Long-lived light neutralinos at future <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi></mml:math> factories
Zeren Simon Wang, Kechen Wang
Abstract
Future lepton colliders such as the Circular Electron Positron Collider (CEPC) and FCC (Future Circular Collider)-ee would run as high-luminosity $Z$-boson factories, which offer a unique opportunity to study long-lived particles which couple to Z bosons. In order to exemplify this particular advantage, in this work, we consider one benchmark physics scenario where the long-lived lightest neutralinos pair $({\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0})$ is produced from $Z$ decays in the context of the R-parity-violating supersymmetry. Our analysis indicates that when assuming $\mathrm{BR}(Z\ensuremath{\rightarrow}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0})={10}^{\ensuremath{-}3}$ and ${m}_{{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}}\ensuremath{\sim}40\text{ }\text{ }\mathrm{GeV}$, the model parameter ${\ensuremath{\lambda}}_{112}^{\ensuremath{'}}/{m}_{\stackrel{\texttildelow{}}{f}}^{2}$ can be discovered down to as low as $\ensuremath{\sim}1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ $(3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14})\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}2}$ at the FCC-ee (CEPC) with center-of-mass energy $\sqrt{s}=91.2\text{ }\text{ }\mathrm{GeV}$ and $150\text{ }(16)\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$ integrated luminosity. These limits exceed the projected sensitivity reaches of the ATLAS experiment at the high-luminosity Large Hadron Collider (LHC) and the proposed LHC experiments with far detectors (AL3X, CODEX-b, FASER, and MATHUSLA).