Probing Trilinear Higgs Self-coupling at the HL-LHC via Multivariate Analysis

Abstract

We perform a multivariate analysis of Higgs-pair production in $HH\to b\bar{b}\gamma \gamma$ channel at the HL-LHC to probe the trilinear Higgs self--coupling ${\lambda }_{3H}$, which takes the value of 1 in the SM. We consider all the known background processes. Also, for the signal we are the first to adopt the most recent event generator of POWHEG-BOX-V2 to exploit the NLO distributions for Toolkit for Multivariate Data Analysis (TMVA), taking account of the full top--quark mass dependence. Through Boosted Decision Tree (BDT) analysis trained for ${\lambda }_{3H}=1$, we find that the significance can reach up to 1.95 with about $9$ signal and $18$ background events. In addition, the Higgs boson self-coupling can be constrained to $1.00<{\lambda }_{3H}<6.22$ at 95\% confidence level (CL). We also perform a likelihood fitting of $M_{\gamma \gamma bb}$ distribution and find the $1\sigma$ confidence interval (CI) of $0.1<{\lambda }_{3H}<2.2\cup 5.4<{\lambda }_{3H}<6.6$ for the ${\lambda }_{3H}=1$ nominal set. On the other hand, using BDTs trained for each value of ${\lambda }_{3H}$, we find a bulk region of $0.5<\sim {\lambda }_{3H}<\sim 4.5$, for which it is hard to pin down the trilinear coupling.

Comments: 18 pages, 6 figures, 4 tables; improved results presented