Observation of quantum entanglement in top-quark pairs using the ATLAS detector
The summary plot, showing the entanglement limit is saturated at low invariant masses, when the top quarks are produced in a spin-singlet state.Abstract
We report the highest-energy observation of entanglement, in top−antitop quark events produced at the Large Hadron Collider, using a proton−proton collision data set with a center-of-mass energy of $\sqrt{s}=13$ TeV and an integrated luminosity of 140 fb$^{−1}$ recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable $D$, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top−antitop quark production threshold, where the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be $D=−0.547\pm 0.002 (\text{stat.})\pm 0.021 (\text{syst.})$ for $340<m_{t\bar{t}}<380$ GeV. The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes both the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement to date.
Baptiste Ravina
Alexander von Humboldt Fellow
I’m an experimental particle physicist looking for new physics at the ATLAS experiment with machine learning.
James Howarth
University Research Fellow (Royal Society)
Jay has worked on top quark physics as part of the ATLAS Collaboration since 2009 and is a leading expert in spin correlations.
