Revealing the origin of neutrino masses through displaced shower searches in the CMS muon system

This is the authors' abstract. We don't add key points for this paper.

We study the potential to probe the origin of neutrino masses, by searching for long-lived right-handed neutrinos (RHNs) <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>N</a:mi></a:math> in the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>B</c:mi><c:mo>−</c:mo><c:mi>L</c:mi></c:math> model and in the RHN-extended Standard Model (SM) effective field theory (EFT). Despite the small active-sterile mixing <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mo stretchy="false">|</e:mo><e:msub><e:mi>V</e:mi><e:mrow><e:mo>ℓ</e:mo><e:mi>N</e:mi></e:mrow></e:msub><e:msup><e:mo stretchy="false">|</e:mo><e:mn>2</e:mn></e:msup></e:math>, RHNs are produced abundantly via SM and exotic Higgs production, as long as the Higgs mixing or EFT operator coefficient is sufficiently large. We reinterpret a search for displaced showers in the CMS muon system and we find that it is sensitive to parameter space at and below the seesaw floor, <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mo stretchy="false">|</i:mo><i:msub><i:mi>V</i:mi><i:mrow><i:mo>ℓ</i:mo><i:mi>N</i:mi></i:mrow></i:msub><i:msup><i:mo stretchy="false">|</i:mo><i:mn>2</i:mn></i:msup><i:mo>≈</i:mo><i:msup><i:mn>10</i:mn><i:mrow><i:mo>−</i:mo><i:mn>12</i:mn></i:mrow></i:msup></i:math> (<m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mo>ℓ</m:mo><m:mo>=</m:mo><m:mi>e</m:mi></m:math>, <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mi>τ</o:mi></o:math>) for <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msub><q:mi>m</q:mi><q:mi>N</q:mi></q:msub><q:mo>≈</q:mo><q:mn>40</q:mn><q:mtext> </q:mtext><q:mtext> </q:mtext><q:mi>GeV</q:mi></q:math>. With existing data constraining such well-motivated scenarios of neutrino mass generation, we determine the projected sensitivity at the HL-LHC, motivating dedicated searches for long-lived RHNs with decay lengths <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:mo>≈</s:mo><s:mn>10</s:mn><s:mtext> </s:mtext><s:mtext> </s:mtext><s:mi mathvariant="normal">m</s:mi></s:math>.