Search for scalar leptoquarks in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS experiment

TL;DR

This paper reports a search for scalar leptoquarks in proton-proton collisions at 13 TeV using the ATLAS detector, setting new mass exclusion limits and improving sensitivity over previous searches.

Contribution

First ATLAS search for scalar leptoquarks at 13 TeV with full 2015 dataset, establishing new mass limits and extending previous exclusion bounds.

Findings

No significant excess observed over Standard Model background.

Lower mass limits for leptoquarks are set at 1100 GeV and 1050 GeV.

Sensitivity surpasses previous ATLAS results for masses above 860 GeV.

Abstract

An inclusive search for a new-physics signature of lepton-jet resonances has been performed by the ATLAS experiment. Scalar leptoquarks, pair-produced in $pp$ collisions at $\sqrt{s}$ = 13 TeV at the Large Hadron Collider, have been considered. An integrated luminosity of 3.2 fb$^{-1}$, corresponding to the full 2015 dataset was used. First (second) generation leptoquarks were sought in events with two electrons (muons) and two or more jets. The observed event yield in each channel is consistent with Standard Model background expectations. The observed (expected) lower limits on the leptoquark mass at 95% confidence level are 1100 GeV and 1050 GeV (1160 GeV and 1040 GeV) for first and second generation leptoquarks, respectively, assuming a branching ratio into a charged lepton and a quark of 100%. Upper limits on the aforementioned branching ratio are also given as a function of leptoquark mass. Compared with the results of earlier ATLAS searches, the sensitivity is increased for leptoquark masses above 860 GeV, and the observed exclusion limits confirm and extend the published results.