Track Selection

The track selection is essential for the efficiency estimation, because not properly reconstructed tracks are the main source of bias for the final efficiency numbers. In order to suppress this effect the selection cuts have been adjusted by Monte Carlo simulation. The final selection criteria are described below.

Station MS01

The first superlayer of the Inner Tracker system is MS01, situated just behind the silicon detector. For the efficiency estimation in this station tracks reconstructed in the silicon detector are used. There are several reasons which motivate this choice:

1. no standalone tracking inside MS01 is possible because only four layers are available,
2. the distance between the silicon detector and MS01 is only a few centimeters and the resolution of the VDS is nearly a factor 10 better than that of the ITR.

In order to reduce the number of wrongly reconstructed segments, which otherwise could introduce a bias in the efficiency measurement, the following requirements are applied to the VDS segments used:

• at least 6 hits in the VDS detector,
• track fit $\chi^2$ probability larger than 0.05,
• at least 2 confirming hits in MS01 (out of 3 possible).

The algorithm looks for confirmation hits within a search window around the predicted impact point calculated using the parameters extrapolated from the last point of the segment to the investigated plane. The size of the search window is chosen according to the extrapolated covariance matrix of the segment.

PC region

The next part of the ITR is the ``PC'' region situated behind the magnet and in front of the RICH vessel. It consists of four superlayers (MS10, MS11, MS12, MS13). In this region the standard pattern recognition program is used. Hits of the investigated layer are excluded for the pattern recognition program, in order to avoid a bias in the efficiency calculation. Tracks reconstructed in the ITR have been used only if they fulfill the following requirements:

• at least 14 hits in the PC region of the ITR,
• at least three crossed superlayers in the ``PC'' region,
• the track has to consist of matched ITR and VDS segments,
• track fit $\chi^2$ probability after refit larger than 0.05,
• momentum less than 100 GeV/c.

TC region

The last part of the ITR is situated in the ``TC'' region (between RICH and ECAL). It consists of two superlayers (MS14, MS15). Only 24 chambers of the installed 48 chambers are read out. No standalone pattern recognition in these chambers is available. The used tracks should meet the following requirements:

• at least 11 hits in the ITR are used for the track reconstruction (excluding TC),
• at least 4 confirming^5.4 hits in stations MS14 and MS15,
• the track segment reconstructed in the main tracker should have a matched VDS segment,
• track fit $\chi^2$ probability after refit larger than 0.05,
• momentum less than 100 GeV/c.

For each selected track it is required that it has to traverse the sensitive volume of the investigated chamber. The hit is defined as found if a cluster is found in a $3\sigma$ region around the track parameter $u$ extrapolated to the z plane of the investigated chamber, $u$ defined as $u=x*cos\alpha+y*cos\alpha$, where $\alpha$ is the rotation angle of the chamber. Sigma is chosen equal to the expected error of the track parameter $u$ obtained via extrapolation of the track's covariance matrix to the z plane of the chamber.