The physics beyond the Standard Model with parameters of the compressed spectrum is well motivated both in a theory side and with phenomenological reasons, especially related to dark matter phenomenology. In this letter, we propose a method to tag so
ft final state particles from a decaying process of a new particle in this parameter space. By taking a supersymmetric gluino search as an example, we demonstrate how the Large Hadron Collider experimental collaborations can improve a sensitivity in these non-trivial search regions.
The presence of two light higgsinos nearly degenerate in mass is one of the important characteristics of suspersymmetric models meeting the naturalness criteria. Probing such higgsinos at the LHC is very challenging, in particular when the mass-split
ting between them is less than 5 GeV. In this study, we analyze such a degenerate higgsino scenario by exploiting the high collinearity between the two muons which originate from the decay of the heavier higgsino into the lighter one and which are accompanied by a high-$p_T$ QCD jet. Using our method, we can achieve a statistical significance $sim 2.9,sigma$ as well as a $S/B sim 17%$ with an integrated luminosity of 3000 fb$^{-1}$ at the 14 TeV LHC, for the pair production of higgsinos with masses 124 GeV and 120 GeV. A good sensitivity can be achieved even for a smaller mass-splitting when the higgsinos are lighter.
We consider the current experimental constraints on the parameter space of the MSSM and NMSSM. Then in the allowed parameter space we examine the Higgs pair production at the 14 TeV LHC via $bbar{b}to hh$ ($h$ is the 125 GeV SM-like Higg boson) with
one-loop SUSY QCD correction and compare it with the production via $ggto hh$. We obtain the following observations: (i) For the MSSM the production rate of $bbar{b} to hh$ can reach 50 fb and thus can be competitive with $gg to hh$, while for the NMSSM $bbar{b} to hh$ has a much smaller rate than $gg to hh$ due to the suppression of the $hbbar{b}$ coupling; (ii) The SUSY-QCD correction to $bbar{b} to hh$ is sizable, which can reach $45%$ for the MSSM and $15%$ for the NMSSM within the $1sigma$ region of the Higgs data; (iii) In the heavy SUSY limit (all soft mass parameters become heavy), the SUSY effects decouple rather slowly from the Higgs pair production (especially the $ggto hh$ process), which, for $M_{rm SUSY}=5$ TeV and $m_A<1$ TeV, can enhance the production rate by a factor of 1.5 and 1.3 for the MSSM and NMSSM, respectively. So, the Higgs pair production may be helpful for unraveling the effects of heavy SUSY.
