1. A module in TrkFixup Gerry Lynch October 1, 2005
TrkLoopFix
A module in TrkFixup
Gerry Lynch
October 1, 2005
Gerry Lynch tools workshop October 1, 2005

2. Gerry Lynch tools workshop October 1, 2005
What is a Looper?
Simple definition:
A track that goes at least a full turn in the detector.
Alternate Definition:
A track that is fragmented into two or more tracks, which share many layers.
Operational Definition:
Pairs of low momentum tracks that are 180 degrees apart.
Gerry Lynch tools workshop October 1, 2005

3. Looper Azimuth difference
Before TrkLoopFix a selection is made that keeps low momentum track pairs that are within 0.2 radians of 180 degrees in both azimuth and dip. These go in the work list..
There is a small (~7%) “background” under the peak.
Gerry Lynch tools workshop October 1, 2005

4. Gerry Lynch tools workshop October 1, 2005
Looper Sample
We see that most of the tracks that are in the looper sample are tracks that hit the outer wall of the DCH.
The preselection for the “work” list used by TrkLoopFix has a cut at 100 cm,
Gerry Lynch tools workshop October 1, 2005

5. Gerry Lynch tools workshop October 1, 2005
Looper Multipicity
Most looper candidates have two tracks
The number of tracks for each looper size is shown here.
Gerry Lynch tools workshop October 1, 2005

6. Apogee, Parigee In the looper at the right,Track 1 is first.
Tracks 1 and 2 form an apogee pair.
Tracks 2 and 3 form a parigee pair.
Our goal is to keep 1 and reject 2 and 3.
The procedure for classifying the looper candidates starts with labeling each pair as apogee. perigee, neither, or either
In any looper pair one tracks is going out and the other going in.
But we fit the tracks as if they were going out. So one is wrong.
Gerry Lynch tools workshop October 1, 2005

7. Gerry Lynch tools workshop October 1, 2005
Method 1
When we plot Sum® against Sum(d0), we See a clear band of apogee pairs.
Very few are rejected.
The vertical black band is a mixture of apogee and perigee pairs.
Gerry Lynch tools workshop October 1, 2005

8. Gerry Lynch tools workshop October 1, 2005
Method 2
In this plot of the calculated number of turns from z02-z01, omega, and tanDip,we see clear apogee and (impure) perigee bands at dip angles above about 0.15.
The number rejected is small, but larger than for method 1
Gerry Lynch tools workshop October 1, 2005

9. Beam-line Chi-squared
Pairs with both tracks primary are not loopers.
Pairs with one track primary are probably apogee pairs.
Note that many of the good apogee pairs have no primary track.
Gerry Lynch tools workshop October 1, 2005

10. Gerry Lynch tools workshop October 1, 2005
Position Chi-squared
We get chi-squareds for the comparison of the orbits at parigee and apogee.
The full chi-squared is not very useful, but the position component is valuable.
This shows how these chi-squared agree with method 2 decisions.
This position chi-squared is used to classify the pairs that were not decided before.
Gerry Lynch tools workshop October 1, 2005

11. Gerry Lynch tools workshop October 1, 2005
Procedures
The result of the classification of single pair loopers is
67% apogee % neither ( many of these are not loopers)
15% perigee % either
For a single pair looper we keep the best track and discard the other
for apogee and perigee pairs and keep both for the others.
For multi-pair loopers the procedure is to choose the best pair
by a formula that prefers the apogee pair with the highest
momentum. If that pair is apogee or parigee, the preferred track in that
pair is kept and all others rejected.
For multi-pair loopers that are classified either or neither, both
tracks in the highest momentum pair are kept.
Gerry Lynch tools workshop October 1, 2005

12. Gerry Lynch tools workshop October 1, 2005
MC Checks
If our apogee pairs are right, the sign of curvature will agree with the Monte Carlo truth.
The present program gets agreement with the MC 98% of the time, showing that the correct track is is being selected.
For perigee pairs the fraction in the opposite curvature sign is 61%. I think that this should be larger.
Another check is to compare fitted track parameters, To do this one needs to pay attention to the track direction and what sheet of the helix the parameters represent.
Gerry Lynch tools workshop October 1, 2005

13. Gerry Lynch tools workshop October 1, 2005
MC Parameter Test
The parameters of the tracks are compared with the Monte Carlo truth.
There is excellent agreement. Multi-pair loopers look almost as good.
Gerry Lynch tools workshop October 1, 2005

14. Gerry Lynch tools workshop October 1, 2005
Problems
As indicated on the MC checks page, the performance for parigee pairs is suspect.
One is tempted to conclude from the MC parameters test that things are ok because when the chi-squared is small the track was accepted.
But all the small chi-squareds are from tracks in apogee pairs. The parigee pair tracks do not have small chi-squareds, probably because they are fitted in the wrong direction,.
One approach to this would be to fit all of the parigee candidate tracks and work with two possible solutions when searching for best solution.
We will have to refit the retained perigee track in any case because it is in the wrong direction.
Gerry Lynch tools workshop October 1, 2005