficients is discussed. The D5F5 interference term that peaks near 900 MeV is verified to be in isospin state T=12 only. We report here also the total neutral cross sections and the cross sections for the production of neutral multipion final states 2π0n and 3π0n. The 4π solid angle and the calibrated energy response of the spark chambers contribute to the accuracy of the results.
High energy factorization predictions for F2^c are derived using BFKL descriptions of the proton structure function F2 at HERA. The model parameters are fixed by a fit of F2 at small x. Two different approaches of the non perturbative proton input are shown to correspond to the factorization at the gluon or quark level, respectively. The predictions for F2^c are in agreement with the data within the present error bars. However, the photon wave-function formulation (factorization at quark level) predicts significantly higher F2^c than both gluon factorization and a next-leading order DGLAP model.
Using a data sample collected with the CLEO II detector at CESR, we have searched for dipion transitions between pairs of $\Upsilon$ resonances at energies near the $\Upsilon(4S)$. We obtain upper limits $B(\Upsilon(4S)\to \Upsilon(2S)\pi^+\pi^-) < 3.9 \times 10^{-4}$ and $B(\Upsilon(4S)\to \Upsilon(1S)\pi^+\pi^-) < 1.2 \times 10^{-4}$. We also observe the transitions $\Upsilon(3S)\to \Upsilon(1S)$, $\Upsilon(3S)\to \Upsilon(2S)$, and $\Upsilon(2S)\to \Upsilon(1S)$, from which we measure the cross-sections for the radiative processes $e^+e^- \to \Upsilon(3S)\gamma$ and $e^+e^- \to \Upsilon(2S)\gamma$.
Angular distributions of the α-particle production differential cross section from the breakup of 6Li and 7Li projectiles incident on a 208Pb target have been measured at seven projectile energies between 29 and 52 MeV. The α-breakup cross section of 6Li was found to be systematically greater than that of 7Li across the entire energy range. These data have been compared with previously reported results and with the predictions of continuum-discretized coupled channels (CDCC) calculations including resonant and nonresonant projectile breakup. The present data compare well with previous measurements, while the CDCC calculations provide a reasonable prediction of the relative α-breakup cross sections but underpredict their absolute values. The calculations confirm that a major factor in the enhancement of the 6Li to 7Li α-breakup cross section is the difference between the α-breakup thresholds of the two isotopes. These results have implications for structural studies of light exotic nuclei based on elastic scattering.
The structure function F2γ for a quasireal photon has been measured in the reaction ee→eeX for Q2 in the range 0.2<Q2<7 GeV2, by use of 9200 multihadron events obtained with the TPC/Two-Gamma detector at the SLAC storage ring PEP. The data have been corrected for detector effects by a regularized unfolding procedure and are presented as F2γ(x,Q2). The structure function shows scaling in the region 0.3<Q2<1.6 GeV2, x<0.3, and rises for higher Q2 and x>0.1. Below Q2=0.3 GeV2, scaling breaks down in accordance with the finite cross-section bound for real photons.
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We have studied the photoproduction of Jψ mesons on H, Be, Fe, and Pb targets using real photons at a mean energy of 120 GeV. The pT2 spectra were used to separate the coherent diffractive signals from the incoherent signals. Parametrizing the per-nucleus cross sections in terms of power-law dependences, Aα, we find that αcoh=1.40±0.06±0.04 for the coherent diffractive signals and αincoh=0.94±0.02±0.03 for the incoherent signals.
CROSS-SECTIONS ARE RELATIVE TO THAT FOR INCOHERENT J/PSI PRODUCTION OFF BERYLLIUM.
We have measured the cross section $\sigma(e^+e^-\to\pi^+\pi^-\gamma(\gamma))$ at DA$\Phi$NE, the Frascati \phi-factory, using events with initial state radiation photons emitted at small angle and inclusive of final state radiation. We present the analysis of a new data set corresponding to an integrated luminosity of 240 pb$^{-1}$. We have achieved a reduced systematic uncertainty with respect to previously published KLOE results. From the cross section we obtain the pion form factor and the contribution to the muon magnetic anomaly from two pion states in the mass range $0.592 < M_{\pi\pi} < 0.975$ GeV. For the latter we find $\Delta a^{\pi\pi}_\mu = (387.2\pm0.5_{\rm stat}\pm2.4_{\rm exp}\pm2.3_{\rm th})\times 10^{-10}$
The differential cross section for the reaction e + e − → γγ has been measured in the CMS energy range between 9.4 and 31.6 GeV. The results are found to be in agreement with the predictions of quantum electrodynamics up to momentum transfers- q 2 of 900 GeV 2 . The data set lower limits of about 40 GeV on QED cut-off parameters. We have searched for the decay υ (9.46) → γγ and obtain an upper limit Γ ( υ → γγ )/ Γ ( υ → all) < 1.4% (95% c.l.).
The results of a study of the annihilation reactions n p → θπ + and n p → ωπ + are reported; the data were collected by the OBELIX apparatus, with antineutrons annihilating in flight (momenta from ∼ 50 MeV/ c to 405 MeV/ c ). Annihilation frequencies and annihilation cross sections have been deduced, for both channels, as a function of antineutron momentum. From the cross section ratio, a substantial deviation from OZI rule expectations is observed. An s s quark content in the nucleon offers a fairly plausible explanation for such an effect.
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