Results on the following π−p reactions involving a hyperon are studied at 4.5 and 6.0 GeV/c from a high-statistics bubble-chamber experiment. (1) π−p→(Λ, Σ0)K0: Differential cross sections and hyperon polarizations are presented. Comparison with the line-reversed reactions K¯N→(Λ, Σ0)π indicates the failure of the predictions of K*(890) and K*(1420) exchange degeneracy. Effective trajectories for these two reactions are compared. Shrinkage is observed in K¯N→Λπ and not in π−p→ΛK0. (2) π−p→(Λ, Σ0)K*(890)0: Differential cross sections, hyperon polarizations, and K*(890)0 density-matrix elements are determined. ΛK*(890)0 decay correlations are found to impose strong constraints on the scattering amplitudes. The data indicate that both natural- and unnatural-parity exchanges contribute large, but opposite, Λ polarizations. This behavior cannot be explained by a simple exchange model utilizing K and the exchange-degenerate K*(890) and K*(1420) only. Additional trajectories or absorption effects are required to obtain the observed Λ-polarization effects. Comparison of ΛK*(890)0 and Σ0K*(890)0 indicates the greater importance of unnatural-parity exchange in the former reaction. We observe no evidence for deviations from isospin predictions in ΛK*(890)0 production where K*(890)0→K+π− and KS0π0. (3) π−p→ΛK*(1420)0 and ΛK*(1300)0: K*(1420)0 density-matrix elements satisfying positivity constraints are determined allowing for s-wave interference effects. Evidence of the existence of a narrow K*(1300)0→Kππ with a dominant K+ρ− decay mode is observed in the 4.5- and 6-GeV/c data. (4) Σ(1385), Λ(1405), Λ(1520) production: Differential cross sections for the quasi-two-body reactions π−p→Y0K0, where Y0 is Λ(1405), Λ(1520), or Σ(1385)0, are presented and found to have a very similar flat slope in the forward direction. Data for forward K+ scattering in the reaction π−p→Σ(1385)−K+ are presented and discussed. It is argued that this forward peak cannot be explained by kinematic reflection or an s-channel effect and therefore must be due to either two-particle exchange or a single exotic exchange in the t channel.
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FIT FOR FORWARD CROSS SECTION AND SLOPE.
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Axis error includes +- 0.0/0.0 contribution (?////NOT GIVEN).
Axis error includes +- 0.0/0.0 contribution (?////NOT GIVEN).
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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.
The reactionsπ−p→K0∑0(1385) andπ−p→K+∑−(1385) are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to approximately 90 events/μb. The total and differential cross sections and the density matrix elements of the Σ(1385) are presented. The results are compared with those obtained for the related processesπpp→K+∑+(1385) and\(K^ -p \to \pi ^ \mp\sum ^ \pm(1385)\) in this energy range. Evidence is presented for the existence of production mechanisms with exotic exchanges in thet channel.
FROM THE CHANNEL PI- P --> LAMBDA K0 PI0 WHICH HAS A CROSS SECTION OF 72 +- 4 MUB.
FROM THE CHANNEL PI- P --> LAMBDA K+ PI- WHICH HAS A CROSS SECTION OF 79 +- 3 MUB.
FORWARD CROSS SECTION.
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The inclusive production of Λ , K S 0 , Σ ± (1385) and K ∗± (892) in π − p interactions at 6 GeV/ c has been studied. The observed cross sections are: σ ( Λ )=0.94±0.06 mb, σ (K S 0 )=0.98±0.06 mb, σ ( Σ + (1385))=60±7 μb , σ ( Σ − (1385))=90±9 μ b, σ( K ∗+ (892))=216±28 μ b and σ( K ∗− (892))=41±8 μ b , respectively. The inclusive spectra of these particles are presented as functions of squared transverse momentum and Feynman scaling variable x . The polarization of Λ has also been investigated. It is found from a comparison with higher-energy data that the inclusive cross sections for Σ ± (1385) and the production ratios Σ ± (1385)/ Λ in π − p at 6 GeV/ c have not reached the high-energy limiting values.
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Cross sections or upper limits are reported for 12 meson-baryon and two baryon-baryon reactions for an incident momentum of 9.9 GeV/c, near 90° c.m.: π±p→pπ±,pp±,π+°±,K+Σ±, (Λ0/Σ0)K0; K±p→pK±; p±p→pp. By studying the flavor dependence of the different reactions, we have been able to isolate the quark-interchange mechanism as dominant over gluon exchange and quark-antiquark annihilation.
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The reactionsπ−p→K0(890) Λ,K0(890)Σ0 andK0(890)Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections, density matrix elements of the vector meson and hyperon polarizations are presented. A transversity amplitude analysis is performed for each of the reactions. The results are compared with those obtained for the SU(3) related processesK−p→ϕΔ, ϕΣ0, ϕΣ0(1385) andϱ−Σ+(1385) and with predictions of the additive quark model and SU(6) sum rules.
BREIT-WIGNER FIT WITH BACKGROUND POLYNOMIAL.
BACKWARD CROSS SECTION.
TOTAL CROSS SECTION USING SLICING TECHNIQUE. FORWARD (-TP < 1.2 GEV**2) CROSS SECTION IS 25 +- 2 MUB: DOUBLE MASS CUT GIVES 20 +- 7 PCT BACKGROUND CONTAMINATION.
We present the final results of a measurement of the polarization parameter P 0 in high-energy n~-p and p-p elastic scattering, performed using a target which contained polarized protons. Data were taken at beam momenta of 6.0, 8.0, 10.0 and 12.0 GeV/c for n-, and of 6.0, 10.0 and 12.0 GeV/c for n+ and p, in the interval of invariant four-momentum transfer squared-t from 0.1 to 0.75 (GeV/c)2.
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The differential elastic scattering cross sections for negative pions on ; protons were measured at incident momenta of 1.51, 2.01, and 2.53 Bev/c with ; emphasis on the angular region outside the diffraction peak. The purpose of the ; experiment was to examine the behavior of the largeangle differential elastic ; cross section as a function of energy from the energy of the highest known ; resonance in the pion-nucleon system into the region where the total. cross ; sections appear to be approaching an asymptotic value. The experiment was ; performed at the Bevatron, using a luminescent chamber system to photograph the ; tracks of the scattered pion and the recoil proton from a liquid hydrogen target. ; A total of 2412 elastic scatterings were analyzed at 1.51 Bev/c, 1300 events at ; 2.01 Bev/c, and 1080 events at 2.53 Bev/c. From the existing data it may be ; noted that the backward bump, which has a maximum height of 2.1 mb/sr at 900 Mev ; and 1.1 mb/sr at 1020 Mev, is down to 0.4 mb/sr at 1.51 Bev/c (1.37 Bev), and is ; not present at 2.01 or 2.53 Bev/c. The angular distributions behind the ; diffraction peak at 2.01 and 2.53 Bev/c are rougly constant, decreasing from 0.18 ; mb/sr at 2.01 Bev/c to 0.125 mb/sr at 2.53 Bev/c. Although the data can be taken ; to suggest some oscillatory structure in this region, they are not inconsistent ; with an isotropic distribution that might be interpreted as evidence for an S-; wave scattering behind the diffraction peak. Large-Angle Elastic Scattering of Negative Pions by Protons at 1.51, 2.01, and 2.53 Bev/c.
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Measurements have been made of the asymmetry in the scattering of π− mesons by a polarized proton target. Scattered π mesons and recoil protons were detected in arrays of scintillation counters; data were obtained at 16 scattering angles at each of 8 beam momenta between 875 and 1578 MeV/c. Analysis of these data together with earlier differential-cross-section measurements shows that there must exist at least three resonances in this energy region: (i) mass 1920 MeV/c2, Γ=170 MeV/c2, I=32, F72; (ii) mass 1682 MeV/c2, Γ=100 MeV/c2, I=12, F52; and (iii) mass 1674 MeV/c2, Γ=100 MeV/c2, I=12, D52.
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The total cross sections for interactions of K+ and 1r+ mesons with protons were measured. The following values were obtained: 21.3 ± 4.6 mb and 21 ± 4.3 mb for 4.75 ± 0.15 Bev/c and 3.7 ± 0.1 Bev/c K+ mesons, respectively; the corresponding values for 1r+ mesons of the same momenta were 33.3 ± 1.3mb and 30 ± 1.2mb. Data on the cross sections for inelastic collisions of K+ and 1r+ mesons with various nuclei have also been obtained.
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The rr- + p- n + rr0 charge-exchange scattering and the rr- + p- n + 1J ( 1J- 2y) reaction were investigated in 1.55-4.5 BeVIc region in a 17-liter propane-xenon bubble chamber. The total cross sections of both reactions were measured in this region. The angular distributions of the rr0 mesons in the charge-exchange reaction were obtained. The backward exchange-scattering cross sections du( rr- + p- n + rr 0 )ldQ were estimated.
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This investigation was performed with a 24-liter propane bubble chamber [i] and is a continu- ation of our previous work on the production of strange particles by 7-8-BeV 1r- mesons on hydrogen and carbon. [ 2 - 5 ] The properties of 1r 0 mesons inferred from the y quanta accom- panying A and K 0 production are given, and are compared with the properties of 1r+ and 7r- mesons emitted in A and K 0 production processes. The possibility of a resonance with radi- ative decay is noted.
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THE study of elastic scattering at high energies in the region of the diffraction maximum has gained in interest recently in connection with the verifica- tion of the asymptotic expressions obtained by cal- culating the Regge-pole trajectories. We have in- vestigated the elastic scattering of 3. 5- Be VIc 7r- mesons by protons. The measurements were made with the aid of a liquid-hydrogen bubble chamber 25 em in diameter, placed in a 14 kOe magnetic field.
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DATA READ FROM GRAPH BY SRS.
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The differential cross section for π ± p elastic scattering below 2 GeV/ c has been measured at small forward pion angles by an electronics experiment. The interference effects observed between the Coulomb and the nuclear interaction have been used to determine the magnitude and sign of the real parts of the π ± p forward scattering amplitude. The latter are compared to the values predicted by the dispersion relations.
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Differential cross sections have been measured for π − p elastic scattering at laboratory momenta in the range 1.2 to 3.0 GeV/ c for the c.m. range 0.97 > cos θ ∗ > −0.98 . The corresponding mass range is 1.78 to 2.56 GeV/ c 2 . The data was obtained from a counter experiment in which the scattered pions and protons were detected in coincidence by arrays of scintillation counters.
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Invariant single-particle cross sections for pion and proton production in π ± p interactions at 8 and 16 GeV/ c are presented in terms of integrated distributions as functions of x , reduced rapidity ζ and p ⊥ 2 , and also in terms of double differential cross sections E d 2 σ /(d x d p ⊥ 2 ) and d ζ d p ⊥ 2 ). A comparison of π ± and π − induced reactions is made and the energy dependence is discussed. It is shown that the single-particle structure function cannot be factorized in its dependece on transverse and longitudinal momentum. For the beam-unlike pion, there is an indication for factorizability in terms of rapidity and transverse momentum in a small central region.
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We have made measurements of polarization in π−p elastic scattering, with emphasis over the backward region, at 1.60 to 2.28 GeVc. The results indicate the absence of u-channel dominance in the backward region, as was observed in the case of π+p scattering. Comparisons have been made with predictions of various phase-shift analyses which show that the agreement is generally very poor in the backward region.
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The asymmetry in the scattering of π− mesons by polarized protons has been measured at 50 different momenta from 0.643 to 2.14 GeV/c. Results were obtained at values of cosθ ranging from approximately +0.9 to -0.95 in the c.m. system at each incident pion momentum. The pion beam was incident on a 7.6-cm-long crystal assembly of lanthanum magnesium nitrate, in which the hydrogen in the water of crystallization was polarized by the "solid effect." The total momentum spread of the beam was 10% (full width at half-height) and data were collected simultaneously in 4 momentum channels, each with 2½% full width at half-height. A gas Čherenkov counter was used to reject incoming electrons. Scattered particles were detected in scintillation counter arrays placed within the 10-cm gap of the polarized target magnet. Encoded information from each array was stored in the memory of a PDP-5 computer connected on-line to a fast electronic logic network. The computer was programmed to classify the events according to momentum and scattering angle and subdivide them into coplanar and noncoplanar categories. The latter provided a measure of the background. The results have been expressed in the form of an expansion in terms of first associated Legendre polynomial series and compared with the predictions of recent phase-shift solutions. It is concluded that although these analyses give satisfactory predictions of the general features of the results, no one solution gives complete agreement with the data above about 1.0 GeV/c.
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The energy dependence of the differential cross section for $\pi^+ p$ elastic scattering at a c.m. angle near 174 ° has been measured. The momentum range of incident $\pi^+$ was 2.06-4.70 GeV/c. On this energy dependence one can see a structure, i.e. maxima corresponding to the baryon resonances $\Delta(2420)$ and $\Delta(2840)$. The structure is used for determination of the parities of these resonances.
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The elastic scattering of 3.55 GeV/ c π + and π − mesons by protons was measured at centre-of-mass angles between 165° and 177°. The angular distributions for 864 events show a steeply rising backward peak for π + p, while the shape is less clear for π − p.
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Extrapolations.
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Backward elastic scattering has been measured for π + p at 2.85 and 3.30 GeV/ c and for π − p at 3.30 GeV/ c . The π + p angular distributions show steep backward peaks, whereas the π − p distribution is flatter. At 2.85 GeV/ c the π + p differential cross section close to 180° is more than twice that at 3.30 GeV/ c , supporting the assignment J P = 11 2 + for Δ δ (2420) resonance. The π + p data at 2.85 GeV/ c indicate the onset of a dip at cos θ c.m. ≈ −0.97.
The data for cos(theta) = 1 is the extrapolation.
The data for cos(theta) = 1 and U = 0 are the extrapolations.
The data for cos(theta) = 1 and U = 0 are the extrapolations.
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The analysis of the eight-prong interactions of 8 GeV/ c π + with protons indicates the existence of the new heavy nucleon isobar with the mass M = 3.69 GeV and the isospin T = 1 2 .
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We have studied ϱ − production at 8 GeV / c . The data cannot be explained by one-pion-exchange with absorption and we conclude that vector exchange contributes. This contrasts with ϱ o production at this energy and ϱ − production at lower energy.
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Cross sections based on total PI+ P cross section =25.8 mb (Vondardel, PRL 8, 173 (1962)).
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FOR PI- MESON: THETA(RF=LAB)=<75 DEGREE.
The results of the experiment to search for charged tachyon production by Π- mesons with the 4.5 GeV/c momenta in a liquid-hydrogen bubble chamber are presented. Analysis of the events chosen is carried out by the method of missing masses. A definite excess of events-candidates, which is difficultly explained by all known backgrounds, is observed. Nevetherless, as interpretation of these events is indefinite, the results obtained are considered as establishment of the upper limits to charged tachyon production cross sections. These limits are on the ∼10-4 level from the total cross section of Π-p interactions, that is considerably lower than the upper limits established up to now to probabilities of tachyon production in hadron reactions
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NAME=THEORY DENOTES THE MONTE-CARLO GENERATED CROSS SECTIONS.
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USING METHOD (A), SEE THE ARTICLE.
USING METHOD (B), SEE THE ARTICLE.
Results are given for the production differential cross sections and the ω decay angular distribution in terms of the ω spin density matrix elements.
PAPER ALSO GIVES OFF-DIAGONAL ELEMENTS OF THE ERROR COVARIANCE MATRIX.
PAPER ALSO GIVES OFF-DIAGONAL ELEMENTS OF THE ERROR COVARIANCE MATRIX.
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We report differential cross sections for π − p → n π 0 in the backward hemisphere at incident momenta of 2.6, 3.5, 4.3, 6.0, and 8.0 GeV/c. We observe less pronounced structure than some previous measurements with a shallow dip displaced from that seen in π + p elastic scattering.
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From a study of peripheral interactions wherein a negative pion of 12 or 18 GeV/c incident on a nucleon produced a pair of high-momentum pions, the pion-pion s-wave interaction was deduced. Normalizing to to the ϱo production cross sections, a pion-pion cross section falling smoothly from 50 mb (300 MeV) to 20 mb (600 MeV) is observed. The forward-backward asymmetry is negative for low dipion masses.
The errors are statistical only.
The errors are statistical only.
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The center of mass longitudinal momentum distributions of π− mesons produced in K+p interactions at 12.7 GeV/c and in π+p interactions at 7 GeV/c exhibit an asymmetry similar to that observed, for example, in single particle production in 25 GeV/c π−p interactions. This asymmetry is discussed in terms of quark structure of hadrons and other dynamical models.
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Mean PL and PT of PI-.
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