Abstract
Search for invisible final states produced at the Large Hadron Collider (LHC) by new physics scenarios are normally carried out resorting to a variety of probes emerging from the initial state, in the form of single-jet, -photon and -$Z$ boson signatures. These are particularly effective for models of Supersymmetry (SUSY) in presence of $R$-parity conservation, owing to the presence in their spectra of a stable neutralino as dark matter candidate. We assume here as theoretical framework Supersymmetric ($B-L$) extension of the Standard Model (BLSSM), wherein a mediator for invisible decays can be $Z'$ boson. The peculiarity of the signal is thus that the final state objects carry a very large (transverse) missing energy, since the $Z'$ is naturally massive and constrained by direct searches and electro-weak precision tests to be at least in TeV scale region. Under these circumstances the efficiency in accessing the invisible final state and rejecting the standard model background is very high. This somehow compensates the rather meagre production rates. Another special feature of this invisible BLSSM signal is its composition, which is often dominated by sneutrino decays (alongside the more traditional neutrino and neutralino modes). Sensitivity of the CERN machine to these two features can therefore help disentangling the BLSSM from more popular SUSY models. We assess in this analysis the scope of the LHC in establishing the aforementioned invisible signals through a sophisticated signal-to-background simulation carried out in presence of parton shower, hadronisation and detector effects. We find that significant sensitivity exists already after 300 fb$^{-1}$ during Run 2. We find that mono-jet events can be readily accessible at the LHC, so as to enable one to claim a prompt discovery, while mono-photon and -$Z$ signals can be used as diagnostic tools of the underlying scenario.
Highlights
SU(3)C × SU(2)L × U(1)Y × U(1)B−L, the simplest generalisation of the Standard Model (SM) gauge group (through an additional U(1)B−L symmetry)
Search for invisible final states produced at the Large Hadron Collider (LHC) by new physics scenarios are normally carried out resorting to a variety of probes emerging from the initial state, in the form of single-jet, -photon and -Z boson signatures
It has been shown that the scale of (B − L) symmetry breaking is related to the SUSY breaking scale [1,2,3,4], so that this SUSY realization predicts several testable signals at the LHC, in the sparticle domain and in the Z (a Z boson emerges from the U(1)B−L breaking), Higgs (an additional singlet state is economically introduced here, breaking the U(1)B−L group) and (s)neutrino sectors [5,6,7,8,9,10,11,12,13,14,15]
Summary
In the BLSSM, the particle content includes the following fields in addition to the MSSM ones: three chiral right-handed superfields (Ni), a vector superfield associated to U(1)B−L (Z ) and two chiral SM singlet Higgs superfields (χ1, χ2) The superpotential of this model is given by. [1,2,3,4], both the (B − L) and EW symmetry can be broken radiatively in supersymmetric theories In this class of models, the EW, (B − L) and soft SUSY breakings can occur at the TeV scale. It can be concluded that, if the lightest right-handed sneutrino is lighter than the lightest slepton and lightest chargino, it decays into light SM-like neutrinos and lightest neutralinos. The Feynman diagrams relevant for our study are found in figure 1
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