Abstract
A gauged U(1)X extension of the Standard Model is a simple and consistent framework to naturally incorporate three right-handed neutrinos (RHNs) for generating the observed light neutrino masses and mixing by the type-I seesaw mechanism. We examine the collider testability of the U(1)X model, both in its minimal form with the conventional charges, as well as with an alternative charge assignment, via the resonant production of the U(1)X gauge boson (Z′) and its subsequent decay into a pair of RHNs. We first derive an updated upper limit on the new gauge coupling gX as a function of the Z′-boson mass from the latest LHC dilepton searches. Then we identify the maximum possible cross section for the RHN pair-production under these constraints. Finally, we investigate the possibility of having one of the RHNs long-lived, even for a TeV-scale mass. Employing the general parametrization for the light neutrino mass matrix to reproduce the observed neutrino oscillation data, we perform a parameter scan and find a simple formula for the maximum RHN lifetime as a function of the lightest neutrino mass eigenvalue (mlightest). We find that for mlightest≲10−5 eV, one of the RHNs in the minimal U(1)X scenario can be long-lived with a displaced-vertex signature which can be searched for at the LHC and/or with a dedicated long-lived particle detector, such as MATHUSLA. In other words, once a long-lived RHN is observed, we can set an upper bound on the lightest neutrino mass in this model.
Highlights
The existence of nonzero neutrino masses and flavor mixing has been unambiguously established by the observation of neutrino oscillation phenomena in solar, atmospheric, reactor and accelerator neutrinos [1]
From the experimental point of view, it is of particular interest if the right-handed neutrinos (RHNs) mass-scale is around TeV or smaller, so that they are kinematically accessible at the Large Hadron Collider (LHC) and can lead to the smoking-gun lepton number violating (LNV) signature of same-sign dilepton plus jets without missing transverse energy [8]
We find that for mlighest 10−5 eV (10−8 eV), the RHN can be long-lived enough to be explored by the high-luminosity phase of the LHC (HL-LHC) (MATHUSLA)
Summary
The existence of nonzero neutrino masses and flavor mixing has been unambiguously established by the observation of neutrino oscillation phenomena in solar, atmospheric, reactor and accelerator neutrinos [1]. We consider two scenarios for the B − L charges of the RHNs in the U (1)X model, both of which are consistent with anomaly cancellation: (i) the conventional case with a B − L charge −1 assigned to all three RHNs, and (ii) the alternative case with a B − L charge −4 assigned to two of the RHNs and +5 for the third one In both cases, we present the dilepton production cross section from the Z boson resonance as a function of the U(1)X gauge coupling (gX) and Z boson mass (mZ ), from which we can read off the upper (lower) bound on gX (mZ ) for a fixed mZ (gX) value by using the current/future LHC constraints.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
