Lepton flavour violating signature in supersymmetric U(1)′ seesaw models at the LHC

Abstract

We consider a U(1) supersymmetric seesaw model in which a right-handed sneutrino is a thermal dark matter candidate whose relic density can be in the right range due to its coupling to relatively lightZ , the superpartner of the extra gauge boson Z . Such lightZ can be produced at the LHC through cascade decays of colored superparticles, in particular, stops and sbottoms, and then decay to a right-handed neutrino and a sneutrino dark matter, which leads to lepton flavor violating signals of same/opposite-sign dileptons (or multileptons) accompanied by large missing energy. Taking some benchmark points, we analyze the opposite-and same-sign dilepton signatures and the corresponding flavour difference i.e., (2e − 2µ). It is shown that 5σ signal significance can be reached for some benchmark points with very early data of ∼ 2 fb −1 integrated luminosity. In addition, 3 and 4 signatures also look promising to check the consistency in the model prediction, and it is possible to reconstruct theZ mass from jj invariant mass distribution.

Displaced lepton flavour violating signatures of right-handed sneutrinos in U(1)′ supersymmetric models

“…The decays of Z → NÑ 1,2 could be an alternative source of such RHN. Being electro-weak in nature, pair production ofZ is suppressed and it is encouraged to look forZ is supersymmetric (SUSY) cascade decays [9]. From figure 13 of [6], we can see that the right-handed down type squark mostly decays toZ for the U(1) χ model, which is a feature of U(1) χ model.…”

“…and a dark matter candidate [6]. The wino-like charginoχ ± 1 is the NLSP and the heavier sneutrinoÑ 2 stays as NNLSP.Z can be produced from the decays oft 1 andb 1 [6,9].…”

“…[9] for fixing the Higgs sector with decoupled first two generations of squark and gluino. The recent bounds from LHC on Higgs data [1], bounds on third generation SUSY masses [16,17] and recent bounds on lighter charginos and neutralinos production crosssections [7,8] are taken into account.…”

“…We consider the U(1) χ model for our explicit analysis as in [6,9,10] and the particle content is as follows:…”

Perspectives on a supersymmetric extension of the standard model with a Y = 0 Higgs triplet and a singlet at the LHC

“…Figure 5 shows the mass splitting between thet 2 andt 1 stops versus λ S , for several v S choices and with A t = 0. Large mass splittings can be generated without a large parameter A t , by a suitably large v S , which is a common choice if the singlet is gauged respect to an extra U(1) [59][60][61][62], due the mass bounds for the additional gauge boson Z [63,64]. The mass matrices for the stop and the sbottom are given by …”