Degradation of Tracking and Vertexing performance

1. Degradation of Tracking and Vertexing performance Katsumi Senyo Nagoya University • Contents • Motivation • Dominant effect of the tracking degradation at current CDC • Result: Drift chamber • Vertexing issue • Summary and outlook

2. The higher occupancy in a detector get… • Tracking/vertexing efficiency may get worse. • Decrease of recon. eff. may cancel L gain? • B full reconstruction, extreme rare decays and so on • Momentum dependency of tracking eff. • slow p, high pt track (ex. pp/Kp/KK) • Tracking/vertexing resolution may get worse. • Limit on physics reach in precision measurements • CP analysis, resonance search, and so on • Bigger background contamination • Impact on S/N • Low reconstruction efficiency (by tighter cuts) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

3. Tracking/Vertexing system Evaluate an impact on the chamber efficiency and SVD vertex resolution under the higher BG/occupancy rate In this MC study, current tracking/vertexing system is used: • Current tracking system • CDC (Central Drift Chamber): Cell size ~ > 1.3 cm • Current vertexing system • SVD2(Silicon Vertex Detector): 4 layer, vertex res. ~ 100mm At Super B factory, the detector system already presented should improve the performance, although it is not used in this study yet. • Pixel/Striplet + Silicon + Finer Granularity Cell Drift Chamber (at the super B upgrade) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

4. About This Study • Geant Based Monte Carlo Study(SVD2 + CDC) • Simple occupancy extrapolation on CDC (i.e. no improvement, no innovation, no effort or no budget on the detector) • Reference(x1 occupancy from actual data): Peak L=0.9x1034(assuming background situation at the early morning on Mar.31 2003) varying occupancy overlay up to x20 • Physics process evaluated (all charged tracks): • Bpp (high p tracking) • BD*(Dpslow)p, (slow p tracking) • BJ/ KS (vertexing) Other-side B decays into daughters according to their natural BF. Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

5. Occupancy Overlay • Classification of the Occupancy Overlay for CDC • x1 Current/nominal Occupancy (@ L~1034) • x5 • x10 • x20 Expected occupancy rate w/ safety factor 2x • For the vertexing study, x 0, x 1, x 2, and x 5 occupancies are used since the finer granularity and faster electronics have to be used to improve the occupancy rate at the Super KEKB. • (Occupancy in the innermost layer reaches upto 200% w/ x20 overlay) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

6. Chamber efficiency Contents • Readout deadtime • High momentum tracking eff. (using B→p+p- ) • Slow pi tracking eff. (using BD*(Dpslow)p ) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

7. Decrease of hits @ x20 occupancy • The electronics(Shaper/QT)deadtime is clouding out proper track hits under the high occupancy. Thus tracking efficiency and resolution depend on the readout system. More proper hits to reconstruct a track! Deadtime = 2200ns Deadtime = 600ns Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

8. Deadtime from Shaper/QT Q • Signal timing and ADC value are converted into the pulse timing and its width in a gate w/ some pedestal. • This has a deadtime (gate width + pedestal + a). • New S/QT w/ 600nsec deadtime has been in mass production stage and already installed in inner 1-3 layers. Original 2200nsec deadtime version is obsolete and replaced gradually in a few years. • There is a further short deadtime version of S/QT for small cell drift chamber. • In this study, the 2200nsec version is only used to make the deadtime effect clear. t Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

9. Tracking eff. with Bp+p- decays With 600ns dead time and under x20 occupancy, CDC keeps about 90% of the single tracking efficiency including geometrical acceptance. (thus the tracking itself has almost 100% eff.) B->pp reconstruction eff. including geometrical acceptance Square root of recon. eff. of the left ~ single track efficiency of mid/high p Occupancy Overlay(times) Occupancy Overlay(times) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

10. Slow p reconstruction efficiency • Slow p reconstruction efficiency is extracted fromBD*(Dpslow)p reconstruction efficiency BD(Kp)p reconstruction efficiency • First step study for an impact on the full reconstruction. • No information used from SVD2. Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

11. Slow p efficiency from BD*(Dpslow)p • About 80% of efficiency is kept in the slow p efficiency under x20 occupancy. • Need higher efficiency to keep full reconstruction eff. recon. eff. of the slow pion ~ single track efficiency of slow p BD*p reconstruction eff. including geometrical acceptance Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

12. What happens in slow p tracking x20 occupancy overlay no (x0) occupancy overlay • Difference between the succeeded and failed in a typical case; • Number of good track hits/samples • Eyeball track fit can still work   A room to improve the pattern recognition for the higher occupancy/luminosity A small cell DC or silicon device may be installed to reduce occupancy Reconstruction succeeded Reconstruction failed Kink (by multiple scattering) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

13. Vertex resolution • Vertex resolution under high occupancy (using BJ/ KS ) • Impacts of occupancy in the first layer on vertex resolution Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

14. Vertex resolution: Another concern • Good vertex resolution is very important to measure time-dependent CP asymmetry, and background reduction in the rare decay search/measurement. • Background/occupancy will highly depend on the structure of the interaction region. • Occupancy is effectively reduced by a high granular silicon device such as a pixel/striplet detector and fast readout, compare to the drift chamber we looked at here.  x0, x1, x2, x5 background overlays are studied This is equivalent to 4 times reduction of the shaping time without a major change. Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

15. Vertex resolution w/ BJ/KS Vertex resolution is kept less than 160mm (ZCP-Ztag) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

16. Closer look: the vertex resolution • Vertex resolution only depends on the occupancy of the first layer.  Reduce the occupancy in the first layer ( 5%).  Tune and optimize vertexing algorithm under the higher occupancy 1* BG on 2, 3, 4lyr 1* BG on 1st lyr Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

17. Study summary with the current detector system • Observed little degradation of tracking and vertexing efficiency/resolution. • D* reconstruction and full reconstruction may be suffered by the tracking degradation under the high occupancy but there is a room to improve. • Current tracking/vertexing system even work under the high occupancy. Newly constructed system will do better. Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

18. Future prospect • Now we can proceed from `What has to be installed?’ to `How to configure it?’ stage. • SVD2+small cell DC are under operation since last autumn. • A design of tracking/vertexing devices will be determined in view of the physics analysis demand in near future. • Detector R&D…(already reported by Tsuboyama and Uno yesterday) Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

19. CDC Hit rate @~8x1033 Inner most layer reached a hit rate of 200kHz and works well. • Layer14 has a peak due to inner/main part connection structure • Here we concentrate into the tracking/vertexing issue. Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

20. Current tracking/vertexing system Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

21. Current tracking/vertexing system Actual Cosmic Data zoom hit histogram All layer working well Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii

22. Reconstruction efficiency and mass resolution: B→pp x1: eff. 82%DE = 18MeV x5: eff. 79%DE = 21MeV rough est. of tracking eff. (square root of reconst. eff.) x1 – 91%x5 – 89%x10 – 86%x20 – 79% x10: eff. 74%DE = 26MeV x20: eff. 63%DE = 33MeV Katsumi Senyo, Nagoya University Super B Factory Workshop in Hawaii