Four-momentum Transfer Distributions Research Articles

Low-energyω(→π0γ)meson photoproduction in the nucleus

The ${\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ invariant mass distribution spectra in the $(\ensuremath{\gamma},{\ensuremath{\pi}}^{0}\ensuremath{\gamma})$ reaction were measured by the TAPS/ELSA Collaboration to look for the hadron parameters of the $\ensuremath{\omega}$ meson in the Nb nucleus. We study the mechanism for this reaction, where we consider that the elementary reaction in the Nb nucleus proceeds as $\ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\omega}N;\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$. The $\ensuremath{\omega}$-meson photoproduction amplitude for this reaction is extracted from the measured four-momentum transfer distribution in the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\omega}p$ reaction. The propagation of the $\ensuremath{\omega}$ meson and the distorted wave function for the ${\ensuremath{\pi}}^{0}$ meson in the final state are described by the eikonal form. The $\ensuremath{\omega}$ and ${\ensuremath{\pi}}^{0}$ mesons' nucleus optical potentials, appearing in the $\ensuremath{\omega}$ meson propagator and ${\ensuremath{\pi}}^{0}$ meson distorted wave function respectively, are estimated using the $t\ensuremath{\varrho}$ approximation. The effects of pair correlation and color transparency are also studied. The calculated results do not show medium modification for the $\ensuremath{\omega}$ meson produced in the nucleus for momentum greater than 200 MeV. It occurs because the $\ensuremath{\omega}$ meson predominantly decays outside the nucleus. The dependence of the cross section on the final-state interaction is also investigated. The broadening of the $\ensuremath{\omega}$-meson mass distribution spectra is shown to occur due to the large resolution width associated with the detector used in the experiment.

Pion diffraction dissociation into five pions at 16 GeV/ c

In π ±p interactions at 16 GeV/ c, evidence is obtained for the existence of the diffractive dissociation of the pion into five pions ( π → 5 π), and possibly also for π → 7 π, on the basis of the Feynman x distribution of the slowest pion. Cross sections for the five-pion diffractive component are estimated for the π + and the π − experiments using two methods. In a selected event sample characterized by the dominance of diffractive production of five-pion systems, an average ϱ 0(770) multiplicity of 1.75 ± 0.20 was measured, indicating ϱ 0 ϱ 0 π contributions in at least 75% of the events. The slope of the four-momentum transfer distribution of the five-pion systems was found to be similar to that of diffractively produced three-pion systems of the same mass. The results are compared with those reported for five-pion systems coherently produced on a deuteron target.

Model-independent analysis of π−n → pπ−π−π0 and π−n → ρ−π−p final states at 5 and 9 GeV/c

The final state π−n → pπ−π−π0 is investigated by means of the LPS technique. Cross-sections, mass spectra and four-momentum transfer distributions in each sector are reported. The sector corresponding to the π−n → (pπ−)(π−π0) grouping is the most aboundantly populated and it is dominated by ρ− production. A model-independent analysis of the three-body final state π−n → ρ−π−p allows us to evaluate the natural- and unnatural-parity exchange contributions as a function of the fourmomentum transfer to the ρ− and of the (pπ−) mass.

Structure in momentum-transfer for (pπ −) systems produced in diffractive dissociation of neutrons on protons

The four-momentum transfer distribution of (pπ −) systems produced in the neutron dissociation reaction n + p → (p π −) + p has substantial structure which depends strongly on the mass and on the angular decay properties of the produced (pπ −) system. No significant energy dependence is observed in the data for incident neutrons in the momentum range between 50 GeV/ c and 300 GeV/ c. The results are compared with a Deck-type of model.

Production mechanism in the four-body reaction π+n → p π+π−π0 at 5.1 and 9 GeV/ c

The π +n → p π + π − π 0 reaction is studied in the longitudinal phase space (LPS). The cross sections, mass spectra and four-momentum transfer distributions are discussed in each LPS sector. The dominant processes seem to be the ΔQ = 0 and G parity positive exchange, and ΔQ = 0, 1 and G parity negative exchange. A low baryon diffraction dissociation is also present.

K+p interactions near 3 GeV/c (II): Baryon resonance production

Abstract Baryon resonance production in quasi-two-body reactions has been studied for the channels K+p→K°pπ+, K+nπ+ and K+pπ° at beam momenta of 2.53, 2.76 and 3.20 GeV/c. The production cross sections, four-momentum transfer distributions and density matrix elements are given for the Δ(1236), N∗(1400), N∗(1500) and N∗(1680) states. The reaction K+p→K°Δ++(1236) is compared to the line reversed reaction K − n → K °Δ − and the charge-exchange SU(3) sum rule for pseudo-scalar meson plus Δ(1236) is tested.

A dual description of the reactions K±p → K*0π±p for incident momenta from 2.7 to 12.7 GeV/cfor incident momenta from 2.7 to 12.7 GeV/c

A model is considered in which the reactions K±p → K*0π±p are simultaneously described in terms of a dual five-point function forp-wave exchanges plus dual-resonance amplitudes for pion exchange and pomeron exchange. Various versions of the model are considered. A convenient parametrization of the imaginary parts of Regge trajectories is introduced. Four free parameters are adapted to obtain good agreement with a vast amount of experimental data, containing effectivemass and four-momentum transfer distributions. These cover the incident-momentum interval from 2.7 to 12.7 GeV/c, and have been subjected to a variety of kinematical cuts in the different experiments which are taken into account in the analysis. Total cross-sections and their composition in terms of contributions of the various amplitudes are predicted. The Q-bump is reproduced out of K*(1420), diffraction dissociation of the K-meson (Q(1300)) and also nondiffractive pion exchange background. The L-bump is shown to be particularly sensitive to interference between pomeron exchange and the remaining part of the amplitude.

The four-momentum transfer distribution of the recoil proton for inelastic pp collisions

The four-momentum transfer distribution of the recoil proton for inelastic pp collisions

Study of the reactions K − + n → Σ± + mesons at 4.93 GeV/c

Data on ten quasi-two-body reactions produced in K −n interactions at 4.93 GeV/ c are presented. Cross sections, four-momentum transfer distributions, and density matrix elements are discussed. Results of a search for inelastic decays of high mass Y ∗ hyperons are given. Precision measurements of the φ o mass and width are reported. Possible direct channel Y ∗ formation is investigated.

The four-momentum transfer distributions of nucleons in π−p interactions at 16 GeV/ c

Distributions of four-momentum transfer from target proton to nucleon, d σ/d t, for 16 GeV/ c π −p reactions giving in the final state 2 to 8 pions, are analysed in terms of the F( t) function, which gives the average t-dependence of the matrix element squared for the reaction in question. It is shown that this function has a shape similar to the squared pion propagator for the reactions containing 3 to 8 pions in the final state. The data for 8 GeV/ c π +p reactions give results qualitatively similar to those for 16 GeV/ c π −p.

Analysis of p π+π− enhancements produced in the reaction π+p → π+p π+π− at 5 GeV/ c

The p π + π − effective mass spectrum is studied in the mass range from 1.2 to 2.3 GeV in the reaction π +p→ π +p π + π − at 5 GeV/ c. A resonant-type-enhancement is observed at 1.71 ± 0.01 GeV whose position is consistent with that of the S 11 pion-nucleon resonance rather than the D 15 or F 15 states, but whose width 66 ± 26 MeV is considerably narrower than that of the S 11. No evidence for an intermediate two-body decay is found. From the small value of the four-momentum transfer distribution slope 3.2 ± 0.4 GeV −2 a diffractive mechanism can be excluded. The p π + π − spectrum also shows a rapid increase near threshold, which, after elimination of peripheral Δϱ events appears as a broad diffractive-like enhancement (average slope 11.0 ± 1.0 GeV −2; the shape of this threshold effect has been obtained from a study of the variation of the four-momentum transfer distribution along the mass spectrum.

Quasi-two-body production in K −n → Σ∓ + mesons at 4.94 GeV/ c

Data on the following quasi-two-body reactions produced in K −n interactions at 4.94 GeV/ c are presented: Σ − π 0, Σ − η 0, Σ − ϱ 0, Σ − ω 0, Σ − η′ 0, Σ − φ 0, Σ −f 0, Σ −f′ 0, Λ(1405) π − and Λ(1520) π −. Cross sections, four-momentum transfer distributions, and density matrix elements are discussed. Assessment of possible exchange mechanisms and comparisons with the predictions of the quark model are made.

Four-momentum transfer distribution in high energy, high multiplicity reactions

The distribution of the four-momentum transfer to the secondary nucleon in high energy high multiplicity π-p interactions is discussed after corrections for the phase space have been correctly introduced. It is shown that the distribution is of the same general shape as that for the two body interactions.