Light Pseudoscalar Mesons Research Articles

Strong Coupling Constants of the Doubly Heavy Spin-1/2 Baryons with Light Pseudoscalar Mesons

The strong coupling constants of hadronic multiplets are fundamental parameters which carry information about the strong interactions among participating particles. These parameters can help us construct the hadron-hadron strong potential and gain information about the structure of the involved hadrons. Motivated by the recent observation of the doubly charmed state by LHCb, we determine the strong coupling constants among the doubly heavy spin-1/2 baryons, , and light pseudoscalar mesons, , K, and within the framework of the light cone QCD sum rules. The obtained results may help experimental groups in analysis of the related data at hadron colliders.

Potential higher radial excitations in the light pseudoscalar meson family

Inspired by the event accumulation around 2.6 GeV in the $\eta^\prime\pi^+\pi^-$ invariant mass spectrum of $J/\psi\to \gamma \eta^\prime\pi^+\pi^-$, 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.

Determination of the strong vertices of doubly heavy baryons with pseudoscalar mesons in QCD

The strong coupling constant of doubly heavy baryons with light pseudoscalar mesons $ \pi $ and $ K $ are computed within the light cone sum rules. We take into account two-particle and three-particle distribution amplitudes of the said pseudoscalar mesons. We compare our result with the one existing in the literature.

Distribution amplitudes of heavy mesons and quarkonia on the light front

The ladder kernel of the Bethe–Salpeter equation is amended by introducing a different flavor dependence of the dressing functions in the heavy-quark sector. Compared with earlier work this allows for the simultaneous calculation of the mass spectrum and leptonic decay constants of light pseudoscalar mesons, the D_u, D_s, B_u, B_s and B_c mesons and the heavy quarkonia eta _c and eta _b within the same framework at a physical pion mass. The corresponding Bethe–Salpeter amplitudes are projected onto the light front and we reconstruct the distribution amplitudes of the mesons in the full theory. A comparison with the first inverse moment of the heavy meson distribution amplitude in heavy quark effective theory is made.

Studying two-body nonleptonic weak decays of hyperons with topological diagram approach

Many decays of light baryons consisting of light u, d, s quarks have been measured, and these measurements will help us to understand the decay properties of light baryons. In this work, we study two-body nonleptonic weak decays of light baryon octets (T8) and baryon decuplets (T10) by the topological diagram approach (TDA) under the SU(3) flavor symmetry for the first time. We find that () the TDA and the SU(3) irreducible representation approach (IRA) match consistently in (P8 is the light pseudoscalar meson octet); (2) almost all relevant not-yet-measured may be predicted by using three experimental data of , and the upper limits of may be obtained from the experimental upper limit of by both the TDA and the IRA together, nevertheless, all new predicted branching ratios are too small to be reached in current experiments; (3) T8 → T8′P8 decays are quite complex in terms of the TDA, and we find that W-exchange diagrams give large and even dominant contributions by using relevant experimental data and the isospin relations.

Light pseudoscalar and axial spectroscopy using AdS/QCD modified soft wall model

We describe the mass spectrum of light pseudoscalar and axial mesons in the context of the modified soft wall model with an extra UV cutoff. In order to include the pseudoscalar and axial states, we define an anomalous dimension that shifts the conformal dimension of the non-interacting bulk fields such that the parity behavior of those states is included, thus inducing chiral symmetry breaking. This idea contrasts with the usual approach that uses interacting scalar, vector and axial bulk fields to give rise the spectrum. Using the extra UV cutoff approach, we can fit six η and six a1 organized in radial trajectories with an RMS error close to 21.1%. We also confirm that chiral symmetry is restored in this model after checking that highly excited ρ and a1 states become degenerate.

Evasion of HSR in the charmless decays of excited P-wave charmonia

We investigate the charmless decays of excited P-wave charmonia chi _{c1}^prime rightarrow VV and chi _{c2}^prime rightarrow VP via intermediate charmed meson loops, where V and P denote the light vector and pseudoscalar mesons, respectively. Within the model parameters, the charmed meson loop contributions are evaluated by using the effective Lagrangian approach. For chi _{c1}^prime rightarrow VV, the partial widths of the rho rho , omega omega , and K^*{bar{K}}^* channels can reach to the order of MeV, while the partial width of the phi phi channel is very small and in the order of keV. For chi _{c2}^prime rightarrow V P, the partial widths of chi _{c2}^{prime } rightarrow K^*bar{K}+c.c turns out to be sizeable, while the partial widths of chi _{c2}^{prime } rightarrow rho ^+pi ^- +c.c is found to be much smaller than the K^*bar{K}+c.c channel. Our calculations may be examined by the future BESIII experiments.

Study of the interactions of the axion with mesons and photons using a chiral effective Lagrangian model

We investigate the most interesting decay processes involving axions, photons and the lightest pseudoscalar mesons, making use of a chiral effective Lagrangian model with L=3 light quark flavors, which also includes the flavor-singlet pseudoscalar meson and implements the U(1) axial anomaly of the fundamental theory. In particular, we compute the electromagnetic coupling of the axion to photons and we compare our result with the prediction of the Chiral Effective Lagrangian with L=2 light quark flavors. Moreover, we study the decay channels eta /eta 'rightarrow pi pi a and we estimate the corresponding decay widths, using the existing bounds on the U(1)_{PQ} breaking scale.

Extraction of the CKM phase γ from the charmless two-body B meson decays * * Supported by National Science Foundation of China (11847040, 11947414, 11521505, 11621131001) and Scientific Research Foundation of Inner Mongolia University

Using all experimentally measured charmless , decay modes, where denotes a light pseudoscalar (vector) meson, we extract the CKM angle by a global fit. All hadronic parameters are determined from the experimental data, such that the approach is least model dependent. The contributions of the various decay modes are classified by the topological weak Feynman diagram amplitudes, which are determined by the global fit. To improve the precision of the approach, we consider the flavor SU(3) breaking effects of the topological diagram amplitudes of the decay modes by including the form factors and decay constants. The fit result for the CKM angle is . It is consistent with the current world average values but has a smaller uncertainty.

Semileptonic decays of D and Ds mesons in the relativistic quark model

The form factors parameterizing the weak $D$ and $D_s$ transitions to light pseudoscalar and vector mesons are calculated in the framework of the relativistic quark model based on the quasipotential approach. The special attention is paid to the systematic account of the relativistic effects including transformation of the meson wave function from the rest to moving reference frame and contributions of the intermediate negative-energy states. The form factors are expressed through the overlap integrals of the meson wave functions, which are taken from previous studies of meson spectroscopy. They are calculated in the whole range of the transferred momentum $q^2$. Convenient parameterization of the form factors which accurately reproduces numerical results is given. The obtained values of the form factors and their ratios at $q^2=0$ agree well with the ones extracted form the experimental data. On the basis of these form factors and helicity formalism, differential and total semileptonic decay rates of $D$ and $D_s$ mesons as well as different asymmetries and polarization parameters are calculated. The detailed comparison of the obtained results with other theoretical calculations and experimental data is given.

A pattern for the flavor dependent quark-antiquark interaction

A flavor dependent kernel is constructed based on the rainbow-ladder truncation of the Dyson-Schwinger and Bethe-Salpeter equations in quantum chromodynamics. The quark-antiquark interaction is composed of a flavor dependent infrared part and a flavor independent ultraviolet part. Our model gives a successful and unified description of the light, heavy and heavy-light ground state pseudoscalar and vector mesons. Our model shows, for the first time, that the infrared enhanced quark-antiquark interaction is stronger and wider for lighter quarks.

Quarks and light (pseudo-)scalar mesons at finite chemical potential

We investigate the properties of light scalar and pseudoscalar mesons at finite (light) quark chemical potential. To this end we solve a coupled set of (truncated) Dyson-Schwinger equations for the quark and gluon propagators in Landau-gauge QCD and extend earlier results for $ N_{\mathrm{f}} = 2+1$ dynamical quark flavors to finite chemical potential at zero temperature. We then determine the meson bound state masses, wave functions, and decay constants for chemical potentials below the first-order phase transition from their homogeneous Bethe-Salpeter equation. We study the changes in the quark dressing functions and Bethe-Salpeter wave functions with chemical potential. In particular, we trace charge-conjugation parity breaking. Furthermore, we confirm the validity of the Silver-Blaze property: all dependencies of colored quantities on chemical potential cancel out in observables and we observe constant masses and decay constants up to and into the coexistence region of the first-order chiral phase transition.

Chiral Imbalance in Hadron Matter: Its Manifestation in Photon Polarization Asymmetries

The possibility of the formation of a local parity breaking (LPB) in a quark-hadron medium is examined as a result of chiral symmetry violation, i.e, the appearance of difference between the average densities of right- and left-handed quarks in the fireball after heavy-ion collisions (HIC). Using the effective meson Lagrangian motivated by QCD extended to the chiral medium the properties of light scalar and pseudoscalar mesons are analyzed. It is establish that exotic decays of scalar mesons arise due to mixing of $\pi$ and $a_0$ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We conjecture that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, FAIR and NICA accelerators.

Implications of chiral symmetry on S -wave pionic resonances and the scalar charmed mesons

The chiral symmetry of QCD requires energy-dependent pionic strong interactions at low energies. This constraint, however, is not fulfilled by the usual Breit--Wigner parameterization of pionic resonances, leading to masses larger than the real ones. We derive relations between nonleptonic three-body decays of the $B$-meson into a $D$-meson and a pair of light pseudoscalar mesons based on SU(3) chiral symmetry. Employing effective field theory methods, we demonstrate that taking into account the final-state interactions, the experimental data of the decays $B^-\to D^+\pi^-\pi^-$, $B_s^0\to \bar{D}^0K^-\pi^+$, $B^0\to\bar{D}^0\pi^-\pi^+$, $B^-\to D^+\pi^-K^-$ and $B^0\to\bar{D}^0\pi^-K^+$ can all be described by the nonperturbative $\pi/\eta/K$-$D/D_s$ scattering amplitudes previously obtained from a combination of chiral effective field theory and lattice QCD calculations. The results provide a strong support of the scenario that the broad scalar charmed meson $D^\ast_0(2400)$ should be replaced by two states, the lower one of which has a mass of around 2.1 GeV, much smaller than that extracted from experimental data using a Breit--Wigner parameterization.

Placing the newly observed state BJ(5840) in bottom spectra along with states B1(5721) , B2*(5747) , Bs1(5830) , B2s*(5840) , and BJ(5970)

In this article, we study the two body strong decays with the emission of light pseudo-scalar mesons $(\pi, \eta, K)$ for higher excited bottom states with in the framework of HQET. Inspired from the recent observation of bottom meson $B_{J}(5840)$ by LHCb collaboration \cite{9}, we classify the six possible $J^{P}$'s for this state on the basis of the theoretically available masses. By analyzing the strong decay widths and the branching ratios for all these six cases of $B_{J}(5840)$, we justify one of them to be the most favorable assignment for it. We also examined the recently observed bottom state $B_{J}(5970)$ as 2S$1^{-}$ and states $B_{J}(5721)$ and $B_{2}^{*}(5747)$ with their strange partners $B_{s1}(5830)$ and $B_{2s}^{*}(5840)$ for their $J^{P}$'s as $1P_{3/2}1^{+}$ and $1P_{3/2}2^{+}$ respectively. The predicted coupling constants $g_{XH}$, $\widetilde{g}_{HH}$ and $g_{TH}$ helps in redeeming the strong decay width of experimentally missing bottom states $B(2 ^{1}S_{0})$, $B_{s}(2 ^{3}S_{1})$, $B_{s}(2 ^{1}S_{0})$, $B(1 ^{1}D_{2})$, $B_{s}(1 ^{3}D_{1})$ and $B_{s}(1 ^{1}D_{2})$. These predictions provide a crucial information for upcoming experimental studies.

Lattice computation of the electromagnetic contributions to kaon and pion masses

We present a lattice calculation of the electromagnetic (EM) effects on the masses of light pseudoscalar mesons. The simulations employ $2+1$ dynamical flavors of asqtad QCD quarks and quenched photons. Lattice spacings vary from $\ensuremath{\approx}0.12\text{ }\text{ }\mathrm{fm}$ to $\ensuremath{\approx}0.045\text{ }\text{ }\mathrm{fm}$. We compute the quantity $\ensuremath{\epsilon}$, which parametrizes the corrections to Dashen's theorem for the ${K}^{+}$--${K}^{0}$ EM mass splitting, as well as ${\ensuremath{\epsilon}}_{{K}^{0}}$, which parametrizes the EM contribution to the mass of the ${K}^{0}$ itself. An extension of the nonperturbative EM renormalization scheme introduced by the BMW group is used in separating EM effects from isospin-violating quark mass effects. We correct for leading finite-volume effects in our realization of lattice electrodynamics in chiral perturbation theory, and remaining finite-volume errors are relatively small. While electroquenched effects are under control for $\ensuremath{\epsilon}$, they are estimated only qualitatively for ${\ensuremath{\epsilon}}_{{K}^{0}}$ and constitute one of the largest sources of uncertainty for that quantity. We find $\ensuremath{\epsilon}=0.78(1{)}_{\text{stat}}(\genfrac{}{}{0}{}{+8}{\ensuremath{-}11}{)}_{\text{syst}}$ and ${\ensuremath{\epsilon}}_{{K}^{0}}=0.035(3{)}_{\text{stat}}(20{)}_{\text{syst}}$. We then use these results on $2+1+1$ flavor pure QCD highly improved staggered quark (HISQ) ensembles and find ${m}_{u}/{m}_{d}=0.4529(48{)}_{\text{stat}}(\genfrac{}{}{0}{}{+150}{\ensuremath{-}67}{)}_{\text{syst}}$.

Note on invisible decays of light mesons

A search for the invisible decays of $\omega$ and $\phi$ mesons in $J/\psi\to \omega (\phi)\eta$ transitions has been performed by the BESIII Collaboration very recently. Inspired by this experimental study, we compute the lowest order contribution to branching ratios of ${\cal B}(V\to\bar{\nu}\nu)$ with $V$ denoting $\rho,\;\omega,\;\phi$, as the standard model background to these invisible decays. Our predictions are far below the upper bounds given by the BESIII experiment. We also analyze the $J/\psi\to \eta(\eta^\prime)\bar{\nu}\nu$ processes, and estimate their decay rates. Furthermore, the invisible decays of light pseudoscalar mesons $P$ including $\pi^0$, $\eta$, and $\eta^\prime$ are reexamined in the present note. It is shown that, due to the helicity suppression of the two-neutrino final state, the standard model contributions to $P\to{\rm invisible}$ decays are dominated by $P\to\bar{\nu}\nu \bar{\nu}\nu$ processes.

New spectrum of negative-parity doubly charmed baryons: Possibility of two quasistable states

The discovery of $\Xi_{cc}^{++}$ by the LHCb Collaboration triggers predictions of more doubly charmed baryons. By taking into account both the $P$-wave excitations between the two charm quarks and the scattering of light pseudoscalar mesons off the ground state doubly charmed baryons, a set of negative-parity spin-1/2 doubly charmed baryons are predicted already from a unitarized version of leading order chiral perturbation theory. Moreover, employing heavy antiquark-diquark symmetry the relevant low-energy constants in the next-to-leading order are connected with those describing light pseudoscalar mesons scattering off charmed mesons, which have been well determined from lattice calculations and experimental data. Our calculations result in a spectrum richer than that of heavy mesons. We find two very narrow $J^P=1/2^-$ $\Omega_{cc}^P$, which very likely decay into $\Omega_{cc}\pi^0$ breaking isospin symmetry. In the isospin-1/2 $\Xi_{cc}^P$ sector, three states are predicted to exist below 4.2~GeV with the lowest one being narrow and the other two rather broad. We suggest to search for the $\Xi_{cc}^{P}$ states in the $\Xi_{cc}^{++}\pi^-$ mode. Searching for them and their analogues are helpful to establish the hadron spectrum.

Weak decays of B_c into two hadrons under flavor SU(3) symmetry

A large number of B_c meson events have been recorded at the LHCb detector, especially some two-body hadronic decay modes. We analyzed the weak decays of the B_c meson into two hadron states under the flavor SU(3) symmetry. The relations among amplitudes of B_c into D+P(V), B+P(V), P(V)+P(V), T_8+bar{T}_8 and T_{10}+{bar{T}}_{10} were investigated systematically, where P ( V) denotes a light pseudoscalar (vector) meson and T_{8,10} denotes a light baryon. The eta -eta ' mixing and omega -phi mixing effects are also considered for the phenomenological discussions. We obtained the relations among decay widths of different B_c decay channels. These results are helpful to study the two-body decay properties of the B_c meson and test the flavor SU(3) symmetry.

Dynamical spin effects in the holographic light-front wavefunctions of light pseudoscalar mesons

We quantify the importance of dynamical spin effects in the holographic light-front wavefunctions of the pion, kaon, $\eta$ and $\eta^\prime$. Using a universal AdS/QCD scale and constituent quark masses, we find that such effects are maximal in the pion where they lead to an excellent simultaneous description of a wide range of data: the decay constant, charge radius, spacelike EM and transition form factors, as well as, after QCD evolution, both the parton distribution function and the parton distribution amplitude data from Fermilab. These dynamical spin effects lead up to a $30\%$ chance of finding the valence quark and antiquark with aligned spins in the pion. The situation is very different for the kaon, where a simultaneous description of the available data (decay constant, radius and spacelike EM form factor) prefer no dynamical spin effects at all. The situation is less clear for the $\eta$ and $\eta^\prime$: while their radiative decay widths data are consistent with dynamical spin effects only in $\eta^\prime$, the data on their spacelike transition form factors clearly favor maximal dynamical spin effects in both mesons.