Exploring Higgs EFT in $$ t\overline{t} hh $$ at high luminosity LHC

A bstract The non-resonant production of a Higgs boson pair in association with a top-antitop quark pair $$ \left( pp\to t\overline{t} hh\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mi>pp</mml:mi> <mml:mo>→</mml:mo> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>hh</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> has only recently begun to be explored at the Large Hadron Collider (LHC) and provides a unique and largely uncharted probe of the top-Higgs sector, offering complementary sensitivity to the Higgs self-coupling and higher-dimensional interactions beyond the Standard Model. In this work, we present a detailed study of this process within the framework of Higgs Effective Field Theory (HEFT) at the High-Luminosity LHC (HL-LHC). A comparative analysis is performed using a traditional cut-based approach in the single-lepton channel and a multivariate parametric boosted decision tree method in both single-lepton and dilepton final states. We derive one- and two-parameter limits at 95% confidence level on the HEFT couplings δκ λ , c 2 , c 2 g , c tg , and c tg 2 . The projected bound on δκ λ is weaker than current experimental constraints from dedicated Higgs-pair measurement; however, this coupling plays a critical role in shaping the multidimensional allowed parameter space. For the remaining HEFT couplings, where no direct experimental limits currently exist, our results provide the first sensitivity projections in the $$ t\overline{t} hh $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>hh</mml:mi> </mml:math> channel. Overall, this study demonstrates the strong potential of the $$ t\overline{t} hh $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>hh</mml:mi> </mml:math> production process to probe extended Higgs and top-quark interactions beyond the Standard Model through the exploitation of the $$ t\overline{t} hh $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>t</mml:mi> <mml:mover> <mml:mi>t</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>hh</mml:mi> </mml:math> data at the HL-LHC.