1. Vertex localization in Lyon Emulsion Workshop 7th-9th Dec. 2006, Nagoya Luisa Arrabito – IPN Lyon

2. Exposure: 1 brick + 2 CS ~ 1000 pions 8 GeV 6 hours of cosmic exposure (without CS)  ~ 1 track/mm 2 tanθ <400 mrad We have scanned and analyzed two bricks: Lyon brick + Bern brick (thanks to Bern people). Vertex localization test beam with pions CERN, Nov. 2004 Lyon Brick (#4) : CHORUS grid  We observed 5 mm shifts and ~20mrad rotations for two consecutive plates. Bern Brick (#6) : OPERA grid.

3. Predictions Scanned area for predictions ~25 cm 2 (CS1 – CS2 – PL1) 288 tracks have been followed Intercalibration zones: 8x8 mm 2 Recalibration parameters: grains > 27 0.05 < slope < 0.25 Scanback parameters: ΔSlope = 0.03 + 0.05*slope ΔPos = (70 + 6*slope) μm Selection criteria: min(ΔPos) # max missing plates = 3 Total Scan parameters: 5X5 mm 2 area 3 upstream plates + 6 downstream plates Muon contamination TX TY Scanback (brick #4)

4. Passing through tracks Stopping tracks TX TY TX TY Stopping plate 61 events 4 < stop plate < 53 Efficiency calculated on passing through tracks ~ 92 % Fill Factor ~62% Passing through

5. Position agreement between found and predicted tracks Sigma ~10.6 μm Plate ID (|ΔX| > 30 μm)Plate ID (|ΔY| > 30 μm) DPXDPY

6. Angular agreement between found and predicted tracks Plate ID (|ΔTX| > 10 mrad) Plate ID (|ΔTY| > 10 mrad) Sigma ~2.4 mrad Intercalibration is not satisfactory for some plates DSXDSY

7. Total Scan results (brick #4) Many volumes were difficult to align, so only some vertices have been reconstructed. Impossible to do a clear vertex classification. Fake stopping points were evaluated to be about 20%. The main cause for fake stops was a position displacement between found and predicted tracks. Primary pion

8. Scanback (brick #6) Efficiency calculated on passing through tracks ~ 91 % Fill Factor Stopping plate 134 events 4 < stopping plate <56 Scanned area for predictions ~54 cm 2 (CS1 – CS2 – PL1) 771 tracks have been followed 69.5% Passing through! (to compare with ~62%)

9. SB brick #4 Sigma ~10.6 μm Comparison between brick #4 and brick #6 Position agreement between found and predicted tracks SB brick #6 Sigma ~8.6 μm DPX DPY DPX DPY

10. Total Scan results (brick #6) Some examples… Vertexing parameters: Max impact parameter = 50 μm ΔZ < 3000 μm (track-vertex maximal distance) 41 interactions58% 12 confirmed stops17% 6 scattering 8% 11 passing through 15% 1 total scan failure 1% Out of 134 volumes, 71 have been analyzed (the rest is in progress). A classification was possible!

11. Interactions « multiprong » ScanBack Track Primary pion

13. Confirmed Stop

14. Scattering

15. Daughter tracks multiplicity Impact parameter

16. Conclusions Vertex localization and reconstruction procedures work well. We are now increasing statistics in order to confirm our results. We have to fine tune vertexing parameters with MC simulation.