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T: Fachverband Teilchenphysik

T 104: Flavor VIII

T 104.2: Vortrag

Donnerstag, 23. März 2023, 16:05–16:20, HSZ/0304

Measurement of the branching fraction and q²-spectrum of B → D^** ℓ ν decays at Belle II — •Eylül Ünlü, Thomas Lück, and Thomas Kuhr — Ludwig-Maximilians-Universität München

There is currently some tension between the measured value of R(D^*)=B(B → D^* τ ν_τ)/ B(B → D^* ℓ ν_ℓ) and the Standard Model prediction, hinting at lepton universality violation. Semileptonic B meson decays to D^** mesons are background to the R(D^*) measurement, where D^** denotes the orbitally excited P-wave charm mesons: D₁(2420), D₂^*(2460), D₀^*(2300), and D₁^′(2430). These decays are not well understood, and there have been discrepancies between past measurements of their yields made by BaBar and Belle. Hence, improved understanding of these decays would reduce an important systematic uncertainty of R(D^*) measurements.

The aim of the present study is to use simulation and data from the Belle II experiment to study these decays, in particular to determine the distribution of q²=(p_B−p_D^**)² which is key to understanding these decays and an important input for theory.

We reconstruct one of the B mesons from the Υ(4S)→ B B decay in the signal channel, B→ D^**(D^*π)ℓν. The other B meson is reconstructed in various hadronic modes using the Full Event Interpretation algorithm, which provides a high purity tag B sample with well known kinematics. We identify signal decays by a peak at zero in the M_missing² (missing mass squared) distribution, and do a fit to the mass difference M(D^* π) − M(D^*) to extract the D^** signal yield.

The current status of the analysis will be presented.