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Revision of CBM Concept for Intermediate Pixel Detector Optimization

This paper explores the need for revising the CBM concept to enhance detector resolution and reduce material budget misfits, focusing on strategies to improve detector occupancy, impact parameter resolution, and cluster merging issues. The study emphasizes the importance of thin MAPS detectors for better resolution and track matching. The discussion includes calculations for impact parameter resolution, detector occupancy, and pointing precision to optimize detector placement and minimize material budget requirements. The conclusion highlights the necessity of intermediate pixel detectors for effective track matching between STS and MVD, emphasizing the significance of compact MVD design for improved track matching at high collision rates.

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Revision of CBM Concept for Intermediate Pixel Detector Optimization

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

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

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

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

  5. Impact-parameter z(Secondary Vtx) Detector resolution? • 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 Let’s calculate the impact parameter resolution of the MVD M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

  6. Primary Vertex Impact-parameter z1 z2 What do we need? M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

  7. z1 = 10 cm Iouri’s “thick detector” IP-resolution [µm] Probable material budget z1 = 5 cm Required Material budget [X0] Iouri’s “thin detector” 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? M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

  8. Occupancy? C. Trageser, Bachelor Thesis (together with S.Seddiki) Hits / coll. / mm² A vertex detector at z = 5cm? Detector lifetime? @10 cm => 12.0 x 1011 min. bias collisions @ 5 cm => 4.4 x 1011 min. bias collisions (46 days at 105 coll/s) Open issue M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

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

  10. Cluster, 3x3 pixel pixel pitch = 15µm Occupied detector surface Free detector surface Station at 5cm => ~ 3.5 tracks / (106 µm²) => Pileup = 2 10 µs time resolution => maximum collision rate ~ 2 x 105/s Cluster merging? M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

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

  12. The minimum material budget of detector stations depends on their position. Accounting for this, we estimate the pointing precision from Station 2 => Station 1 Pointing resolution Station 2 has to be placed at z = ~ 8 cm => Hit density ~1.5 / mm² / coll Pos (station 2) [cm] What about track matching? Material budget [% X0] Detector – Position [cm] Station 3 has to be placed at z = ~ 11.5 cm, mat. budget = 700 µm Si equivalent Hit density: ~1.2 / mm² / coll. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

  13. 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?) MVD – STS – Track matching z = 11.5 cm z = 7.5 cm 500 µm Si z = 5 cm STS 1, z = 30 cm Target MVD M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

  14. 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 ~ 105 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 > 105 col/s operation? Needs to be simulated. • Neglect the occupancy from delta electrons in simulation is not justified. M. Deveaux, CBM collaboration meeting, 14.-17. Oct. 2008, Dubna, Russia

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