The energy dependence of backward π+p elastic scattering has been measured for incident π momenta 2.0-6.0 GeV/c in steps of typically 100 MeV/c. Values are presented for both the differential cross section extrapolated to 180° and the slope of the backward peak as a function of momentum. In the s channel we see the effects of the established Δ++ resonances and evidence for the Δ(3230). Also, the data show the existence of a negative-parity Δ resonance with mass ∼2200 MeV/c2.
No description provided.
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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We present a measurement of the total cross section σ t in proton-proton collisions at the CERN ISR. The method involves determination of the total interaction rate and machine luminosity. A two-arm scintillation hodoscope observes ∼ 90% of the total interaction rate, while a streamer chamber is employed for event topologies missed by the main trigger. An increase of about 10% in σ t is observed in the energy range √ s = 23.6 to √ s = 62.8 GeV/ c in agreement with previous experiments.
VAN DER MEER METHOD.
We present a study of the transverse momentum spectrum of π 0 's produced at c.m. angles θ = 90° and 53° in pp collisions at √ s = 23.6, 30.8, 45.1, 53.2, and 62.9 GeV. The experiment was performed with a lead-glass detector. The data can be described with the usual parametrization p T −n ƒ;(x T , θ) , with n = 7.2 ± 0.2. Comparison between the 90° and 53° data further indicates no appreciable dependence on θ , at least for x T < 0.3. Two-particle inclusive cross sections for π 0 's produced alongside are also presented. They are observed to have a dependence upon the transverse momentum of the dipion similar to that of single-particle cross sections and with the same value of n . Two-photon decays of η mesons are observed between 3 and 4 GeV/ c transverse momentum with a production cross section half of that of π 0 .
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Approximately 12 000 examples of the reaction pp→Δ++(1236)n have been identified at 6 GeV / c in a spark-chamber experiment performed at the Argonne National Laboratory Zero Gradient Synchrotron. The experimental invariant-mass and momentum-transfer-squared distributions are in agreement with predictions of the Chew-Low one-pion-exchange model, suitably modified to account for form factors or absorption. The data have been extrapolated from the physical region to the pion pole. It is found that the Dürr-Pilkuhn and Benecke-Dürr models, in conjunction with quadratic extrapolations in t, reproduce the known on-mass-shell dependence of the cross section for the elastic π+p scattering.
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The reaction γ V p → p π + π − was studied in the W , Q 2 region 1.3–2.8 GeV, 0.3–1.4 GeV 2 using the streamer chamber at DESY. A detailed analysis of rho production via γ V p→ ϱ 0 p is presented. Near threshold rho production has peripheral and non-peripheral contributions of comparable magnitude. At higher energies ( W > 2 GeV) the peripheral component is dominant. The Q 2 dependence of σ ( γ V p→ ϱ 0 p) follows that of the rho propagator as predicted by VDM. The slope of d σ /d t at 〈 Q 2 〉 = 0.4 and 0.8 GeV 2 is within errors equal to its value at Q 2 = 0. The overall shape of the ϱ 0 is t dependent as in photoproduction, but is independent of Q 2 . The decay angular distribution shows that longitudinal rhos dominate in the threshold region. At higher energies transverse rhos are dominant. Rho production by transverse photons proceeds almost exclusively by natural parity exchange, σ T N ⩾ (0.83 ± 0.06) σ T for 2.2 < W < 2.8 GeV. The s -channel helicity-flip amplitudes are small compared to non-flip amplitudes. The ratio R = σ L / σ T was determined assuming s -channel helicity conservation. We find R = ξ 2 Q 2 / M ϱ 2 with ξ 2 ≈ 0.4 for 〈 W 〉 = 2.45 GeV. Interference between rho production amplitudes from longitudinal and transverse photons is observed. With increasing energy the phase between the two amplitudes decreases. The observed features of rho electroproduction are consistent with a dominantly diffractive production mechanism for W > 2 GeV.
DIPION CHANNEL CROSS SECTION.
THE TOTAL CROSS SECTION WAS OBTAINED BY THE AUTHORS FROM A FIT TO THE SINGLE ARM DATA OF S. STEIN ET AL., PR D12, 1884 (1975).
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Qausi-elastic ω production by ep scattering in the kinematic region 0.3. < Q 2 < 1.4 GeV 2 and 1.7 < W < 2.8 GeV was studied using a streamer chamber at DESY. The production angular distribution for γ V p → ω p has a strong non-peripheral component for W < 2 GeV. The ω production cross section falls by a factor of 4 as W changes from 1.7 to 2.8 GeV. In contrast the cross section for ω production with | t | < 0.5 GeV 2 is W independent between 1.7 and 2.8 GeV and for W > 2.0 GeV consistent in both W and Q 2 dependence with the predictions of a model based on one-pion exchange and diffraction.
FOR ALL T-VALUES. THE GAMMA* P TOTAL CROSS SECTION WAS TAKEN FROM A FIT TO THE DATA OF S. STEIN ET AL., PR D12, 1884 (1975). 'PPD'.
'PPD'. PERIPHERAL OMEGA PRODUCTION.
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Charged hadron production via e + e − → h ± X where h ± = π ± , K ± , p ̄ has been measured for s values between 13 and 25 GeV 2 . Inclusive cross sections and the evidence for scaling are presented.
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The total cross section for K ± production in e + e − collisions was measured for cms energies between 3.6 and 5 GeV and was found to increase by a factor of 2–3 from 3.6 to 4.1 GeV.
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The multiplicity distribution of inclusive electron events above 4 GeV cm energy shows two distinct classes of events: two prong no photon and high multiplicity events. If the high multiplicity events are attributed to the semi-leptonic decay of charmed particles the two prong no photon events must come from the weak decay of a different type of particle. The charged K to π ratio was measured for these events. The average number of charged kaons is 0.07 ± 0.06 per two prong event and 0.90 ± 0.18 per multiprong event. Thus the weak current responsible for the low multiplicity events has a small coupling to strange particles.
NUMBER OF CHARGED PARTICLES OBSERVED .EQ. 2.
NUMBER OF CHARGED PARTICLES OBSERVED .GE. 3.
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