Two-body Final States Research Articles

Properties of the reaction [formula omitted] at 2.32 GeV/c

An analysis of a data sample of 1296 events of the reaction pp → K + K −π +π − at 2.32 GeV/ c is presented. The reaction cross section is 300 ± 20 μb. A number of tests of C conservation were made with careful attention to possible systematic errors, yielding no clear evidence of C violation. Various quasi two-body and quasi three-body final states contributing to this reaction were studied. The final state φπ + π − appears to be produced via a Zweig's rule violating mechanism. An analysis of the quasi three-body final state, K ∗0K −π + (with K ∗0→ K +π − ) plus charge conjugate, whose cross section is 84 ± 12 μb, is given. The properties of this final state are compared with expectations based on a simple baryon exchange model, and poor agreement is found. A quark model allows a successful qualitative interpretation of the properties of this three-body final state.

K −p reactions from 0.960 to 1.355 GeV/ c involving two-body final states

Data are presented from a high statistics bubble chamber experiment to study K −p interactions in the c.m. energy range 1775 to 1957 MeV. For the reactions K −p → K −p, K − p → K 0 n , K −p → Λπ 0 and K −p → Σ ± π ∓ channel cross sections, differential cross sections and, where appropriate, polarisation distributions have been obtained. The channel cross sections for K −p → Σ 0 π 0 are presented. In general the results are in agreement with those previously published although a significant discrepancy has been found in the Σ ± π ∓ cross sections at the lower energies. New measurements of the Σ ± lifetimes have also been obtained ( τ Σ − = 1.49 ± 0.03 × 10 −10 sec, τ Σ + = 0.807 ± 0.013 × 10 −10 sec).

Some aspects of lambda production in the exclusive reactions K −p→ Λ0 + n pions at 8.25 GeV/ c

Cross sections are given for the various exclusive reactions K −p→ Λ 0 + n pions, as well as for quasi two-body final states involving ϱ 0, ω 0 and Y 1 ∗(1385) resonance production. The general features of Λ 0 production are presented as a function of the pion multiplicity n. Production of Y 1 ∗+(1385) is clearly observed at all multiplicities while the Y 1 ∗−(1385) signals grow with the multiplicity, as expected in a non-exotic exchange picture. The polarisation of the Λ 0 is consistent with zero everywhere, except when it is a decay product of Y 1 ∗(1385), when non-zero values are found for odd values of n. The reactions Λ 0 + 2π and Λ 0 + 3π are analysed in terms of the Plahte-Roberts model and good overall agreement is obtained for the various effective mass distributions and the p L ∗ , p T and cos θ distributions for the individual particles.

K −p charge exchange and hyperon production cross sections from 860 to 1000 MeV/ c

The K −p reactions leading to charge exchange and hyperon final states have been studied at nine momenta between 862 and 1001 MeV/ c using data from a 600 000 picture exposure of the Lawrence Berkeley Laboratory 25″ liquid hydrogen bubble chamber. Partial cross sections are determined for all final states resolved by kinematic fitting. In addition, differential cross sections are presented for the two-body final states K o n , Λπ o and Σ +- π -+ along with hyperon polarization angular distributions for Λπ o and Σ + π −.

Two-body hyperon final states in antiproton interactions at 2.2 GeV/c

The reactions\(\bar pp \to \bar \Lambda \Lambda \),\(\bar \Lambda \Sigma ^0 + C.C.\),\(\bar \Sigma ^ + \Sigma ^ + \) and\(\bar \Sigma ^ - \Sigma ^ - \) are studied at 2.2 GeV/c. The cross-section, differential cross-section, polarization and spin correlations (between the\(\bar \Lambda \) and Λ hyperons) are discussed.

Energy Dependence of the Double-Charge-Exchange Reactionsπ−p→K+Σ−,K−p→π+Σ−, andK−p→K+Ξ−

In an experiment at the Argonne National Laboratory zero-gradient synchrotron we have determined the forward differential cross sections for the double-charge-exchange reactions ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{\ensuremath{-}}$, ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\Sigma}}^{\ensuremath{-}}$, and ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Xi}}^{\ensuremath{-}}$ for incident beam momenta up to 5 GeV/c. The production angle and momentum of the forward-going positive particle (${\ensuremath{\pi}}^{+}$ or ${K}^{+}$) were measured with a high-resolution focusing wire-spark-chamber spectrometer and the two-body final states were selected by the missing-mass technique.

A study of the Regge recurrence of the Δ(1236) produced in 10 GeV/c K +p interactions

Data are presented on a high mass I 3 2 Δ resonance produced in 10 GeV/ c K +p interactions. The mass and width of the resonance, determined by a maximum likelihood fit to the p π + spectrum in the final state K +p π + π −, are 1895±15 MeV/ c 2230±50 MeV/ c 2 respectively. The differential cross sections, d σ/d t, for the quasi two-body final states K ∗(890)Δ(1236) and K ∗(890)Δ(1900) are well described by the one pion exchange model. In addition the moments of the Gottfried-Jackson angular distribution of the p π + system agree with those computed from on-shell π +p elastic scattering data. We conclude that the two final states are produced mainly by π exchange and associate the structure observed in the moments up to NH(6,0) in the 1900 MeV region with the 7 2 + Regge recurrence of the Δ(1236). The dominant decay mode of the resonance is Δ ++(1900)→p π + but decays to p π + π 0 and n π + π + are also observed. Cross sections are determined for the production of the quasi two-body final states K ∗(890)Δ(1236), K ∗(890) Δ(1900), K ∗(1420)Δ(1236) and K ∗(1420)Δ(1900).

Quantum number transfer in K −p interactions

Five-body final states from K −p interactions at 6, 10 and 16 GeV/ c are separated into sub-reactions depending upon which particles go forward in the c.m. system. The relative population and energy dependence of the various sub-reactions are shown to be closely related to the quantum numbers exchanged between the forward and backward going particles. In particular the energy dependence is the same as that found for the production of two-body final states involving exchange of the same quantum numbers. Single diffraction dissociation of the incident kaon and proton are shown to be important processes in these five-body states. We refer to this technique of separating events as binary LPS.

One pion production in pp collisions at 16.2 GeV/ c

A study of pp interactions at an incident momentum of 16.2 GeV/ c leading to two-prong non-strange final states was carried out in an exposure of the 2m CERN hydrogen bubble chamber. The c.m. angle and momentum distributions for the outgoing particles in the final states pn π + and pp π 0 are presented and discussed. These final states were analysed in terms of quasi two-body final states - N(Nπ), with the pion-nucleon system in an I = 1 2 or I = 3 2 state. A determination of these two isospin amplitudes and their interference term is then carried out. The reaction pp → pn π + is found to be well described by a Reggeized exchange model, as well as by a double Regge-exchange model.

Two-body final states in K-p interactions at 14.3 GeV/c

Event selection and weighting. In Fig. 1 a), the distribution of the square of the missing mass to the K0 in all zero-prong plus one K ~ events is displayed; a clear neutron signal is visible with a half-width of approximately 0.4 (GeV)L In the study of reaction (1) we use all events with missing mass less than the A(1236) mass. The cross-section is corrected for the few neutron events above this cut by double-counting the symmetrical region below the neutron mass. We also correct for the background reaction

Relativistic kinematics for two-body final states

Title of program: TWOBDY Catalogue number: ABOS Program obtainable from: CPC Program Library, Queen’s University of Belfast, N. Ireland (see application form in this issue) Computer: IBM 360/91. Installation: Princeton University Operating system: OS 360 Programming language used: FORTRAN IV High speed store required: 1597 words. No. of bits in a word: 64 Is the program overlaid? No No. of magnetic tapes required: None What other peripherals are used? Card Reader; Line Printer No. of cards in combined program and test deck: 185 Card punching code: EBCDIC

K−p interactions from 450 to 670 MeV/c

Angular distributions and polarizations of the two-body final states of the K−p system have been investigated at eight incident K− momenta from 450 to 670 MeV/c. The measured Legendre coefficients appear to be smooth functions of the energy, an upper limit of 5% for the elasticity of the Σ(1616) has been estimated. The result of a multichannel partial-wave analysis is also discussed.

The K+p interaction from 864 to 1585 MeV/c; angular distributions for inelastic scattering

We present angular distributions for production and decay of the quasi- two-body final states KΔ(1236) and K∗(891)p produced in K+p interactions at 864, 969, 1207, 1367 and 1585 MeV/c. The analysis of these distributionsleads to the following conclusions: (a) KΔ(1236) production near threshold is largely via P-waves and is, except for coupling constants, fairly well approximated at all momenta by the predictions of the Stodolsky-Sakurai ϱ-exchange model; (b) K∗(891)p production appears dominated by vector exchange down to threshold, and no evidence of significant relative increase in pseudoscalar exchange contribution at low energy is seen; (c) study of the partial-wave structure of KΔ(1236) production shows no evidence of resonant behavior at the total cross-section peak near 1200 MeV/c.

Some Two-Body Final States ofK−pInteractions at 1.33GeVc

Some Two-Body Final States of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mi>p</mml:mi></mml:math>Interactions at 1.33<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mi mathvariant="normal">GeV</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:mfrac></mml:math>

Quasi-Two-Body Final States Produced inπ+pInteractions Between 3 and 4 GeV/c

Cross sections and angular distributions for the quasi-two-body final states ${N}^{*++}{\ensuremath{\rho}}^{0}$, ${N}^{*++}{\ensuremath{\omega}}^{0}$, and ${N}^{*++}{\ensuremath{\eta}}^{0}$ were measured at five incident ${\ensuremath{\pi}}^{+}$ momenta between 3 and 4 GeV/c. These cross sections, when combined with results at higher momenta, indicate that the momentum dependence of the ${N}^{*++}{\ensuremath{\rho}}^{0}$ cross section deviates from that expected for a meson-exchange reaction, and that there is shrinking of the diffraction peak. Dips in the production angular distributions are observed, similar to those observed in two-body final states.

Study of YY production in two, three and four body final states by 3.0, 3.6 and 4.0 GeV/c antiprotons in hydrogen

We present the results on hyperon-antihyperon production by 3.0, 3.6 and 4.0 GeV/c antiprotons in hydrogen. We used about 300 000 pictures taken in an antiproton beam from the CERN proton synchrotron with the 81 cm Saclay hydrogen bubble chamber. A systematic study was made of interactions leading to a hyperon and an antihyperon with or without additional pions in the final states. The analysis indicates that the cross-sections for each of these processes are of the order of few tens of microbarns or less and that, whereas for the two-body final states the cross-sections decrease when the\(\bar p\) momentum increases from 3.0 to 4.0 GeV/c, the cross-sections for 3 and 4 body final states remain constant. For most of these events the angular distributions show a strong forward peaking of the antihyperon in the c.m.s. of the interaction. This suggests that a peripheral-type mechanism is predominant in these processes. About half of the events of the type\(\bar pp \to Y\bar Y\pi \) or\(\bar pp \to Y\bar Y\pi \pi \) proceed via the formation of hyperon or antihyperon resonances. The\(\overline {Y\mathop *\limits_1 } (1385)\),\(\overline {Y\mathop *\limits_0 } (1405)\),\(\overline {Y\mathop *\limits_0 } (1520)\) resonances and their charge con ugates are produced with masses, widths and decay branching ratios consistent with the values found in other experiments. The cross-sections for the reactions\(\bar pp \to A\bar Y\) or\(A\overline {Y*} \) are consistently larger by a factor varying from 2 to 6 than those corresponding to the reactions\(\bar pp \to \Sigma ^0 \bar Y\) or\(\Sigma ^0 \overline {Y*} \).

Study of the I = 2 Σπ system in π + N interactions

A study of the effective-mass distributions for systems recoiling against mesons (k/sup +/) produced both in pi /sup -/ + p and pi /sup -/ + n interactions is reported. Although all the known energetically accessible resonances are produced the data show no systematic enhancement that can be identified as arising from an I = 2 Y pi resonant state. A more favorable situation exists for SIGMA /sup -/ pi /sup 0/ and SIGMA /sup 0/ pi /sup -/ systems recoi ling against mesons(k/sup +/). The effective-mass distributions for all two-body final states produced in association with mesons(k/sup +/) are plotted. (C.E.S.) perimentally observed nucleon-nucleon scattering. Requirements of unitarity were not imposed, and the dispersion relations depend only on causality and the empirical spectrum of masses, spins, parities, and coupling constants. (C.E.S.)