arXiv subjects
Publications and source records attributed to B. Loiseau.
The scalar-isoscalar, scalar-isotensor and vector-isovector pion-pion partial wave amplitudes are analyzed. Preliminary results indicate that only the scalar-isoscalar amplitude fitted to the "down-flat" data satisfies Roy's equations and consequently crossing symmetry.
The latest measurements of the atomic level width in Sigma-hyperonic Pb atom offer the most accurate datum in the region of low-energy Sigma-hyperon physics. Atomic widths are due to the conversion of Sigma-nucleon into Lambda-nucleon. In high angular momentum states this conversion is dominated by the one-pion exchange. A joint analysis of the data of the scattering of negative-Sigma on proton converting into a Lambda and a neutron and of the atomic widths allows to extract a pseudovector pion-hyperon-Sigma coupling constant of 0.048 with a statistical error of +-0.005 and a systematic one of +-0.004. This corresponds to a pseudoscalar coupling constant of 13.3 with a statistical uncertainty of 1.4 and a systematic one of 1.1.
Interactions in coupled channels pipi, KKbar and an effective 2pi2pi in scalar-isoscalar wave have been analysed. Influence of interchannel couplings on analytical structure of multichannel interaction amplitudes has been studied. Interplay of S-matrix zeroes and poles and their relation with parameters of scalar resonances has been investigated.
The Coulomb-like backward peak of the neutron-proton scattering differential cross section is due to one-pion exchange. Extrapolation to the pion pole of precise data should allow to obtain the value of the charged pion-nucleon coupling constant. This was classically attempted by the use of a smooth physical function, the Chew function, built from the cross section. To improve accuracy of such an extrapolation one has introduced a difference method. It consists of extrapolating the difference between the Chew function based on experimental data and that built from a model where the pion-nucleon coupling is exactly known. Here we cross-check to which precision can work this novel extrapolation method by applying it to differences between models and between data and models. With good reference models and for the 162 MeV neutron-proton Uppsala single energy precise data with a normalisation error of 2.3 %, the value of the charged pion-nucleon coupling constant is obtained with an accuracy close to 1.8 %.
The isovector GMO sum rule for zero energy forward pion-nucleon scattering is critically studied to obtain the charged pion-nucleon coupling constant using the precise negatively charged pion-proton and pion-deuteron scattering lengths deduced recently from pionic atom experiments. This direct determination leads to a pseudoscalar charged pion-nucleon coupling constant of 14.23 +- 0.09 (statistic) +- 0.17 (systematic). We obtain also accurate values for the pion-nucleon scattering lengths.
Scalar-isoscalar mesons are studied using an unitary model in three channels: pi-pi, K-anti K and an effective 2pi-2pi. All the solutions, fitted to the pi-pi and K-anti K data, exhibit a wide f0(500), a narrow f0(980) and two relatively narrow resonances, lying on different sheets between 1300 MeV and 1500 MeV. These latter states are similar to the f0(1370) and f0(1500) seen in experiments at CERN. Branching ratios are compared with available data. We have started investigations of some crossing symmetry and chiral constraints imposed near the pi-pi threshold on the scalar-isoscalar, scalar-isotensor and P-wave pi-pi amplitudes.
We critically evaluate the isovector GMO sumrule for the charged $πN N$ coupling constant using recent precision data from $π^-$p and $π^-$d atoms and with careful attention to systematic errors. From the $π^-$d scattering length we deduce the pion-proton scattering lengths ${1/2}(a_{π^-p}+a_{π^-n})=(-20\pm 6$(statistic)$ \pm 10$ (systematic))~$\cdot 10^{-4}m_{π_c}^{-1}$ and ${1/2}(a_{π^-p}-a_{π^-n})=(903 \pm 14)\cdot 10^{-4}m_{π_c}^{-1}$. From this a direct evaluation gives $g^2_c(GMO)/4π=14.20\pm 0.07$(statistic)$\pm 0.13$(systematic) or $f^2_c/4π= 0.0786\pm 0.0008$.
Properties of scalar--isoscalar mesons in a mass range from pi-pi threshold up to 1800 MeV are analysed using an unitary model with separable interactions in three decay channels: pi-pi, K-anti K and an effective 2pi-2pi. Different solutions are obtained by fitting pi-pi and K-anti K data. Analytical structure of the meson-meson multichannel amplitudes is studied with a special emphasis on the important role played by the S-matrix zeroes. The dependence of the positions of S-matrix singularities on the interchannel coupling strength is investigated. Poles, located in the complex energy plane not too far from the physical region, are interpreted as scalar resonances: a wide f0(500), a narrow f0(980) and a relatively narrow f0(1400). In all our solutions two resonances, lying on different sheets, in the energy region between 1300 MeV and 1500 MeV are found. These states may be compared with the resonances f0(1370) and f0(1500) seen in the experiments at CERN. Total, elastic and inelastic channel cross sections, branching ratios and coupling constants are evaluated and compared with available data.
Properties of scalar-isoscalar mesons are analysed using separable interactions in three decay channels: pion-pion, kaon-antikaon and an effective 2pion-2pion. We obtain different solutions by fitting various data on the pion-pion and kaon-antikaon phase shifts and inelasticities including the CERN-Cracow-Munich measurements of the pion- p --> pion+ pion- n reaction on a polarized target. Analytical structure of the meson-meson multichannel amplitudes is studied with a special emphasis on the role played by the S-matrix zeroes. S-matrix poles are found in the complex energy plane and interpreted as scalar resonances. We see a wide f0(500), a narrow f0(980) and a relatively narrow f0(1400). In one solution a resonance at about 1700 MeV is also found. Total, elastic and inelastic channel cross sections, branching ratios and coupling constants are evaluated and compared with data. We construct approximation to our model and show that the Breit-Wigner approach has a limited phenomenological applicability.
We report here a preliminary value for the piNN coupling constant deduced from the GMO sumrule for forward piN scattering. As in our previous determination from np backward differential scattering cross sections we give a critical discussion of the analysis with careful attention not only to the statistical, but also to the systematic uncertainties. Our preliminary evaluation gives $g^2_c$(GMO) = 13.99(24).
A novel extrapolation method has been used to deduce the charged Pion-Nucleon coupling constant from backward $np$ differential scattering cross sections. We applied it to new measurements performed at 162 MeV at the The Svedberg Laboratory in Uppsala. In the angular range $150^\circ-180^\circ$, the carefully normalized data are steeper than those of most previous measurements. The extracted value, $g^2_{π^\pm} = 14.52 \pm 0.26$, in good agreement with the classical value, is higher than those determined in recent nucleon-nucleon partial-wave analyses.
The scalar -- isoscalar pi-pi phase shifts are analysed using a separable potential model of three coupled channels (pipi, KK and an effective 2pi2pi system). Model parameters are fitted to two sets of solutions obtained in a recent analysis of the CERN-Cracow-Munich measurements of the pi^- p --> pi^+ pi^- n reaction on a polarized target. A relatively narrow (90 -- 180 MeV) scalar resonance f_0(1400-1460) is found, together with a wide f_0(500) (Gamma = 500 MeV) and the narrow f_0(980) state.
A pi-pi, Kbar-K, and rho-rho(omega-omega) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities for elastic pi-pi scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the meson resonance table of the Particle Data Group. As expected, the pi-pi inelasticity is very strongly related to the opening of the Kbar-K channel near 1 GeV, and the opening of rho-rho(4pi) and omega-omega(6pi) channels in the 1.5 GeV region. The predictions of this model are compared to the various elastic pi-pi to pi-pi amplitudes, that were obtained from analyses of pi(-) p to pi(-) pi(+) n data. The role of the various resonances, in particular the glueball candidate f_0(1500) and the f_J(1710) is investigated.
New solutions on the scalar -- isoscalar $ππ$ phase shifts are analysed together with previous $K\bar{K}$ results using a separable potential model of three coupled channels ($ππ$, $K\bar{K}$ and an effective $2π2π$ system). Model parameters are fitted to two sets of solutions obtained in a recent analysis of the CERN-Cracow-Munich measurements of the $π^- p_{\uparrow} \to π^+ π^- n$ reaction on a polarized target. A relatively narrow (90 -- 180 MeV) scalar resonance $f_0(1400-1460)$ is found, in contrast to a much broader ($Γ\approx 500$ MeV) state emerging from the analysis of previous unpolarized target data.
We show that the $πNN$ coupling constant extracted model-independently from $\bar pp$ charge exchange is subject to a systematic correction, and, more importantly, that the strong absorption in the critical region prevents a determination of the coupling constant to high precision using this process. This attenuates the possible conflict with the value determined from the np charge exchange cross sections.
A simple $ππ$, $\bar{K}K$, and $ρρ$($ωω$) fully coupled channel model is proposed to predict the isoscalar S-wave phase shifts and inelasticities for $ππ$ scattering in the 1.0 to 2.0 GeV region. The S-matrix is required to exhibit poles corresponding to the established isoscalar J$^π$ = 0$^+$ resonances f$_0$(975), f$_0$(1400), and f$_0$(1710). A dominant feature of the experimental $ππ$ inelasticity is the clear opening of the $\bar{K}K$ channel near 1 GeV, and the opening of another channel in the 1.4 - 1.5 GeV region. The success of our model in predicting this observed dramatic energy dependence indicates that the effect of multi-pion channels is adequately described by the $ππ$ coupling to the $\bar{K}K$ channel, the $ρρ$(4$π$) and $ωω$(6$π$) channels.