J.M. Heuser et al. CBM Silicon Tracker 1 Requirements for the Silicon Tracking System of CBM Johann M. Heuser, M. Deveaux (GSI) C. Müntz, J. Stroth (University of Frankfurt) for the CBM Collaboration 10 th Semiconductor Detector Symposium, Wildbad Kreuth, June 2005 Overview: The future accelerator facility FAIR in Darmstadt The CBM experiment: Physics Motivation Detector Concept Silicon Tracker – Physics Requirements and Impact on the Design
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1 J.M. Heuser et al. CBM Silicon Tracker Requirements for the Silicon Tracking System of CBM Johann M. Heuser, M. Deveaux (GSI) C. Müntz, J. Stroth (University.
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J.M. Heuser et al. CBM Silicon Tracker 1
Requirements for theSilicon Tracking System of CBM
Johann M. Heuser, M. Deveaux (GSI)C. Müntz, J. Stroth (University of Frankfurt)
for the CBM Collaboration
10th Semiconductor Detector Symposium, Wildbad Kreuth, June 2005
Overview:
The future accelerator facility FAIR in Darmstadt
The CBM experiment:
Physics Motivation
Detector Concept
Silicon Tracker – Physics Requirements and Impact on the Design
J.M. Heuser et al. CBM Silicon Tracker 2
Facility for Antiproton and Ion Research
Future accelerator complex FAIR at GSI, Darmstadt:
Research program includes:
• Radioactive Ion beams: Structure of nuclei far from stability
• Anti-proton beams: hadron spectroscopy, anti hydrogen
• Ion and laser induced plasmas: High energy density in matter
• High-energy nuclear collisions: Strongly interacting matter at high baryon densities
SIS 100 Tm
SIS 300 Tm
U: 35 AGeV
p: 90 GeV
Compressed Baryonic Matter Experiment
J.M. Heuser et al. CBM Silicon Tracker 3
Facility for Antiproton and Ion Research
Photomontage of the existing and the planned research facility at GSI/FAIR.
- TOO SLOW for CBM: ~ ms/Mpixel- rad. hard. limited by bulk damage
Improve r/o time, radiation hardness.
Hybrid Pixel Detectors:- fast readout, - radiation hard- larger pixels: 50 x ~400 µm2 - spatial resol.: ~15 (115) µm- thick: standard > 350 µm
Reduce pixel size and thickness.
We started persuing the MAPS option.
J.M. Heuser et al. CBM Silicon Tracker 13
Pixel Detector Stations
Detector module: BTeV inspired design
ladders mounted on either side of a substrate providing (active?) cooling.
Active cooling support:
a carbon fibre structure with micro pipes? ~ 0.3% X0
glass or silicon wafers with buried micro channels? ~ 0.1-0.3% X0
CMOS MAPS chips for CBM:
- size: ~0.5 x 1 cm2 - 50% sensor, 50% r/o.- column readout in 5-10 µs
CBM MAPS ladders with 4 or 5 chips.
J.M. Heuser et al. CBM Silicon Tracker 14
Silicon Strip Detector Stations
Basic sensor elements: 200 m thick silicon wafers.double-sided, rad-tolerant. 25 m strip pitch.
Inner : 6x4 cm Middle : 6x12 cmOuter : 6X20 cm
Open questions: strip length, stereo angle
(to reduce fake hits) location of read-out
(on sensor, all at edge ?)
Four detector stations:built from few wafer types
J.M. Heuser et al. CBM Silicon Tracker 15
Tracking in the Silicon Strip StationsCellular automaton/Kalman filter method.
First attempts: Problem - High occupancy with many combinatorial hit points.
Recent approach: - start with long “stiff” tracks- 4 strip stations + 1 pixel station (“no pile-up”)- attached strips are removed - this cleans up the hit pool, reduces the fake strip combinations.
Work in progress.
Ideal conditions: full sensor efficiency, no pile-up:
~ 1% “ghost tracks” remain.
J.M. Heuser et al. CBM Silicon Tracker 16
Consider more Tracking Redundancy
vacuum
1
11
3
vertexing
track finding
track seeding
4
8
9larger area ?larger acceptance, faster r/o?
Under real conditions: - event pile-up in pixels - fake hits in strips
At present: - forward tracking hampered by pile-up - backward tracking hampered by fakes - need for clean track seeds
Consider: - more tracking stations - shorter strips – lower occupancy - fast pixels with clean event association
J.M. Heuser et al. CBM Silicon Tracker 17
Low Mass Dilepton Spectroscopy
If missed ...
ee 0
ee
... fake open pair is formed.
Signal: vector meson decays , , e+e-
Background:
0 decay (365/event)
0 e+e- (1.2%) 0 98.8%)
conversion e+e-
Detector requirements:
first stations with large acceptance
tracking efficiency down to p = 0.1 GeV/c to suppress background
detect conversion pairs: → small pixels
J.M. Heuser et al. CBM Silicon Tracker 18
Delta Electrons
study by I. Vassiliev, GSI
Beam ions on target:
produce delta-rays dominate occupancy when integrated over many events.
high local radiation damage hits spoil track finding limits rate capability
Only way out:
Fast detector readout to avoid electron hit pile-up.
hits in 1st MAPS station: 1000 min. bias URQMD events, Au+Au 25 AGeV.
J.M. Heuser et al. CBM Silicon Tracker 19
Particle Fluence – Detector LifetimeImpact on D Meson Measurements
Fluence at 1st MAPS station, z = 5cm, r = 5mm: ~ 10 1 MeV nequiv per event.
MAPS readout in potentially 10 s. No pileup at event rate <105/s.
The MAPS lifetime is then about 1 1012/105 s = 1 107 s = 16 weeks.
D0→Kπ: 4 10-5 0.038 0.05 = 7.6 10-8 per event. In MAPS lifetime: 7.6104 D0.
Fluence of 1 MeV nequiv./cm2 in 1st MAPS station at z = 5cm
J.M. Heuser et al. CBM Silicon Tracker 20
CBM Silicon Tracker Requirements- Summary -
Tracking exclusively performed with the Silicon Tracker:Very important detector, key to the physics of CBM.
The Silicon Tracker must deliver high performance: Open charm detection is the bench mark. Pixel planes near the target are of special importance: Thin, small pixels, fast readout, radiation hard.
Such detector does not exist . What comes closest ? What R&D? We chose to start investigating MAPS. Alternative ?
Discussions on latest detector technologies are very welcome!