Simulations with Simulations with event pile up in MVDevent pile up in MVD

1.1. Improvement of the MVD-digitiserImprovement of the MVD-digitiser

2.2. General simulations with pile upGeneral simulations with pile up

3.3. Open charm reconstructionOpen charm reconstruction

Christina Dritsa

Outline:

Accumulated charge: some termsAccumulated charge: some terms

RED RED : seed pixel : seed pixel (Highest charge)(Highest charge)

YellowYellow : 1 : 1stst crown + seed: 9 pixels crown + seed: 9 pixels GreenGreen : 2 : 2ndnd crown + seed: 25 pixels crown + seed: 25 pixels Blue Blue :: 3 3rdrd crown + seed: 49 pixels crown + seed: 49 pixels

Cluster Formation in digitiser: ReminderCluster 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.

Incident angle: 75°

Initial Version (currently in trunk)Initial Version (currently in trunk)

MPV are similar

But the widths (sigma)are not!

ImprovementImprovement

Initially:Initially: ““Gain” multiplies MPV and Sigma:Gain” multiplies MPV and Sigma: Charge = Charge = GainGain**LandauRandomLandauRandom((MPVMPV, , SigmaSigma))

Correction:Correction: ““Gain” multiplies only Gain” multiplies only MPVMPV:: Charge = Charge = LandauRandomLandauRandom((Gain*MPVGain*MPV, , SigmaSigma))

Result:Result: Only MPV is multiplied with Only MPV is multiplied with Gain Gain , not , not Sigma.Sigma.

75°

Improved VersionImproved Version

Intermediate summaryIntermediate summary

A bug in the digitiser has been fixedA bug in the digitiser has been fixed

(thanks Michael)(thanks Michael)

The tails of the charge deposition in a The tails of the charge deposition in a cluster are well reproduced for the higher cluster are well reproduced for the higher incident angles.incident angles.

General Pile Up simulationsGeneral Pile Up simulations

GOAL:GOAL:Study the behaviour of combinatorial Study the behaviour of combinatorial background with respect to pile up.background with respect to pile up.

Check the efficiency of cuts in different cases Check the efficiency of cuts in different cases before proceeding to a complete feasibility before proceeding to a complete feasibility study of open charm measurement.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• 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

Motivation of the simulation modelMotivation of the simulation model

MIMOSIS2 is foreseen for CBM. MIMOSIS2 is foreseen for CBM. Key parameters of MIMOSIS2 are already Key parameters of MIMOSIS2 are already

visible in MIMOSA26 visible in MIMOSA26 Pixel pitch Pixel pitch : 18.4 : 18.4 ×× 18.4 18.4 µmµm22

Motivation of the simulation modelMotivation of the simulation model

Thickness of sensors - Geometry usedThickness of sensors - Geometry used11stst MAPS @ 5 cm is 300 MAPS @ 5 cm is 300 µm thickµm thick22ndnd MAPS @ 10 cm is 500 µm thick MAPS @ 10 cm is 500 µm thick

Station Z (cm) Rinner [mm]Router [mm]

1 5 5.5 25

2 10 5.5 50

Towards the MVD: HP-2 ULISI

Diamond 200-300 µm

~ 60(1) -150(2) µm Si

< 200 µm Si

~ 60(1) -150(2) µm Si

~ 320(1)-500(2) µm Si

Metal lines SensorPolyamide

Build an ultra thin ladder.Partners: IPHC, IKF, IMEC

(1) first MVD station(2) last MVD station M.Deveaux, DPG meeting 2010

Readout settingsReadout settings

Analogue readoutAnalogue readout ADC 12 bits ADC 12 bits

(4096 channels)(4096 channels) 1 electron / channel1 electron / channel Cut on charge: Cut on charge:

75 ADC units = 75 e75 ADC units = 75 e

Digital readoutDigital readout ADC 1 bit ADC 1 bit

(2 channels)(2 channels) 75 electrons / channel75 electrons / channel Cut on charge:Cut on charge:

1 ADC unit = 75 e1 ADC unit = 75 e

For each setting, three cases were studied:1. No pile up in MVD ( 1 central + 100 Ions )2. Pile up of 5 collisions ( 1central + 4 mbias + 500 Ions)3. Pile up of 10 collisions ( 1 central + 9 mbias + 1000 Ions )

Analogue readout: Occupancy Analogue readout: Occupancy Fired pixels / All pixelsFired pixels / All pixels

MVD @ 5 cmMVD @ 5 cm

[e-]

Merged Clusters in MVDMerged Clusters in MVD

5 10 15

0

2

4

6

8

10

12

14

16

18

Mer

ged

clus

ters

/Tot

al c

lust

ers

[%]

MVD position [cm]

Pile Up 1 Pile Up 2 Pile Up 5 Pile Up 8 Pile Up 10

C.

Tra

gese

r

Analogue readout: PV sigmaAnalogue readout: PV sigma

Efficiency of cuts: an example Efficiency of cuts: an example PV > 3PV > 3··σσ

Momentum reconstructionMomentum reconstruction

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

Tracking Performance (AllSet)Tracking Performance (AllSet)~85 % for trackswith P>1GeV/c

Taken from CbmL1Performance.cxx

Pile Up 5

Pile Up 10

Hit merging and track reconstructionHit 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 (?)

Secondary Vertex ResolutionSecondary 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.

No pile upNo pile up 85 %85 %

Pile up 5Pile up 5 70 %70 %

Pile up 10Pile up 10 50 %50 %

Percentage of D0’s within [-200, 200] µm (shaded area)

>95% expected for a Gaussian

Secondary Vertex ResolutionSecondary Vertex Resolution

Primary Vertex ResolutionPrimary Vertex Resolution

Results for digital readoutResults for digital readoutNo 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.

Intermediate summary & conclusionIntermediate summary & conclusion

The effect on the background rejection efficiency and the The effect on the background rejection efficiency and the vertex resolution for a pile up of 5 and 10 collisions in the vertex resolution for a pile up of 5 and 10 collisions in the MVD has been studied. MVD has been studied.

The impact parameter distribution (PVsigma) and the The impact parameter distribution (PVsigma) and the secondary vertex resolution suggest that the background secondary vertex resolution suggest that the background rejection with a pile up of 10 collisions is insufficient for rejection with a pile up of 10 collisions is insufficient for an open charm reconstruction with the current CBM an open charm reconstruction with the current CBM setup.setup.

Further studies are needed to demonstrate the Further studies are needed to demonstrate the feasibility measurement of open charm when 5 collisions feasibility measurement of open charm when 5 collisions are piled up in the MVD.are piled up in the MVD.

Open charm reconstructionOpen 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)

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

Expected statistics in CBMExpected statistics in CBM

Collision ratesCollision rates Radiation dosesRadiation doses

Expected statisticsExpected statistics CBM year: CBM year: 55··10106 6 ss ≈ 2 months ≈ 2 months Assumed sensor time resolution: Assumed sensor time resolution: ttintint = 30 = 30 µsµs

* BR=0.038, Multipl. =1.2 ·10-4 D0 / centr Au-Au @ 25 AGeV 1 central / 10 mbias

Collision rateCollision rate(interactions/s)(interactions/s)

Collisions/yearCollisions/year(mbias)(mbias)

DD00 → →ππ++KK--

(generated) (generated) **

No pile upNo pile up 3 3 ··10 10 44 1.51.5·10·101111 68 00068 000

Pile up 5Pile up 5 1.5 1.5 ··10 10 55 7.57.5··10101111 340 000 340 000

Can we measure this statistics before the detector is “dead” from radiation?

Radiation doses in CBMRadiation doses in CBMSimulations by M.Deveaux:Old setup (Alligator Field)Delta electrons included

Simulations by D.Bertini:Current setup (Muon Field)Delta electrons NOT included

Fluence [nFluence [neqeq/cm/cm22]]

Collisions (mbias)Collisions (mbias) GEANT + GCALOR (2007)GEANT + GCALOR (2007) FLUKA (2009)FLUKA (2009)

5. 105. 101313 1.5 1.5 ··10 10 1515 2.5 2.5 ··10 10 1515

1 1 3030 5050

Nominal Intensity : AuAu: 109 p/s · 1% · 5 · 106 s = 5. 1013 coll/year

Collisions (mbias)Collisions (mbias)

Fluence [nFluence [neqeq/cm/cm22]]

MAPS lifetimeMAPS lifetime#GEANT + GCALOR (2007)GEANT + GCALOR (2007) FLUKA (2009)FLUKA (2009)

3·1013 10 10 1212 6 6 ··10 10 1111

# http://ulisi-wiki.gsi.de/pub/Meetings/ULISIWorkshop1/M.Winter-Status-P3.pdf

No pile upNo pile up 1.5 1.5 ·· 10 1011 11

pile up 5pile up 5 7.5 7.5 ·· 10 101111

In the studies shown next, normalisation is done according to the corresponding measured statistics for one run.

SetupSetup

CBMROOT Oct2009 (trunk)CBMROOT Oct2009 (trunk) Updated tracking performanceUpdated tracking performance

2 MAPS @ 5, 10 cm2 MAPS @ 5, 10 cm 8 STS, staggered strips.8 STS, staggered strips. Digitisers for MAPS, STSDigitisers for MAPS, STS Delta electrons includedDelta electrons included Realistic track finder, track fitter (KF)Realistic track finder, track fitter (KF) Au-Au @ 25 AGeVAu-Au @ 25 AGeV 1 D1 D00 → → ππ++ + K + K- - embedded per central collisionembedded per central collision

Station Z (cm) Rinner [mm] Router [mm]

1 5 5.5 25

2 10 5.5 50

Choice of parameters (MVD)Choice of parameters (MVD) ttintint = 30 = 30 µsµs Pixel pitch Pixel pitch : 18.4 : 18.4 ×× 18.4 18.4 µmµm22

11stst MAPS @ 5 cm is 300 MAPS @ 5 cm is 300 µm thickµm thick 22ndnd MAPS @ 10 cm is 500 µm thick MAPS @ 10 cm is 500 µm thick

~2 mm

0.7 mm

BS

S

Quantities studiedQuantities studied

BS

generatedmeasured SS

Signal-to-BackgroundSignal-to-Background

SignificanceSignificance

Detection efficiencyDetection efficiency

S and B calculationS and B calculation

max

min

)(~

m

m

mGaussS max

min

)(~

m

m

mExpoB

S

signalNorm bgNorm

B

No pile upNo 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 1.5·1010 central collisions

• ANALOGUE READOUT: 12 bits ADC

No pile upNo pile up

S/B=2.5Eff=0,9%Signif=21

[1/1

50 M

eV/c

2]

No pile up: Rapidity coverageNo pile up: Rapidity coverage

Input Signal Pt-YOutput Signal Pt-Y

(after cuts)

Pile up 5Pile 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 7.5·1010 central collisions

• BINARY READOUT: 1 bit ADC

Pile Up 5Pile Up 5

Pile Up 5: Fitting of Si & BgPile Up 5: Fitting of Si & Bg

S/B=0.6Sign=26Det.Eff=0.55%(1700 D0 expected)

Pile Up 5: Rapidity coveragePile Up 5: Rapidity coverage

SignificanceSignificance

Summary Summary The effect of pile up on the track reconstruction The effect of pile up on the track reconstruction

has been studied.has been studied.

The simulation setup was chosen according to The simulation setup was chosen according to the most updated estimations on the parameters the most updated estimations on the parameters of the MVD (pitch, tof the MVD (pitch, t int int , mat. budget), mat. budget)

The feasibility of open charm measurement has The feasibility of open charm measurement has been investigated for two scenarios: been investigated for two scenarios: No pile up and analogue readout Pile up 5 and digital readout

… … and Conclusion (1)and Conclusion (1)

Due to the relatively long tDue to the relatively long t intint ( = 30 ( = 30 µs µs ) of the ) of the MVD, it is important to operate with pile up and MVD, it is important to operate with pile up and measure higher statistics of Dmeasure higher statistics of D00 particles. particles.

The event pile up causes a high occupancy in the The event pile up causes a high occupancy in the MVD and introduces difficulties in the track MVD and introduces difficulties in the track reconstruction.reconstruction.

The loss in precision of the track reconstruction The loss in precision of the track reconstruction causes a drop in the efficiency of the selection causes a drop in the efficiency of the selection cuts with increasing pile up.cuts with increasing pile up.

… … and Conclusion (2)and Conclusion (2) The inefficiency of cuts suggests that open charm The inefficiency of cuts suggests that open charm

measurement with pile up of 10 collisions is very measurement with pile up of 10 collisions is very difficult with the current CBM setup.difficult with the current CBM setup.

Open charm reconstruction with a pile up of 5 Open charm reconstruction with a pile up of 5 collisions shows higher significance but very low collisions shows higher significance but very low S/B with respect to no pile up.S/B with respect to no pile up.

Further improvements in the CBM setup are Further improvements in the CBM setup are needed in order to increase the background needed in order to increase the background rejection efficiency with increasing pile up.rejection efficiency with increasing pile up.

Proposal for improvementsProposal for improvements Hardware::

Invest effort on R&D for developing a MIMOSIS2 with Invest effort on R&D for developing a MIMOSIS2 with shorter integration time.shorter integration time.

Explore different MVD geometries Explore different MVD geometries move the 1move the 1stst MVD a few cm more downstream to reduce MVD a few cm more downstream to reduce

occupanciesoccupancies vary detector shapes vary detector shapes

Magnetic FieldMagnetic Field

Software:: Use timestamp from STS to match tracks and hits from Use timestamp from STS to match tracks and hits from

pile uppile up Improve the MVD Hit reconstruction algorithm in order Improve the MVD Hit reconstruction algorithm in order

to disentangle close hits (pattern recognition)to disentangle close hits (pattern recognition) Adapt tracking to the input of pattern recognition.Adapt tracking to the input of pattern recognition.

BackupBackup

0°

Initial VersionInitial Version

15°

30°

45°

60°

L

BN sels

BS

S

s

s

1

zt pp

s

dd

d 2

sss LN

Luminosity

Process Cross Section

Detection Efficiency

SignificanceSignificance