Feasibility studies of Feasibility studies of open charm reconstruction open charm reconstruction

with pile upwith pile up

1.1. General simulations with pile upGeneral simulations with pile up

2.2. Open charm reconstructionOpen charm reconstruction

Christina Dritsa

Outline:

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

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 thickPixel pitch Pixel pitch : 18.4 : 18.4 ×× 18.4 18.4 µmµm2 2 (From MIMOSA 26)(From MIMOSA 26)

Station Z [cm]Thickness

[µm]Rinner [mm]

Router [mm]

1 5 300 5.5 25

2 10 500 5.5 50

Readout settingsReadout settings

Analogue readoutAnalogue readout ADC 12 bits ADC 12 bits

(4096 channels)(4096 channels) 1 electron / channel1 electron / channel

Digital readoutDigital readout ADC 1 bit ADC 1 bit

(2 channels)(2 channels) 75 electrons / channel75 electrons / channel

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 )

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 (?)

Analogue readout: PV sigmaAnalogue readout: PV sigma

Pile UpPile UpSignal EfficiencySignal Efficiency

(PV>3)(PV>3)

Background rejectionBackground rejection

(PV>3)(PV>3)

00 30.0 %30.0 % 99.4 %99.4 %

55 29.8 %29.8 % 98.0 %98.0 %

1010 30.8 %30.8 % 92.2 %92.2 %

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

Intermediate summary & conclusionIntermediate summary & conclusion

The efficiency of the selection cuts with respect The efficiency of the selection cuts with respect to pile up has been studied. to pile up has been studied.

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

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

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 DD00 → → ππ++ + K + K--

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

1 5 5.5 25

2 10 5.5 50

BS

S

Quantities studiedQuantities studied

BS

generatedmeasured SS

Signal-to-BackgroundSignal-to-Background

SignificanceSignificance

Detection efficiencyDetection efficiency

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

0,3 0,4 0,5 0,6 0,71000

1500

2000

2500

3000

Exp

ect

ed

num

ber

of D

0

S/B

0,0

0,2

0,4

0,6

0,8

1,0

Significance

Detection E

fficiency [%]

16

18

20

22

24

26

28

30

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

Input

After cuts

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 reject more efficiently the needed in order to reject more efficiently the background with increasing pile up.background 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:: 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.

Back upBack up

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

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

MVD @ 5 cmMVD @ 5 cm

[e-]

S and B calculationS and B calculation

max

min

)(~

m

m

mGaussS max

min

)(~

m

m

mExpoB

S

signalNorm bgNorm

B

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.

Simulated incident angleSimulated 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°

....

...)3()2()1(

3,32,21,1

23,3

22,2

21,1

2

uvuvuv

uvuvuv

QQQ

vQvQvQ

Q

VQWidth defined by :

- 0°- 80°

V cluster width

U c

lust

er

wid

th

V cluster width

Can the inclination of the track be derived from cluster properties?

80°v=

u

Pixel multiplicity in cluster

1 1

1 1 1 1

1 1 1

Multiplicity vs aspect ratioM

ultip

licity

Aspect ratio

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.

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

Taken from CbmL1Performance.cxx

Pile Up 5

Pile Up 10

Momentum reconstructionMomentum reconstruction

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

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

Pile up 5ADC 1

1000 evts

Pile up 10ADC 1

1000 evts