Top Quark Pair Analysis

The LHC is a top quark factory and studying and understanding top quark physics is one of the major goals of the ATLAS physics programme. This understanding is crucial for studying rarer processes as top quark pair production is a background to virtually all processes having leptons and multiple jets in their final states. Top quark pair production can be studied in the ATLAS open data dataset in both the semileptonic and dileptonic final state. Statistics are expected to be sucient for producing detailed distributions and exploring advanced techniques like the reconstruction of the top quark pair system.

This analysis mimics a standard top quark pair selection in the semileptonic channel. The standard object selection criteria are applied. The event selection is defined as:

• Single electron or muon trigger is satisfied;
• Event in real data passes the Good Run List;
• Event has a good vertex (N_tracks > 4);
• Exactly one good lepton with p_T > 25 GeV;
• At least four good jets;
• At least two b-tagged jets (MV1 @70%);
• E_T^miss > 30 GeV;
• m_T^W > 30GeV.

Figures 1 to 4 depict the lepton kinematics of the leptons with the simulated data reproducing the real data well.

Figure 1: Top Analysis: Leading lepton transverse momentum p_T.

Figure 2: Top Analysis: Leading lepton energy E.

Figure 3: Top Analysis: Leading lepton pseudorapidity η.

There is a small disagreement in normalisation of approximately 5% between simulated and real data. This may be attributed to the fact that the b-tagging scale factor is not applied despite two b-tags being required. A survey of the shapes of all presented histograms reveals no obvious discrepancies.

Continue reading about this analysis and more in our public document ATL-OREACH-PUB-2016-001

Figure 4: Top Analysis: Leading lepton azimuthal angle φ.