Search for nonresonant pair production of Higgs bosons in the $b\bar{b}b\bar{b}$ final state in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for nonresonant Higgs boson pair production in the four-bottom-quark final state using 13 TeV proton-proton collision data, setting limits on production cross-sections and Higgs couplings.

Contribution

First search for nonresonant Higgs pair production in the $b\bar{b}b\bar{b}$ channel with ATLAS data, providing new constraints on Higgs couplings and effective field theory parameters.

Findings

No evidence of Higgs pair production was observed.

Upper limit on production cross-section is 5.4 times the Standard Model prediction.

Constraints on Higgs self-coupling and couplings to vector bosons were established.

Abstract

A search for nonresonant Higgs boson pair production in the $b\bar{b}b\bar{b}$ final state is presented. The analysis uses 126 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}={13}$ TeV collected with the ATLAS detector at the Large Hadron Collider, and targets both the gluon-gluon fusion and vector-boson fusion production modes. No evidence of the signal is found and the observed (expected) upper limit on the cross-section for nonresonant Higgs boson pair production is determined to be 5.4 (8.1) times the Standard Model predicted cross-section at 95% confidence level. Constraints are placed on modifiers to the $HHH$ and $HHVV$ couplings. The observed (expected) $2\sigma$ constraints on the $HHH$ coupling modifier, $\kappa_\lambda$, are determined to be $[-3.5, 11.3]$ ($[-5.4, 11.4]$), while the corresponding constraints for the $HHVV$ coupling modifier, $\kappa_{2V}$, are $[-0.0, 2.1]$ ($[-0.1, 2.1]$). In addition, constraints on relevant coefficients are derived in the context of the Standard Model effective field theory and Higgs effective field theory, and upper limits on the $HH$ production cross-section are placed in seven Higgs effective field theory benchmark scenarios.