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Feasibility studies of open charm reconstruction with pile up

Feasibility studies of open charm reconstruction with pile up. Christina Dritsa. General simulations with pile up Open charm reconstruction. Outline:. General Pile Up simulations. GOAL: Study the behaviour of combinatorial background with respect to pile up.

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Feasibility studies of open charm reconstruction with pile up

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  1. Feasibility studies of open charm reconstruction with pile up Christina Dritsa General simulations with pile up Open charm reconstruction Outline:

  2. 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.

  3. 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

  4. 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 • Pixel pitch : 18.4 × 18.4 µm2 (From MIMOSA 26)

  5. Analogue readout ADC 12 bits (4096 channels) 1 electron / channel Digital readout ADC 1 bit (2 channels) 75 electrons / channel 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 )

  6. 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 (?)

  7. Analogue readout: PV sigma

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

  9. Primary Vertex Resolution

  10. Intermediate summary & conclusion • The efficiency of the selection cuts with respect to pile up 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 of open charm measurement when 5 collisions are piled up in the MVD.

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

  12. Expected statistics in CBM Collision rates Radiation doses

  13. 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

  14. 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

  15. 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 • D0 → π+ + K-

  16. Quantities studied

  17. 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

  18. No pile up

  19. [1/150 MeV/c2] S/B=2.5 Eff=0,9% Signif=21

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

  21. 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

  22. Pile Up 5

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

  24. Pile Up 5: Rapidity coverage Input After cuts

  25. Significance

  26. 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

  27. … 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.

  28. … 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 reject more efficiently the background with increasing pile up.

  29. 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: • Improve the MVD Hit reconstruction algorithm in order to disentangle close hits (pattern recognition) • Adapt tracking to the input of pattern recognition.

  30. Back up

  31. ~ 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

  32. Merged Clusters in MVD C. Trageser

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

  34. S and B calculation

  35. 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.

  36. Simulated incident angle ~100% of particles from primary collision are within -30°<θ<30° 100 Au Ions, 25 AGeV >10% of delta electrons are outside -30°<θ<30° Incident angle (°)

  37. 0° 15° 30° 45° 60° 80°

  38. V cluster width Can the inclination of the track be derived from cluster properties? 80° v=u U cluster width • 0° • 80° V cluster width Width defined by :

  39. Pixel multiplicity in cluster

  40. Multiplicity vs aspect ratio Multiplicity Aspect ratio

  41. 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.

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

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

  44. 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

  45. Pile up 5 ADC 1 1000 evts

  46. Pile up 10 ADC 1 1000 evts

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