-
E Abat,
A Abdesselam,
T N Addy,
T P A Åkesson,
P P Allport,
L Andricek,
F Anghinolfi,
R Apsimon,
E Arik,
M Arik, [......],
D Whittington,
A Wildauer,
I Wilhelm,
H H Williams,
J A Wilson,
M W Wolter,
S L Wu,
A Zhelezko,
H Z Zhu,
A Zsenei
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in the centre of the ATLAS experiment at the Large Hadron Collider (LHC). The Inner Detector consists of three subdetectors: the Pixel Detector, the Semiconductor Tracker (SCT), and the Transition Radiation Tracker (TRT). This paper summarizes the tests that were carried out at the final stage of SCT+TRT integration prior to their installation in ATLAS. The combined operation and performance of the SCT and TRT barrel and endcap detectors was investigated through a series of noise tests, and by recording the tracks of cosmic rays. This was a crucial test of hardware and software of the combined tracker detector systems. The results of noise and cross-talk tests on the SCT and TRT in their final assembled configuration, using final readout and supply hardware and software, are reported. The reconstruction and analysis of the recorded cosmic tracks allowed testing of the offline analysis chain and verification of basic tracker performance parameters, such as efficiency and spatial resolution, in combined operation before installation.
Journal of Instrumentation 08/2008; 3(08):P08003. · 1.87 Impact Factor
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J. Bernabeu,
J. V. Civera,
M J Costa,
C. Escobar,
J Fuster,
C Garcia, J.E. Garcia Navarro,
F Gonzalez,
S. Gonzalez-Sevilla,
C Lacasta,
G. Llosa,
S. Marti-Garcia,
M. Minano,
V.A. Mitsou,
P Modesto,
J Nacher,
R Rodriguez-Oliete,
F. J. Sanchez,
L Sospedra,
V. Strachko
[show abstract]
[hide abstract]
ABSTRACT: ATLAS experiment, designed to probe the interactions of particles emerging out of proton proton collisions at energies of up to 14 TeV, will assume operation at the Large Hadron Collider (LHC) at CERN in 2007. This paper discusses the assembly and the quality control tests of forward detector modules for the ATLAS silicon microstrip detector assembled at the Instituto de Fisica Corpuscular (IFIC) in Valencia. The construction and testing procedures are outlined and the laboratory equipment is briefly described. Emphasis is given on the module quality achieved in terms of mechanical and electrical stability. Comment: 23 pages, 38 EPS figures, uses JINST LaTeX class
09/2007;
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E. Fretwurst,
J. Adey,
A. Al-Ajili,
G. Alfieri,
P.P. Allport,
M. Artuso,
S. Assouak,
B.S. Avset,
L. Barabash,
A. Barcz, [......],
S. Worm,
V. Wright,
R. Wunstorf,
Y. Yiuri,
P. Zabierowski,
A. Zaluzhny,
M. Zavrtanik,
M. Zen,
V. Zhukov,
N. Zorzi
[show abstract]
[hide abstract]
ABSTRACT: The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 1016 hadrons/cm2. Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2005; 552:7-19. · 1.21 Impact Factor
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M. Bruzzi,
J. Adey,
A. Al-Ajili,
P. Alexandrov,
G. Alfieri,
P P Allport,
A Andreazza,
M. Artuso,
S. Assouak,
B.S. Avset, [......],
I Wilhelm,
S Worm,
V. Wright,
R Wunstorf,
P. Zablerowski,
A. Zaluzhny,
M. Zavrtanik,
M. Zen,
V Zhukov,
N. Zorzi
[show abstract]
[hide abstract]
ABSTRACT: An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work. 2005 Published by Elsevier B.V.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2005; 541:189-201. · 1.21 Impact Factor
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M. Moll,
J. Adey,
A. Al-Ajili,
G. Alfieri,
P P Allport,
M. Artuso,
S. Assouak,
B.S. Avset,
L. Barabash,
A. Barcz, [......],
S Worm,
V. Wright,
R Wunstorf,
Y. Yiuri,
P. Zabierowski,
A. Zaluzhny,
M. Zavrtanik,
M. Zen,
V Zhukov,
N. Zorzi
[show abstract]
[hide abstract]
ABSTRACT: The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 10(35) cm(-2) s(-1) Will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented. (c) 2005 Elsevier B.V. All rights reserved.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2005; 546:99-107. · 1.21 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: In recent years, ATLAS Semiconductor Tracker (SCT) silicon strip detector mod-ules have been routinely tested in beam tests at the H8 beamline of the CERN SPS and in the π2 beamline of the KEK PS. Measurements have established the track-ing performance of prototypes of the final design of the various SCT geometrical module types under different operating conditions. Tests of irradiated modules have allowed estimation of the performance after 10 years of operation in the LHC. In this article, the test beam setup and methodology is described and an overview of the most important results presented.
-
E Fretwurst,
J. Adey,
A. Al-Ajili,
G. Alfieri,
P P Allport,
M. Artuso,
S. Assouak,
B.S. Avset,
L. Barabashi,
A. Barcz, [......],
S Worm,
V. Wright,
R Wunstorf,
Y. Yiuri,
P. Zabierowski,
A. Zaluzhny,
M. Zavrtanik,
M. Zen,
V Zhukov,
N. Zorzi
[show abstract]
[hide abstract]
ABSTRACT: The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 10(16) hadrons/cm(2). Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed. (c) 2005 Elsevier B.V. All rights reserved.
Physics Research Publications.
-
F. Campabadal,
C. Fleta,
M. Key,
M. Lozano,
C. Martinez,
G. Pellegrini,
J.M. Rafi,
M. Ullan,
L.G. Johansen,
B. Mohn, [......],
C. Garcia, J.E. Garcia-Navarro,
S. Gonzalez-Sevilla,
C. Lacasta,
G. Llosa,
S. Marti-Garcia,
P. Modesto,
F.J. Sanchez,
L. Sospedra,
M. Vos
[show abstract]
[hide abstract]
ABSTRACT: The ABCD3TA is a 128-channel ASIC with binary architecture for the readout of silicon strip particle detectors in the Semiconductor Tracker of the ATLAS experiment at the Large Hadron Collider (LHC). The chip comprises fast front-end and amplitude discriminator circuits using bipolar devices, a binary pipeline for first level trigger latency, a second level derandomising buffer and data compression circuitry based on CMOS devices. It has been designed and fabricated in a BiCMOS radiation resistant process. Extensive testing of the ABCD3TA chips assembled into detector modules show that the design meets the specifications and maintains the required performance after irradiation up to a total ionising dose of 10 Mrad and a 1-MeV neutron equivalent fluence of 2×1014 n/cm2, corresponding to 10 years of operation of the LHC at its design luminosity. Wafer screening and quality assurance procedures have been developed and implemented in large volume production to ensure that the chips assembled into modules meet the rigorous acceptance criteria.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
-
M. Moll,
J. Adey,
A. Al-Ajili,
G. Alfieri,
P.P. Allport,
M. Artuso,
S. Assouak,
B.S. Avset,
L. Barabash,
A. Barcz, [......],
S. Worm,
V. Wright,
R. Wunstorf,
Y. Yiuri,
P. Zabierowski,
A. Zaluzhny,
M. Zavrtanik,
M. Zen,
V. Zhukov,
N. Zorzi
[show abstract]
[hide abstract]
ABSTRACT: The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 1035 cm−2 s−1 will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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G. Aad,
E. Abat,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz, [......],
S Zimmermann,
M. Zinna,
M Ziolkowski,
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
M zur Nedden,
V. Zychacek
[show abstract]
[hide abstract]
ABSTRACT: A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.
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G. Aad,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz,
H. Abreu, [......],
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of mu, the average number of inelastic interactions per bunch crossing. Residual time- and mu-dependence between the methods is less than 2% for 0
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A. Abdesselam,
T. Akimoto,
P.P. Allport,
J. Alonso,
B. Anderson,
L. Andricek,
F. Anghinolfi,
R.J. Apsimon,
G. Barbier,
A.J. Barr, [......],
M.R.M. Warren,
R.L. Wastie,
M. Weber,
A.R. Weidberg,
P. Weilhammer,
P.S. Wells,
M. Wilder,
I. Wilhelm,
J.A. Wilson,
M. Wolter
[show abstract]
[hide abstract]
ABSTRACT: This paper describes the silicon microstrip modules in the barrel section of the SemiConductor Tracker (SCT) of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The module requirements, components and assembly techniques are given, as well as first results of the module performance on the fully assembled barrels that make up the detector being installed in the ATLAS experiment.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 568(2):642-671. · 1.21 Impact Factor
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A. Abdesselam,
P P Allport,
C. Anastopoulos,
B Anderson,
L. Andricek,
F. Anghinolfi,
R Apsimon,
T. Atkinson,
D. J. Attree,
N. Austin, [......],
P Werneke,
M.J. White,
M Wiesmann,
I Wilhelm,
I Wilmut,
J A Wilson,
M.W. Wolter,
S L Wu,
H. Z. Zhu,
A Zsenei
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS SemiConductor Tracker (SCT) was built in three sections: a barrel and two end-caps. This paper describes the design, construction and final integration of the barrel section. The barrel is constructed around four nested cylinders that provide a stable and accurate support structure for the 2112 silicon modules and their associated services. The emphasis of this paper is directed at the aspects of engineering design that turned a concept into a fully-functioning detector, as well as the integration and testing of large sub-sections of the final SCT barrel detector. The paper follows the chronology of the construction. The main steps of the assembly are described with the results of intermediate tests. The barrel service components were developed and fabricated in parallel so that a flow of detector modules, cooling loops, opto-harnesses and Frequency-Scanning-Interferometry (FSI) alignment structures could be assembled onto the four cylinders. Once finished, each cylinder was conveyed to the next site for the mounting of modules to form a complete single barrel. Extensive electrical and thermal function tests were carried out on the completed single barrels. In the next stage, the four single barrels and thermal enclosures were combined into the complete SCT barrel detector so that it could be integrated with the Transition Radiation Tracker (TRT) barrel to form the central part of the ATLAS inner detector. Finally, the completed SCT barrel was tested together with the TRT barrel in noise tests and using cosmic rays.
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G. Aad,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz,
H. Abreu, [......],
V Zhuravlov,
R Zimmermann,
S Zimmermann,
M Ziolkowski,
L Zivkovic,
G Zobernig,
A. Zoccoli,
M zur Nedden,
V Zutshi,
S. Tricaz-Duvoid
[show abstract]
[hide abstract]
ABSTRACT: The simulation software for the ATLAS Experiment at the Large Hadron Collider is being used for large-scale production of events on the LHC Computing Grid. This simulation requires many components, from the generators that simulate particle collisions, through packages simulating the response of the various detectors and triggers. All of these components come together under the ATLAS simulation infrastructure. In this paper, that infrastructure is discussed, including that supporting the detector description, interfacing the event generation, and combining the GEANT4 simulation of the response of the individual detectors. Also described are the tools allowing the software validation, performance testing, and the validation of the simulated output against known physics processes.
European Physical Journal C.
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G. Aad,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz,
H. Abreu, [......],
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full dataset (L=36/pb) acquired by the ATLAS detector during the 2010 sqrt(s)=7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high energy regime.
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G. Aad,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz,
H. Abreu, [......],
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this paper a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton-proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb-1. No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of squarks and gluinos. The influence of R-hadron interactions in matter was studied using a number of different models, and lower mass limits for stable sbottoms and stops are found to be 294 and 309 GeV respectively. The lower mass limit for a stable gluino lies in the range from 562 to 586 GeV depending on the model assumed. Each of these constraints is the most stringent to date.
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G. Aad,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz,
H. Abreu, [......],
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from sqrt{s} = 7 TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb-1. No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. For A_0 = 0 GeV, tan beta = 3, mu > 0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.
Physical Review Letters.
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G. Aad,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz,
H. Abreu, [......],
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi,
L Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally-segmented electromagnetic and hadronic calorimeters. The underlying event is measured and subtracted event-by-event, giving estimates of jet transverse energy above the ambient background. The transverse energies of dijets in opposite hemispheres is observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, and which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.
Physical Review Letters.
-
F. Campabadal,
C Fleta,
M Key,
M Lozano,
C Martinez,
G Pellegrini,
J.M. Rafi,
M. Ullan,
L.G. Johansen,
B Mohn, [......],
C Garcia, J.E. Garcia Navarro,
S. Gonzalez-Sevilla,
C Lacasta,
G. Llosa,
S. Marti-Garcia,
P Modesto,
F. J. Sanchez,
L Sospedra,
M Vos
[show abstract]
[hide abstract]
ABSTRACT: The ABCD3TA is a 128-channel ASIC with binary architecture for the readout of silicon strip particle detectors in the Semiconductor Tracker of the ATLAS experiment at the Large Hadron Collider (LHC). The chip comprises fast front-end and amplitude discriminator circuits using bipolar devices, a binary pipeline for first level trigger latency, a second level derandomising buffer and data compression circuitry based on CMOS devices. It has been designed and fabricated in a BiCMOS radiation resistant process. Extensive testing of the ABCD3TA chips assembled into detector modules show that the design meets the specifications and maintains the required performance after irradiation up to a total ionising dose of 10 Mrad and a 1-MeV neutron equivalent fluence of 2×1014 n/cm2, corresponding to 10 years of operation of the LHC at its design luminosity. Wafer screening and quality assurance procedures have been developed and implemented in large volume production to ensure that the chips assembled into modules meet the rigorous acceptance criteria.
Nuclear Physics fields.
-
G. Aad,
E. Abat,
B Abbott,
J Abdallah,
A.A. Abdelalim,
A. Abdesselam,
O. Abdinov,
B. Abi,
M Abolins,
H Abramowicz, [......],
M Ziolkowski,
R Zitoun,
L Zivkovic,
V.V. Zmouchko,
G Zobernig,
A. Zoccoli,
Y Zolnierowski,
A Zsenei,
M zur Nedden,
V Zutshi
[show abstract]
[hide abstract]
ABSTRACT: The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |eta|<2.5 and pT>500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at eta = 0 is measured to be 1.333 +/- 0.003 (stat.) +/- 0.040 (syst.), which is 5-15% higher than the Monte Carlo models predict.
