Common Aspects in Searches for New Physics in \(t\bar{t}\) Final States with Additional Heavy-Flavor Jets
This chapter describes the commonalities in event preselection, background modeling and treatment of systematic uncertainties for the different analyses in the \(t\bar{t}+\mathrm {HF}\) final state. A very precise modeling of the \(t\bar{t}\) +jets and \(
- PDF / 1,439,554 Bytes
- 39 Pages / 439.37 x 666.142 pts Page_size
- 12 Downloads / 174 Views
Common Aspects in Searches for New Physics in t t¯ Final States with Additional Heavy-Flavor Jets
This chapter describes the commonalities in event preselection, background modeling and treatment of systematic uncertainties for the different analyses in the t t¯ + HF final state. A very precise modeling of the t t¯+jets and t t¯ + bb¯ backgrounds is crucial for the analyses and will be discussed in detail. Finally, the quality of the modeling that is achieved is illustrated with a comparison to ATLAS data.
5.1 Analysis Strategy After the production and decay of the different signals targeted in this dissertation, a final state with typically at least one t t¯ pair is produced. Additional b-jets from decays of heavy resonances, such as H → bb¯ are also present. As a reminder, this final state can be obtained trough the SM production of t t¯ H or the pair production of 0 new exotic particles and the subsequent decays: T → H t, t˜2 → χ˜ 1 H t, A( j,k) → t t¯, σ → t t¯. The top quark decays to a W boson and a b-quark almost 100 % of the times, and the W boson decays to a lepton and a neutrino with BR(W → lν) ≈ 0.32, or hadronically with the remaining fraction. The possible t t¯ decays are defined by the W boson decay combinations: dilepton when both W bosons decay leptonically, lepton+jets if one W boson decays leptonically and the other one hadronically, and all-hadronic if both W bosons decay into quarks. From the different topologies of the t t¯ decay the analyses described here target the lepton+jets final state since it offers the best compromise between reduced backgrounds and high branching fraction. Events with exactly one lepton1 are selected and classified into exclusive categories, referred to as “regions”, according to the number of reconstructed jets and b-tagged jets. A given region with m jets of which n are b-jets is referred to as 1 In
the following the word “lepton” is used to refer to either an electron or a muon, assumed to originate from the decay of a W boson or a τ lepton.
© Springer International Publishing Switzerland 2016 J. Montejo Berlingen, Search for New Physics in t t¯ Final States with Additional Heavy-Flavor Jets with the ATLAS Detector, Springer Theses, DOI 10.1007/978-3-319-41051-7_5
87
88
5 Common Aspects in Searches for New Physics …
“(mj, nb)”. Signal events produce final states with high jet and b-tag multiplicity, and this requirement is very effective at suppressing SM backgrounds. The region with highest jet and b-tag multiplicity that is considered, and therefore the one with highest sensitivity, is the (≥6j, ≥4b) region. Cuts on kinematic variables and further splittings of the regions can be defined in order to isolate sub-regions with increased sensitivity. A combined fit to signal-rich and signal-depleted regions is performed to search for the signal while simultaneously obtaining an improved background prediction with reduced uncertainties. The fit procedure and statistical analysis is described in detail in Chap. 6.
5.2 Data Sample The data sample used for the
Data Loading...
