Heavy neutral gauge bosons at the LHC in an extended MSSM

Abstract

Searching for heavy neutral gauge bosons Z ′ , predicted in extensions of the Standard Model based on a U(1) ′ gauge symmetry, is one of the challenging objectives of the experiments carried out at the Large Hadron Collider. In this paper, we study Z ′ phenomenology at hadron colliders according to several U(1) ′ -based models and in the Sequential Standard Model. In particular, possible Z ′ decays into supersymmetric particles are included, in addition to the Standard Model modes so far investigated. We point out the impact of the U(1) ′ group on the MSSM spectrum and, for a better understanding, we consider a few benchmarks points in the parameter space. We account for the D-term contribution, due to the breaking of U(1) ′ , to slepton and squark masses and investigate its effect on Z ′ decays into sfermions. Results on branching ratios and cross sections are presented, as a function of the MSSM and U(1) ′ parameters, which are varied within suitable ranges. We pay special attention to final states with leptons and missing energy and make predictions on the number of events with sparticle production in Z ′ decays, for a few values of integrated luminosity and centre-of-mass energy of the LHC.

Phenomenology of supersymmetric Z $$'$$ ′ decays at the Large Hadron Collider

“…[8,9,12] yielded substantial decay rates into supersymmetric particles and was consistent with the present exclusion limits, but did not take into account for the recent discovery of a Higgs-like boson. In this paper, I shall extend the work in [8,9] giving some useful benchmarks for possible Z searches within supersymmetry. First, it will be chosen a set of points in the parameter space yielding a SM-like Higgs boson with a mass around 125 GeV.…”

“…In this section, I shall discuss the theoretical framework of supersymmetric Z decays, already thoroughly reviewed in [5] and, more recently, in [8,9]. As discussed in [1,2], U(1) groups typically arise from the breaking of a Grand Unification gauge group E 6 of rank 6.…”

“…Possible decays Beyond the Standard Model (BSM), e.g. in supersymmetric particles, were investigated first in [5] and lately reconsidered in [6][7][8][9] within the Minimal Supersymmetric Standard Model [10,11]. Although SM decays are still dominant and the most promising for the searches, the opening of new channels decreases the branching ratios into electron and muon pairs and therefore the mass exclusion limits.…”

“…Although SM decays are still dominant and the most promising for the searches, the opening of new channels decreases the branching ratios into electron and muon pairs and therefore the mass exclusion limits. Reference [12], using a representative point of the MSSM parameter space as in [8,9], found that the LHC exclusion limits decrease by an amount m Z 150-300 GeV, once accounting for BSM decay modes at √ s = 8 TeV. From the viewpoint of supersymmetry, the lack of evidence of new particles in the LHC runs at 7 and 8 TeV, together with the discovery of a boson with mass m h = 125.7± 0.4 GeV [13] and properties consistent with the Standard Model Higgs boson [14,15], sets some tight constraints on the mass spectra and couplings of possible supersymmetric models.…”

“…On the contrary, Refs. [8,9] only calculated total production cross sections and branching ratios and left the investigation of differential distributions as an open issue. Furthermore, I shall also account for an effective supersymmetric extension of the Sequential Standard Model, denoted by S-SSM hereafter, wherein the couplings of the Z and Z to supersymmetric particles are the same.…”