Aspects of the same-sign diboson signature from wino pair production with light higgsinos at the high luminosity LHC

Naturalness arguments applied to simple supersymmetric (SUSY) theories require a set of light higgsinos with mass $\sim |\mu|$ not too far from $m_h$. These models have an inverted electroweakino spectrum with $|\mu| \ll M_2$ which leads to a rather clean, hadronically quiet, same-sign diboson (SSdB) signature at hadron colliders arising from neutral-plus-charged wino pair production. We improve and expand our earlier studies of this signature for discovering SUSY in natural SUSY models by (i) including backgrounds which were not previously considered and which turn out to be significant, (ii) devising more efficient cuts to successfully contend with these larger backgrounds and determining the discovery reach and exclusion ranges for winos with these cuts, emphasizing projections for the updated integrated luminosity target for HL-LHC of 3 ab$^{-1}$, and (iii) emphasizing the utility of this channel for natural models without gaugino mass unification. We display the kinematic characteristics of the relatively jet-free same sign dilepton+$\not\!\!\!{E_T}$ events (from leptonic decays of both $W$s) and find that these are only weakly sensitive to the parent wino mass. We also examine the charge asymmetry in these events and show that its measurement can be used to check the consistency of the wino origin of the signal. Finally, we show that -- because the wino branching fractions in natural SUSY are essentially independent of details of the underlying model -- a determination of the rate for clean, same-sign dilepton events yields a better than 10% determination of the wino mass over the entire mass range where experiments at the HL-LHC can discover the wino signal.