Observation of charm mixing at CDF

TL;DR

This paper reports the first observation of charm meson mixing at CDF, measuring decay ratios over time to confirm oscillations with high statistical significance, consistent with the Standard Model.

Contribution

It provides the first measurement of charm mixing parameters at a hadron collider, confirming oscillations with a significance of 6.1 sigma and consistent with previous results.

Findings

Charm mixing observed with 6.1 sigma significance

Measured mixing parameters: x'^2, y', R_D

Results align with Standard Model expectations

Abstract

We report on the observation of $D^0$--$\bar{D}^0$ oscillations by measuring the time-dependent ratio of yields for the rare decay $D^0 \rightarrow K^+\pi^-$ to the favored decay $D^0 \rightarrow K^-\pi^+$ at the Collider Detector at Fermilab (CDF). Using 9.6 fb$^{-1}$ of integrated luminosity of $\sqrt{s}$ = 1.96 TeV $p$$\bar{p}$ collisions recorded in the full CDF Run II, the signals of $7.6 \times 10^6$ $D^0\rightarrow K^-\pi^+$ and $33 \times 10^3$ $D^0\rightarrow K^+\pi^-$ decays are reconstructed in $D^{*}$-tagged events, with proper decay times between 0.75 and 10 mean $D^0$ lifetimes. We measure the mixing parameters $x'^2 = (0.08 \pm 0.18)\times 10^{-3}$, $y' = (4.3 \pm 4.3) \times 10^{-3}$, and $R_D = (3.51 \pm 0.35) \times 10^{-3}$. Our results are consistent with standard model expectations and similar results from proton-proton collisions and exclude the no-mixing hypothesis with a significance equivalent to 6.1 standard deviations.