Measurement of the branching fractions of doubly Cabibbo-suppressed $D$ decays

TL;DR

This work reports measurements of the branching fractions for several doubly Cabibbo-suppressed D meson decays using 20.3 fb^{-1} of e^+e^- data at 3.773 GeV with the BESIII detector. A double-tag approach is employed for D0 decays (semileptonic tags) and for D+ decays (hadronic tags), enabling absolute branching fraction determinations and facilitating searches for additional final states. The analysis yields precise BFs for multiple DCS modes, observes first signals for some new channels, and sets an upper limit for one D0 decay; the results are combined with world averages to extract DCS/CF ratios, testing expectations from tan^4 theta_C. The findings advance understanding of charm decay dynamics, provide data to scrutinize SU(3) flavor symmetry, and lay groundwork for future amplitude analyses at BESIII and forthcoming facilities.

Abstract

By analyzing $e^+e^-$ collision data collected at the center-of-mass energy of 3.773~GeV with the BESIII detector, corresponding to an integrated luminosity of 20.3~fb$^{-1}$, we measure the branching fractions of the doubly Cabibbo-suppressed (DCS) decays $D^0\to K^+π^-$, $D^0\to K^+π^-π^-π^+$, $D^0\to K^+π^-π^0$, $D^0\to K^+π^-π^0π^0$, $D^+\to K^+π^+π^-$, and $D^+\to K^+K^+K^-$. We also perform the first searches for $D^0\to K^+π^-η$, $D^0\to K^+π^-π^0η$, $D^+\to K^+π^+π^-η$, $D^{+} \to K^{+} \left(π^{+} π^{-} η\right)_{{\rm non}-η^{\prime}}$, and $D^+\to K^+ηη$ and report the first observations and evidence for some of these final states. Combining the measurements with the world averages of the corresponding Cabibbo-favored (CF) decays, the ratios of the DCS/CF branching fractions are obtained. For the $D^{+} \to K^{+} \left(π^{+} π^{-} η\right)_{{\rm non}-η^{\prime}}$ decay, the ratio is significantly larger than the corresponding ratios of the other DCS decays.

Figures (5)

• Figure 1: Distributions of $M^{\rm sig}_{\rm BC}$ versus $U_{\mathrm{miss}}$ of the DT candidate events for (a) $D^0\to K^+\pi^-$, (b) $D^0\to K^+\pi^-\pi^-\pi^+$, (c) $D^0\to K^+\pi^-\pi^0$, (d) $D^0\to K^+\pi^-\pi^0\pi^0$, (e) $D^0\to K^+\pi^-\eta$ and (f) $D^0\to K^+\pi^-\pi^0\eta$ in data. In each pair, the left plot is for $\bar{D}^0\to K^+ e^-\bar{\nu}_e$ tags and the right is for $\bar{D}^0\to K^+ \mu^-\bar{\nu}_\mu$ tags. The red shaded areas show the $M^{\rm sig}_{\rm BC}$ signal regions.
• Figure 2: Fits to the $U_{\mathrm{miss}}$ distributions of the DT candidate events for (a) $D^0\to K^+\pi^-$, (b) $D^0\to K^+\pi^-\pi^-\pi^+$, (c) $D^0\to K^+\pi^-\pi^0$, (d) $D^0\to K^+\pi^-\pi^0\pi^0$, (e) $D^0\to K^+\pi^-\eta$ and (f) $D^0\to K^+\pi^-\pi^0\eta$ in data. In each plot pair, the left panel is $\bar{D}^0\to K^+ e^-\bar{\nu}_e$ tags and the right one is $\bar{D}^0\to K^+ \mu^-\bar{\nu}_\mu$ tags. The points with error bars are data and the solid blue curves are the total fit results. The dotted red curves are the fitted signal portion, the dashed black curves are the summed BKGI+BKGII background components, and the dot-dashed pink curves are the BKGII contributions.
• Figure 3: Distribution of the normalized likelihood versus the signal yield $N_{\rm DT}$ and the normalized BF of $D^0\to K^+\pi^-\pi^0\eta$. The dashed red and solid black curves show the results obtained with and without incorporating the systematic uncertainty, respectively. The black arrow shows the value corresponding to the 90% confidence level.
• Figure 4: Fits to the $M^{\rm tag}_{\rm BC}$ distributions of the ST $D^-$ candidates. The points with error bars correspond to the data, the blue curves are the fit results, and the dashed red curves describe the fitted combinatorial background.
• Figure 5: Fits to the $M_{\rm BC}^{\rm sig}$ distributions of the DT candidates in data. The points with error bars are data, the solid blue curves are the fit results, the dashed red and solid pink curves are the fitted signals and combinatorial backgrounds, respectively.