Probing light stops with stoponium

Abstract

We derive new limits on light stops from diboson resonance searches in the γγ, Zγ, ZZ, WW and hh channels from the first run of the LHC. If the two-body decays of the light stop are mildly suppressed or kinematically forbidden, stoponium bound states will form in pp collisions and subsequently decay via the pair annihilation of the constituent stops to diboson final states, yielding striking resonance signatures. Remarkably, we find that stoponium searches are highly complementary to direct collider searches and indirect probes of light stops such as Higgs coupling measurements. Using an empirical quarkonia potential model and including the first two S-wave stoponium states, we find that in the decoupling limit $$ {m_{\tilde{t}}}_1\lesssim 130 $$ GeV is excluded for any value of the stop mixing angle and heavy stop mass by the combination of the latest resonance searches and the indirect constraints. The γγ searches are the most complementary to the indirect constraints, probing the stop “blind spot” parameter region in which the $$ {h}^0{\tilde{t}}_1{\tilde{t}}_1^{*} $$ trilinear coupling is small. Interestingly, we also find that the Zγ searches give a stronger constraint, $$ {m_{\tilde{t}}}_1\lesssim 170 $$ GeV, if the stop is primarily left-handed. For a scenario with a bino LSP and stop NLSP, several gaps in the direct collider searches for stops can unambiguously be filled with the next run of the LHC. For a stop LSP decaying through an R-parity violating UDD coupling, the stoponium searches can fill the gap 100 GeV ≲ $$ {m}_{\tilde{t}1} $$ ≲ 200GeV in the direct searches for couplings λ′′ ≲ 10−2.