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Violation in Mixing

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1.2 Neutral � Mesons 17<br />

and � and the branch<strong>in</strong>g ratios for such channels are at or below the level of : s<strong>in</strong>ce various channels<br />

contribute with differ<strong>in</strong>g signs, their sum is not expected to exceed the <strong>in</strong>dividual level so ¡ �� � �� is<br />

a rather safe and model <strong>in</strong>dependent assumption [13]. On the other hand, ¡Ñ�� has been measured [14].<br />

¡ ��� �� � Ç<br />

� �� ¦ �<br />

Ü� � ¡Ñ�� � ��<br />

Equations 1.23 imply that, to Ç accuracy, Eqs. 1.14, 1.15 and 1.16 simplify <strong>in</strong>to:<br />

¡Ñ� �Å �<br />

¡ � Ê� Å £ ��Å �<br />

Õ�Ô �Å ��Å<br />

¡ � � ¡Ñ�� (1.23)<br />

Any � state can then be written as a comb<strong>in</strong>ation of the states �À and �Ä, and the amplitudes of this<br />

comb<strong>in</strong>ation evolve <strong>in</strong> time as<br />

�À Ø ��À � �ÅÀ Ø � À Ø<br />

�Ä Ø ��Ä � �ÅÄØ � ÄØ �<br />

A state which is created at time Ø � as <strong>in</strong>itially pure � , is denoted �� Ô�Ý× �: it has �Ä � �À �<br />

� Ô . Similarly an <strong>in</strong>itially pure � can be called �� Ô�Ý×�, and has �Ä � �À � � Õ . The time<br />

evolution of these states is thus given by<br />

where<br />

� Ø �� �ÅØ � Ø� Ó× ¡Ñ� Ø�<br />

� Ø �� �ÅØ � Ø� � ×�Ò ¡Ñ� Ø�<br />

Å � ÅÀ ÅÄ<br />

� À Ä À Ä<br />

�� Ô�Ý× Ø � � � Ø �� � Õ�Ô � Ø �� � (1.24)<br />

�� Ô�Ý× Ø � � Ô�Õ � Ø �� � � Ø �� �� (1.25)<br />

remember<strong>in</strong>g equations 1.23. Furthermore, it is useful to go beyond the lead<strong>in</strong>g approximation for the ratio<br />

, from Eqs. 1.12 the relevant expression is:<br />

Õ<br />

Ô<br />

Õ<br />

Ô �<br />

�<br />

Å £ � £<br />

�<br />

Å<br />

and the first two orders of the expansion are<br />

�<br />

�<br />

Å £<br />

�<br />

Å<br />

� �<br />

�<br />

� £<br />

� Å £<br />

�� �<br />

�<br />

�<br />

�<br />

Å<br />

��<br />

�È VIOLATION IN THE �� SYSTEM

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