Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10723192 | Physics Letters B | 2010 | 8 Pages |
Abstract
We study the prospects of measuring the CKM matrix element |Vts| at the LHC with the top quarks produced in the processes ppâtt¯X and ppât/t¯X, and the subsequent decays tâW+s and t¯âWâs¯. To reduce the jet activity in top quark decays, we insist on tagging the W± leptonically, W±ââ±νâ (â=e,μ,Ï), and analyse the anticipated jet profiles in the signal process tâWs and the dominant background from the decay tâWb. To that end, we analyse the V0 (K0 and Î) distributions in the s- and b-quark jets concentrating on the energy and transverse momentum distributions of these particles. The V0s emanating from the tâWb branch have displaced decay vertexes from the interaction point due to the weak decays bâcâs and the b-quark jets are rich in charged leptons. Hence, the absence of secondary vertexes and of the energetic charged leptons in the jet provide additional (b-jet vs. s-jet) discrimination in top quark decays. These distributions are used to train a boosted decision tree (BDT), a technique used successfully in measuring the CKM matrix element |Vtb| in single top production at the Tevatron. Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we calculate the BDT(D)-response functions corresponding to the signal (tâWs) and background (tâWb). Detailed simulations undertaken by us with the Monte Carlo generator PYTHIA are used to estimate the background rejection versus signal efficiency for three representative LHC energies s=7 TeV, 10 TeV and 14 TeV, of which only the analysis for the s=14 TeV case is shown in detail. We argue that a benchmark with 10% accuracy for the signal (tâWs) at a background (tâWb) rejection by a factor 103 (required due to the anticipated value of the ratio |Vts|2/|Vtb|2â1.6Ã10â3) can be achieved at the LHC@14 TeV with an integrated luminosity of 10 fbâ1.
Keywords
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Nuclear and High Energy Physics
Authors
Ahmed Ali, Fernando Barreiro, Theodota Lagouri,