| 1. |
- Abdallah, J, et al.
(författare)
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Rapidity-alignment and p(T) compensation of particle pairs in hadronic Z(0) decays
- 2002
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 533:3-4, s. 243-252
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Tidskriftsartikel (refereegranskat)abstract
- Observation is made of rapidity-alignment of K+K- and (p) over barp pairs which results from their asymmetric orientation in rapidity, with respect to the direction from primary quark to antiquark. The K+K- and (p) over barp data are consistent with predictions from the fragmentation string model. However, the (p) over barp data strongly disagree with the conventional implementation of the cluster model. The non-perturbative process of 'gluon splitting to diquarks' has to be incorporated into the cluster model for it to agree with the data. Local conservation of PT between particles nearby in rapidity (i.e., p(T) compensation) is analysed with respect to the thrust direction for pi(+)pi(-), K+K-, and (p) over barp pairs. In this case, the string model provides fair agreement with the data. The cluster model is incompatible with the data for all three particle pairs. The model with its central premiss of isotropically-decaying clusters predicts a p(T) correlation not seen in the data. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 2. |
- Abdallah, J, et al.
(författare)
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Search for charged Higgs bosons in e(+)e(-) collisions root s=189-202 GeV
- 2002
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 525:1-2, s. 17-28
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Tidskriftsartikel (refereegranskat)abstract
- A search for pair-produced charged Higgs bosons was performed in the high energy data collected by the DELPHI detector at LEP II at centre-of-mass energies from 189 GeV to 202 GeV. The three different final states, taunutaunu, c (s) over bar(c) over bars and c (s) over bar taunu were considered. New methods were applied to reject wrong hadronic jet pairings and for the tau identification, where a discriminator based on tau polarisation and polar angles was used. No excess of data compared to the expected Standard Model processes was observed and the existence of a charged Higgs boson with mass lower than 71.5 GeV/c(2) is excluded at the 95% confidence level. (C) 2002 Published by Elsevier Science B.V.
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| 3. |
- Abdallah, J, et al.
(författare)
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Searches for neutral Higgs bosons in e(+)e(-), collisions from root s=191.6 to 201.7 GeV
- 2002
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 23:3, s. 409-435
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Tidskriftsartikel (refereegranskat)abstract
- Neutral Higgs bosons of the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM) were searched for in the data collected in 1999 by the DELPHI experiment at centre-of-mass energies between 191.6 and 201.7 GeV with a total integrated luminosity of 228 pb(-1). These analyses, in combination with our results at lower energies, set 95% confidence level lower mass bounds on the Standard Model Higgs boson (107.3 GeV/c(2)) and on the lightest neutral scalar (85.9 GeV/c(2)) and neutral pseudoscalar (86.5 GeV/c(2)) Higgs bosons in representative scans of the MSSM parameter space. An extended scan of the MSSM parameter space was also performed to test the robustness of these limits.
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| 4. |
- Abdallah, J, et al.
(författare)
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Study of inclusive J/psi production in two-photon collisions at LEP II with the DELPHI detector
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 565:1-4, s. 76-86
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/psi production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction gammagamma --> J/psi + X is seen. The number of observed N(J/psi --> mu(+)mu(-)) events is 36+/-7 for an integrated luminosity of 617 pb(-1), yielding a cross-section of sigma(J/psi + X) = 45+/-9(stat) +/- 17(syst) pb. Based on a study of the event shapes of different types of gammagamma processes in the PYTHIA program, we conclude that (74+/-22) % of the observed J/psi events are due to 'resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon. (C) 2003 Published by Elsevier B.V.
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| 5. |
- Abreu, P, et al.
(författare)
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b-tagging in DELPHI at LEP
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 32:2, s. 185-208
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Tidskriftsartikel (refereegranskat)abstract
- The standard method used for tagging b-hadrons in the DELPHI experiment at the CERN LEP Collider is discussed in detail. The main ingredient of b-tagging is the impact parameters of tracks, which relies mostly on the vertex detector. Additional information, such as the mass of particles associated to a secondary vertex, significantly improves the selection efficiency and the background suppression. The paper describes various discriminating variables used for the tagging and the procedure of their combination. In addition, applications of b-tagging to some physics analyses, which depend crucially on the performance and reliability of b-tagging, are described briefly.
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| 6. |
- Abreu, P., et al.
(författare)
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Measurement of the mass and width of the W boson in e+e- collisions at √s = 189 GeV
- 2001
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 511:2-4, s. 159-177
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the W mass and width has been performed by the DELPHI Collaboration using the data collected during 1998. The data sample has an integrated luminosity of 155 pb-1 and an average centre-of-mass energy of 188.6 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W- → lvlqq′ and W+W- → qq′qq′ channels. The W mass result for the 1998 data set is MW = 80.387 ± 0.087(stat) ± 0.034(syst) ± 0.017(LEP) ± 0.035(FSI) GeV/c2, where FSI represents the uncertainty due to final state interaction effects in the qq′qq′ channel, and LEP represents that arising from the knowledge of the beam energy of the accelerator. Combining this result with those previously published by the DELPHI Collaboration gives the result MW = 80.359 ± 0.074(stat) ± 0.032(syst) ± 0.017(LEP) ± 0.033(FSI) GeV/c2. The combined value for the W width is λW = 2.266 ± 0.176(stat)± 0.056(syst)± 0.052(FSI) GeV/c2.
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| 7. |
- Almehed, Sverker, et al.
(författare)
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Regional research exploitation of the LHC: A case-study of the required computing resources
- 2002
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Ingår i: Computer Physics Communications. - 0010-4655. ; 145:3, s. 341-350
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Tidskriftsartikel (refereegranskat)abstract
- A simulation study to evaluate the required computing resources for a research exploitation of the Large Hadron Collider (LHC) has been performed. The evaluation,vas done as a case study. assuming existence of a Nordic regional centre and using the requirements for per-forming a specific physics analysis as a yard-stick. Other input parameters were: assumption for the distribution of researchers at the institutions involved, an analysis model, and two different functional structures of the computing resources.
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| 8. |
- Nygren, Andreas, et al.
(författare)
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Total cross-section measurements in gamma gamma collisions at very low Q(2) at LEP2
- 2002
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Ingår i: Photon 2001. - 9789812380531 ; , s. 158-161
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Konferensbidrag (refereegranskat)abstract
- The multihadron production in the reaction e(+)e(-) -> e(+)e(-) + hadrons has been studied for the first time at LEP2 energies with both scattered e(+) and e(-) detected at very low Q(2), measured by the DELPHI VSAT. A reasonable agreement between data and full simulation is demonstrated and the total gamma gamma hadronic cross-section is estimated for the gamma gamma center of mass energy up to 100 GeV.
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| 9. |
- Åkesson, Torsten, et al.
(författare)
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ATLAS High-Level Trigger, Data Acquisition and Controls Technical Design Report
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This Technical Design Report (TDR) for the High-level Trigger (HLT), Data Acquisition (DAQ) and Controls of the ATLAS experiment builds on the earlier documents published on these systems: Trigger Performance Status Report, DAQ, EF, LVL2 and DCS Technical Progress Report, and High-Level Triggers, DAQ and DCS Technical Proposal. Much background and preparatory work relevant to this TDR is referenced in the above documents. In addition, a large amount of detailed technical documentation has been produced in support of this TDR. These documents are referenced in the appropriate places in the following chapters. This section introduces the overall organization of the document. The following sections give an overview of the principal system requirements and functions, as well as a brief description of the principal data types used in the Trigger/DAQ (TDAQ) system. The document has been organized into four parts: Part I — Global View Chapters 2, 3 and 4 address the principal system and experiment parameters which define the main requirements of the HLT, DAQ and Controls system. The global system operations, and the physics requirements and event selection strategy are also addressed. Chapter 5 defines the overall architecture of the system and analyses the requirements of its principal components, while Chapters 6 and 7 address more specific fault-tolerance and monitoring issues. Part II — System Components This part describes in more detail the principal components and functions of the system. Chapter 8 addresses the final prototype design and performance of the Data Flow component. These are responsible for the transport of event data from the output of the detector Read Out Links (ROLs) via the HLT system (where event selection takes place) to mass storage. Chapter 9 explains the decomposition of the HLT into a second level trigger (LVL2) and an Event Filter (EF). It details the design of the data flow within the HLT, the specifics of the HLT system supervision, and the design and implementation of the Event Selection Software (ESS). Chapter 10 addresses the Online Software which is responsible for the run control and DAQ supervision of the entire TDAQ and detector systems during data taking. It is also responsible for miscellaneous services such as error reporting, run parameter accessibility, and histogramming and monitoring support. Chapter 11 describes the Detector Control System (DCS), responsible for the control and supervision of all the detector hardware and of the services and the infrastructure of the experiment. The DCS is also the interface point for information exchange between ATLAS and the LHC accelerator. Chapter 12 draws together the various aspects of experiment control detailed in previous chapters and examines several use-cases for the overall operation and control of the experiment, including: data-taking operations, calibration runs, and operations required outside data-taking. Part III — System Performance Chapter 13 addresses the physics selection. The tools used for physics selection are described along with the event-selection algorithms and their performance. Overall HLT output rates and sizes are also discussed. An initial analysis of how ATLAS will handle the first year of running from the point of view of TDAQ is presented. Chapter 14 discusses the overall performance of the HLT/DAQ system from various points of view, namely the HLT performance as evaluated in dedicated testbeds, the overall performance of the TDAQ system in a testbed of ~10% ATLAS size, and functional tests of the system in the detector test beam environment. Data from these various testbeds are also used to calibrate a detailed discrete-event -simulation model of data flow in the full-scale system. Part IV — Organization and Planning Chapter 15 discusses quality-assurance issues and explains the software-development process employed. Chapter 16 presents the system costing and staging scenario. Chapter 17 presents the overall organization of the project and general system-resource issues. Chapter 18 presents the short-term HLT/DAQ work-plan for the next phase of the project as well as the global development schedule up to LHC turn-on in 2007.
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| 10. |
- Åkesson, Torsten, et al.
(författare)
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High transverse momentum physics at the large hadron collider
- 2002
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Ingår i: EPJ direct. - 1435-3725. ; 4:CN1, s. 1-61
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Forskningsöversikt (refereegranskat)abstract
- This note summarizes many detailed physics studies done by the ATLAS and CMSCollab orations for the LHC, concentrating on processes involving the production of high mass states. These studies show that the LHC should be able to elucidate the mechanism of electroweak symmetry breaking and to study a variety of other topics related to physics at the TeV scale. In particular, a Higgs boson with couplings given by the Standard Model is observable in several channels over the full range of allowed masses. Its mass and some of its couplings will be determined. If supersymmetry is relevant to electroweak interactions, it will be discovered and the properties of many supersymmetric particles elucidated. Other new physics, such as the existence of massive gauge bosons and extra dimensions can be searched for extending existing limits by an order of magnitude or more.
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