Triplet with a doubly-charged lepton at the LHC

Abstract

We studied the signatures of an electroweak SU(2) lepton triplet which contains a doubly charged heavy lepton. The most interesting and easily detected final states are originating from the doubly charged lepton pair and single production, that we analyzed at a center of mass energy of 14 TeV. We propose useful kinematic cuts to reduce the backgrounds and computed the integrated luminosity needed to discover or exclude the doubly charged leptons for various masses.PACS numbers: 14.60. Hi, 14.60.Pq, 14.60.St, 12.15.Ff INTRODUCTIONAlthough the Standard Model (SM) of electroweak interactions explains with great accuracy almost all of the available experimental data, there are good reasons to believe that it is not the ultimate theory to describe Nature. The main motivation behind the expectation of new physics around the TeV scale is the naturalness of the Higgs mass, and consequently of the the electroweak scale. The discovery of a light scalar with the properties expected for the SM Higgs boson at the LHC, announced on july 4 th 2012, has completed the list of particles predicted by the SM, and also brought to reality the problem of naturalness.In fact we now know that there exists a light scalar associated with the breaking of the electroweak scale, and a reason for its lightness is still lacking.Many models of new physics addressing the naturalness problem have been proposed in the last few years, and a common feature is the prediction of the existence of new particles 2 not far from the TeV scale, which is now being tested at the LHC. Even though all the searches have given negative results, there is still plenty of space for the presence of new particles below the TeV. In fact, a hasty glimpse at the bounds on new physics, both supersymmetric and exotic, can leave the impression that most of the bounds are well above the TeV scale: the reason for this is that the quoted bounds refer to particles which are easy to detect and with large production rates. Such cases often correspond to less motivated or interesting scenarios. Light states are still allowed if their couplings are suppressed, or they decay into finals states affected by large backgrounds, or they are not efficiently produced at the LHC. In this paper we are interested in the latter case: we will in fact consider the LHC phenomenology of heavy exotic leptons, which have small production cross sections compared to colored states. Such states would be interesting per se as a challenging channel for the LHC experiments, moreover some models predict their presence.For instance, Little Higgs models, models of composite Higgs and extra dimensions all include leptonic partners together with quark partners. If partners of the top are necessary to cancel the large quadratic divergences generated by the top mass [1], leptonic partners are necessary for a consistent inclusion of the lepton mass generation and a study of their phenomenology in models with T-parity can be found in [2]. New leptonic (un-colored) states are also necessary in some technicol...

A call for new physics: The muon anomalous magnetic moment and lepton flavor violation

“…Doubly charged fermions, which appear as components of fermionic SU (2) L triplet fields [223], exotic doublets [224], as well as in composite Higgs models with extended isospin multiplets [225][226][227][228]. They interact with SM leptons as follows:…”

New vector-like fermions and flavor physics

“…6 Despite the stated uncertainty, the probability that all 7 observed events were due to background was quoted as 0.001 [41]. 7 At the SM level, B → Kνν is expected to get large backgrounds from B → K * νν [28]. While Br(B → Kνν) depends only on C+ν , Br(B → K * νν) also depends on C−ν , slightly complicating the analysis.…”

“…(For some earlier studies of such models, see, e.g., refs. [1][2][3][4][5][6][7][8][9][10].) We focus on vector-like fermions that can have Yukawa couplings involving the Higgs field and the SM fermions.…”

Doubly charged lepton from an exotic doublet at the LHC

“…[17]. After introducing the general parametrization of a model that is a simple extension of the standard model plus the new lepton doublet, we will present the results of the application of the searches studied in our previous work [11] to the doublet case, and discuss the prospects to distinguish the two representations at the LHC at 14 TeV. …”