This paper discusses the potential of ATLAS to study supersymmetry in the “focus point” region of the parameter space of mSUGRA models. The potential to discover a deviation from standard model ...expectations with the first few fb-1 of LHC data was studied using the parametrized simulation of the ATLAS detector. Several signatures were considered, involving hard jets, large missing energy, and either b-tagged jets, opposite-sign isolated electron or muon pairs, or top quarks reconstructed exploiting their fully-hadronic decays. With only 1 fb-1 of data each of these signatures may allow for observing an excess of events over standard model expectations with a statistical significance exceeding five standard deviations. Furthermore, each of the two invariant mass distributions of the two leptons produced by the \(\tilde\chi^0_3\rightarrow\tilde\chi^0_1 l^+ l^-\) and the \(\tilde\chi^0_2\rightarrow\tilde\chi^0_1 l^+ l^-\) three-body decays has a kinematic endpoint that measures the difference between the masses of the parent and daughter neutralino. An analytical expression was derived for the shape of this distribution and was used to fit the simulated LHC data. A measurement of the \(\tilde\chi^0_2-\tilde\chi^0_1\) and \(\tilde\chi^0_3-\tilde\chi^0_1\) mass differences was obtained and this information was used to constrain the MSSM parameter space.
A detailed simulation of silicon pixel detectors irradiated to the very high fluences, in the range (10 15 divide10 16 n eq cm -2 ) foreseen for vertex detectors after the Large Hadron Collider ...luminosity upgrade, is presented. The charge collection properties and the detector response were computed for different silicon materials (Standard Float Zone, Diffusion Oxygenated Float Zone, Czochralski, epitaxial silicon), operating conditions (bias voltage, temperature) and detector geometries (sensor thickness, electrode size). At the maximum fluence (10 16 n eq cm -2 ) the signal is limited by charge trapping rather than by the thickness of the active volume. Since all the silicon materials studied so far have a similar trapping cross section, they are all expected to collect an average signal of 2000-2500 electrons at 600V bias voltage. A detection threshold of 1000-1200 electrons is required in order to have a 97% detection efficiency
Results are reported from beam tests of prototype Si pixel sensors and front-end electronics with analog readout developed for use in the ATLAS experiment at the Large Hadron Collider (LHC). Both ...irradiated and unirradiated assemblies were tested for charge collection, efficiency and position resolution measurements. These indicate that n/sup +/ in n silicon pixel detectors with p-spray isolation can operate after irradiation to fluences of up to 10/sup 15/ n/sub eq//cm/sup 2/ without significant degradation in performance. The depletion depth of irradiated sensors was measured and their behaviour in a magnetic field was studied. The Lorentz angle was found to decrease significantly after irradiation. Comparison between performance on spatial resolution obtained with digital or with analogical readout is also presented.
Radiation hardness performance of ATLAS pixel tracker Troncon, Clara
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2004, Letnik:
530, Številka:
1
Journal Article
Recenzirano
The first ATLAS pixel assemblies with both radiation tolerant sensors and
0.25
μm
electronics have been produced and irradiated with
24
GeV/c
protons up to a fluence of
1.1×10
15
1
MeV
n
eq
cm
−2
and ...a dose of
60
Mrad
. They have been tested in a beam and were found to fulfill all the requirements to operate at the LHC in terms of in-time efficiency and resolution. The depletion depth and charge collection efficiency to m.i.p. of n
+-in-n DOFZ silicon pixel sensors have been measured for different defect annealing scenarios as well as charge trapping time constants. Results are presented here.
Silicon pixel sensors developed by the ATLAS collaboration to meet LHC requirements and to withstand hadronic irradiation to fluences of up to
10
15
n
eq
/
cm
2
have been evaluated using a test beam ...facility at CERN providing a magnetic field. The Lorentz angle was measured and found to alter from 9.0° before irradiation, when the detectors operated at
150
V
bias at
B=1.48
T
, to 3.1° after irradiation and operating at
600
V
bias at
1.01
T
. In addition to the effect due to magnetic field variation, this change is explained by the variation of the electric field inside the detectors arising from the different bias conditions.
The depletion depths of irradiated sensors at various bias voltages were also measured. At
600
V
bias
280
μm
thick sensors depleted to
≈200
μm
after irradiation at the design fluence of
1×10
15
1
MeV
n
eq
/
cm
2
and were almost fully depleted at a fluence of
0.5×10
15
1
MeV
n
eq
/
cm
2
.
The spatial resolution was measured for angles of incidence between 0° and 30°. The optimal value was found to be better than
5.3
μm
before irradiation and
7.4
μm
after irradiation.
A chip removal facility for indium bump bonded pixel detectors Airoldi, A.; Alimonti, G.; Amati, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2005, Letnik:
540, Številka:
2
Journal Article
Recenzirano
Yield maximization in multichip hybrid pixel sensors is a crucial issue in large volume productions planned for future High-Energy Physics experiments. Bump bonding process optimization can guarantee ...statistical single bump failure rates at the acceptable level of 10–100
ppm; nevertheless, systematic effects connected to process repeatability can affect the functionality of a full chip in a module to a much larger extent. Because of this, the reversibility of the bonding procedure has been investigated. A feasibility study on single chip assemblies for the ATLAS experiment has been successfully completed, proving the possibility of reworking. As a result of it, a dedicated facility has been conceptually designed, engineered and commissioned. The characteristics of the facility in terms of motion, temperature and tensile strength control are outlined, together with the main results.
Detailed studies of the ATLAS pixel detectors Troncon, C.
1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019),
1999, Letnik:
1
Conference Proceeding
Results are reported from beam tests of prototype silicon pixel sensors and front-end electronics with analog readout developed for use in the ATLAS experiment at the Large Hadron Collider (LHC). ...Both irradiated and unirradiated assemblies were tested for charge collection, efficiency and position resolution measurements. These indicate that n/sup +/ in n silicon pixel detectors with p-spray isolation can operate after irradiation to fluences of up to 10/sup 15/ n/sub eq//cm/sup 2/ without significant degradation in performance. The depletion depth of irradiated sensors was measured and their behaviour in a magnetic field was studied. The Lorentz angle was found to decrease significantly very after irradiation. Comparison between performance on spatial resolution obtained with digital or analog readout is also presented.
A detailed simulation of silicon pixel detectors irradiated to very high fluences, in the range foreseen for vertex detectors after the Large Hadron Collider luminosity upgrade, is presented. The ...charge collection properties and the detector response were computed for different silicon materials (standard float zone, diffusion oxygenated float zone, Czochralski, epitaxial silicon) and operating conditions. At the maximum fluence (10/sup 16/ n/sub eq/cm/sup -2/) the signal is limited by charge trapping rather than by the thickness of the active volume. Since all the silicon materials studied so far have a similar trapping cross section, they are all expected to collect a signal of 2000-2500 electrons at 600 V bias voltage. A detection threshold of 1000-1200 electrons is required in order to have a 97% detection efficiency.
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