Simulations with event pile up in MVD

1. Simulations with event pile up in MVD Christina Dritsa Improvement of the MVD-digitiser General simulations with pile up Open charm reconstruction Outline:

2. RED : seed pixel (Highest charge) Yellow : 1st crown + seed: 9 pixels Green : 2nd crown + seed: 25 pixels Blue : 3rd crown + seed: 49 pixels Accumulated charge: some terms

3. Cluster Formation in digitiser: Reminder Energy: Taken randomly from the accumulated charge distribution on 25 pixels (2nd crown) Shape: From the “profile” of the real cluster.

4. Initial Version (currently in trunk) Incident angle: 75° MPV are similar But the widths (sigma) are not!

5. Improvement • Initially: • “Gain” multiplies MPV and Sigma: • Charge = Gain*LandauRandom(MPV, Sigma) • Correction: • “Gain” multiplies only MPV: • Charge = LandauRandom(Gain*MPV, Sigma) • Result: Only MPV is multiplied with Gain , not Sigma.

6. Improved Version 75°

7. Intermediate summary • A bug in the digitiser has been fixed (thanks Michael) • The tails of the charge deposition in a cluster are well reproduced for the higher incident angles.

8. General Pile Up simulations GOAL: Study the behaviour of combinatorial background with respect to pile up. Check the efficiency of cuts in different cases before proceeding to a complete feasibility study of open charm measurement.

9. MIMOSA roadmap for CBM (by Marc Winter) • MimoSIS-1: • 2D-chip for SIS100 (D mesons in pA collisions) • Established AMS 0.35µm process • 3 prototypes (2010,2011,2012) final prototype by summer 2012 • tInt < 40 µs, rad. tol. ~ 3 x 1012 neq/cm² • MimoSIS-2: • 2D-chip for SIS300 (D meson in AA collisions) • Novel process with small feature size, stitching? • tInt < 30 µs, rad. tol. <1014neq/cm² • final prototype by 2015 • MimoSIS-3 • 3D-chip for SIS300, phase 2 • tInt < 10 µs, rad. tol. ~1014neq/cm² • Development start by 2009 • final prototype > 2015 if 3D technology works

10. Motivation of the simulation model • MIMOSIS2 is foreseen for CBM. • Key parameters of MIMOSIS2 are already visible in MIMOSA26 • Pixel pitch : 18.4 × 18.4 µm2

11. Motivation of the simulation model • Thickness of sensors - Geometry used • 1st MAPS @ 5 cm is 300 µm thick • 2nd MAPS @ 10 cm is 500 µm thick

12. ~ 60(1) -150(2) µm Si Diamond 200-300 µm < 200 µm Si ~ 60(1) -150(2) µm Si ~ 320(1)-500(2) µm Si Towards the MVD: HP-2 ULISI Build an ultra thin ladder. Partners: IPHC, IKF, IMEC Polyamide Metal lines Sensor (1) first MVD station (2) last MVD station M.Deveaux, DPG meeting 2010

13. Analogue readout ADC 12 bits (4096 channels) 1 electron / channel Cut on charge: 75 ADC units = 75 e Digital readout ADC 1 bit (2 channels) 75 electrons / channel Cut on charge: 1 ADC unit = 75 e Readout settings • For each setting, three cases were studied: • No pile up in MVD ( 1 central + 100 Ions ) • Pile up of 5 collisions ( 1central + 4 mbias + 500 Ions) • Pile up of 10 collisions ( 1 central + 9 mbias + 1000 Ions )

14. [e-] Analogue readout: Occupancy Fired pixels / All pixels MVD @ 5 cm

15. Merged Clusters in MVD C. Trageser

16. Analogue readout: PV sigma

17. Efficiency of cuts: an example PV > 3·σ

18. Momentum reconstruction The reconstruction efficiency of low momentum tracks (<1.5 GeV/c ) is slightly reduced with increasing pile up.

19. Pile Up 5 Pile Up 10 Tracking Performance (AllSet) ~85 % for tracks with P>1GeV/c Taken from CbmL1Performance.cxx

20. 1: High P track 2: Low P track Hit merging and track reconstruction STS MVD • The high P track will be reconstructed first and will “own” the hit. • The track parameters will be slightly modified. • Hit sharing is not allowed in the MVD: The low momentum track does not “find” the hit. There is a probability to pick up a wrong neighbouring hit (?)

21. Only Bg! Secondary Vertex Resolution Secondary vertex resolution for background tracks deteriorates significantly with pile up. This effect might have an impact on the efficiency of the secondary vertex cut.

22. Percentage of D0’s within [-200, 200] µm (shaded area) >95% expected for a Gaussian Secondary Vertex Resolution

23. Primary Vertex Resolution

24. Results for digital readout No pile up Pile up 10 In the case of digital readout, the distributions are the same as for the analogue readout. The effect on the single point resolution, introduced by the digital readout, is dominated by the multiple scattering effects.

25. Intermediate summary & conclusion • The effect on the background rejection efficiency and the vertex resolution for a pile up of 5 and 10 collisions in the MVD has been studied. • The impact parameter distribution (PVsigma) and the secondary vertex resolution suggest that the background rejection with a pile up of 10 collisions is insufficient for an open charm reconstruction with the current CBM setup. • Further studies are needed to demonstrate the feasibility measurement of open charm when 5 collisions are piled up in the MVD.

26. Open charm reconstruction No collision pile up in MVD (only central coll.) Pile Up of 5 collisions (1 central + 4 peripheral)

27. MIMOSA roadmap for CBM (by Marc Winter) • MimoSIS-1: • 2D-chip for SIS100 (D mesons in pA collisions) • Established AMS 0.35µm process • 3 prototypes (2010,2011,2012) final prototype by summer 2012 • tInt < 40 µs, rad. tol. ~ 3 x 1012 neq/cm² • MimoSIS-2: • 2D-chip for SIS300 (D meson in AA collisions) • Novel process with small feature size, stitching? • tInt < 30 µs, rad. tol. <1014neq/cm² • final prototype by 2015 • MimoSIS-3 • 3D-chip for SIS300, phase 2 • tInt < 10 µs, rad. tol. ~1014neq/cm² • Development start by 2009 • final prototype > 2015 if 3D technology works

28. Expected statistics in CBM Collision rates Radiation doses

29. CBM year: 5·106 s ≈ 2 months Assumed sensor time resolution: tint = 30 µs Can we measure this statistics before the detector is “dead” from radiation? Expected statistics * BR=0.038, Multipl. =1.2 ·10-4 D0 / centr Au-Au @ 25 AGeV 1 central / 10 mbias

30. Radiation doses in CBM Simulations by D.Bertini: Current setup (Muon Field) Delta electrons NOT included Simulations by M.Deveaux: Old setup (Alligator Field) Delta electrons included Nominal Intensity : AuAu: 109 p/s · 1% · 5 · 106 s = 5. 1013 coll/year In the studies shown next, normalisation is done according to the corresponding measured statistics for one run. #http://ulisi-wiki.gsi.de/pub/Meetings/ULISIWorkshop1/M.Winter-Status-P3.pdf

31. Setup • CBMROOT Oct2009 (trunk) • Updated tracking performance • 2 MAPS @ 5, 10 cm • 8 STS, staggered strips. • Digitisers for MAPS, STS • Delta electrons included • Realistic track finder, track fitter (KF) • Au-Au @ 25 AGeV • 1 D0 → π+ + K- embedded per central collision

32. 0.7 mm ~2 mm Choice of parameters (MVD) • tint = 30 µs • Pixel pitch : 18.4 × 18.4 µm2 • 1st MAPS @ 5 cm is 300 µm thick • 2nd MAPS @ 10 cm is 500 µm thick

33. Quantities studied

34. S and B calculation

35. No pile up • Signal in simulation = 7 000 D0 • Per central collision: 100 Ions (δe-),1 D0→ π+ K- • Background in simulation = 83 000 000 evts (SE) • BR = 0.038 • Multiplicity =1.2 ·10-4 D0 / centr Au-Au @ 25 AGeV • 1 central / 10 mbias • Normalise to 1.5·1010central collisions • ANALOGUE READOUT: 12 bits ADC

36. No pile up

37. [1/150 MeV/c2] S/B=2.5 Eff=0,9% Signif=21

38. No pile up: Rapidity coverage Input Signal Pt-Y Output Signal Pt-Y (after cuts)

39. Pile up 5 • Signal in simulation = 9 000 D0 • Per central collision: 100 Ions (δe-),1 D0→ π+ K- • Background in simulation = 676 000 000 evts (SE) • BR = 0.038 • Multiplicity =1.2 ·10-4 D0 / centr Au-Au @ 25 AGeV • 1 central / 10 mbias • Normalise to 7.5·1010central collisions • BINARY READOUT: 1 bit ADC

40. Pile Up 5

41. Pile Up 5: Fitting of Si & Bg S/B=0.6 Sign=26 Det.Eff=0.55% (1700 D0 expected)

42. Pile Up 5: Rapidity coverage

43. Significance

44. Summary • The effect of pile up on the track reconstruction has been studied. • The simulation setup was chosen according to the most updated estimations on the parameters of the MVD (pitch, tint , mat. budget) • The feasibility of open charm measurement has been investigated for two scenarios: • No pile up and analogue readout • Pile up 5 and digital readout

45. … and Conclusion (1) • Due to the relatively long tint ( = 30 µs ) of the MVD, it is important to operate with pile up and measure higher statistics of D0 particles. • The event pile up causes a high occupancy in the MVD and introduces difficulties in the track reconstruction. • The loss in precision of the track reconstruction causes a drop in the efficiency of the selection cuts with increasing pile up.

46. … and Conclusion (2) • The inefficiency of cuts suggests that open charm measurement with pile up of 10 collisions is very difficult with the current CBM setup. • Open charm reconstruction with a pile up of 5 collisions shows higher significance but very low S/B with respect to no pile up. • Further improvements in the CBM setup are needed in order to increase the background rejection efficiency with increasing pile up.

47. Proposal for improvements • Hardware: • Invest effort on R&D for developing a MIMOSIS2 with shorter integration time. • Explore different MVD geometries • move the 1st MVD a few cm more downstream to reduce occupancies • vary detector shapes • Magnetic Field • Software: • Use timestamp from STS to match tracks and hits from pile up • Improve the MVD Hit reconstruction algorithm in order to disentangle close hits (pattern recognition) • Adapt tracking to the input of pattern recognition.

48. Backup

50. Initial Version 0°