Showing papers on "Meson published in 2018"
TL;DR: In this paper, first-principle results for quark, gluon, and meson 1PI correlation functions were obtained by solving their functional renormalization group equations in a systematic vertex expansion, aiming at apparent convergence.
Abstract: We present nonperturbative first-principle results for quark, gluon, and meson 1PI correlation functions of two-flavor Landau-gauge QCD in the vacuum. These correlation functions carry the full information about the theory. They are obtained by solving their functional renormalization group equations in a systematic vertex expansion, aiming at apparent convergence. This work represents a crucial prerequisite for quantitative first-principle studies of the QCD phase diagram and the hadron spectrum within this framework. In particular, we have computed the gluon, ghost, quark, and scalar-pseudoscalar meson propagators, as well as gluon, ghost-gluon, quark-gluon, quark, quark-meson, and meson interactions. Our results stress the crucial importance of the quantitatively correct running of different vertices in the semiperturbative regime for describing the phenomena and scales of confinement and spontaneous chiral symmetry breaking without phenomenological input.
172 citations
TL;DR: In this paper, a coalescence plus fragmentation approach was used to calculate the heavy baryon/meson ratio and the ρτεγγεγε ε ≥ 1.5 GeV in a wide range of transverse momentum from low ρεγε up to about 10 GeV.
Abstract: In a coalescence plus fragmentation approach we calculate the heavy baryon/meson ratio and the $$p_T$$
spectra of charmed hadrons $$D^{0}$$
, $$D_{s}$$
and $$\varLambda _{c}^{+}$$
in a wide range of transverse momentum from low $$p_T$$
up to about 10 GeV and discuss their ratios from RHIC to LHC energies without any change of the coalescence parameters. We have included the contribution from decays of heavy hadron resonances and also the one due to fragmentation of heavy quarks which do not undergo the coalescence process. The coalescence process is tuned to have all charm quarks hadronizing in the $$p_T\rightarrow 0$$
limit and at finite $$p_T$$
charm quarks not undergoing coalescence are hadronized by independent fragmentation. The $$p_T$$
dependence of the baryon/meson ratios are found to be sensitive to the masses of coalescing quarks, in particular the $$\varLambda _{c}/D^{0}$$
can reach values of about $$\mathrm 1\div 1.5 $$
at $$p_T \approx \, 3$$
GeV, or larger, similarly to the light baryon/meson ratio like $$p/\pi $$
and $$\varLambda /K$$
, however a marked difference is a quite weak $$p_T$$
dependence with respect to the light case, such that a larger value at intermediate $$p_T$$
implies a relatively large value also for the integrated yields. A comparison with other coalescence model and with the prediction of thermal model is discussed.
124 citations
TL;DR: In this paper, the transverse momentum (p_T) spectrum of prompt D0 mesons and their antiparticles has been measured via the hadronic decay channels D^0 → K^−π+ and D^‾0 → k^+π^− in pp and PbPb collisions at a centre-of-mass energy of 5.02
113 citations
TL;DR: In this paper, the authors provide results for the full set of form factors describing semileptonic $B$-meson transitions to pseudoscalar mesons, including vector mesons.
Abstract: We provide results for the full set of form factors describing semileptonic $B$-meson transitions to pseudoscalar mesons $\pi$, $K$, $\bar{D}$ and vector mesons $\rho$, $K^*$, $\bar{D}^*$. Our results are obtained within the framework of QCD Light-Cone Sum Rules with $B$-meson distribution amplitudes. We recalculate and confirm the results for the leading-twist two-particle contributions in the literature. Furthermore, we calculate and provide new expressions for the two-particle contributions up to twist four. Following new developments for the three-particle distribution amplitudes, we calculate and provide new results for the complete set of three-particle contributions up to twist four. The form factors are computed numerically at several phase space points using up-to-date input parameters, including correlations across phase space points and form factors. We use a model ansatz for all contributing $B$-meson distribution amplitudes that is self-consistent up to twist-four accuracy. We find that the higher-twist two-particle contributions have a substantial impact on the results, and dominate over the three-particle contributions. Our numerical results, including correlations, are provided as machine-readable ancillary files. We discuss the qualitative phenomenological impact of our results on the present $b$ anomalies.
112 citations
TL;DR: In this article, the authors point out that processes involving vector mesons typically dominate the physics of dark matter freeze-out and significantly widen the viable mass range for these models, and explain how to ensure dark matter stability.
Abstract: A natural possibility for dark matter is that it is composed of the stable pions of a QCD-like hidden sector. Existing literature largely assumes that pion self-interactions alone control the early universe cosmology. We point out that processes involving vector mesons typically dominate the physics of dark matter freeze-out and significantly widen the viable mass range for these models. The vector mesons also give rise to striking signals at accelerators. For example, in most of the cosmologically favored parameter space, the vector mesons are naturally long-lived and produce standard model particles in their decays. Electron and proton beam fixed-target experiments such as HPS, SeaQuest, and LDMX can exploit these signals to explore much of the viable parameter space. We also comment on dark matter decay inherent in a large class of previously considered models and explain how to ensure dark matter stability.
109 citations
TL;DR: In this article, the light meson spectrum in QCD was determined in the presence of background magnetic fields using quenched Wilson fermions and the vector meson mass was found to remain nonzero.
Abstract: We determine the light meson spectrum in QCD in the presence of background magnetic fields using quenched Wilson fermions. Our continuum extrapolated results indicate a monotonous reduction of the connected neutral pion mass as the magnetic field grows. The vector meson mass is found to remain nonzero, a finding relevant for the conjectured $\ensuremath{\rho}$-meson condensation at strong magnetic fields. The continuum extrapolation was facilitated by adding a novel magnetic field--dependent improvement term to the additive quark mass renormalization. Without this term, sizable lattice artifacts that would deceptively indicate an unphysical rise of the connected neutral pion mass for strong magnetic fields are present. We also investigate the impact of these lattice artifacts on further observables like magnetic polarizabilities and discuss the magnetic field--induced mixing between $\ensuremath{\rho}$-mesons and pions. We also derive Ward-Takashi identities for $\mathrm{QCD}+\mathrm{QED}$ both in the continuum formulation and for (order $a$--improved) Wilson fermions.
109 citations
TL;DR: In this article, an effective σ/f0(500) resonance was used to evaluate the contribution of scalar mesons to the hadronic light-by-light (HLbL) scattering component of the anomalous magnetic moment aμ of the muon.
95 citations
TL;DR: In this paper, the authors studied the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond, and obtained experimental constraints on the Wilson coefficients corresponding to each operator and provided predictions for branching fractions and other polarization observables in different new physics scenarios.
Abstract: We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to c\tau
u$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.
87 citations
TL;DR: In this paper, a Bayesian model-to-data analysis was applied to estimate the temperature and momentum dependence of the heavy quark diffusion coefficient in an improved Langevin framework, and the posterior range of the diffusion coefficient was obtained by performing a Markov chain Monte Carlo random walk and calibrating on the experimental data of $D$-meson.
Abstract: By applying a Bayesian model-to-data analysis, we estimate the temperature and momentum dependence of the heavy quark diffusion coefficient in an improved Langevin framework. The posterior range of the diffusion coefficient is obtained by performing a Markov chain Monte Carlo random walk and calibrating on the experimental data of $D$-meson ${R}_{\mathrm{AA}}$ and ${v}_{2}$ in three different collision systems at the Relativistic Heavy-Ion Collidaer (RHIC) and the Large Hadron Collider (LHC): Au-Au collisions at 200 GeV and Pb-Pb collisions at 2.76 and 5.02 TeV. The spatial diffusion coefficient is found to be consistent with lattice QCD calculations and comparable with other models' estimation. We demonstrate the capability of our improved Langevin model to simultaneously describe the ${R}_{\mathrm{AA}}$ and ${v}_{2}$ at both RHIC and the LHC energies, as well as the higher order flow coefficient such as $D$ meson ${v}_{3}$. We show that by applying a Bayesian analysis, we are able to quantitatively and systematically study the heavy flavor dynamics in heavy-ion collisions.
82 citations
TL;DR: In this paper, the authors revisited experimental constraints on QCD axions in the 10 MeV mass window, and found a variant axion model that remains compatible with existing constraints.
Abstract: The QCD axion is one of the most compelling solutions of the strong CP problem. There are major current efforts into searching for an ultralight, invisible axion, which is believed to be the only phenomenologically viable realization of the QCD axion. Visible axions with decay constants at or below the electroweak scale are believed to have been long excluded by laboratory searches. Considering the significance of the axion solution to the strong CP problem, we revisit experimental constraints on QCD axions in the $$ \mathcal{O} $$
(10 MeV) mass window. In particular, we find a variant axion model that remains compatible with existing constraints. This model predicts new states at the GeV scale coupled hadronically, and a variety of low-energy axion signatures, such as rare meson decays, nuclear de-excitations via axion emission, and production in e+e− annihilation and fixed target experiments. This reopens the possibility of solving the strong CP problem at the GeV scale.
81 citations
Abstract: In a previous publication, we have presented a model for the photoproduction of $J/\ensuremath{\psi}$ vector mesons off protons, where the proton structure in the impact-parameter plane is described by an energy-dependent hot-spot profile. Here we extend this model to study the photonuclear production of $J/\ensuremath{\psi}$ vector mesons in coherent and incoherent interactions of heavy nuclei. We study two methods to extend the model to the nuclear case: using the standard Glauber-Gribov formalism and using geometric scaling to obtain the nuclear saturation scale. We find that the incoherent cross section changes sizably with the inclusion of subnucleonic hot spots and that this change is energy dependent. We propose to search for this behavior by measuring the ratio of the incoherent to coherent cross sections at different energies. We compare the results of our model to results from the Relativistic Heavy-Ion Collider (RHIC) and from run 1 at the Large Hadron Collider (LHC), finding satisfactory agreement. We also present predictions for the LHC at the new energies reached in run 2. The predictions include $J/\ensuremath{\psi}$ production in ultraperipheral collisions, as well as the recently observed photonuclear production in peripheral collisions.
TL;DR: In this paper, the Cabibbo-suppressed decay Λ$(2S)pππ$−−1) was observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb$−1}$ of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV.
Abstract: The Cabibbo-suppressed decay Λ$_{b}^{0}$ → ψ(2S)pπ$^{−}$ is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb$^{−1}$ of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μ$^{+}$μ$^{−}$ final state. The branching fraction with respect to that of the Λ$_{b}^{0}$ → ψ(2S)pK$^{−}$ decay mode is measured to be
TL;DR: In this article, the prompt D0 meson azimuthal anisotropy coefficients, v2 and v3, are measured at midrapidity (|y| < 1.0) in Pb-Pb collisions at a center-of-mass energy sNN=5.02
Abstract: The prompt D0 meson azimuthal anisotropy coefficients, v2 and v3, are measured at midrapidity (|y|<1.0) in Pb-Pb collisions at a center-of-mass energy sNN=5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (pT) range of 1 to 40 GeV/c, for central and midcentral collisions. The v2 coefficient is found to be positive throughout the pT range studied. The first measurement of the prompt D0 meson v3 coefficient is performed, and values up to 0.07 are observed for pT around 4 GeV/c. Compared to measurements of charged particles, a similar pT dependence, but smaller magnitude for pT<6 GeV/c, is found for prompt D0 meson v2 and v3 coefficients. The results are consistent with the presence of collective motion of charm quarks at low pT and a path length dependence of charm quark energy loss at high pT, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.
TL;DR: In this article, the authors explored the possibility that some of the five narrow π cπε cπδπε π πcπε δππεπτετε resonance at LHCb could correspond to pentaquark states, structured as meson-baryon bound states.
Abstract: We explore the possibility that some of the five narrow $\Omega_{c}$
resonances recently observed at LHCb could correspond to pentaquark states, structured as meson-baryon bound states or molecules. The interaction of the low-lying pseudoscalar mesons with the ground-state baryons in the charm +1 , strangeness -2 and isospin 0 sector is built from t-channel vector meson exchange, using effective Lagrangians. The resulting s-wave coupled-channel unitarized amplitudes show the presence of two structures with similar masses and widths to those of the observed $\Omega_{c}(3050)^{0}$
and $\Omega_{c}(3090)^{0}$
. The identification of these resonances with the meson-baryon bound states found in this work would also imply assigning the values $1/2^{-}$
for their spin-parity. An experimental determination of the spin-parity of the $ \Omega_{c}(3090)^{0}$
would contribute to a better understanding of its structure, as the quark-based models predict its spin-parity to be either $ 3/2^{-}$
or $ 5/2^{-}$
. Predictions for the analogue bottom $\Omega_{b}^{-}$
resonances are also given.
[...]
TL;DR: In this paper, the existence of stable tetron bound states in the large N c limit of a mesonic system with two heavy quarks and two light antiquarks was studied.
TL;DR: In this paper, it was shown that the production points for heavy quarks are forward-backward symmetric and shifted in the transverse plane with respect to the fireball, leading to a very large directed flow for heavy mesons in noncentral Au-Au collisions.
Abstract: Thermalized matter created in noncentral relativistic heavy-ion collisions is expected to be tilted in the reaction plane with respect to the beam axis. The most notable consequence of this forward-backward symmetry breaking is the observation of rapidity-odd directed flow for charged particles. On the other hand, the production points for heavy quarks are forward-backward symmetric and shifted in the transverse plane with respect to the fireball. The drag on heavy quarks from the asymmetrically distributed thermalized matter generates substantial directed flow for heavy flavor mesons. We predict a very large rapidity-odd directed flow of $D$ mesons in noncentral Au-Au collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{GeV}$, several times larger than for charged particles. A possible experimental observation of a large directed flow for heavy flavor mesons would represent an almost direct probe of the three-dimensional distribution of matter in heavy-ion collisions.
TL;DR: In the wake of the recent measurements of the decays B c → J / ψ π (K ) and B c − η c transitions in full kinematical region within covariant confined quark model, the authors in this article calculate the form factors for the Bc → J/ ψ and Bc − ǫ c transitions and evaluate the partial decay widths of the B c meson.
TL;DR: In this paper, the authors reported the measurement of ΔΦ = 42.4 ± 0.5° using Λ→πππ$^{−}$ and Λ ≥ 0.004, a precise direct test of charge parity symmetry violation in Λ decays.
Abstract: Particles directly produced at electron–positron colliders, such as the J/ψ meson, decay with relatively high probability into a baryon–antibaryon pair 1 . For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase ΔΦ between the transition amplitudes to these helicity states results in a transverse polarization of the baryons 2$^{–}$4 . From the joint angular distribution of the decay products of the baryons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of ΔΦ = 42.4 ± 0.6 ± 0.5° using Λ → pπ$^{−}$ and $\bar \Lambda \to \bar p\pi ^ + ,\bar n\pi ^0$ decays at BESIII. We find a value for the Λ → pπ$^{−}$ decay parameter of α$_{−}$ = 0.750 ± 0.009 ± 0.004, 17 ± 3% higher than the current world average, which has been used as input for all Λ polarization measurements since 1978 5$^{,}$6 . For $\bar \Lambda \to \bar p\pi ^ +$ we find α$_{+}$ = −0.758 ± 0.010 ± 0.007, giving A$_{CP}$ = (α$_{−}$ + α$_{+}$)/(α$_{−}$ − α$_{+}$) = −0.006 ± 0.012 ± 0.007, a precise direct test of charge–parity symmetry (CP) violation in Λ decays.
TL;DR: The Quark-Meson-Coupling (QMC) model as discussed by the authors, which selfconsistently relates the dynamics of the internal quark structure of a hadron to the relativistic mean fields arising in nuclear matter, provides a natural explanation to many open questions in low energy nuclear physics, including the origin of many-body nuclear forces and their saturation, the spin-orbit interaction and properties of hadronic matter at a wide range of densities up to those occurring in the cores of neutron stars.
TL;DR: In this article, the authors show that a measurement of a CP-violating observable, which is induced through interference between mixing and decay processes, is essential to obtain the full picture, in particular to establish new scalar contributions and CPviolating phases.
Abstract: The decay $$B^0_s\rightarrow \mu ^+\mu ^-$$
is a key probe for the search of physics beyond the Standard Model. While the current measurements of the corresponding branching ratio agree with the Standard Model within the uncertainties, significant New-Physics effects may still be hiding in $$B^0_s\rightarrow \mu ^+\mu ^-$$
. In order to reveal them, the observable $$\mathcal {A}^{\mu \mu }_{\Delta \Gamma _s}$$
, which is provided by the decay width difference $$\Delta \Gamma _s$$
of the $$B^0_s$$
-meson system, plays a central role. We point out that a measurement of a CP-violating observable $$\mathcal{S}_\mathrm{\mu \mu }$$
, which is induced through interference between $$B^0_s$$
–
$${\bar{B}}^0_s$$
mixing and $$B_s\rightarrow \mu ^+\mu ^-$$
decay processes, is essential to obtain the full picture, in particular to establish new scalar contributions and CP-violating phases. We illustrate these findings with future scenarios for the upgrade(s) of the LHC, exploiting also relations which emerge within an effective field theory description of the Standard Model, complemented with New Physics entering significantly beyond the electroweak scale.
TL;DR: In this paper, strongly interacting massive particles (SIMPs) are identified as dark pions in dark chiral perturbation theory (ChPT) in which both light mass and strong coupling needed for SIMPs can be realized by strong dynamics.
Abstract: We consider a light dark matter candidate that is produced by the freeze-out mechanism with 3→2 annihilations, the so-called strongly interacting massive particles (SIMPs). SIMPs are identified as dark pions in dark chiral perturbation theory (ChPT) in which both light mass and strong coupling needed for SIMPs can be realized by strong dynamics. In QCD-like theories with SU(3)L×SU(3)R/SU(3)V flavor symmetry, including dark vector mesons in the hidden local symmetry scheme, we illustrate that dark vector mesons unitarize the dark ChPT efficiently, thus determining the correct relic density condition within the validity of the dark ChPT.
TL;DR: In this paper, the meson curvature, pole and screening masses were derived from the effective meson Lagrangian density with minimal coupling to the magnetic field, by employing derivative expansion for both meson fields and Schwinger phases.
Abstract: We study neutral and charged meson properties in the magnetic field. Taking the bosonization method in a two-flavor Nambu--Jona-Lasinio model, we derive effective meson Lagrangian density with minimal coupling to the magnetic field, by employing derivative expansion for both the meson fields and Schwinger phases. We extract from the effective Lagrangian density the meson curvature, pole and screening masses. As the only Goldstone mode, the neutral pion controls the thermodynamics of the system and propagates the long range quark interaction. The magnetic field breaks down the space symmetry, and the quark interaction region changes from a sphere in vacuum to a ellipsoid in magnetic field.
TL;DR: In this paper, a search for resonance-like structures in the Bs0π± invariant mass spectrum was performed using proton-proton collision data collected by the CMS experiment at the LHC at s=8.7
Abstract: A search for resonancelike structures in the Bs0π± invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at s=8 TeV, corresponding to an integrated luminosity of 19.7 fb-1. The Bs0 mesons are reconstructed in the decay chain Bs0→J/ψϕ, with J/ψ→μ+μ- and ϕ→K+K-. The Bs0π± invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed Bs0 and π± candidates. Upper limits are set on the relative production rates of the X(5568) and Bs0 states times the branching fraction of the decay X(5568)±→Bs0π±. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into Bs0π±.
TL;DR: In this paper, the mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model using numerical solution of Schrodinger equation.
Abstract: The mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model. We have employed the numerical solution of Schrodinger equation to obtain their mass spectra using only four parameters namely quark mass (
$$m_c$$
, $$m_b$$
) and confinement strength (
$$A_{c\bar{c}}$$
, $$A_{b\bar{b}}$$
). The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are computed perturbatively to determine the mass spectra of excited S, P, D and F states. Digamma, digluon and dilepton decays of these mesons are computed using the model parameters and numerical wave functions. The predicted spectroscopy and decay properties for quarkonia are found to be consistent with available data from experiments, lattice QCD and other theoretical approaches. We also compute mass spectra and life time of the $$B_c$$
meson without additional parameters. The computed electromagnetic transition widths of heavy quarkonia and $$B_c$$
mesons are in tune with available experimental data and other theoretical approaches.
TL;DR: In this article, the exclusive decays of the Higgs and Z bosons into a J/ψ, ψ(2S), or ϒ(nS) ( n=1,2,3 ) meson and a photon are performed with a pp collision data sample corresponding to an integrated luminosity of 361fb−1 collected at s=13TeV with the ATLAS detector at the CERN Large Hadron Collider.
TL;DR: Modern numerical methods used in the determination and solution of Bethe–Salpeter and Dyson–Schwinger equations are reviewed in detail and the self-consistent calculation of form-factors is described.
17 Nov 2018
TL;DR: In this article, the dispersive analysis of the decay η → 3π is reviewed and thoroughly updated with the aim of determin- ing the quarkmassratio Q = 22.1(7) where the error covers all of the uncertainties encountered in the course of the calculation.
Abstract: The dispersive analysis of the decay η → 3π is reviewed and thoroughly updated with the aim of determin- ingthequarkmassratio Q²=(m²s−m²ud)/(m²d−m²u). With the number of subtractions we are using, the effects generated by the final state interaction are dominated by low energy ππ scattering. Since the corresponding phase shifts are now accurately known, causality and unitarity determine the decay amplitude within small uncertainties – except for the values of the subtraction constants. Our determination of these constants relies on the Dalitz plot distribution of the charged channel, which is now measured with good accu- racy. The theoretical constraints that follow from the fact that the particles involved in the transition represent Nambu– Goldstone bosons of a hidden approximate symmetry play an equally important role. The ensuing predictions for the Dalitz plot distribution of the neutral channel and for the branching ratio Γη→3π⁰/Γη→π+π−π⁰ are in very good agreement with experiment. Relying on a known low-energy theorem that relates the meson masses to the masses of the three lightest quarks, our analysis leads to Q = 22.1(7), where the error covers all of the uncertainties encountered in the course of the calculation: experimental uncertainties in decay rates and Dalitz plot distributions, noise in the input used for the phase shifts, as well as theoretical uncertainties in the constraints imposed by chiral symmetry and in the evaluation of isospin breaking effects. Our result indicates that the current algebra formulae for the meson masses only receive small corrections from higher orders of the chiral expansion, but not all of the recent lattice results are consistent with this conclusion.
TL;DR: In this paper, a symmetry-preserving truncation of meson and baryon bound-state equations in quantum field theory is used to develop a unified description of systems constituted from light and heavy quarks.
Abstract: We use a symmetry-preserving truncation of meson and baryon bound-state equations in quantum field theory in order to develop a unified description of systems constituted from light- and heavy-quarks In particular, we compute the spectrum and leptonic decay constants of ground-state pseudoscalar- and vector-mesons: $q^\prime \bar q$, $Q^\prime \bar Q$, with $q^\prime,q=u,d,s$ and $Q^\prime,Q = c,b$; and the masses of $J^P=3/2^+$ baryons and their first positive-parity excitations, including those containing one or more heavy quarks This Poincare-covariant analysis predicts that such baryons have a complicated angular momentum structure For instance, the ground states are all primarily $S$-wave in character, but each possesses $P$-, $D$- and $F$-wave components, with the $P$-wave fraction being large in the $qqq$ states; and the first positive-parity excitation in each channel has a large $D$-wave component, which grows with increasing current-quark mass, but also exhibits features consistent with a radial excitation The configuration space extent of all such baryons decreases as the mass of the valence-quark constituents increases
TL;DR: In this paper, the dispersive analysis of the decay is reviewed and thoroughly updated with the aim of determining the quark mass ratio, which is based on a known low-energy theorem that relates the meson masses to the masses of the three lightest quarks.
Abstract: The dispersive analysis of the decay $$\eta \rightarrow 3\pi $$
is reviewed and thoroughly updated with the aim of determining the quark mass ratio $$Q^2=(m_s^2-m_{ud}^2)/(m_d^2-m_u^2)$$
. With the number of subtractions we are using, the effects generated by the final state interaction are dominated by low energy $$\pi \pi $$
scattering. Since the corresponding phase shifts are now accurately known, causality and unitarity determine the decay amplitude within small uncertainties – except for the values of the subtraction constants. Our determination of these constants relies on the Dalitz plot distribution of the charged channel, which is now measured with good accuracy. The theoretical constraints that follow from the fact that the particles involved in the transition represent Nambu–Goldstone bosons of a hidden approximate symmetry play an equally important role. The ensuing predictions for the Dalitz plot distribution of the neutral channel and for the branching ratio $$\varGamma _{\eta \rightarrow 3\pi ^0}/ \varGamma _{\eta \rightarrow \pi ^+\pi ^-\pi ^0}$$
are in very good agreement with experiment. Relying on a known low-energy theorem that relates the meson masses to the masses of the three lightest quarks, our analysis leads to $$Q=22.1(7)$$
, where the error covers all of the uncertainties encountered in the course of the calculation: experimental uncertainties in decay rates and Dalitz plot distributions, noise in the input used for the phase shifts, as well as theoretical uncertainties in the constraints imposed by chiral symmetry and in the evaluation of isospin breaking effects. Our result indicates that the current algebra formulae for the meson masses only receive small corrections from higher orders of the chiral expansion, but not all of the recent lattice results are consistent with this conclusion.
TL;DR: In this paper, the authors present a comprehensive discussion of the phenomenology of flavourful axions, including both standard Peccei-Quinn axions associated with the solution to the strong CP problem, and non-standard axion-like particles (ALPs).
Abstract: We present a comprehensive discussion of the phenomenology of flavourful axions, including both standard Peccei-Quinn (PQ) axions, associated with the solution to the strong CP problem, and non-standard axion-like particles (ALPs). We give the flavourful axion-fermion and axion-photon couplings and calculate the branching ratios of heavy meson (K, D, B) decays involving a flavourful axion. We also calculate the mixing between axions and heavy mesons K0, D0, B0 and B
0
, which affects the meson oscillation probability and mass difference. Mixing also contributes to meson decays into axions and axion decays into two photons, and may be relevant for ALPs. We discuss charged lepton flavour-violating decays involving final state axions of the form l1 → l2a(γ), as well as μ → eee and μ − e conversion. Finally we describe the phenomenology of a particular “A to Z” Pati-Salam model, in which PQ symmetry arises accidentally due to discrete flavour symmetry. Here all axion couplings are fixed by a fit to flavour data, leading to sharp predictions and correlations between flavour-dependent observables.