Search for new physics with charm rare decays at BESIII

TL;DR

The paper exploits BESIII’s large charm and charmonium data sets to search for new physics in charm rare decays, focusing on FCNC processes such as $J/\psi\to D^{0}\mu^{+}\mu^{-}$ and $J/\psi\to D^{0}\gamma$ and on LD-dominated $D_{s}^{+}$ decays to $h(h')e^{+}e^{-}$, as well as $J/\psi$ weak decays containing a D meson. No FCNC signals are observed, yielding stringent upper limits on branching fractions, e.g. $\mathcal{B}(J/\psi\to D^{0}\mu^{+}\mu^{-})<1.1\times10^{-7}$ and $\mathcal{B}(J/\psi\to D^{0}\gamma)<9.1\times10^{-8}$, while several $J/\psi$ weak-decay modes remain below experimental sensitivity. Notably, the LD-dominated $D_{s}^{+}$ decays to $\pi^{+}\phi$ and $\rho^{+}\phi$ with $\phi\to e^{+}e^{-}$ are observed (significance 7.8σ and 4.4σ, respectively) with branching fractions around the $10^{-5}$ level, and four-body modes are constrained by upper limits. Collectively, the results are consistent with the Standard Model and impose meaningful constraints on new-physics scenarios in the charm sector.

Abstract

Search for new physics with charm rare decays at BESIII. The BESIII experiment has collected 2.6 billion $ψ(3686)$ events, 10 billion $J/ψ$ events, $20 fb^{-1}$ D meson pairs at 3.773 GeV, and $7.33 fb^{-1}~D_{s}D_{s}^{*}$ events from 4.128 to 4.226 GeV. The huge data samples allow us to search for rare processes in charm hadron decays. In this paper, we report the FCNC decay in $J/ψ\to D^0μ^+μ^-$, $J/ψ\to D^0γ$ and $D_{s}^{+}\to h(h')e^+e^-$. The search for $J/ψ$ weak decays containing a D meson, $J/ψ\to D_{s}^{-}π^{+}$, and $J/ψ\to D_{s}^{-}ρ^{+}$ will also be presented.

Figures (7)

• Figure 1: Feynman diagrams in the SM.
• Figure 2: The distributions of $M_{D^{0}\mu^{+}\mu^{-}}$ for $J/\psi\to D^{0}\mu^{+}\mu^{-}$ of the selected candidates in data, signal MC sample, and inclusive MC sample. The simultaneous fit result is shown in the top left, and the individual fit result for each mode is shown in the other three sub-figures, respectively. The black dots with error bars are data, the magenta dotted-dashed line shows the shape of the signal MC sample scaled to $\mathcal{B}(J/\psi\to D^{0}\mu^{+}\mu^{-}) = 1.0 \times 10^{-6}$ for the three tags. The blue shaded histogram is the inclusive MC sample, the red line is the fit result, and the blue solid lines are the fitted background.
• Figure 3: The unbinned simultaneous fit on the invariant mass distributions for $J/\psi\to D^{0}\gamma$ of modes (a) I, (b) II, and (c) III, where the dots with error bar are data, the blue lines are the fit result, and the red dotted and purple curves are the fitted signal and background, respectively.
• Figure 4: Fits to the $M(D_{s}^{+})$ distributions for (a) $D_{s}^{+}\to\pi^{+}\phi(\to e^{+}e^{-})$, $D_{s}^{+}\to\rho^{+}(\to\pi^{+}\pi^{0})\phi(\to e^{+}e^{-})$, (b) $D_{s}^{+}\to \pi^{+}\pi^{0}e^{+}e^{-}$, $D_{s}^{+}\to K^{+}\pi^{0}e^{+}e^{-}$, and $D_{s}^{+}\to K_{S}^{0}\pi^{+}e^{+}e^{-}$. The signals are shown as the magenta dashed curves. The blue long-dashed curves are the combinatorial background components, and the dots with error bars are data.
• Figure 5: Feynman diagrams in the SM.