Search for D0-D0bar Mixing Using Semileptonic Decay Modes

TL;DR

This study searches for D0-D0bar mixing using semileptonic decay modes with a large dataset, employing neural networks for event selection, and finds results consistent with no mixing, setting an upper limit on the mixing rate.

Contribution

First search for D0-D0bar mixing using semileptonic decays with neural network-based event reconstruction and data-driven modeling.

Findings

Measured mixing rate R_{mix} = 0.0023 ± 0.0012 ± 0.0004

Set an upper limit R_{mix} < 0.0042 at 90% CL

Result consistent with no charm mixing

Abstract

Based on an 87-fb$^{-1}$ dataset collected by the Babar detector at the PEP-II asymmetric-energy $B$-Factory, a search for $D^{0}$--$\bar{D}^{0}$ mixing has been made using the semileptonic decay modes $D^{*+} \to \pi^{+} D^{0}, D^{0} \to K^{(*)}e\nu$ (+c.c.). The use of these modes allows unambiguous flavor tagging and a combined fit of the $D^{0}$ decay time and $D^{*+}$--$D^{0}$ mass difference ($\Delta M$) distributions. The high-statistics sample of unmixed semileptonic $D^{0}$ decays is used to model the $\Delta M$ distribution and time-dependence of mixed events directly from the data. Neural networks are used to select events and reconstruct the $D^{0}$. A result consistent with no charm mixing has been obtained, $R_{\rm{mix}}=0.0023 \pm 0.0012 \pm 0.0004$. This corresponds to an upper limit of $R_{\rm{mix}}<0.0042$ (90% CL).