Estimated constraints on t-channel Leptoquark exchange from LHC contact interaction searches

TL;DR

This paper derives constraints on first-generation scalar leptoquarks from LHC contact interaction searches, translating experimental bounds into limits on leptoquark couplings and masses beyond direct detection reach.

Contribution

It provides an analytical method to translate LHC contact interaction bounds into constraints on leptoquark parameters, addressing model-specific interference issues.

Findings

Bounds on leptoquark couplings: λ² ≤ (m_{LQ}/2 TeV)²

Leptoquark masses beyond 830 GeV are constrained indirectly

Interference effects complicate direct application of experimental bounds

Abstract

The t-channel exchange of a first generation leptoquark could contribute to the cross-section for q q-bar to e+e-. The leptoquark is off-shell, so this process can be sensitive to leptoquarks beyond the mass reach of pair production searches at the LHC (currently m_{LQ}> 830 GeV). We attempt to analytically translate ATLAS bounds on $ (\bar{q} \gamma ^\mu q) (\bar{e} \gamma _\mu e) $ contact interactions to the various scalar leptoquarks, and obtain a bound on their quark-lepton coupling of order $\lambda^2 \leq (m_{LQ}/2$ TeV)$^2$. The greatest difficulty in this translation is that the leptoquarks do not induce the contact interaction studied by ATLAS, so the interference with the Standard Model is different. If bounds were quoted on the functional dependance of the cross-section on s-hat, rather than on particular contact interaction models, this difficulty in applying experimental bounds to theoretical models could be circumvented.