1. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia A revision of the concept of the CBM – MVD Or: Do we need an intermediate pixel detector? Why a revision of the concept? Strategies to improve detector resolution Occupancy and consequences Summary and conclusion M. Deveaux, Goethe University Frankfurt/Main

2. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Why a revision? Conclusion: “To measure  c + CBM needs thin (less 200  m !) MAPS detectors.” Harder impact parameter-cut Sufficient S/B

3. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Why a revision M. Deveaux et al.: “R&D activities for the CBM Micro Vertex Detector (MVD)” CBM collaboration meeting, 25. – 28. Feb 2008, GSI, Darmstadt z = 10 cm Requirement Our running conditions Optimistic estimate of the material budget of the first MVD-station There is an obvious misfit between required and possible material budget Revise global MVD concept

4. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Standard detector layout (reminder) MVD 1 z=10cm MVD 2 z=20cm Strip 1 z=30cm Target

5. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Detector resolution? 1)A good detector resolution. Detector needs to be better than a standard MVD with a first station at 10 cm and 200 µm silicon. What does this means in terms of resolution? Primary Vertex Secondary Vertex z(Secondary Vtx) Impact-parameter Let’s calculate the impact parameter resolution of the MVD

6. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia What do we need? Primary Vertex Impact-parameter z1z1 z2z2

7. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Impact parameter resolution We are multiple scattering dominated. We have to reach an IP-resolution of ~ 45 µm (Easy if first station at z=5 cm). Open: Can one put the first station to 5 cm? z 1 = 5 cm Material budget [X 0 ] IP-resolution [µm] Required Iouri’s “thin detector” Probable material budget Iouri’s “thick detector” z 1 = 10 cm

8. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia A vertex detector at z = 5cm? Detector lifetime? @10 cm => 12.0 x 10 11 min. bias collisions @ 5 cm => 4.4 x 10 11 min. bias collisions (46 days at 10 5 coll/s) Open issue Occupancy? C. Trageser, Bachelor Thesis (together with S.Seddiki) Hits / coll. / mm²

9. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Cluster merging? Assume: We want a < 1% probability for cluster merging. How to estimate max. occupancy? Cluster Detector Free detector surface Occupied detector surface !

10. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Cluster merging? Free detector surface Occupied detector surface Cluster, 3x3 pixel pixel pitch = 15µm 10 µs time resolution => maximum collision rate ~ 2 x 10 5 /s Station at 5cm => ~ 3.5 tracks / (10 6 µm²) => Pileup = 2

11. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Track matching probability MVD 1 z = 5 cm MVD 2 z= ??? Strip 1 z=30cm Target Wrong charm signature To avoid this scenario, pointing resolution of station 2 to station 1 must be sufficiently good. Assume: Search cone = cluster size (~ 20 µm) => P Amb < 1%

12. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia What about track matching? Material budget [% X 0 ] Detector – Position [cm] The minimum material budget of detector stations depends on their position. Accounting for this, we estimate the pointing precision from Station 2 => Station 1 Station 2 has to be placed at z = ~ 8 cm => Hit density ~1.5 / mm² / coll Pos (station 2) [cm] Pointing resolution Station 3 has to be placed at z = ~ 11.5 cm, mat. budget = 700 µm Si equivalent Hit density: ~1.2 / mm² / coll.

13. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia MVD – STS – Track matching MVD Target z = 7.5 cm z = 5 cm z = 11.5 cm STS 1, z = 30 cm 500 µm Si Old Geometrie (with Deltas): Old Geometrie (no Deltas): Track matching from STS to MVD turns into a crucial issue. Probably: Intermediate detectors are needed (Hybrid pixels?)

14. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia Summary and conclusion Higher, realistic material budget reduces the selectivity of the MVD To remain sensitive for open charm, the MVD must be placed closer to the target Close distance to target + delta electrons generate very high occupancy Hit finding and track matching become crucial already at ~ 10 5 coll. /s A “compact MVD” design is seems required for reasonable track matching in MVD Intermediate pixel detectors might be needed for STS=> MVD track matching. Assumptions made are conservative: Hot spot occupancy is assumed Option to detect/reject bad clusters or ambiguous tracks is ignored Might clever algorithms allow for > 10 5 col/s operation? Needs to be simulated. Neglect the occupancy from delta electrons in simulation is not justified.