Measurement of the shape of the Λb0→Λc+μ−ν¯

Abstract

The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, q 2 , is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions. DOI: 10.1103/PhysRevD.96.112005 I. INTRODUCTIONIn the Standard Model (SM) of particle physics, quarks participate in a rich pattern of flavor-changing transitions. The relevant couplings form a complex 3 × 3 matrix, known as the Cabibbo-Kobayashi-Maskawa (CKM) matrix, characterized by just four independent parameters [1]. A vast body of measurements of individual CKM elements exists, and thus the overall consistency of the SM picture of charged current interactions is highly overconstrained. Decades of experimental work have demonstrated the impressive consistency of experimental data with the CKM paradigm [2,3]; nonetheless, the motivation to probe the CKM matrix remains strong. Effects of physics beyond the SM may be subtle; thus, more precise measurements are necessary to unveil them. Semileptonic decays of heavyflavored hadrons are commonly used to measure CKM parameters, as they involve only one hadronic current, parametrized in terms of scalar functions known as form factors. The number of form factors needed to describe a particular decay depends upon the spin of the initial-and final-state hadrons [4,5]. A precise calculation of these form factors has been elusive for many years as it is not possible in perturbative QCD. Heavy-Quark Effective Theory (HQET) provides the framework to systematically include nonperturbative corrections in computations involving hadrons containing heavy quarks. In particular, in the limit of infinite heavy-quark mass, all the form factors describing the semileptonic decay of a heavyflavored hadron are proportional to a universal function, known as the Isgur-Wise (IW) function [6]. Lattice QCD, namely the use of lattice formulations of QCD in large scale numerical simulations, has emerged in recent years as a technique with well-defined and systematically improvable uncertainties which can be applied to a wide range of processes and physical quantities [7]. Predictions from the infinite heavy-quark mass limit are useful as a check of several lattice QCD calculations [8].The decay Λ 0 b → Λ þ c μ −ν μ is described by six form factors corresponding to the vector and axial-vector components of the flavor-changing charged current [9]. In HQET, Λ is related to the squared four-momentum transfer between the heavy baryons, q 2 , by are the corresponding invariant masses. Nonperturbative corrections to the static limit can be expressed in terms of an expansion in powers of 1=m c and 1=m b , where m c and m b represent the c-and b-quark masses, respectively. It has been shown in Ref. [12] that the 1=m c term can be expressed in terms of ξ B ðwÞ and one dimensionful constant. Moreover, partial cancellations lead to small first-order corrections near w ¼ 1 [13].

Beyond R(D(*)) with the general type-III 2HDM for Martı́nez1, Sierra2, Valencia3 2018Phys. Rev. D325230View full textAdd to dashboardCite

“…From the partial decay width Eq. (52), we first obtain the Λ b → Λ c µν µ normalised spectral distribution for the SM and compare it with the one measured by LHCb [70] in Figure 6. The green and yellow shaded areas indicate the estimated 10% and 20% errors in the prediction according to [64].…”

“…Once again, this figure serves to calibrate the performance of the CCQM form factors in this case. The points are the LHCb data [70] and the dashed black line, green and yellow areas mark the central CCQM results and a 10% and 20% deviation respectively.…”

Weak decays of heavy baryons in the light-front approach

“…Particularly there are rapid progresses in the study of Λ c decays at BESIII [22][23][24][25][26][27] and some recent studies on Λ b and Λ c decays by LHCb can be found in Refs. [28][29][30][31][32][33]. It is anticipated that many more decay modes will be established in future.…”

Determining the Efficacy of different parameterizations of the z-expansion

“…It would be interesting to examine this process in other decay processes such as as B → D ν and Λ b → Λ c ν. The each of these decays have analyses ( [11] and [12]) with available covariance matrices and partial branching fractions, although the volume of publicly data available is less than that of B → π ν, this methodology can be used to help rule out other parameterizations of the form factors for these decays.…”