A lattice study of the form factors A(0) and A(3) in the decay (B)over-bar(0)->rho(+)l(-)(nu)over-bar(l)

We report on a lattice calculation of the form factors A(0) and A(3) for the pseudoscalar to vector meson semileptonic decay (B) over bar(0) --> rho(+)l(-)(1). We find that resonant (or pole-type) contributions alone are unable to describe these two form factors simultaneously. For the quantity A(0)(q(2) = 0), which is important phenomenologically for the determination of \V-ub\, we extract a range of values, A(0)(q(2) = 0) = (0.16-0.35)(-6)(+9), where the range is due to systematic uncertainty and the quoted error is statistical. We have also determined A(2)(q(2) = 0) = 0.28(-6-5)(+9+4).

Improved B ->pi l nu(iota) 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 \V-ub\ 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(3) x 48 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.

Flavor physics in the quark sector

218 páginas, 106 figuras, 89 tablas.-- arXiv:0907.5386v2.-- Report of the CKM workshop, Rome 9-13th Sep. 2008.-- et al.

Extracting vertical bar V-ub vertical bar from B ->pi l nu decays using a multiply-subtracted Omnes dispersion relation

We use a multiply-subtracted Omnes dispersion relation for the form factor f(+) in B ->pi semileptonic decay, allowing the direct input of experimental and theoretical information to constrain its dependence on q(2), thereby improving the precision of the extracted value of vertical bar V-ub vertical bar. Apart from these inputs we use only unitarity and analyticity properties. We obtain vertical bar V-ub vertical bar=(4.02 +/- 0.35)x10(-3), improving the agreement with the value determined from inclusive methods, and competitive in precision with them.

Pion form factor from RBC and UKQCD

Andreas Juttner, P.A. Boyle, C. Kelly, C. Maynard, J.M. Zanotti, J.M. Flynn, H.P. de Lima, C.T. Sachrajda

Semileptonic B ->pi decays from an Omnes improved nonrelativistic constituent quark model

The semileptonic $B\to \pi l^+ \nu_l$ decay is studied starting from a simple quark model which includes the influence of the $B^*$ pole. To extend the predictions of a nonrelativistic constituent quark model from its region of applicability near $q^2_{\rm max}=(m_B-m_\pi)^2$ to all $q^2$ values accessible in the physical decay, we use a novel multiply-subtracted Omn\`es dispersion relation, which considerably diminishes the form factor dependence on the elastic $\pi B \to \pi B$ scattering amplitudes at high energies. By comparison to the experimental branching fraction we extract $|V_{ub}| = 0.0034 \pm 0.0003 ({\rm exp}) \pm 0.0007 ({\rm theory})$. To further test our framework, we also s…

Lattice study of the decay (B)over-bar(0)->p(+)l(-)(v)over-bar(l): Model-independent determination of vertical bar V-ub vertical bar

We present results of a lattice computation of the vector and axial-vector current matrix elements relevant for the semileptonic decay (B) over bar(0) --> rho(+)l(-)(l). The computations are performed in the quenched approximation of lattice QCD on a 24(3) x 48 lattice at beta = 6.2, using an O(a) improved fermionic action. Our principal result is for the differential decay rate, d Gamma/dq(2), for the decay (B) over bar(0) --> rho(+)l(-)(l), in a region beyond the charm endpoint, allowing a model-independent extraction of \V-ub\ from experimental measurements. Heavy quark symmetry relations between radiative and semileptonic decays of (B) over bar mesons into light vector mesons are also d…

Vertical bar V-ub vertical bar from exclusive semileptonic B ->pi decays

We use Omnes representations of the form factors f(+) and f(0) for exclusive semileptonic B -> pi decays, paying special attention to the treatment of the B* pole and its effect on f(+). We apply them to combine experimental partial branching fraction information with theoretical calculations of both form factors to extract vertical bar V-ub vertical bar. The precision we achieve is competitive with the inclusive determination and we do not find a significant discrepancy between our result. vertical bar V-ub vertical bar (3.90 +/- 0.32 +/- 0.18) x 10(-3), and the inclusive world average value, (4.45 +/- 0.20 +/- 0.26) x 10(-3).

Study of the semileptonic decays B→π, D→π and D→K

The semileptonic decay B->pi is studied starting from a simple quark model that takes into account the effect of the B* resonance. A novel, multiply subtracted, Omnes dispersion relation has been implemented to extend the predictions of the quark model to all q^2 values accesible in the physical decay. By comparison to the experimental data, we extract |V_ub|=0.0034 +/- 0.0003(exp.) +/- 0.0007(theory). As a further test of the model, we have also studied D->pi and D->K decays for which we get good agreement with experiment.

Triply heavy baryons and heavy quark spin symmetry

We study the semileptonic $b\to c$ decays of the lowest-lying triply-heavy baryons made from $b$ and $c$ quarks in the limit $m_b, m_c \gg \Lambda_\mathrm{QCD}$ and close to the zero recoil point. The separate heavy quark spin symmetries strongly constrain the matrix elements, leading to single form factors for $ccb\to ccc$, $bbc\to ccb$, and $bbb\to bbc$ baryon decays. We also study the effects on these systems of using a $Y$-shaped confinement potential, as suggested by lattice QCD results for the interaction between three static quarks.

Semileptonic bc to cc baryon decay and heavy quark spin symmetry

We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons (Xi(('*))(bc)->Xi((*))(cc) and Omega(('*))(bc)->Omega((*))(cc)), in the limit m(b),m(c)>Lambda(QCD) and close to the zero-recoil point. The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor. We recover results derived previously by White and Savage in a manner which we think is more straightforward and parallels the method applied later to study B-c semileptonic decays. We further discuss the resemblance between the bc baryon decays and those of B-c mesons to eta(c) and J/psi mesons and comment on the relation between the slopes of the si…

$b\to c$ semileptonic decay of triply heavy baryons and $c\to s,d$ semileptonic decays of ground-state $cb$ baryons

Vertical bar V-ub vertical bar from exclusive semileptonic Beta ->pi decays revisited

We update the extraction of |V-ub| from exclusive semileptonic B ->pi decays, combining experimental partial branching fraction information with theoretical form-factor calculations, using the recently revised HPQCD results for the form factors f(+) and f(0). We use Omnes representations to provide the required parametrizations of the form factors. The extracted value is |V-ub|=(3.47 +/- 0.29 +/- 0.03)x10(-3), in striking agreement with |V-ub| extracted using all other inputs in CKM fits and showing some disagreement with |V-ub| extracted from inclusive semileptonic B ->pi decays.

Elastic s-wave B pi, D pi, DK and K pi scattering from lattice calculations of scalar form factors in semileptonic decays

We show how theoretical, principally lattice calculations of the scalar form factors in semileptonic pseudoscalar-to-pseudoscalar decays can be used to extract information about the corresponding elastic s-wave scattering channels. We find values for the scattering lengths m(pi)a=0.179(17)(14), 0.26(26) and 0.29(4) for elastic s-wave isospin-1/2 K pi, B pi and D pi channels, respectively. We also determine phase shifts. For the DK channel we find hints that there is a bound state which can be identified with the recently discovered D-s0(+)(2317).

Kl3form factor withNf= 2 +1 dynamical domain wall fermions

We present the latest results from the UKQCD/RBC collaborations for the Kl3 form factor from simulations with 2 + 1 flavours of dynamical domain wall quarks. Simulations are performed on lattices with two different volumes and four values of the light quark mass, allowing for an extrapolation to the chiral limit. The analysis includes a thorough investigation into the sources of systematic error in our fits. After interpolating to zero momentum transfer, we obtain f+(0) = 0.964(5) (or ?f = -0.013(5)) which, when combined with the latest experimental results for Kl3 decays, leads to |Vus| = 0.2249(14).

Form Factors for B -> pi l nu-bar_l and B -> K* gamma Decays on the Lattice

We present a unified method for analysing form factors in B --> pi l ($) over bar nu(l) and B --> K*gamma decays. The analysis provides consistency checks on the q(2) and 1/M extrapolations necessary to obtain the physical decay rates. For the first time the q(2) dependence of the form factors is obtained at the B scale. In the B --> pi l ($) over bar nu(l) case, we show that pole fits to f(+) may not be consistent with the q(2) behaviour of f(0), leading to a possible factor of two uncertainty in the decay rate and hence in the value of /V-ub/(2) deduced from it. For B --> K*gamma, from the combined analysis of form factors T-1 and T-2, we find the hadronisation ratio R(K)* of the exclusiv…

Semileptonic bc to cc and bb to bc baryon decays and heavy quark spin symmetry

5th International Conference on Quarks and Nuclear Physics (QNP09). Inst High Energy Phys Chinese Acad Sci, Beijing, PEOPLES R CHINA, SEP 21-25, 2009