The resolution and efficiency of a precision drift-tube chamber for the ATLAS muon spectrometer with final read-out electronics was tested at the Gamma Irradiation Facility at CERN in a
100
GeV
muon ...beam at photon irradiation rates of up to
990
Hz
/
cm
2
, which corresponds to twice the highest background rate expected in ATLAS. A silicon strip detector telescope served as external reference in the beam. The pulse-height measurement of the read-out electronics was used to perform time-slewing corrections, which lead to an improvement of the average drift-tube resolution from 104 to
82
μ
m
without irradiation, and from 128 to
108
μ
m
at the maximum expected rate. The measured drift-tube efficiency agrees with the expectation from the dead time of the read-out electronics up to the maximum expected rate.
Crystallization represents a long-standing problem in statistical physics and is of great relevance for many practical and industrial applications. It often occurs in the presence of container walls ...or impurities, which are usually unavoidable or might even be desirable to facilitate crystallization by exploiting heterogeneous nucleation. Heterogeneous nucleation relies on a seed. Here we discuss the role of the seed and concentrate on a very generic situation, namely crystallization of hard and soft colloidal spheres in the presence of flat or curved hard walls. Curvature serves as a simple means to introduce a tunable mismatch between the seed-induced crystal lattice and the thermodynamically-favoured lattice. The mismatch induces distortions and elastic stress, which accumulate while the crystallite grows. This has an important consequence: once the crystallite reaches a critical size, it detaches from the seed allowing it to relax. The relaxed crystal continues to grow in the bulk, but crystallization ceases before reaching the seed, which now represents an impurity. Therefore, while seeds favour nucleation, any mismatch, like the seed curvature or an incommensurate structure, induces unfavourable distortions and can lead to the detachment of the crystallite. An additional mechanism to relax distortions is available to soft spheres, which can exploit their interaction potential and possibly deform. The different multi-step processes have been investigated by confocal microscopy, which provides particle-level information, and compared to computer simulations and theoretical results.
The muon detectors of the experiments at the Large Hadron Collider (LHC) have to cope with unprecedentedly high neutron and gamma ray background rates. In the forward regions of the muon spectrometer ...of the ATLAS detector, for instance, counting rates of
1.7
kHz
/
cm
2
are reached at the LHC design luminosity. For high-luminosity upgrades of the LHC, up to 10 times higher background rates are expected which require replacement of the muon chambers in the critical detector regions. Tests at the CERN Gamma Irradiation Facility showed that drift-tube detectors with 15
mm diameter aluminum tubes operated with
Ar
:
CO
2
(
93
:
7
)
gas at 3
bar and a maximum drift time of about 200
ns provide efficient and high-resolution muon tracking up to the highest expected rates. For 15
mm tube diameter, space charge effects deteriorating the spatial resolution at high rates are strongly suppressed. The sense wires have to be positioned in the chamber with an accuracy of better than
50
μ
m
in order to achieve the desired spatial resolution of a chamber of
50
μ
m
up to the highest rates. We report about the design, construction and test of prototype detectors which fulfill these requirements.
We report on studies of fast triggering and high precision tracking using Resistive Plate Chambers (RPCs). Two beam tests were carried out with the 180GeV/c muon beam at CERN using glass RPCs with ...gas gaps of 1.15mm and equipped with readout strips with 1.27mm pitch. This is the first beam test of RPCs with fine-pitch readout strips that explores precision tracking and triggering capabilities. RPC signals were acquired with precision timing and charge integrating readout electronics at both ends of the strips. The time resolution was measured to be better than 600ps and the average spatial resolution was found to be 220μm using charge information and 287μm only using signal arrival time information. The dual-ended readout allows the determination of the average and the difference of the signal arrival times. The average time was found to be independent of the incident particle position along the strip and is useful for triggering purposes. The time difference yielded a determination of the hit position with a precision of 7.5mm along the strip. These results demonstrate the feasibility using RPCs for fast and high-resolution triggering and tracking.
Pressurized drift-tube chambers are efficient detectors for high-precision tracking over large areas. The Monitored Drift-Tube (MDT) chambers of the muon spectrometer of the ATLAS detector at the ...Large Hadron Collider (LHC) reach a spatial resolution of
35
μ
m
and almost 100% tracking efficiency with 6 layers of 30
mm diameter drift tubes operated with an Ar:CO
2 (93:7) gas mixture at 3 bar and a gas gain of 20
000. The ATLAS MDT chambers are designed to cope with background counting rates due to neutrons and
γ
rays of up to about 300
kHz per tube which will be exceeded for LHC luminosities larger than the design value of 10
34
cm
−1
s
−1. Decreasing the drift-tube diameter to 15
mm while keeping the other parameters, including the gas gain, unchanged reduces the maximum drift time from about 700 to 200
ns and the drift-tube occupancy by a factor of 7. New drift-tube chambers for the endcap regions of the ATLAS muon spectrometer have been designed. A prototype chamber consisting of 12 times 8 layers of 15
mm diameter drift tubes of 1
m length has been constructed with a sense wire positioning accuracy of
20
μ
m
. The 15
mm diameter drift-tubes have been tested with cosmic rays in the Gamma Irradiation Facility at CERN at
γ
counting rates of up to 1.85
MHz.
The ATLAS Muon Spectrometer is designed to measure the momentum of muons with a resolution of dp/p=3% at 100GeV and 10% at 1TeV. For this task, the spectrometer employs 355,000 Monitored Drift Tubes ...(MDTs) arrayed in 1200 chambers. Calibration (RT) functions convert drift time measurements into tube-centered impact parameters for track segment reconstruction. RT functions depend on MDT environmental parameters and so must be appropriately calibrated for local chamber conditions. We report on the creation and application of a gas monitor system based calibration program for muon track reconstruction in the LHC startup phase.
First experience with the ATLAS muon spectrometer Dubbert, J.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2007, Letnik:
581, Številka:
1
Journal Article
Recenzirano
The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is currently being assembled to be ready to take first data in fall 2007. Its muon spectrometer is designed to achieve a momentum ...resolution of better than 10% up to transverse muon momenta of 1
TeV. The spectrometer consists of one barrel and two endcap superconducting air-core toroid magnets instrumented with three layers of precision drift chambers as tracking detectors and with a dedicated trigger system. We report on our experience with the commissioning and installation of the precision and trigger chambers. First results of the cosmic ray test of the barrel muon spectrometer with magnetic field are presented, including results of the calibration of the drift chambers and of the spectrometer alignment.
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