Drell-Yan Tails Beyond the Standard Model

Abstract

We investigate the high-p T tails of the pp → ν and pp → 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, τ ν) and dilepton (ee, µµ, τ τ , 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 O(1/Λ 2 ) and O(1/Λ 4 ) 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-p T processes, electroweak pole measurements and low-energy flavor data for the b → cτ ν transition, showing the complementarity between these different observables. Our results are compiled in HighPT, 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.

Novel leptoquark pair production at LHC

“…As the strength of interaction between the quark-lepton pairs and a leptoquark is gradually increased, the collider searches for signals from several other processes start to be relevant in constraining the leptoquark parameter space. These processes, at the LHC, are a single leptoquark production, a non-resonant production of the Drell-Yan type [1][2][3][4][5][6][7], and a resonant leptoquark production [8][9][10][11][12].…”

Combining low- and high-energy constraints on flavourful EFTs

“…Combining low-and high-energy constraints on flavourful EFTs and their likelihoods can be computed within HighPT (for more details on the package see [4,5] and the talk by Florentin Jaffredo at this conference). In Figure 1 we show the results of the fit, including also EW observables, for the 𝑈 1 case.…”

Probing Flavor in semileptonic transitions at High-$p_T$

“…where 𝑋, 𝑌 ∈ {𝐿, 𝑅} are the chiralities of the anti-lepton and anti-quark fields, P 𝑅,𝐿 = (1 ± 𝛾 5 )/2 are the chirality projectors, 𝑣 = ( √ 2𝐺 𝐹 ) −1/2 stands for the electroweak vacuum-expectation-value (vev), and fermion masses have been neglected. 𝑘 = 𝑝 𝑞 + 𝑝 q , and we take the Mandelstam variables to be ŝ = 𝑘 2 = ( 𝑝 𝑞 + 𝑝 q ) 2 , t = ( 𝑝 𝑞 − 𝑝 ℓ − ) 2 and û = ( 𝑝 𝑞 − 𝑝 ℓ + ) 2 = − ŝ − t. We perform a similar expansion for the charged processes [7].…”

“…Previous works on this subject considered either a specific channel or assumed a particular coupling structure [1][2][3][4][5][6], see also Ref. [7] and references therein. In this work, we combine all the channels probing semileptonic transitions at the LHC for the various leptonic final states: mono-lepton (𝑒𝜈, 𝜇𝜈, 𝜏𝜈) and dilepton (𝑒𝑒, 𝜇𝜇, 𝜏𝜏, 𝑒𝜇, 𝑒𝜏, 𝜇𝜏).…”