Probing unparticle theory via lepton-flavor violating process J/ψ→ll′ at BESIII

Abstract

The lepton flavor violating process J/ψ → ll ′ (l = l ′ ) serves as an ideal place to probe the unparticle theory. Such process can only occur at loop level in the Standard model (SM), so that should be very suppressed, by contrast in unparticle scenario, it happens at tree level and its contribution may be sizable for practical measurement. Moreover, the BESIII will offer the largest database on J/ψ which makes more accurate measurements possible. Furthermore, for such purely leptonic decays background is relatively low and signal would be cleaner. Our work carefully investigates the possibility of observing such processes from both theoretical and experimental aspects.

Mini-review of rare charmonium decays at BESIII

“…Here ∆M ν is the difference between the masses of neutrinos of different flavor and M W is the mass of the charged weak vector boson. Hence, CLFV offers an opportunity to probe signature of new physics [42][43][44][45][46]. The CLFV charmonium decays J/ψ → ll ′ (l and l ′ = τ, µ, e, l = l ′ ) are predicted by various theoretical models that allow tree-level FCNC, including, e.g., unparticle theory [46,47], R-parity violating and large tanβ SUSY scenarios, leptoquarks, and other models inspired by the idea of grand unification [44,45].…”

The Decay Rate of J /ψ to Λ c + in and beyond the Standard Model

“…At first sight, the unparticle scenario might provide a larger contribution to the decay mode because no heavy weak scale M W exists at its propagator. However, the data of D 0 − D0 mixing, [13] neutrino experiment [24] and lepton flavor violation [25] rigorously constrain the effective couplings of the unparticle and the SM particles, thus one cannot freely adjust anything at all. The resultant contribution of the unparticle to the decay width is many orders of magnitude smaller than that of the SM.…”

The lepton flavor violating decays of vector mesons in the MRSSM

“…Nevertheless, the branching ratios of the LFV decays can be enhanced in various extensions of the SM, such as the grand unified models [10][11][12], the supersymmetric models with and without R-parity [13,14], the left-right symmetry models [15][16][17] and so on. The LFV decays of the neutral vector mesons have been studied in several new physics scenarios [9,[18][19][20][21][22][23] and in a model-independent way [24][25][26][27][28][29]. It has been shown that BR(V → l 1 l2 ) can be significantly enhanced close to the current or future experimental sensitivities.…”