Probing Heavy Spin-2 Bosons with γγ final states from Vector Boson Fusion Processes at the LHC

Abstract

New massive spin-2 particles are predicted in theoretical extensions to the Standard Model (SM) attempting to solve the hierarchy problem. Such theories postulate that gravity is diluted compared to the other fundamental forces because it can propagate in extra spatial dimensions. While such theoretical models are of high experimental interest because they predict massive spin-2 particles (Y2) potentially detectable by collider experiments, searches at the Large Hadron Collider (LHC) have thus far produced no significant evidence for their existence. This work considers a hypothetical physics scenario where low coupling strengths between the Y2 and quarks/gluons is the underlying reason behind the null Y2 search results at the LHC, which have mainly relied on Drell-Yan and gluon-gluon fusion production mechanisms. The focus of this paper is a feasibility study to search for Y2 particles using vector boson fusion (VBF) processes at the LHC. In the context of an effective field theory approach with varying couplings κV between Y2 and the weak bosons of the SM, we consider the Y2 → γγ decay mode to show that the requirement of a diphoton pair combined with two high pT forward jets with large dijet mass and with large separation in pseudorapidity can significantly √ reduce the SM backgrounds. Assuming proton-proton collisions at present the total VBF production cross sections, Y2 decay widths, and Y2 → γγ branching ratios as a function of m(Y2), considering universal and non-universal couplings to the SM particles. The unitarity-violating phase space is described. The proposed VBF Y2 → γγ search is expected to achieve a discovery reach with signal significance greater than 5σ for Y2 masses up to 4.4 TeV and κV couplings down to 0.5.