1. Development of a Silicon Tracking and Vertex Detection System for the CBM Experiment at FAIR
Johann M. Heuser, GSI Darmstadt, Germany for the CBM Collaboration
VERTEX 2006, Perugia, Italy, September 2006
The international Facility for Antiproton and Ion Research
The Compressed Baryonic Matter experiment
The Silicon Tracking and Vertex Detection System:
Performance requirements, Detector concept, R&D activities
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

2. Facility for Antiproton and Ion Research
@ GSI Darmstadt
FAIR
existing GSI
Start of construction: 2007/2008
staged commissioning:
Full operation, CBM:
International project:
Observers:
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

3. Five Research Communities at FAIR
Heavy-ion synchrotrons
Ion source
SIS-100, SIS-300
SIS-18
U 35 GeV/n
p 90 GeV
Unilac
CBM
Nuclear Matter Physics with
HI beams, GeV/n, x1000
HESR
Rare Isotope
Prod. Target
Super
FRS
Hadron Physics
with antiprotons
GeV
Antiproton
Prod. Target
Nuclear Structure & Astrophysics
with radioactive beams, x10 000
and excellent cooling
FLAIR
CR-
RESR
Plasma Physics: x600 higher target energy density 600kJ/g
NESR
High EM Field (HI) _
Fundamental Studies (HI & p)
Applications (HI)
100 m
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

4. Compressed Baryonic Matter-Experiment
SIS-300: up to U92+,15-35 GeV/nucleon, beam intensities up to 109/s,
Z/A = 0.5 nuclei up to 45 GeV/nucleon
→ exploration of the QCD phase diagram with heavy-ion collisions!
→ investigation of nuclear matter at highest baryon densities but still moderate temperatures in A+A collisions
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

5. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
CBM – Physics Case
Milestone in mapping the QCD phase diagram would be the (unambiguous) discovery of either the critical point or the 1st order phase transition
Top-energy SPS, RHIC, LHC :
high T, low mB region –
most probably phase crossover
High mB region !
- onset of deconfinement?
- 1st order phase transition?
- critical point?
Earlier experiments: at AGS, low-energy SPS:
limited in observables, statistics
New : RHIC plans low energy runs
SIS FAIR: ideal for 2nd generation experiment!
CBM: rare probes, high interaction rates charm, dileptons, fluctuations, correlations
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

6. > 40 institutions > 350 Members
CBM collaboration
Croatia:
RBI, Zagreb
China:
Wuhan Univ.
Hefei Univ.
Cyprus:
Nikosia Univ.
Czech Republic:
CAS, Rez
Techn. Univ. Prague
France:
IReS Strasbourg
Hungaria:
KFKI Budapest
Eötvös Univ. Budapest
India:
VECC Kolkata
IOP Bhubaneswar*
Univ. Chandighar*
Univ. Varanasi*
Korea:
Korea Univ. Seoul
Pusan National Univ.
Norway:
Univ. Bergen
Germany:
Univ. Heidelberg, Phys. Inst.
Univ. HD, Kirchhoff Inst.
Univ. Frankfurt
Univ. Kaiserslautern
Univ. Mannheim
Univ. Münster
FZ Rossendorf
GSI Darmstadt
Poland:
Krakow Univ.
Warsaw Univ.
Silesia Univ. Katowice
Nucl. Phys. Inst. Krakow*
Portugal:
LIP Coimbra
> 40 institutions > 350 Members
Romania:
NIPNE Bucharest
Russia:
IHEP Protvino
INR Troitzk
ITEP Moscow
KRI, St. Petersburg
Kurchatov Inst., Moscow
LHE, JINR Dubna
LPP, JINR Dubna
LIT, JINR Dubna
MEPHI Moscow
Obninsk State Univ.
PNPI Gatchina
SINP, Moscow State Univ.
St. Petersburg Polytec. U.
Ukraine:
Shevshenko Univ. , Kiev
* to be approved by CB
open for new partners!
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

7. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
The CBM Experiment
tracking, momentum, vertex reconstruction: silicon pixel/strip detectors (STS) in magnetic dipole field
electron ID: RICH & TRD (& ECAL)
 p suppression  104
hadron ID: TOF (& RICH)
photons, p0, m ID: ECAL
event characterization (PSD)
high speed DAQ, only high-level triggers
not necessarily fixed layout!
more like „facility“
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

8. Alternative CBM setup: Dimuons
Dimuon setup studied with active muon absorbers (Fe + C + detector layers) after the Silicon Tracker
... move absorbers out for hadron runs.
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

9. Silicon Tracking and Vertexing
Challenge: Au+Au collisions, 25 GeV/n:
high track densities:
 600 charged particles in  25o
high r/o speed, radiation hardness: MHz interaction rate (109 ions/s on 1% int target), only high-level triggers.
Tasks:
track reconstruction for particles with 0.1 GeV/c < p  GeV/c , momentum resolution ~ 1% at 1 GeV/c, large lateral coverage
primary and secondary vertex reconstruction (resolution  50 mm)
V0 track pattern recognition (low-mass vector mesons lepton pairs, open charm decays, hyperons, e+e- pairs from g-conversion)
D+ → p+p+K- (ct = 317 mm)
D0 → K-p+ (ct = 124 mm)
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

10. Conceptional Detector Geometry
Vertexing: "VTS"
2 (3) MAPS stations.  z = (5), 10, 20 cm  150 µm Si  In vacuum. No layout yet.
Tracking: "STS"
2 HYBRID Pixel stations:  z = 30, 40 cm  750 µm Si  No layout yet.
4 Micro-STRIPS stations:  z = 50, 60, 75, 100 cm  400 µm Si  Detailed station layout.
vacuum
2.5º
25º
VTS
STS
very thin
low-mass
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

11. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
GEANT implementation:
dipole magnet,
1Tm bending power
VTS in vacuum section
beam pipe
STS stations
1 m
Activities started on: optimization of layout,
robust tracking,
vertexing,
detector/system R&D
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

12. Microstrip Tracking Stations
Sensor arrangement and hit digitization scheme.
Old concept:
"radial" arrangement of sectors
r/o electronics
sensors
detector module
New concept:
 double-sided sensors  50 µm strip pitch, deg stereo angle  strip lengths 4-12 cm  r/o through thin, long analog cables !
r/o
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

13. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
Microstrip Stations:
conceptional structure
Station 5 z = 50 cm
Station 6 z = 60 cm
Station 8 z = 100 cm
Station 7 z = 75 cm
r/o electronics
sensors
detector module
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

14. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
Momentum Resolution
standard
thin
thick
thick-2
thick-3
Thickness: effective, sensor + support/cables.
How much passive material (support, cables etc) will finally add up?
Readout: What sensor thickness for what S/N?
Detailed simulations being prepared.
Study impact on physics.
thin: standard: thick: thick-2: thick-3:
MAPS 2×150 µm 2×150 µm 2×150 µm 2× 150 µm 2× 150 µm Hybrid 2×200 µm 2×750 µm 2×800 µm 2×1000 µm 2×1600 µm Strips 4×200 µm 4×400 µm 4×800 µm 4×1000 µm 4×1600 µm
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

15. Track Reconstruction Efficiency
Track finder: Cellular Automaton and Kalman Filter: with 2 Hybrid Pixel + 4 Strip Stations, standard settings:  include vertex,  hits in >3 consecutive stations.
primary tracks
97.02 ± 0.09
all reconstructed tracks
92.17 ± 0.14
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

16. Microstrip-Only Track Reconstruction
standard detector configuration: L1 tracking with 2 Hybrid pixel + 4 Strip Stations
2 Strip Stations (avoid 2nd technology)
primary tracks
94.88 ± 0.12
all reconstructed tracks
90.01 ± 0.15
What's the design goal?
Important: Include robustness!
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

17. Tracking with four strip projections per station:
Microstrip-only tracker
Frontal view
xy+uv
Side view
xy uv
robust "space points"
Tracking: double stations strips
Vertexing with 2 MAPS stations: either: at 5 cm + 10 cm,
or: at 10 cm + 15 cm.
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

18. Microstrip Double-Stations
xy uv
3.75o 0o
-3.75o
3.75o
-11.25o
11.25o
Δz  1 cm
4 hit projections on the strip planes
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

19. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
Tracking Stations: Layout Studies
Occupancies:
Up to 5% in hottest sectors of station 5 (central collisions).
Go down with radial distance from the beam axis, and with distance from the target as expected.
The CA track finder yields tracking efficiencies ~97%.
Together with tracking study: powerful design tool.
Design criteria: - Save r/o channels in outer regions: Longer strips there! - Short strips close to beam line.
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

20. Microstrip Sensor Development
r/o direction
Two streams of activities:
double-sided, different technologies
1) In CBM Collaboration (R&D at MSU SiLab, Moscow)
300 µm, polysilicon biassing, p-stop
connectivity: top/bottom + sides
2) R&D at GSI, together with CIS, Germany
300 µm, punch-through biassing, p-spray, double-metal
connectivity: r/o at top/bottom edge LY LX
n side: "vertical" strips
p side: "stereo" strips
r/o direction I II
n side: "vertical" strips
p side with "double metal"
blue: double metal connections of strips in regions I to III
III
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

21. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
R&D with CIS Erfurt, Germany: (
256 x 256 strips 80 µm pitch 90 deg stereo angle
256 x 256 strips 50 µm pitch 90 deg stereo angle
1024 x 1024 strips 50 µm pitch 15 deg stereo angle
4" wafer, 280 µm thick
design finished
design finished
design partly finished
CBM: Opportunity to participate in reseach project of CIS (focus on rad hard detectors).
CBM sensor prototypes as "test objects".
Sensor design: finished 10/2006. End 2006: batch of ~ 20+ wafers.
Plenty of sensors for a variety of tests of r/o electronics and detector concept.
Set up Silicon labs at GSI + other institutes. Test beam + telescope at GSI.
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

22. Microstrip Detector Readout
Two streams of activities:
1) In the CBM Collaboration (MEPhi/MSU, Moscow): R&D on fast self-triggered low-power electronics blocks
2) Exploration of the NXYTER chip in collaboration with the Consortium DETectors for Neutron Imaging
dual polarity
input pitch: 50.7 µm
128 channels per chip
amplitude measurement
data driven token-ring r/o architecture
count rates: ~160 kHz/strip
charge collection 30 ns peaking time
small (~2 ns) timing jitter
thresholds: > 2700 e
dynamic range: different for +/-
power: ~ 13 mW/channel (high!!!)
produced in 0.35 m CMOS
Specs very similar to the CBM needs!
1st chip submission in March 2006.
Close ties to the project through Head of GSI Detector Lab
GSI: significant participation in funding of chip submission (Summer 2006).
Aim: Test and modify this chip. Construction of a demonstrator microstrip detector module for CBM.
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

23. N-XYTER Submitted via CMP Dies Expected Sept. 25th 2006
8 LVDS
output lines
at 4 x 32MHz:
time stamp,
channel no. +
1 differential,
analog
output
128
analog
inputs
poisson
distributed
at 32 MHz
total
average
input rate
AMS CMOS 0.35µ with thick metal four
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

24. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
Study on Mechanical Structure Elements (microstrip module):
2-module structure, building block of detector stations
Study together with ITEP Moscow:
Based on ALICE ITS studies, and CBM STS layout concept. Carbon fibre.
module
"very preliminary,
brain-storming designs"
flat cable routing
sensor holders
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

25. Vertex Tracking System
Sensor Requirements:
pitch 20 μm 
thickness below 100 μm 
single hit resolution :  3 μm 
radiation tolerant, design goal neq/cm2
ultimate read-out time 5-10 μs
Hybrid pixels:
at least for now:
- too thick - too large pixels
- power dissipation requires cooling.
Monolithic Active Pixel Sensors (MAPS)
R&D together with IPHC (IReS) Strasbourg
development of fast column//architecture
development of radiation tolerant sensors (from some 1012 to 1013 neq /cm2)
SOI pixels:
in a small process: interesting!
MAPS with depletion layer:
sounds interesting!
longer lifetime of first MAPS station:
enlarge distance from target: 5 cm → 10 cm
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

26. R&D goals with MAPS: Radiation tolerance & readout speed
radiation tolerance: ~1012  MeV nequiv.
readout time: sec, column parallel r/o
Expected situation in CBM:
Fluence at 1st MAPS station:
~10 1-MeV nequiv. per event
 detector partly destroyed after 1012 reactions  corresponds to 105 D mesons detected (already decent measurement!)
Possible running conditions:
a) 1 day detector lifetime at 107 reactions/s, events piled up, or
b)  4 month detector lifetime at 105 reactions/s, no pile-up events.
URQMD, Au+Au 25 GeV/nucleon
Fluence of 1 MeV nequiv./cm2 in 1st MAPS station at z = 5cm
 K p n
What about retracting the 1st MAPS station from the target?
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

27. Benchmark for SVT and STS Performance:
D0 mesons, Au+Au collisions at 25 AGeV
realistic tracking in magnetic field,
2 MAPS, 2 Hybrid pixel, 4 Strip stations
proton identification required
D0 production cross section from HSD
25 AGeV Au+Au from UrQMD
minimum bias collisions
1st MAPS station at z = 5 cm D0
S/B = 3.5
1st MAPS station at z = 10 cm
dose × ¼
S/B × ¼
 no gain!!
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

28. J.M. Heuser  CBM Silicon Tracking and Vertex Detection System
Summary - CBM
CBM is a baseline experiment at FAIR. Running from 2014/15.
CBM offers very interesting physics program on the QCD phase diagram.
Unique features expected in CBM energy range: First order phase transition, critical point
As a 2nd generation experiment, CBM will be able to study: rare probes, fluctuations and correlations!
Detector development under way
Increasingly realistic feasibility studies are performed
→ Technical Proposal in ~2007.
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

29. Summary – Silicon Detectors
The Silicon Tracking and Vertex Detection System is the core of CBM.
Detector concept: Tracker (Microstrips) + Vertex Detector (MAPS)
R&D activities:
- layout optimization: Ongoing. New and powerful tools available for realistic detector/physics simulations.
- tracking studies: Ongoing
- sensor development: Ongoing
- r/o electronics development: Ongoing
- mechanical studies: Beginning
Still may gaps to fill, including:
- realistic sensor shapes, support material in simulations realistic FLUKA radiation study R&D on module prototypes: Microstrips & MAPS. - thin sensors, low-mass r/o cables, low-mass support structures
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System

30. Data-Push Architecture, Data Flow
Each detector channel detects autonomously all hits  FEE design.
An absolute time stamp, precise to a fraction of the sampling period, is associated with each hit.
All hits are shipped to the next layer (usually data concentrators).
Association of hits with events done later using time correlation.
Typical parameters:
(few % occupancy, 107 interaction rate)
some 100 kHz hit rate per channel
few MByte/sec per channel
whole CBM detector: ~ 1 Tbyte/sec
J.M. Heuser  CBM Silicon Tracking and Vertex Detection System