1) Increases the CKF search window from 1 chi2 to 10 chi2. This is why all tracks had a low track count. The window was just too small. You can see the effect of this on slide 11.
2) Decreases the "collision region" from 75 mm to 1 mm when finding seeds. Tightening this parameter significantly reduces the number of CKF seeds significantly. This was the key to get ACTS track reconstruction to complete within a few minutes. Also it is necessary for a good reconstruction efficiency. See slides 5-7.
The two changes are as follows, with references to the following presentation.
1) Increases the CKF search window from 1 chi2 to 10 chi2. This is why all tracks had a low track count. The window was just too small. You can see the effect of this on slide 11.
2) Decreases the "collision region" from 75 mm to 1 mm when finding seeds. Tightening this parameter significantly reduces the number of CKF seeds significantly. This was the key to get ACTS track reconstruction to complete within a few minutes. Also it is necessary for a good reconstruction efficiency. See slides 5-7.