Reanalysis of the 2019 B0 → D*- l+ vl data of Belle and extraction of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb|

Abstract

The Standard Model of Particle Physics describes the weak, electromagnetic and strong interaction between the elementary particles. In the Standard Model, the Cabibbo-Kobayashi-Maskawa matrix (CKM matrix) describes the strength of transitions between the three flavor generations of quarks when interacting with a W boson. It is important to understand the CP violation. The CKM matrix is a 3x3 matrix and has only four independent parameters because of its unitarity. These four parameters are not predicted by the Standard Model of Particle Physics and must be determined experimentally. The determination of the matrix element |Vcb| of the CKM matrix is of particular interest because there is a discrepancy between the results when using exclusive and inclusive semileptonic decays.In this work, the exclusive semileptonic decay B0 −→ D∗−l+νl (l = e,μ) is analyzed and a reanalysis of the data published by Belle 2019 is done. The data were recorded with the detector at the KEKB electron-positron collider. The Belle analysis contains a data set of 711fb−1 at the Υ(4S) resonance, which corresponds to (772 ± 11) × 10^6 BB ̄ pairs. The differential decay rate was mea- sured as a function of the hadronic recoil w and the angles θl, θν and χ. The Caprini Lellouch Neubert (CLN) parametrization is used to describe the differ- ential decay rate with the four parameters ρ2, R1(1), R1(2) and F(1)|Vcb|ηEW. The matrix element |Vcb| and the four parameters of the CLN parametrization are determined from the measured data with a four-dimensional fit. The fit re- sults are checked for their stability under various assumptions such as different numbers of fitted bins or consideration of the D’Agostini bias.The parameters of the CLN parametrization are determined with ρ2 = 1.166±0.034,R1(1)=1.184±0.028,R2(1)=0.848±0.022andF(1)|Vcb|ηEW = (36.49 ± 0.46) × 10^−3 taking into account the D’Agostini bias and the results are stable with respect to various assumptions.