Fourth standard model family neutrino at future linear colliders

Abstract

It is known that Flavor Democracy favors the existence of the fourth standard model (SM) family. In order to give nonzero masses for the first three family fermions Flavor Democracy has to be slightly broken. A parametrization for democracy breaking, which gives the correct values for fundamental fermion masses and, at the same time, predicts quark and lepton CKM matrices in a good agreement with the experimental data, is proposed. N 1 )→ µ ± W ∓ ) provide cleanest signature at e⁺e⁻ colliders. Meanwhile, in our parametrization this channel is dominant. W bosons produced in decays of the fourth family neutrinos will be seen in detector as either di-jets or isolated leptons. As an example we consider the production of 200 GeV mass fourth family neutrinos at GeV 500 s = linear colliders by taking into account di-muon plus four-jet events as signatures.

Flavor Democracy in Particle Physics

“…The masses of the first three SM family fermions, as well as observable interfamily mixings, are generated due to the small deviations from the full flavor democracy [11,13,14]. The parametrization proposed in [11] gives the values of the fundamental fermion masses and at the same time predicts the values of the quark and the lepton CKM matrices which are in good agreement with the experimental data. In principle, flavor democracy provides the possibility to obtain the small masses for the first three neutrino species without the see-saw mechanism [15].…”

“…The fourth family leptons will clearly manifest themselves at the future lepton and photon colliders [11,23]. Also, the number of different fourth family quarkonium states can be produced resonantly at lepton and photon machines.…”

“…An ultimate upper limit for fourth family fermions is 2.5 TeV, which corresponds to a 2 /4π = 1. The situation may be quite different in neutrino sector if their masses have Majorana nature (for details, see [11]). Let us mention that Majorana neutrinos relax the restriction on the number of extra families coming from the precision electroweak data because their give negative contribution to parameter S.…”

“…The mass resolution is estimated to be 20 (40) GeV for m u4 = 300 (700) GeV. The small interfamily mixings [11,14] lead to the formation of the fourth family quarkonia [16,18]. The most promising candidate for the LHC is the pseudo-scalar quarkonium state, η 4 , which will be produced resonantly resonantly via gluon-gluon fusion.…”

Prospects for the discovery of 4th family quarks with the ATLAS detector

“…This is also experimentally hinted by the value of the ρ parameter which is close to unity [8]. Therefore, if the fourth SM family exists, the Large Hadron Collider (LHC) will copiously produce its quarks [9] and the proposed linear colliders will provide opportunity to discover its leptons [10]. As the single production of the new quarks in LHC is suppressed as compared to their pair production, due to the small value of the CKM matrix elements, the latter is considered.…”