Abstract
Searching for heavy vector bosons Z′, predicted in models inspired by Grand Unification Theories, is among the challenging objectives of the LHC. The ATLAS and CMS collaborations have looked for Z′ bosons assuming that they can decay only into Standard Model channels, and have set exclusion limits by investigating dilepton, dijet and, to a smaller extent, top-antitop final states. In this work we explore possible loopholes in these Z′ searches, by studying supersymmetric as well as leptophobic scenarios. We demonstrate the existence of realizations in which the Z′ boson automatically evades the typical bounds derived from the analyses of the Drell-Yan invariant-mass spectrum. Dileptonic final states can in contrast only originate from supersymmetric Z′ decays and are thus accompanied by additional effects. This feature is analyzed in the context of judiciously chosen bench-mark configurations, for which visible signals could be expected in future LHC data with a 4σ − 7σ significance. Our results should hence motivate an extension of the current Z′ search program to account for supersymmetric and leptophobic models.
Highlights
BM I BM II7 pT (l1) > 300 GeV8 pT (l2) > 200 GeV9 E/ T > 100 GeV sZA a30s0u0pfebr−sy1 momf petpriccocllaissicoandse.atFo√rsea=ch14cuTte,Vwefoprrobvoitdhe the expected number of surviving background and signal benchmark events for scenariosBM I and BM II
The results presented in the previous section have shown that the inclusion of supersymmetric decays has a substantial effect on the Z searches and exclusion limits, but the ATLAS bounds originating from the dilepton channel strongly constrain any phenomenologically viable UMSSM realization
Motivated by the latest ATLAS and CMS measurements which imposed improved lower bounds on the Z mass, we analyzed models with an additional U(1) gauge symmetry group arising from the breaking of E6 supersymmetric Grand Unification Theories (GUT)
Summary
There are different ways to implement a U(1) extension in the MSSM: one of the most commonly used parameterizations is inspired by grand-unified models, based on a rank-6 group E6, where the symmetry-breaking scheme proceeds via multiple steps, E6 → SO(10) ⊗ U(1)ψ → SU(5) ⊗ U(1)χ ⊗ U(1)ψ → SU(3)C ⊗ SU(2)L ⊗ U(1)Y ⊗ U(1). We shall neglect the two generations of such states and focus on the ‘true’ Higgs bosons, which exhibit a non-zero vacuum expectation values and are denoted by Hu and Hd. The 16 representation of SO(10) is decomposed in terms of those of SU(5) as 16 = 10⊕5⊕1. Mass mixing matrices and mass eigenstates of the two generations of Higgs bosons with zero vacuum expectation values are thoroughly debated in [31]. After electroweak symmetry breaking, for each generation of Higgs fields, one is left with two charged and four neutral scalar bosons, namely one pseudoscalar and three neutral scalars, including a novel singlet-like scalar Higgs, inherited by the U(1) symmetry. The charged bosons, h and H the MSSM-like neutral scalars, with h roughly corresponding to the Standard Model Higgs, A the pseudoscalar and H the extra scalar associated with the U(1) gauge group. The corresponding Lagrangian reads, in terms of the gauge boson component fields, Lkin
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