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

Abstract

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 ($H\rightarrow c\bar{c}$) 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 $H\rightarrow c\bar{c}$ production cross-section times branching ratio is 41 (28) times the SM prediction at 95% confidence level. Combining this search with the previous $H\rightarrow c\bar{c}$ search in associated production with a $W$ or $Z$ boson yields an observed (expected) limit on the Higgs-charm Yukawa coupling modifier of $|κ_{c}| $ < 4.7 (3.9). Higgs bosons decaying into a bottom quark-antiquark pair ($H\rightarrow b\bar{b}$) are measured simultaneously using the 51.5 fb$^{-1}$ dataset at $\sqrt{s}$=13.6 TeV, with an observed signal strength of 0.97$^{+0.57}_{-0.50}$ relative to the SM expectation. When combined with previous $H\rightarrow b\bar{b}$ results at 13 TeV, the observed (expected) significance reaches 3.2 (3.6) standard deviations, providing evidence for $H\rightarrow b\bar{b}$ events from vector-boson fusion.

Figures (2)

• Figure 1: Higgs candidate mass distribution with all SRs weighted by $\ln(1+s/b)$ and summed for the (a) $H \to b\bar{b}$ channel and (b) $H \to c\bar{c}$ channel. The value of $s$ ($b$) is calculated from the observed Higgs boson signal (post-fit background yields) in each region. The bottom panel shows the difference between the weighted data and the Non-res. bkgd. The diagonally striped band represents the total uncertainty of the fitted background and signal.
• Figure 2: Distributions of ANN output scores for the $\text{VBF } H\to c\bar{c}$ signal MC events, $\text{VBF } H\to b\bar{b}$ signal MC events, ggF MC events, and data sidebands in the (a) $b\bar{b}$ Run-3, (b) $c\bar{c}$ Run-2, and (c) $c\bar{c}$ Run-3 channels. The errors are statistical only. Vertical lines indicate the ANN score thresholds defining the six signal regions (SR1--SR6), in right-to-left order, with the rightmost region SR1 being the most signal-like. No separation between $b\bar{b}$ and $c\bar{c}$ signals is expected in the $b\bar{b}$ ANN since tagging information is not used in this channel, while such separation is visible in the $c\bar{c}$ ANN, which includes tagging inputs.