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Register a new userAmplitudes separation and strong-electromagnetic relative phase in the $psi(2S)$ decays into baryons
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The strong, electromagnetic and mixed strong-electromagnetic amplitudes of the $psi(2S)$ decays into baryon-anti-baryon pairs have been obtained by exploiting all available data sets in the framework of an effective Lagrangian model. We observed that at the $psi(2S)$ mass the QCD regime is not completely perturbative, as can be inferred by the relative strength of the strong and the mixed strong-electromagnetic amplitudes. Recently a similar conclusion has been reached also for the $J/psi$ decays. The relative phase between the strong and the electromagnetic amplitudes is $varphi = (58pm 8)^circ$, to be compared with $varphi = (73pm 8)^circ$ obtained for the $J/psi$. On the other hand, in the case of the $psi(2S)$ meson, different values of the ratio between strong and mixed strong-electromagnetic amplitudes are phenomenologically required, while for the $J/psi$ meson only one ratio was enough to describe the data. Finally, we also observed a peculiar behavior of the mixed strong-electromagnetic amplitudes of the decays $psi(2S)toSigma^+ overline Sigma{}^-$ and $psi(2S)toSigma^- overline Sigma{}^+$.
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The Feynman amplitude for the decay of the $J/psi$ meson into baryon-antibaryon can be written as a sum of three sub-amplitudes: a purely strong, a purely electromagnetic and a mixed strong-electromagnetic. Assuming that the strong and mixed strong-electromagnetic sub-amplitudes have the same phase, the branching ratio of the decay contains an interference term that depends on the relative phase $varphi$ between strong and electromagnetic sub-amplitudes. In this work we calculate this phase, by using an effective strong Lagrangian density and considering, as final states, pairs of baryons, $mathcal{B}overline{mathcal{B}}$, belonging to the spin-1/2 SU(3) octet. Moreover, we obtain the purely strong, purely electromagnetic and mixed strong-electromagnetic contributions to the total branching ratio and hence the moduli of the corresponding sub-amplitudes, for each pair of baryons. Of particular interest is the mixed strong-electromagnetic contribution that, not only is determined for the first time, but it is proven to be crucial, in the framework of our model, for the correct description of the decay mechanism. Finally we use the purely electromagnetic branching ratio to calculate the Born non-resonant cross section of the annihilation processes $e^+ e^- to mathcal{B}overline{mathcal{B}}$ at the $J/psi$ mass. By taking advantage from all available data, we obtain the relative phase between strong and electromagnetic sub-amplitudes: $varphi = (73pm 8)^circ$.
Using 16 energy points of $e^{+}e^{-}$ annihilation data collected in the vicinity of the $J/psi$ resonance with the BESIII detector and with a total integrated luminosity of around 100 pb$^{-1}$, we study the relative phase between the strong and electromagnetic amplitudes of $J/psi$ decays. The relative phase between $Jpsi$ electromagnetic decay and the continuum process ($e^{+}e^{-}$ annihilation without the $J/psi$ resonance) is confirmed to be zero by studying the cross section lineshape of $mu^{+}mu^{-}$ production. The relative phase between $J/psi$ strong and electromagnetic decays is then measured to be $(84.9pm3.6)^circ$ or $(-84.7pm3.1)^circ$ for the $2(pi^{+}pi^{-})pi^{0}$ final state by investigating the interference pattern between the $J/psi$ decay and the continuum process. This is the first measurement of the relative phase between $J/psi$ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state $etapi^{+}pi^{-}$ with $etatopi^{+}pi^{-}pi^{0}$, which provides additional information about the phase between the $J/psi$ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of $J/psito 2(pi^{+}pi^{-})pi^{0}$ is measured to be $(4.73pm0.44)%$ or $(4.85pm0.45)%$, and the branching fraction of $J/psitoetapi^{+}pi^{-}$ is measured to be $(3.78pm0.68)times10^{-4}$. Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.
BESIII data show a particular angular distribution for the decay of the $J/psi$ and $psi(2S)$ mesons into the hyperons $Lambdaoverline{Lambda}$ and $Sigma^0overline{Sigma}^0$. More in details the angular distribution of the decay $psi(2S) to Sigma^0overline{Sigma}^0$ exhibits an opposite trend with respect to that of the other three channels: $J/psi to Lambdaoverline{Lambda}$, $J/psi to Sigma^0overline{Sigma}^0$ and $psi(2S) to Lambdaoverline{Lambda}$. We define a model to explain the origin of this phenomenon.
There has been important experimental progress in the sector of heavy baryons in the past several years. We study the strong decays of the S-wave, P-wave, D-wave and radially excited charmed baryons using the $^3P_0$ model. After comparing the calcul
ated decay pattern and total width with the available data, we discuss the possible internal structure and quantum numbers of those charmed baryons observed recently.
We have investigated the electromagnetic decays of the antitriplet and sextet charmed baryon systems with $J^P= frac{1}{2}^+, frac{3}{2}^+$ in the framework of the heavy baryon chiral perturbation theory. We first construct the chiral Lagrangians at $O(p^2)$ and $O(p^3)$. Then we calculate the electromagnetic (EM) decay amplitudes of the charmed baryon systems up to $O(p^3)$. With the help of the quark model, we estimate the low energy constants. The numerical results of the EM decay widths show good convergence of the chiral expansion. We notice that the two neutral EM decay processes $Xi_c^0rightarrowgamma+Xi_c^0$ and ${Xi_c^*}^0rightarrowgamma+Xi_c^0$ are strongly suppressed by the SU(3) U-spin flavor symmetry. With the same formalism, we also estimate the EM decay widths of the bottomed baryons. The EM decay widths of the heavy baryons may be measured at facilities such as LHCb and JPARC. The explicit chiral structures of the heavy baryon decay amplitudes derived in this work may be useful to the possible chiral extrapolations of the future lattice simulations of these EM decay amplitudes.
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