# Observation of the weak time’s arrow in B mesons

- Institution: CERN
- Department: EP Seminar
- Speaker: Fernando Martinez-Vidal
- Year: 2012
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3014860)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

The mechanism of CP violation in weak interactions, as arising from the single physical phase in the CKM matrix, has been validated by more than a decade of intense experimental work probing CP violation, particularly with studies with B mesons. Since the Standard Model theory is CPT invariant, it predicts a "weak arrow of time" matching the large observed matter-antimatter asymmetry in B mesons. However, until recently there has been no direct observation of the expected, large time reversal (T) asymmetry. In this seminar we shall discuss how the BABAR experiment at SLAC has conducted a new data analysis where the decays of entangled neutral B mesons allow comparisons between the rates of four different transitions and their inverse, as a function of the time evolution of the B meson. The results lead to the first high significance, direct observation of T non-invariance through the exchange of initial and final states in transitions that can only be connected by a T symmetry transformation..

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## Lectures

1. [Observation of the weak time’s arrow in B mesons](https://invisiblenetwork.ai/learn/cern/3014860/86c7ab86802d), 1 h 1 min (CERN's player)