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UKQCD Collaboration

Publications and source records attributed to UKQCD Collaboration.

At least 73 records · Page 4Linked to original sources
arXiv2000

Leptonic and semi-leptonic B decays

We present results for the semi-leptonic and leptonic decays of B mesons. These non-perturbative matrix elements are important for constraining the CKM matrix. Results are presented for the pseudoscalar and vector decay constants, as well as flavour breaking ratios and heavy quark symmetry relations. We consider the chiral and momentum dependence of the semi-leptonic form factors of the decay B-> pi l nu and the soft pion relation (SPR) on the lattice. These calculations were performed in the quenched approximation at two values of the coupling with non-perturbatively order a improved action and currents.

hep-lat↗
arXiv2000

The radial wavefunctions of a heavy-light meson calculated on a lattice

A brief review is given of attempts to understand the energies of four-quark systems calculated on a lattice in terms of nuclear-physics-inspired many-body techniques involving interquark potentials. Results are given for the next stage of this study where the wavefunctions of heavy-light mesons are also calculated on a lattice.

hep-lat↗
arXiv2000

The topological susceptibility and pion decay constant from lattice QCD

We study the topological susceptibility, chi, in two flavour lattice QCD. We find clear evidence for the expected suppression of chi at small quark mass. The estimate of the pion decay constant, f_pi = 105 +/-5 +18/-10 MeV, is consistent with the experimental value of approximately 93 MeV. We compare chi to the large-N_c prediction and find consistency over a large range of quark masses.

hep-lat↗
arXiv2000

Improved B -> pi l nu_l form factors from the lattice

We present the results of a lattice computation of the form factors for B^0 ->pi^- l^+nu_l decays near zero-recoil. These results will allow a determination of the CKM matrix element |Vub| when measurements of the differential decay rate become available. We also provide models for extrapolation of the form factors and rate to the full recoil range. Our computation is performed in the quenched approximation to QCD on a 24^3x48 lattice at beta=6.2, using a non-perturbatively O(a)-improved action. The masses of all light valence quarks involved are extrapolated to their physical values.

hep-lat↗
arXiv2000

Instability in the Molecular Dynamics Step of Hybrid Monte Carlo in Dynamical Fermion Lattice QCD Simulations

We investigate instability and reversibility within Hybrid Monte Carlo simulations using a non-perturbatively improved Wilson action. We demonstrate the onset of instability as tolerance parameters and molecular dynamics step sizes are varied. We compare these findings with theoretical expectations and present limits on simulation parameters within which a stable and reversible algorithm is obtained for physically relevant simulations. Results of optimisation experiments with respect to tolerance prarameters are also presented.

hep-lat↗
arXiv2000

Quenched QCD with O(a) improvement: I. The spectrum of light hadrons

We present a comprehensive study of the masses of pseudoscalar and vector mesons, as well as octet and decuplet baryons computed in O(a) improved quenched lattice QCD. Results have been obtained using the non-perturbative definition of the improvement coefficient c_sw, and also its estimate in tadpole improved perturbation theory. We investigate effects of improvement on the incidence of exceptional configurations, mass splittings and the parameter J. By combining the results obtained using non-perturbative and tadpole improvement in a simultaneous continuum extrapolation we can compare our spectral data to experiment. We confirm earlier findings by the CP-PACS Collaboration that the quenched light hadron spectrum agrees with experiment at the 10% level.

hep-lat↗
arXiv2000

String breaking in zero-temperature lattice QCD

The crossing from a static quark-antiquark system to a system of two static-light mesons when the separation of the static quarks is increased is calculated in zero-temperature lattice QCD. The mixing of these two states is extracted from the lattice operators. We also discuss the breaking of an excited string of a hybrid meson.

hep-lat↗
arXiv1999

Techniques for using the overlap-Dirac operator to calculate hadron spectroscopy

We report on our progress in using the overlap-Dirac fermion operator in simulations of lattice QCD. We have investigated the Lanczos based method of Borici, as well as various rational approximations, to calculate the step function in the overlap-Dirac operator. The QCD simulations were performed at beta = 5.85 with a lattice volume of 8**3*32.

hep-lat↗
arXiv1999

An Investigation of the Soft Pion Relation in Quenched Lattice QCD

A lattice determination of the form factor and decay constants for the semileptonic decay of heavy pseudoscalar (PS) mesons at zero recoil is presented from which the soft pion relation is satisfied. Chiral extrapolation of the form factor is performed at constant $q^2$. Pole dominance is used to extrapolate the form factor in heavy quark mass. At the B mass, the form factor at zero recoil lies somewhat below the ratio of decay constants; the relation remains satisfied within error.

hep-lat↗
arXiv1999

The Isgur Wise function from the Lattice

We derive the form factors relevant for decays of pseudo-scalar mesons corresponding to the semi-leptonic decay B->D l nu. The simulations are performed in the quenched approximation at beta=6.0 and beta=6.2 using a non-perturbatively improved clover action. The slope of the Isgur Wise function and |Vcb| are extracted from the form factors.

hep-lat↗
arXiv1999

Determination of Vub from B->pi l nu on the lattice

We present results of a lattice study of the form factors in the decay B-> pi l nu. We attempt to disentangle the the dependence of the form factors on the light quark masses and the momentum transfer. Using models of the q^2 dependence we calculate the total decay rate, and compare to the experimental measure to extract Vub. This study was performed in the quenched approximation at beta=6.2 on a 24^3 X 48 lattice, with a non-perturbatively improved SW fermion action.

hep-lat↗
arXiv1999

Flavour-singlet pseudoscalar and scalar mesons

We measure correlations appropriate for favour-singlet mesons using dynamical quark configurations from UKQCD. Improved methods of evaluating the disconnected quark diagrams are presented. The scalar and pseudoscalar meson channels are explored, with special reference to the mixing of scalar mesons with scalar glueballs.

hep-lat↗
arXiv1999

A non-perturbative calculation of the mass of the Bc

We present a calculation of the mass of the 1S0 pseudoscalar anti-b c (Bc) state using a non-perturbative measurement from quenched lattice QCD. We find M_Bc = 6.386(9)(98)(15) GeV where the first error is statistical, the second systematic due to the quark mass ambiguities and quenching and the third the systematic error due to the estimation of mass of the eta_b.

hep-lat↗
arXiv1999

Semi-leptonic decays of heavy mesons

We present results of a lattice computation of the matrix elements of the vector currents which are relevant for the semileptonic decays of D to K, D to pi and B to pi. The computations are performed in the quenched approximation on a 24^3x48 lattice at beta=6.2, using an O(a) non-perturbatively improved fermionic action.

hep-lat↗
arXiv1999

Two heavy-light mesons on a lattice

The potential between two heavy-light mesons as a function of the heavy quark separation is calculated in quenched SU(3) lattice QCD. We study the case of heavy-light mesons with a static heavy quark and light quarks of mass close to the strange quark mass. We explore the case of light quarks with the same and with different flavours, classified according to the light quark isospin. We evaluate the appropriate light quark exchange contributions and explore the spin-dependence of the interaction. Comparison is made with meson exchange.

hep-lat↗
arXiv1998

Hadrons with a heavy colour-adjoint particle

We discuss the spectrum of hadrons with a heavy colour-adjoint particle - motivated by the gluino of supersymmetry. Using the lattice approach, we explore in detail the gluonic bound states - the `glueballino' or `gluelump'. We also make a first determination of the spectrum of the `adjoint mesons' - which have a light quark and antiquark bound to the heavy adjoint particle. A comparison of the spectra of these two systems is also made.

hep-lat↗
arXiv1998

Quark mass dependence of hadron masses from lattice QCD

We discuss lattice methods to obtain the derivatives of a lattice meson mass with respect to the bare sea and valence quark masses. Applications are made to quenched and dynamical fermion configurations. We find evidence for significant differences between quenched and dynamical fermion configurations. We discuss how to relate dependence on the bare lattice parameters to more phenomenologically useful quantities.

hep-lat↗