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Register a new user$Kpi$ $I=1/2$ $S$-wave from $eta_c$ decay data at BaBar and classic Meson-Meson scattering from LASS
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A recent analysis of data on the two photon production of the $eta_c$ and its decay to $K(Kpi)$ has determined the $Kpi$ $S$-wave amplitude in a model-independent way assuming primarily that the additional kaon is a spectator in this decay. The purpose of this paper is to fit these results, together with classic $Kpi$ production data from LASS, within a formalism that implements unitarity for the di-meson interaction. This fixes the $I=1/2$ $Kpito Kpi$ $S$-wave amplitude up to 2.4 GeV. This resolves the Barrelet ambiguity in the original LASS analysis, and constrains the amount of inelasticity in $Kpi$ scattering, highlighting that this becomes significant beyond 1.8 GeV. This result needs to be checked by experimental information on the many inelastic channels, in particular $Keta^prime$ and $Kpipipi$. Our analysis provides a single representation for the $Kpi$ $S$-wave from threshold, controlled by Chiral Perturbation Theory, through the broad $kappa$, $K_0^*(1430)$ and $K_0^*(1950)$ resonances. There is no arbitrary sum of Breit-Wigner forms and random backgrounds for real $Kpi$ masses. Rather the form provides a representation that can be translated to other processes with $Kpi$ interactions with their own coupling functions, while automatically maintaining consistency with the chiral dynamics near threshold, with the LASS data and the new results on $eta_c$ decay.
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We summarize our lattice QCD determinations of the pion-pion, pion-kaon and kaon-kaon s-wave scattering lengths at maximal isospin with a particular focus on the extrapolation to the physical point and the usage of next-to-leading order chiral perturbation theory to do so. We employ data at three values of the lattice spacing and pion masses ranging from around 230 MeV to around 450 MeV, applying Lueschers finite volume method to compute the scattering lengths. We find that leading order chiral perturbation theory is surprisingly close to our data even in the kaon-kaon case for our entire range of pion masses.
We present a lattice-QCD determination of the elastic isospin-$1/2$ $S$-wave and $P$-wave $Kpi$ scattering amplitudes as a function of the center-of-mass energy using Luschers method. We perform global fits of $K$-matrix parametrizations to the finite-volume energy spectra for all irreducible representations with total momenta up to $sqrt{3}frac{2pi}{L}$; this includes irreps that mix the $S$- and $P$-waves. Several different parametrizations for the energy dependence of the $K$-matrix are considered. We also determine the positions of the nearest poles in the scattering amplitudes, which correspond to the broad $kappa$ resonance in the $S$-wave and the narrow $K^*(892)$ resonance in the $P$-wave. Our calculations are performed with $2+1$ dynamical clover fermions for two different pion masses of $317.2(2.2)$ and $175.9(1.8)$ MeV. Our preferred $S$-wave parametrization is based on a conformal map and includes an Adler zero; for the $P$-wave we use a standard pole parametrization including Blatt-Weisskopf barrier factors. The $S$-wave $kappa$-resonance pole positions are found to be $left[0.86(12) - 0.309(50),iright]:{rm GeV}$ at the heavier pion mass and $left[0.499(55)- 0.379(66),iright]:{rm GeV}$ at the lighter pion mass. The $P$-wave $K^*$-resonance pole positions are found to be $left[ 0.8951(64) - 0.00250(21),i right]:{rm GeV}$ at the heavier pion mass and $left[0.8718(82) - 0.0130(11),iright]:{rm GeV}$ at the lighter pion mass, which corresponds to couplings of $g_{K^* Kpi}=5.02(26)$ and $g_{K^* Kpi}=4.99(22)$, respectively.
The problem of scalar mesons still remains a challenging puzzle, for which we do not even know which are the right pieces to set up. The proliferation of resonances (some of them are very broad and appear on top of hadronic thresholds) and of coupled channels that interact strongly among each other makes the study of this sector a hard task. Our objective is the study of the strongly interacting mesons in coupled channels with quantum numbers J^{PC} = 0^{++} and I=0 and I=1/2, up to a center of mass energy sqrt{s} < 2 GeV. Our framework is based on Unitary Chiral Perturbation Theory. We include for I=0 the channels: pipi, Kbar{K}, etaeta, sigmasigma, etaeta, rhorho, omegaomega, etaeta, omegaphi, phiphi, K^ast bar{K}^ast, a_1(1260)pi and pi^{star}(1300)pi. In addition, and in order to constrain our fits, we also study the I=1/2, 3/2 channels given by Kpi, Keta and Keta. We finally present the resonant content of our fits with the $sigma$, $f_0(980)$, $f_0(1310)$, $f_(1500)$, $f_0(1710)$ and $f_0(1790)$.
On a lattice with 2+1-flavor dynamical domain-wall fermions at the physical pion mass, we calculate the decay constants of $D_{s}^{(*)}$, $D^{(*)}$ and $phi$. The lattice size is $48^3times96$, which corresponds to a spatial extension of $sim5.5$ fm with the lattice spacing $aapprox 0.114$ fm. For the valence light, strange and charm quarks, we use overlap fermions at several mass points close to their physical values. Our results at the physical point are $f_D=213(5)$ MeV, $f_{D_s}=249(7)$ MeV, $f_{D^*}=234(6)$ MeV, $f_{D_s^*}=274(7)$ MeV, and $f_phi=241(9)$ MeV. The couplings of $D^*$ and $D_s^*$ to the tensor current ($f_V^T$) can be derived, respectively, from the ratios $f_{D^*}^T/f_{D^*}=0.91(4)$ and $f_{D_s^*}^T/f_{D_s^*}=0.92(4)$, which are the first lattice QCD results. We also obtain the ratios $f_{D^*}/f_D=1.10(3)$ and $f_{D_s^*}/f_{D_s}=1.10(4)$, which reflect the size of heavy quark symmetry breaking in charmed mesons. The ratios $f_{D_s}/f_{D}=1.16(3)$ and $f_{D_s^*}/f_{D^*}=1.17(3)$ can be taken as a measure of SU(3) flavor symmetry breaking.
We consider meson-baryon interactions in S-wave with strangeness -1. This is a non-perturbative sector populated by plenty of resonances interacting in several two-body coupled channels.We study this sector combining a large set of experimental data. The recent experiments are remarkably accurate demanding a sound theoretical description to account for all the data. We employ unitary chiral perturbation theory up to and including cal{O}(p^2) to accomplish this aim. The spectroscopy of our solutions is studied within this approach, discussing the rise from the pole content of the two Lambda(1405) resonances and of the Lambda(1670), Lambda(1800), Sigma(1480), Sigma(1620) and Sigma(1750). We finally argue about our preferred solution.
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