Heavy-light Systems Research Articles

(Pseudo)scalar charmonium in finite temperature QCD

The hadronic parameters of pseudoscalar ($\eta_c$) and scalar ($\chi_c$) charmonium are determined at finite temperature from Hilbert moment QCD sum rules. These parameters are the hadron mass, leptonic decay constant, total width, and continuum threshold ($s_0$). Results for $s_0(T)$ in both channels indicate that $s_0(T)$ starts approximately constant, and then it decreases monotonically with increasing $T$ until it reaches the QCD threshold, $s_{th} = 4 m_Q^2$, at a critical temperature $T = T_c \simeq 180 \; \mbox{MeV}$ interpreted as the deconfinement temperature. The other hadronic parameters behave qualitatively similarly to those of the $J/\psi$, as determined in this same framework. The hadron mass is essentially constant, the total width is initially independent of T, and after $T/T_c \simeq 0.80$ it begins to increase with increasing $T$ up to $T/T_c \simeq 0.90 \; (0.95)$ for $\chi_c$ ($\eta_c$), and subsequently it decreases sharply up to $T \simeq 0.94 \; (0.99) \; T_c$, for $\chi_c$ ($\eta_c$), beyond which the sum rules are no longer valid. The decay constant of $\chi_c$ at first remains basically flat up to $T \simeq 0.80\; T_c$, then it starts to decrease up to $T \simeq 0.90 \;T_c$, and finally it increases sharply with increasing $T$. In the case of $\eta_c$ the decay constant does not change up to $T \simeq 0.80 \;T_c$ where it begins a gentle increase up to $T \simeq 0.95 \;T_c$ beyond which it increases dramatically with increasing $T$. This behaviour contrasts with that of light-light and heavy-light quark systems, and it suggests the survival of the $\eta_c$ and the $\chi_c$ states beyond the critical temperature, as already found for the $J/\psi$ from similar QCD sum rules. These conclusions are very stable against changes in the critical temperature in the wide range $T_c = 180 - 260 \; \mbox{MeV}$.

Form Factors of Heavy–Light Systems in Point-Form Relativistic Quantum Mechanics: The Isgur-Wise Function

We investigate electromagnetic and weak form factors of heavy-light mesons in the context of point-form relativistic quantum mechanics. To this aim we treat the physical processes from which such electroweak form factors are extracted by means of a coupled channel approach which accounts for the dynamics of the intermediate gauge bosons. It is shown that heavy-quark symmetry is respected by this formulation. A simple analytical expression is obtained for the Isgur-Wise function in the heavy-quark limit. Breaking of heavy-quark symmetry due to realistic values of the heavy-quark mass are studied numerically.

QCD sum rules and thermal properties of Charmonium in the vector channel

The thermal evolution of the hadronic parameters of charmonium in the vector channel, i.e. the J / ψ resonance mass, coupling (leptonic decay constant), total width, and continuum threshold is analyzed in the framework of thermal Hilbert moment QCD sum rules. The continuum threshold s 0 , as in other hadronic channels, decreases with increasing temperature until the PQCD threshold s 0 = 4 m Q 2 is reached at T ≃ 1.22 T c ( m Q is the charm quark mass) and the J / ψ mass is essentially constant in a wide range of temperatures. The other hadronic parameters behave in a very different way from those of light-light and heavy-light quark systems. The total width grows with temperature up to T ≃ 1.04 T c beyond which it decreases sharply with increasing T. The resonance coupling is also initially constant beginning to increase monotonically around T ≃ T c . This behavior strongly suggests that the J / ψ resonance might survive beyond the critical temperature for deconfinement, in agreement with lattice QCD results.

Decay Properties of the Heavy-Light Mesons

We study the decay properties of a heavy-light meson. We reformulate the decay amplitudes for the heavy-light systems and find a new way to calculate decay rates. Applying this formulation, we find a new sum rule for the radiative decays of one heavy-light meson into another, $H_1\to H_2+\gamma$ with various combinations of $H_i$.

MOMENTUM-SPACE FADDEEV CALCULATIONS FOR GROUND-STATE TRIPLY AND DOUBLY HEAVY BARYONS IN THE CONSTITUENT QUARK MODEL

In the framework of constituent quark model, mass spectra of the ground-state baryons consisting of three or two heavy (b or c) and one light (u, d or s) quarks are calculated by solving three-body Faddeev equations. The results imply that, it is possible to obtain a unified model to describe heavy baryons spectra, as well as meson and SU(3) octet and decuplet baryon spectra. We find that, when taking into account the relativistic correction quark–diquark approximation and three-body Faddeev approach tend to give similar predictions for heavy–light systems. We also study the spin splitting of JP = (1/2+) and JP = (3/2+).

Charmonium in the vector channel at finite temperature from QCD sum rules

Thermal Hilbert moment QCD sum rules are used to obtain the temperature dependence of the hadronic parameters of charmonium in the vector channel, i.e. the $J/\ensuremath{\psi}$ resonance mass, coupling (leptonic decay constant), total width, and continuum threshold. The continuum threshold ${s}_{0}$, which signals the end of the resonance region and the onset of perturbative QCD, behaves as in all other hadronic channels, i.e. it decreases with increasing temperature until it reaches the perturbative QCD threshold ${s}_{0}=4{m}_{Q}^{2}$, with ${m}_{Q}$ the charm quark mass, at $T\ensuremath{\simeq}1.22{T}_{c}$. The rest of the hadronic parameters behave very differently from those of light-light and heavy-light quark systems. The $J/\ensuremath{\psi}$ mass is essentially constant in a wide range of temperatures, while the total width grows with temperature up to $T\ensuremath{\simeq}1.04{T}_{c}$ beyond which it decreases sharply with increasing $T$. The resonance coupling is also initially constant and then begins to increase monotonically around $T\ensuremath{\simeq}{T}_{c}$. This behavior of the total width and of the leptonic decay constant provides a strong indication that the $J/\ensuremath{\psi}$ resonance might survive beyond the critical temperature for deconfinement.

D and Ds in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1−(13D1) and the 3−(13D3) Ds agree well with those of recently observed Ds1(2700)± and DsJ(2860), respectively.

Nonperturbative Heavy-Quark Interactions in the QGP

We adopt a T-matrix approach to study quarkonium properties and heavy-quark transport in a Quark-Gluon Plasma. The T-matrix approach is well suited to implement potential scattering and thus provides a common framework for low-momentum transfer interactions in heavy-heavy and heavy-light quark systems. We assume that the underlying potentials can be estimated from the heavy-quark free energy computed in lattice QCD. We discuss constraints from vacuum spectroscopy, uncertainties arising from different choices of the potential, and the role of elastic and inelastic widths which are naturally accounted for in the T-matrix formalism.

Three-particle contributions to the renormalisation ofB-meson light-cone distribution amplitudes

We study light-cone distribution amplitudes of heavy-light systems, such as a B-meson. By an explicit computation, we determine how two-parton distribution amplitudes mix with three-parton ones at one loop: \phi_+ is shown to mix only into itself, whereas \phi_- mixes with the difference of three-parton distribution amplitudes \Psi_A-\Psi_V. We determine the corresponding anomalous dimension and we check the gauge independence of our result by considering a general covariant gauge. Finally, we comment on some implications of our result for phenomenological models of these distribution amplitudes.

Heavy quark masses from lattice QCD

I outline the basic strategies for the computation of charm and bottom quark masses by means of lattice QCD, where particular emphasis is placed on the non-perturbative renormalization of the effective theory for the b-quark in heavy-light systems. A few selected results in the quenched approximation are reviewed, and the current status of extending these calculations to QCD with dynamical quarks is summarized.

Multiquark structures in heavy-light meson systems

We look for possible signatures of multiquark structures in the heavy-light meson spectra. The controversial D s 0 ∗ ( 2317 ) and D s 1 ∗ ( 2460 ) states are properly described if considered as a mixture of conventional P-wave q q ¯ and four-quark components. The recently discovered D s J ∗ ( 2860 ) appears as the orthogonal partner of the D s 0 ∗ ( 2317 ) . Similar structures are predicted in the B s sector. We also consider the possible existence of isolated I = 1 four-quark resonances and we argue that their existence can disentangle the ϒ ( n S ) → ϒ ( m S ) π π decay puzzle.

First nonperturbative test of a relativistic heavy quark action in quenched lattice QCD

We perform a numerical test of a relativistic heavy quark(RHQ) action, recently proposed by Tsukuba group, in quenched lattice QCD at $a\simeq 0.1$ fm. With the use of the improvement parameters previously determined at one-loop level for the RHQ action, we investigate a restoration of rotational symmetry for heavy-heavy and heavy-light meson systems around the charm quark mass. We focused on two quantities, the meson dispersion relation and the pseudo-scalar meson decay constants. It is shown that the RHQ action significantly reduces the discretization errors due to the charm quark mass. We also calculate the S-state hyperfine splittings for the charmonium and charmed-strange mesons and the $D_s$ meson decay constant. The remaining discretization errors in the physical quantities are discussed.

Microscopic derivation of the pion coupling to heavy-light mesons

The Goldberger-Treiman relation for heavy-light systems is derived in the context of a quark model. As a paradigmatic example, the case of $\overline{D}\ensuremath{\rightarrow}{\overline{D}}^{\ensuremath{'}}\ensuremath{\pi}$ is studied in detail. The fundamental role played by the pion two-component wave function, in the context of the Salpeter equation, is emphasized.

New Developments in Heavy-Light Systems

The study of the narrow excited states in the ( c s ¯ ) heavy-light system provides new insight into QCD dynamics. These effects involve the light quarks and are unaccounted for in relativistic potential models.

Heavy meson chiral perturbation theory in finite volume

We present the first step towards the estimation of finite volume effects in heavy-light meson systems using heavy meson chiral perturbation theory. We demonstrate that these effects can be amplified in both light-quark and heavy-quark mass extrapolations (interpolations) in lattice calculations. As an explicit example, we perform a one-loop calculation for the neutral B meson mixing system and show that finite volume effects, which can be comparable with currently quoted errors, are not negligible in both quenched and partially quenched QCD.

Comprehensive Four-Quark Interpretation ofDs(2317),Ds(2457), andDs(2632)

The recently observed new member of the charm-strange family D(s)(2632), which has a surprisingly narrow width, is challenging our theory. D(s)(2317) and D(s)(2457), which were observed earlier, have similar behaviors and receive various theoretical explanations. Some authors use the heavy hadron chiral effective theory to evaluate heavy-light quark systems and obtain a reasonable evaluation on the masses of D(s)(2317) and D(s)(2457). An alternative picture is to interpret them as four-quark or molecular states. In this work, we are following the latter and propose a unitive description for all three new members, D(s)(2632), D(s)(2317), and D(s)(2457), and, at least, so far our picture is consistent with the data.

Chiral multiplets of heavy-light mesons

The recent discovery of a narrow resonance in ${D}_{s}{\ensuremath{\pi}}^{0}$ by the BaBar Collaboration is consistent with the interpretation of a heavy ${J}^{P}{(0}^{+}{,1}^{+})$ spin multiplet. This system is the parity partner of the ground state ${(0}^{\ensuremath{-}}{,1}^{\ensuremath{-}})$ multiplet, which we argue is required in the implementation of ${\mathrm{SU}(3)}_{L}\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}(3)}_{R}$ chiral symmetry in heavy-light meson systems. The ${(0}^{+}{,1}^{+})\ensuremath{\rightarrow}{(0}^{\ensuremath{-}}{,1}^{\ensuremath{-}})+\ensuremath{\pi}$ transition couplings satisfy a Goldberger-Treiman relation, ${g}_{\ensuremath{\pi}}=\ensuremath{\Delta}{M/f}_{\ensuremath{\pi}},$ where $\ensuremath{\Delta}M$ is the mass gap. The BaBar resonance fits the ${0}^{+}$ state, with a kinematically blocked principal decay mode to $D+K.$ The allowed ${D}_{s}+\ensuremath{\pi},$ ${D}_{s}+2\ensuremath{\pi},$ and electromagnetic transitions are computed from the full chiral theory and found to be suppressed, consistent with the narrowness of the state. This state establishes the chiral mass difference for all such heavy-quark chiral multiplets, and precise predictions exist for the analogous ${B}_{s}$ and strange doubly heavy baryon states.

Perturbative study of anisotropic lattice actions for heavy quarks

Anisotropic lattice fermion actions are investigated with one-loop perturbative calculations aiming at constructing a formulation for a heavy quark with controlled systematic uncertainties. For heavy-light systems at rest an anisotropic lattice with small temporal lattice spacing ${a}_{t}$ suppresses the discretization error by a power of ${a}_{t}{m}_{Q}$ for a heavy quark of mass ${m}_{Q}.$ We discuss the issue of large discretization errors, which scale as ${a}_{s}{m}_{Q}$ with ${a}_{s}$ the spatial lattice spacing. By performing one-loop calculations of the speed-of-light renormalization for several possible lattice actions in the limit of ${a}_{t}\ensuremath{\rightarrow}0,$ we show that one can eliminate the large systematic error on the anisotropic lattice.

Heavy-light mesons with staggered light quarks

We demonstrate the viability of improved staggered light quarks in studies of heavy-light systems. Our method for constructing heavy-light operators exploits the close relation between naive and staggered fermions. The new approach is tested on quenched configurations using several staggered actions combined with nonrelativistic heavy quarks. Exploratory calculations of the ${B}_{s}$ meson kinetic mass, the hyperfine and $1P\mathrm{\ensuremath{-}}1S$ splittings in ${B}_{s},$ and the decay constant ${f}_{{B}_{s}}$ are presented and compared to previous quenched lattice studies. An important technical detail, Bayesian curve fitting, is discussed at length.

Heavy quark action on anisotropic lattices

We investigate the $O(a)$ improved quark action on anisotropic lattice as a potential framework for the heavy quark, which may enable precision computation of hadronic matrix elements of heavy-light mesons. The relativity relations of heavy-light mesons as well as of heavy quarkonium are examined on a quenched lattice with spatial lattice cutoff $a_\sigma^{-1} \simeq$ 1.6 GeV and the anisotropy $\xi=4$. We find that the bare anisotropy parameter tuned for the massless quark describes both the heavy-heavy and heavy-light mesons within 2% accuracy for the quark mass $a_\sigma m_Q < 0.8$, which covers the charm quark mass. This bare anisotropy parameter also successfully describes the heavy-light mesons in the quark mass region $a_\sigma m_Q \leq 1.2$ within the same accuracy. Beyond this region, the discretization effects seem to grow gradually. The anisotropic lattice is expected to extend by a factor $\xi$ the quark mass region in which the parameters in the action tuned for the massless limit are applicable for heavy-light systems with well controlled systematic errors.