1) The document describes a scan back procedure used to analyze tracks in emulsion sheets and reconstruct interaction vertices. 2) Over 400 tracks were followed starting from 2 cosmic-ray sheets and one additional sheet, with 99 stopping points identified across 8 plates around each point. 3) Using an impact parameter method, 81 interaction vertices were successfully reconstructed, including 57 multi-track vertices and 24 kink vertices. 4) The results demonstrate the scan back procedure can be used to identify neutral hadron interaction vertices in emulsion, but the procedure needs further fine-tuning and efficiency measurement through Monte Carlo studies.

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)