e
+e
− annihilation into quark–antiquark pairs is a valuable platform for the investigation of the strong interaction. The level of sophistication reached by theory and experiment allows one to ...verify predictions with significant precision for centre-of-mass energies ranging from the
τ lepton mass up to about
200
GeV
. This report summarizes studies of the dependence of the strong interaction on the energy scale. Determinations of
α
S from total cross-sections, hadronic branching fractions of the
τ lepton and of heavy quarkonia, jet rates, and event shape observables confirm the energy dependence of the strong coupling constant. Tests of the flavour independence of the strong interaction and mass effects are reviewed. Perturbation calculations of mass effects allow the determination of the bottom quark mass at high energies and, therefore, the scale dependence of quark masses predicted by
qcd. Experimental studies of theoretical approaches to hadronization are presented. Besides fragmentation functions, scaling violations, and longitudinal cross-sections, successes of the modified leading-logarithmic approximation and local parton–hadron duality are exemplified. Power suppressed corrections, which are expected to be related to hadronization, are discussed for mean values and distributions of event shape observables. From the energy dependence of the strong interaction missing higher-order terms of the perturbation series can be determined. The scrutiny of the scale dependence of
α
S showed no evidence for power corrections, light gluinos, or anomalous strong couplings. The results on
α
S from e
+e
− annihilation are also very consistent with determinations of the strong coupling constant from other hard processes.
Novel developments in micropattern detector technology require fast and precise methods to measure large area topologies in the order of a few square meters. Standard tactile coordinate measurement ...systems have resolutions better 10μm, but suffer from relatively long measuring time of several hours for one cycle. Sensitive structures may be damaged when touched by the tactile sensor. We present a method using laser distance sensors. Such a device is able to scan surfaces fast without touching them. The presented device has the capability to measure semitransparent surfaces. The vertical translator to mount the sensor is able to move in sub-mm steps. Using this we are able to measure the position and height of copper on FR4 with an accuracy better than 10μm. We report on the performance of the sensor scanning non-transparent as well as semi-transparent surfaces. This includes studies to minimize the measurement time without a loss in resolution. Our method to calibrate the measurement system will also be shown. This calibration is needed to reach a resolution better than 10μm.
Floating strip Micromegas are high-accuracy and discharge insensitive gaseous detectors, able to track single particles at fluxes of 7MHz/cm2 with 100μm resolution. We developed low-material-budget ...detectors with one-dimensional strip readout, suitable for tracking at highest particle rates as encountered in medical ion transmission radiography or inner tracker applications. Recently we additionally developed Kapton-based floating strip Micromegas with two-dimensional strip readout, featuring an overall thickness of 0.011 X0.
These detectors were tested in high-rate proton and carbon-ion beams at the tandem accelerator in Garching and the Heidelberg Ion-Beam Therapy Center, operated with an optimized Ne:CF4 gas mixture. By coupling the Micromegas detectors to a new scintillator based range detector, ion transmission radiographies of PMMA and tissue-equivalent phantoms were acquired. The range detector with 18 layers is read out via wavelength shifting fibers, coupled to a multi-anode photomultiplier.
We present the performance of the Micromegas detectors with respect to timing and single plane track reconstruction using the μTPC method. We discuss the range resolution of the scintillator range telescope and present the image reconstruction capabilities of the combined system.
Predictions of analytical models for hadronisation, namely the dispersive model, the shape function and the single dressed gluon approximation, are compared with moments of hadronic event shape ...distributions measured in e
+
e
−
annihilation at centre-of-mass energies between 14 and 209 GeV. In contrast to Monte Carlo models for hadronisation, analytical models require to adjust only two universal parameters, the strong coupling and a second quantity parametrising non-perturbative corrections. The extracted values of
α
S
are consistent with the world average and competitive with previous measurements. The variance of event shape distributions is compared with predictions given by some of these models. Limitations of the models, probably due to unknown higher order corrections, are demonstrated and discussed.
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.
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.
TPC-like readout for thermal neutron detection using a GEM-detector Flierl, B.; Hertenberger, R.; Biebel, O. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2016, Letnik:
824
Journal Article
Recenzirano
Odprti dostop
Spatial resolution of less than 200μm is challenging for thermal neutron detection. A novel readout scheme based on the time-projection-chamber (TPC) concept is used in a gaseous electron multiplier ...(GEM) detector 1. Thermal neutrons are captured in a single 2μm thick Boron-10 converter cathode and secondary Helium and Lithium ions are produced with a combined energy of 2.8MeV. These ions have sufficient energy to form straight tracks of several mm length. With a time resolving 2-dimensional readout of 400μm pitch in both directions, based on APV25 chips, the ions are tracked and their respective origin in the cathode converter foil is reconstructed. Using an Ar–CO2 93:7% gas mixture, a resolution of 100μm (FWHM 235μm) has been observed with a triple GEM-detector setup at the Garching neutron source (FRMII) for neutrons of 4.7Å.
•Time resolved readout method improves resolution for thermal neutron detection.•Neutrons are detected in a GEM-detector with a single Boron-10 conversion layer.•He or Li ions from the conversion layer can be reconstructed in the gas volume.•Full reconstruction of the ion track delivers much higher spatial resolution.
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