Neutral Pseudoscalar Mesons Research Articles

Test of the Classicality Concept in Entangled States of Neutral Pseudoscalar Mesons with the Aid of Three-Time Wigner Inequalities

Test of the Classicality Concept in Entangled States of Neutral Pseudoscalar Mesons with the Aid of Three-Time Wigner Inequalities

Exclusive production of double light neutral mesons at the e+e− colliders

In this work we investigate the exclusive production of a pair of light neutral mesons in e+e− annihilation, where the final state bears an even C-parity. The production processes can be initiated via the photon fragmentation or the nonfragmentation mechanism. While the fragmentation contribution can be rigorously accounted, the nonfragmentation contributions are calculated within the framework of collinear factorization, where only the leading-twist light-cone distribution amplitudes (LCDAs) of mesons are considered. Mediately solely by the nonfragmentation mechanism, the production rates of double light neutral pseudoscalar mesons are too small to be observed at the commissioning e+e− facilities. In contrast, the production rates of a pair of light neutral vector mesons are greatly amplified owing to the significant kinematic enhancement brought by the fragmentation mechanism. It is found that, at s=3.77 GeV, after including the destructive interference between the nonfragmentation and fragmentation contributions, the production rates for e+e−→ρ0ρ0 and ρ0ω can be lowered by about 10% and 30% relative to the fragmentation predictions. Future precise measurement of these exclusive double neutral vector meson production channels at BESIII experiment may provide useful constraints on the LCDAs of light vector mesons. Published by the American Physical Society 2024

Neutral pseudoscalar and vector meson masses under strong magnetic fields in an extended NJL model: Mixing effects

Mixing effects on the mass spectrum of light neutral pseudoscalar and vector mesons in the presence of an external uniform magnetic field $\vec B$ are studied in the framework of a two-flavor NJL-like model. The model includes isoscalar and isovector couplings both in the scalar-pseudoscalar and vector sectors, and also incorporates flavor mixing through a 't Hooft-like term. Numerical results for the $B$ dependence of meson masses are compared with present lattice QCD results. In particular, it is shown that the mixing between pseudoscalar and vector meson states leads to a significant reduction of the mass of the lightest state. The role of chiral symmetry and the effect of the alignment of quark magnetic moments in the presence of the magnetic field are discussed.

Determining some pseudoscalar meson masses from axial anomaly

Following our previous work [C. Y. Liu, Mod. Phys. Lett. A 36, 2150080 (2021), doi:10.1142/S0217732321500802], we investigate the masses of some pseudoscalar mesons which have the anomalous decays from axial anomaly (the Adler–Bell–Jackiw anomaly). We apply a non-perturbative mass formula to study the neutral single flavor pseudoscalar meson [Formula: see text]. We find the mass of pseudoscalar meson [Formula: see text] which can solve the problem of double [Formula: see text] production in [Formula: see text] annihilation at [Formula: see text] and obtain the mass of pseudoscalar meson [Formula: see text] which is the same as the invariant mass of [Formula: see text] pairs produced in association with [Formula: see text] jet in [Formula: see text]-collisions at the LHC. We generalize this formula to three flavors pseudoscalar mesons, we obtain the mass of [Formula: see text] meson [Formula: see text] which is almost the same as the experimental value [Formula: see text].

Dyson-Schwinger equations and the muon g-2

We present a brief introduction to the Dyson-Schwinger equations (DSEs) approach to hadron and high-energy physics. In particular, how this formalism is applied to calculate the electromagnetic form factors $\gamma^* \gamma^* \to \textbf{P}^0$ and $\gamma^* \textbf{P}^\pm \to \textbf{P}^\pm$ (with $\textbf{P}^\pm$ and $\textbf{P}^0$ charged and neutral ground-state pseudoscalar mesons, respectively) is discussed. Subsequently, the corresponding contributions of those form factors to the muon anomalous magnetic moment ($g-2$) are estimated. We look forward to promoting the DSE approach to address theoretical aspects of the muon $g-2$, highlighting some calculations that could be carried out in the future.

Chiral condensates and screening masses of neutral pseudoscalar mesons in thermomagnetic QCD medium

We point out that chiral condensates at nonzero temperature and magnetic fields are in strict connection to the space-time integral of corresponding two-point neutral meson correlation functions in the pseudoscalar channel via the Ward-Takahashi identity. Screening masses of neutral pseudoscalar mesons, which are defined as the exponential decay of the corresponding spatial correlation functions in the long distance, thus are intrinsically connected to (inverse) magnetic catalysis of chiral condensates. To study this we performed lattice simulations of ($2+1$)-flavor QCD on ${32}^{3}\ifmmode\times\else\texttimes\fi{}{N}_{t}$ lattices with pion mass ${M}_{\ensuremath{\pi}}\ensuremath{\simeq}220\text{ }\text{ }\mathrm{MeV}$ in a fixed scale approach having temperature $T\ensuremath{\in}[17,281]\text{ }\text{ }\mathrm{MeV}$ and magnetic field strength $eB\ensuremath{\in}[0,2.5]\text{ }\text{ }{\mathrm{GeV}}^{2}$. We find that screening lengths, i.e., inverses of screening masses of ${\ensuremath{\pi}}^{0}$, ${K}^{0}$ and ${\ensuremath{\eta}}_{s\overline{s}}^{0}$, turn out to have the similar complex $eB$ and $T$ dependences of the corresponding chiral condensates. Although the transition temperature is found to always decrease as $eB$ grows, we show that the suppression due to magnetic fields becomes less significant for hadron screening length and chiral condensates with heavier quarks involved, and ceases to occur for ${\ensuremath{\eta}}_{s\overline{s}}^{0}$ and strange quark chiral condensate. The complex $eB$ and $T$ dependences of both screening masses and chiral condensates, reflecting the crossover nature of the QCD transition, are attributed to the competition between sea and valence quark effects. These findings could be useful to guide low-energy models and effective theories of QCD.

On the group generated by C, P and T: I 2 = T 2 = P 2 = ITP = −1, with applications to pseudo-scalar mesons

We study faithful representations of the discrete Lorentz symmetry operations of parity P and time reversal T , which involve complex phases when acting on fermions. If the phase of P is a rational multiple of π then P 2n = 1 for some positive integer n and it is shown that, when this is the case, P and T generate a discrete group, a dicyclic group (also known as a generalised quaternion group) which are generalisations of the dihedral groups familiar from crystallography. Charge conjugation C introduces another complex phase and, again assuming rational multiples of π for complex phases, TC generates a cyclic group of order 2m for some positive integer m. There is thus a doubly infinite series of possible finite groups labelled by n and m. Demanding that C commutes with P and T forces n = m = 2 and the group generated by P and T is uniquely determined to be the quaternion group. Neutral pseudo-scalar mesons can be simultaneous C and P eigenstates, T commutes with P and C when acting on fermion bi-linears so neutral pseudo-scalar mesons can also be T eigenstates. The T -parity should therefore be experimentally observable and the CPT theorem dictates that T = CP.

Chiral properties of ( 2+1 )-flavor QCD in strong magnetic fields at zero temperature

We present lattice QCD results for masses and magnetic polarizabilities of light and strange pseudoscalar mesons, chiral condensates, decay constants of neutral pion, and neutral kaon in the presence of background magnetic fields with $eB$ ranging up to around 3.35 GeV$^2$ ($\sim70~M_\pi^2$) in the vacuum. The computations were carried out in (2+1)-flavor QCD mostly on $32^3 \times 96$ lattices using the highly improved staggered quark action with $M_{\pi} \approx $ 220 MeV at zero temperature. We find that the masses of neutral pseudoscalar mesons monotonously decrease as the magnetic field strength grows and then saturate at a nonzero value, while there exists a nonmonotonous behavior of charged pion and kaon masses in the magnetic field. We observe a $qB$ scaling of the up and down quark flavor components of neutral pion mass, neutral pion decay constant as well as the quark chiral condensates at 0.05 $\lesssim eB\lesssim$ 3.35 GeV$^2$. We show that the correction to the Gell-Mann-Oakes-Renner relation involving the neutral pion is less than 6% and the correction for the relation involving neutral kaon is less than 30% at $eB\lesssim$ 3.35 GeV$^2$. We also derive the Ward-Takahashi identities for QCD in the magnetic field in the continuum formulation including the relation between integrated neutral pseudoscalar meson correlators and chiral condensates.

Charged multihadron systems in lattice QCD+QED

Systems with the quantum numbers of up to twelve charged and neutral pseudoscalar mesons, as well as one-, two-, and three-nucleon systems, are studied using dynamical lattice quantum chromodynamics and quantum electrodynamics (QCD+QED) calculations and effective field theory. QED effects on hadronic interactions are determined by comparing systems of charged and neutral hadrons after tuning the quark masses to remove strong isospin breaking effects. A non-relativistic effective field theory, which perturbatively includes finite-volume Coulomb effects, is analyzed for systems of multiple charged hadrons and found to accurately reproduce the lattice QCD+QED results. QED effects on charged multi-hadron systems beyond Coulomb photon exchange are determined by comparing the two- and three-body interaction parameters extracted from the lattice QCD+QED results for charged and neutral multi-hadron systems.

Coherent photoproduction of two neutral pseudoscalar mesons on light nuclei

Coherent photoproduction of ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{0}\ensuremath{\eta}$ on nuclei with $A\ensuremath{\le}7$ is systematically studied in the energy region from the threshold to the laboratory photon energy ${E}_{\ensuremath{\gamma}}=2$ GeV. The amplitude of photoproduction on nuclei is derived in the impulse approximation taking account of certain processes responsible for the meson-nucleus final-state interaction. For the first time, the unified microscopic approach is used to calculate effects such as rescattering of the $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\pi}N$ and $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\eta}N$ pions from spectator nucleons, photoproduction of ${\ensuremath{\pi}}^{+/\ensuremath{-}}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{+/\ensuremath{-}}{\ensuremath{\pi}}^{0}\ensuremath{\eta}$, and the follow-on absorption of ${\ensuremath{\pi}}^{+/\ensuremath{-}}$ by spectator nucleons, as well as three-body $\ensuremath{\pi}\text{\ensuremath{-}}NN$ and $\ensuremath{\eta}\text{\ensuremath{-}}NN$ interaction among effects being responsible for the meson-nucleus final-state interaction. Direct calculation shows total cross sections of ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{0}\ensuremath{\eta}$ photoproduction to be strongly dependent both on the target nucleus isospin, and the target nucleus model.

Hunting for light dark matter with DUNE PRISM

We present the prospects for exploring low-scale dark sectors with the future DUNE experiment and the impact of the movable off-axis near detector concept, DUNE-PRISM, and a higher energy beam configuration. We focus on a simple scenario which extends the Standard Model by a “dark” U(1), comprising scalar or fermion dark matter and a dark photon kinetically mixed with the photon. We consider nucleus and electron scattering signatures of dark matter produced in the beam via neutral pseudoscalar meson decays. Our results show that, by analysing the energy spectra of single electron events in multiple off-axis angle, DUNE-PRISM can substantially increase the experimental sensitivity to these models, reaching theoretical targets for thermal relic dark matter for a wide range of dark photon and dark matter masses.

Effect of the anomalous magnetic moment of quarks on the phase structure and mesonic properties in the NJL model

Employing a field dependent three-momentum cut-off regularization technique, we study the phase structure and mesonic masses using the $2$-flavour Nambu-Jona Lasinio model at finite temperature and density in presence of arbitrary external magnetic field. This approach is then applied to incorporate the effects of the anomalous magnetic moment(AMM) of quarks on constituent quark mass and thermodynamic observables as a function of temperature/baryonic density. The critical temperature for transition from chiral symmetry broken to the restored phase is observed to decrease with the external magnetic field, which can be classified as inverse magnetic catalysis, while an opposite behaviour is realized in the case of a vanishing magnetic moment, implying magnetic catalysis. These essential features are also reflected in the phase diagram. Furthermore, the properties of the low lying scalar and neutral pseudoscalar mesons are also studied in presence of a hot and dense magnetized medium including AMM of the quarks using random phase approximation. For non-zero values of magnetic field, we notice a sudden jump in the mass of the Goldstone mode at and above the Mott transition temperature which is found to decrease substantially with the increase in magnetic field when the AMM of the quarks are taken into consideration.

Test of the Hypothesis of Realism Using a Modified Version of Wigner Inequality

In the current work we present a modified Wigner inequality for test of the hypothesis of realism. This modified Wigner inequality is suitable for test of realism not only in systems that obey the laws of non-relativistic quantum mechanics, but also in systems that obey the laws of quantum field theory. We show how this inequality can be violated in systems of neutral pseudoscalar mesons.

Test of a hypothesis of realism in quantum theory using a Bayesian approach

In this paper we propose a time-independent \textit{equality} and time-dependent \textit{inequality}, suitable for an experimental test of the hypothesis of realism. The derivation of these relations is based on the concept of conditional probability and on Bayes' theorem in the framework of Kolmogorov's axiomatics of probability theory. The equality obtained is intrinsically different from the well known GHZ-equality and its variants, because violation of the new equality might be tested in experiments with only two microsystems in a maximally entangled Bell state $\big\vert\, \Psi^-\,\big\rangle$, while a test of the GHZ-equality requires at least three quantum systems in a special state $\big\vert\, \Psi^{\textrm{GHZ}}\,\big\rangle$. The obtained inequality differs from Bell's, Wigner's, and Leggett-Garg inequalities, because it deals with spin $s=1/2$ projections onto only two non-parallel directions at two different moments of time, while a test of the Bell and Wigner inequalities requires at least three non-parallel directions, and a test of the Leggett-Garg inequalities -- at least three distinct moments of time. Hence, the proposed inequality seems to allow one to avoid the "contextuality loophole". Violation of the proposed equality and inequality is illustrated with the behaviour of a pair of anti-correlated spins in an external magnetic field and also with the oscillations of flavour-entangled pairs of neutral pseudoscalar mesons.

Decays of a NMSSM CP-odd Higgs in the low-mass region

A popular regime in the NMSSM parameter space involves a light CP-odd Higgs A1. This scenario has consequences for e.g. light singlino Dark Matter annihilating in the A1-funnel. In order to confront the pseudoscalar to experimental limits such as flavour observables, Upsilon decays or Beam-Dump experiments, it is necessary to control the interactions of this particle with hadronic matter and derive the corresponding decays. The partonic description cannot be relied upon for masses close to {m_A}_{{}_1} ∼ 1GeV and we employ a chiral lagrangian, then extended to a spectator model for somewhat larger masses, to describe the interplay of the CP-odd Higgs with hadrons. Interestingly, a mixing can develop between A1 and neutral pseudoscalar mesons, leading to substantial hadronic decays and a coupling of A1 to the chiral anomaly. Additionally, quartic A1-meson couplings induce tri-meson decays of the Higgs pseudoscalar. We investigate these effects and propose an estimate of the Higgs widths for masses below {m_A}_{{}_1} ≲ 3 GeV. While we focus on the case of the NMSSM, our results are applicable to a large class of models.

Light-by-Light Hadronic Corrections to the Muon G-2 Problem Within the Nonlocal Chiral Quark Model

Results of calculation of the light-by-light contribution from the lightest neutral pseudoscalar and scalar mesons and the dynamical quark loop to the muon anomalous magnetic moment are discussed in the framework of the nonlocal SU(3) × SU(3) chiral quark model. The model is based on four-quark interaction of the Nambu–Jona–Lasinio type and Kobayashi–Maskawa–‘t Hooft six-quark interaction. The full kinematic dependence of vertices with off-shell mesons and photons in intermediate states in the light-by-light scattering amplitude is taken into account. All calculations are elaborated in explicitly gauge-invariant manner. These results complete calculations of all hadronic light-by-light scattering contributions to aμ in the leading order in the 1/Nc expansion. The final result does not allow the discrepancy between the experiment and the Standard Model to be explained.

Pion transition form factor in the domain model of QCD vacuum

Domain model of QCD allows for description of wide range of meson observables, dynamical chiral symmetry breaking, and resolution of $U_A(1)$ and strong $CP$ problems. The purpose of the present study is transition form-factor of neutral pseudoscalar mesons, and how they are influenced by the typical vacuum configurations of the model -- almost everywhere homogeneous Abelian (anti-)self-dual fields. Asymptotic behavior of the calculated pion form-factor supports Belle trend, but the asymptotic value of $Q^2F_{\pi\gamma^*\gamma}$ differs from the prediction of factorization theorems.

On the extraction of cross sections for π0 and η photoproduction off neutrons from deuteron data

We discuss the procedure of extracting the photoproduction cross section for neutral pseudoscalar mesons off neutrons from deuteron data. The main statement is that the final-state interaction (FSI) corrections for the proton and neutron target are in general not equal, but for pi0 production there are special cases were they have to be identical and there are large regions in the parameter space of incident photon energy and pion polar angle, \theta^*, where they happen to be quite similar. The corrections for both target nucleons are practically identical for $\pi_0$ production in the energy range of the Delta(1232)3/2+ resonance due to the specific isospin structure of this excitation. Also above the $\Delta$-isobar range large differences between proton and neutron correction factors are only predicted for extreme forward angles ($\theta^*$ < 20 deg), but the results are similar for larger angles. Numerical results for the gp-->pi0p and gn-->pi0n correction factors are discussed. Also the model description for the available data on the differential gd-->pi0pn cross sections are given.

Polarizability of pseudoscalar mesons from the lattice calculations

We explore the energy dependence of neutral and charge pions of the background constant abelian magnetic field in SU(3) lattice gauge theory without dynamical quarks. The energy of neutral pseudoscalar meson diminishes with the field, while the energy of charged one increases according with the theoretical expectations. Based on these data we estimate the magnetic polarizabilities of π 0 and π ± mesons for various quark masses.

Investigation of properties of time-dependent bell inequalities in Wigner’s form for nonstationary and open quantum systems

A radically new class of Bell inequalities in Wigner’s form was obtained on the basis of Kolmorov’s axiomatization of probability theory and the hypothesis of locality. These inequalities take explicitly into account the dependence on time (time-dependent Bell inequalities in Wigner’s form). By using these inequalities, one can propose a means for experimentally testing Bohr’ complementarity principle in the relativistic region. The inequalities in question open broad possibilities for studying correlations of nonrelativistic and relativistic quantum systems in external fields. The violation of the time-dependent inequalities in quantum mechanics was studied by considering the behavior of a pair of anticorrelated spins in a constant external magnetic field and oscillations of neutral pseudoscalar mesons. The decay of a pseudoscalar particle to a fermion–antifermion pair is considered within quantum field theory. In order to test experimentally the inequalities proposed in the present study, it is not necessary to perform dedicated noninvasive measurements required in the Leggett–Garg approach, for example.