Abstract:
This paper presents the reconstruction of missing transverse momentum (
$$p_{\text {T}}^{\text {miss}}$$
p
T
miss
) in proton–proton collisions, at a center-of-mass energy of 13 TeV. This is a challenging task involving many detector inputs, combining fully calibrated electrons, muons, photons, hadronically decaying
$$\tau $$
τ
-leptons, hadronic jets, and soft activity from remaining tracks. Possible double counting of momentum is avoided by applying a signal ambiguity resolution procedure which rejects detector inputs that have already been used. Several
$$p_{\text {T}}^{\text {miss}}$$
p
T
miss
‘working points’ are defined with varying stringency of selections, the tightest improving the resolution at high pile-up by up to 39% compared to the loosest. The
$$p_{\text {T}}^{\text {miss}}$$
p
T
miss
performance is evaluated using data and Monte Carlo simulation, with an emphasis on understanding the impact of pile-up, primarily using events consistent with leptonic Z decays. The studies use
$$140~\text {fb}^{-1}$$
140
fb
-
1
of data, collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. The results demonstrate that
$$p_{\text {T}}^{\text {miss}}$$
p
T
miss
reconstruction, and its associated significance, are well understood and reliably modelled by simulation. Finally, the systematic uncertainties on the soft
$$p_{\text {T}}^{\text {miss}}$$
p
T
miss
component are calculated. After various improvements the scale and resolution uncertainties are reduced by up to
$$76\%$$
76
%
and
$$51\%$$
51
%
, respectively, compared to the previous calculation at a lower luminosity.
