"$m_\mathrm{MMC}$ distribution in low-mass SR ($m_A$ = 20 GeV)" of "Search for a light CP-odd Higgs boson decaying into a pair of $\tau$-leptons in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector"

Post-fit $m_\mathrm{MMC}$ distribution in the low-mass SR for the $m_A = 20\,\mathrm{GeV}$ signal mass hypothesis. $m_\mathrm{MMC}$ is the mass reconstructed by the Missing Mass Calculator. Processes contributing to the background Others are $Z/\gamma^* \rightarrow ee/\mu\mu$ and SM Higgs. The subscript on the $A\to\tau\tau$ process indicates the mass of the $A$ boson. Total includes all backgrounds and the signal process.
The low-mass Signal Region is defined as:
- 1 electron and 1 muon with opposite charge
- $p_\mathrm{T}$ requirements of the leptons are a combination of the following:
- $p_\mathrm{T}^e > 18\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 15\,\mathrm{GeV}$
- $p_\mathrm{T}^e > 10\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 25\,\mathrm{GeV}$
- $p_\mathrm{T}^e > 27\,\mathrm{GeV}$ and $p_\mathrm{T}^\mu > 10\,\mathrm{GeV}$
- $\vert \eta_e \vert < 2.47$, excluding $1.37 < \vert \eta_e \vert < 1.52$
- $\vert \eta_\mu \vert < 2.7$
- no jets with $b$-quarks
- $\Delta R_{\ell\ell} < 0.7$
- $E_\mathrm{T}^\mathrm{miss} > 50\,\mathrm{GeV}$
- $m_\mathrm{T}^\mathrm{tot} = \sqrt{\left(p_\mathrm{T}^e+p_\mathrm{T}^\mu+E_\mathrm{T}^\mathrm{miss}\right)^2-\left(\vec{p}_\mathrm{T}^{\,e}+\vec{p}_\mathrm{T}^{\,\mu}+\vec{E}_\mathrm{T}^{\,\mathrm{miss}}\right)^2} < 45\,\mathrm{GeV}$
- $m_\mathrm{MMC} > 0\,\mathrm{GeV}$