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Register a new userLearning to increase matching efficiency in identifying additional b-jets in the $text{t}bar{text{t}}text{b}bar{text{b}}$ process
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Added by
Cheongjae Jang
Publication date
2021
fields
Informatics Engineering
and research's language is
English
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The $text{t}bar{text{t}}text{H}(text{b}bar{text{b}})$ process is an essential channel to reveal the Higgs properties but has an irreducible background from the $text{t}bar{text{t}}text{b}bar{text{b}}$ process, which produces a top quark pair in association with a b quark pair. Therefore, understanding the $text{t}bar{text{t}}text{b}bar{text{b}}$ process is crucial for improving the sensitivity of a search for the $text{t}bar{text{t}}text{H}(text{b}bar{text{b}})$ process. To this end, when measuring the differential cross-section of the $text{t}bar{text{t}}text{b}bar{text{b}}$ process, we need to distinguish the b-jets originated from top quark decays, and additional b-jets originated from gluon splitting. Since there are no simple identification rules, we adopt deep learning methods to learn from data to identify the additional b-jets from the $text{t}bar{text{t}}text{b}bar{text{b}}$ events. Specifically, by exploiting the special structure of the $text{t}bar{text{t}}text{b}bar{text{b}}$ event data, we propose several loss functions that can be minimized to directly increase the matching efficiency, the accuracy of identifying additional b-jets. We discuss the difference between our method and another deep learning-based approach based on binary classification arXiv:1910.14535 using synthetic data. We then verify that additional b-jets can be identified more accurately by increasing matching efficiency directly rather than the binary classification accuracy, using simulated $text{t}bar{text{t}}text{b}bar{text{b}}$ event data in the lepton+jets channel from pp collision at $sqrt{s}$ = 13 TeV.
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We present results of a computation of NLO QCD corrections to the production of an off-shell top--antitop pair in association with an off-shell $text{W}^+$ boson in proton--proton collisions. As the calculation is based on the full matrix elements for the process $text{p}text{p}to {text{e}}^+ u_{text{e}},mu^-bar{ u}_mu,tau^+ u_tau,{text{b}},bar{text{b}}$, all off-shell, spin-correlation, and interference effects are included. The NLO QCD corrections are about $20%$ for the integrated cross-section. Using a dynamical scale, the corrections to most distributions are at the same level, while some distributions show much larger $K$-factors in suppressed regions of phase space. We have performed a second calculation based on a double-pole approximation. While the corresponding results agree with the full calculation within few per cent for integrated cross-sections, the discrepancy can reach $10%$ and more in regions of phase space that are not dominated by top--antitop production. As a consequence, on-shell calculations should only be trusted to this level of accuracy.
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