Search

Ratios ms/md and mu/md of the light quark masses have been determined from expressions for squared masses of pseudoscalar mesons and obtained with an accuracy of the second order in chiral symmetry breaking. The fit of the theoretical expressions for and to their phenomenological values leads to a functional relation between the ratios ms/md and mu/md, which is described by a third-order curve. The application of the lattice calculation result ms/mud = 27.23(10), where mud = (mu + md)/2, reported by the flavor lattice averaging group (FLAG) for the case of four quark flavors provides an additional constraint, which significantly reduces the error (~2%) for the ratio mu/md = 0.455(8). The absolute values of the quark masses have been then obtained. [ABSTRACT FROM AUTHOR]

Partial widths and double- and single-differential distributions are calculated on the framework of the Standard Model for the four-lepton decays , where = and . The contribution of virtual-photon emission by a light quark and a heavy quark, the bremsstrahlung contribution from charged leptons in the final state, the weak-annihilation contribution, and the contribution of wide vector resonances are taken into account. The contribution of narrow and resonances is excluded. Virtual-photon emission by the light quark of a meson is described on the framework of the vector-meson-dominance model, within which only the contributions of the lightest vector mesons containing pairs are taken into account. For the meson, this is the resonance. For the meson, the contributions of the and resonances are taken into account. Two possibilities are considered in the present study. The first is that where the contributions of the narrow and mesons are excluded from the partial widths with respect to the corresponding decays. The second is that where the contributions of narrow resonances are taken into account in partial widths. The problem of the influence of the subtraction procedure on the partial widths with respect to the decays is studied individually. [ABSTRACT FROM AUTHOR]

We present our first set of results for charm physics, using the mixed-action setup introduced in a companion paper [1]. Maximally twisted Wilson valence fermions are used on a sea of non-perturbatively O(a)-improved Wilson fermions, made up by CLS N f = 2 + 1 ensembles. Our charm-sector observables are free from O (a m c) discretisation effects, without need of tuning any improvement coefficient, and show continuum-limit scaling properties consistent with leading cutoff effects of O (a 2) . We consider a subset of CLS ensembles – including four values of the lattice spacing and pion masses down to 200 MeV – allowing to take the continuum limit and extrapolate to the physical pion mass. A number of techniques are incorporated in the analysis in order to estimate the systematic uncertainties of our results for the charm quark mass and the D (s) -meson decay constants. This first study of observables in the charm sector, where the emphasis has been on the control of the methodology, demonstrates the potential of our setup to achieve high-precision results. [ABSTRACT FROM AUTHOR]

The proton spin puzzle has inspired a vast programme of experiments and theoretical work challenging our understanding of QCD and its role in the structure of hadrons. The proton's internal spin structure is connected to chiral symmetry and, through gluon degrees of freedom in the flavor singlet channel, to the physics of the η ′ meson. Why do quarks contribute just about one third of the proton's spin? Why are η ′ mesons and their interactions so sensitive to gluonic degrees of freedom? We review the status of these topics and some key observables for forthcoming experiments. [ABSTRACT FROM AUTHOR]

The Schwinger confinement mechanism stipulates that a massless fermion and a massless antifermion are confined as a massive boson when they interact in the Abelian QED interaction in (1+1)D.If we approximate light quarks as massless and apply the Schwinger confinement mechanism to quarks, we can infer that a light quark and a light antiquark interacting in the Abelian QED interaction are confined as a QED meson in (1+1)D. Similarly, a light quark and a light antiquark interacting in the QCD interaction in the quasi-Abelian approximation will be confined as a QCD meson in (1+1)D. The QED and QCD mesons in (1+1)D can represent physical mesons in (3+1)D when the flux tube radius is properly taken into account. Such a theory leads to a reasonable description of the masses of π 0 , η , and η ′ , and its extrapolation to the unknown QED sector yields an isoscalar QED meson at about 17 MeV and an isovector QED meson at about 38 MeV. The observations of the anomalous soft photons, the hypothetical X17 particle, and the hypothetical E38 particle bear promising evidence for the possible existence of the QED mesons. Pending further confirmation, they hold important implications on the properties on the quarks and their interactions. [ABSTRACT FROM AUTHOR]

This study focuses on the presence of (multi)fractal structures in hadronic matter through the momentum distributions of mesons produced in proton-proton collisions between 23 GeV and 63 GeV. The analysis demonstrates that the q-exponential behaviour of the particle momentum distributions is consistent with fractal characteristics, exhibiting fractal structures in confined hadronic matter with features similar to those observed in the deconfined quark-gluon plasma (QGP) regime. Furthermore, the systematic analysis of meson production in hadronic collisions at energies below 1 TeV suggests that specific fractal parameters are universal, independently of confinement or deconfinement, while others may be influenced by the quark content of the produced meson. These results pave the way for further research exploring the implications of fractal structures on various physical distributions. [ABSTRACT FROM AUTHOR]

This article elucidates the pivotal role of b-mesons and bottomonium states in exploring the existence and properties of hot QCD matter (commonly known as quark-gluon-plasma (QGP) produced within the crucible heavy-ion collision experiments). Owing to the complex and confounding nature of strong interaction force the direct detection of probing the hot QCD matter is not feasible. In light of this, investigating the dynamics of b-quarks and anti-quarks within the hot QCD medium emerges as an invaluable indirect probe. The impact of b-quarks and the mesons spans a spectrum of interesting domains regarding the physics of QCD at finite temperature, encompassing the QCD phase transition, color screening, quarkonia dissociation, heavy quark energy loss and collective flow, anisotropic aspects, and strongly coupled nature of hot QCD medium. These aspects underscore the indispensable nature of B-mesons in the quest to create and explore the complex nature of strong interaction force through the QGP/hot QCD matter. In this context, we mainly focus on works related to transport studies of b-mesons in hot QCD medium, lattice QCD, and effective field theory studies on bottomonium states, and finally, open quantum system frameworks to quarkonia to explore the properties of hot QCD medium in relativistic heavy-ion collision experiments. [ABSTRACT FROM AUTHOR]

We discuss the main issues in dealing with heavy quarks on the lattice and shortly present the different approaches used. We discuss a selection of computations covering first the b-quark mass and the B (s) meson decay constants as the consolidated results (neglecting isospin breaking corrections). In the second part, we consider recent calculations of form factors for tree-level semileptonic decays with emphasis on the tensions between the results produced by different collaborations. We propose benchmark quantities and tests suited to investigate the origin of such tensions. Finally, we review computations of the bag parameters parameterising neutral meson mixing and provide an overview on a few recent developments in the field. [ABSTRACT FROM AUTHOR]

Flavour physics is one of the essential elements of the Standard Model (SM). Experimental studies of weak decays of B and D mesons at B factories have, together with the discovery of the Higgs boson at LHC, provided the final confirmation of the validity of the SM. The present generation of precision flavour physics experiments is looking for departures from the SM. We discuss studies of anomalies in b hadron decays, and studies of rare decays, which are a very promising method for searching for new physics. This article is part of the theme issue 'The particle-gravity frontier'. [ABSTRACT FROM AUTHOR]

The work is devoted to the transverse polarization () of -hyperons and corresponding antihyperons produced in meson–proton and meson–nuclear interactions in inclusive reactions. The currently available experimental data are compared with calculations based on the chromomagnetic polarization of quark (CPQ) model. The main features of the CPQ model are the prediction of hyperon polarization oscillations depending on the Feynman variable in the case of a sufficiently strong chomomagnetic field and resonant dependence of the polarization on the c.m. energy () for some reactions. Calculations based on the CPQ model were performed for still unexplored kinematic regions and various targets and can be tested in the SPASCHARM experiment at the NRC "Kurchatov Institute"—IHEP. [ABSTRACT FROM AUTHOR]

A unified set of predictions for pion and kaon elastic electromagnetic and gravitational form factors is obtained using a symmetry-preserving truncation of each relevant quantum field equation. A key part of the study is a description of salient aspects of the dressed graviton + quark vertices. The calculations reveal that each meson's mass radius is smaller than its charge radius, matching available empirical inferences; and meson core pressures are commensurate with those in neutron stars. The analysis described herein paves the way for a direct calculation of nucleon gravitational form factors. [ABSTRACT FROM AUTHOR]

A mechanism of the heavy quark dominance in the orbital excitation is proposed in this paper which is testified to be reasonable for singly and doubly heavy baryons. In the relativistic quark model, an analysis of the Hamiltonian figures out the mechanism that the excitation mode with lower energy levels is always associated with the heavy quark(s), and the splitting of the energy levels is suppressed by the heavy quark(s). So, the heavy quarks dominate the orbital excitation of singly and doubly heavy baryons. Furthermore, a physical understanding of this mechanism is given in a semi-classical way. Accordingly, the predicted mass spectra of singly and doubly heavy baryons confirm the rationality of this mechanism. In addition, an interesting consequence of this mechanism is that a heavy-light meson is more likely to be produced in the strong decay of the high-orbital excited states, which is supported by experiments. This mechanism is rooted in the breakdown of the mass symmetry. Therefore, it may be also valid for other multi-quark systems, such as the tetraquarks Qqqq and QQqq, or the pentaquarks Qqqqq and QQqqq. [ABSTRACT FROM AUTHOR]

In this paper, we calculate the electromagnetic (EM) transition decay widths between two mesons containing different heavy quarks (c and b) for the process; B c ∗ → B c + γ , using the Bethe–Salpeter (BS) framework. The calculated results are found to be in a reasonable agreement with other theoretical models but the experimental data for this problem is not yet available. [ABSTRACT FROM AUTHOR]

We attempt to present an unified description of the light meson spectra and the light diquark spectra by applying the Regge trajectory approach. However, we find that the direct application of the linear Regge trajectory formula for the light mesons and baryons fails. To address this issue, we fit the experimental data of light meson spectra and the light diquark spectra obtained by other theoretical approaches. By considering the light quark mass and the parameter C in the Cornell potential, we provide a provisional Regge trajectory formula. We also crudely estimate the masses of the light diquarks (ud), (us), and (ss), and find that they agree with other theoretical results. The diquark Regge trajectory not only becomes a new and very simple approach for estimating the spectra of the light diquarks, but also can explicitly show the behavior of the masses with respect to l or n r . Moreover, it is expected that the diquark Regge trajectory can provide a simple method for investigating the ρ -mode excitations of baryons, tetraquarks and pentaquarks containing diquarks. [ABSTRACT FROM AUTHOR]

We carry out a comprehensive study of the quark-to-meson fragmentation function in the 't Hooft model, i.e., the two-dimensional quantum chromodynamics (QCD) in N c → ∞ limit, following the operator definition pioneered by Collins and Soper. We apply the Hamiltonian approach as well as the diagrammatic approach to construct the functional form of the quark-to-meson fragmentation function in terms of the meson's light-cone wave function. For the sake of comparison, we also investigate the heavy quark fragmentation into quarkonium in two-dimensional QCD within the framework of the nonrelativistic QCD (NRQCD) factorization, at the lowest order in quark velocity. In the heavy quark limit, the quark fragmentation function obtained from the ab initio method agrees well, both analytically and numerically, with that obtained from the NRQCD approach. This agreement might be regarded as a nontrivial justification for the validity of both field-theoretical approaches to compute the heavy quark fragmentation function. [ABSTRACT FROM AUTHOR]

We establish a statistical two-body fractal (STF) model to study the spectrum of J / ψ . J / ψ serves as a reliable probe in heavy-ion collisions. The distribution of J / ψ in hadron gas is influenced by flow, quantum and strong interaction effects. Previous models have predominantly focused on one or two of these effects while neglecting the others, resulting in the inclusion of unconsidered effects in the fitted parameters. Here, we study the issue from a new point of view by analyzing the fact that all three effects induce a self-similarity structure, involving a J / ψ - π two-meson state and a J / ψ , π two-quark state, respectively. We introduce modification factor q T B S and q 2 into the probability and entropy of charmonium. q T B S denotes the modification of self-similarity on J / ψ , q 2 denotes that of self-similarity and strong interaction between c and c ¯ on quarks. By solving the probability and entropy equations, we derive the values of q T B S and q 2 at various collision energies and centralities. Substituting the value of q T B S into distribution function, we successfully obtain the transverse momentum spectrum of low- p T   J / ψ , which demonstrates good agreement with experimental data. The STF model can be employed to investigate other mesons and resonance states. [ABSTRACT FROM AUTHOR]

The flavor-changing neutral current (FCNC) decays of charmed hadrons with missing energy (Ɇ) can serve as potentially promising hunting grounds for hints of new physics, as the standard-model backgrounds are very suppressed. A few of such processes have been searched for in recent experiments, specifically D0→ Ɇ by Belle and D0→ π0Ɇ and Λ c + → pɆ by BESIII, resulting in upper bounds on their branching fractions. We consider them to illuminate the possible contributions of the quark transition c → uɆ with a couple of invisible spinless bosons carrying away the missing energy, assuming that they are not charge conjugates of each other and hence can have unequal masses. We find that these data are complementary in that they constrain different sets of the underlying operators and do not cover the same ranges of the bosons' masses, but there are regions not yet accessible. From the allowed parameter space, we show that other D-meson decays, such as D → ρɆ, and the charmed-baryon ones Ξc → (Σ, Λ)Ɇ can have sizable branching fractions and therefore may offer further probes of the new-physics interactions. We point out the importance of D0 → γɆ which are not yet searched for but could access parts of the parameter space beyond the reach of the other modes. In addition, we look at a scenario where the invisibles are instead fermionic, namely sterile neutrinos, and a scalar leptoquark mediates c → uɆ. We discuss the implications of the aforesaid bounds for this model. The predictions we make for the various charmed-hadron decays in the different scenarios may be testable in the near future by BESIII and Belle II. [ABSTRACT FROM AUTHOR]

We consider SU(2) quantum chromodynamics in 1 + 1 dimensions with a single quark in the spin J representation of the gauge group and study the theory in the large J limit where the gauge coupling g2 → 0 and J → ∞ with λ = g2J2 fixed. We work with a Dirac spinor field for arbitrary J, and with a Majorana spinor for integer J since the integer spin representations of SU(2) are real, and analyze the two cases separately. The theory is reformulated in terms of global colour non-singlet fermion bilocal operators which satisfy a W∞ × U(2J + 1) algebra. In the large J limit, the dynamics of the bilocal fields is captured by fluctuations along a particular coadjoint orbit of the W∞ algebra. We show that the global colour-singlet sector of the bilocal field fluctuations satisfy the same integral equation for meson wavefunctions that appears in the 't Hooft model. For Majorana spinors in the integer spin J representation, the Majorana condition projects out half of the meson spectrum, as a result of which the linear spacing of the asymptotic meson spectrum for Majorana fermions is double that of Dirac fermions. The Majorana condition also projects out the zero mass bound state that is present for the Dirac quark at zero quark mass. We also consider the formulation of the model in terms of local charge densities and compute the quark spectral function in the large J limit: we see evidence for the absence of a pole in the quark propagator. [ABSTRACT FROM AUTHOR]

Lepton flavor universality exists in the Standard Model, and hence any observation of the violation of this universality will be a hint for new physics. Recent experimental searches for processes violating this symmetry have attracted much attention among theorists and experimentalists alike. In recent years, such hints have been observed in flavor changing neutral current weak processes such as b → s l l and charged current weak processes such as b → c l ν processes by collider experiments like Belle, Belle II, BaBar, LHCb, ATLAS, and CMS collaborations, where b , s , c are the bottom, strange, and charm quarks, respectively, and l , ν stand for lepton and the corresponding lepton neutrino, respectively. This article is a review of some of the interesting anomalies observed in the B-sector and includes decays of B s mesons. [ABSTRACT FROM AUTHOR]

We attempt to apply the Regge trajectory approach to the heavy-light diquarks composed of one heavy quark and one light quark. However, we find that the direct application of the usual Regge trajectory formula for the heavy-light mesons and baryons fails. In order to correctly estimate the masses of the heavy-light diquarks, it is needed to consider the light quark mass correction and the parameter C in the Cornell potential within the Regge trajectory formula. By using the modified Regge trajectory formulas, we are able to estimate the masses of the heavy-light diquarks (cu), (cs), (bu) and (bs), which agree with other theoretical results. It is illustrated that the heavy-light diquarks satisfy the universal descriptions irrespective of heavy quark flavors, similar to other heavy-light systems such as the heavy-light mesons, the heavy-light baryons composed of one heavy quark (diquark) and one light diquark (quark), and the heavy-light tetraquarks composed of one heavy diquark (antidiquark) and one light antidiquark (diquark). The diquark Regge trajectory provides a new and very simple approach for estimating the spectra of the heavy-light diquarks. [ABSTRACT FROM AUTHOR]

Relativistic corrections to the pair production of mesons and baryons consisting of heavy quarks and in the Higgs boson decay are calculated. Relativistic amplitudes and decay rates are constructed within perturbative Standart Model and relativistic quark model. The numerical values of the relativistic effects turn out to be significant and must be taken into account in order to achieve good calculation accuracy. [ABSTRACT FROM AUTHOR]

At present, production, properties, and decays of heavy baryons are vigorously studied both experimentally and theoretically. The flavor symmetry allows an existence of a large number of hidden charm pentaquark states which differ by their light quark content. Here, ratios of weak decay widths of bottom baryons into a pentaquark and light meson are presented. The most interesting for experimental observation decays of bottom baryons are specified. [ABSTRACT FROM AUTHOR]

Heavy and light quarks produced in high- p T partonic collisions radiate differently. Heavy quarks regenerate their color field, stripped-off in the hard reaction, much faster than the light ones and radiate a significantly smaller fraction of the initial quark energy. This peculiar feature of heavy-quark jets leads to a specific shape of the fragmentation functions observed in e + e − annihilation. Differently from light flavors, the heavy quark fragmentation function strongly peaks at large fractional momentum z, i.e., the produced heavy–light mesons, B or D, carry the main fraction of the jet momentum. This is a clear evidence of the dead-cone effect, and of a short production time of a heavy–light mesons. Contrary to propagation of a small q q ¯ dipole, which survives in the medium due to color transparency, a heavy–light Q q ¯ dipole promptly expands to a large size. Such a big dipole has no chance to remain intact in a dense medium produced in relativistic heavy ion collisions. On the other hand, a breakup of such a dipole does not affect much the production rate of Q q ¯ mesons, differently from the case of light q q ¯ meson production. [ABSTRACT FROM AUTHOR]

The quark-antiquark components of the U(3) lightest scalar meson nonet are investigated by considering the Nambu-Jona-Lasinio model with flavor-dependent coupling constants that were derived by considering (non-perturbative) gluon exchange. The strange quark effective mass ( M s * ) is varied such that the strangeness content of these scalar mesons can be analyzed further. The neutral states S 0, S 8, and S 3 are adopted as the most relevant quark-antiquark components, respectively, of the σ (500), f 0(980) and A 0 0 (980) mesons. As a result, the mass hierarchy between states S 0 and S 8, and K 0 * (700) − A 0 (980) mesons, can be, respectively, inverted and corrected for quite low values of the strange quark constituent mass. In addition, for some particular values of M s * , the masses of σ (500) and f 0(980) can also be obtained by considering the mixing coupling constant G 08. However, the masses of all the nine mesons are not described simultaneously in a self-consistent procedure and this goes along with the need of non-quark-antiquark states to completely describe their masses. A neutral-meson mixing matrix is defined and the leading mixing angle is found by fitting a correct value of the σ (500) − f 0(980) mass difference. Two different estimates for the strengths of the mixings A 0 0 → f 0 and f 0 → A 0 0 are proposed, leading to somewhat different behaviors. First by assuming leading transitions to intermediary flavor eigenstates and second by considering a dynamical evolution. The results may be in good agreement with experimental values from BESS-III depending on the value of the strange quark effective mass. [ABSTRACT FROM AUTHOR]

In this paper, we consider the soft-wall holographic model with the linear dilaton background. The model leads to a Hydrogen-like meson spectrum which can be interpreted as the static limit with very large quark masses when the Coulomb interaction dominates. The mass scale introduced by the linear dilaton is matched to the quark mass. The resulting model is analyzed for the scalar, vector and tensor cases. The electromagnetic coupling constants predicted by the model are decreasing with the radial number in contrast to the soft-wall model with quadratic dilaton where these couplings represent a universal constant. The given prediction is qualitatively consistent with the corresponding experimental data in vector quarkonia. The proposed model can thus be used as a constituent part of more elaborated holographic models for heavy quarkonia. A particular example of such a model is put forward. [ABSTRACT FROM AUTHOR]

We investigate the weak leptonic and semileptonic decay widths of pseudoscalar light and heavy mesons in a Dirac formalism. We take relativistic-independent quark model of the form V q (r) = 1 2 (1 + γ 0) (a 2 r + V 0) , where a > 0. This is computed using the binding quark eigenfunction and taking the assumptions of a significant relationship between the quark and antiquark momenta inside the decaying meson in the rest frame. To calculate the decay constant (f M) , decay width and branching fractions of pseudoscalar mesons, we employ the model parameters that we used earlier. The experimental findings and various similar models are in good agreement with our predictions such as " f B C > f B S > f B , f D S > f D , f D > f B and f B > f π ". Finally, we calculate the form factors and branching fractions for the semileptonic D (D 0) decays " D + → K S 0 e + ν e ,  D + → K L 0 e + ν e ,  D + → π 0 e + ν e ,  D 0 → K − e + ν e and D 0 → π − e + ν e " and find reasonable agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Corrections to the Wess–Zumino–Witten anomaly caused by the explicit breaking of the chiral symmetry are studied using the effective meson Lagrangian based on the Nambu–Jona-Lasinio model with the simultaneous expansion in derivatives, current quark masses, and 1/Nc powers. The leading contribution and the first correction for the amplitudes of the π0, η, η' → γγ decays and the contact term in the amplitudes have been calculated. The results are compared with similar 1/Nc chiral perturbation calculations and existing experimental data. [ABSTRACT FROM AUTHOR]

We address the nonperturbative calculation of the inclusive decay rate of semileptonic B(s)-meson decays from lattice QCD. Precise Standard-Model predictions are key ingredients in searches for new physics, and this type of computation may eventually provide new insight into the long-standing tension between the inclusive and exclusive determinations of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements |Vcb| and |Vub|. We present results from a pilot lattice computation for Bs → Xclνl, where the initial b quark described by the relativistic-heavy-quark (RHQ) formalism on the lattice and the other valence quarks discretised with domain-wall fermions are simulated approximately at their physical quark masses. We compare two different methods for computing the decay rate from lattice data of Euclidean n-point functions, namely Chebyshev and Backus-Gilbert approaches. We further study how much the ground-state meson dominates the inclusive decay rate and indicate our strategy towards a computation with a more comprehensive systematic error budget. [ABSTRACT FROM AUTHOR]

We investigate the unpolarized transverse momentum dependent (TMD) structure of light mesons at low Q 2 scales in nonperturbative region of quantum chromodynamics (QCD). To this end, we calculate the unpolarized TMD valence quark distribution functions of pion and kaon based on the covariant parton model in which the flavour dependent covariant momentum distribution of quarks is needed. We apply the statistical model for this momentum distribution, for the first time, and also consider the quarks to be massive. The results of TMD valence distributions of light mesons show convenient general properties. We also obtain the integrated valence quark distributions of pion and kaon and compare our results with those of other models. [ABSTRACT FROM AUTHOR]

We compute the electromagnetic mass difference for the B-, D- and K-mesons using QCD sum rules with double dispersion relations. For the B- and D-mesons we also compute the linear quark mass correction, whereas for the K the standard soft theorems prove more powerful. The mass differences, which have not previously been computed via a double dispersion, are fully consistent with experiment, albeit with large uncertainties. [ABSTRACT FROM AUTHOR]

In this study, we calculate the pressure of the interacting pion gas using the Beth–Uhlenbeck approach to the relativistic virial expansion with Breit–Wigner phase shifts for the σ - and ϱ -meson resonances. The repulsive phase shift δ 0 2 is taken from the quark interchange model of Barnes and Swanson, which is in very good agreement with the experimental data. In this work we show that the cancellation of the attractive (I = 0) and repulsive (I = 2) isospin channel contributions to the scalar π π interaction in the low-energy region that is known for the vacuum phase shifts also takes place at a finite temperature. This happens despite the strong medium dependence of these phase shifts that enters our model by the temperature dependence of the σ -meson and constituent quark masses, because for these masses the relation M σ (T) ≈ 2 m q (T) holds and the scattering length approximation is valid as long as the strong decay channel σ → π π is open. Exploiting the Nambu–Jona-Lasinio model for describing the dynamical breaking of chiral symmetry in the vacuum and its restoration at a finite temperature, we justify with our approach that the σ -meson should be absent from the hadron resonance gas description at low temperatures because the above cancellation holds. However, since this cancellation breaks down in the vicinity of the hadronization transition, where due to chiral symmetry restoration the decay channel σ → π π closes and the σ -meson becomes a good resonance, the latter should be included into the statistical model description of chemical freeze-out in heavy-ion collisions. [ABSTRACT FROM AUTHOR]

In this work, we propose to search for the exotic doubly charmed meson T cc + and its analog T c c s ¯ + in B c + decays, which provide a good environment for the formation of the exotic state containing double charm quarks. Within the molecular scheme, the production of T cc + and T c c s ¯ + through various rescattering processes with different intermediate states are investigated. For the moderate values of model parameters, the branching ratios of B c + decaying into T cc + D ¯ 0 , T cc + D ¯ ∗ 0 , T c c s ¯ + D ¯ 0 and T c c s ¯ + D ¯ ∗ 0 are estimated to be of the order of 10 - 7 , 10 - 5 , 10 - 6 and 10 - 4 , respectively, which may be tested by future experiments. [ABSTRACT FROM AUTHOR]

We investigate the production of X b in the process Υ (5 S , 6 S) → γ X b , where X b is assumed to be a B B ¯ ∗ molecular state. Two kinds of meson loops of B (∗) B ¯ (∗) and B 1 ′ B ¯ (∗) were considered. To explore the rescattering mechanism, we calculated the relevant branching ratios using the effective Lagrangian based on the heavy quark symmetry. The branching ratios for the Υ (5 S , 6 S) → γ X b were found to be at the orders of 10 - 7 ∼ 10 - 6 . Such sizeable branching ratios might be accessible at BelleII, which would provide important clues to the inner structures of the exotic state X b . [ABSTRACT FROM AUTHOR]

The masses of the low-lying scalar mesons are investigated in the three-flavor Nambu–Jona-Lasinio (NJL) model by treating the scalar mesons as composite objects of a quark and an antiquark. It is known that a simple |$\bar{q}q$| picture fails to reproduce the so-called inverse mass ordering for the scalar mesons. Recently a new mechanism to reproduce the observed mass spectrum of the scalar mesons was proposed in a linear sigma model by introducing flavor symmetry breaking induced by the U(1) axial anomaly. Motivated by this proposal, we examine whether this new mechanism also works in the NJL model. By calculating the scalar meson masses, we find that the NJL model reproduces the observed mass ordering with sufficient strength of the new term. With this mechanism, it turns out that the constituent strange quark mass becomes degenerate to that of the up and down quarks if the inverse mass ordering is reproduced. We also discuss the scalar diquark masses to check the consistency of the degeneracy of the constituent quark masses with the light baryon masses. [ABSTRACT FROM AUTHOR]

Nonleptonic B c decays to P -wave charmonia and light π + , K + , and ρ + , K ∗ + mesons are analyzed using factorization. The hadronic form factors parametrizing the B c → χ c J (h c) matrix elements are expressed in terms of universal functions at the leading order of an expansion in the relative velocity of the heavy quarks in the B c rest-frame and in 1 / m Q . Several ratios of branching fractions are evaluated, and when experimental information can be used, single branching fractions are presented. Both the 1 P and 2 P charmonia are considered. If the exotic candidate state χ c 1 (3 8 7 2) corresponds to χ c 1 (2 P) , it should be produced in nonleptonic B c decays with predicted abundances with respect to the other states in the charmonium 2 P spin four-plet. [ABSTRACT FROM AUTHOR]

In an approach predicted by the independent quark model with scalar-vector linear potential, we compute the leptonic decay widths and electromagnetic decay constants of vector mesons. We derive the quark-antiquark momentum distribution wave function from bound Quark eigenmode, Supposing a strong association between quark-antiquark momenta within the meson, so that the total momentum identically zero in the mesons center of mass frame. We obtain the leptonic decay width of ρ, ω, ϕ, ψ and Υ as 6.61 keV, 0.71 keV, 1.26 keV, 5.49 keV, and 1.31 keV and decay constants of ρ, ω, ϕ, ψ, and Υ as 0.19 GeV, 0.064 GeV, 0.074 GeV, 0.089 GeV and 0.021 GeV using our model parameter. These values are consistent with the said relevant experimental observations. [ABSTRACT FROM AUTHOR]

Within the color singlet model, we calculate the exclusive production of double charmonia, double bottomonia, and double B c mesons at future super Z factory. The two heavy quarkonia or B c 's are either two S-wave Fock states ( 1 S 0 , 3 S 1 ), or one S-wave and one P-wave states ( 1 P 1 , 3 P J (J = 0 , 1 , 2) ). The top three Z 0 propagated channels in cross sections for double charmonia are σ (J / ψ + h c) Z 0 = (454. 0 - 59.2 + 39.1) × 10 - 5 f b , σ (η c + χ c 2) Z 0 = (284. 2 - 35.3 + 22.2) × 10 - 5 f b , and σ (η c + χ c 0) Z 0 = (137. 0 - 16.4 + 9.9) × 10 - 5 f b . For double bottomonia, they are σ (η b + Υ) Z 0 = (428. 6 - 60.9 + 67.9) × 10 - 4 f b , σ (Υ + χ b 2) Z 0 = (230. 6 - 22.2 + 23.6) × 10 - 4 f b , and σ (Υ + Υ) Z 0 = (119. 9 - 16.6 + 18.4) × 10 - 4 f b . For double B c mesons, they are σ (B c ∗ + + B c ∗ -) Z 0 = (1150 - 84 + 87) × 10 - 3 f b , σ (B c ∗ + + χ b c 2 -) Z 0 = (1133 + 22 - 16) × 10 - 3 f b , and σ (η bc + + B c ∗ -) Z 0 = (634. 6 - 45.8 + 47.8) × 10 - 3 f b . Here the uncertainties come from the varying masses of constituent heavy quarks, which bring up to 20% corrections. The cross sections of double B c mesons are roughly one order of magnitude larger than those of the double bottomonia, and two orders of magnitude larger than those of the double charmonia. To make it helpful for experimental study, we present the total cross sections σ as functions of CM energy s , σ as functions of the renormalization scale μ , the angle distributions d σ / d c o s θ , and the p T distributions d σ / d p t . We also find that the initial state radiation can bring about 30–40% suppresions when 1% m Z energy is losing, and cross sections can increase by about 2–3 times or decrease by an order of magnitude when adopting different potential models which becomes the major source of uncertainty. The numerical results show that it might be not optimistic for the experimental observation, but it is still far from excluded at the FCC-ee and also the CEPC running in the Z factory mode. [ABSTRACT FROM AUTHOR]