Implication of the ALEPH 30 GeV dimuon resonance at the LHC
  Recent reanalysis of ALEPH data on Z -> b bar{b} + X seems to indicate an existence of the dimuon excess around 30 GeV with a branching fraction for Z -> b bar{b} mu^+ mu^- around 1.1 X 10^{-5}. In this letter, we discuss three different types of simplified models for this possible excess. In the first class of models, we assume a new resonance couples to both b bar{b} and mu^+ mu^-. Within the allowed parameter space for the ALEPH data, this type of models is excluded because of too large Drell-Yan production of dimuon from the b bar{b} collision at the LHC. In the second model, we assume that the 30 GeV excess is a new gauge boson Z' that couples to the SM b and a new vectorlike singlet B quark heavier than Z and not to b bar{b}. Then one can account for the ALEPH data without conflict with the DY constraint. The new vectorlike quark B can be pair produced at the LHC 8/13 TeV by QCD with sigma(BB) ~ O(100-1000) pb, and Bq production rate is sigma(Bq) ~ a few pb which is larger than sigma(Bb) roughly by an order of magnitude. Their signatures at the LHC would be 2b + 4mu, bj + 2mu and 2b + 2mu, respectively, which however might have been excluded already by LHC run I and II data since the multi-muon events have low SM background and are rare at the LHC. In the third model, we consider Z -> Z' phi followed by Z' -> mu^+ mu^- and phi -> b bar{b} assuming that the Higgs field for Z' mass is also charged under the SM U(1)_Y gauge symmetry. In this class of model, we could accommodate the Br(Z -> b bar{b} mu^+ mu^-) ~ 1.1 X 10^{-5} if we assume very large U(1)' charge for the U(1)' breaking Higgs field. Finally, we study various kinematic distributions of muons and b jets in all the three models, and find that none of the models we consider in this paper are not compatible with the kinematic distributions extracted from the ALEPH data. 
P. Ko, Jinmian Li, Chaehyun Yu
hep-ph hep-ex