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Register a new userThe sigma and f_0(980) from K_e4+pi-pi, gamma-gamma scatterings, J/psi, phi to gamma sigma_B and D_s to l nu sigma_B
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Authors
G. Mennessier
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We extract the pole positions, hadronic and gamma-gamma widths of sigma and f_0(980, from pi-pi and gamma-gamma scattering data using an improved analytic K-matrix model. Our results favour a large gluon component for the sigma and a bar ss or/and gluon component for the f_0(980) but neither a large four-quark nor a molecule component. Gluonium sigma_B production from J/psi, phi radiative and D_s semi-leptonic decays are also discussed.
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We study the $J/psi to gamma pi^+ pi^-$, $gamma pi^0 eta$ reactions from the perspective that they come from the $J/psi to phi(omega) pi^+ pi^-, rho^0pi^0 eta$ reactions, where the $rho^0$, $omega$, and $phi$ get converted into a photon via vector meson dominance. Using models successfully used previously to study the $J/psi to omega (phi) pipi$ reactions, we make determinations of the invariant mass distributions for $pi^+ pi^-$ in the regions of the $f_0(500)$, $f_0(980)$, and for $pi^0 eta$ in the region of the $a_0(980)$. The integrated differential widths lead to branching ratios below present upper bounds, but they are sufficiently large for future check in updated facilities.
We perform calculations for the $bar B_s^0 to J/psi pi^0 f_0(980)$ and $bar B_s^0 to J/psi pi^0 a_0(980)$ reactions, showing that the first one is isospin-suppressed while the second one is isospin-allowed. The reaction proceeds via a triangle mechanism, with $bar B_s^0 to J/psi K^* bar K +c.c.$, followed by the decay $K^* to Kpi$ and a further fusion of $Kbar K$ into the $f_0(980)$ or $a_0(980)$. We show that the mechanism develops a singularity around the $pi^0 f_0(980)$ or $pi^0 a_0(980)$ invariant mass of 1420 MeV where the $pi^0 f_0$ and $pi^0 a_0$ decay modes are magnified and also the ratio of $pi^0 f_0$ to $pi^0 a_0$ production. Using experimental information for the $bar B_s^0 to J/psi K^* bar K +c.c.$ decay, we are able to obtain absolute values for the reactions studied which fall into the experimentally accessible range. The reactions proposed and the observables evaluated, when contrasted with actual experiments should be very valuable to obtain information on the nature of the low lying scalar mesons.
In this work, we have investigated the process $D_s^+to K^+ K^- pi^+$, taking into account the contributions from the $S$-wave pseudoscalar-pseudoscalar interaction within the chiral unitary approach, and also the intermediate $phi$ resonance. By analyzing the BESIII and {it BABAR} measurements, we conclude that the $f_0(980)$ state, dynamically generated from the $S$-wave pseudoscalar-pseudoscalar interaction, gives the dominant contribution close to the $K^+K^-$ threshold in the $K^+K^-$ invariant mass distribution of the decay $D_s^+to K^+ K^- pi^+$ in $S$-wave. On the other hand, our results imply that the lineshape adopted by BESIII and {it BABAR} for the resonances $a_0(980)$ and $f_0(980)$ is not advisable in the fit to the data close to the $K^+K^-$ threshold.
The $a_0^0(980)-f_0(980)$ mixing is one of the most potential tools to learn about the nature of $a_0^0(980)$ and $f_0(980)$. Using the $f_0(980)$-$a_0^0(980)$ mixing intensity $xi_{af}$ measured recently at BESIII, we calculate the the branching ratio of the the isospin violation decay $J/psi rightarrowgammaeta_c rightarrow gamma pi^0 a_0^0(1450)rightarrow gamma pi^0 a_0^0(980)f_0(500)rightarrow gamma pi^0 f_0(980) f_0(500) rightarrow gamma pi^0 pi^+pi^- pi^+pi^-$. The value of the branching ratio is found to be $O(10^{-6})$, which can be observed with $10^{10}$ $J/psi$ events collected at BESIII. The narrow peak from the $f_0(980)$-$a_0^0(980)$ mixing in the $pi^+pi^-$ mass square spectrum can also be observed. In addition, we study the non-resonant decay $a_0^0(1450)rightarrow f_0(980) pi^+pi^-(text{non-resonant})$, which is dominated by the $a_0^0(980)$-$f_{0}(980)$ mixing. We find that the non-resonant decay $a_0^0(1450)rightarrow f_0(980) pi^+pi^-$ and the decay $a_0^0(1450)rightarrow f_0(980) f_0(500)$ can be combined to measure the mixing intensity $xi_{af}$ in experiment. These decays are the perfect complement to the decay $chi_{c1}rightarrow f_{0}(980)pi^{0}topi^{+}pi^{-}pi^{0}$ which had been observed at BESIII, the observations of them will make the measurement of the mixing intensity $xi_{af}$ more precisely.
We study the effect of the meson cloud dressing in the octet baryon to decuplet baryon electromagnetic transitions. Combining the valence quark contributions from the covariant spectator quark model with those of the meson cloud estimated based on the flavor SU(3) cloudy bag model, we calculate the transition magnetic form factors at $Q^2=0$ ($Q^2=-q^2$ and $q$ the four-momentum transfer), and also the decuplet baryon electromagnetic decay widths. The result for the $gamma^ast Lambda to Sigma^{ast 0}$ decay width is in complete agreement with the data, while that for the $gamma^ast Sigma^+ to Sigma^{ast +}$ is underestimated the data by 1.4 standard deviations. This achievement may be regarded as a significant advance in the present theoretical situation.
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