Göttingen 2025 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 51: Top Physics III (Cross Sections, Entanglement)

T 51.5: Vortrag

Mittwoch, 2. April 2025, 17:15–17:30, VG 1.103

Measurement of tt spin entanglement in the lepton+jets 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 characteristic quantum effects such as 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 lepton+jets tt decay channel for quantum entanglement measurements in the m_tt threshold region 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. Furthermore, the potential effects of a possible tt quasi-bound state in the turn-on region, known as "toponium", are discussed.

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