Karlsruhe 2024 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 23: Top physics 1

T 23.2: Vortrag

Montag, 4. März 2024, 16:15–16:30, Geb. 30.95: Audimax

Measurement of tt spin entanglement in the 1-lepton channel in ATLAS — Katharina Behr, Eleanor Jones, and •Fiona Ann Jolly — DESY, Hamburg, Germany

The top quark, one of the heaviest known elementary particles, is mostly produced in pairs (tt) at the LHC. These tt final states are sensitive to undetected and rare processes predicted by the Standard Model (SM), one of them being the quantum entanglement of tt spins. One of the kinematic regions most sensitive to entanglement is characterised by low values of the invariant mass of the tt system, just above the kinematic ‘turn-on’ for tt production (m_tt ≥ 2m_t) The presence of entanglement is probed via a high-precision measurement of an angular variable sensitive to the tt spin correlation in this region.

In this talk, sensitivity studies for using the 1-lepton tt decay channel for quantum entanglement measurements in the resolved decay topology are presented. The calculation of the relevant angular variable relies on the identification of the down-type quark jet coming from the W boson decay, which has the highest spin-analysing power among the hadronic top quark decay products. If this jet is not identified, the b-jet coming from the hadronic top quark decay is used. Hence, one of the key challenges is the correct assignment of jets to the tt decay products. To achieve this, the tt system is reconstructed using a reconstruction approach called SpaNet. Background estimates in the turn-on region are also shown.

Keywords: top quark; entanglement; spin; jets; ATLAS