Heavy Majorana Neutrinos ate+e−Colliders

Abstract

We investigate possibilities for detecting heavy Majorana neutrinos (N's) in e 1 e 2 at LEP200 and future linear colliders. We concentrate on the processes where the pairs of intermediate heavy N's produce a clear signal of total lepton number violation ͑e 1 e 2 ! NN ! W 1 l 2 W 1 l 02 ͒. Such a signal is not possible if the heavy neutrinos are of Dirac nature. Our approach is general in the sense that the intermediate N's can be either on shell or off shell. Discussion of the relative numerical importance of the s and the t 1 u channels of the NN production is also included. [S0031-9007(99) There has been a significant amount of activity in the high energy physics community towards discerning the nature of the neutrino sector. A basic question is: Are neutrinos Dirac or Majorana particles? If there are no right-handed currents, then it is virtually impossible to discern the nature of the light neutrinos [1]. If there are heavy neutrinos ͑M ϳ 10 2 GeV͒, then present and future experiments offer a realistic prospect of establishing their nature. The production cross section of heavy Majorana neutrinos (N's), mostly via the e 1 e 2 collisions, has therefore been investigated in the past [2]. Most of these works have been done within specific (classes of) models, and it has been assumed that the center-of-mass (CMS) energy p s in the process is high enough for the production of on-shell (OS) heavy N's. The effects of the offshell (nOS) N's have been ignored. Moreover, to our knowledge, various distributions of N's decay products ͓N ! W 6 ᐉ 7 ͑! jets 1 ᐉ 7 ͔͒, which are produced in the full reaction and which can actually be detected, have not been investigated in a quantitative way. The main reason for this was that the expressions for invariant amplitudes with two on-shell N's apparently do not allow a straightforward calculation of such distributions. We note that the detection of events for the reactions e 1 e 2 ! NN ! W 6 ᐉ 7 W 6 ᐉ 07 ! jets 1 ᐉ 7 ᐉ 07 , which violate the total lepton number, would be a clear signal of the Majorana character of the intermediate neutrinos.We present some results of calculations for the aforementioned reactions. We do not restrict ourselves to any specific (classes of) models. In contrast to the available literature, our approach allows us to account also for the effects of off-shell intermediate N's on the cross sections s. This enables us to investigate deviations from the previously known s's, in the "2OS" kinematic region ͑ p s . 2M . 2M W ͒ where both intermediate N's can, but need not, be on shell-these deviations are termed "finite width effects." Our approach allows us to calculate the s's, and various distributions, also in the "1OS"where at most one intermediate N can (but need not) be on shell, and in the "nOS" region ͑M 1 M W . p s ͒, where both N's always have to be off shell. Our approach makes possible a straightforward calculation of various distributions of final particles. As an illustration, we include an angular distribution of the final state leptons ᐉ, ᐉ 0 ....

Heavy Majorana neutrino production at electron-muon colliders

“…Eq. (2)] are severely restricted by available experimental data (LEP and low-energy data) [13,14]: 3 In the simpler 1OS and 2OS expressions for |M| 2 , these factors are different. For the 2OS expression, the factor is (1/2) because the two intermediate on-shell N 's are indistinguishable, and thus their decay product pairs (W + ℓ − i , W + ℓ − j ) are also kinematically indistinguishable.…”

“…The second point does not apply in the case of µ − µ + colliders, the case which we therefore do not consider in the present paper. As in the previous paper [3], our analysis is rather general, in the sense that we do not restrict ourselves to any specific (classes of) models. Further, we use basically the same set of programs developed by us there, this time adjusted to the case of eµ colliders.…”

Signature of heavy sterile neutrinos at CEPC

“…A stringent constraint on jR eN j 2 has been set for a mass region from 80 GeV to 205 GeV. Some efforts have been made to study the production and signature of heavy neutrinos in e þ e − or e − e − collision processes with both pair and single heavy neutrino productions, and various neutrino decay chains, lW, νZ and νH [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]; for a review, see [24]. Currently, new electronpositron colliders, such as CEPC, Future Circular Collider (FCC), and International Linear Collider (ILC), are under proposal.…”

Signatures of right-handed Majorana neutrinos and gauge bosons ineγcollisions

“…They provide beautiful signatures which can be tested at various collider options. Estimates of the discovery probability for heavy Majorana neutrinos at the LHC were done in [4] and for electron-positron colliders in [5]. An electron-electron collider provides specific and very useful option for Majorana neutrino search, the so called "the inverse double-β decay" process.…”