Abstract
We study the effective field theory sensitivity of an LHC analysis for the τν final state with an associated b-jet. To illustrate the improvement due to the b-tagging, we first recast the recent CMS analysis in the τν channel, using an integrated luminosity of 35.9 fb−1 at sqrt{s} = 13 TeV, and provide limits on all the dimension-six effective operators which contribute to the process. The expected limits from the b-tagged analysis are then derived and compared. We find an improvement of approximately ∼ 30% in the bounds for operators with a b quark. We also discuss in detail possible angular observables to be used as a discriminator between dimension-six operators with different Lorentz structure. Finally, we study the impact of these limits on some simplified scenarios aimed at addressing the observed deviations from the Standard Model in lepton flavor universality ratios of semileptonic B-meson decays. In particular, we compare the collider limits on those scenarios set by our analysis either with or without the b-tagging, assuming an integrated luminosity of 300 fb−1, with relevant low-energy flavor measurements.
Highlights
13 TeV, and provide limits on all the dimension-six effective operators which contribute to the process
While the dominant SM contribution to the τ ν final state comes from the parton distribution function (PDF) of light quarks, the beyond the SM (BSM) contribution of interest are initiated by cb and ub initial state partons
We investigate the implication of the kinematic cuts on the angular distributions using the partonic MC events of pp → τ νb process in terms of the angular variables shown in figure 7, motivated by what has been explored in the single top process [41]
Summary
New physics effects in low-energy flavor observables are usually discussed in terms of an effective Hamiltonian defined at the low-energy scale with quarks in the mass basis. The OV RL operator is generated at dimension-6 in the SMEFT only via anomalous W boson couplings to right-handed quarks, and at energies above the electroweak scale is resolved into a vertex correction for the W , so does not behave as a four-fermion operator (no growth with energy of the scattering amplitude). It can be generated as a dimension-8 operator, receiving a further v2/Λ2 suppression compared to dimension-6 operators. We refer to [10] for a more detailed discussion of possible caveats due to the EFT expansion in the pp → τ ν(+b) process at the LHC
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