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Laurent Lellouch

Publications and source records attributed to Laurent Lellouch.

53 records · Page 3Linked to original sources
arXiv2000

Weak transition matrix elements from finite-volume correlation functions

The two-body decay rate of a weakly decaying particle (such as the kaon) is shown to be proportional to the square of a well-defined transition matrix element in finite volume. Contrary to the physical amplitude, the latter can be extracted from finite-volume correlation functions in euclidean space without analytic continuation. The K -> pi pi transitions and other non-leptonic decays thus become accessible to established numerical techniques in lattice QCD.

hep-lat↗
arXiv2000

Neutral B Meson Mixing and Decay Constants from Lattice QCD

We present updates of our results for neutral $B$-meson mixing and leptonic decay constants obtained in the quenched approximation from a mean-field-improved Sheikholeslami-Wohlert action at two values of lattice spacing. We consider quantities such as $B_{B_{d(s)}}$, $f_{D_{(s)}}$, $f_{B_{(s)}}$ and the full $ΔB=2$ matrix-elements, as well as the corresponding SU(3)-breaking ratios.

hep-ph↗
arXiv2000

Neutral B Meson Mixing and Heavy-light Decay Constants from Quenched Lattice QCD

We present high-statistics results for neutral $B$-meson mixing and heavy-light-meson leptonic decays in the quenched approximation from tadpole-improved clover actions at $β= 6.0$ and $β= 6.2$. We consider quantities such as $B_{B_{d(s)}}$, $f_{D_{d(s)}}$, $f_{B_{d(s)}}$ and the full $ΔB=2$ matrix elements as well as the corresponding SU(3)-breaking ratios. These quantities are important for determining the CKM matrix element $|V_{td}|$.

hep-lat↗
arXiv1999

Chiral symmetry breaking from Ginsparg-Wilson fermions

We calculate the large-volume and small-mass dependences of the quark condensate in quenched QCD using Neuberger's operator. We find good agreement with the predictions of quenched chiral perturbation theory, enabling a determination of the chiral lagrangian parameter Σ, up to a multiplicative renormalization.

hep-lat↗
arXiv1998

Delta S=2 and Delta I=3/2 Matrix Elements in Quenched QCD

We present preliminary results for B_K, B_7^{3/2} and B_8^{3/2} from two high-statistics lattice computations. These calculations are performed at beta=6.0 and 6.2 in the quenched approximation, using mean-field-improved Sheikholeslami-Wohlert fermionic actions.

hep-lat↗
arXiv1997

Lattice-Constrained Parametrizations of Form Factors for Semileptonic and Rare Radiative B Decays

We describe the form factors for B to rho lepton neutrino and B to K* gamma decays with just two parameters and the two form factors for B to pi lepton neutrino with a further two or three parameters. The parametrizations are consistent with heavy quark symmetry, kinematic constraints and lattice results, which we use to determine the parameters. In addition, we test versions of the parametrizations consistent (or not) with light-cone sum rule scaling relations at q^2=0.

hep-lat↗
arXiv1996

Semileptonic $B \to ρ$ and $B \to π$ Decays: Lattice and Dispersive Constraints

I present two recent pieces of work on semileptonic $B \to π, ρ$ decays where it is shown how lattice QCD calculations can be used to test heavy-quark symmetry and determine phenomenologically relevant quantities despite the limits on these calculations' kinematical reach. The study of semileptonic $B \to ρ$ decays was performed with the UKQCD Collaboration.

hep-ph↗
arXiv1996

Lattice-Constrained Unitarity Bounds for $\bar B^0 \to π^+ l^- \bar ν_l$ Decays

Lattice results, kinematical constraints and QCD dispersion relations are combined for the first time to derive model-independent bounds for QCD form factors and corresponding rates. To take into account the error bars on the lattice results we develop a general formalism which ascribes well-defined statistical properties to these bounds. We concentrate on $\bar B^0 \to π^+ l^- \barν_l$ decays because of the relative simplicity of the analytical behavior of the relevant polarization functions and because of their immediate phenomenological relevance. To determine the range of applicability of the dispersive matching required to obtain the bounds, we have evaluated the leading perturbative and non-perturbative QCD corrections to the relevant polarization functions. Despite the lattice results' large error bars and limited kinematical range, the bounds we obtain appear to favor certain parametrizations for the form factors over others. The bounds also enable the determination of $|V_{ub}|$ from the total experimental rate with a theoretical error ranging from 27% to 37%, depending on the assumptions made. The techniques developed here are, in fact, quite general and are not limited to use with lattice results nor to semileptonic $\bar B^0 \to π^+ l^- \barν_l$ decays.

hep-ph↗
arXiv1995

Semileptonic $B\to D$ and $B\to D^*$ Decays from the Lattice

We obtain form factors relevant for semileptonic $B\to D$ and $B\to D^*$ decays from a quenched lattice QCD calculation. Our results enable us to test Heavy-Quark Symmetry, determine the Isgur-Wise function as well as obtain the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{cb}$ from a measurement, by the CLEO collaboration, of the differential decay rate for semileptonic $B\to D^*$ decays. We find that the Isgur-Wise function has a slope of $-(0.9\er{4}{4})$ at zero recoil and that $|V_{cb}|K(1)=0.037\er{1}{1}\er{4}{2}\; (0.99/(1+\b_{A_1}(1)))$, where the first set of errors is due to experimental uncertainties and the second to our errors on $ρ^2$. Here $K(1)$ and $\b_{A_1}(1)$ denote respectively power and radiative corrections at zero recoil.

hep-ph↗
arXiv1994

Weak Decays of $B$ Mesons and Lattice QCD

After a pedagogical introduction to the calculation of weak matrix elements on the lattice, I review some of the lattice's most recent predictions concerning the weak decays of $B$-mesons. Amongst the topics covered are the determinations of the leptonic decay constant $f_B$, of the form factors relevant for semi-leptonic $B\to D(D^*)\ell\barν$ decays and of the hadronic matrix element which describes the rare decay $B\to K^*γ$. Emphasis is placed on the results of the UKQCD Collaboration. Corrections to the heavy-quark limit are discussed extensively.

hep-ph↗
arXiv1994

Semi-Leptonic Decays of $B$-Mesons

Form factors relevant for semi-leptonic $B\to D,\ D^*$ decays are obtained in quenched lattice QCD. Tests of heavy-quark symmetry as well as determinations of the Isgur-Wise function and $|V_{cb}|$ are presented.

hep-lat↗
arXiv1993

The Isgur-Wise Function from the Lattice

We calculate the Isgur-Wise function by measuring the elastic scattering amplitude of a $D$ meson in the quenched approximation on a $24^3\times48$ lattice at $β=6.2$, using an $O(a)$-improved fermion action. We use this result, in conjunction with heavy-quark symmetry, to extract $|V_{cb}|$ from the experimentally measured $\bar B\to D^*l\barν\,$\ differential decay width.

hep-ph↗
arXiv1993

The Rate for $e^+e^-\to B B^\pm π^\mp$ and its Implications for the Study of CP Violation, $B_s$ Identification, and the Study of $B$ Meson Chiral Perturbation Theory

H.~Yamamoto has proposed employing $B$ mesons produced in conjunction with a single charged pion at an $Υ$ resonance for studies of CP violation in the neutral $B$ meson system at a symmetric $e^+$-$e^-$ collider. The sign of the charged pion would tag the neutral $B$ meson. We estimate this branching ratio, employing the heavy meson chiral effective field theory. We find a negligible branching ratio to $B B^{\pm} π^{\mp}$ at the $Υ$(5S) and a branching ratio of only a few percent at the $Υ$(6S). However, if nonresonant studies of neutral $B$ mesons should prove feasible, Yamamoto's proposal could be a good method for tagging neutral $B$'s for the study of CP violation at a symmetric collider. We also explore the possibility of studying $B_s$ at the $Υ$(5S). The rate is low but depends sensitively on the precise value of the mass of the $B_s$. The background we compute is comparable to the rate at the largest allowed value of the $B_s$ mass. Finally, we discuss the extraction of the axial pion coupling to $B$ mesons from measurement of the $B\bbarπ$ branching fraction in a restricted region of phase space, where chiral perturbation theory should work well.

hep-ph↗