NRQCD Heavy Quarks Research Articles

More on heavy tetraquarks in lattice QCD at almost physical pion mass

We report on our progress in studying exotic, heavy tetraquark states, qq′ Q̅Q̅′. Using publicly available dynamical nf = 2 + 1 Wilson-Clover gauge configurations, generated by the PACS-CS collaboration, with pion masses ≃ 164, 299 and 415 MeV, we extend our previous analysis to heavy quark components containing heavier than physical bottom quarks Q̅Q̅′ = b̅′b̅′ or Q̅Q̅′ = b̅b̅′, charm and bottom quarks c̅b̅ and also only charm quarks c̅ c̅. Throughout we employ NRQCD and relativistic heavy quarks for the heavier than bottom, bottom and charm quarks. Using our previously established diquark-antidiquark and meson-meson operator basis we comment in particular on the dependence of the binding energy on the mass of the heavy quark component Q̅Q̅, with heavy quarks ranging from mQ = 0:85… 6.3 · mb. In the heavy flavor non-degenerate case, Q̅Q̅′, and especially for the tetraquark channel udc̅d̅, we extend our work to utilize a 3 × 3 GEVP to study the ground and threshold states thereby enabling a clear identification of possible binding. Finally, we present initial work on the Q̅Q̅′ = c̅c̅ system where a much larger operator basis is available in comparison to flavor combinations with NRQCD quarks.

Semileptonic B Decays with [formula omitted] Dynamical Quarks

Semileptonic, B --> pi l,nu, decays are studied on the MILC dynamical configurations using NRQCD heavy and Asqtad light quarks. We work with light valence quark masses ranging between m_s and m_s/8. Preliminary simple linear chiral extrapolations have been carried out for form factors f_para and f_perp at fixed E_pi. The chirally extrapolated results for the form factors f_+(q^2) and f_0(q^2) are then fit to the Becirevic-Kaidalov (BK) ansatz. Preliminary estimates of the CKM matrix element |V_{ub}| are presented based on the recently published branching fractions for B exclusive semileptonic decays by the CLEO collaboration.

Heavy-light meson semileptonic decays with staggered light quarks

We report on exploratory studies of heavy-light meson semileptonic decays using Asqtad light quarks, NRQCD heavy quarks and Symanzik improved glue on coarse quenched lattices. Oscillatory contributions to three-point correlators coming from the staggered light quarks are found to be handled well by Bayesian fitting methods. B meson decays to both the Goldstone pion and to one of the point-split non-Goldstone pions are investigated. One-loop perturbative matching of NRQCD/Asqtad heavy-light currents is incorporated.

Semileptonic B decays from an NRQCD/D234 action

Semileptonic B decays are studied on quenched anisotropic lattices using Symanzik improved glue, NRQCD heavy quark and D234 light quark actions. We employ constrained fits to extract ground state contributions to two- and three-point correlators. Results for the B → π, lν¯decay form factors are compared with previous lattice results. We find that our systematic errors (excluding quenching errors) are dominated by chiral extrapolation uncertainties.

SemileptonicBdecays from a NRQCD and D234 action

Semileptonic, B --> pi, l nubar, decays are studied on quenched anisotropic lattices using tree-level tadpole improved Symanzik glue, NRQCD heavy quark and D234 light quark actions. Constrained fitting methods are applied to extract groundstate contributions to two-point and three-point correlators. We agree with previous lattice determinations of the form factors. The major source of systematic error here, as in previous work, comes from the chiral extrapolation to the physical pion mass. Future calculations must work at lighter quark masses to resolve this.

Can one study heavy meson semileptonic decays on coarse anisotropic lattices?

Exploratory studies of heavy meson semileptonic decays on coarse lattices using Symanzik improved glue, NRQCD heavy and D234 light quarks are discussed. Comparisons are made between calculations on anisotropic and isotropic lattices. We find evidence that having an anisotropy helps in extracting better signals at higher momenta.

Perturbative renormalization of the Δ B = 2 four-quark operators in lattice NRQCD

We present a perturbative calculation of the renormalization constants for the Δ B = 2 four-quark operators, which is needed to evaluate the bag parameters B B and B S in lattice QCD. The one-loop coefficients are calculated for the O(1/ M) NRQCD heavy quark action and the O( a)-improved Wilson action for light quark. Using these coefficients, which remove O(α s / aM) error, we reanalyze our previous calculation of the bag parameters.

Scaling and further tests of heavy meson decay constant determinations from nonrelativistic QCD

We present results for the B_s meson decay constant f_{B_s} from simulations at three lattice spacings in the range a^{-1}=1.1 to 2.6 GeV using NRQCD heavy quarks and clover light quarks in the quenched approximation. We study scaling of this quantity and check the consistency between mesons decaying from rest and from a state with nonzero spatial momentum. The cancellation of power law contributions that arise in the NRQCD formulation of heavy-light currents is discussed. On the coarsest lattice the D_s meson decay constant f_{D_s} is calculated. Our best values for the decay constants are given by f_{B_s} = 187(4)(4)(11)(2)(7)(6) MeV and f_{D_s} = 223(6)(31)(38)(23)(9)(^{+3}_{-1}) MeV.

Formula omitted] Form factors with NRQCD heavy quark and clover light quark actions

We report results on semileptonic B → πl v decay form factors near q max 2 using NRQCD heavy quark and clover light quark actions and currents improved through O(α a). An inconsistency with the soft pion relation f 0 ( q max 2 = f B / f π found in a previous work is confirmed, and a possible solution with nonperturbative renormalization is discussed. We find that f +( q 2) is well described by the B ∗ pole near q max 2, and its 1/ M B scaling is also consistent with the prediction of the pole dominance model.

Heavy-light spectrum and decay constant from NRQCD with two flavors of dynamical quarks

We report on a study of B mesons on N f = 2 full QCD configurations using an RG-improved gauge action, NRQCD heavy quark action and tadpole-improved clover light quark action. Results on the heavy-light spectrum and the decay constants from 16 3 × 32 lattices at a −1 ≈ 1.5 GeV are presented, and compared with quenched results obtained with the same action combination at matching lattice spacings.

Semi-leptonic decays heavy-light to heavy-light

We present results for the QCD matrix elements involved in semi-leptonic decays of B-mesons into pseudo scalar heavy light states. The application of NRQCD heavy quarks allows for quark masses around the physical b-quark. We investigate the dependence of the form factors on the external momenta and looked at the mass dependence at zero recoil. For the first time, results for radially excited decay products are presented.

Heavy-light spectrum and decay constant from NRQCD with two flavors of dynamical quarks

We report on a study of B mesons on N_f = 2 full QCD configurations using an RG-improved gauge action, NRQCD heavy quark action and tadpole-improved clover light quark action. Results on the heavy-light spectrum and the decay constants from 16^3x32 lattices at a^{-1} ~ 1.5 GeV are presented, and compared with quenched results obtained with the same action combination at matching lattice spacings.

Perturbative matching of lattice and continuum heavy-light currents with NRQCD heavy quarks

The temporal and spatial components of the heavy-light vector current and the spatial components of the axial current are expressed in terms of lattice-regulated operators suitable for simulations of B and D mesons. The currents are constructed by matching the appropriate scattering amplitudes in continuum QCD and a lattice model to one-loop order in perturbation theory. In the lattice theory, the heavy quarks are treated using the nonrelativistic (NRQCD) formulation and the light quarks are described by the tadpole-improved clover action. The light quarks are treated as massless. Our currents include relativistic and discretization corrections through O(alpha_s/M, a alpha_s), where M is the heavy-quark mass, a is the lattice spacing, and alpha_s is the QCD coupling. As in our previous construction of the temporal component of the heavy-light axial current, mixing between several lattice operators is encountered at one-loop order, and O(a alpha_s) dimension-four improvement terms are identified.

Perturbative matching of heavy-light currents with NRQCD heavy quarks

We present further results for one-loop matching of heavy-light axial and vector currents between continuum QCD and a lattice theory with NRQCD heavy quarks and massless clover quarks.

Scaling behavior of f B with NRQCD

We investigate the scaling behavior of the B meson decay constant f B and f B s , at β=5.7, 5.9, 6.1, employing the NRQCD heavy quark action and the clover light quark action. Mixing effect from dimension-4 operator in the heavy-light axial-vector current is studied, and we find that the a dependence of f B is significantly reduced. Our preliminary result for the decay constants in the quenched approximation is f B =162( +35 −18) MeV, f B s =190( +40 −19) MeV, and f B s / f B =1.18( +6 −6).

First study of B → π semileptonic decay form factors using NRQCD

We present a quenched calculation of the form factors of the semileptonic weak decay B → πl ν with O(1/ m Q ) NRQCD heavy quark and Wilson light quark on a 16 3 × 32 lattice at β = 5.8. The form factors are evaluated at six heavy quark masses, in the range of m Q ∼ 1.5 – 8 GeV. 1/ m Q dependence of matrix elements are investigated and compared with HQET predictions. We observed clear signal for the form factors near q max 2, even at the b-quark mass range. f 0( q max 2) is compared with f B f π based on the soft poin theorem and significant difference is observed.

Bdecay constants from NRQCD with dynamical fermions

We present a lattice investigation of the heavy-light meson decay constants using Wilson light quarks and NRQCD heavy quarks, partially including the effects of dynamical sea quarks. We calculate the pseudoscalar and vector decay constants over a wide range in heavy quark mass and are able to perform a detailed analysis of heavy quark symmetry. We find consistency between the extrapolation of the NRQCD results and the static case, as expected. We find the slope of the decay constants with $1/M$ is significantly larger than naive expectations and the results of previous lattice calculations. For the first time we extract the non-perturbative coefficients of the slope arising from the $O(1/M)$ heavy quark interactions separately and show the kinetic energy of the heavy quark is dominant and responsible for the large slope. In addition, we find that significant systematic errors remain in the decay constant extracted around the $B$ meson mass due to truncating the NRQCD series at $O(1/M)$. We estimate the higher order contributions to $f_B$ are approximately $20\%$; roughly the same size as the systematic errors introduced by using the Wilson action for light quarks.

B physics from NRQCD with dynamical fermions

We present {\it preliminary} results for the spectrum and decay constants of B mesons using NRQCD heavy and Wilson light quarks on configurations at $\beta=5.6$ with two dynamical flavours of staggered fermions. All terms to order $1/M_Q$ are included in the NRQCD action; matrix elements are corrected to this order by calculating the small components of the heavy quark propagator.