Heavy Mesons Research Articles

Study of the hidden charm DD¯* interactions in chiral effective field theory

We study the chiral interactions of the hidden charm $D\bar{D}^*$ system within chiral effective field theory. Chiral Lagrangians are constructed by incorporating the chiral symmetry, heavy quark symmetry as well as proper charge conjugation properties of the heavy mesons. The interacting potentials of the $S$-wave $D\bar{D}^*$ are calculated up to second chiral order at 1-loop level, where complete two-pion exchange interactions are included. We further investigate the behaviors of the potentials in coordinate space, as well as their bound state properties. Our studies indicate that there exists a interacting strength ordering among considered four channels: $\text{str.}[0^+(1^{++})]>\text{str.}[0^-(1^{+-})] > \text{str.}[1^+(1^{+-})] > \text{str.}[1^-(1^{++})]$ where str. stands for the strength of the $D\bar{D}^*$ interaction. Moreover, we find that $X(3872)$ can be treated as a good candidate of $0^+(1^{++})$ molecular state. There also tends to form $0^-(1^{+-})$ and $1^+(1^{+-})$ molecular states and we expect the experiments to search for the predicted multi-structures around the $D\bar{D}^*$ mass region.

On Asymptotic Regge Trajectories of Heavy Meson Resonances

We performed the analysis of the asymptotic behavior of Regge trajectories of nonstrange and strange mesons and found that thewidth of heavy hadrons for these trajectories cannot linearly depend on their mass. Such a finding clearly demonstrates that a widely spread belief on the linear mass dependence of the resonance width contradicts the linearity of Regge trajectories on theMandelstam variable s. Using the data on masses and widths for ρJ––, ωJ––, aJ++,, and fJ++ mesons with the spin values J ≤ 6 and for K*J mesons with J ≤ 5, we extracted the parameters of the asymptotically linear Regge trajectories predicted by the finite-width model of quark gluon bags. It is shown that the parameters obtained for the data sets B and D are consistent with the cross-over temperaturedetermined by the lattice QCD simulations at the vanishing baryonic density and with the kinetic freeze-out temperature of early hadronizing particles found in relativistic heavy ion collisions at and above the highest SPS energy. Comparing the resonance width of sets B and D evaluated at the masses of Z and W bosons, respectively, we discovered that the calculated width values match that of the gauge bosons. We argue that such matches provide us with indirect, but the first experimental evidence for the compositeness of Z and W bosons. Based on these findings, we assume that Z, W, and Higgs bosons have the Regge trajectories which are similar to the asymptotic trajectories of the studied mesons. The predictions for the masses and widths of the Regge partners of Z and W bosons and for the mass dependence of the widths of Higgs boson Regge partners along with the values for the mass and width of the scalar Higgs mesons are made as well.

Holographic QCD model for Nf=4

We establish a holographic QCD model for four flavors, where a light scalar field $X$ and a heavy scalar field $H$ are introduced, separately. The $H$ field is responsible for the breaking of $SU(N_f=4)$ to $SU(N_f=3)$. The ground state and its Regge excitation of meson spectra in the light flavor sector and heavy flavor sector as well as the ligh-heavy mesons are well in agreement with the Particle data group (PDG). Due to the additional introduction of the $H$ field in the model, different Regge slopes for light and heavy mesons can be achieved.

Analytical solutions to the Schrodinger equation for a generalized Cornell potential and its applications to diatomic molecules and heavy mesons

Here, analytical expressions of energy eigenvalues and eigen functions for a generalized Cornell potential are obtained by solving the non-relativistic Schrodinger equation using the Nikiforov–Uvarov functional analysis method along with Greene–Aldrich approximation. Energy spectra of three physically important potentials viz the pseudoharmonic, the Kratzer and the Coulomb perturbed potentials are derived from the general results. Further, within the framework of the Kratzer potential, energy eigenvalue spectra of diatomic molecules [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are computed. The mass spectra of two heavy mesons are also investigated using the Coulomb perturbed potential, a form of the generalized Cornell potential. The obtained results are in good agreement with the results of others studies. The study is further extended to calculate and draw the partition function and other associated thermodynamic quantities for heavy mesons.

First measurement of the Bc+ meson nuclear modification factor in PbPb collisions with CMS

The Bc+ meson is observed in lead-lead and proton-proton collisions at a center-of-mass energy per nucleon pair of √SNN = 5.02 TeV, via the Bc+ → (J/ψ → μ+μ−)μ+vμ decay and using 2017 and 2018 data from the CMS detector. The resulting Bc+ nuclear modification factor is measured in two bins of the trimuon transverse momentum and of the collision centrality. Less suppression is observed than for other quarkonia and most open heavy flavour mesons. This first observation of the Bc+ meson in heavy ion collisions will shed light on the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.

Open and hidden heavy flavor measurements at RHIC

Quarks of heavy flavors are useful tool to study quark-gluon plasma created in heavy-ion collisions. Due to their high mass and early production time, heavy quarks experience the entire evolution of the system created in these collisions. Open heavy flavor meson measurements are sensitive to the energy loss in the QGP, while quarkonia are sensitive to the temperature of the QGP as they dissociate because of Debye-like screening of color charges. This presentation is a summary of the latest heavy flavor studies performed at RHIC. Results from both STAR and PHENIX experiments are presented, compared to theoretical calculations and the implications discussed.

Exploring the role of hyperons in high density matter in the Quark-Meson-Coupling model

Microscopic composition and properties of matter at super-saturation densities have been a subject of intense investigations for decades. Experimental and observational data and fundamental laws of physics indicate that heavy strange baryons and mesons are essential components of the matter. The Quark-Meson-Coupling-Model (QMC) is well suited for such a study. The model is based on interaction between quarks in individual baryons instead between the baryons as entities without internal structure. This approach significantly increases transparency and reduces the number of variable parameters of the model, thus offering deeper insight into the physics of high density hadronic matter. In this contribution, we review the effect of hyperons on neutron star (NS) properties, the speed of sound and the symmetry energy, both at zero and finite temperature. The QMC results are contrasted with the outcome of the traditional relativistic mean field DD2Y model. The (lack of) the so-called ‘hyperon puzzle’ in both models is discussed.

Thermal modification of open heavy-flavor mesons from an effective hadronic theory

We have developed a self-consistent theoretical approach to study the modification of the properties of heavy mesons in hot mesonic matter which takes into account chiral and heavy-quark spin-flavor symmetries. The heavylight meson-meson unitarized scattering amplitudes in coupled channels incorporate thermal corrections by using the imaginary-time formalism, as well as the dressing of the heavy mesons with the self-energies. We report our results for the ground-state thermal spectral functions and the implications for the excited mesonic states generated dynamically in the heavy-light molecular model. We have applied these to the calculation of meson Euclidean correlators and transport coefficients for D mesons and summarize here our findings.

Impact of fully coherent energy loss on heavy meson production in pA collisions

Hadron production in proton-nucleus (pA) collisions was previously shown to be suppressed by medium-induced fully coherent energy loss (FCEL). We show that the quenching of D and B mesons in pPb collisions at the LHC due solely to FCEL is, at least, on par with other nuclear effects such as gluon shadowing or saturation. This is consistent with previous findings for both quarkonium and light hadron production in pA collisions, emphasising that FCEL effects need to be included for a reliable understanding of hadron production measurements in pA collisions.

Revisiting quark-hadron duality for heavy meson non-leptonic decays in two-dimensional QCD

We study lifetimes of heavy mesons in the 't Hooft model, a large-Nc theory of strong interaction in two-dimensional spacetime. Since this model is solvable, one can evaluate the total decay widths through hadronic amplitudes that are determined unambiguously within the formalism. We investigate quark-hadron duality by numerically comparing the exclusive result and one from the heavy quark expansion, with the contribution of Pauli interference being consistently incorporated. Within certain numerical accuracy, we find that the maximal difference between inclusive and exclusive rates for τ[Ds+]/τ[D0](τ[B+]/τ[B0]) is as large as the current experimental (theoretical) error in four-dimensions unlike τ[D+]/τ[D0], where an excellent agreement between the rates is seen.

Holographic charm and bottom pentaquarks. III. Excitations through photoproduction of heavy mesons

We consider the photo-excitation of charm and bottom pentaquarks with the holographic assignments $[\frac 12\frac 12^-]_{S=0,1}$ and $[\frac 12\frac 32^-]_{S=1}$, in the photo-production of heavy vector mesons such as charmonia and bottomonia near threshold. We use a Witten diagram to combine the s-channel photo-excitation of holographic pentaquarks with a massive t-channel graviton or tensor glueball exchange, to extract the scattering amplitude for heavy meson photo-production in the threshold region. The pentaquark signal is too weak to be detected at current electron facilities.

Holographic charm and bottom pentaquarks. I. Mass spectra with spin effects

We revisit the three non-strange pentaquarks $[\frac 12\frac 12^-]_{S=0,1}$ and $[\frac 12\frac 32^-]_{S=1}$ predicted using the holographic dual description, where chiral and heavy quark symmetry are manifest in the triple limit of a large number of colors, large quark mass and strong $^\prime$t Hooft gauge coupling. In the heavy quark limit, the pentaquarks with internal heavy quark spin $S$ are all degenerate. The holographic pentaquarks are dual to an instanton bound to heavy mesons in bulk, without the shortcomings related to the nature of the interaction and the choice of the hard core inherent to the molecular constructions. We explicitly derive the spin-spin and spin-orbit couplings arising from next to leading order in the heavy quark mass, and lift totally the internal spin degeneray, in fair agreement with the newly reported charmed pentaquarks from LHCb. New charm and bottom pentaquark states are predicted.

Pure annihilation decay of strange beauty meson into two charm heavy mesons

In this study, the heavy to heavy decay of is evaluated through the factorization approach by using the final state interaction as an effective correction. Under the factorization approach, this decay mode occurs only through the annihilation process, so a small amount is produced. Feynman's rules state that six meson pairs can be assumed for the intermediate states before the final meson pairs are produced. By taking into account the effects of twelve final state interaction diagrams in the calculations, a significant correction is obtained. These effects correct the value of the branching ratio obtained by the pure factorization approach from to . The value obtained for the branching ratio of the decay is consistent with the experimental results.

Heavy + light pseudoscalar meson semileptonic transitions

A symmetry-preserving regularisation of a vector times vector contact interaction (SCI) is used to deliver a unified treatment of semileptonic transitions involving pi , K, D_{(s)}, B_{(s,c)} initial states. The framework is characterised by algebraic simplicity, few parameters, and the ability to simultaneously treat systems from Nambu–Goldstone modes to heavy+heavy mesons. Although the SCI form factors are typically somewhat stiff, the results are comparable with experiment and rigorous theory results. Hence, predictions for the five unmeasured B_{s,c} branching fractions should be a reasonable guide. The analysis provides insights into the effects of Higgs boson couplings via current-quark masses on the transition form factors; and results on B_{(s)}rightarrow D_{(s)} transitions yield a prediction for the Isgur–Wise function in fair agreement with contemporary data.

Effect of magnetic screening mass on the diffusion of heavy quarks

The drag and diffusion coefficients of heavy quarks propagating through quark–gluon plasma (QGP) have been estimated by shielding the infra-red divergences using electric and magnetic screening masses. The electric-type screening in perturbative quantum chromodynamics (pQCD) has been widely studied and used in evaluating the diffusion coefficient of heavy quarks (HQs). The impact of magnetic screening on diffusion coefficients of HQs is not studied before to the best of our knowledge. We explore the effect of magnetic screening mass on the drag and diffusion coefficients of HQs and found it to be non-negligible. Therefore, the effect of magnetic screening should be taken into consideration to characterize hot and dense matter formed in the collisions of nuclei at ultra-relativistic energies. We estimate the suppression of heavy flavored mesons in heavy ion collisions compared to proton+proton collisions at high transverse momenta and found that the suppression is less with the inclusion of magnetic screening. The value of the magnetic screening mass is not known exactly because of its nonperturbative nature. Moreover, it may not be possible to single out the effect of magnetic mass because of the uncertainties in other parameters involved in the diffusion process of HQs. Still it is important to include the effects of magnetic screening because of its physical origin in QCD.

Effect of thermal gluon absorption and medium fluctuations on heavy flavour nuclear modification factor at RHIC and LHC energies

The presence of thermal gluons reduces the stimulated gluon emission off a heavy quark propagating in the quark-gluon plasma (QGP) while absorption causes reduction of the radiative energy loss. On the other hand, the chromo-electromagnetic field fluctuations present in the QGP lead to collisional energy gain of the heavy quark. The net effect of the thermal gluon absorption and field fluctuations is a reduction of the total energy loss of the heavy quark, prominent at the lower momenta. We consider both kind of the energy gains along with the usual losses, and compute the nuclear modification factor ($R_{AA}$) of heavy mesons, viz., $D$ and $B$ mesons. The calculations have been compared with the experimental measurements in Au-Au collisions at $\sqrt{s_{NN}} = 200$ GeV from STAR and PHENIX experiments at the RHIC and Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV and $5.02$ TeV from CMS and ALICE experiments at the LHC. We find a significant effect of the total energy gain due to thermal gluon absorption and field fluctuations on heavy flavour suppression, especially at the lower transverse momenta.

Ground state pseudoscalar mesons on the light front: From the light to heavy sector

We extract the leading Fock-state light front wave functions (LF-LFWFs) of both the light and heavy pseudoscalar mesons, e.g., the pion (at masses of 130 MeV, 310 MeV and 690 MeV), $\eta_c$ and $\eta_b$, from their covariant Bethe-Salpeter wave functions within the rainbow-ladder (RL) truncation. It is shown that the LF-LFWFs get narrower in $x$ (the longitudinal momentum fraction of meson carried by the quark) with the increasing current quark mass, and the leading twist parton distribution amplitudes (PDAs) inherit this feature. Meanwhile, we find in the pion the LF-LFWFs only contribute around 30\% to the total Fock-state normalization, indicating the presence of significant higher Fock-states within. In contrast, in the $\eta_c$ and $\eta_b$ the LF-LFWFs contribute more than $90$\%, suggesting the $Q\bar{Q}$ valence Fock-state truncation as a good approximation for heavy mesons. We thus study the 3-dimensional parton distributions of the $\eta_c$ and $\eta_b$ with the unpolarized generalized parton distribution function (GPD) and the transverse momentum dependent parton distribution function (TMD). Through the gravitational form factors in connection with the GPD, the mass radii of the $\eta_c$ and $\eta_b$ in the light-cone frame are determined to be $r_{E,{\rm LC}}^{\eta_c} =0.150$ fm and $r_{E,{\rm LC}}^{\eta_b} =0.089$ fm respectively.

Mesons and baryons: Parity partners

We calculate masses of light and heavy mesons as well as baryons of negative parity containing $u,d,s,c$ and $b$ quarks. It is an extension of our previous work where we had studied the positive parity baryons. We adopt a quark-diquark picture of baryons where the diquarks are non-pointlike with a finite spatial extension. The mathematical foundation for this analysis is implemented through a symmetry-preserving Schwinger-Dyson equations treatment of a vector-vector contact interaction, which preserves key features of quantum chromodynamics, such as confinement, chiral symmetry breaking, axial vector Ward-Takahashi identity and low-energy Goldberger-Treiman relations. This treatment simultaneously describes mesons and provides attractive correlations for diquarks in the $\overline{3}$ representation. Employing this model, we compute the spectrum and masses of all spin-1/2 and spin-3/2 baryons of negative parity, supplementing our earlier evaluation of positive parity baryons, containing 1, 2 or 3 heavy quarks. In the process, we calculate masses of a multitude of mesons and corresponding diquarks. Wherever possible, we make comparisons of our results with known experimental observations as well as theoretical predictions of several models and approaches including lattice quantum chromodynamics, finding satisfactory agreement. We also make predictions for heavier states not yet observed in the experiment.

Charged current electroproduction of a charmed meson at an electron-ion collider

We calculate the amplitude for exclusive electroweak production of a pseudoscalar ${D}_{s}$ or a vector ${D}_{s}^{*}$ charmed strange meson on an unpolarized nucleon, through a charged current, in leading order in ${\ensuremath{\alpha}}_{s}$. We work in the framework of the collinear QCD approach where generalized gluon distributions factorize from perturbatively calculable coefficient functions. We include both $O({m}_{c})$ terms in the coefficient functions and $O({M}_{D})$ mass term contributions in the heavy meson distribution amplitudes. We show that this process may be accessed at future electron-ion colliders.

Scaling behaviors of heavy flavor meson suppression and flow in different nuclear collision systems at the LHC

We explore the system size dependence of heavy-quark-QGP interaction by studying the heavy flavor meson suppression and elliptic flow in Pb–Pb, Xe–Xe, Ar–Ar and O–O collisions at the LHC. The space-time evolution of the QGP is simulated using a (3+1)-dimensional viscous hydrodynamic model, while the heavy-quark-QGP interaction is described by an improved Langevin approach that includes both collisional and radiative energy loss inside a thermal medium. Within this framework, we provides a reasonable description of the D meson suppression and flow coefficients in Pb–Pb collisions, as well as predictions for both D and B meson observables in other collision systems yet to be measured. We find a clear hierarchy for the heavy meson suppression with respect to the size of the colliding nuclei, while their elliptic flow coefficient relies on both the system size and the geometric anisotropy of the QGP. Sizable suppression and flow are predicted for both D and B mesons in O–O collisions, which serve as a crucial bridge of jet quenching between large and small collision systems. Scaling behaviors between different collision systems are shown for heavy meson suppression factor and the bulk-eccentricity-rescaled heavy meson elliptic flow as functions of the number of participant nucleons in heavy-ion collisions.