Kaon Mass Research Articles

Impact of Finite Volume on Kaon, Antikaon, and ϕ Meson Masses and Decay Widths in Asymmetric Strange Hadronic Matter

Abstract In the present work, we investigate the impact of finite volume on the in-medium properties of kaons ($K^+$, $K^0$), antikaons ($K^-$, $\bar{K^0}$), and $\phi$ mesons in the isospin asymmetric strange hadronic medium at finite density and temperature. We use the chiral SU(3) hadronic mean-field model, which accounts for the interactions between baryons through the exchange of scalar ($\sigma , \zeta , \delta$) and vector ($\omega$, $\rho$, $\phi$) fields. To investigate the effects of finite volume, we apply the multiple reflection expansion technique for calculations of the density of states. At high baryon density, an increase of the isospsin asymmetry of the medium from zero to a finite value is found to impact the nonstrange scalar field $\sigma$ more than the strange scalar field $\zeta$, whereas the opposite is the case as a function of the strangeness fraction of the medium. For example, in an infinite nuclear medium at $\rho _B = 4\rho _0$, for an increase of isospin asymmetry from zero to ${\sim}0.3$, the magnitudes of the scalar fields $\sigma$ and $\zeta$ increase by ${\sim}3.0$% and ${\sim}0.1$%, respectively. On the other hand, for a symmetric medium, an increase of $f_s$ from 0 to 0.5 leads to an increase in the magnitude of $\sigma$ by ${\sim}0.4$% and a decrease in $\zeta$ by ${\sim}16$%. We use the medium-modified masses of kaons and antikaons calculated using the chiral SU(3) model to obtain the masses and decay widths of $\phi$ mesons in the finite volume hadronic medium. To obtain the masses and decay widths of $\phi$ mesons, an effective Lagrangian approach with $\phi$K$\bar{K}$ interactions at the one-loop level is used in the present work. We obtain the effective masses and decay widths in the finite volume matter for a spherical geometry of a medium with Neumann and Dirichlet boundary conditions as well as for a cubic geometry. At baryon density 4$\rho _0$, the Dirichlet boundary conditions with spherical geometry of the medium leads to changes of ${\sim}4$%, ${\sim}3$%, and ${\sim}0.6$% in the effective masses of the K, $\bar{K}$, and $\phi$ mesons, as the system size decreases from $R = \infty$ to 2 fm in a symmetric nuclear medium.

A feasibility study of the measurement of kaonic lead X-rays at DA[formula omitted]NE for the precise determination of the charged kaon mass

An HPGe detector equipped with a transistor reset preamplifier and readout with a CAEN DT5781 fast pulse digitizer was employed in the measurement of X-rays from kaonic lead at the DAΦNE e+e− collider at the Laboratori Nazionali di Frascati of INFN. A thin scintillator in front of a lead target was used to select kaons impinging on it and to form the trigger for the HPGe detector. We present the results of the kaonic lead feasibility measurement, where we show that the resolution of the HPGe detector in regular beam conditions remains the same as that without the beam and that a satisfactory background reduction can be achieved. This measurement serves as a test bed for future dedicated kaonic X-rays measurements for the more precise determination of the charged kaon mass.

Kaon superfluidity in the early Universe

Previously, it was found that pion superfluidity could be realized in the quantum chromodynamics (QCD) epoch of the early Universe, when lepton flavor asymmetry |le+lμ| is large enough to generate a charge chemical potential |μQ| larger than vacuum pion mass. By following the same logic, kaon superfluidity might also be possible when |le+lμ| is so large that |μQ| becomes larger than vacuum kaon mass. Such a possibility is checked by adopting Ginzburg-Landau approximation within the three-flavor Polyakov–Nambu–Jona-Lasinio model. Consider the case with full chemical balance, though kaon superfluidity could be stable compared to the chiral phases with only σ condensations, it would get killed by the more favored homogeneous pion superfluidity. If we introduce mismatch between s and d quarks, kaon superfluidity would require so large s quark density that such a state is impossible in the early Universe. Published by the American Physical Society 2024

The charge and mass symmetry breaking in the KK K¯ system

In the framework of the Faddeev equations in configuration space, we investigate the K(1460) meson as a resonant state of the KKK¯ kaonic system. We perform calculations for the particle configurations K 0 K + K − and K0K+K0¯ within two models: the ABC model, in which all three particles are distinguishable, and the AAC model when two particles are identical. The models differ in their treatment of the kaon mass difference and the attractive Coulomb force between the K + K − pair. We found that the Coulomb shift adds over 1 MeV to the three-body binding energy. The expected correction to the binding energy due to mass redistribution from AA to AB is found to be negligible, up to a maximum of 6% of the relative mass correction. At the same time, the symmetry of the wave function is distorted depending on the mass ratio value. We found that the repulsive KK interaction plays an essential role in the binding energy of the KKK¯ system and reports the mass of 1461.8 or 1464.1 MeV for the neutral K 0(1460) and 1466.5 or 1468.8 MeV for the charged K +(1460) resonances, respectively, depending on the parameter sets for KK and KK¯ interactions.

New insights into the nature of the Λ(1380) and Λ(1405) resonances away from the SU(3) limit

Starting from the SU(3) limit, we consider the nature of the dynamically generated resonances Λ(1380), Λ(1405) and Λ(1680) as the pion and kaon masses are tuned to their physical values. We show that the accidental symmetry of the two octets due to the leading order Weinberg-Tomozawa term is broken by the next-to-leading order terms. Most interestingly, we observe an interchange of the two trajectories of the Λ(1380) and the Λ(1405) away from the SU(3) limit at next-to-leading order. This remarkable phenomenon can be investigated using lattice QCD calculations that start from the SU(3) limit.

Testing Heavy Neutral Leptons in Cosmic Ray Beam Dump experiments

In this work, we discuss the possibility to test Heavy Neutral Leptons (HNLs) using “Cosmic Ray Beam Dump” experiments. In analogy with terrestrial beam dump experiments, where a beam first hits a target and is then absorbed by a shield, we consider high-energy incident cosmic rays impinging on the Earth’s atmosphere and then the Earth’s surface. We focus here on HNL production from atmospherically produced kaon, pion and D-meson decays, and discuss the possible explanation of the appearing Cherenkov showers observed by the SHALON Cherenkov telescope and the ultra-high energy events detected by the neutrino experiment ANITA. We show that these observations can not be explained with a long-lived HNL, as the relevant parameter space is excluded by existing constraints. Then we propose two new experimental setups that are inspired by these experiments, namely a Cherenkov telescope pointing at a sub-horizontal angle and shielded by the mountain cliff at Mount Thor, and a geostationary satellite that observes part of the Sahara desert. We show that the Cherenkov telescope at Mount Thor can probe currently untested HNL parameter space for masses below the kaon mass. We also show that the geostationary satellite experiment can significantly increase the HNL parameter space coverage in the whole mass range from 10 MeV up to 2 GeV and test neutrino mixing |Uα4|2 down to 10−11 for masses around 300 MeV.

Momentum dependence of mixing in the pion vector form factor and its effect on * *Supported in part by the Fundamental Research Funds for the Central Universities (FRF-BR-19-001A), and the National Natural Science Foundation of China (11975028, 11974043)

The inclusion of the mixing effect is essential for a precise description of the pion electromagnetic form factor in the process, which quantifies the two-pion contribution to the anomalous magnetic moment of muon . In this study, we analyze the momentum dependence of mixing by considering loop contributions at the next-to-leading order in expansion within the framework of resonance chiral theory. We revisit a previous study [Y. H. Chen, D. L. Yao, and H. Q. Zheng, Commun. Theor. Phys. 69, 1 (2018)] and consider the contribution arising from the kaon mass splitting in the kaon loops and latest experimental data. We perform two types of fits (with momentum-independent or momentum-dependent mixing amplitude) to describe and data within the energy region of 600900 MeV and decay width of . Furthermore, we compare their results. Our findings indicate that the momentum-independent and momentum-dependent mixing schemes provide appropriate descriptions of the data. However, the momentum-dependent scheme exhibits greater self-consistency, considering the reasonable imaginary part of the mixing matrix element obtained. Regarding the contribution to the anomalous magnetic moment of the muon, , the results obtained from the fits considering the momentum-dependent mixing amplitude are in good agreement with those obtained without incorporating the momentum dependence of mixing, within the margin of errors. Furthermore, based on the fitted values of the relevant parameters, we observe that the decay width of is predominantly influenced by the mixing effect.

Hadronic light-by-light contribution to the muon g−2 from holographic QCD with solved U(1)A problem

We employ the comparatively minimal extension of hard-wall AdS/QCD due to Katz and Schwartz which takes into account the U(1)$_A$ anomaly for computing hadronic light-by-light scattering contributions of pseudoscalar and axial vector mesons to the anomalous magnetic moment of the muon $a_\mu$. By including a gluon condensate as one extra tunable parameter besides those fixed by $f_\pi$ and the pion, kaon, and rho masses, we obtain remarkably accurate fits for $\eta$ and $\eta'$ masses and their decay rates to photons, leading to $a_\mu$ contributions in complete agreement with the Standard Model result by the Muon $g-2$ Theory Initiative. Turning to the less well understood axial vector contributions, we update our previous predictions obtained in flavor-symmetric hard-wall AdS/QCD models without U(1)$_A$ breaking.

Coupled-channel dynamics with chiral long-range forces in the open-charm sector of QCD

We perform an analysis of lattice QCD data in the open-charm sector based on the chiral SU(3) Lagrangian. The low-energy constants are adjusted to recover the open-charm meson masses on lattice QCD ensembles from HPQCD, ETMC, and HSC with pion and kaon masses smaller than 550 MeV. A significant set of low-energy parameters is obtainable only if the most recent information from HSC on scattering observables is included in our global fit. For the first time our analysis considers the effect of left-hand cuts as developed in terms of a generalized potential approach previously by one of the authors. Here we use coupled-channel interaction terms at the one-loop level. The elastic s-wave and p-wave $D\ensuremath{\pi}$, $DK$, and $D\overline{K}$ scattering phase shifts on ensembles with nominal pion masses of about 239 and 391 MeV are reproduced faithfully. Based on such low-energy parameters we predict s- and p-wave phase shifts and inelasticities at physical quark masses, where the statistical uncertainties in the phase shifts are smaller than 1 degree always. Most striking would be the exotic s-wave ${D}_{s}\ensuremath{\pi}$ channel, for which we predict a resonance state at about 2.287 GeV where the phase shift passes through 90 degrees.

Pion and Kaon Distribution Amplitudes from Lattice QCD.

We present a state-of-the-art lattice QCD calculation of the pion and kaon light-cone distribution amplitudes (DAs) using large-momentum effective theory. The calculation is done at three lattice spacings a≈{0.06,0.09,0.12} fm and physical pion and kaon masses, with the meson momenta P_{z}={1.29,1.72,2.15} GeV. The result is nonperturbatively renormalized in a recently proposed hybrid scheme with self-renormalization, and extrapolated reliably to the continuum as well as the infinite momentum limit. We find a significant deviation of the pion and kaon DAs from the asymptotic form, and a large SU(3) flavor breaking effect in the kaon DA.

Constraining active-sterile neutrino mixing via lepton flavor violating decays of mesons

As a hypothetic particle, a sterile neutrino can exist in types of new physics models. In this work by investigating flavor violating semileptonic and leptonic decays of K,D, and B mesons induced by the GeV scale sterile neutrino, we explore its allowed regions in parameter space. Analytically, we derive branching fractions of semileptonic decay M^{+}_{h}to M_{l}^{+}ell _{1}^{+}ell _{2}^{-} and leptonic decay M^{0}to ell _{1}^{-}ell _{2}^{+}, including the contribution from a new box diagram contribution due to the massive sterile neutrino. Imposing its mass ranges, we numerically analyze the active-sterile neutrino mixings in corresponding regions. We find that when the sterile neutrino mass is located in between pion and kaon mass, K+→π+e±μ∓ gives the strongest constraint while B+→π+e±μ∓ provides the dominated constraint when its mass in between of kaon and B meson. If the sterile neutrino is even heavier than Bmesons, the LHCb B^{0}_{s}to mu ^{pm } e^{mp } results gives the strongest constraint.

The charm-quark contribution to light-by-light scattering in the muon (g-2) from lattice QCD

We compute the hadronic light-by-light scattering contribution to the muon g-2 from the charm quark using lattice QCD. The calculation is performed on ensembles generated with dynamical (u, d, s) quarks at the SU(3)_mathrm{f} symmetric point with degenerate pion and kaon masses of around 415 MeV. It includes the connected charm contribution, as well as the leading disconnected Wick contraction, involving the correlation between a charm and a light-quark loop. Cutoff effects turn out to be sizeable, which leads us to use lighter-than-physical charm masses, to employ a broad range of lattice spacings reaching down to 0.039 fm and to perform a combined charm-mass and continuum extrapolation. We use the eta _c meson to define the physical charm-mass point and obtain a final value of a_mu ^mathrm{HLbL,c}= (2.8pm 0.5) times 10^{-11}, whose uncertainty is dominated by the systematics of the extrapolation. Our result is consistent with the estimate based on a simple charm-quark loop, whilst being free of any perturbative scheme dependence on the charm mass. The mixed charm–light disconnected contraction contributes a small negative amount to the final value.

Electromagnetic and strong isospin breaking in light meson masses

We study electromagnetic as well as strong isospin breaking effects in the isospin mass splittings of light pseudoscalar and vector mesons. To this end we employ a coupled system of quark Dyson-Schwinger and meson Bethe-Salpeter equations whose interaction kernels contain gluon, pion and photon exchange interactions. In bound states, QCD-induced isospin breaking is manifest on different levels. On the one hand, a different explicit up- and down-quark mass directly affects the propagators of the constituent quarks. On the other hand, it leads to different interaction kernels within the isospin multiplets. In addition, electromagnetic isospin breaking is induced via a photon exchange diagram. Using the kaon iso-doublet and the charged pion masses as input to determine the up, down and strange quark masses we find for the pion, kaon and rho meson mass splittings different patterns each. In particular, our results provide evidence that the effects from two sources of mass splittings, the different quark masses and the different quark charges, do not add up linearly.

The decay and the mixing * *This work is partly supported by the National Natural Science Foundation of China (11975083, 12147211). This work is also partly supported by the Spanish Ministerio de Economia y Competitividad and European FEDER funds (FIS2017-84038-C2-1-P B) and Generalitat Valenciana (PROMETEO/2020/023). This project has received funding from the European Unions Horizon 2020 research and innovation programme

We study the and reactions, and pay attention to the different sources of isospin violation and mixing of and resonances where these resonances are dynamically generated from meson–meson interactions. We find that the main cause of isospin violation is isospin breaking in the meson–meson transition T matrices, and the other source is that the loops involving kaons in the production mechanism do not cancel due to the different masses of charged and neutral kaons. We obtain a branching ratio for production of the order of . Future experiments can address this problem, and the production rate and shape of the mass distribution will definitely help to better understand the nature of scalar resonances.

Magnetic field induced corrections to the NJL model coupling constant from vacuum polarization

Magnetic field dependent corrections for the coupling constant of the Nambu-Jona-Lasinio model are calculated by considering the one-loop background field method. These coupling constants turn out to break chiral and flavor symmetries and they lead to a slight improvement of the numerical values of the up and down quark condensates when compared to results from lattice QCD. The corresponding magnetic field dependencies of the neutral pion and kaon masses are also presented and compared with available lattice QCD calculations. The resulting magnetic field correction to the $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ mixing angle is also estimated.

Heavy neutral leptons below the kaon mass at hodoscopic neutrino detectors

Heavy neutral leptons ($N$) below the kaon mass are severely constrained by cosmology and lab-based searches for their decays in flight. If $N$ interacts via an additional force, $N\to\nu e^+e^-$ decays are enhanced and cosmological limits can be avoided. We show that the T2K and MicroBooNE neutrino experiments provide the best limits on the mixing of $N$ with muon-neutrinos, outperforming past-generation experiments, previously thought to dominate. We constrain models with electromagnetically-decaying and long-lived $N$, such as in a transition-magnetic-moment portal and in a leptophilic axion-like particle portal, invoked to explain the MiniBooNE excess. By considering these models as representative examples, our results show that explanations of the MiniBooNE excess that involve $e^+e^-$ pairs from long-lived particles are in tension with T2K, PS191, and MicroBooNE data. Similarly, these searches also constrain MiniBooNE explanations based on single photons due to the associated $e^+e^-$ decay mode via a virtual photon.

QCD chiral condensate and pseudoscalar-meson properties in the nuclear medium at finite temperature

The pion and kaon properties in a nuclear medium at nonvanishing temperature as well as the quantum chromodynamics (QCD) chiral condensate in the presence of a magnetic field for various baryon densities are studied in the Nambu–Jona–Lasinio (NJL) model with the help of the proper-time regularization (PTR) scheme, simulating a QCD confinement. The density dependence of the quark mass in symmetric nuclear matter is obtained from the quark-meson coupling (QMC) model, which shares the same covariant feature with the NJL model, at quark level. We then analyze the QCD chiral condensates and dynamical masses for various baryon densities at finite temperature and magnetic field as well as the pion and kaon masses, pion and kaon weak-decay constants, pion- and kaon-quark coupling constants, and wave function renormalization factors for various baryon densities at finite temperature. We find that the QCD chiral condensates suppress with increasing temperature and baryon density and enhance under the presence of a magnetic field, which are consistent with other model predictions. Interestingly, the wave function renormalization factors for the pion and kaon increase with respect to temperature and reduce as the baryon density increases are found.

Lattice QCD calculation of K→ℓνℓℓ′+ℓ′− decay width

We develop a methodology for the computation of the $K\to \ell\nu_\ell \ell'^+ \ell'^-$ decay width using lattice QCD and present an exploratory study here. We use a scalar function method to account for the momentum dependence of the decay amplitude and adopt the infinite volume reconstruction method to reduce the systematic errors such as the temporal truncation effects and the finite-volume effects. We then perform a four-body phase-space integral to obtain the decay width. The only remaining technical problem is the possible power-law finite-volume effects associated with the process of $K\to\pi\pi \ell\nu_\ell\to \ell\nu_\ell \ell'^+ \ell'^-$, where the intermediate state involves multiple hadrons. In this work, we use a gauge ensemble of twisted mass fermion with a pion mass $m_\pi=352$ MeV and a nearly-physical kaon mass. At this kinematics, the $\pi\pi$ in the intermediate state cannot be on shell simultaneously as $2m_\pi>m_K$ and the finite-volume effects associated with $\pi\pi$ state are exponentially suppressed. Using the developed methods mentioned above, we calculate the branching ratios for four channels of $K\to \ell\nu_\ell\ell'^+ \ell'^-$, and obtain the results comparable to the experimental measurements and ChPT predictions. Our work demonstrates the capability of lattice QCD to improve Standard Model prediction in $K\to \ell\nu_\ell \ell'^+ \ell'^-$ decay width.

Scalar, vector, and tensor form factors for the pion and kaon from lattice QCD

We present a calculation of the scalar, vector, and tensor form factors for the pion and kaon in lattice QCD. We use an ensemble of two degenerate light, a strange and a charm quark (${N}_{f}=2+1+1$) of maximally twisted mass fermions with clover improvement. The corresponding pion and kaon masses are about 265 MeV and 530 MeV, respectively. The calculation is done in both rest and boosted frames obtaining data for four-vector momentum transfer squared up to $\ensuremath{-}{q}^{2}=2.5\text{ }\text{ }{\mathrm{GeV}}^{2}$ for the pion and $3\text{ }\text{ }{\mathrm{GeV}}^{2}$ for the kaon. The excited-states effects are studied by analyzing six values of the source-sink time separation for the rest frame (1.12--2.23 fm) and for four values for the boosted frame (1.12--1.67 fm). The lattice data are renormalized nonperturbatively and the results for the scheme- and scale-dependent scalar and tensor form factors are presented in the $\overline{\mathrm{MS}}$ scheme at a scale of 2 GeV. We apply different parametrizations to describe ${q}^{2}$-dependence of the form factors to extract the scalar, vector, and tensor radii, as well as the tensor anomalous magnetic moment. We compare the pion and kaon form factors to study SU(3) flavor symmetry breaking effects. By combining the data for the vector and tensor form factors we also obtain the lowest moment of the densities of transversely polarized quarks in the impact parameter space. Finally, we give an estimate for the average transverse shift in the $y$ direction for polarized quarks in the $x$ direction.

Particle configurations in the NNK̅ system

Three-body AAB model for the NNK(snn = 0) kaonic cluster is considered based on the configuration space Faddeev equations. Within a singlechannel approach, the difference between masses of nucleons and kaons and the charge independence breaking of nucleon-nucleon interaction are taken into consideration. We definite the particle configurations in the system according to the particle masses and pair potentials. There are two sets of the particle configurations, ppK, npK and nnK°, npK, charged and neutral. The three-body calculations are performed by applying NN and NK phenomenological isospin-dependent potentials. The mass and energy spectra related to the particle configurations are presented. We evaluate the mass and energy uncertainties for the NNK model. An analogy to NNN model for the H and He nuclei is proposed.