Production of Excited Neutrino at LHC

The proliferation of quarks and leptons can be naturally explained by the assumption that they are composite objects. According to models of compositeness[1], known fermions are bound states of more fundamental constituents – preons [2] or a fermion and a boson [3]. In the framework of these models, constituents of known fermions interact by means of new strong gauge interactions. One of the main consequences of the non-trivial substructure of the standard model (SM) fermions would be a rich spectrum of excited states[1, 4]. Observation of such fermionic excitations would be clear evidence of the underlying subtructure of known fermions. Therefore, one of the tasks of great importance for TeV energy scale colliders is to probe possible substructures of leptons and quarks and test the variety of compositeness models. The SM can be considered as the low energy limit of a more fundamental theory which is characterized by a large mass scale Λ. The existence of four-fermion contact interactions would be a signal of new physics beyond the SM. The nature of this new physics can be probed if the experimental energy scale is high enough. It is expected that the next generation of hadron colliders like the LHC, which will achieve very high centre of mass energies, will extend the search for composite states. In particular, contact interactions may be an important source for excited lepton production at the CERN LHC. The excited states of the SM fermions can interact via SM gauge field interactions and also via new gauge strong interactions between preons. The later leads to effective contact interactions between quarks and leptons and/or their excited states in the low energy limit. Many recent experimental studies have been devoted to the search for quark and lepton compositeness and excited states at LEP([5]), HERA([6]), and TEVATRON([7]). No signals from contact interactions and excited fermions have been found so far. Studies mentioned above put limits: i) on the compositeness scale in the range of 2-8 TeV, depending on the type of the contact interactions, and ii) on the excited fermion mass up to the collider center-of-mass energy. Based on previous studies [8, 4, 9, 10, 11], we expect that the LHC collider will put the most stringent constraints on the composite models and/or the masses of excited fermions.