A novel method of reconstructing semileptonic $B$ decays

TL;DR

This paper introduces a new method for reconstructing semileptonic B meson decays that significantly improves efficiency by utilizing vertex and kinematic information, enhancing precision in measuring CKM matrix elements and testing lepton universality.

Contribution

The novel method reconstructs B meson semileptonic decays without relying on recoil-side B meson reconstruction, increasing efficiency by up to two orders of magnitude.

Findings

Efficiency of decay reconstruction improved significantly.

Potential for more precise measurements of CKM elements.

Enhanced testing of lepton universality at B-factories.

Abstract

Semileptonic decays of charged and neutral $B$ mesons play a critical role in the determination of the magnitudes of the CKM-matrix elements $V_{cb}$ and $V_{ub}$, and in the test of the lepton universality which is a basic assumption of the Standard Model. Due to the missing neutrino in the semileptonic decays, the measurements depend strongly on the tag efficiency of the $B$ meson in the recoil side which is at a few per mille to a few per cent level, and this values a limiting factor for high precision measurement and high sensitivity test mentioned above. We develop a novel method of reconstructing semileptonic decays of the $B$ mesons by introducing the $B$ momentum information calculated from the $B$ decay vertex and the interaction point, as well as the kinematic information of $e^{+}e^{-}\to B\overline{B}$ at the $B$-factories such as BaBar, Belle, and Belle II. As this method does not depend on the reconstruction of the $B$ meson in the recoil side, the gain in the efficiency could be as large as two orders of magnitudes. This makes high precision measurement of CKM-matrix elements $|V_{cb}|$ and $|V_{ub}|$ and high precision test of lepton universality at $B$-factories more promising. We present the algorithms for the semileptonic decays of neutral and charged $B$ mesons separately, as they are affected by the magnetic field in the detector differently.