Search for Higgs Boson Decay to a Charm Quark-Antiquark Pair in Proton-Proton Collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$

A search for the standard model Higgs boson decaying to a charm quark-antiquark pair, $H\to c\overline{c}$, produced in association with a leptonically decaying $V$ ($W$ or $Z$) boson is presented. The search is performed with proton-proton collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ collected by the CMS experiment, corresponding to an integrated luminosity of $138\text{}\text{}{\mathrm{fb}}^{-1}$. Novel charm jet identification and analysis methods using machine learning techniques are employed. The analysis is validated by searching for $Z\to c\overline{c}$ in $VZ$ events, leading to its first observation at a hadron collider with a significance of 5.7 standard deviations. The observed (expected) upper limit on $\sigma \left(VH\right)B\left(H\to c\overline{c}\right)$ is 0.94 (${0.50}_{-0.15}^{+0.22}$)pb at 95% confidence level (C.L.), corresponding to 14 (${7.6}_{-2.3}^{+3.4}$) times the standard model prediction. For the Higgs-charm Yukawa coupling modifier, ${\kappa }_{c}$, the observed (expected) 95% C.L. interval is $1.1<|{\kappa }_{c}|<5.5$ ($|{\kappa }_{c}|<3.4$), the most stringent constraint to date.