1. Challenges with decay vertex detection in CBM using an ultra-thin pixel detector system
M. Deveaux, S. Amar-Youcef, C. Dritsa, J. Heuser, I. Fröhlich, C. Müntz, C. Schrader, F. Rami, S. Seddiki, J. Stroth, T. Tischler, C. Trageser and B. Wiedemann on behalf the CBM collaboration. :
Outline:
The CBM experiment (a reminder)
Requirements for the CBM vertex detector
Technology choices and consequences
Running conditions
Summary and Conclusion
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

2. CBM@FAIR CBM: Fixed target heavy ion experiment 10-45 AGeV beam energy
RICH
TRD
TOF
ECAL
MVD+STS
Beam
and
Target
CBM:
Fixed target heavy ion experiment
10-45 AGeV beam energy
Located at GSI/FAIR, Darmstadt, Germany
First collision ~2015
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

3. The Physics case of CBM
Explore the nuclear phase diagram in the region of high net baryon density
CBM
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

4. Observables of interest
Onset of chiral symmetry restoration at high B
in-medium modifications of hadrons (,, e+e-(μ+μ-), D)
Deconfinement phase transition at high B
excitation function and flow of strangeness (K, , , , )
excitation function and flow of charm (J/ψ, ψ', D0, D, c)
charmonium suppression, sequential for J/ψ and ψ' ?
The equation-of-state at high B
collective flow of identified hadrons
particle production at threshold energies (open charm)
QCD critical endpoint
excitation function of event-by-event fluctuations (K/π,...)
flow
charm
fluctuations
dileptons
Our topic for today
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

5. Global layout of the CBM experiment
electron ID: RICH & TRD
 p suppression  104
muon ID: absorber + detector layer sandwich
 move out absorbers for hadron runs
MVD + STS
aim: optimize setup to include both, electron and muon ID
→ would be the best crosscheck of results we can ever do!
MVD: Micro Vertex Detector, STS: Main Silicon Tracking System
RICH + TRD: electron identification, TOF: Time of Flight system for hadron identification, MUCH Muon detector (replacing the RICH), ECAL
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

6. The open charm challenge
D : c ~ 312 m
D+  K- + + (9.5%)
D0 : c ~ 123 m
D0  K- + (3.8%)
D0  K- + + - (7.5%)
Ds : c ~ 150 m
D+s  K+ K- + (5.3%)
Multiplicities / central collision
SIS18
SIS100/
300
+c : c ~ 60 m
+c  p K- + (5.0%)
[W. Cassing, E. Bratkovskaya, A. Sibirtsev,
Nucl. Phys. A 691 (2001) 745]
High interaction rate required => CBM is designed as fixed target experiment
Beam intensity provided by SIS300: Up to 109 ions/s (slow extraction)
Needs excellent secondary vertex resolution ~50 µm
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

7. How to get the resolution
Hybrid pixels
CMOS-Sensors
Assuming first
station 5cm
behind the target.
Simulation of the sec. vtx resolution of the MVD
C. Dritsa
Sec. vtx. resolution demands for thin sensors like CMOS-Sensors (MAPS)
Can’t tolerate material of the beam pipe. Vertex detector must be placed in (moderate) vacuum.
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

8. Minimum Ionizing Particle MOS Active Pixel Sensor
CMOS-sensors (MAPS)
Minimum Ionizing Particle MOS Active Pixel Sensor
Features of the MIMOSA – detectors:
Single point resolution 1.5µm - 2.5µm
Pixel – pitch µm
Thinning achieved µm
S/N for MIPs 20 – 40
Radiation hardness: 1MRad ; 1 x 1013 neq/cm²
Time resolution ~ 20 µs (massive parallel readout)
MIMOSA IV
We follow the R&D for SoI-Detectors and 3D-VLSI-detectors
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

9. The time resolution of MAPS vs. collision rate
On - chip zero suppression
Discriminators
Sensor
array
Bonding pads
+ output Amplis.
Consecutive readout
of pixels required
=> expected time
resolution ~10 µs
(~100 kFrame/s)
Readout bus
Pixel column
Expected collision rates:
Up to 109 heavy ions / sec (up to 35 AGeV)
1% - target => Up to 107 collisions / s
Expect pile up of nuclear collisions in the vertex detector
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

10. Running conditions (1) ~130 hits / evt Y (cm) X (cm)
Average hit density from nuclear collisions 10cm)
Hits/mm²/coll. x 1000
X (cm)
Y (cm)
~130 hits / evt
Typical non-central
collision
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

11. Hot spots up to 1 hit / evt / mm2
Running conditions (1)
Mean hit density from nuclear collisions 10cm)
Incl. delta electrons from the target
~700 hits / evt
Hits/mm²/coll. x 1000
Rate Hits (Max.)
100 kHz => 0.7k (1/mm²)
1 MHz => 7k (10/mm²)
10 MHz => 70k (100/mm²)
Adapt beam to abilities
of the detector!
Hot spots up to 1 hit / evt / mm2
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

12. Running conditions Hits/event distance between station and target[cm]
The occupancy is dominated by delta electrons generated in the target.
Handling them needs detector with very high granularity
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

13. Running conditions and consequences
Occupancy estimate:
Fired pixels / hit
(from Mimosa16 beam test)
Pixel pitch: ~ 15 µm => 4.4k pixel /mm²
Assume collision rate of ~ 1MHz for the
first years + 5 fired pixels / hit:
1.2 % 10cm
4.0 % 5cm
IPHC-Strasbourg
CEA-Saclay
3.5 mV
7.8 mV
A. Besson
(modified)
Data flow estimate:
Assume on-chip zero suppression:
40-80 bit/cluster (including addresses)
1 MHz collision rate
~ cm
~ cm
Tracking?
Start in fast detectors of the STS,
Extrapolate tracks to the MVD.
Validated excluding Delta-electrons
To be confirmed accounting for them
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

14. Radiation dose and tolerance
Full collision rate => few 1015 neq/year
Radiation tolerance of MAPS
Mi-9
Mi-15
Mi-18
z=5 cm
z=10 cm
Assumption today:
Detector may tolerate 1013 neq/cm²
=> two weeks beam on target (1 MHz)
~ 5 x cm
~ 1 x cm
=> Replace detector after one beam time
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

15. Artistic view on the CBM-MVD
How it might look like
Artistic view on the CBM-MVD
Power: ~ 1W /cm²
S. Belogurov et. al
Cool with heat conduction:
TPG - ~1400 W/(m K), 3-4 times better than Cu
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

16. Preliminary Material budget? Assuming 15 µm pitch Acceptable area
More speed needs more power => More material for cooling & cables
Larger diameter needs more pixels => Even more power & cables
Larger diameter needs longer ways for heat conduction => More material
Time resolution might need fine tuning accounting for material budget
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

17. Some simulation results (25 AGeV)
Multiplicity based
on HSD model
M ~
BR = 9.51%
ε D+ = 1% and S/B2σ = 0.4
We expect ~ 5k (up to few 10k) reconstructed D+ within 2 weeks of measurement (1012 coll. at 106 coll./s, 25 AGeV). λC can be seen.
Expect better results for 35 AGeV (higher multiplicities)
But: Material budget of the detector must not exceed ~0.3% X0 per layer
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

18. Research lines for the MVDmm
Dose [neq / cm2 / coll. ]
BEAM
Delta electrons produced in
the target
Mechanical system integration R&D
@ Frankfurt
Simulation studies
@ GSI + IPHC
The CBM
Micro Vertex Detector
Design studies
Electronic system integration R&D
@ Frankfurt
MAPS R&D
@ IPHC
Rad. hardness studies:
Frankfurt, IPHC, FRM II
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

19. Summary and conclusion
The CBM experiment aims for a first time to measure open charm being emitted
from heavy ion collisions at beam energies between 10 and 45 AGeV
This requires a vertex detector with:
very low material budget (~0.3 % X0 /layer)
good radiation hardness (minimum 1013 neq/cm², optimal > 1015 neq/cm²)
good time resolution (minimum ~10µs, optimal < 100 ns)
good spatial resolution (~ 5 µm or better)
vacuum compatible design and cooling
Currently we consider CMOS sensors (by IPHC Strasbourg) as guideline technology Excessive R&D seems required to match the requirements.
R&D on radiation hardness of CMOS sensors, mechanical and electronical
detector integration have started at GSI (Darmstadt) and Goethe University Frankfurt
We will presumably build our detector in two phases:
A CMOS sensor based vtx detector operating roughly 2015 (min. performance)
A novel technology based detector operating few years later
Challenges in vertex detector design?
We have plenty of them 
We are open to alternative technologies, advices and collaborators.
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

20. The CBM collaboration 46 institutions > 400 members Russia:
IHEP Protvino
INR Troitzk
ITEP Moscow
KRI, St. Petersburg
China:
CCNU Wuhan
USTC Hefei
Croatia:
RBI, Zagreb
Portugal:
LIP Coimbra
Romania:
NIPNE Bucharest
Poland:
Krakow Univ.
Warsaw Univ.
Silesia Univ. Katowice
Nucl. Phys. Inst. Krakow
LIT, JINR Dubna
MEPHI Moscow
Obninsk State Univ.
PNPI Gatchina
SINP, Moscow State Univ.
St. Petersburg Polytec. U.
Ukraine:
Shevchenko Univ. , Kiev
Cyprus:
Nikosia Univ.
Univ. Mannheim
Univ. Münster
FZ Rossendorf
GSI Darmstadt
Czech Republic:
CAS, Rez
Techn. Univ. Prague
France:
IPHC Strasbourg
Germany:
Univ. Heidelberg, Phys. Inst.
Univ. HD, Kirchhoff Inst.
Univ. Frankfurt
Univ. Kaiserslautern
Hungaria:
KFKI Budapest
Eötvös Univ. Budapest
India:
VECC Kolkata
SAHA Kolkata
IOP Bhubaneswar
Univ. Chandigarh
Univ. Varanasi
IlT Kharagpur
Korea:
Korea Univ. Seoul
Pusan National Univ.
Norway:
Univ. Bergen
Kurchatov Inst. Moscow
LHE, JINR Dubna
LPP, JINR Dubna
46 institutions
> 400 members
Strasbourg, September 2006
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

21. Backup
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

22. First vacuum compatibility tests
High-tech prototype ladder for vacuum tests (silicon glued on TPG)
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

23. Radiation hardness of MAPS
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

24. Outlook Radiation hardness
Non-ionizing radiation hardness:
Limitation:
Slow charge collection in the sensor + reduced lifetime of signal electrons
Approach (1): Speed up charge collection:
Diode
Diode
P+ => P- P+ P- P+ P+ P- P+
Pixel with gradient doping.
Attractive build in potential?
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

25. Outlook Radiation hardness
Approach (2): Restore lifetime of electrons
Recombination
destroys the signal
Efficient approach for depleted N-doped detectors.
BUT: MAPS are P-doped and undepleted.
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

26. The power dissipation of MAPS
On - chip cluster-finding processor
Discriminators
Sensor
array
Bonding pads
+ output Amplis.
Readout bus
Power scales with
occupency. Neglegted
in the follwing
Pixel column
Only one pixel / col. ac-tive, low power dissipation
Permanently biased,
high consumption.
1 cell : „Pcol“
Basic assumption: Power scales with number of the end of
column logics (discriminator + cluster finding processor)
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

27. The power dissipation of MAPS
f pixels / s p p
Time resolution of MAPS
Readout freq. (Pixels / time)
Power of one logic cell
The surface of one collumn is:
With:
pixels
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

28. The material buget of the MVD
Details: See talk of M.Deveaux, MVD-working group
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

29. Correlations of the thickness
(Simplified)
Big stations are thick stations
Small pixels make thick
Fast pixels save material
Fast frame rates make thick stations
Time resolution of MAPS
Readout freq. (Pixels / time)
Pixel pitch
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

30. Correlation of thickness
Material budget (revised)
Material budget according to earlier studies
3000 D0/lifetime, S/B=0.3, Det. Eff. 0.7%
@ Au+Au 25AGeV (preliminary)
z = 10 cm
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

31. Electronic system integration studies (Readout concept)
Demo-Aux-PCB
@ End of the ladder
Voltage regulation
Signal buffering
Single ended signal
=> differential signal
Mi17
Clock, bias,
slow control
Sync. signals
Analogue output
16 x 50 MHz <=> 1.2 GB/s
FPC
Up to
280 pins
Analog
output
Sync
Clock
JTAG
ADC + FPGA
Bias (8V DC) PC
Data transfer
Online
monitoring
Reset
Data processing/reduction
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

32. How to study things more in detail => R&D in Frankfurt
MAPS
clock,
fast
control
MAPS
Analog
signal
MAPS
slow
control
MAPS
sync
4 x ADC
12-bit, 50 MHz
Digital
front-end
Virtex 4
FPGA
512 MB
SDRAM
Bases on existing USB-FPGA board (IPHC, Strasbourg)
Allows for:
FPGA-based data sparsification (CDS, clustering, data compression)
Pipeline readout of MIMOSA-17 (~ 1 ms time resolution) without dead time
Add-on
board
12 Gbit/s
Optical link
2 Gbit/s
TRB-II
Sparsified
data
DAQ
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN

33. Needs still to be scaled with pile – up (up to factor 100)
Running conditions
Needs still to be scaled with pile – up (up to factor 100)
M. Deveaux, Vertex 2008, 27 July 2008 to 01 August 2008 , Utö, Stockholm, SWEDEN