# Observation of electroweak production of a same-sign $W$ boson pair in association with two jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

## TL;DR

This paper reports the first observation of electroweak production of same-sign W boson pairs with two jets at the LHC, using ATLAS data, with a significance of 6.5 sigma and measured cross section.

## Contribution

It provides the first measurement and observation of same-sign W boson pair production via electroweak processes at 13 TeV with the ATLAS detector.

## Key findings

- Observed 122 candidate events against 69 ± 7 background
- Signal significance of 6.5 standard deviations
- Measured fiducial cross section of 2.89^{+0.51}_{-0.48} fb

## Abstract

This Letter presents the observation and measurement of electroweak production of a same-sign $W$ boson pair in association with two jets using 36.1 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=13$ TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of $69 \pm 7$ events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial signal cross section is $\sigma^{\mathrm {fid.}}=2.89^{+0.51}_{-0.48} \mathrm{(stat.)} ^{+0.29}_{-0.28} \mathrm{(syst.)}$ fb.