Heavy Majorana neutrino production at e−γ colliders

We study signatures of heavy Majorana neutrinos at e−γ colliders. Since these particles violate lepton number, they can give rise to the reactions e−γ→W−W−e+ and e−γ→W+μ−μ−ν. The Standard Model background contains extra light neutrinos that escape detection, and can be reduced to an unobservable level after imposing appropriate kinematical cuts. We analyze the physics potential of an e−γ collider, with centre of mass energies s=0.5-1TeV and a total integrated luminosity of 100 fb−1, for detecting heavy Majorana neutrinos with masses mN=100-400GeV. Assuming that heavy neutrinos couple predominantly to only one lepton flavour at a time, we find that 10 expected background-free events can be established for a WeN-coupling |BeN|≳4.6×10−3 or for a WμN-coupling |BμN|≳9.0×10−2. Instead, if no signal is observed, this will imply that |BeN|≲2.7×10−3 and |BμN|≲0.05 at the 90% confidence level.