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ZPD p erformance: b est tick selection
Olya Igonkina (University of Oregon)
February 19, 2004

What is a gain of selecting best tick for ZPD

· what is best tick · what is good track

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· The quality is equal to number of hitted superlayers (nHits). (nHits-a · z 0err is considered but found to be about the same)

·

Best tick is tick where quality of the track is maximal.

· The track is found in several ticks if ticks have tracks in the same sector with the similar curvature and tanDip (difference less than 4)

·

Wrong tick is when track is rejected by DecMod in best tick but accepted in another ticks

· the comparison is done for events passed L3OutDch and for events rejected by L3 (all L3 bits but L3OutL1Open are 0 )

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Track performance, Track quality = nHits

There are large number of tracks found, but many are rejected by Decision module :

Run 44246 (colliding beams, but ConfigAlias=BACKGROUND) : 4 tracks / event,

75% of all found ZPD tracks have DecMod bit0 set (pT > 0.8, no Z 0 cut) 60% of all found ZPD tracks have DecMod bit1 set (pT > 0.2, Z 0 < 15) 3% of tracks are rejected by DecMod in best tick, but accepted in other ticks.

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Comparison with L3. Track quality = nHits
Run 44246 (colliding beam, ConfigAlias=BACKGROUND) Nevents L3OutDch accepted L3 rejected 16926 1564 14946 Accepted by ZPD DecMod in best tick wrong tick best tick wrong tick bit 0, pT > 0.8, no cut on Z0 1299 3 6650 61 bit 1, pT > 0.2, |z 0| < 15 1517 3 10673 237 run 44256 , HER only Nevents 10965 Accepted by ZPD DecMod in bit 0, pT > 0.8, no cut on Z0 bit 1, pT > 0.2, |z 0| < 15

L3OutDch accepted 94 best tick wrong tick 31 2 93 0

L3 rejected 10765 best tick wrong tick 3658 41 6966 182

The wrong L1 trigger decision due to wrong tick selection is made in 3% cases of L3 rejected events (less than 0.5% in tick before best tick)
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MC. Track quality = nHits

999 BBbar events

Nevents 999 Accepted by ZPD DecMod in bit 0, pT > 0.8, no cut on Z0 bit 1, pT > 0.2, |z 0| < 15

L3OutDch accepted 997 best tick wrong tick 877 10 997 0

L3 rejected 0 best tick wrong tick 0 0 0 0

MC efficiency is as expected
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Events selected in wrong tick, Track quality = nHits
wrong tick - best tick delta Nhit vs nHits

nHits (wrong) - nHits(best)

10 8

300

2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 -8 -6 -4 -2 0 2 4 6 8 10

250 6 4 2 0 -2 100 -4 -6 -8 0 2 4 6 8 10 0 50 150 200

wrong tick - best tick
diff in z0err versus z0err diff in z0 versus z0

nHits

z0Err(wrong) - Z0Err(best)

10 8 6 4 2 0 -2 -4 -6 200 -8 0 2 4 6 8 10 12 14 16 18 0 800 600 400 1400 1200 1000

z0(wrong) - z0(best)

25 20 15 10 5

22 20 18 16 14 12

0 -5 -10 -15 -20 -30 -20 -10 0 10 20 30 40

10 8 6 4 2 0

z0Err

z0

events are from all data samples : beam background, HER only, LER only, cosmic
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Attempt to use z0err

L3 accepted
ZpdHdwSimTrksl._z0err:ZpdHdwSimTrksl._hitMap[0]+ZpdHdwSimTrksl._hitMap[1]+ZpdHdwSimTrksl._hitMap[2]+ZpdHdwSimTrksl._hitMap[3]+ZpdHdwSimTrksl._hitMap[4]+ZpdHdwSimTrksl._hitMap[5]+ZpdHdwSimTrksl._hitMap[6]+ZpdHdwSimTrksl._hitMap[7]+ZpdHdwSimTrksl._hitMap[8]+ZpdHdwSimTrksl._hitMap[9] {(_oepoutline&0xfeffff)!=0&&ZpdHdwSimTrksl._z0err<15}

z0err

3.5 3 2.5 2 1.5 1

L3 accepted

100

z0err

4

12

10 80 8 60

L3 rejected
102

6

40

4

10

20 0.5 0 3 4 5 6 7 8 9 10 nhits 0

2

0

2

3

4

5

6

7

8

9

10 Nhits

1

z0err may be used to select best tick, however the proportion of the wrong selected events is about the same. The stronger cuts on z0err in decision module helps more than selection of the best tick
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Conclusions

· One could reduce background by selecting making decision in best tick.

· This requires calculation of number of the hitted superlayers

· The gain is about 3% of the events which are rejected by L3, and 15% of the L3OutDch accepted events (beam background)

· The stronger cuts on Z0, Z0err on decision module, might help as well.

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