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Violation in Mixing

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172 Analysis of the time-dependent �È -violat<strong>in</strong>g asymmetry <strong>in</strong> � � � � decays<br />

Parameter Fit Result Scaled PRL<br />

Æ�� � ¦ �<br />

ÆÃ� � ¦ � �<br />

�Ã� � ¦ � � �<br />

ÆÃà �� ¦ ��� ���<br />

Æ��� �� ¦ �� ��<br />

Æ�Ã� ¦ �� � �<br />

��Ã� � � ¦ � � �<br />

Æ�Ãà ¦ �� �<br />

Table 7-5. Results of a fit to the Run 1 data with the new analysis cuts. The PRL results, scaled by the<br />

relative efficiency, are shown for comparison.<br />

7.4.2 Comparison with the branch<strong>in</strong>g fraction analysis result<br />

Table 7-5 shows the new nom<strong>in</strong>al fit results for the Run 1 dataset, <strong>in</strong>clud<strong>in</strong>g all of the cuts <strong>in</strong> Table 7-3. For<br />

comparison, the expected values, based on the PRL results <strong>in</strong> Tab. 7-1 and the relative efficiency of the new<br />

cuts, are also shown. The likelihood function for this fit is equivalent to the one used <strong>in</strong> the branch<strong>in</strong>g ratio<br />

analysis. The relative efficiency is � for signal events and � for background events.<br />

7.5 Background characterization<br />

7.5.1 Composition<br />

The sample selected with the cuts described <strong>in</strong> the previous section conta<strong>in</strong>s �� cont<strong>in</strong>uum background.<br />

The � � purity can be estimated from the fit result <strong>in</strong> Table 7-5 as ���� �� � � . The background is<br />

aga<strong>in</strong> ÕÕ cont<strong>in</strong>uum and is made up of � Ù�×, � charm, and tau events.<br />

The relative amount of ��, Ã�, and Ãà events varies significantly over the different background samples.<br />

The charm sample has a much larger fraction of Ã� and Ãà decays than Ù�× events due to the dom<strong>in</strong>ance<br />

of � × decays. The tau sample conta<strong>in</strong>s no kaons and is dom<strong>in</strong>ated by events where one or both of<br />

the tracks come from a � � � decay. These differences affect the relative fraction of ��, Ã�, and ÃÃ<br />

background <strong>in</strong> each tagg<strong>in</strong>g category, which we take <strong>in</strong>to account <strong>in</strong> the maximum likelihood fit.<br />

Table 7-6 shows the percentage of events tagged <strong>in</strong> each category for the different species from fits us<strong>in</strong>g the<br />

���Ö�Ò�ÓÚ angle to separate ��, Ã�, and Ãà events. For Monte Carlo the results are cross-checked us<strong>in</strong>g<br />

truth <strong>in</strong>formation. The same trends are observed <strong>in</strong> data and Monte Carlo, with similar absolute tagg<strong>in</strong>g<br />

efficiencies. As a cross-check on the real data, we <strong>in</strong>clude the parameterization obta<strong>in</strong>ed from the fit region<br />

by float<strong>in</strong>g the tag efficiencies. The fit region and side-band regions are <strong>in</strong> excellent agreement, giv<strong>in</strong>g<br />

MARCELLA BONA

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