An Effective Approach to VMD at One Loop Order and the Departure from Ideal Mixing Vector Mesons
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Benayoun, M.↗
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Operators for scattering of particles with spin
Operators for simulating the scattering of two particles with spin are constructed. Three methods are shown to give the consistent lattice operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar meson, vector meson and nucleon. The projection method leads to one or several operators OG;r;n that transform according to a given irreducible representation G and row r. However, it gives little guidance on which continuum quantum numbers of total J, spin S, orbital momentum L or single-particle helicities l1;2 will be related with a given operator. This is remedied with the helicity and partial-wave methods. There first the operators with good continuum quantum numbers (J;P;l1;2) or (J;L;S) are constructed and then subduced to the irreps G of the discrete lattice group. The results indicate which linear combinations OG;r;n of various n have to be employed in the simulations in order to enhance couplings to the states with desired continuum quantum numbers. The total momentum of two hadrons is restricted to zero since parity P is a good quantum number in this case.
Prelovsek, Sasa↗
Quasibound states in the continuum: A dynamical coupled-channel calculation of axial-vector charmed mesons
Masses and widths of the axial-vector charmed mesons D{sub 1}(2420), D{sub 1}(2430), D{sub s1}(2536), and D{sub s1}(2460) are calculated nonperturbatively in the resonance-spectrum-expansion model, by coupling various open and closed meson-meson channels to the bare J{sup P}=1{sup +} cq (q=u, d) and cs states. The coupling to two-meson channels dynamically mixes and lifts the mass degeneracy of the spectroscopic {sup 3}P{sub 1} and {sup 1}P{sub 1} states, as an alternative to the usual spin-orbit splitting. Of the two resulting S-matrix poles in either case, one stays very close to the energy of the bare state, as a quasibound state in the continuum, whereas the other shifts considerably. This is in agreement with the experimental observation that the D{sub 1}(2420) and D{sub s1}(2536) have much smaller widths than one would naively expect. The whole pattern of masses and widths of the axial-vector charmed mesons can thus be quite well reproduced with only two free parameters, one of which being already strongly constrained by previous model calculations. Finally, predictions for pole positions of radially excited axial-vector charmed mesons are presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Different Contributions of the {phi}{yields}K{sup 0}K-bar{sup 0}{gamma} Decay
The scalar mesons and vector mesons contribution to the radiative decay {phi}{yields}K{sup 0}K-bar{sup 0}{gamma} are studied within the framework of the phenomenological approach. The branching ratio of this decay is calculated to be 10{sup -8}-10{sup -12}. Furthermore, obtained values are compared with the experimental and theoretical results existing in the literature.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Vector meson-baryon interaction to study dynamical generation of resonances
With the motivation to find dynamical generation of resonances, we study vector-meson baryon interaction by taking s-,t-,u-channel diagrams and a contact interaction into account. A comparison of the different contributions obtained from these diagrams is done in the SU(2) limit, which shows that these diagrams could be equally important. We find it worthwhile to pay attention to the structure of the total interaction between the two non-zero spin particles which possess similar masses and find spin dependent interaction similar to the nucleon-nucleon case.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Dynamically generated hadron resonances
As an example of dynamically generated resonances we mention the interaction of vector mesons with baryons within the local hidden gauge formalism which gives rise to a large amount of such states, many of which can be associated to known resonances, while others represent predictions for new resonances. The width of these states coming from decay into pseudoscalar baryon is also addressed. We also mention recent states coming from {rho}{pi} interaction obtained with Faddeev equations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
{eta} Prime {yields}{pi}{sup 0}{gamma}{gamma} and {eta} Prime {yields}{eta}{gamma}{gamma}: A primer analysis
The electromagnetic rare decays {eta} Prime {yields}{pi}{sup 0}{gamma}{gamma} and {eta} Prime {yields}{pi}{sup 0}{gamma}{gamma} are analysed for the first time and their predicted branching ratios given. The vector meson exchange dominant contribution is treated using Vector Meson Dominance and the scalar component is estimated by means of the Linear Sigma Model. The agreement between our calculation and the measurement of the related process {eta} Prime {yields}{pi}{sup 0}{gamma}{gamma} is a check of the procedure. Scalar meson effects are seen to be irrelevant for {eta} Prime {yields}{pi}{sup 0}{gamma}{gamma}, while a significant scalar contribution due to the {sigma}(500) resonance seems to emerge in the case of {eta} Prime {yields}{pi}{sup 0}{gamma}{gamma}. Future measurements coming from KLOE-2, Crystal Ball, WASA, and BES-III will elucidate if any of these processes carry an important scalar contribution or they are simply driven by the exchange of vector mesons.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
J/ψ photoproduction at the threshold with GlueX
High-statistics total cross sections for the vector meson photoproduction at the threshold: γp → ωp (from A2 at MAMI, ELPH, and CBELSA), γp → ϕp (from CLAS6 at JLab and LEPS at SPring-8), and γp → J/ψp (from GlueX at JLab) allow one to extract the absolute value of vector meson nucleon scattering length using Vector Meson Dominance (VMD) model. The “young” vector meson hypothesis may explain the fact that the obtained scattering length values for the nucleon. ϕ-meson compared to the typical hadron size of approximately ∼ 1 fm indicates that the proton is more transparent for the ϕ-meson compared to the ω-meson and is much less transparent than the J/ψ-meson. The extended analysis of Υ-meson photoproduction using quasi-data from the QCD approach is in perfect agreement with the light-meson findings using experimental data. Finally, the ability of J-PARC to measure $π^{–}p → ϕn$ and $π^{–}p → J/ψn$ at the threshold, which are free from the VMD model, is presented. It enables one to understand the dynamics of $s\bar{s}$ and $c\bar{c}$ production at threshold and to search for the effects of LHCb’s heavy quark exotic states.
Vector meson nucleon scattering length↗
Modern nuclear and astrophysical constraints of dense matter in a redefined chiral approach
Here, we explore the quantum chromodynamics (QCD) phase diagram’s complexities, including quark deconfinement transitions, liquid-gas phase changes, and critical points by using the chiral mean-field (CMF) model that is able to capture all these features. We introduce a vector meson field redefinition within the CMF framework, enabling precise adjustments of meson masses and coupling strengths related to vector meson interactions. Performing a new fit to the deconfinement potential, we are able to replicate recent lattice QCD results, low-energy nuclear physics properties, neutron star observational data, and key phase diagram features as per modern constraints. This approach enhances our understanding of vector mesons’ roles in mediating nuclear interactions and their impact on the equation of state, contributing to a more comprehensive understanding of the QCD phase diagram and its implications for nuclear and astrophysical phenomena.
QCD phase transitions↗
Nonleptonic two-body decays of charmed mesons
Nonleptonic decays of charmed mesons into two pseudoscalar mesons or one pseudoscalar meson and one vector meson are studied on the basis of a generalized factorization method considering the resonance effects in the pole model for the annihilation contributions. Large strong phases between different topological diagrams are considered in this work, simply taking the phase in the coefficients a{sub i}. We find that the annihilation-type contributions calculated in the pole model are large in both of the PP and PV modes, which make our numerical results agree with the experimental data better than those previous calculations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Lepton decay constants of light mesons
A theory of lepton decay constants based on the path-integral formalism is given for chiral and vector mesons. Decay constants of the pseudoscalar and vector mesons are calculated and compared to other existing results.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Photoproduction of ω mesons off nuclei and impact of polarization on the meson-nucleon interaction
We consider photoproduction of ω mesons off complex nuclei to study interactions of transversely and longitudinally polarized vector mesons with nucleons. Whereas the total cross section for interactions of the transversely polarized vector mesons with nucleons σ T = σ(V T N) can be obtained from coherent photoproduction, measurements of vector meson photoproduction in the incoherent region provide a unique opportunity to extract the not-yet-measured total cross section for longitudinally polarized mesons σ L = σ(V L N). The predictions for the latter strongly depend on the theoretical approaches. Furthermore, this work is stimulated by the construction of the new experiment GlueX at Jefferson Lab, designed to study the photoproduction of mesons in a large beam energy range up to 12 GeV.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Can η mesons have a magnetic moment?
The response of pseudoscalar and vector mesons to strong magnetic fields is studied within a simple constituent quark model using analogy with bound states of Positronium. Magnetic moments of charged vector mesons K *, D *, B * are predicted and it is found that η mesons have magnetic polarizability. In extremely strong magnetic fields, behaviour of J /Ψ mesons is discussed. We speculate on the existence of an induced magnetic moment of η meson.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Charm physics with overlap fermions on 2+1-flavor domain wall fermion configurations*
Decay constants of pseudoscalar mesons D, D s , η c , and vector mesons D*, D$^{*}_{s}$, J/ψ are determined from the N f = 2 + 1 lattice QCD at a lattice spacing a ~ 0.08 fm. For vector mesons, the decay constants defined by tensor currents are given in the $\overline{MS}$ scheme at 2 GeV. The calculation is performed on domain wall fermion configurations generated by the RBC-UKQCD collaborations and the overlap fermion action is used for the valence quarks. Comparing the current results with our previous results at a coarser lattice spacing a ~ 0.11 fm provides a better understanding of the discretization error. We obtain $f$$^{T}_{D^*_s}$($\overline{MS}$, 2 GeV)/f D$^{*}_{s}$ = 0.909(18) with a better precision than our previous result. Combining our f D$^{*}_{s}$ = 277(11) MeV with the total width of D$^{*}_{s}$ determined in a recent study gives a branching fraction 4.26(52) x 10 –5 for D$^{*}_{s}$ leptonic decay.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Ordinary and exotic mesons in the extended Linear Sigma Model
The extended Linear Sigma Model (eLSM) is a hadronic model based on the global symmetries of QCD and the corresponding explicit, anomalous, and spontaneous breaking patterns. In its basic three-flavor form, its mesonic part contains the dilaton/glueball as well as the nonets of pseudoscalar, scalar, vector, and axial–vector mesons, thus chiral symmetry is linearly realized. In the chiral limit and neglecting the chiral anomaly, only one term – within the dilaton potential – breaks dilatation invariance, and all terms are chirally symmetric. Spontaneous symmetry breaking is implemented by a generalization of the Mexican-hat potential, with explicit symmetry breaking responsible for its tilting. The overall mesonic phenomenology up to ~2 GeV is in agreement with the PDG compilation of masses and partial and total decay widths. The eLSM was enlarged in a straightforward way to include other conventional quark–antiquark nonets (pseudovector and orbitally excited vector mesons, tensor and axial-tensor mesons, radially excited (pseudo)scalar mesons, etc.), as well as two nonets of hybrid mesons, the lightest one with exotic quantum numbers J $\mathscr{PC}$ = 1 -+ not allowed for $\bar{q}q$ objects, such as the resonance π 1 (1600) and the recently discovered η 1 (1855) . In doing so, different types of chiral multiplets are introduced: heterochiral and homochiral multiplets, which differ in the way they transform under chiral transformations. Moreover, besides the scalar glueball that is present from the beginning as dilaton, other glueballs, the tensor, the pseudoscalar and the vector glueballs were coupled to the eLSM: the scalar resonance ƒ 0 (1710) turns out to be mostly gluonic, the tensor glueball couples strongly to vector mesons, and the pseudoscalar glueball couples sizably to $ππη'$ and can be assigned to X (2370) or X (2600). In all cases above, masses and decays can be analyzed allowing for a better understanding of both conventional and non-conventional mesons: whenever data are available, a comparison is performed and, when this is not the case, predictions of decay widths and decay ratios are outlined. The eLSM contains chiral partners on an equal footing and is therefore well suited for studies of chiral symmetry restoration at nonzero temperature and densities: this is done by coupling it to the Polyakov loop. Finally, the QCD phase diagram and the location of the critical endpoint were investigated within this framework.
Chiral symmetry↗
Ultra high-energy neutrinos via heavy-meson synchrotron emission in strong magnetic fields
We explore the generation and possibility for the detection of heavy-meson synchrotron emission due to the acceleration of ultra-relativistic protons (and possibly nuclei) in the presence of strong magnetic fields (H ≳ 10{sup 15} G) in transient astrophysical environments such as magnetar flares. We show that, in addition to the well-known pion synchrotron emission, heavy vector mesons like ρ, D{sub S} , J/Ψ, and Y could be generated. For high enough energies and magnetic field strengths, such heavy vector mesons can be formed with high intensity (∼10{sup 3} times the photon intensity) through strong couplings to the ultra-relativistic nucleons. We examine in particular the synchrotron emission and subsequent cooling and decay of the heavy ρ{sup 0} and Y(1S) mesons, e.g., via p → p' + Y(1S), Y(1S) → τ{sup +} + τ{sup –}, τ{sup −}→μ{sup −}+ ν-bar {sub μ}+ν{sub τ} and e{sup −}+ ν-bar {sub e}+ν{sub τ}. We evaluate the spectra of escaping ν {sub e}, ν{sub μ}, and ν{sub τ} due to the decay of short-lived τ mesons. We deduce the possible event rate in a terrestrial TeV neutrino detector. We estimate that neutrinos produced from the heavy vector-meson synchrotron radiation from a strong magnetar soft gamma repeater burst will only be detectable with the current generation of detectors if the source is very nearby (<30 pc). Nevertheless, if ever detected, the existence of heavy meson synchrotron emission might be identifiable by the unique signature of energetic tau neutrinos emanating from the source.
79 ASTRONOMY AND ASTROPHYSICS↗
Dark mesons at the LHC
A new, strongly-coupled “dark” sector could be accessible to LHC searches now. These dark sectors consist of composites formed from constituents that are charged under the electroweak group and interact with the Higgs, but are neutral under Standard Model color. In these scenarios, the most promising target is the dark meson sector, consisting of dark vector-mesons as well as dark pions. In this paper we study dark meson production and decay at the LHC in theories that preserve a global SU(2) dark flavor symmetry. Dark pions — like the pions of QCD — can be pair-produced through resonant dark vector meson production, pp → ρ D → π D π D , and decay in one of two distinct ways: “gaugephobic”, when π D →$f\bar{f}$' generally dominates; or “gaugephilic”, when π D → W + h, Z + h dominates once kinematically open. Unlike QCD, the decay π$^D_0$ → γγ is virtually absent due to the dark flavor symmetry. We recast a vast set of existing LHC searches to determine the current constraints on (and future opportunities for) dark meson production and decay. When m ρD is slightly heavier than 2m π${_D}$ and ρ$^{±,0}_D$ kinetically mixes with the weak gauge bosons, the 8 TeV same-sign lepton search strategy sets the best bound, m π${_D}$ > 500 GeV. Yet, when only the ρ$^0_D$ kinetically mixes with hypercharge, we find the strongest LHC bound is m π${_D}$ > 130 GeV, that is only slightly better than what LEP II achieved two decades ago. We find the relative insensitivity of LHC searches, especially at 13 TeV, can be blamed mainly on their penchant for high mass objects or large missing energy. Dedicated searches would undoubtedly yield substantially improved sensitivity. We provide a GitHub page to speed the implementation of these searches in future LHC analyses. Our findings for dark meson production and decay provide a strong motivation for model-independent searches of the form pp → A → B + C → SM SM + SM SM where the theoretical prejudice is for SM to be a 3rd generation quark or lepton, W, Z, or h.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗