Speakers
Description
B°/anti-B° pairs produced in the decays of the Upsilon(4S) and (5S) are supposed to be in an entangled state. At the (4S) it should be antisymmetric C=-1 state, at the (5S) both the antisymmetric (C=-1) and the symmetric (C=+1) state are possible.
The entanglement at the (4S) is an important condition for the measurement of time dependent CP violation, any admixture of other states would modify the entanglement and would lead to biases in the measurement of CP-violation parameters. Such admixtures could be due to higher order contributions. Though supposed to be small, the precision aimed for the CP-violation measurements motivates a study of such effects.
The presence of different quantum states at the (5S) allows for interesting studies. By post-selection samples of pure or arbitrarily mixed states can be prepared which could be completely entangled or disentangled (or anything inbetween).
A conclusive study of the above-mentioned effects needs quantum tomography: the complete determination of the density matrix of the B°/anti-B° system. This turns out not to be easy for the B°d, since the small value of Delta_Gamma allows only a subset of the density matrix to be measured if flavor flavor correlations are used (see Kun Cheng et al, arXiv:2507.12513v1, 2025). We show that full tomography is possible using correlation of decays into CP-eigenstates.
The poster will first give an introduction in the phenomenology of quantum entanglement at the Upsilon (4S) and (5S). We will show examples how admixtures of different quantum states may bias CP violation measurements. Then we show how complete quantum tomography is possible using decays in CP-eigenstates.