Search for low-mass leptoquarks using the llqq final states in Pb-Pb ultra-peripheral collisions

Abstract

Abstract After a review over past experiments and theoretical requirements from low-energy flavour physics, we argue that the possibility of low-mass leptoquarks (LQ) cannot be fully excluded due to the assumptions made in the measurements. Therefore we propose to search for the pair production of low-mass leptoquarks in Pb-Pb ultra-peripheral collisions with the least model dependence (assuming a small coupling constant ≲ 0.1). There are a couple of advantages: 1) high photon flux provides high production rate for low mass LQs; 2) the background contamination is much lower than that in p-p collisions. The analysis strategy permits a leptoquark to decay to all possible lepton-plus-quark modes. Taking the scalar LQ, S3, with an electric charge $$ \left|q\right|=\frac{4}{3}e $$ q = 4 3 e , as example, the mass point of 100 GeV can be excluded at the 95% confidence level using a dataset of 4 pb−1 Pb-Pb ultra-peripheral collisions at $$ \sqrt{s} $$ s = 5.02 TeV and the performance of the ATLAS detector in Run 2. The proposed method also applies to searching for high-mass LQs in p-p collisions as long as the LQ pair production mechanism dominates.