No Arabic abstract
Stimulated by the BESIII observation of $X(2100)$, $X(2500)$, and $eta(2225)$, we try to pin down new pseudoscalar meson nonets including these states. The analysis of mass spectra and the study of strong decays indicate that $X(2120)$ and $eta(2225)$ associated with $pi(2070)$ and the predicted kaon $K(2150)$ may form a new pseudoscalar meson nonet. In addition, more experimental data for $X(2100)$ are necessary to determine its structure of nonets. Then, $X(2500)$, $X(2370)$, $pi(2360)$, and the predicted kaon $K(2414)$ can be grouped into another new nonet. These assignments to the discussed pseudoscalar states can be further tested in experiment.
We present our model-independent and data-driven method to describe pseudoscalar meson transition form factors in the space- and (low-energy) time-like regions. The method is general and conforms a toolkit applicable to any other form factor, of one and two variables, with the potential to include both high- and low-energy QCD constraints altogether. The method makes use of analyticity and unitary properties of form factors, it is simple, systematic and can be improved upon by including new data. In the present discussion, the method is used to show the impact of experimental data for precision calculations in the low-energy sector of the Standard Model. In particular, due to its relevance for New Physics searches, we have considered the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon (the pseudoscalar exchange contribution), the pseudoscalar decays into lepton pairs, and the determination of the mixing parameters of the $eta$ and $eta$ system. For all of them we provide the most updated results in a data-driven manner.
A symmetry-preserving regularisation of a vector$times$vector contact interaction (SCI) is used to deliver a unified treatment of semileptonic transitions involving $pi$, $K$, $D_{(s)}$, $B_{(s,c)}$ initial states. The framework is characterised by algebraic simplicity, few parameters, and the ability to simultaneously treat systems from Nambu-Goldstone modes to heavy+heavy mesons. Although the SCI form factors are typically somewhat stiff, the results are comparable with experiment and rigorous theory results. Hence, predictions for the five unmeasured $B_{s,c}$ branching fractions should be a reasonable guide. The analysis provides insights into the effects of Higgs boson couplings via current-quark masses on the transition form factors; and results on $B_{(s)}to D_{(s)}$ transitions yield a prediction for the Isgur-Wise function in fair agreement with contemporary data.
We study, at leading order in the large number of colours expansion and within the Resonance Chiral Theory framework, the odd-intrinsic-parity $e^+ e^- rightarrow pi^+ pi^- (pi^0, eta)$ cross-sections in the energy regime populated by hadron resonances, namely $3 , m_{pi} lsim E lsim 2 , mbox{GeV}$. In addition we implement our results in the Monte Carlo generator PHOKHARA 7.0 and we simulate hadron production through the radiative return method.
Inspired by the event accumulation around 2.6 GeV in the $eta^primepi^+pi^-$ invariant mass spectrum of $J/psito gamma eta^primepi^+pi^-$, which was reported by the BESIII Collaboration, we carry out the study of the mass spectrum and decay behavior of four radial excitations in the pseudoscalar meson family, which include $eta^{(prime)}(6S)$ and $eta^{(prime)}(7S)$. Combining with these analysis, we present the calculation of the reactions induced by a pion or kaon on the proton target which are relevant to these four discussed states. According to this information, we give concrete experimental suggestion of searching for them, which will become a new task for future experiments.
We observe that four peaks seen in the high energy part of the $Omega_b$ spectrum of the recent LHCb experiment are in remarkable agreement with predictions made for molecular $Omega_b$ states stemming from the meson-baryon interaction, with an approach that applied to the $Omega_c$ states gave rise to three states in good agreement with experiment in masses and widths. While the statistical significance of the peaks prevents us from claims of states at the present time, the agreement found should be an incentive to look at this experiment with increased statistics to give an answer to this suggestive idea.