Absolute measurements of the elastic electron-proton cross section have been made with a precision of about 4% for values of the square of the four-momentum transfer, q2, in the range 6.0 to 30.0 F−2 and for electron scattering angles in the range 45° to 145°. To within the experimental errors, it is found that the charge and magnetic form factors of the proton have a common dependence on q2 when normalized to unity at q2=0, and that an accurate representation of the behavior of the form factor and that of the cross sections themselves can be given in terms of a three-pole approximation to the dispersion theory of nucleon form factors.
Axis error includes +- 2./2. contribution (RANDOM ERROR).
Axis error includes +- 2./2. contribution (RANDOM ERROR).
Axis error includes +- 2./2. contribution (RANDOM ERROR).
Elastic electron-proton scattering cross sections were measured at backward angles (80°-90°) in the laboratory for four-momentum transfers between 7 F−2 and 45 F−2. Experimental errors range from 3.1% to 5.3%, including a systematic error estimated to be 1.9% added in quadrature. Electric and magnetic form factors are computed from all the recent data in this q2 range, with allowance made for possible normalization differences. The results show a deviation from the scaling law.
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41 ± 8 events of the type X 0 → γγ have been observed in a study of the reaction π − p → n(X 0 → γγ ) at 1.6 GeV/ c incident π -momentum. This provides further evidence to our previous observation of this new X 0 decay mode and allows the determination of the branching ratio Γ(X 0 →γγ) Γ(X 0 → total =(1.7 ± 0.4)%. The theoretical implications of this result are discussed.
THIS MEASUREMENT WHEN COMBINED WITH THE ETAPRIME PRODUCTION CROSS SECTION OF M. BASILE ET AL., NC 3A, 371 (1971) YIELDS A BR(ETAPRIME --> 2GAMMA) OF 1.7 +- 0.4 PCT.
The reactions π−p→ n+(X0→total) and π−p→ n+(X0→neutrals) have been studied at 1.6 GeV/c with the Bologna-CERN neutron missing-mass spectrometer. Both reactions have been detected without the use of visual techniques. The results are: σ(X0→total)=(108±14) μb and σ(X0→neutrals)=(20.0±3.5) μb, giving a branching ratio Γ(X0→neutrals)/Γ(X0→total)=(18.5±2.2)%. The branching ratio for other possible, so far undetected, neutral decay modes of the X0 turns out to be (2.4±1.9)%.
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Final results for 3678 six-prong π+p events at 8 GeV/c are presented. Single-particle distributions are compared with the predictions of the Chan-Loskiewicz-Allison model and the phenomenological model of the F(t) function. Differences between the transverse momenta of the π+ and π− and between the transverse momenta of secondaries emitted forward and backward in the c.m. system are observed. Cross sections for production of the ρ0, ρ+, ρ−, η, ω0, X0, and D0 mesons and the N33*++ and N33*− isobars are given, together with upper limits for some other resonances. The D0 meson is observed in the seven-body channel in the ηπ+π− system, with some evidence for the cascade decay D0→δ±π∓→ηπ+π−. The branching ratio (f0→2π+2π−)(f0→2π) is determined to be (2.2−2.2+4.5)%. Upper limits for the decay of A mesons into X0π systems are quoted. The cross section for the two-body reaction π+p→N33*++X0 is determined to be 30 ± 13 μb, from which the η0−X0 mixing angle is derived. Associated production of N33*++ and ρ0 in the six-body channel and of N33*++, ρ0, and ω0 in the seven-body channel is studied, and the cross sections for reactions involving simultaneous production of these resonances are estimated. The Goldhaber-Goldhaber-Lee-Pais effect is studied and shown to be strong in the six-body channel, especially for selected events with low energy of the pion system.
TOTAL NUMBER EVENTS=504. DATA FROM T 1.
TOTAL NUMBER EVENTS=1075. DATA FROM T 1.
TOTAL NUMBER EVENTS=425. DATA FROM T 1.
We give new experimental results on ρω interference and two-body cross sections in p¯p annihilation at 2.3GeVc. These are used, together with ρω interference results from lower energies, to argue that the annihilation process is not mediated by discrete s-channel mesonic resonances in the mass range 2.1-2.6 GeV.
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In a study of the production mechanism of quasi-two-body final states at the five incident π+ momenta 2.95, 3.2, 3.5, 3.75, and 4.08 GeV/c, approximately 40 000 events with four outgoing charged particles were investigated. The cross sections for the processes π+p→N*++ρ, π+p→N*++ω, π+p→N*++η, and π+p→N*++f have been measured as a function of the pion energy. The differential cross sections and the decay density-matrix elements are discussed in terms of one-meson-exchange models [with absorption (OPEA) and with form factor (OPEW)] and Regge models. For the N*++ρ and the N*++ω reactions, the joint-decay matrix elements are calculated. The formation of N*(2850) in the direct channel is also investigated.
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A study is made of η 0 production in p p → 3π + 3π − π 0 (7500 events) at an incident momentum of 720 MeV/ c . The reaction is dominated by production of ω 0 (≈68 o/o). The η o production has been studied by means of two independent methods: the first, a study of correlations between the (4 π ) ± and (5 π ) 0 and the (3 π ) 0 systems, circumvents the problem of ω 0 reflections. The second attempts to isolate the η 0 4π channel by means of rigorous selections using the decay properties of η 0 and ω 0 . The results of the two methods are consistent and confirnm the production of σ +- , D 0 and E 0 with the decays ifD 0 → σ ± π ± → η 0 π + π ( su −), E 0 → σ ± π ∓ → η ( su 0) π + π − , E 0 → η 0 π + π − .
CORRECTED FOR UNOBSERVED ETA DECAYS AND I=0 ASSUMED FOR ETAPRIME, D(1285) AND E(1420) --> ETA PI0 PI0.
Lambda production is studied in K − p interactions at 10.1 GeV/ c , where the dominant reaction is K − p → Λ + pions. General characteristics such as the distributions of the double differential cross section in the lab system, of the variable x = p L ∗ p max ∗ , of p ⊥ 2 and of the missing mass to the lambda are presented. Total cross sections for Λ production and for the various channels are given. Differential cross sections d σ d t , d σ d t′ and d σ d u′ are presented. Forward and backward peaks are observed in the d σ d t′ and d σ d u′ distributions, respectively. It is found that the exponential slope of these distributions decreases with increasing missing mass to the lambda and, for d σ d t′ , also for increasing multiplicity in the final state. The polarization of the lambdas is studied as a function of multiplicity, p L ∗ , (Λπ ± ) effective mass, t ′ and u ′. The forward lambdas show
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POSSIBLE FORWARD DIP.
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