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Register a new userCP violating anomalous top-quark couplings at the Large Hadron Collider
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Authors
Sudhir Kumar Gupta
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In this talk, I review the T-odd correlations induced by CP violating anomalous top-quark couplings at both production and decay level in the process gg --> t t_bar --> (b mu+ nu_mu) (b_bar mu-nu_mu_bar). In addition I will also focus on experimental sensitivities corresponding to the anomalous couplings at the LHC.
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We study the T odd correlations induced by CP violating anomalous top-quark couplings at both production and decay level in the process gg --> t t_bar --> (b mu+ nu_mu) (b_bar mu- nu_mu_bar). We consider several counting asymmetries at the parton level and find the ones with the most sensitivity to each of these anomalous couplings at the LHC.
We revisit the effect of CP violating anomalous top-quark couplings in $tbar{t}$ production and decay. We consider $tbar{t}$ production through gluon fusion (and light $q{bar q}$ annihilation) followed by top-quark decay into $bW$ or $bell u$. We find explicit analytic expressions for all the triple products generated by the anomalous couplings that fully incorporate all spin correlations. Our results serve as a starting point for numerical simulations for the LHC.
We investigate the anomalous flavour changing neutral current (FCNC) interactions of top quark through the process $e^{-}pto e^{-}W^{pm}q+X$. We calculate the signal and background cross sections in electron proton collisions at Large Hadron electron Collider (LHeC) with a 7 TeV proton beam from the LHC and a new 60 GeV electron beam from energy recovery linac (ERL). We study the relevant background processes including one electron and three jets in the final state. The distributions of the invariant mass of two jets and an additional jet tagged as $b$-jet are used to account signal and background events after the analysis cuts. We find upper bounds on anomalous FCNC couplings $lambda$ of the order of $10^{-2}$ at LHeC for a luminosity projection of $100$ fb$^{-1}$ together with the fast simulation of detector effects. As a matter of interest, we analyze the sensitivity to the couplings $(lambda_{u},lambda_{c})$ and find an enhanced sensitivity to $lambda_{c}$ at the LHeC when compared to the results from the HERA.
We consider QCD tbar{t}gamma and tbar{t}Z production at hadron colliders as a tool to measure the ttgamma and ttZ couplings. At the Tevatron it may be possible to perform a first, albeit not very precise, test of the ttgamma vector and axial vector couplings in tbar{t}gamma production, provided that more than 5 fb^{-1} of integrated luminosity are accumulated. The tbar{t}Z cross section at the Tevatron is too small to be observable. At the CERN Large Hadron Collider (LHC) it will be possible to probe the ttgamma couplings at the few percent level, which approaches the precision which one hopes to achieve with a next-generation e^+e^- linear collider. The LHCs capability of associated QCD tbar{t}V (V=gamma, Z) production has the added advantage that the ttgamma and ttZ couplings are not entangled. For an integrated luminosity of 300 fb^{-1}, the ttZ vector (axial vector) coupling can be determined with an uncertainty of 45-85% (15-20%), whereas the dimension-five dipole form factors can be measured with a precision of 50-55%. The achievable limits improve typically by a factor of 2-3 for the luminosity-upgraded (3 ab^{-1}) LHC.
Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, tbar t production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. The identification of very energetic top quarks is crucial in such an analysis. We consider in detail the tbar ttoell^pm u bbar bqbar q (ell=e, mu) final state for high p_T top quarks. In this phase space region, two or more of the final state quarks can merge into a single jet due to the large Lorentz boost of the parent top quark. As a result, a large fraction of tbar ttoell^pm u bbar bqbar q events with an invariant mass in the TeV region contains less than four observable jets. Requiring one or two tagged b-quarks, we calculate the W+jets, Wb+jets, Wbbar b+jets, Wbt, and single top plus jets backgrounds for these final states, and identify cuts which help to suppress them. In particular, we discuss whether a cut on the jet invariant mass may be useful in reducing the background in the ell u+2 jets channel. We also investigate how next-to-leading order QCD corrections affect high p_T top quark production at the LHC. We find that the ell u+2 jets and ell u+3 jets final states with one or two $b$-tags will significantly improve the chances for discovering new heavy particles in the tbar t channel at the LHC.
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