Search

Motivated by UV explanations of the B-physics anomalies, we study a dark sector containing a Majorana dark matter candidate and a coloured coannihilation partner, connected to the Standard Model predominantly via a U1 vector leptoquark. A TeV scale U1 leptoquark, which couples mostly to third generation fermions, is the only successful single-mediator description of the B-physics anomalies. After calculating the dark matter relic surface, we focus on the most promising experimental avenue: LHC searches for the coloured coannihilation partner. We find that the coloured partner hadronizes and forms meson-like bound states leading to resonant signatures at colliders reminiscent of the quarkonia decay modes in the Standard Model. By recasting existing dilepton and monojet searches we exclude coannihilation partner masses less than 280 GeV and 400 GeV, respectively. Since other existing collider searches do not significantly probe the parameter space, we propose a new dedicated search strategy for pair production of the coloured partner decaying into bbττ final states and dark matter particles. This search is expected to probe the model up to dark matter masses around 600 GeV with current luminosity. [ABSTRACT FROM AUTHOR]

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 analyze the prospects of probing the C P -odd i κ ˜ t ¯ γ 5th interaction at the LHC and its projected upgrades, the high-luminosity and high-energy LHC, directly using associated on-shell Higgs boson and top quark or top quark pair production. To this end we first construct a C P -odd observable based on top quark polarization in Wb → th scattering with optimal linear sensitivity to κ ˜ . For the corresponding hadronic process pp → thj we present a method of extracting the phase-space dependent weight function that allows to retain close to optimal sensitivity to κ ˜ . We project future sensitivity to the signal in pp → t(→ ℓ휈b)h(→ b b ¯ )j. We also propose novel C P -odd observables for top quark pair production in association with the Higgs, pp → t t ¯ h, with semileptonically decaying tops and h → b b ¯ , that rely solely on measuring the momenta of leptons and b-jets from the decaying tops without having to distinguish the charge of the b-jets. Among the many possibilities we single out an observable that can potentially probe κ ˜ ∼ 0.1 at the high-energy LHC with 2휎 confidence. [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]

We confront the indications of lepton flavor universality (LFU) violation observed in semi-tauonic B meson decays with new physics (NP) searches using high p T tau leptons at the LHC. Using effective field theory arguments we correlate possible non-standard contributions to semi-tauonic charged currents with the τ + τ − signature at high energy hadron colliders. Several representative standard model extensions put forward to explain the anomaly are examined in detail: (i) weak triplet of color-neutral vector resonances, (ii) second Higgs doublet and (iii) scalar or (iv) vector leptoquark. We find that, in general, τ + τ − searches pose a serious challenge to NP explanations of the LFU anomaly. Recasting existing 8 TeV and 13 TeV LHC analyses, stringent limits are set on all considered simplified models. Future projections of the τ + τ − constraints as well as caveats in interpreting them within more elaborate models are also discussed. [ABSTRACT FROM AUTHOR]

We summarize our recent work on how to infer on jet formation processes directly from substructure data using generative statistical models. We recount in detail how to cast jet substructure observables' measurements in terms of Bayesian mixed membership models, in particular Latent Dirichlet Allocation. Using a mixed sample of QCD and boosted t t ¯ jet events and focusing on the primary Lund plane observable basis for event measurements, we show how using educated priors on the latent distributions allows to infer on the underlying physical processes in a semi-supervised way. [ABSTRACT FROM AUTHOR]

We summarize our recent proposals for probing the C P -odd i κ ˜ t ¯ γ 5 t h interaction at the LHC and its projected upgrades directly using associated on-shell Higgs boson and top quark or top quark pair production. We first recount how to construct a C P -odd observable based on top quark polarization in W b → t h scattering with optimal linear sensitivity to κ ˜ . For the corresponding hadronic process p p → t h j we then present a method of extracting the phase-space dependent weight function that allows to retain close to optimal sensitivity to κ ˜ . For the case of top quark pair production in association with the Higgs boson, p p → t t ¯ h , with semileptonically decaying tops, we instead show how one can construct manifestly C P -odd observables that rely solely on measuring the momenta of the Higgs boson and the leptons and b-jets from the decaying tops without having to distinguish the charge of the b-jets. Finally, we introduce machine learning (ML) and non-ML techniques to study the phase-space optimization of such C P -odd observables. We emphasize a simple optimized linear combination α · ω that gives similar sensitivity as the studied fully fledged ML models. Using α · ω we review sensitivity projections to κ ˜ at HL-LHC, HE-LHC, and FCC-hh. [ABSTRACT FROM AUTHOR]

We analyse how U(3)5 and U(2)5 flavour symmetries act on the Standard Model Effective Field Theory, providing an organising principle to classify the large number of dimension-six operators involving fermion fields. A detailed counting of such operators, at different order in the breaking terms of both these symmetries, is presented. A brief discussion about possible deviations from these two reference cases, and a simple example of the usefulness of this classification scheme for high-pT analyses at the LHC, are also presented. [ABSTRACT FROM AUTHOR]

Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes p p → ℓ k ℓ l (with k ≠ l ). The current (projected) limits derived in this paper from LHC data with 36 fb - 1 ( 3 ab - 1 ) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic b → d transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays K → π ℓ k ± ℓ l ∓ , B → π ℓ k ± ℓ l ∓ and B → K (∗) ℓ k ± ℓ l ∓ . [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]