Article

# Semileptonic form factors D \rightarrow \pi, K and B \rightarrow \pi, K from a fine lattice

• ##### A. Schäfer
ETH Zürich Institute for Theoretical Physics 8093 Zürich Switzerland; Deutsches Elektronen-Synchrotron DESY 22603 Hamburg Germany
European Physical Journal A (Impact Factor: 2.04). 43(1). DOI: 10.1140/epja/i2009-10893-3
Source: OAI

ABSTRACT We extract the form factors relevant for semileptonic decays of D and B mesons from a relativistic computation on a fine lattice in the quenched approximation. The lattice spacing is a = 0.04 fm (corresponding to a
-1 = 4.97 GeV), which allows us to run very close to the physical B meson mass, and to reduce the systematic errors associated with the extrapolation in terms of a heavy-quark expansion. For decays of D and Ds mesons, our results for the physical form factors at

$\ensuremath q^2 = 0$
are as follows:

$\ensuremath f_+^{D\rightarrow\pi}(0) = 0.74(6)(4)$
,

$\ensuremath f_+^{D \rightarrow K}(0) = 0.78(5)(4)$
and

$\ensuremath f_+^{D_s \rightarrow K} (0) = 0.68(4)(3)$
. Similarly, for B and Bs we find

$\ensuremath f_+^{B\rightarrow\pi}(0) = 0.27(7)(5)$
,

$\ensuremath f_+^{B\rightarrow K} (0) = 0.32(6)(6)$
and

$\ensuremath f_+^{B_s\rightarrow K}(0) = 0.23(5)(4)$
. We compare our results with other quenched and unquenched lattice calculations, as well as with light-cone sum rule predictions, finding good agreement.

1 Bookmark
·
120 Views
• Source
##### Article: Rare decay B→Kℓ^{+}ℓ^{-} form factors from lattice QCD
[Hide abstract]
ABSTRACT: We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay B→Kℓ^{+}ℓ^{-} in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks and the highly improved staggered quark formulation for the light valence quarks. We employ the MILC 2+1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q^{2}. We construct the ratios f_{0}/f_{+} and f_{T}/f_{+}, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables.
Physical Review D 09/2013; 88(5). · 4.69 Impact Factor
• Source
##### Article: Standard Model predictions for B -> Kll with form factors from lattice QCD
[Hide abstract]
ABSTRACT: We calculate, for the first time using unquenched lattice QCD form factors, the Standard Model differential branching fractions $dB/dq^2(B \to Kll)$ for $l=e, \mu, \tau$ and compare with experimental measurements by Belle, BABAR, CDF, and LHCb. We report on $\mathcal{B}(B \to Kll)$ in $q^2$ bins used by experiment and predict $\mathcal{B}(B \to K \tau \tau) = (1.41 \pm 0.15) 10^{-7}$. We also calculate the ratio of branching fractions $R^\mu_e = 1.00029(69)$ and predict $R^\tau_l = 1.176(40)$, for $l=e, \mu$. Finally, we calculate the "flat term" in the angular distribution of the differential decay rate $F_H^{e, \mu, \tau}$ in experimentally motivated $q^2$ bins.
Physical Review Letters 06/2013; 111(16). · 7.73 Impact Factor
• Source
##### Article: Determination of the pion distribution amplitude
[Hide abstract]
ABSTRACT: Right now, we have not enough knowledge to determine the hadron distribution amplitudes (DAs) which are universal physical quantities in the high energy processes involving hadron for applying pQCD to exclusive processes. Even for the simplest pion, one can't discriminate from different DA models. Inversely, one expects that processes involving pion can in principle provide strong constraints on the pion DA. For example, the pion-photon transition form factor (TFF) can get accurate information of the pion wave function or DA, due to the single pion in this process. However, the data from Belle and BABAR have a big difference on TFF in high $Q^2$ regions, at present, they are helpless for determining the pion DA. At the present paper, we think it is still possible to determine the pion DA as long as we perform a combined analysis of the most existing data of the processes involving pion such as $\pi \to \mu \bar{\nu}$, $\pi^0 \to \gamma \gamma$, $B\to \pi l \nu$, $D \to \pi l \nu$, and etc. Based on the revised light-cone harmonic oscillator model, a convenient DA model has been suggested, whose parameter $B$ which dominates its longitudinal behavior for $\phi_{\pi}(x,\mu^2)$ can be determined in a definite range by those processes. A light-cone sum rule analysis of the semi-leptonic processes $B \to \pi l \nu$ and $D \to \pi l \nu$ leads to a narrow region $B = [0.01,0.14]$, which indicate a slight deviation from the asymptotic DA. Then, one can predict the behavior of the pion-photon TFF in high $Q^2$ regions which can be tested in the future experiments. Following this way it provides the possibility that the pion DA will be determined by the global fit finally.
Physical Review D 05/2013; 88(3). · 4.69 Impact Factor