Abstract
We propose a model independent approach for the analysis of interference effects in the process of QCD pair production of new heavy quarks of different species that decay into Standard Model particles, including decays via flavour changing neutral currents. By adopting as ansatz a simple analytical formula we show that one can accurately describe the interference between two different such particles pairs leading to the same final state using information about masses, total widths and couplings. A study of the effects on differential distributions is also performed showing that, when interference plays a relevant role, the distributions of the full process can be obtained by a simple rescaling of the distributions of either quark contributing to the interference term. We also present the range of validity of the analytical expression that we have found.
Highlights
We show that this can be done through a simple formula, which enables one to correctly model such interference effects at both inclusive and exclusive levels
We propose a model independent approach for the analysis of interference effects in the process of QCD pair production of new heavy quarks of different species that decay into Standard Model particles, including decays via flavour changing neutral currents
In this paper we assume that these effects can be computed and that particle wave-function as well as Feynman rules are already formulated for mass-eigenstates, i.e., the masses and widths that we will be using are those obtained after computing the rotations of the states due to the one-loop mixing terms, so that interference effects can be explored in a model-independent way
Summary
We will assume throughout the analysis that the new heavy quarks undergo two-body decays to SM particles and we will not consider chain decays of heavy quarks into other new states, possibly including dark matter candidates. It is worth mentioning that, for the classes of models under consideration, we have quarks of identical charge and with couplings to the same particles, so that the effects of the mixing between such quarks at loop level could be important and should (eventually) be taken into account These effects are modeldependent though and involve computation of loops that may contain states belonging to new sectors (e.g., new gauge bosons). We would like to make the ansatz that, in case of chiral new quarks i and assuming small Γi/mi values, the interference is proportional to the couplings of the new quarks to the final state particles and to the integral of the scalar part of the propagator. The analytical expression which should describe the interference in the case of chiral QV pair production of species i and j followed by their decay into the same final state, is given by. |gjL1|2 + |gjR1|2 |gjL2|2 + |gjR2|2 m2i Γ2i + (miΓi + mj Γj )2 − m2i − m2j 2 (miΓi + mj Γj )2 + m2i − m2j 2 2
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