Drell-Yan tails beyond the Standard Model

Abstract

We investigate the high-pT tails of the pp → ℓν and pp → ℓℓ Drell-Yan processes as probes of New Physics in semileptonic interactions with an arbitrary flavor structure. For this purpose, we provide a general decomposition of the 2 → 2 scattering amplitudes in terms of form-factors that we match to specific scenarios, such as the Standard Model Effective Field Theory (SMEFT), including all relevant operators up to dimension-8, as well as ultraviolet scenarios giving rise to tree-level exchange of new bosonic mediators with masses at the TeV scale. By using the latest LHC run-II data in the monolepton (eν, μν, τν) and dilepton (ee, μμ, ττ, eμ, eτ, μτ) production channels, we derive constraints on the SMEFT Wilson coefficients for semileptonic four-fermion and dipole operators with the most general flavor structure, as well as on all possible leptoquark models. For the SMEFT, we discuss the range of validity of the EFT description, the relevance of $$ \mathcal{O} $$ O (1/Λ2) and $$ \mathcal{O} $$ O (1/Λ4) truncations, the impact of d = 8 operators and the effects of different quark-flavor alignments. Finally, as a highlight, we extract for several New Physics scenarios the combined limits from high-pT processes, electroweak pole measurements and low-energy flavor data for the b → cτν transition, showing the complementarity between these different observables. Our results are compiled in HighPT (https://highpt.github.io), a package in Mathematica which provides a simple way for users to extract the Drell-Yan tails likelihoods for semileptonic effective operators and for leptoquark models.

Third-Family Quark-Lepton Unification and Electroweak Precision Tests

“…We consider the tail of pp → τ τ distributions obtained at the LHC experiments. The likelihood is obtained using HighPT [28], and for the theory input we use the semi-leptonic SMEFT coefficients computed at NLO in g 4 , as discussed in Appendix A 6. The likelihood is constructed using data from ATLAS [50].…”

“…The rich phenomenology following from the quark-lepton unification hypothesis has been studied in detail in several previous works, including implications for τ decays [24], ∆F = 2 and ∆F = 1 transitions [25][26][27], and high-p T collider signatures [28][29][30][31]. An element that has been missing so far, however, is a systematic study of the implications for electroweak precision observables (EWPO), which constitutes the main objective of this paper.…”

The Rumble in the Meson: a leptoquark versus a Z′ to fit b → sμ+μ− anomalies including 2022 LHCb $$ {R}_{K^{\left(\ast \right)}} $$ measurements

“…These Drell-Yan constraints, unlike the di-leptoquark search, do not scale only with the leptoquark mass but also scale with the size of its coupling λ to quark-lepton pairs, and so they provide complementary information. Using the HighPT package [103,104], we computed the χ-squared statistic as a function of the leptoquark model parameters (λ, θ 23 ) using the CMS di-muon search [105] implemented within, for a benchmark leptoquark mass of M S 3 = 3 TeV (a value which satisfies the di-leptoquark production bound mentioned above). For this mass, we find the 95% CL limit from pp → µ + µ − to be weak, essentially giving no further constraint on the best-fit region to flavour data that we plot in figure 6 (left panel).…”

SMEFT restrictions on exclusive b → uℓν decays

“…The constraints from measurements of Drell-Yan (DY) processes at high p T have been shown to be highly complementary to various low energy flavor processes, in particular in the sectors of rare b decays b → sℓℓ and b → dℓℓ [35,91,92], charged-current b → cτ ν decays [93][94][95][96], lepton flavor violating transitions [97,98], and in the charm sector [99,100]. In this work, we study the complementarity between low-energy b → uℓν processes and high-mass DY.…”