Leptophobic Z ′ in models with multiple Higgs doublet fields

We study the collider phenomenology of the leptophobic Z ′ boson from an extra U(1)′ gauge symmetry in models with N -Higgs doublet fields. We assume that the Z ′ boson at tree level has (i) no Z - Z ′ mixing, (ii) no interaction with the charged leptons, and (iii) no flavour-changing neutral current. Under such a setup, it is shown that in the N = 1 case, all the U(1)′ charges of left-handed quark doublets and right-handed up- and down- type quarks are required to be the same, while in the N ≥ 3 case one can take different charges for the three types of quarks. The N = 2 case is not well-defined under the above three requirements. We study the pp → Z ′ V → b b ¯ V $$ pp\to Z^{\prime }V\to b\overline{b}V $$ processes ( V = γ , Z and W ± ) with the leptonic decays of Z and W ± at the LHC. The most promising discovery channel or the most stringent constraint on the U(1)′ gauge coupling constant comes from the Z ′γ process below the t t ¯ $$ t\overline{t} $$ threshold and from the t t ¯ $$ t\overline{t} $$ process above the threshold. Assuming the collision energy of 8 TeV and integrated luminosity of 19.6 fb −1 , we find that the constraint from the Z ′γ search in the lower mass regime can be stronger than that from the UA2 experiment. In the N ≥ 3 case, we consider four benchmark points for the Z ′ couplings with quarks. If such a Z ′ is discovered, a careful comparison between the Z ′γ and Z ′ W signals is crucial to reveal the nature of Z ′ couplings with quarks. We also present the discovery reach of the Z ′ boson at the 14-TeV LHC in both N = 1 and N ≥ 3 cases