'Bs --> Ds l nu' near zero recoil in and beyond the Standard Model

We compute the normalization of the form factor entering the Bs --> Ds l nu decay amplitude by using numerical simulations of QCD on the lattice. From our study with Nf=2 dynamical light quarks, and by employing the maximally twisted Wilson quark action, we obtain in the continuum limit G(1) = 1.052(46). We also compute the scalar and tensor form factors in the region near zero recoil and find f0(t0)/f+(t0)=0.77(2), fT(t0,mb)/f+(t0)=1.08(7), for t0=11.5 GeV^2. These latter results are useful for searching the effects of physics beyond the Standard Model in Bs --> Ds l nu decays. Our results for the similar form factors relevant to the non-strange case indicate that the method employed here can be used to achieve the precision determination of the B --> D l nu decay amplitude as well.Comment: 17 pages (6 tables, 6 plots), published versio

The controversy about "1/m_Q duality violation" ; a quark model point of view

A detailed discussion based on exact calculations, possible in the non relativistic quark model, is given to show that there is no 1/m_Q term in the heavy quark expansion of totally integrated semileptonic decay rates. More generally, it is shown that OPE holds with very few terms in the expansion, at least in the harmonic oscillator model.Comment: 10 pages, full articl

Semileptonic B decays into charmed D (**) mesons from lattice QCD

Les désintégrations semileptoniques du méson $B$ participent à la détermination de certains paramètres fondamentaux du Modèle Standard. Ce travail décrit essentiellement l'étude des deux canaux de désintégrations $B_s \to D_s \ell \bar\nu_\ell$ et $B\to D^{**} \ell\bar\nu_\ell$ (où les $D^{**}$ sont les premières excitations orbitales des mésons $D$ ayant une parité positive). Le cadre théorique est celui de la QCD sur réseau qui, en discrétisant l'espace-temps, permet de calculer non perturbativement les fonctions de Green de la théorie. En utilisant l'action à masse twistée avec deux saveurs dégénérées de quarks dynamiques ($N_f=2$), nous avons commencé par étudier la spectroscopie des états charmés scalaires $D_0^*$ et tenseurs $D_2^*$. Ensuite, nous avons réalisé la détermination du facteur de forme $G_s(1)$ décrivant le processus $B_s\to D_s \ell \bar\nu_\ell$ dans le Modèle Standard. Ce paramètre offre un moyen d'extraire l'élément de la matrice CKM $V_{cb}$. Par ailleurs, et pour la première fois en QCD sur réseau, nous avons déterminé les rapports $F_0(q^2)/F_+(q^2)$ et $F_T(q^2)/F_+(q^2)$ dans la région proche du recul nul: ces contributions sont en effet nécessaires afin de discuter ce canal de désintégration dans certains modèles au-delà du Modèle Standard. Enfin, une étude préliminaire du canal de désintégration $B\to D^{**}$ a été abordée où nous avons trouvé une valeur non nulle de l'élément de matrice décrivant la désintégration $B\to D_0^*$ à recul nul contrairement de ce qui est connu à la limite des quarks lourds. Dans le cas du $B \to D_2^*$, nos résultats ont montré un signal indiquant une différence par rapport aux prédictions de masse infinie. Ces calculs sont indispensables afin de tirer une conclusion plus solide concernant le puzzle 1/2 vs 3/2''.Semileptonic decays of $B$ mesons provide a rich source of knowledge for determining fundamental parameters of the Standard Model. This work reports mainly on the study of two semileptonic decay channels: the $B_s \to D_s \ell\bar\nu_\ell$ and $B\to D^{**} \ell\bar\nu_\ell$ (where the $D^{**}$ are the first orbitally excited states of the $D$ mesons having a positive parity). The theoretical framework is Lattice QCD which is considered as the only satisfying approach which calculates in a non perturbative way the transition amplitudes from first principles. By using the twisted mass QCD on the lattice with $N_f = 2$ dynamical flavors we studied, first, the spectroscopy of the scalar $D_0^*$ and the tensor $D_2^*$ states. Then, we determined the normalization $G_s(1)$ of the form factor dominating $B_s \to D_s \ell \bar\nu_\ell$ in the Standard Model which provides a means of extracting the CKM matrix element $V_{cb}$. Next, we make the first lattice determination of $F_0(q^2)/F_+(q^2)$ and $F_T(q^2)/F_+(q^2)$ near the zero recoil. The obtained results are important for the discussion of this decay in various scenarios of physics beyond the Standard Model. Finally, we did a preliminary study of $B\to D^{**}$ where we have obtained a non vanishing matrix element corresponding to the decay of $B$ into the $D_0^*$ at zero recoil contrary to what was known in the heavy quark limit. Moreover, the computations corresponding to $B\to D_2^*$ show a signal indicating a difference with respect to the infinite mass limit prediction. These results are important to draw a firm conclusion on the 1/2 vs 3/2 puzzle''.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Testing OPE for ghosts, gluons and αs\alpha_s

We present here our results on extracting Wilson coefficients from different quantities such as ghost and gluon propagators which are calculated by means of Lattice QCD. The results confirm the validity of our method for the calculation of the strong coupling constant as well as allow to estimate the range of momenta where OPE is applicable.Comment: arXiv admin note: substantial text overlap with arXiv:1301.759

Quantitative predictions for B semileptonic decays into D, D*, and the orbitally excited D** in quark models in the manner of Bakamjian and Thomas

Once chosen the dynamics in one frame, the rest frame in this paper, the Bakamjian and Thomas method allows to define relativistic quark models in any frame. These models have been shown to provide, in the infinite quark mass limit, fully covariant current form factors as matrix elements of the quark current operator. In this paper we use the rest frame dynamics fitted from the meson spectrum by various authors, already shown to provide a reasonable value for $\rho^2$. From the general formulae for the scaling invariant form factors $\xi^{(n)}(w)$, $\tau_{1/2}^{(n)}(w)$ and $\tau_{3/2}^{(n)}(w)$, we predict quantitavely the $B$ semileptonic branching ratios to the ground state and orbitally excited charmed mesons $D, D^\ast$ and $D^{\ast\ast}$. We check Bjorken's sum rule and discuss the respective contributions to it. We find $\xi(w)\simeq (2/(1+w)) ^2$, resulting from the fact that the ground state wave function is Coulomb-like. We also find $\tau_{3/2}\simeq 0.5 (2/(1+w))^3$ and $\tau_{1/2}(w)\ll \tau_{3/2}(w)$. Very small branching ratios into $j=1/2$ orbitally excited $D$'s results. The overall agreement with experiment is rather good within the present accuracy which is poor for the orbitally excited charmed mesons. We predict a ratio $Br(B\to D^\ast_2 l \nu)/Br(B\to D_1 l \nu)=1.55\pm 0.15$ as a mere consequence of the heavy quark symmetry. If some faint experimental indications that $Br(B\to D_1 l \nu)\simeq Br(B\to D^\ast_2 l \nu)$ were confirmed, it would indicate a sizeable $O(1/m_c)$ correction

Duality in semileptonic inclusive B-decays in potential models: regular versus singular potentials

International audienceMaking use of the nonrelativistic potential model for the description of mesons, and working in the Shifman–Voloshin limit, we compare the integrated rate Γ (B → X c lν) calculated as a sum of the individual decay rates to the quantum-mechanical analog of the OPE. In the case of a potential regular at the origin, we find a well-defined duality violation, which is, however, exponentially small. It corresponds to the charm resonances kinematically forbidden in the decay process, but apparently picked up by the OPE. For singular potentials, we do not obtain a full OPE series, but only a limited Taylor expansion, since the coefficients become infinite beyond some order. In this case, we do not find an indication of duality violation: the difference is smaller than the last term of the limited expansion. This emphasizes that the case of singular potentials, which may be relevant for QCD, deserves further study. 2001 Published by Elsevier Science B.V

Eléments de physique de la Beauté

N° d'ordre : HDR 218La physique du B constitue un pan important de la physique des particules, aussi bien du point de vue théorique qu'expérimental. L'objectif de ce mémoire est d'adresser un certain nombre d'aspects relatifs à cette physique et, dans un premier temps, certaines hypothèses théoriques utilisées : - hypothèse de dualité : la plupart des calculs inclusifs sur les transitions entre états hadroniques repose implicitement sur le fait que ces processus peuvent être décrits en ne faisant intervenir que les transitions entre les quarks constituant ces hadrons. Nous avons testé cette hypothèse dans le cadre des désintégrations semileptoniques des mésons $B$ et cherché les causes d'éventuelles violations. - hypothèse de factorisation : cette hypothèse simplificatrice, couramment employée dans le domaine, permet par exemple l'étude des désintégrations non-leptoniques des mésons B en deux autres mésons. Nous avons réalisé une étude exhaustive comparative entre les données expérimentales disponibles et une version améliorée de cette hypothèse. Ensuite, nous présentons un problème lié à la production des états de moment cinétique orbital l=1 lors des désintégrations des mésons B : les données expérimentales vont à contre sens de tous les modèles théoriques phénoménologiques ; nous proposons alors une tentative de résolution par QCD sur réseau de ce puzzle. Enfin, nous décrivons le projet APEnext (projet européen d'ordinateur à architecture parallèle dédié aux calculs sur réseau)

Simple operator formulation of the Bakamjian-Thomas approach to heavy quark current , with generalisation to HQET, and with applications to transitions of Lambda-b

Starting from the general formulation of current matrix elements in the Bakamjian-Thomas (BT) approach to quark models, certain aspects of their heavy quark limit are exhibited in an intuitive form, allowing a common treatment for any number of quarks and angular momenta j,j'. We use the general Falk interpretation of Isgur-Wise functions as overlaps of light parton states in motion. Then, in BT, for small collinear velocities, the motion of these states is described by a very simple dimensionless differential operator O acting on the internal wave functions of the light quarks, which a relativistic generalisation of the dipole operator times the quark mass : it appears as the generator of Lorentz transformations for N free light particles

Design and characterization of a near-field gamma imager for in situ measurements of fuel rod deformations

International audienceA prototype of gamma imager system has been developed for detecting fuel rod deformations, based on the WidePIX hybrid pixel detector, associated with a collimator. The WidePIX detector used in the frame of these developements is made of 2×5 Timepix devices hybridized with a 1 mm-thick cadmium telluride semiconductor. A specific collimator was designed, offering the best compromise between mechanical feasibility, cost, signal-to-noise ratio and angular resolution, and making it possible to visualise the the fuel rod deformations. In this work, we present the design of the collimator carried out by numerical Monte-Carlo simulations, and experimental results obtained with this prototype on a Cs-137 and Co-60 metrological irradiator