Scan Back and Vertex Analysis

1. Scan Back
and
Vertex Analysis
Gerardo Di Iorio

2. 8 GeV/c pions
exposure
Nov 2004
• Nominal density of the brick:~ 0.1 tracks/mm2
/400 mrad
• Exposure of the brick at 6h cosmic ray (~ 1 tracks/mm2
/400mrad )
•The CS sheets accumulated a lot of tracks during the flight from japan
Single CS
~ 26 tracks/mm2
/400 mrad

3. Prediction selection
Scanning area 25 cm2
2 CS and the last sheet of the brick
2 CS and PL01
~ 0.17 tracks/mm2
/400 mrad
433 tracks recostruct

4. Scan Back procedure
 1x1 cm2
scanning area for plate-to-plate inter-calibration
 Calculation of scanning area for each prediction, taking into
account the affine transformation
 Only 1 view scanning to search for candidates
 Candidates defined on the basis of the angular and the
position agreement with the prediction (chi2 analysis)

5. Scan Back procedure (2)
•Take the best χ2 track if less than 6 (99.9% prob.)
•Look for predictions for 2 additional plates (1 per mill inefficiency) if not found
2
2
2
2
2
2
2
2
2
yxy
y
x
x yx
σσσ
ϑ
σ
ϑ
χ
ϑϑ
∆
+
∆
+
∆
+
∆
= |)|*41()0()( θσθσ ++=
Without chi2 cut

6. Position accuracy
∆x = x_cand – x_pred (µm) ∆y = y_cand – y_pred
(µm)
σ = 7.3 µm σ = 5.0 µm
Tagli –50,50 Profile to get the parameterization

7. σ = 5.3 mrad
predxcandxx −− −=∆ ϑϑϑ
Angular accuracy
σ = 4.9 mrad
predycandyy −− −=∆ ϑϑϑ

8. Vertex plate definition
Lead
Impurity due to random
coincidences between CS to
brick connection (4.7 mm gap):
high single plate background
beam
beam
Numberofpredictions
Sheet number
Vertex defined
from the track
disapperance on 3
consecutive
sheets

9. Vertex Analysis (1)
Scanning area 5x5 mm2
on 4 sheets upstream and 4 downstream the
lead plate in which the scan-back track is stopped
Vertex plate
vertex
The stopping point is confirmed and the
interaction vertex is reconstructed by using
impact parameter method (Fedra)

10. Vertex Analysis (2)
• Vertex scanning of all tracks stop from sheet 4 to 52:
350???tracks
• Vertex analysis of 119 volume (~ 30940 mm3
)
Impact parameter
Scatter Plot
Impact parameter – angular track

11. Vertex analysis results
Class Number of
events
Multi-track vertex
57
Kink
24
Multiple scattering
6
Stopping tracks without
vertex
2
Passing through
6
Alignment problems
4
Total volumes 99
Reconstructed interactions
57+24+(6)=81 (87)
Scan-Back track
Neutral hadron interactions
Confirmed by eye check

12. Vertex recostructed (1)
beam
Impact
parameter:
1) 7.5 µm
2) 7.9 µm
3) 10.5 µm
4) 5.5 µm
5) 7.5 µm
6) 4.5 µm
1
2
3
4
56

13. Vertex recostructed (2)
Impact parameter
1) 6.9 µm
2) 6.5 µm
3) 1.8 µm
4) 2.5 µm
5) 8.4 µm
beam
1
2
3
4 5

14. Conclusions and Outlook
 Our first scan-back trial
 Definition of the scan-back procedure (chi2 analysis)
 413 tracks followed in the ECC brick starting from
2CS+pl01 used as trigger (very high background
density)
 99 stopping points (3 missing segments)
 25 mm2 x 8 plate volume analysed around the
stopping point
 81 vertex interactions reconstructed
 Fine tuning of the procedure
 Monte-Carlo study to measure the efficiency
 Implement the procedure in the Oracle database

15. Stima dei vertici di interazione
attesi
cm17int =λ
Attese 84 interazioni di pioni primari
int/
0)( λz
enzn −
=
[ ] 84)/exp(1341 int0 ≈−−×= λzNattese
mmz 480 ≈spessore del mattone:
particelle sopravvissute dopo spessore z
(sovrastima del 10÷15 % nella normalizzazione a 341, a causa della molteplicità dei
secondari negli eventi)