Improved Constraints on D0-D0bar Mixing in D0 -> K+ pi- Decays from the Belle Detector

TL;DR

This paper reports the most stringent experimental constraints on D0-D0bar mixing parameters using a large dataset from the Belle detector, improving our understanding of charm meson mixing phenomena.

Contribution

It provides the first comprehensive analysis of D0-D0bar mixing parameters with both CP conservation and violation assumptions, setting new experimental limits.

Findings

x'^2<0.72 x 10^{-3} at 95% CL

-9.9 x 10^{-3}<y'<6.8 x 10^{-3} at 95% CL

R_D=(0.377+-0.008+-0.005)% assuming no mixing

Abstract

We report the results of a search for D0-D0bar mixing in D0 -> K+ pi- decays based on 400 fb^{-1} of data accumulated by the Belle detector at KEKB. Both assuming CP conservation and allowing for CP violation, we fit the decay-time distribution for the mixing parameters x' and y', as well as for the parameter R_D, the ratio of doubly-Cabibbo-suppressed decays to Cabibbo-favored decays. The 95% confidence level region in the (x'^2,y') plane is obtained using a frequentist method. Assuming CP conservation, we find x'^2<0.72 x 10^{-3} and -9.9 x 10^{-3}<y'<6.8 x 10^{-3} at the 95% confidence level; these are the most stringent constraints on the mixing parameters to date. The no-mixing point (0,0) has a confidence level of 3.9%. Assuming no mixing, we measure R_D=(0.377+-0.008+-0.005)%.