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L. Oliver

Publications and source records attributed to L. Oliver.

At least 55 records · Page 3Linked to original sources
arXiv2001

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

Making use of the nonrelativistic potential model for the description of mesons, and working in the Shifman-Voloshin limit, we compare the integrated rate $Γ(B\to X_clν)$ 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 cofficients 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.

hep-ph↗
arXiv2000

Semileptonic inclusive heavy meson decay: duality in a nonrelativistic potential model in the Shifman-Voloshin limit

Quark-hadron duality in the inclusive semileptonic decay $B\to X_c lν$ in the Shifman-Voloshin limit $Λ\ll δm=m_b - m_c \ll m_b, m_c$ is studied within a nonrelativistic potential model. The integrated semileptonic decay rate is calculated in two ways: first, by constructing the Operator Product Expansion, and second by a direct summation of the exclusive channels. Sum rules (Bjorken, Voloshin, etc.) for the potential model are derived, providing a possibility to compare the two representations for $Γ(B\to X_c lν)$. An explicit difference between them referred to as duality-violation effect is found. The origin of this effect is related to higher charm resonances which are kinematically forbidden in the decay process but are nevertheless picked up by the OPE. Within the considered $1/m_c^2$ order the OPE and the sum over exclusive channels match each other, up to the contributions of higher resonances, by virtue of the sum rules. In particular this is true for the terms of order $δm^2/m_c^2$ and $Λδm/m_c^2$ which are present in each of the decay channels and cancel in the sum of these channels due to the Bjorken and Voloshin sum rules, respectively. The size of the duality violation effects is estimated to be of the order $O(Λ^{2+b}/m_c^2δm^b)$ with $b>0$ depending on the details of the potential. Constraints for a better accuracy are discussed.

hep-ph↗
arXiv2000

Duality in the non-relativistic harmonic oscillator quark model in the Shifman-Voloshin limit : a pedagogical example

The detailed way in which duality between sum of exclusive states and the free quark model description operates in semileptonic total decay widths, is analysed. It is made very explicit by the use of the non relativistic harmonic oscillator quark model in the SV limit, and a simple interaction current with the lepton pair. In particular, the Voloshin sum rule is found to eliminate the mismatches of order $δm/m_b^2$.

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arXiv2000

One Interesting New Sum Rule Extending Bjorken's to order {1/m_Q}

We explicitly check quark-hadron duality to order $(m_b-m_c)Λ/m_b^2$ for $b \to c lν$ decays in the limit $m_b-m_c \ll m_b$ including ground state and orbitally excited hadrons. Duality occurs thanks to a new sum rule which expresses the subleading HQET form factor $ξ_3$ or, in other notations, $a_+^{(1)}$ in terms of the infinite mass limit form factors and some level splittings. We also demonstrate the sum rule, which is not restricted to the condition $m_b-m_c \ll m_b$, applying OPE to the longitudinal axial component of the hadronic tensor without neglecting the $1/m_b$ subleading contributions to the form factors. We argue that this method should produce a new class of sum rules, depending on the current, beyond Bjorken, Voloshin and the known tower of higher moments. Applying OPE to the vector currents we find another derivation of the Voloshin sum rule. From independent results on $ξ_3$ we derive a sum rule which involves only the $τ_{1/2}^{(n)}$ and $τ_{3/2}^{(n)}$ form factors and the corresponding level splittings. The latter strongly supports a theoretical evidence that the $B$ semileptonic decay into narrow orbitally-excited resonances dominates over the decay into the broad ones, in apparent contradiction with some recent experiments. We discuss this issue.

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arXiv1999

Inclusive decay of B mesons into $D_s$ or $D^*_s$

We compute the inclusive decay rates $b \to D_s^-(D^{*-}_s) c$ including lowest order QCD corrections on the quark legs, and compare with existing data. Unlike the short distance QCD corrections, that are of higher order, these corrections are of order $α_s$. In the on-shell renormalization scheme and for $α_s(m_b) \cong 0.2$ we find a correction of -10% to the inclusive rate computed using factorization. This gives a total rate $BR(b \to D_s^-(D^{*-}_s)c) \cong 8%$ consistent within $1σ$ with the measured value $BR(B \to D_s^{\pm}X) = (10.0 \pm 2.5)%$. The general formulae given here include the case of vanishing mass for the final quark $b \to D_s^-(D_s^{*-})u$. The radiative correction to this rate is -17%. We show in another place that this process can be useful for the measurement of the CKM matrix element $V_{ub}$. We also give the renormalized vertex at the interesting values $q^2 = 0$ and $q^2 = q_{max}^2$, and compare with existing literature.

hep-ph↗
arXiv1999

Measuring $|V_{ub}|$ with B$\to D_s^+ X_u$ transitions

We propose the determination of the CKM matrix element $|V_{ub}|$ by the measurement of the spectrum of $B \to D_s^+ X_u$, dominated by the spectator quark model mechanism $\bar{b} \to D_s^{(*)+} \bar{u}$. The interest of considering $B \to D_s^+X_u$ versus the semileptonic decay is that more than 50 % of the spectrum for $B \to D_s^+ X_u$ occurs above the kinematical limit for $B \to D_s^+ X_c$, while most of the spectrum $B \to l νX_u$ occurs below the $B \to l νX_c$ one. Furthermore, the measure of the hadronic mass $M_X$ is easier in the presence of an identified $D_s$ than when a $ν$ has been produced. As a consistency check, we point out that the rate $\bar{b} \to D_s^{(*)+} \bar{c}$ (including QCD corrections that we present elsewhere) is consistent with the measured $BR (B \to D_s^{\pm} X)$. Although the hadronic complications may be more severe in the mode that we propose than in the semileptonic inclusive decay, the end of the spectrum in $B \to l νX_u$ is not well understood on theoretical grounds. We argue that, in our case, the excited $D_s^{**}$, decaying into $D K$, do not contribute and, if there is tagging of the $B$ meson, the other mechanisms to produce a $D_s$ of the right sign are presumably small, of $O(10^{-2})$ relative to the spectator amplitude, or can be controlled by kinematical cuts. In the absence of tagging, other hadronic backgrounds deserve careful study. We present a feasability study with the BaBar detector.

hep-ph↗
arXiv1999

Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit of QCD

We argue that the Large Energy Effective Theory (LEET), originally proposed by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative and rare heavy-to-light transitions in the region where the energy release E is large compared to the strong interaction scale and to the mass of the final hadron, i.e. for q^2 not close to the zero-recoil point. We derive the Effective Lagrangian from the QCD one, and show that in the limit of heavy mass M for the initial hadron and large energy E for the final one, the heavy and light quark fields behave as two-component spinors. Neglecting QCD short-distance corrections, this implies that there are only three form factors describing all the pseudoscalar to pseudoscalar or vector weak current matrix elements. We argue that the dependence of these form factors with respect to M and E should be factorizable, the M-dependence (sqrt(M)) being derived from the usual heavy quark expansion while the E-dependence is controlled by the behaviour of the light-cone distribution amplitude near the end-point u=1. The usual expectation of the (1-u) behaviour leads to a 1/E^2 scaling law, that is a dipole form in q^2. We also show explicitly that in the appropriate limit, the Light-Cone Sum Rule method satisfies our general relations as well as the scaling laws in M and E of the form factors, and obtain very compact and simple expressions for the latter. Finally we note that this formalism gives theoretical support to the quark model-inspired methods existing in the literature.

hep-ph↗
arXiv1999

Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit: Covariant Quark Model Approach

We prove the full covariance of the heavy-to-light weak current matrix elements based on the Bakamjian-Thomas construction of relativistic quark models, in the heavy mass limit for the parent hadron and the large energy limit for the daughter one. Moreover, this quark model representation of the heavy-to-light form factors fulfills the general relations that were recently argued to hold in the corresponding limit of QCD, namely that there are only three independent form factors describing the B -> pi (rho) matrix elements, as well as the factorized scaling law sqrt(M)z(E) of the form factors with respect to the heavy mass M and large energy E. These results constitute another good property of the quark models à la Bakamjian-Thomas, which were previously shown to exhibit covariance and Isgur-Wise scaling in the heavy-to-heavy case.

hep-ph↗
arXiv1998

New CP observables in B0(t) -> hyperon + antihyperon from parity violation in the sequential decay

We consider the decay B0(t) -> hyperon + antihyperon, followed by hyperon weak decay. We show that parity violation in the latter allows to reach new CP observables: not only Im(lambda_f) but also Re(lambda_f) can be measured. In the decay B0_d(t) -> Lambda LambdaBar (BR ~ 10-6), Lambda -> p pi- these observables reduce to sin(2alpha) and cos(2alpha) in the small Penguin limit, the latter solving the discrete ambiguity alpha -> pi/2 -alpha. For beta one could consider the Cabibbo suppressed mode B0_d(t) -> Lambda_c Lambda_cBar (BR \~ 10-4), Lambda_c -> Lambda pi+, p K0bar, ... (with BR ~ 10-2). The pure Penguin modes B0_s(t)->Sigma-Sigma-Bar, Xi-Xi-Bar, Omega-Omega-Bar (BR ~ 10-7) can be useful in the search of CP violation beyond the Standard Model. Because of the small total rates, the study of these modes could only be done in future high statistics experiments. Also, in the most interesting case Lambda LambdaBar the time dependence of the asymmetry can be difficult to reconstruct. On the other hand, we show that B_d mesons, being a coherent source of Lambda LambdaBar, is useful to look for CP violation in Lambda decay. We also discuss B0_d(t) -> J/Psi K*0 -> l+ l- K_S pi0 where the secondary decays conserve parity, and angular correlations allow to determine terms of the form cos(delta)cos(2beta), delta being a strong phase. This phase has been measured by CLEO, but we point out that a discrete ambiguity prevents to determine sign(cos(2beta)). However, if one assumes small strong phases, like in factorization and as supported by CLEO data, one could have information on sign(cos(2beta)). Similar remarks can be done for cos(2alpha) in the decay B_d0(t) -> rho rho -> 4pi.

hep-ph↗
arXiv1998

B0(t) -> DPP time-dependent Dalitz plots, CP-violating angles 2beta, 2beta+gamma, and discrete ambiguities

We study CP-violation in resonant three-body B -> DPP decays, where PP stands for either Dpi, DK_S, pipi or piK_S. Analogously to the B -> 3pi channel and the extraction of 2alpha, the first three channels are shown to measure cos(2beta) in addition to sin(2beta), thus allowing to resolve the beta -> pi/2 -beta ambiguity, while the DpiK_S final state leads to a measurement of 2beta+gamma. The B0(t) -> D+D-pi0 channel via the interference between D** orbitally excited resonances is taken as an example, although this Cabibbo-suppressed decay suffers from irreducible penguin uncertainties. Then two penguin-free and Cabibbo-dominant modes are proposed: B0(t) -> D+D-K_S with the D_s** resonances, and B0(t) -> D0_CP pi+pi- with the D** plus the rho. Finally, the B0(t) -> D+-pi-+K_S channel with the D_s** and K* resonances provides a new clean method to measure the unusual angle 2beta+gamma. We present in all cases a crude estimate of the number of cos(2beta) (respectively 2beta+gamma) sensitive events. We show that this number is an increasing function of the resonance mass, a favorable situation compared to the more extensively studied three-pion Dalitz plot. However, the poor detection efficiency of the D mesons could pose a problem. As an annex and speculative application of these Dalitz plot based methods, the penguin-dominated B0(t) -> K_SK_SK_L decay also measures 2beta.

hep-ph↗
arXiv1997

Decay constants in the heavy quark limit in models à la Bakamjian and Thomas

In quark models à la Bakamjian and Thomas, that yield covariance and Isgur-Wise scaling of form factors in the heavy quark limit, we compute the decay constants $f^{(n)}$ and $f^{(n)}_{1/2}$ of S-wave and P-wave mesons composed of heavy and light quarks. Heavy quark limit scaling $\sqrt{M} f = Cst$ is obtained, and it is shown that this class of models satisfies the sum rules involving decay constants and Isgur-Wise functions recently formulated by us in the heavy quark limit of QCD. Moreover, the model also satisfies the selection rules of the type $f^{(n)}_{3/2} = 0$ that must hold in this limit. We discuss different Ansätze for the dynamics of the mass operator at rest. For non-relativistic kinetic energies ${p^2 \over 2m}$ the decay constants are finite even if the potential $V(r)$ has a Coulomb part. For the relativistic form $\sqrt{p^2 + m^2}$, the S-wave decay constants diverge if there is a Coulomb singularity. Using phenomenological models of the spectrum with relativistic kinetic energy and regularized short distance part (Godfrey-Isgur model or Richardson potential of Colangelo et al.), that yield $ρ^2 \simeq 1$ for the elastic Isgur-Wise function, we compute the decay constants in the heavy quark limit, and obtain $f_B \simeq$ 300 MeV, of the same order although slightly smaller than in the static limit of lattice QCD. We find the decay constants of $D^{**}$ with $j =1/2$ of the same order of magnitude. The convergence of the heavy quark limit sum rules is also studied.

hep-ph↗
arXiv1997

Quantitative Predictions for $B$ semileptonic decays into $D,D^*$ and the orbitally excited $D^{**}$ in quark models à la Bakamjian-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 $ρ^2$. From the general formulae for the scaling invariant form factors $ξ^{(n)}(w)$, $τ_{1/2}^{(n)}(w)$ and $τ_{3/2}^{(n)}(w)$, 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 $ξ(w)\simeq (2/(1+w)) ^2$, resulting from the fact that the ground state wave function is Coulomb-like. We also find $τ_{3/2}\simeq 0.5 (2/(1+w))^3$ and $τ_{1/2}(w)\ll τ_{3/2}(w)$. 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 $Br(B\to D^\ast_2 l ν)/Br(B\to D_1 l ν)=1.55\pm 0.15$ as a mere consequence of the heavy quark symmetry. If some faint experimental indications that $Br(B\to D_1 l ν)\simeq Br(B\to D^\ast_2 l ν)$ were confirmed, it would indicate a sizeable $O(1/m_c)$ correction.

hep-ph↗
arXiv1997

Slope of the Isgur-Wise function in the heavy mass limit of quark models à la Bakamjian-Thomas

The slope of the Isgur-Wise function for ground state mesons is evaluated for the heavy mass limit of quark models à la Bakamjian-Thomas, which has been previously discussed by us in general terms. A full calculation in various spectroscopic models with relativistic kinetic energy gives a rather stable result $ρ^2 \approx 1$, much lower than previous estimates. Attention is paid to a careful comparison of this result with the ones of QCD fundamental methods (lattice QCD, QCD sum rules) and with experimental data.

hep-ph↗
arXiv1996

New Heavy Quark Limit Sum Rules involving Isgur-Wise Functions and Decay Constants

We consider the dominant $c\bar{c}$ contribution to $ΔΓ$ for the $B_s^0$-$\bar{B}_s^0$ system in the heavy quark limit for both $b$ and $c$ quarks. In analogy with the Bjorken-Isgur-Wise sum rule in semileptonic heavy hadron decay, we impose duality between the parton model calculation of $ΔΓ$ and its estimation by a sum over heavy mesons. Varying the mass ratio $m_c/m_b$ and assuming factorization and saturation by narrow resonances $(N_c \to \infty$), we obtain new sum rules that involve the Isgur-Wise functions $ξ^{(n)}(w)$ and $τ^{(n)}_{1/2}(w)$ and the decay constants $f^{(n)}$, $f^{(n)}_{1/2}$ ($n$ stands for any radial excitation). Alternatively, we deduce the sum rules with another method free of the factorization hypothesis, from the saturation of the expectation value of a product of two currents by heavy hadrons and by the corresponding free quarks. The sum rules read $\sum\limits_{n}{f^{(n)} \over f^{(0)}} ξ^{(n)}(w) = 2 \sum\limits_{n}{f^{(n)}_{1/2} \over f^{(0)}} τ^{(n)}_{1/2}(w) = 1$, valid for all $w$. Moreover, we obtain, in the heavy quark limit, $f^{(n)}_{3/2} = 0$. As a consequence, unlike the BIW sum rule, the slope of the elastic function $ξ(w)$ is related to radial excitations alone. These are generalizations, rigorous for QCD in the heavy quark limit, of results that have an easy understanding in the non-relativistic quark model.

hep-ph↗
arXiv1996

$B\to D^{\ast\ast}$ semileptonic decay in covariant quark models à la Bakamjian Thomas

Once chosen the dynamics in one frame, for example the rest frame, the Bakamjian and Thomas method allows to define relativistic quark models in any frame. These models have been shown to provide, in the heavy quark limit, fully covariant current form factors as matrix elements of the quark current operator. They also verify the Isgur-Wise scaling and give a slope parameter $ρ^2>3/4$ for all the possible choices of the dynamics. In this paper we study the $L=1$ excited states and derive the general formula, valid for any dynamics, for the scaling invariant form factors $τ_{1/2}^{(n)}(w)$ and $τ_{3/2}^{(n)}(w)$. We also check the Bjorken-Isgur-Wise sum rule already demonstrated elsewhere in this class of models.

hep-ph↗
arXiv1996

Exact Duality and Bjorken Sum Rule in Heavy Quark Models à la Bakamjian-Thomas

The heavy mass limit of quark models based on the Bakamjian-Thomas cons\-truction reveals remarkable features. In addition to previously demonstrated properties of covariance and Isgur-Wise scaling, exact duality, leading to the Bjorken-Isgur-Wise sum rule, is proven, for the first time to our knowledge in relativistic quark models. Inelastic as well as elastic contributions to the sum rule are then discussed in terms of ground state averages of a few number of operators corresponding to the nonrelativistic dipole operator and various relativistic corrections.

hep-ph↗
arXiv1995

Covariant quark model of form factors in the heavy mass limit

We show that quark models of current matrix-elements based on the Bakamjian-Thomas construction of relativistic states with a fixed number of particles, plus the additivity assumption, are covariant in the heavy-quark limit and satisfy the full set of heavy-quark symmetry relations discovered by Isgur and Wise. We find the lower bound of $ρ^2$ in such models to be $3/4$ for ground state mesons, independently of any parameter. Another welcome property of these models is that in the infinite momentum limit the wave functions vanish outside the domain $0\le x \le 1$.

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