Optimization of the Silicon Tracking System (STS) layout
and beam pipe configuration for the CBM experiment.
Andrey Chernogorov, Sergey Belogurov, ITEP, Moscow
Outline
• The main idea. “Pipe” = “Window”+”Tube”.
Balance between measurable particles (window)
and ions (tube)
• Beam pipe first section and vacuum chamber’s
window effect on the STS performance
• Effects of the junction between STS and RICH
sections
• The implementation into cbmroot package of
spatial and angular distributions of ions incident to
the target for realistic beam emittance simulation
• Stereo angle effects on STS performance
• Sensors’ overlapping effects on STS
performance
• Conclusions
• Plans
FAIR seminar, 21-22 June 2011, Moscow
Beam pipe first section and vacuum chamber’s window
effect on the STS performance
Studied configurations
Some of “Ideal ” configurations.
Effects: cylinder-cone; Be-Al.
Al: window – scaling from VELO, cone
– “simple” manufacturing.
1st
“Realistic” configurations.
Effects of bellows, width of “Tube”.
1.6º configuration fits to carbon fiber (CF) ladders
without cutting the central rib.
Any configuration has a weld 1x10 mm
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
2
Results for UrQMD central events at 25 AGeV: IR
Range distribution
window
welding
Figure of merit: integrated range in
the pipe: IR=Σli·qi2· ne
li – range of a particle inside the
pipe
qi - its charge
ne – relative electron density
Total ionization losses and number
of d-electrons are roughly
proportional to IR
Distribution of integrated ranges of charged particles in the beam pipe’s walls for several configurations.
IR,cm
Cylinder is optimal with MF, cone – without MF (The same for 8 AGeV). No
contradiction with the conclusions of HERAb and LHCb.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
3
Results for UrQMD central events at 25 AGeV:
Track finding quality
Clear trends for “ideal” configurations (the narrower the better), for “real” ones no big difference.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
4
Results for UrQMD central events at 25 AGeV
Comparison of Al and Be cones
30%/7%
Momentum distribution of ghost tracks
Efficiency of tracks’ secondary particles
restoration as a function of momentum
30-50%,
mainly soft
ghosts
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
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Results for UrQMD central events at 25 AGeV :
reconstruction of short lived particles
The narrower the better for “ideal” configurations,
for “real” ones more narrow seems slightly better.
Vertex resolution much worse than expected from
multiple scattering and not indicative.
Thanks to I. Vassiliev for the basic analysis routine
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
6
Results for UrQMD central events at 8 AGeV :
Track finding quality
STS with given layout works perfectly with any beam pipe. As any optimistic conclusion
should be double checked. Probably for SIS-100, STS layout may be simplified and made
cheaper. However, taking into account realistic STS simulation may change the answer!
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
7
Results for UrQMD central events at 8 AGeV :
reconstruction of short lived particles
Only S/B and mass resolution are somewhat sensitive to Al beam pipe.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
8
Flange/window effects on RICH
Default cbmroot geometry: 1-st
section of pipe
with Be window h0.1mm on the end
with flange 2.0x2.5cm on the end
with a weld 2.5x0.2cm on the end
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
9
Flange/window effects on RICH
The influence of the flange is almost imperceptible. There is a slight decrease of parameters
when using Be window, while passing 20 or more ions. In general, when the number of ions
no more than 20, the configuration of the window can be used.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
10
The implementation into cbmroot package of spatial and angular
distributions of ions incident to the target for realistic beam
simulation with collimators.
Section of the beam on
the CBM target without
collimation (left) and with
collimation (right) for SIS300 energy. Simulations
by M. Kats.
Parameters of the
projection of beam cross
section on the CBM target
without collimation (left)
and with collimation (right)
for SIS-300 energy after
the fitting.
- The description of the ion beam by a Gaussian distribution (class FairPrimaryGenerator now) is not adequate;
- More correct to describe the collimated beam by the product of a Gaussian distribution and a trapezium
(symmetric now and more complex function if it is necessary in next amendment process);
- The distributions for description of realistic beam emittance are done and will be implemented in next
CBMROOT release after completion of testing. A similar smearing of the angular distribution is implemented too.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
11
Stereo angle effects on STS performance
Big number of fakes is a big problem for track finding, especially for extending the algorithm to the
segments with missed points. We looked at sensors with smaller stereo angles…
Stereo angle – between strips on the opposite sides of double side sensor.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
12
Stereo angle effects on STS performance
Big number of fakes is a big problem for track finding, especially for extending the algorithm
to the segments with missed points. We looked at sensors with smaller stereo angles….
SIS-300
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
13
Stereo angle effects on STS performance
SIS-100
SIS-100
For both SIS 100 and SIS 300, stereo angle of 6 ° is the best for track finding. Momentum
resolution becomes worse bellow 6°. In simulations of short-lived particle reconstruction 8° is
considered because technologically preferable (dm).
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
14
Sensors’ overlapping effects on STS performance (SIS-300)
1.2-1.4%
5%
10%
5%
Overlap is due to the guard rings but could be bigger due to geometrical reasons (DZ between
neighboring sensors up to 1 cm)
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
15
Sensors’ overlapping effects on STS performance (SIS-100)
1.2-1.4%
4%
5%
10%
Study the influence of sensors’ overlapping on tracking system properties showed that the properties
dependence of the overlap is sufficiently weak. Overlap does not represent a problem and allowed.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
16
Conclusions
-
Influence of shape and material of the beam pipe on the STS performance is studied. Pipe is
considered as a composition of “window” and “tube”;
-
A comprehensive study of the effect of the beam pipe’s first section and the vacuum chamber
window on tracking system properties for central collisions of gold-gold at 25 AGeV (SIS-300)
and 8 AGeV (SIS-100) was completed. For 8 AGeV only S/B and mass resolution are
somewhat sensitive to Al beam pipe. It should be checked with more realistic STS;
-
Decrease of the stereo angle may help to reduce number of fakes and improve track finding
performance;
-
Study the influence of sensors’ overlapping on tracking system properties showed that the
properties dependence of the overlap is sufficiently weak. Overlap does not represent a
problem and allowed.
-
The influence of the flange/window between the first and the second sections of the beam pipe
was studied;
-
The distributions for description of realistic beam emittance are done and will be implemented
in next CBMROOT release after completion of testing. A similar smearing of the angular
distribution is implemented too.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
17
Plans
-
Tuning and adjustment of the realistic (i.e. including noises and clustering) STS Monte Carlo
model for correct description of low energy secondaries generation and accounting for small
energy releases in the sensors. This model is necessary for further design justification;
-
Feasibility study of 8 degree stereo angle in silicon sensors. Realistic STS and track
propagation to downstream detectors will be taken into account;
-
Careful Monte Carlo justification will be done for reduction of the number of channels in the
STS for SIS 100 by increasing the length of the sectors. This work will allow to save funds for
STS construction without loss of the physical performance. However in such a scenario an
upgrade of STS will be needed before operation at SIS300;
-
The effects of the auxiliary equipment in the gap of the magnet on the performance of the STS
will be studied. It is important for engineering of the service equipment for STS and the vertex
detector;
-
Feasibility study for the central part of the ECAL made of the tungsten based modules with
small Moliere radius will be performed. This work is important for having maximum physical
information from the compact start version of the ECAL. The work will include both simulation
of the ECAL and building of the Prototype module;
-
The design optimization and justification work for the RICH and downstream sections of the
beam pipe will be continued.
A.Chernogorov, S.Belogurov, ITEP, Moscow
FAIR seminar, Moscow, 22.06.2011
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