Search for $H\to c\bar{c}$ and measurement of $H\to b\bar{b}$ in vector-boson fusion production with the ATLAS Detector

A search for Standard Model (SM) Higgs bosons produced via vector-boson fusion at the Large Hadron Collider and decaying into a charm quark-antiquark pair ($H\to c\bar{c}$) is presented. The datasets used correspond to integrated luminosities of 37.5 fb${}^{-1}$ and 51.5 fb${}^{-1}$ and were collected by the ATLAS detector from proton-proton collisions at $\sqrt{s}$=13 and 13.6 TeV, respectively. The observed (expected) upper limit on the $H\to c\bar{c}$ production cross-section times branching ratio is 41 (28) times the SM prediction at 95% confidence level. Combining this search with the previous $H\to c\bar{c}$ search in associated production with a $W$ or $Z$ boson yields an observed (expected) limit on the Higgs-charm Yukawa coupling modifier of $\mathrm{\mid }{\kappa }_c\mathrm{\mid }$ < 4.7 (3.9). Higgs bosons decaying into a bottom quark-antiquark pair ($H\to b\bar{b}$) are measured simultaneously using the 51.5 fb${}^{-1}$ dataset at $\sqrt{s}$=13.6 TeV, with an observed signal strength of 0.97${}_{-0.50}^{+0.57}$ relative to the SM expectation. When combined with previous $H\to b\bar{b}$ results at 13 TeV, the observed (expected) significance reaches 3.2 (3.6) standard deviations, providing evidence for $H\to b\bar{b}$ events from vector-boson fusion.