Looking for SUSY virtually through loop-induced Higgs processes

Abstract

Any particle reaction forbidden at the tree level, but induced through a quantum loop, is a candidate process for distinguishing between the standard electroweak model, and the supersymmetric metric (SUSY) version, even if SUSY particles are too heavy to be produced at accelerators. The reason is that virtual SUSY particles circulating in the loop induce O(1) quantum corrections of the amplitude. We investigate the dependence of all processes with external HZγ, Hγγ or H-gluon-gluon on the parameters of supersymmetry, and find that SUSY rates are increased or decreased by up to three orders of magnitude compared to the rates predicted by the standard model. Amplitudes with an external Higgs are chosen because (i) the SUSY contributions remain significant even as the SUSY masses go to infinity, and (ii) in SUSY models, one (of three) neutral Higgs is necessarily lighter than Z; the process Z → H γ is guaranteed to occur. We show that a measurement of Γ( Z or Z ∗ → Hγ) at SLC or LEP would not only reveal a Higgs, but together with measurement of Z → H μ + μ − or Toponium → H γ tree-level modes can also distinguish minimal supersymmetry from the standard model.