Observation of $B^{0} \rightarrow p\bar{\Lambda} D^{(*)-}$

TL;DR

This paper reports the first observation of specific B meson decays into a proton, anti-Lambda, and D mesons, measuring their branching fractions and noting a threshold enhancement in the di-baryon system, challenging existing theoretical predictions.

Contribution

First experimental observation and measurement of branching fractions for $B^0 ightarrow par{ ext{Lambda}} D^{(*)-}$ decays, with findings inconsistent with generalized factorization models.

Findings

Branching fractions measured as (25.1±2.6±3.5)×10^{-6} and (33.6±6.3±4.4)×10^{-6}.

Significant excesses observed with 19.8σ and 10.8σ significance.

Threshold enhancement observed in the di-baryon system.

Abstract

We report the first observation of the decays $B^0 \rightarrow p\bar{\Lambda} D^{(*)-}$. The data sample of $711$ fb$^{-1}$ used in this analysis corresponds to $772$ million $B\bar{B}$ pairs, collected at the $\Upsilon(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We observe $19.8\sigma$ and $10.8\sigma$ excesses of events for the two decay modes and measure the branching fractions of $B^0 \rightarrow p\bar{\Lambda} D^{-}$ and $B^0 \rightarrow p\bar{\Lambda} D^{*-}$ to be $(25.1\pm2.6\pm3.5)\times10^{-6}$ and $(33.6\pm6.3\pm4.4)\times10^{-6}$, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the di-baryon ($p\bar{\Lambda}$) system is observed, consistent with that observed in similar $B$ decays.