A prism plot analysis of the reaction π − p→p π + π − π − at 16 GeV/ c has been made and the results are compared with those obtained in a similar analysis of the reaction π + p→ p π + π + π − at the same energy. The three dominating reaction mechanisms (pion dissociation, reggeon exchange, proton diffraction dissociation) appear to be well separated, while considerable residual overlaps are present inside these classes. The prism plot method is discussed as a means for detecting hidden structures and some evidence is presented for a broad three-pion enhancement around 2 GeV decaying primarily into ϱ 0 π − .
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A4(1900) IS CALLED A*(1800) BY AUTHORS. PI+ P CROSS SECTIONS PREVIOUSLY PUBLISHED IN M. DEUTSCHMANN ET AL., NP B99, 397 (1975).
Analyzing a sample of 220 000 events from an experiment still in progress at the CERN Proton Synchrotron (PS), 60 pairs of electrons with an energy above 700 MeV have been observed. The electrons, produced by annihilation of antiprotons stopped in a liquid-hydrogen target, are detected with optical spark chambers and scintillation counters. Twenty-nine out of these 60 pairs have been found to be collinear; normalizing with respect to the hadronic two-body channels π + π − and K + K − , a braching ratio B ee =Γ( p ̄ p → e + e − )/Γ( p ̄ p → total ) = (3.2 ± 0.9) × 10 −7 has been obtained
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The reactions K L o p→K S o p, π + Λ , π + Σ o have been measured for center-of-mass energies from 1540 to 1610 MeV. Channel cross sections and coefficients of the Legendre polynomial expansion of the differential cross sections and hyperon polarizations are presented. We see no evidence in the πΛ channel for the suggested 3 2 − resonance at 1580 MeV. The cross section for the K S o p channel shows an energy dependence which is not predicted by the existing phase shift solutions based on charged kaon data.
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Results are reported for the invariant differential cross-section of charged pions produced at x = 0 in proton-proton collisions at the CERN ISR. The range covered is 40 to 400 MeV/c in transverse momentum and 23 to 63 GeV in collision energy. The inclusive cross-section for π + and π − are increasing by 36 ± 2% and 41 ± 2%, respectively over the ISR energy range with a somewhat stronger increase at the lowest transverse momenta. The transverse momentum distribution is well described by an exponential in the transverse energy.
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We have performed a simultaneous measurement of the large transverse momentum (1.6 to 3.8 GeV/ c ) yields of single photons and of photon pairs at 90° production angle in pp collisions at ISR energies. Production cross sections for each of these two processes are compared.
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New experimental results are reported on diffractive dissociation of protons into (nπ + ) in proton-proton collisions at a centre-of-mass energy of s = 45 GeV . The data were obtained using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. We have searched for resonance contributions and found peaks at mass values of 1.5 GeV, 1.65 GeV, and 2.1 GeV. A dip in d σ d t is observed at low t and low mass; it is most pronounced for events with neutrons emitted at 90° in the Gottfried-Jackson frame. The correlation between mass and slope depends strongly on θ J . The cross section of the channel pp → pnπ + is 400 ± 110 μb at s = 45 GeV , giving an energy dependence of s −0.30±0.07 for isospin exchange zero in this channel.
SCALE UNCERTAINTY 20 PCT IS INCLUDED IN ERROR.
SIG(P P --> P N PI+) IS NEARLY EQUAL TO SIG(P P --> P (N PI+)) WHICH WAS ACTUALLY MEASURED, SINCE THE CROSS SECTION OF THE REACTION P P --> N (P PI+) IS LESS THAN .1 MUB AS MEASURED BY N. KWAK ET AL., PL 62B, 359, 1976.
EXTRAPOLATING TO T=0 AND ALLOWING FOR OTHER DECAY MODES YIELDS RESULT.
A comparison of K±p and p±p elastic scattering is made for incident energy 50 to 175 GeV. Average values of 0.19±0.04 and 0.11±0.02 GeV2 were found for the invariant-momentum-transfer values of the Kp and pp crossover points, respectively.
KP AND PP CROSSOVER POINTS AT -T = 0.19 +- 0.04 AND 0.11 +- 0.02 GEV**2 (AVERAGE VALUES) RESPECTIVELY.
The production and decay of the quasi-two-body final states KΔ(1232) and K ∗ (892)N produced in K + d interactions below 1.5 GeV/ c have been studied in a bubble chamber experiment.
RESONANCE CROSS SECTIONS COMPUTED BY MULTIPLYING THE PRODUCTION PERCENTAGES GIVEN BY THE INTERFERENCE MODEL BY THE CHANNEL CROSS SECTIONS GIVEN IN G. GIACOMELLI ET AL., NP B37, 577 (1972).
DIFFERENTIAL CROSS SECTIONS FROM DEUTERIUM DATA, NORMALIZED TO THE EXPERIMENTAL INTEGRATED CROSS SECTIONS QUOTED IN T 2.
LEGENDRE COEFFICIENTS FROM DEUTERIUM DATA.
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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Inclusive production of Λ and Λ in K + p interactions is studied at incident momenta of 8.2 and 16.0 GeV/ c . Cross sections and single-particle distributions are presented, the correlation between longitudinal and transverse momentum is investigated, and the dependence of average charge multiplicity on missing mass measured. For Λ production, early scaling is observed in the target fragmentation region when the data are presented in terms of ( M 2 - M th 2 )/ s and t , where M th is the threshold value of the missing mass M . Furthermore, a triple-Regge analysis in these variable yields an effective exchange trajectory which passes through the K, Q and L mesons. There is evidence for beam fragmentation in Λ and Λ production, but the contributions seem not to be dominant in the fragmentation region. Nevertheless, the parameter values in a triple-Regge description are estimated, and together with those for target fragmentation in Λ production, provide a complete description of the fragmentation contributions to the two reactions. Integration of the resultant distribution functions over the complete Chew-Low plot yields fragmentation cross sections increasing approximately as log s ; in addition the observed features of the x , p L and p T 2 projections and of the p L - p T correlation are well-described in the fragmentation regions. Central production contributions are isolated by subtracting the calculated fragmentation distributions
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