Extrapolation of ATLAS sensitivity to $H\rightarrow b\bar{b}$ and $H\rightarrow c\bar{c}$ decays in $VH$ production at the HL-LHC

The expected sensitivity of the measurements of Higgs boson decays into $b\bar{b}$ and $c\bar{c}$ with the ATLAS detector at the HL-LHC is estimated by extrapolating the results obtained using a dataset of $\sqrt{s}=13\,\mathrm{TeV}$ $pp$ collisions corresponding to an integrated luminosity of $139\,\mathrm{fb^{-1}}$. The associated production of a Higgs boson with either a $W$ or a $Z$ boson, targeting Higgs boson decays to $b$- or $c$-quarks and $W$ or $Z$ boson decays to leptons, is presented. A HL-LHC scenario in which a dataset of $\sqrt{s}=14\,\mathrm{TeV}$ $pp$ collisions corresponding to an integrated luminosity of $3000\,\mathrm{fb^{-1}}$ is assumed. The projection of the existing measurements is performed accounting for both statistical and systematic uncertainties. For the measurements of the $ZH,H\to b\bar{b}$ and $WH,H\to b\bar{b}$ processes, projected uncertainties are estimated to be 7\% and 8\% respectively. Fiducial cross-sections for the $VH,H\to b\bar{b}$ processes are measured as a function of the vector boson transverse momentum in kinematic fiducial volumes. The estimated total uncertainties vary from 7\% in the high transverse momentum regions to 18\% in the low transverse momentum regions. For Higgs boson decays to $c\bar{c}$, produced in association with a $W$ or a $Z$ boson, an expected upper limit of $6.4$ times the predicted cross-section times branching fraction for the process is estimated, corresponding to an expected constraint on the charm quark Yukawa coupling modifier $|\kappa_c| < 3.0$, at the 95\% confidence level. The combination of the measurements of the $VH,H\to b\bar{b}$ and $VH,H\to c\bar{c}$ processes leads to an expected constraint on the ratio of coupling modifiers $|\kappa_c/\kappa_b| < 2.7$ at 95\% confidence level.