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We study bottomonium production in association with an \\[\\eta \\] meson in \\[e^+e^-\\] annihilations near the \\[\\varUpsilon (5S)\\], at a centre-of-mass energy of \\[\\sqrt{s}=10.866\\] GeV. The results are based on the 121.4 fb\\[^{-1}\\] data sample collected by the Belle experiment at the asymmetric-energy KEKB collider. Only the \\[\\eta \\] meson is reconstructed and the missing-mass spectrum of \\[\\eta \\] candidates is investigated. We observe the \\[e^+e^-\\rightarrow \\eta \\varUpsilon _J(1D)\\] process and find evidence for the \\[e^+e^-\\rightarrow \\eta \\varUpsilon (2S)\\] process, while no significant signals of \\[\\varUpsilon (1S)\\], \\[h_b(1P)\\], nor \\[h_b(2P)\\] are found. Cross sections for the studied processes are reported.

We study the three-body baryonic \\[B\\rightarrow {{\\mathbf{B}}\\bar{\\mathbf{B}}'}M\\] decays with M representing the \\[\\eta \\] or \\[\\eta '\\] meson. Particularly, we predict that \\[\\mathcal{B}(B^-\\rightarrow \\Lambda \\bar{p}\\eta ,\\Lambda \\bar{p}\\eta ') =(5.3\\pm 1.4,3.3\\pm 0.7)\\times 10^{-6}\\] or \\[(4.0\\pm 0.7,4.6\\pm 1.1)\\times 10^{-6}\\], where the errors arise from the non-factorizable effects as well as the uncertainties in the \\[0\\rightarrow {{\\mathbf{B}}\\bar{\\mathbf{B}}'}\\] and \\[B\\rightarrow {{\\mathbf{B}}\\bar{\\mathbf{B}}'}\\] transition form factors, while the two different results are due to overall relative signs between the form factors, causing the constructive and destructive interference effects. For the corresponding baryonic \\[\\bar{B}_s^0\\] decays, we find that \\[\\mathcal{B}(\\bar{B}^0_s\\rightarrow \\Lambda \\bar{\\Lambda } \\eta ,\\Lambda \\bar{\\Lambda } \\eta ') =(1.2\\pm 0.3,2.6\\pm 0.8)\\times 10^{-6}\\] or \\[(2.1\\pm 0.6,1.5\\pm 0.4)\\times 10^{-6}\\] with the errors similar to those above. The decays in question are accessible to the experiments at BELLE and LHCb.

A bstract The exploration of long-lived particles in the MeV-GeV region is a formidable task but it may provide us a unique access to dark sectors. Fixed-target facilities with sufficiently energetic and intense proton beams are an ideal tool for this challenge. In this work we show that the production rate of Axion-Like-Particles (ALPs) coupled pre-dominantly to photons receives a significant contribution from daughter-photons of secondary π 0 and η mesons created in the proton shower. We carefully compare the PYTHIA simulated spectra of such secondaries to experimental literature, compute the ALP flux from the Primakoff conversion of these photons, and finally revisit existing limits on ALPs and update the prospects for a set of existing and future searches. Our results show that taking this production mechanism into account significantly enhances the sensitivity compared to previous studies based on coherent ALP production in primary proton-nucleus interactions.

We report preliminary measurements of the branching fractions of the decays τ−→ K−nπ0 ντ (n = 0, 1, 2, 3) and τ−→ π−nπ0ντ (n = 3, 4), excluding the contributions that proceed through the decay of intermediate K0 and η mesons. The measurements are based on a data sample of 435 million τ pairs produced in e+e− collisions at and near the γ(4S) peak and collected with the BABAR detector in 1999–2008. The measured branching fractions are B(τ−→ K− ντ) = (7.174±0.033±0.213)×10−3, B(τ−→ K−π0ντ) = (5.054± 0.021 ± 0.148) × 10−3, B(τ−→ K−2π0ντ) = (6.151 ± 0.117 ± 0.338) × 10−4, B(τ−→ K−3π0ντ) = (1.246 ± 0.164 ± 0.238) × 10−4, B(τ−→ π−3π0ντ) = (1.168 ±0.006 ±0.038) ×10−2, B(τ−→ π−4π0ντ) = (9.020 ±0.400 ±0.652) × 10−4, where the ?rst uncertainty is statistical and the second one systematic.

The KLOE-2 experiment at the Frascati φ−factory ended its data-taking in March 2018 collecting more than 5 fb −1 at the φ peak. The new data sample, together with the KLOE one, corresponds to 2.4 ×10 10 φ and 3.1×10 8 η meson events. It represents the largest sample ever collected at the φ peak in e + e − colliders, allowing to study light mesons with unprecedented statistics. Recent results obtained with KLOE data on hadron physics e.g. – measurement of the running of the fine structure constant below 1 GeV, the combination of hadron cross section measurements with determination of$ a_\\mu ^{\\pi \\pi } $ , the new preliminary η → π + π − limit, and progress in γγ studies – will be presented.

A key motivation for the two-photon physics program of the BESIII collaboration is the need of high precision data on electromagnetic transition form factors as input to the calculations of the contribution of hadronic Light-by-light scattering to the anomalous magnetic moment of the muon. The data collected with the BESIII detector allow to study the momentum dependence of the form factors at small momentum transfers, which is of special relevance for α μ . In this presentation the ongoing measurements of the transition form factors of π 0 , η and η ' mesons, as well as pion pairs, are discussed, and the potential for first double-tagged measurements at BESIII are pointed out.

A bstract Based on the chiral perturbation theory at the leading order, we show a signal of the presence of a new phase in rapidly rotating QCD matter with two flavors, that is a domain-wall Skyrmion phase. Based on the chiral Lagrangian with a Wess-Zumino-Witten (WZW) term responsible for the chiral anomaly and chiral vortical effect, it was shown that the ground state is a chiral soliton lattice (CSL) consisting of a stack of η -solitons in a high density region under rapid rotation. In a large parameter region, a single η -soliton decays into a pair of non-Abelian solitons, each of which carries SU(2) V / U(1) ≃ ℂ P 1 ≃ S 2 moduli as a consequence of the spontaneously broken vector symmetry SU(2) V . In such a non-Abelian CSL, we construct the effective world-volume theory of a single non-Abelian soliton to obtain a d = 2 + 1 dimensional ℂ P 1 model with a topological term originated from the WZW term. We show that when the chemical potential is larger than a critical value, a topological lump supported by the second homotopy group π 2 ( S 2 ) ≃ ℤ has negative energy and is spontaneously created, implying the domain-wall Skyrmion phase. This lump corresponds in the bulk to a Skyrmion supported by the third homotopy group π 3 [SU(2)] ≃ ℤ carrying a baryon number. This composite state is called a domain-wall Skyrmion, and is stable even in the absence of the Skyrme term. An analytic formula for the effective nucleon mass in this medium can be written only in terms of the meson’s constants as 4 2 π f π f η / m π ~ 1.21 GeV with the decay constants f π and f η of the pions and η meson, respectively, and the pion mass m π . This is reasonably heavier than the nucleon mass in the QCD vacuum.

We have investigated eta-prime meson photoproduction on the nucleon using an isobar model within an effective Lagrangian approach. This model incorporates background contributions, including Born terms and relevant vector meson exchanges, as well as the effects of intermediate nucleon resonances. Nucleon resonances with spin up to 7/2 and at least two-star status in the 2024 edition of the Review of Particle Physics (RPP) by the Particle Data Group (PDG) were included in the model. The free parameters of the model were fitted using available experimental differential cross section data from the A2 Collaboration at MAMI (2017) and the CLAS Collaboration (2009). By employing this approach, we phenomenologically obtained effective couplings related to the partial decay widths and helicity amplitudes of nucleon resonances. These results provide insight into the properties of nucleon resonances involved in eta-prime meson photoproduction.

A bstract We study the θ -dependent mass spectrum of the massive 2-flavor Schwinger model in the Hamiltonian formalism using the density-matrix renormalization group (DMRG). The masses of the composite particles, the pion and sigma meson, are computed by two independent methods. One is the improved one-point-function scheme, where we measure the local meson operator coupled to the boundary state and extract the mass from its exponential decay. Since the θ term causes a nontrivial operator mixing, we unravel it by diagonalizing the correlation matrix to define the meson operator. The other is the dispersion-relation scheme, a heuristic approach specific to Hamiltonian formalism. We obtain the dispersion relation directly by measuring the energy and momentum of the excited states. The sign problem is circumvented in these methods, and their results agree with each other even for large θ . We reveal that the θ -dependence of the pion mass at m/g = 0 . 1 is consistent with the prediction by the bosonized model. We also find that the mass of the sigma meson satisfies the semi-classical formula, M σ /M π = 3 , for almost all region of θ . While the sigma meson is a stable particle thanks to this relation, the eta meson is no longer protected by the G -parity and becomes unstable for θ ≠ 0.

A bstract The ground state of QCD with two flavors at a finite baryon chemical potential under rapid rotation is a chiral soliton lattice (CSL) of the η meson, consisting of a stack of sine-Gordon solitons carrying a baryon number, due to the anomalous coupling of the η meson to the rotation. In a large parameter region, the ground state becomes a non-Abelian CSL, in which due to the neutral pion condensation each η soliton decays into a pair of non-Abelian sine-Gordon solitons carrying S 2 moduli originated from Nambu-Goldstone (NG) modes localized around it, corresponding to the spontaneously broken vector symmetry SU(2) V . There, the S 2 modes of neighboring solitons are anti-aligned, and these modes should propagate in the transverse direction of the lattice due to the interaction between the S 2 modes of neighboring solitons. In this paper, we calculate excitations including gapless NG modes and excited modes around non-Abelian and Abelian ( η ) CSLs, and find three gapless NG modes with linear dispersion relations (type-A NG modes): two isospinons ( S 2 modes) and a phonon corresponding to the spontaneously broken vector SU(2) V and translational symmetries around the non-Abelian CSL, respectively, and only a phonon for the Abelian CSL because of the recovering SU(2) V . We also find in the deconfined phase that the dispersion relation of the isospinons becomes of the Dirac type, i.e. linear even at large momentum.