Probing a new strongly interacting sector via composite diboson resonances

Abstract

Diphoton resonance was a crucial discovery mode for the 125 GeV Standard Model Higgs boson at the Large Hadron Collider (LHC). This mode or the more general diboson modes may also play an important role in probing for new physics beyond the Standard Model. In this paper, we consider the possibility that a diphoton resonance is due to a composite scalar or pseudoscalar boson, whose constituents are either new hyperquarks Q or scalar hyperquarks Q˜ confined by a new hypercolor force at a confinement scale Λh. Assuming the mass mQ (or mQ˜) ≫Λh, a diphoton resonance could be interpreted as either a QQ¯(S10) state ηQ with JPC=0-+ or a Q˜Q˜†(S01) state ηQ˜ with JPC=0++. For the QQ¯ scenario, there will be a spin-triplet partner ψQ which is slightly heavier than ηQ due to the hyperfine interactions mediated by hypercolor gluon exchange; while for the Q˜Q˜† scenario, the spin-triplet partner χQ˜ arises from higher radial excitation with nonzero orbital angular momentum. We consider productions and decays of ηQ, ηQ˜, ψQ, and χQ˜ at the LHC using the nonrelativistic QCD factorization approach. We discuss how to test these scenarios by using the Drell-Yan process and the forward dijet azimuthal angular distributions to determine the JPC quantum number of the diphoton resonance. Constraints on the parameter space can be obtained by interpreting some of the small diphoton “excesses” reported by the LHC as the composite scalar or pseudoscalar of the model. Another important test of the model is the presence of a nearby hypercolor-singlet but color-octet state like the S01 state ηQ8 or ηQ˜8, which can also be constrained by dijet or monojet plus monophoton data. Both possibilities of a large or small width of the resonance can be accommodated, depending on whether the hyper-glueball states are kinematically allowed in the final state or not.