The inclusive proton spectrum for\bar pd \to 3\pi p at rest re-examined

We re-analyze the spectator proton distribution for ¯pd→π ⁺ π^? π^? p. For this channel previous calculations underestimated the cross section for proton momenta of 300 to 600 MeV/c by about a factor 7 while the channels with higher pion multiplicities and the ¯pd→K¯ Kmπp reactions were well explained. By using detailed experimental information on ¯pn and ¯pp annihilation, meson rescattering can in fact explain the cross section also for the 3π case. The¯ pp annihilation followed by charge exchange pion rescattering is much larger than in the 5π case. Vector meson exchange is small but not negligible at high spectator momenta.     

Relativistic calculation for the reactions\bar p d → 5πp and\bar p d → 3πp at rest

We present a fully relativistic calculation for ¯pd → 5πp and ¯pd → 3πp that includes angular momentum and spin dynamics. We calculate the inclusive proton distributions from two diagrams: the leading “tree” diagram, and the diagram for pion rescattering. Pion-nucleon rescattering proceeds through the Δ, in the RaritaSchwinger formalism, thus preserving the correct angular dependence. We use realistic parameterizations of the deuteron, keeping both theS andD states. The loop integrations for the rescattering amplitude and the phase space integrations have been done numerically. We find that the combined effects of a correct treatment of the rescattered pion and relativity are small in comparison with a simple non-relativistic calculation.     

Study of the reaction ¯pd→p s π+2π−π0 at 5.5 GeV/c incident momentum

A study of a 150000-picture exposure of ¯pd at 5.5 GeV/c yielded 152 events satisfying the hypothesis ¯pd→p _s π⁺2π^?π⁰. For the events with proton spectator in the momentum range 100–280 MeV/c we obtained the cross section of 0.11±0.02 mb. Assuming the validity of the impulse approximation we estimate a cross section of 0.43±0.06 mb for the reaction ¯pn→ π⁺2π^?π⁰. The rate for single ? meson production and an upper limit for double ? production are given. A modified multiperipheral Regge model was used in order to describe the general features of the data.     

Evidence against a strong sub-threshold structure in the¯p p amplitude

Spectator nucleon distributions in¯pd →mπN are directly related to the antiproton-nucleon annihilation process below threshold. To demonstrate this quantitatively, we analyse the available¯pd → 3πN and¯pd → 5πN data. For these data, (and others) the shape of the annihilation spectrum in the peak region is well described by the tree diagram, and reflects mainly theS-state part of the deuteron wave function. The data are not consistent with a strong structure in the antinucleon-nucleon sub-thresh-old amplitude as reported in the dispersion analysis of¯pp while a weak structure is consistent with the existing data.     

Analysis of the processes¯NN→3π,¯pp→ηπ+π− and¯pp→ωπ+π− as a test of a dual four-point-function without parity doublets

The five annihilation processes at rest:¯pn→π⁺π^?π^?,¯pp→π⁰π⁺π^?,¯pp→3π⁰,¯pp→ηπ⁺π^? and¯pp→ωπ⁺π^? are simultaneously analyzed by means of a dual quark-symmetric four-point-function without parity doublets. The qualitative features of the mass-spectra are reproduced without free parameters. Predictions for¯pp→3π⁰ are made and compared with the results of Lovelace's model. In connection with the calculation of the ratios of rates we discuss the problem of the mass extrapolation for the external particles. The ?—? puzzle turns out to be a key problem for the processes under consideration.     

Singlet-to-triplet ratio in the deuteron breakup reaction pd→pnp at 585 MeV

Available experimental data on the exclusive pd→pnp reaction at 585 MeV show a narrow peak in the proton–neutron final-state interaction region. It was supposed previously, on the basis of a phenomenological analysis of the shape of this peak, that the final spin-singlet pn state provided about one third of the observed cross section. By comparing the absolute value of the measured cross section with that of pd elastic scattering using the Fäldt–Wilkin extrapolation theorem, it is shown here that the pd→pnp data can be explained mainly by the spin-triplet final state with a singlet admixture of a few percent. The smallness of the singlet contribution is compatible with existing pN→pNπ data and the one-pion exchange mechanism of the pd→pnp reaction.     

Rates for the reactions\bar pp \to \pi \phi andγ φ

We study ¯pp annihilation at rest intoπφ andγφ. Rescattering by ¯K^*K+K^*¯K and ρ⁺ρ^? for ¯pp→πφ states is sizable, of order (0.90 to 2.6) × 10^?4 in the branching ratio, but smaller than experiment. For ¯pp→γφ the rescattering contributions are negligible, but theγφ channel is well explained by aρφ intermediate state combined with vector meson dominance.     

Measurements of the inclusive pd breakup cross section at low and intermediate energies

Inclusive measurements of the D(p, p)pn reaction were made at incident proton energies of 248?MeV and 13?MeV, to investigate the global feature of the pd breakup reaction at intermediate and low energies. At 248?MeV, the cross section and analyzing power A _y were measured at four angles from 7° to 20°. The data largely disagree with Faddeev calculations even if 2π-exchange three-nucleon force (2π3NF) or Δ-isobar is included, and the disagreement increases at forward angles. At 13?MeV, the cross section was measured at eight angles from 10° to 70°. The data are well reproduced by a recent pd Faddeev calculation, and the effects of Δ-isobar at 13?MeV are very small.     

Two meson doorway calculation forpp → Øπ including off-shell effects and the OZI rule

The leading two meson doorway contributions to the reactionpp → øπ, φπ, due to K^*K andpp intermediate states are calculated beyond unitarity approximation. The dependence of the results on the off-shell parametrization is explored and the effect of the finite width of the propagating mesons is estimated. The rates obtained from the rescattering mechanisms are in agreement with the data for ¯pp →φπ annihilation at rest. The vertices entering the calculation do not require any unexplained OZI violation, in particular no substantials? configuration in the nucleon appears to be needed.     

Manifestation of the bound state \bar NN (1870) in the annihilation process \bar pd \to p_s 5\pi

It is shown that the existence of an N?N bound state with a mass of approximately 1870 MeV and width 10 MeV follows from analysis of the experimental data on the momentum distribution of recoil protons in the annihilation process p?d→p _s5π.     

π° photoproduction on quasi-free neutrons in the reactionγd→π°np in theΔ region

The possibility of obtaining information about the reactionγn→π°n in theΔ resonance region from the reactionγd→π°np is analyzed. To this aim, the differential cross sectionsd ³ σ/dE _n dΩ _π dΩ _n both for unpolarized particles and in case of polarized photons and deuterons as well as the asymmetryΣ for linearly-polarized photons are calculated at photon energies from 250 to 400 MeV in the diagrammatic approach. The contributions from the pole diagrams as well as one-loop diagrams both withn-p andπ-N-rescattering are taken into account. The main contribution to the differential cross sections ofπ° photoproduction on the neutron in the quasi-free kinematics arises from the neutron pole diagram. The correction due ton-p rescattering decreases with increasing pion angle and becomes to be less than 8% atΘ _π ≥ 90°. The contributions of the proton pole diagram and the one ofπ-N rescattering were found to be negligible. Background effects are more pronounced in the case of the asymmetryΣ. However, they are also strongly suppressed in the neutron quasi-free kinematics at photon energies above 300 MeV.     

Regge pole model for invariant functions. IV

TheNN→NN andγN→πN differential cross sections for polarized targets are discussed in terms of invariant functions. In former fits of high energy experimental data certain of these invariant functions came out to be small. Based on these fits thepn→np,p¯p→ n¯n, γp→ nπ ⁺ andγn→ pπ ^? differential cross sections are predicted to be independent of the target polarization.     

Deuteron screening at high energies: an application of triple-regge analysis

We use a Regge pole analysis of the CERN-IHEP Boson Spectrometer measurements of the reaction Fπ^?p→p + anything at 25 and 40 GeV/c to estimate Glauber corrections to πd scattering. Inelastic rescattering becomes appreciable above 20 GeV/c, and accounts for recent experimental observations. Deuteron screening can serve as an internal-consistency check for the Reggeon calculus; to this end, additional experiments are suggested.     

Study of the centrally produced ωρ0 and ωω systems inpp interactions at 300 GeV/c

We have performed a search for vector-vector final states centrally produced in proton proton interactions at 300 GeV/c using the CERN Ω spectrometer. Evidence is found for ωρ⁰ production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s and for ωω production in the reactionpp→p _f (2π⁺2π^?2π⁰)p _s . However no evidence is found for ωø production in the reactionpp→p _f (K ⁺ K ^?π⁺π^?π⁰)p _s .     

Multi-nucleon mechanism for subthreshold antiproton production in proton-nucleus reactions

We study a many-body (multipion) mechanism for ¯p subthreshold production in proton-nucleus collisions. The incoming proton and the interacting nucleons in the target act as sources of pions that merge to produce a nucleon-antiproton pair. The calculation takes fully into account the initial state interaction and antiproton absorption in the final state. The cooperation of several nucleons in the initial state reduces the threshold for the reaction allowing for production rates that may account for 15–50% of the total ¯p production. We point out that this contribution should be added to the primary ¯p production mechanism due toΔ formation and rescattering, as found by other groups, and should be taken into account when trying to extract information about ¯p properties in the nuclear medium.     

Prediction of the one pion exchange contribution to the processπ − p→π − pω with the help of the Veneziano model

The one pion exchange contribution to the differentialπ ^? p→π ^? pω cross-section is calculated assuming that theπ→πω amplitude associated with one of the vertices is described by the Veneziano formula, and that only a trivial dependence of the latter on the mass of the exchanged pion needs to be taken into account. The remaining unknown overall constant is then fixed by considering the decayω→3π. A rough comparison with preliminary data from a 16 GeV/cπ ^? p experiment shows that the one pion exchange model could possibly describe the reactionπ ^? p→π ^? pω forπω masses above 1.4 GeV.     

Production properties ofD 0,D +,D *+ andD s + in 230 GeV/cπ − andK −-Cu interactions

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D _s ⁺ →K ⁺ K ^?π⁺, 543D°→K ^?π⁺ andK ^?π⁺π^?π⁺ as well as 249D ⁺→K ^?π⁺π⁺ (or charge conjugate). 147 mesons out of our \({{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-0em} {\bar D^0 }}\) sample were produced via chargedD ^* state. For all charmed mesons we determine the total production cross-section and study thex _F andp _t ² distributions.     

Prediction of Re ɛ fromK 13 decays in an extended cabibbo model

With the help of an extended Cabibbo model for the weak hadronic vector current which includes the 10 and ¯10 representations to account for possibleΔS=-ΔQ transitions, a prediction is made for the quantity (1-¦x¦²)/¦1?x¦² wherex=A(K⁰→π^üe^?¯v)/A(¯K⁰→π^üe^?¯v) using the experimental branching ratio Γ(K^?→ π⁰e^?¯v/Γ(K _L ⁰ →π^üe^?¯v). From the known charge asymmetry in the decay of the long lived kaon one then obtains Re?.     

Pion and nucleon dissociation in π−p→π−π+π−p at 205 GeV/c

In a 48 000-picture exposure of the Fermilab 30-inch hydrogen bubble chamber to a 205 GeV/cπ^?beam, we have measured 169 events of the reaction, π^?p→π^?π⁺π^?p, with a cross section of 635 ± 61 μb. This reaction proceeds almost entirely via low mass π^? → 3π and p → pππ dissociation. Factorization is satisfied for p → pππ dissociation in πp and pp interactions.