Search for the standard model Higgs boson decaying to charm quarks

A direct search for the standard model Higgs boson H produced in association with a W or Z boson and decaying to a charm quark pair is presented. The search uses a dataset of proton-proton collisions corresponding to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$ collected by the CMS experiment at the CERN LHC in 2016 at a centre-of-mass energy of 13 TeV. The search is carried out in mutually exclusive categories defined by the lepton multiplicity of the vector boson decays: $\text{W}\rightarrow\ell\nu$, $\text{Z}\rightarrow \ell\ell$, and $\text{Z}\rightarrow \nu\nu$, where $\ell$ is an electron or a muon. To fully exploit the topology of the H decay, two strategies are followed. In one, the H candidate is reconstructed via two resolved jets arising from the two charm quarks from the H decay. This strategy mainly targets events with lower vector boson transverse momentum. A second strategy identifies the case where the two charm quarks from the H decay merge to form a single jet, which generally only occurs when the vector boson has higher transverse momentum. Both strategies make use of novel methods for charm jet identification, while jet substructure techniques are also exploited to suppress the background for the merged-jet topology. The two analyses are combined to yield an observed (expected) upper limit on the $\frac{\sigma\left(\text{VH}\right) \times \mathcal{BR}\left(\text{H} \rightarrow \text{c}\bar{\text{c}} \right)}{\sigma_{SM}\left(\text{VH}\right) \times \mathcal{BR}_{SM}\left(\text{H} \rightarrow \text{c}\bar{\text{c}} \right)}$ of 70 ($37^{+16}_{-10}$) at $95\%$ confidence level.