Search for Flavor-Changing-Neutral-Current $D$ Meson Decays

We study the flavor-changing-neutral-current process $c\to u{\mu }^{+}{\mu }^{-}$ using $1.3{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded by the D0 detector operating at the Fermilab Tevatron Collider. We see clear indications of the charged-current mediated $D_s^{+}$ and $D^{+}\to \varphi {\pi }^{+}\to {\mu }^{+}{\mu }^{-}{\pi }^{+}$ final states with significance greater than 4 standard deviations above background for the $D^{+}$ state. We search for the continuum neutral-current decay of $D^{+}\to {\pi }^{+}{\mu }^{+}{\mu }^{-}$ in the dimuon invariant mass spectrum away from the $\varphi$ resonance. We see no evidence of signal above background and set a limit of $\mathcal{B}(D^{+}\to {\pi }^{+}{\mu }^{+}{\mu }^{-})<3.9\times {10}^{-6}$ at the 90% C.L. This limit places the most stringent constraint on new phenomena in the $c\to u{\mu }^{+}{\mu }^{-}$ transition.

Figure 1

The inclusive $m({\mu }^{+}{\mu }^{-})$ invariant mass spectrum. The fitting function includes components from the $\eta$, $\rho$, $\omega$, and $\varphi$ resonances.

Figure 2

The $m({\pi }^{+}{\mu }^{+}{\mu }^{-})$ mass spectrum in the $0.98<m({\mu }^{+}{\mu }^{-})<1.06\mathrm{GeV}/c^2$ $\varphi$ mass window. The result of a binned likelihood fit to the distribution including contributions for $D^{+}$, $D_s^{+}$, and combinatoric background is overlaid on the histogram.

Figure 3

Final ${\pi }^{+}{\mu }^{+}{\mu }^{-}$ invariant mass spectrum. The $\pm 2\sigma$ $D^{+}$ signal region, within the dashed lines, contains 19 events. The background level determined from the sidebands is $25.8\pm 4.6$ events.