Search

Motivated by the recent LHCb announcement of a 3.1σ violation of lepton- flavor universality in the ratio RK = Γ(B → Kμ+μ−)/Γ(B → Ke+e−), we present an updated, comprehensive analysis of the flavor anomalies seen in both neutral-current (b → sℓ+ℓ−) and charged-current (b → cτ ν ¯ ) decays of B mesons. Our study starts from a model-independent effective field-theory approach and then considers both a simplified model and a UV-complete extension of the Standard Model featuring a vector leptoquark U1 as the main mediator of the anomalies. We show that the new LHCb data corroborate the emerging pattern of a new, predominantly left-handed, semileptonic current-current interaction with a flavor structure respecting a (minimally) broken U(2)5 flavor symmetry. New aspects of our analysis include a combined analysis of the semileptonic operators involving tau leptons, including in particular the important constraint from Bs- B ¯ s mixing, a systematic study of the effects of right-handed leptoquark couplings and of deviations from minimal flavor-symmetry breaking, a detailed analysis of various rare B-decay modes which would provide smoking-gun signatures of this non-standard framework (LFV decays, di-tau modes, and B → K(*) ν ν ¯ ), and finally an updated analysis of collider bounds on the leptoquark mass and couplings. [ABSTRACT FROM AUTHOR]

We design a search strategy for the Standard Model t t ¯ t t ¯ production at the LHC in the same-sign dilepton and trilepton channels. We study different signal features and, given the small expected number of signal events, we scrutinize in detail all reducible and irreducible backgrounds. Our analysis shows that by imposing a basic set of jet and lepton selection criteria, the SM p p → t t ¯ t t ¯ process could be evidenced in the near future, within Run-II, when combining both multi-lepton search channels. We argue that this search strategy should also be used as a guideline to test New Physics coupling predominantly to top-quarks. In particular, we show that a non-resonant New Physics enhancement in the four-top final state would be detectable through this search strategy. We study two top-philic simplified models of this kind, a neutral scalar boson and a Z ′ , and present current and future exclusion limits on their mass and couplings. [ABSTRACT FROM AUTHOR]

Abstract We analyze the possibility to accommodate current b → s ℓ + ℓ − anomalies with TeV-scale mediators that couple to right-handed top quarks and muons, contributing to b → s ℓ + ℓ − at the one-loop level. We use the Standard Model Effective Field Theory (SMEFT) framework but also look at specific scenarios by taking into account all possible irreducible representations of the Lorentz and Standard Model gauge group for the mediators. From a global fit of b → s ℓ + ℓ − data and LEP-I observables we find that the Wilson coefficients of two SMEFT operators: O ℓ u = ( ℓ ¯ L μ γ α ℓ L μ) ( t ¯ R γ α t R) and O e u = ( μ ¯ R γ α μ R) ( t ¯ R γ α t R) need to satisfy C e u ∼ C ℓ u. New physics enters then in b → s ℓ + ℓ − mainly through the operator O 9 = (s ¯ γ μ P L b) (ℓ ¯ γ μ ℓ) of the Weak Effective Theory. After discussing all possible mediators, we concentrate on two scenarios: A vector boson in the irreducible representation Z μ ′ ∼ (1 , 1 , 0) of the Standard Model gauge group with vectorial coupling to muons, and a combination of two leptoquarks: the scalar R 2 ∼ (3 , 2 , 7 / 6) and the vector U ˜ 1 μ ∼ (3 , 1 , 5 / 3). We derive LHC constraints by recasting di-muon resonance, p p → t t ¯ t t ¯ and SUSY searches. Additionally, we analyze the prospects for discovering these mediators during the high-luminosity phase of the LHC. [ABSTRACT FROM AUTHOR]