Exploring nonstandard Hbb¯ interactions at future electron-proton colliders

In this paper, we use the charged-current Higgs boson production process at future electron-proton colliders, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msup><a:mi>e</a:mi><a:mo>−</a:mo></a:msup><a:mi>p</a:mi><a:mo stretchy="false">→</a:mo><a:mi>H</a:mi><a:mi>j</a:mi><a:msub><a:mi>ν</a:mi><a:mi>e</a:mi></a:msub></a:math>, with the subsequent decay of the Higgs boson into a <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mi>b</d:mi><d:mover accent="true"><d:mi>b</d:mi><d:mo stretchy="false">¯</d:mo></d:mover></d:math> pair, to probe the Standard Model effective field theory with dimension-six operators involving the Higgs boson and the bottom quark. The study is performed for two proposed future high-energy electron-proton colliders, the Large Hadron Electron Collider (LHeC) and the Future Circular Collider (FCC-he) at the center-of-mass energies of 1.3 TeV and 3.46 TeV, respectively. Constraints on the <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mi>C</h:mi><h:mi>P</h:mi></h:math>-even and <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mi>C</j:mi><j:mi>P</j:mi></j:math>-odd <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi>H</l:mi><l:mi>b</l:mi><l:mover accent="true"><l:mi>b</l:mi><l:mo stretchy="false">¯</l:mo></l:mover></l:math> couplings are derived by analyzing the simulated signal and background samples. A realistic detector simulation is performed and a multivariate technique using the gradient boosted decision trees algorithm is employed to discriminate the signal from background. Expected limits are obtained at 95% confidence level for the LHeC and FCC-he assuming the integrated luminosities of 1, 2 and <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mrow><p:mn>10</p:mn><p:mtext> </p:mtext><p:mtext> </p:mtext><p:msup><p:mrow><p:mi>ab</p:mi></p:mrow><p:mrow><p:mo>−</p:mo><p:mn>1</p:mn></p:mrow></p:msup></p:mrow></p:math>. We find that using <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mrow><r:mn>1</r:mn><r:mtext> </r:mtext><r:mtext> </r:mtext><r:msup><r:mrow><r:mi>ab</r:mi></r:mrow><r:mrow><r:mo>−</r:mo><r:mn>1</r:mn></r:mrow></r:msup></r:mrow></r:math> of data, the <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mi>C</t:mi><t:mi>P</t:mi></t:math>-even and <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:mi>C</v:mi><v:mi>P</v:mi></v:math>-odd <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:mi>H</x:mi><x:mi>b</x:mi><x:mover accent="true"><x:mi>b</x:mi><x:mo stretchy="false">¯</x:mo></x:mover></x:math> couplings can be constrained with accuracies of the order of <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"><bb:msup><bb:mn>10</bb:mn><bb:mrow><bb:mo>−</bb:mo><bb:mn>3</bb:mn></bb:mrow></bb:msup></bb:math> and <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msup><db:mn>10</db:mn><db:mrow><db:mo>−</db:mo><db:mn>2</db:mn></db:mrow></db:msup></db:math>, respectively, and a significant region of the unprobed parameter space becomes accessible.