arXiv subjects

UKQCD collaboration

Publications and source records attributed to UKQCD collaboration.

8 recordsLinked to original sources

arXiv2004

First determination of the strange and light quark masses from full lattice QCD

We compute the strange quark mass $m_s$ and the average of the $u$ and $d$ quark masses $\hat m$ using full lattice QCD with three dynamical quarks combined with experimental values for the pion and kaon masses. The simulations have degenerate $u$ and $d$ quarks with masses $m_u=m_d\equiv \hat m$ as low as $m_s/8$, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the $\msbar$ scheme using perturbation theory at $O(alpha_s)$. Our results are: $m_s^\msbar$(2 GeV) = 76(0)(3)(7)(0) MeV, $\hat m^\msbar$(2 GeV) = 2.8(0)(1)(3)(0) MeV and $m_s/\hat m$ = 27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively.

hep-lat↗

arXiv2004

Sea quark effects in B_K from N_f=2 clover-improved Wilson fermions

We report calculations of the parameter B_K appearing in the Delta S=2 neutral kaon mixing matrix element, whose uncertainty limits the power of unitarity triangle constraints for testing the standard model or looking for new physics. We use two flavours of dynamical clover-improved Wilson lattice fermions and look for dependence on the dynamical quark mass at fixed lattice spacing. We see some evidence for dynamical quark effects and in particular B_K decreases as the sea quark masses are reduced towards the up/down quark mass.

hep-lat↗

arXiv2002

Excitations of the nucleon with dynamical fermions

We measure the spectrum of low-lying nucleon resonances using Bayesian fitting methods. We compare the masses obtained in the quenched approximation to those obtained with two flavours of dynamical fermions at a matched lattice spacing. At the pion masses employed in our simulations, we find that the mass of the first positive-parity nucleon excitation is always greater than that of the parity partner of the nucleon.

hep-lat↗

arXiv2001

Hadron spectroscopy of twisted mass lattice QCD at beta = 6.0

Simulations that use the clover action in quenched QCD calculations have a lower limit to the quark mass that can be reached, because of the fluctuations caused by exceptional configurations. From this low statistics study, we find that the twisted clover action, recently introduced by the ALPHA collaboration, can be used to simulate quenched QCD at quark masses below those attainable by simulations that use the clover action.

hep-lat↗

arXiv2001

The Isgur-Wise function on the lattice

The h+, h_A1 form factors for the semi-leptonic B->D and B->D* decays are evaluated in quenched lattice QCD with beta=6.2. The action and the operators are fully O(a) non-perturbatively improved. The Isgur-Wise function is evaluated and fitted to extract its slope; the latter is found to be rho^2=1.1(2)(3) from the B->D* decay and rho^2=1.0(2)(3) from the B->D decay. The form factors ratios R_1, R_2 are evaluated and found to be in agreement with experimental determinations.

hep-lat↗

arXiv2000

The unquenched Upsilon spectrum

We describe the bottomonium spectrum obtained on the UKQCD dynamical ensembles and its comparison to quenched results. We include a determination of alpha_s and m_b from the dynmaical results.

hep-lat↗

arXiv1995

Masses and decay constants of the light mesons in the quenched approximation using the tadpole--improved SW-clover action

We present results for the masses and decay constants of the light mesons in quenched QCD using the standard gluon action and a tadpole--improved SW--clover fermionic action to reduce discretisation errors. The calculation has been carried out at fixed volume and three lattice spacings corresponding to $β=5.7$, $6.0$ and $6.2$. We make comparisons with the conventional SW--clover scheme. We use our results to extract continuum limits and to quantify the size of discretisation errors at smaller $β$-values.

hep-lat↗

arXiv1992

Pure-gauge SU(2) on large lattices

We have calculated the $q\bar q$ potential over a wide range of lattice separations on a $48^3\cdot56$ lattice at $β= 2.85$. We are able to investigate both long-range and (by correcting for the effects of lack of rotational invariance) short-range potentials. From the former we estimate the string tension and from the latter we are able to investigate asymptotic scaling. Fitting to this enables us to give an estimate for the $Λ$-parameter of pure-gauge SU(2).

hep-lat↗