Measurement of the Energy Asymmetry in Top Quark Pair plus Jet Production with the CMS Experiment

The measurement of the energy asymmetry in top quark pair production in association with one additional high-$p_{\text{T}}$ jet is presented, using 137.1 fb$^{-1}$ of data recorded with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 13 TeV.
The presented measurement focuses on the semileptonic decay process of the top quark pair and requires a boosted event topology of the $\text{t}\bar{\text{t}}j$ system.
Different types of clustered final-state particles are considered for the reconstruction, having the minimal common requirement of one charged electron or muon, missing transverse momentum due to the corresponding neutrino, and one hard jet in the central region of the detector.
The primary focus is to reconstruct events in the boosted regime using top tagged fat jets.
If this is not possible, an attempt is taken to reconstruct events in the resolved regime with slim jets under the employment of boosted decision trees.
In order to unfold the results, a reconstruction of simulated signal process events on particle level is performed either in the boosted regime, the resolved regime, or using parton information of the event. ... mehr
The unfolding is performed with a maximum likelihood fit, splitting the signal process into different subcategories according to the event kinematic properties on particle level.
Both signal and background processes are obtained fully from simulation and the systematic uncertainties are considered as nuisance parameters in the fit.

This analysis is the first measurement of the energy asymmetry and yields an observed value of

\begin{align*}
A_{E, \text{unf.}}^{\text{opt}} = -3.0\,\% \;^{+4.0\,\%}_{-5.5\,\%} \,(\text{stat + syst})
\end{align*}

in a fiducial phase space. This result is in agreement with the corresponding SM expectation of $ A_{E}^{\text{opt}} = -1.59\,\% \pm 1.00\,\%\,\text{(stat)} \pm 0.37\,\%\,\text{(syst)}$.