Feasibility studies of open charm reconstruction with pile up 1. General simulations with pile up 2. Open charm reconstruction Christina Dritsa Outline:

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.

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 t Int < 40 µs, rad. tol. ~ 3 x n eq /cm² MimoSIS-2: 2D-chip for SIS300 (D meson in AA collisions) Novel process with small feature size, stitching? t Int < 30 µs, rad. tol. <10 14 n eq /cm² final prototype by 2015 MimoSIS-3 3D-chip for SIS300, phase 2 t Int < 10 µs, rad. tol. ~10 14 n eq /cm² Development start by 2009 final prototype > 2015 if 3D technology works

Motivation of the simulation model Thickness of sensors - Geometry used Thickness of sensors - Geometry used 1 st 5 cm is 300 µm thick 1 st 5 cm is 300 µm thick 2 nd 10 cm is 500 µm thick 2 nd 10 cm is 500 µm thick Pixel pitch : 18.4 × 18.4 µm 2 (From MIMOSA 26) Pixel pitch : 18.4 × 18.4 µm 2 (From MIMOSA 26) StationZ [cm] Thickness [µm] R inner [mm] R outer [mm]

Readout settings Analogue readout ADC 12 bits ADC 12 bits (4096 channels) (4096 channels) 1 electron / channel 1 electron / channel Digital readout ADC 1 bit ADC 1 bit (2 channels) (2 channels) 75 electrons / channel 75 electrons / channel For each setting, three cases were studied: 1.No pile up in MVD ( 1 central Ions ) 2.Pile up of 5 collisions ( 1central + 4 mbias Ions) 3.Pile up of 10 collisions ( 1 central + 9 mbias Ions )

Hit merging and track reconstruction 1: High P track 2: Low P track MVD STS 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 (?)

Analogue readout: PV sigma Pile Up Signal Efficiency (PV>3) Background rejection (PV>3) % 99.4 % % 98.0 % % 92.2 %

No pile up 85 % Pile up 5 70 % Pile up % Percentage of D 0 ’s within [-200, 200] µm (shaded area) >95% expected for a Gaussian Secondary Vertex Resolution

Primary Vertex Resolution

Intermediate summary & conclusion The efficiency of the selection cuts with respect to pile up has been studied. 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. 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. Further studies are needed to demonstrate the feasibility of open charm measurement when 5 collisions are piled up in the MVD.

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

Expected statistics in CBM Collision rates Collision rates Radiation doses Radiation doses

Expected statistics CBM year: 5·10 6 s ≈ 2 months CBM year: 5·10 6 s ≈ 2 months Assumed sensor time resolution: t int = 30 µs Assumed sensor time resolution: t int = 30 µs * BR=0.038, Multipl. =1.2 ·10 -4 D 0 / centr 25 AGeV 1 central / 10 mbias Collision rate (interactions/s)Collisions/year(mbias) D 0 →π + K - (generated) * No pile up 3 · · Pile up · · Can we measure this statistics before the detector is “dead” from radiation?

Radiation doses in CBM Simulations by M.Deveaux: Old setup (Alligator Field) Delta electrons included Simulations by D.Bertini: Current setup (Muon Field) Delta electrons NOT included Fluence [n eq /cm 2 ] Collisions (mbias) GEANT + GCALOR (2007) FLUKA (2009) · · Nominal Intensity : AuAu: 10 9 p/s · 1% · 5 · 10 6 s = coll/year Collisions (mbias) Fluence [n eq /cm 2 ] MAPS lifetime MAPS lifetime # GEANT + GCALOR (2007) FLUKA (2009) 3· ·10 11 # No pile up 1.5 · pile up · In the studies shown next, normalisation is done according to the corresponding measured statistics for one run.

Setup CBMROOT Oct2009 (trunk) CBMROOT Oct2009 (trunk) Updated tracking performance Updated tracking performance 2 5, 10 cm 2 5, 10 cm 8 STS, staggered strips. 8 STS, staggered strips. Digitisers for MAPS, STS Digitisers for MAPS, STS Delta electrons included Delta electrons included Realistic track finder, track fitter (KF) Realistic track finder, track fitter (KF) 25 AGeV 25 AGeV D 0 → π + + K - D 0 → π + + K - StationZ (cm)R inner [mm]R outer [mm]

Quantities studied Signal-to-BackgroundSignificance Detection efficiency

No pile up Signal in simulation = D 0 Per central collision: 100 Ions (δ e- ), 1 D 0 → π + K - Background in simulation = evts (SE) BR = Multiplicity =1.2 ·10 -4 D 0 / centr 25 AGeV 1 central / 10 mbias Normalise to 1.5·10 10 central collisions ANALOGUE READOUT: 12 bits ADC

No pile up

S/B=2.5 Eff=0,9% Signif=21 [1/150 MeV/c 2 ]

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

Pile up 5 Signal in simulation = D 0 Per central collision: 100 Ions (δ e- ), 1 D 0 → π + K - Background in simulation = evts (SE) BR = Multiplicity =1.2 ·10 -4 D 0 / centr 25 AGeV 1 central / 10 mbias Normalise to 7.5·10 10 central collisions BINARY READOUT: 1 bit ADC

Pile Up 5

Pile Up 5: Fitting of Si & Bg S/B=0.6 Sign=26 Det.Eff=0.55% (1700 D 0 expected)

Pile Up 5: Rapidity coverage Input After cuts

Significance

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

… and Conclusion (1) Due to the relatively long t int ( = 30 µs ) of the MVD, it is important to operate with pile up and measure higher statistics of D 0 particles. Due to the relatively long t int ( = 30 µs ) of the MVD, it is important to operate with pile up and measure higher statistics of D 0 particles. The event pile up causes a high occupancy in the MVD and introduces difficulties in the track reconstruction. 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. The loss in precision of the track reconstruction causes a drop in the efficiency of the selection cuts with increasing pile up.

… 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. 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. 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. Further improvements in the CBM setup are needed in order to reject more efficiently the background with increasing pile up.

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

Back up

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

Merged Clusters in MVD C. Trageser

Analogue readout: Occupancy Fired pixels / All pixels 5 cm [e-]

S and B calculation

Results for digital readout No pile upPile 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.

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

0°15°30° 45°60° 80°

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

Pixel multiplicity in cluster

Multiplicity vs aspect ratio Multiplicity Aspect ratio

Secondary Vertex Resolution Only Bg! 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.

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

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

Choice of parameters (MVD) t int = 30 µs t int = 30 µs Pixel pitch : 18.4 × 18.4 µm 2 Pixel pitch : 18.4 × 18.4 µm 2 1 st 5 cm is 300 µm thick 1 st 5 cm is 300 µm thick 2 nd 10 cm is 500 µm thick 2 nd 10 cm is 500 µm thick ~2 mm 0.7 mm

Pile up 5 ADC evts

Pile up 10 ADC evts