Heavy Meson Spectra Research Articles

Heavy mesons in the Quark Model

Since the discovery of theJ/ψ, the quark model was very successful in describing the spectrum and properties of heavy mesons including only q̄ components. However since 2003, with the discovery of theX(3872), many states that can not be accommodated on the naive quark model have been discovered, and they made unavoidable to include higher Fock components on the heavy meson states. We will give an overview of the success of the quark model for heavy mesons and point some of the states that are likely to be more complicated structures such as meson-meson molecules.

Mass spectra of heavy mesons with instanton effects

We investigate the mass spectra of ordinary heavy mesons, based on a nonrelativistic potential approach. The heavy-light quark potential contains the Coulomb-type potential arising from one-gluon exchange, the confining potential, and the instanton-induced nonperturbative local heavy-light quark potential. All parameters are theoretically constrained and fixed. We carefully examine the effects from the instanton vacuum. Within the present form of the local potential from the instanton vacuum, we conclude that the instanton effects are rather marginal on the charmed mesons.

Heavy meson dissociation in a plasma with magnetic fields

The fraction of heavy vector mesons detected after a heavy ion collision provides information about the possible formation of a plasma state. An interesting framework for estimating the degree of dissociation of heavy mesons in a plasma is the holographic approach. It has been recently shown that a consistent picture for the thermal behavior of charmonium and bottomonium states in a thermal medium emerges from holographic bottom up models. A crucial ingredient in this new approach is the appropriate description of decay constants, since they are related to the heights of the quasiparticle peaks of the finite temperature spectral function.Here we extend this new holographic model in order to study the effect of magnetic fields on the thermal spectrum of heavy mesons. The motivation is that very large magnetic fields are present in non central heavy ion collisions and this could imply a change in the dissociation scenario. The thermal spectra of cc¯ and bb¯ S wave states is obtained for different temperatures and different values of the magnetic eB field.

Heavy and Heavy-Light Mesons in the Covariant Spectator Theory

The masses and vertex functions of heavy and heavy-light mesons, described as quark-antiquark bound states, are calculated with the Covariant Spectator Theory (CST). We use a kernel with an adjustable mixture of Lorentz scalar, pseudoscalar, and vector linear confining interaction, together with a one-gluon-exchange kernel. A series of fits to the heavy and heavy-light meson spectrum were calculated, and we discuss what conclusions can be drawn from it, especially about the Lorentz structure of the kernel. We also apply the Brodsky-Huang-Lepage prescription to express the CST wave functions for heavy quarkonia in terms of light-front variables. They agree remarkably well with light-front wave functions obtained in the Hamiltonian basis light-front quantization (BLFQ) approach, even in excited states.

An approach to the instanton effect in B system

We discuss the constraint on the size of QCD instanton effects in low-energy effective theory. Among various instanton effects in meson mass spectrum and dynamics, we concentrate on the instanton-induced masses of light quarks. The famous instanton-induced six-quark interaction, so-called ’t Hooft vertex, could give nonperturbative quantum corrections to light quark masses. Many works have already been achieved to constrain the mass corrections in light meson system, or the system of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], and now we know for a fact that the instanton-induced mass of up-quark is too small to realize the solution of the strong CP problem by vanishing current mass of up-quark. In this work, we give a constraint on the instanton-induced mass correction to light quarks from the mass spectrum of heavy mesons, [Formula: see text], [Formula: see text], [Formula: see text] and their antiparticles. To accomplish this, the complete second-order chiral symmetry breaking terms are identified in heavy meson effective theory. We find that the strength of the constraint from heavy meson masses is at the same level of that from light mesons, and it would be made even stronger by more precise data from future [Formula: see text] factories and lattice calculations.

Threshold effects in hadron spectrum: a new spectroscopy?

The exploration of energies above the open-flavor threshold in the meson spectra has led to the appearance of unexpected states difficult to accommodate in the naive picture of a bound state of a quark and an antiquark. Many of such states are located close to meson-meson thresholds, which suggests that molecular structures may be a relevant component in the total wave function of such resonances. In this work, the state of meson-meson molecules calculations is reviewed, using a nonrelativistic constituent quark model that has been applied to a wide range of hadronic observables, and therefore all model parameters are completely constrained. The model has been able to reproduce, among others, the properties of the X(3872), described as a mixture of cc and DD* states, or the spectrum of the P-wave charm-strange mesons, which are well reproduced only if DK and D*K structures are taken into account. We show that such constituent quark model, which is able to describe the ordinary heavy meson spectra, is also capable of providing a good description of many new states recently reported.

Energy loss of heavy quarks and B and D meson spectra in PbPb collisions at LHC energies

We study the production and evolution of charm and bottom quarks in hot partonic medium produced in heavy ion collisions. The heavy quarks loose energy in the medium which is reflected in the transverse momentum spectra of heavy mesons. The collisional energy loss of heavy quarks has been calculated using QCD calculations. The radiative energy loss is obtained using two models namely reaction operator formalism and generalized dead cone approach. The nuclear modification factors, RAA as a function of transverse momentum by including shadowing and energy loss are calculated for D0 and B+ mesons in PbPb collisions at sNN=5.02 TeV and for D0 mesons at sNN=2.76 TeV and are compared with the recent measurements. The radiative energy loss from generalized dead cone approach alone is sufficient to produce measured D0 meson RAA at both the LHC energies. The radiative energy loss from reaction operator formalism plus collisional energy loss gives good description of D0 meson RAA. For the case of B+ meson, the radiative energy loss from generalized dead cone approach plus collisional energy loss gives good description of the CMS data. The radiative process is dominant for charm quarks while for the bottom, both the radiative process and the elastic collisions are important.

Covariant Spectator Theory of heavy–light and heavy mesons and the predictive power of covariant interaction kernels

The Covariant Spectator Theory (CST) is used to calculate the mass spectrum and vertex functions of heavy-light and heavy mesons in Minkowski space. The covariant kernel contains Lorentz scalar, pseudoscalar, and vector contributions. The numerical calculations are performed in momentum space, where special care is taken to treat the strong singularities present in the confining kernel. The observed meson spectrum is very well reproduced after fitting a small number of model parameters. Remarkably, a fit to a few pseudoscalar meson states only, which are insensitive to spin-orbit and tensor forces and do not allow to separate the spin-spin from the central interaction, leads to essentially the same model parameters as a more general fit. This demonstrates that the covariance of the chosen interaction kernel is responsible for the very accurate prediction of the spin-dependent quark-antiquark interactions.

Dmesons in a magnetic field

We investigate the mass spectra of open heavy flavor mesons in an external constant magnetic field within QCD sum rules. Spectral Ans\"atze on the phenomenological side are proposed in order to properly take into account mixing effects between the pseudoscalar and vector channels, and the Landau levels of charged mesons. The operator product expansion is implemented up to dimension-5 operators. As a result, we find for neutral $D$ mesons a significant positive mass shift that goes beyond simple mixing effects. In contrast, charged $D$ mesons are further subject to Landau level effects, which together with the mixing effects almost completely saturate the mass shifts obtained in our sum rule analysis.

Heavy quarkonia in strong magnetic fields

We investigate the influence of a homogeneus and constant strong external magnetic field on the heavy-meson spectrum. Quarkonium states $c\bar{c}$ and $b\bar{b}$ are described within a non-relativistic framework and by means of a suitable potential model based on the Cornell parametrization. In particular, in this work we propose a model which takes into account the possible anisotropies emerging at the level of the static quark-antiquark potential, as observed in recent lattice studies. The investigation is perfomed both with and without taking into account the anisotropy of the static potential, in order to better clarify its effects

Spectra of heavy mesons in the Bethe-Salpeter approach

We present a calculation of the spectrum of charmonia, bottomonia and B_c-meson states with `ordinary' and exotic quantum numbers. We discuss the merits and limitations of a rainbow-ladder truncation of Dyson-Schwinger and Bethe-Salpeter equations and explore the effects of different shapes of the effective running coupling on ground and excited states in channels with quantum numbers J <= 3. We furthermore discuss the status of the X(3872) as a potential (excited) quark-antiquark state and give predictions for the masses of charmonia and bottomonia in the tensor channels with J=2,3.

Unraveling the pattern of the XYZ mesons

We present a plausible mechanism for the origin of the XYZ mesons in the heavy meson spectra within a standard quark-model picture. We discuss the conditions required for the existence of four-quark bound states or resonances contributing to the heavy meson spectra, being either compact or molecular. We concentrate on charmonium and bottomonium spectra, where several new states, difficult to understand as simple quark–antiquark pairs, have been reported by different experimental collaborations. The pivotal role played by entangled meson–meson thresholds is emphasized.

Generalized screened potential model

A new non relativistic quark model to calculate the spectrum of heavy quark mesons is developed. The model is based on an interquark potential interaction that implicitly incorporates screening effects from meson-meson configurations. An analysis of the bottomonium spectrum shows the appearance of extra states as compared to conventional non screened potential models.

Analytical properties of the quark propagator from a truncated Dyson-Schwinger equation in complex Euclidean space

In view of the mass spectrum of heavy mesons in vacuum the analytical properties of the solutions of the truncated Dyson-Schwinger equatio for the quark propagator within the rainbow approximation are analysed in some detail. In Euclidean space, the quark propagator is not an analytical function possessing, in general, an infinite number of singularities (poles) which hamper to solve the Bethe-Salpeter equation. However, for light mesons (with masses M_{q\bar q} <= 1 GeV) all singularities are located outside the region within which the Bethe-Salpeter equation is defined. With an increase of the considered meson masses this region enlarges and already at masses >= 1 GeV, the poles of propagators of u,d and s quarks fall within the integration domain of the Bethe-Salpeter equation. Nevertheless, it is established that for meson masses up to M_{q\bar q}~=3 GeV only the first, mutually complex conjugated, poles contribute to the solution. We argue that, by knowing the position of the poles and their residues, a reliable parametrisation of the quark propagators can be found and used in numerical procedures of solving the Bethe-Salpeter equation. Our analysis is directly related to the future physics programme at FAIR with respect to open charm degrees of freedom.

Hadron form factors and large-Ncphenomenology

The half width rule provides a way to consider 1/Nc corrections to hadronic models containing resonances. Consequences of such ideas for hadron form factors and Regge trajectories are explored, with special emphasis on the possibility to describe the spectrum of light and heavy unflavored vector mesons in a universal way.

Readout Hardware and Firmware Architecture of the HFT PXL Detector at STAR

The “Heavy Flavor Tracker” (HFT) is an approved micro-vertex detector upgrade to the STAR experiment at RHIC, consisting of three subsystems with various technologies of silicon sensors arranged in 4 concentric cylinders, to be installed in STAR by 2014. This new vertex detector will improve the track-pointing resolution in STAR to a distance of closest approach (DCA) of ~ 30 μm in order to allow for a direct and full topological reconstruction of heavy quark meson decays and a better determination of the heavy quark meson spectra. The two innermost layers of the HFT close to the beam pipe, the Pixel (“PXL”) subsystem, employ CMOS monolithic active pixel sensor (MAPS) technology that integrates the sensor, front-end electronics, and zero-suppression circuitry in one silicon wafer. The PXL layers of the HFT will consist of 400 MAPS sensors arranged in 40 ladders (10 ladders at a radius of 2.5 cm and 30 ladders at 8 cm from the beam), each containing 10 of these sensors. This paper will present selected design characteristics of the PXL detector part of the HFT and the hardware and firmware architecture of the proposed readout system for this detector, as well as its integration into the existing STAR framework. A prototype of this readout system has recently been used at CERN to take data from a telescope consisting of 7 sensors arranged in parallel planes and shown to be fully functional.

CONSTITUENT QUARK MODEL DESCRIPTION OF CHARMONIUM PHENOMENOLOGY

We review how quark models are able to describe the phenomenology of the charm meson sector. The spectroscopy and decays of charmonium and open charm mesons are described in a particular quark model and compared with the data and the results of other existing models in the literature. A quite reasonable global description of the heavy meson spectra is reached. A new assignment of the ψ(4415) resonance as a 3D state leaving aside the 4S state to the X(4360) is tested through the analysis of the resonance structure in e+e- exclusive reactions around the ψ(4415) energy region. We make tentative assignments of some of the XYZ mesons. To elucidate the structure of the 1+cs states, i.e., Ds1(2460) and Ds1(2536), we study the strong decay properties of the Ds1(2536) meson. We also perform a calculation of the branching fractions for the semileptonic decays of B and Bs mesons into final states containing orbitally excited charmed and charmed-strange mesons, which have become a very important source of information about the structure of heavy mesons. Analysis of the nonleptonic B-meson decays into D(*)DsJ are also included.

Heavy flavor relaxation in a hadronic medium

Charm and bottom transport coefficients in a medium constituted of light mesons, such as is formed in the hadronic phase of Heavy Ion Collisions, are obtained within an effective field theory approach implementing heavy quark symmetry and chiral symmetry breaking. Heavy flavor propagates in the medium as $D/B$ and $D^*/B^*$ degrees of freedom, and unitarization of the lowest order heavy-light meson amplitudes is used in order to reach high temperatures. The latter accounts for dynamically generated resonances in isospin 1/2 channels, a feature that leads to a more efficient heavy flavor diffussion. We discuss the temperature and momentum dependence of the friction and diffusion coefficients in a transport approach up to temperatures of about $T\simeq 150$ MeV, and provide estimates of the charm/bottom relaxation lengths and momentum loss. Implications for heavy meson spectrum observables in Heavy Ion Collisions are discussed.

Ground state heavy meson spectrum in the frame work of constituent quark models

The mass spectrum of the S-wave heavy mesons is considered in the frame work of non-relativistic, semi-relativistic and relativistic models. A good agreement is obtained with the experimental masses. The role of one-gluon-exchange potential and confined-one-gluon-exchange potential is discussed.

Empirical determination of charm quark energy loss and its consequences for azimuthal anisotropy

We propose an empirical model to determine the form of energy loss of charm quarks due to multiple scatterings in quark gluon plasma by demanding a good description of production of D mesons and non-photonic electrons in relativistic collision of heavy nuclei at RHIC and LHC energies. The best results are obtained when we approximate the momentum loss per collision ΔpT = α pT, where α is a constant depending on the centrality and the centre of mass energy. Comparing our results with those obtained earlier for drag coefficients estimated using the Langevin equation for heavy quarks, we find that up to half of the energy loss of charm quarks at the highest RHIC energy could be due to collisions while that at LHC energy at 2760 GeV/A the collisional energy loss could be about one-third of the total. Estimates are obtained for azimuthal anisotropy in momentum spectra of heavy mesons, due to this energy loss. We further suggest that the energy loss of charm quarks may lead to an enhanced production of D-mesons and single electrons at low pT in AA collisions.Communicated by SA Bass