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Journal ArticleDOI

Performance of the silicon detectors for the CMS barrel tracker

TL;DR: The Compact Muon Solenoid (CMS) is a detector designed for the Large Hadron Collider (LHC) as discussed by the authors, which is made of 816 modules arranged in three layers.
Abstract: The Compact Muon Solenoid is a detector designed for the Large Hadron Collider. High particle rates combined with a magnetic field of 4 T make particle tracking a challenge. The baseline is to use silicon pixel and microstrip detectors and microstrip gas chambers. This note focuses on the barrel part of the silicon tracker. It is made of 816 modules (368 single-sided and 448 double-sided) arranged in three layers. The basic module consists of four 300 μm thick silicon microstrip detectors, glued together to obtain a total active area of 51.2 × 250 mm 2 . The choice of silicon strip detector is based primarily on three elements: AC-coupling integrated on the detector substrates; polysilicon resistors used as bias elements; p-stop isolation to control the interstrip resistance of the ohmic side in double-sided detectors. A review of beam test results is described for different parts of the CMS barrel tracker.

Summary (2 min read)

1 Introduction

  • The Compact Muon Solenoid (CMS) experiment is built around a large, 13 m long, 6 m diameter, high-field superconducting solenoid leading to a compact design for the muon spectrometer.
  • The electromagnetic and hadronic calorimeters are located inside the 4 T field produced by the coil, while a sophisticated tracking system performs track reconstruction, momentum measurement and pattern recognition [1].

2 The CMS Central Tracking

  • The goal of the CMS central tracking system is to reconstruct isolated high PT muons and electrons with a momentum resolution better than PT PT = 0:15PT (where PT in TeV) at high efficiencies over a rapidity range of j j < 2:6.
  • The main problem for the central tracker will be the pattern recognition.
  • At a luminosity of 1034cm 2s 1, interesting events will be superimposed to a background of about 500 soft charged tracks within the rapidity range considered from 15 minimum bias events occurring in the same bunch crossing.
  • Their vertices are distributed along the beam direction (z-axis) with a r.m.s. of 5.3 cm.
  • In CMS silicon and gas microstrip detectors provide the required granularity and precision.

3 The Silicon Microstrip Detector

  • The silicon tracker is required to have a powerful vertex finding capability in the transverse plane over a large momentum range for b-tagging and heavy quark physics and must be able to distinguish different interaction vertices at full luminosity.
  • Each barrel wheel (Fig. 2) is instrumented with detector modules arranged in 16 spirals.
  • The first two and the last two modules contain double-sided detectors, while the intermediate three use single-sided detectors.
  • The stereo strips make an angle of 60 mrad with the corresponding electrodes on the p-side.
  • A similar structure is produced on the ohmic side of the double-sided devices with the addition of an isolation p-stop box surrounding each electrode.

4 The Silicon Barrel Module

  • The basic microstrip detector module for the barrel (Fig. 3) consists of four 300 m thick silicon wafers glued together to obtain a total length of 25 cm with 1024 strips that run parallel to the beam.
  • Two detectors are daisychained and connected to the readout electronics.
  • The support of the readout unit, containing front-end amplifiers, control chips and connectors, is made out of a low mass, high thermal conductivity carbon fibre.

5 Beam Test Results

  • The results described in this paper were obtained in two beam tests performed at the SPS at Cern in 1995: one in July in the H2 beam line with 300 GeV/c muons and the second one in September in the X7 beam with 50 GeV/c pions.
  • In both cases the detectors under test were mounted on an optical bench and two external reference systems were used for particle tracking.
  • This value stayed almost constant when a voltage bias scan was performed.
  • The lower part of the same figure shows that there is a good uniformity in the position resolution along the readout strips.
  • The resolution improves slightly with the angle, as one may expect, when the average cluster size increases from the value of 1.3 strips to around 2.

6 Conclusions

  • The baseline layout of the CMS silicon tracker is defined.
  • Many details of the design are still in evolution; infact a lot of beam-tests and montecarlo studies are foreseen.
  • The optimisation process is expected to converge for the end of 1997 (Technical Design Report).

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Available on CMS information server CMS NOTE 1996/005
CMS Note
The Compact Muon Solenoid Experiment
Mailing address: CMS CERN, CH-1211 GENEVA 23, Switzerland
Performance of the Silicon Detectors for the CMS
Barrel Tracker
L. Silvestris
Istituto Nazionale di Fisica Nucleare, Sezione di Bari, Via Amendola 173, 70126 Bari, Italy
Abstract
The Compact Muon Solenoid is a detector designed for the Large Hadron Collider. High particle rates
combined with a magnetic field of 4 Tmake particletracking a challenge. The baseline is to use silicon
pixel and microstrip detectors and microstrip gas chambers.
This talk focuses on the barrel part of the silicon tracker. It is made of 816 modules (368 single-sided
and 448 double-sided) arranged in three layers. The basic module consists of four
300
m
thick silicon
microstrip detectors, glued together to obtain a total active area of
51
:
2
250
mm
2
.
Thechoiceof siliconstripdetectoris based primarilyon threeelements: AC-couplingintegratedon the
detector substrates; polysilicon resistorsused as bias elements; p-stopisolation to control theinterstrip
resistance of the ohmic side in double-sided detectors.
A review of beam test results is described for different parts of the CMS Barrel Tracker.
\conference{Presented at {\em Position-Sensitive Detectors},
The University of Manchester, 9-13 September 1996}
Submitted to Elsevier Preprint

Figure 1:
Layout of the Tracking System of CMS
1 Introduction
The Large Hadron Collider (LHC) will produce high energy collisionsof protonsat a center-of-mass (CM) energy
of
14
TeV
and luminosity up to
10
34
cm
2
s
1
. The potential physics at LHC will include the discovery or exclu-
sion of the Standard Model Higgs Boson at masses above the maximum reach at LEP (order of 100 GeV) to 1 TeV;
the study of WW,WZ,ZZ scattering at large CM energies, the discovery of Higgs Bosons in the Minimum Super-
symmetric Standard Model (MSSM), the search for composite structures in quarks, gluons and weak bosons, the
studyofCP-Violationin theb-quark sector. TheCompact MuonSolenoid(CMS)experiment isbuiltarounda large,
13 m long, 6 m diameter, high-field superconducting solenoid leading to a compact design for the muon spectrom-
eter. The electromagnetic and hadronic calorimeters are located inside the 4 T eld produced by the coil, while a
sophisticated tracking system performs track reconstruction, momentum measurement and pattern recognition [1].
2 The CMS Central Tracking
The goal of the CMS central tracking system is to reconstruct isolated high
P
T
muons and electrons with a mo-
mentum resolution better than
P
T
P
T
= 0
:
15
P
T
(where
P
T
in TeV) at high efficiencies over a rapidity range of
j
j
<
2
:
6
. These values were defined using as a benchmark process the detection of an intermediate mass Higgs
boson which decays in
H
!
ZZ
!
4
l
[1, 2].
The high rate of interactions at the full luminosity determines a challenging environment for an advanced tracking
system.
The main problem for the central tracker will be the pattern recognition. At a luminosity of
10
34
cm
2
s
1
,in-
teresting events will be superimposed to a background of about 500 soft charged tracks within the rapidity range
considered from
15
minimum bias events occurring in the same bunch crossing. Their vertices are distributed
along the beam direction (z-axis) with a r.m.s. of 5.3 cm. To solve the pattern recognitionproblem at highluminos-
ity detectors with small cell sizes are required. In CMS silicon and gas microstrip detectors provide the required
granularity and precision. Strip lengths of the order of 10 cm are needed to maintain cell occupancy below
1%
.
This leads to a large number of channels (
10
7
)[3].
Anotherimportanteffect isthepresence oftheveryhighradiationlevel inthecollisionregion. Thisisdueto primary
interactions and to the presence of neutrons evaporated from nuclear interactions in the material of the electromag-
netic calorimeter. Therefore, radiation resistance is required both for detectors and read-out electronics.
The requirements in terms of pattern recognition, radiation hardness and tracking resolution lead to a tracking sys-
tem based on silicon pixel, microstrip detectors and microstrip gas chamber (MSGC). Fig. 1 shows how the detec-
tor planes are distributed in the cylindrical tracking volume of CMS with dimensions
j
z
j
<
3
:
0
m,
R<
1
:
3
m.
The entire tracker is subdivided into barrel and forward regions meeting at
j
j
1
:
8
. The detailed design of the
tracker is still evolving. At the moment a track in the barrel region encounters first two layers of pixel detectors
(
125
125
m
2
) providing a measurement accuracy of
15
m
in both coordinates, then three layers of microstrip
silicon detectors of
50
m
read-out pitch providing in
r
high precision points of
15
m
, followed by seven
layers of
200
m
MSGC giving a point resolution around
40
m
[4].
3 The Silicon Microstrip Detector
The silicon tracker is required to have a powerful vertex finding capability in the transverse plane over a large mo-
mentum range for b-tagging and heavy quark physics and must be able to distinguish different interaction vertices
at full luminosity.
The barrel part covers the radial region
20
cm<r<
40
cm
is divided into 9 wheels. Each barrel wheel (Fig. 2) is
instrumentedwithdetector modulesarranged in16 spirals. In the5 centralwheels each arm containsseven modules.
The first two and the last two modulescontain double-sided detectors, while the intermediate three use single-sided
1

Figure 2:
Layout of the Silicon Barrel Wheel
cooling pipe support
pin
positioning
carbon fibre rail
silicon detectors
read-out unit
front-end
chips
control chip
connector
Figure 3:
The Basic Microstrip Detector Module
detectors. In the barrel region the strips oriented along the beam direction are read-out with a
50
m
pitch in (
r;
).
The stereo stripsmake an angle of
60
mrad
with the corresponding electrodes on the p-side. The read-out pitch
is 200
m
. Double-sided and single-sided detectors have identical p-side design. Each strip is AC-coupled to ex-
ternal amplifiers by means of integrated capacitors grown on the wafer via a deposition of thindielectric layers. A
polysilicon resistor provides the bias to the strips via the guard-ring structure. A similar structure is produced on
the ohmic side of the double-sided devices with the addition of an isolation p-stop box surroundingeach electrode.
In the devices featuring the double-metal technology the ohmic electrodes are connected, through a small contact,
with a set of metal electrodes deposited on top of a thick insulator layer.([5]).
4 The Silicon Barrel Module
The basic microstrip detector module for the barrel (Fig. 3) consists of four
300
m
thick silicon wafers glued to-
gether to obtain a total length of 25 cm with 1024 strips that run parallel to the beam. Two detectors are daisy-
chained and connected to the readout electronics. The support of the readout unit, containing front-end amplifiers,
control chips and connectors, is made out of a low mass, high thermal conductivitycarbon fibre. This acts as a heat
2

Residual
0
5
10
15
20
25
30
35
40
45
-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
residual along the detector
Figure 4:
Residual Distribution in the
r
plane for the full size module a) and Residual Distribution along the detector b)
bridge for the power dissipated by the electronics [6].
5 Beam Test Results
The results described in this paper were obtained in two beam tests performed at the SPS at Cern in 1995: one in
July in the H2 beam line with 300 GeV/c muons and the second one in September in the X7 beam with 50 GeV/c
pions. In both cases the detectors under test were mounted on an optical bench and two external reference systems
were used for particle tracking. Both systems used silicon detectors: details can be found in [7, 8].
Using a single-sided full size detector (1024 strips with a pitch of
50
m
) and defining the signal-to-noise ratio as
the ratio between the most probable cluster charge and the mean of the cluster noise a value of 25:1 was measured.
This value stayed almost constant when a voltage bias scan was performed. This means that no worsening of the
module behaviour was found.
In Fig. 4 the residual distributionfor thesame detector is shown. If the effects of the track extrapolationerror and of
the multiplescattering due to the material in front of thedetectors are taken into account we find a detector intrinsic
resolution in
r
better than
15
m
for perpendicular tracks. The lower part of the same gure shows that there
is a good uniformity in the position resolution along the readout strips. In Tab. 1 the
r
resolution versus the
tilting angle is quoted. This study was made using double-sided detectors. The resolution improves slightly
Table 1:
Resolution and Number of Strips per Cluster versus Tilt Angle
angle(degree)
0. 5. 14. 20 25.
r
resolution 14.7 14.1 13.1 14.2 19.3
nb. strips per cluster 1.3 1.4 1.6 2.1 2.4
with the angle, as one may expect, when the average cluster size increases from the value of 1.3 strips to around 2.
There is a worsening of the resolution when the cluster size exceeds two strips. The same behaviour is observed
for the
r
z
residuals. The space resolution in the
r
z
view is evaluated looking at the detector response in
double-sided modules on the n-side. A study for different read-out pitches (100
m
and 200
m
) was made. The
resolutionvalues obtainedfor the
r
z
coordinate, reconstructed from n-side stripsat thestereo angleof
100
mrad
,
is 325
m
for 100
m
and 375
m
for 200
m
respectively. Comparing these two values one can conclude that
it’s possible to save the cost of half the electronics channels preserving a good performance.
6 Conclusions
The baseline layout of the CMS silicon tracker is defined. Many details of the design are still in evolution; infact
a lot of beam-tests and montecarlo studies are foreseen. The optimisation process is expected to converge for the
end of 1997 (Technical Design Report).
3

References
[1] The Compact Muon Solenoid, Technical Proposal, CERN/LHCC 94-38 LHCCC/P1, 15 December 1994
[2] T. S. Virdee,”PP Physics at the LHC”, CMS TN/95-168
[3] A. Khanov and N. Stepanov, The CMS Tracker performance estimations with CMSIM100”, CMS TN/95-199
[4] F. Angelini et al., N.I.M. A343 (1994) 441
[5] P. Weiss et al., “Wafer-Scale Technology for Double-Sided Silicon Microstrip Particle Detectors, The
7
th
In-
ternational Conference on Solid-State Sensors and Actuators
[6] RD20 Collaboration: RD20 Status Report 1995, CERN-LHCC/96-2
[7] L. Celano et al., “A High ResolutionBeam Telescope Builtwith Double Sided Silicon Strip Detectors”,CERN
PPE/95-106, Submitted to N.I.M.
[8] C. Albajar et al, N.I.M. A 364 (1995) 473-487
4
Citations
More filters
Journal ArticleDOI
TL;DR: In this paper, the results of some test beams performed on a monolithic strip silicon detector telescope developed in collaboration with the INFN and ST-microelectronics were presented, where the induction on the ΔE stages, generated by the charge released in the E stage, was used to obtain the position of the detected particle.
Abstract: We show the results of some test beams performed on a new monolithic strip silicon detector telescope developed in collaboration with the INFN and ST-microelectronics. Using an appropriate design, the induction on the ΔE stages, generated by the charge released in the E stage, was used to obtain the position of the detected particle. The position measurement, together with the low threshold for particle charge identification, allows the new detector to be used for a large variety of applications due to its sensitivity of only a few microns measured in both directions.

4 citations

Dissertation
01 Jan 2009
TL;DR: The development of a monitoring system that will enable the checking of data generated by the Tracker to address the issues discussed above and has two parts, one dealing with the data used to monitor the Tracker and a second one that deals with statistical methods used to check the quality of the data.
Abstract: The CMS Tracker is an all silicon detector and it is the biggest of its kind to be built. The system consists of over 15,000 individual detector modules giving rise to readout through almost 10 channels. The data generated by the Tracker system is close to 650 MB at 40 MHz. This has created a challenge for the CMS collaborators in terms of data storage for analysis. To store only the interesting physics data the readout rate has to be reduced to 100 Hz where the data has to be filtered through a monitoring system for quality checks. The Tracker being the closest part of the detector to the interaction point of the CMS creates yet another challenge that needs the data quality monitoring system. As it operates in a very hostile environment the silicon detectors used to detect the particles will be degraded. It is very important to monitor the changes in the sensor behaviour with time so that to calibrate the sensors to compensate for the erroneous readings. This thesis discusses the development of a monitoring system that will enable the checking of data generated by the tracker to address the issues discussed above. The system has two parts, one dealing with the data used to monitor the Tracker and a second one that deals with statistical methods used to check the quality of the data.

3 citations


Cites background from "Performance of the silicon detector..."

  • ...Understanding the Higgs Mechanism through experimental study can elucidate the mathematical consistency of the Standard Model (SM) at energy scales of about 1 TeV[5]....

    [...]

References
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DOI
01 Dec 1990

49 citations


"Performance of the silicon detector..." refers background in this paper

  • ...\conference{Presented at {\em Position-Sensitive Detectors}, The University of Manchester, 9-13 September 1996} Submitted to Elsevier Preprint Figure 1: Layout of the Tracking System of CMS...

    [...]

  • ...…exclusion of the Standard Model Higgs Boson at masses above the maximum reach at LEP (order of 100 GeV) to 1 TeV; the study of WW,WZ,ZZ scattering at large CM energies, the discovery of Higgs Bosons in the Minimum Supersymmetric Standard Model (MSSM), the search for composite structures in quarks,…...

    [...]

Journal ArticleDOI
TL;DR: In this paper, a compact and portable beam telescope was built using four 1.92 ×1.92 cm2 double sided silicon microstrip detectors with 50 μm read-out pitch.
Abstract: A compact and portable beam telescope has been built using four 1.92 × 1.92 cm2 double sided silicon microstrip detectors with 50 μm read-out pitch. Tests using 50 GeV pions have shown that the beam position can be defined with a precision of 5 and 7 μm on the p-side and n-side respectively with an overall detection efficiency of 93.0%.

31 citations

Journal ArticleDOI
TL;DR: In this article, the behavior of the microstrip gas chamber has been studied in strong magnetic fields (up to 2.3 T), and an almost complete compensation of the effect due to the E × B factor, which is otherwise responsible for a degradation of the spatial resolution, has been obtained by applying a small tilt to the chamber equal to the Lorentz angle.
Abstract: The behaviour of the microstrip gas chamber has been studied in strong magnetic fields (up to 2.3 T). An almost complete compensation of the effect due to the E × B factor, which is otherwise responsible for a degradation of the spatial resolution, has been obtained by applying a small tilt to the chamber equal to the Lorentz angle. Different. gas mixtures have been studied: an improvement in the resolution has been achieved using gas mixtures with higher cluster density (DME-CO 2 , DME-CF 4 ).

14 citations

Journal ArticleDOI
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Related Papers (5)
Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Performance of the silicon detectors for the cms barrel tracker" ?

The Compact Muon Solenoid ( CMS ) tracker this paper is a tracker designed for the Large Hadron Collider.