ITR Contribution and Stability

The Inner Tracker participated during the minimum bias data taking in 2002-2003 and the contribution from ITR tracks to $V_0$ signal is estimated to be of the order of $\approx$ 20%. Since the ITR data was used in the analysis the question about the performance stability is very important. Studies of the ITR hit efficiency are described in Chapter 5.

For the acceptance and stability studies a special set of tracks is used. Tracks which are reconstructed with the help of at least 10 hits found in the ITR are called tracks with significant contribution from the ITR detector. This criterion is chosen because 10 ITR hits correspond to approximately two superlayers crossed by a track. The distribution of ITR hits used for track reconstruction is shown in Fig. 6.14 left.

Figure 6.14: Left: distribution of the number of hits used in the Inner Tracker detector for reconstruction of track segments (run 20768). The applied cut is indicated by the arrow. On the right, the $x_F$ distribution for $K^0_S$ obtained with tracks with a large fraction of ITR hits (dashed), overlapped with $x_F$ distribution obtained with all tracks.

For those tracks which fulfilled the requirement mentioned above, the $x_F$ distribution for $K^0_S$ is shown in Fig. 6.14 (right plot), for comparison the $x_F$ spectrum for $K^0_S$ obtained with all tracks is overlapped. The contribution of the ITR is mainly in the positive $x_F$ region, and the fraction of $V_0$s with large number of ITR hits is approximately 17-18%.

The next important point is the performance stability check. All runs which were proposed for the analysis were checked and a decision about the usability was done based on the following information: recorded module synchronization problems, power failures and data performance plots from the off-line reconstruction DQ. In addition the number of $V_0$s reconstructed with large fraction of ITR hits (more than 10 hits) and the number of $V_0$s reconstructed with all tracks are plotted versus time. The distribution of the number of reconstructed $K^0_S$ versus time obtained for one of the runs is shown in Fig. 6.15. This run is one of the problematic runs, during it a power failure of MS13- and MS12+ happened. This failure can be seen as a drop of the number of $K^0_S$ reconstructed with the help of the ITR tracks versus time at the middle plot.

Figure 6.15: Number of $K^0_S$ reconstructed with all tracks (OTR+ITR) and number of $K^0_S$ reconstructed with tracks with a large fraction of ITR hits in the run 20695. Each bin contains approximately 50,000 consecutive events.

Those runs which showed instabilities (like in the Fig. 6.15) are excluded from the analysis. In all other runs ITR tracks were kept in order to increase the statistics and to extend the kinematical acceptance.