Unveiling the invisible: ALPs and sterile neutrinos at the LHC and HL-LHC

A bstract We investigate the potential of using the signature of mono-Higgs plus large missing energies to constrain on two new ph ysics models, namely the model of an axion-like particle (ALP) and the model of sterile neutrinos. We focus on the Higgs-ALP interactions starting at dimension-six and the Higgs-sterile neutrino interactions starting at dimension-five, via the processes pp → haa for ALP production and pp → hNN for sterile neutrinos at the LHC and High Luminosity LHC (HL-LHC), followed by the Higgs decay $$ h\to b\overline{b} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>h</mml:mi> <mml:mo>→</mml:mo> <mml:mi>b</mml:mi> <mml:mover> <mml:mi>b</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> . We establish bounds on the ALP-Higgs coupling $$ \frac{C_{aH}}{\Lambda^2} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:msub> <mml:mi>C</mml:mi> <mml:mi>aH</mml:mi> </mml:msub> <mml:msup> <mml:mi>Λ</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mfrac> </mml:math> and sterile neutrino-Higgs coupling $$ \frac{\lambda_3}{M_{\ast }} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:msub> <mml:mi>λ</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>∗</mml:mo> </mml:msub> </mml:mfrac> </mml:math> , respectively, for ALP and sterile-neutrino mass ranging from 1 to 60 GeV, using the recent ATLAS data on mono-Higgs plus missing energies at the LHC ( $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV and $$ \mathcal{L} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>L</mml:mi> </mml:math> = 139 fb −1 ). The most stringent constraint occurs in the missing transverse energy M ET range 200 &lt; M ET ≤ 350 GeV. We also estimate the sensitivities that we can achieve at the HL-LHC ( $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 14 TeV and $$ \mathcal{L} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>L</mml:mi> </mml:math> = 3000 fb −1 ). We obtain improved sensitivities across various missing energy regions. The ALP model exhibits better sensitivities, particularly at lower mass range, compared to the sterile neutrino model, which shows weaker sensitivities across similar mass and energy ranges. Our results underscore the potential of the mono-Higgs signature as a robust probe for physics beyond the Standard Model.