Results on the search for a light charged Higgs boson ${\rm H^{+}}$ decaying to ${\rm c\bar{b}}$ in top quark pair events using the CMS detector at the LHC are presented. %It is the first search for a charged Higgs boson in this decay mode. The total dataset corresponds to 19.7 ${\rm fb^{-1}}$ of proton-proton collisions at $\sqrt{s}$ = 8 TeV. In ${\rm t\bar{t}}$ decays, if one top quark decays to ${\rm H^{+} b}$, instead of ${\rm W b}$, and the ${\rm H^{+}}$ subsequently decays to ${\rm c \bar{b}}$, while other top quark decays leptonically (${\rm \bar{t} \rightarrow W^{-}\bar{b}} \rightarrow l \bar{\nu} {\rm \bar{b}})$), the final state then consists of four jets (three ${\rm b}$ quark jets), one lepton (electron or muon), and missing energy: ${\rm t\bar{t} \rightarrow (H^{+}b)(W^{-}\bar{b})}$ $\rightarrow {\rm (c\bar{b} b)} (l \bar{\nu} {\rm \bar{b}})$. The main observable used in the analysis is an invariant mass of two jets, one of which is identified as a b quark jet. The dijet pair is selected from at least four jets in an event by a dedicated kinematic fitter. No signal for the presence of a charged Higgs boson is observed and upper limits are set at 95\% confidence level on the branching ratio for ${\rm t \rightarrow H^{+} b}$ from 1.1--0.4\% for the charged Higgs boson mass in the range 90--150~GeV in the assumption of branching ratio of ${\rm B(H^{+} \rightarrow c\bar{b})=100\%}$ for the first time.

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