Prospects for exotic h→4τ decays in single and di-Higgs boson production at the LHC and future hadron colliders

We study the prospects for observing exotic decays of the Standard Model Higgs boson <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>h</a:mi></a:math> into light beyond the Standard Model scalars <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>a</c:mi></c:math> with mass <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi>m</e:mi><e:mi>a</e:mi></e:msub><e:mo>≲</e:mo><e:msub><e:mi>m</e:mi><e:mi>h</e:mi></e:msub><e:mo>/</e:mo><e:mn>2</e:mn></e:math> in the single Higgs and Higgs pair production channels at the high luminosity run of the Large Hadron Collider (HL-LHC). Discovery prospects for single Higgs production in the gluon-gluon fusion and vector boson fusion modes with the Higgs boson decaying via the exotic mode <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>h</g:mi><g:mo stretchy="false">→</g:mo><g:mi>a</g:mi><g:mi>a</g:mi><g:mo stretchy="false">→</g:mo><g:mn>4</g:mn><g:mi>τ</g:mi></g:math> are analyzed at the HL-LHC. The projected sensitivity for exotic Higgs decays in the nonresonant Higgs pair production channel <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>p</k:mi><k:mi>p</k:mi><k:mo stretchy="false">→</k:mo><k:mi>h</k:mi><k:mi>h</k:mi><k:mo stretchy="false">→</k:mo><k:mo stretchy="false">(</k:mo><k:mi>h</k:mi><k:mo stretchy="false">→</k:mo><k:mi>b</k:mi><k:mover accent="true"><k:mi>b</k:mi><k:mo stretchy="false">¯</k:mo></k:mover><k:mo stretchy="false">)</k:mo><k:mo stretchy="false">(</k:mo><k:mi>h</k:mi><k:mo stretchy="false">→</k:mo><k:mi>a</k:mi><k:mi>a</k:mi><k:mo stretchy="false">→</k:mo><k:mn>4</k:mn><k:mi>τ</k:mi><k:mo stretchy="false">)</k:mo><k:mo stretchy="false">→</k:mo><k:mn>2</k:mn><k:mi>b</k:mi><k:mn>4</k:mn><k:mi>τ</k:mi></k:math> at the HL-LHC and a future <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:msqrt><y:mi>s</y:mi></y:msqrt><y:mo>=</y:mo><y:mn>100</y:mn><y:mtext> </y:mtext><y:mtext> </y:mtext><y:mi>TeV</y:mi></y:math> hadron collider (FCC-hh) are also estimated. Furthermore, we study HL-LHC’s potential reach for the Higgs-strahlung process in the <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mn>2</ab:mn><ab:mi>b</ab:mi><ab:mn>4</ab:mn><ab:mi>τ</ab:mi></ab:math> channel, taking into account the contamination from nonresonant Higgs pair production. Finally, the potential reach for resonant Higgs pair production in the <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"><cb:mn>2</cb:mn><cb:mi>b</cb:mi><cb:mn>4</cb:mn><cb:mi>τ</cb:mi></cb:math> channel at the HL-LHC is also explored for several choices of <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"><eb:mo stretchy="false">{</eb:mo><eb:msub><eb:mi>m</eb:mi><eb:mi>H</eb:mi></eb:msub><eb:mo>,</eb:mo><eb:msub><eb:mi>m</eb:mi><eb:mi>a</eb:mi></eb:msub><eb:mo stretchy="false">}</eb:mo></eb:math>. Our studies suggest that significant improvements over existing bounds are achievable in several production channels, motivating new dedicated searches for <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:mi>h</ib:mi><ib:mo stretchy="false">→</ib:mo><ib:mi>a</ib:mi><ib:mi>a</ib:mi><ib:mo stretchy="false">→</ib:mo><ib:mn>4</ib:mn><ib:mi>τ</ib:mi></ib:math> at the HL-LHC and future colliders. Published by the American Physical Society 2024