| 1. |
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| 2. |
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| 3. |
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| 4. |
- Schael, S., et al.
(författare)
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Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
- 2013
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 532:4, s. 119-244
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Forskningsöversikt (refereegranskat)abstract
- Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.
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| 5. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 6. |
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- 2017
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 96:2
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Abadie, J., et al.
(författare)
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Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
- 2012
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 539
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Tidskriftsartikel (refereegranskat)abstract
- Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of wide-field telescopes.
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| 8. |
- Adrian-Martinez, S., et al.
(författare)
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A first search for coincident gravitational waves and high energy neutrinos using LIGO, Virgo and ANTARES data from 2007
- 2013
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :6
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.
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| 9. |
- Abadie, J., et al.
(författare)
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All-sky search for periodic gravitational waves in the full S5 LIGO data
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on an all-sky search for periodic gravitational waves in the frequency band 50-800 Hz and with the frequency time derivative in the range of 0 through -6 x 10(-9) Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10x increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150 Hz our upper limit on worst-case linearly polarized strain amplitude h(0) is 1 x 10(-24), while at the high end of our frequency range we achieve a worst-case upper limit of 3.8 x 10(-24) for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational-wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long-period binary companion.
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| 10. |
- Abadie, J., et al.
(författare)
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Search for Gravitational Waves Associated with Gamma-Ray Bursts during LIGO Science Run 6 and Virgo Science Runs 2 and 3
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X. ; 760:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole, and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10(-2) M-circle dot c(2) at 150 Hz, with a median limit of 17 Mpc. For short-hard GRBs we place exclusion distances on binary neutron star and neutron-star-black-hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc, respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.
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| 11. |
- Abadie, J., et al.
(författare)
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Search for gravitational waves from low mass compact binary coalescence in LIGO's sixth science run and Virgo's science runs 2 and 3
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:8
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Tidskriftsartikel (refereegranskat)abstract
- We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M(circle dot); this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron star-black hole, and binary black hole systems are 1.3 x 10(-4), 3.1 x 10(-5), and 6.4 x 10(-6) Mpc(-3) yr(-1), respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.
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| 12. |
- Abadie, J., et al.
(författare)
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All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:12
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Tidskriftsartikel (refereegranskat)abstract
- We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration less than or similar to 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc(3) for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range similar to 5 x 10(-22) Hz(-1/2) to similar to 1 x 10(-20) Hz(-1/2). The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.
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| 13. |
- Abadie, J., et al.
(författare)
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First low-latency LIGO plus Virgo search for binary inspirals and their electromagnetic counterparts
- 2012
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 541
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the low-latency gravitational-wave triggers. The results of the electromagnetic image analysis will be described elsewhere. Results. Over the course of the science run, three gravitational-wave triggers passed all of the low-latency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitational-wave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitational-wave data.
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| 14. |
- Abadie, J., et al.
(författare)
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Search for gravitational waves from intermediate mass binary black holes
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:10
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450 M-circle dot and with the component mass ratios between 1: and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 M-circle dot, for nonspinning sources, the rate density upper limit is 0.13 per Mpc(3) per Myr at the 90% confidence level.
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| 15. |
- Abadie, J., et al.
(författare)
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Upper limits on a stochastic gravitational-wave background using LIGO and Virgo interferometers at 600-1000 Hz
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:12
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Tidskriftsartikel (refereegranskat)abstract
- A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of Omega(GW)(f) = Omega(3)(f/900 Hz)(3), of Omega(3) < 0.32, assuming a value of the Hubble parameter of h(100) = 0.71. These new limits are a factor of seven better than the previous best in this frequency band.
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| 16. |
- Aasi, J., et al.
(författare)
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Einstein@Home all-sky search for periodic gravitational waves in LIGO S5 data
- 2013
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 87:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of an all-sky search for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative range of similar to[-20, 1.1] x 10(-10) Hz s(-1) for the fifth LIGO science run (S5). The search uses a noncoherent Hough-transform method to combine the information from coherent searches on time scales of about one day. Because these searches are very computationally intensive, they have been carried out with the Einstein@Home volunteer distributed computing project. Postprocessing identifies eight candidate signals; deeper follow-up studies rule them out. Hence, since no gravitational wave signals have been found, we report upper limits on the intrinsic gravitational wave strain amplitude h(0). For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h(0) greater than 7.6 x 10(-25) at a 90% confidence level. This search is about a factor 3 more sensitive than the previous Einstein@Home search of early S5 LIGO data.
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| 17. |
- Aasi, J., et al.
(författare)
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Search for gravitational waves from binary black hole inspiral, merger, and ringdown in LIGO-Virgo data from 2009-2010
- 2013
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20, 20)M-circle dot coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and 28M(circle dot) of 3:3 x 10(-7) mergers Mpc(-3) yr(-1).
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| 18. |
- Aasi, J., et al.
(författare)
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The characterization of Virgo data and its impact on gravitational-wave searches
- 2012
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Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 1361-6382 .- 0264-9381. ; 29:15
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Tidskriftsartikel (refereegranskat)abstract
- Between 2007 and 2010 Virgo collected data in coincidence with the LIGO and GEO gravitational-wave (GW) detectors. These data have been searched for GWs emitted by cataclysmic phenomena in the universe, by non-axisymmetric rotating neutron stars or from a stochastic background in the frequency band of the detectors. The sensitivity of GW searches is limited by noise produced by the detector or its environment. It is therefore crucial to characterize the various noise sources in a GW detector. This paper reviews the Virgo detector noise sources, noise propagation, and conversion mechanisms which were identified in the three first Virgo observing runs. In many cases, these investigations allowed us to mitigate noise sources in the detector, or to selectively flag noise events and discard them from the data. We present examples from the joint LIGO-GEO-Virgo GW searches to show how well noise transients and narrow spectral lines have been identified and excluded from the Virgo data. We also discuss how detector characterization can improve the astrophysical reach of GW searches.
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| 19. |
- Evans, P. A., et al.
(författare)
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Swift Follow-up Observations of Candidate Gravitational-wave Transient Events
- 2012
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 203:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors (within less than 10 minutes) and their candidate sky locations were observed by the Swift observatory (within 12 hr). Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge." With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime, multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.
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| 20. |
- Aasi, J., et al.
(författare)
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Parameter estimation for compact binary coalescence signals with the first generation gravitational-wave detector network
- 2013
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 88:6
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Tidskriftsartikel (refereegranskat)abstract
- Compact binary systems with neutron stars or black holes are one of the most promising sources for ground-based gravitational-wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance, that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection'' where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron-star and black-hole binary parameter space over the component mass range 1M(circle dot)-25M(circle dot) and the full range of spin parameters. The cases reported in this study provide a snapshot of the status of parameter estimation in preparation for the operation of advanced detectors.
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| 21. |
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| 22. |
- Campbell, PJ, et al.
(författare)
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Pan-cancer analysis of whole genomes
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 578:7793, s. 82-
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Tidskriftsartikel (refereegranskat)abstract
- Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale1–3. Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4–5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter4; identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation5,6; analyses timings and patterns of tumour evolution7; describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity8,9; and evaluates a range of more-specialized features of cancer genomes8,10–18.
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| 23. |
- Abate, E., et al.
(författare)
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Combined performance tests before installation of the ATLAS Semiconductor and Transition Radiation Tracking Detectors
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3
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Tidskriftsartikel (refereegranskat)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.
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| 24. |
- Abreu, P., et al.
(författare)
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Measurement of the gluon fragmentation function and a comparison of the scaling violation in gluon and quark jets
- 2000
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 13:4, s. 573-589
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the DELPHI detector at the Z resonance between 1992 and 995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy e+e- annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio CA/CF is measured to be: CA/CF = 2.26 ± 0.09stat. ± 0.06sys. ± 0.12clus.,scale..
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| 25. |
- Abreu, P., et al.
(författare)
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Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
- 2001
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Muon pair production in the process e+e- → e+e- μ+μ- is studied using the data taken at LEP1 (√s ≃ mz) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb-1. The QED predictions have been tested over the whole Q2 range accessible at LEP1 (from several GeV2/c4 to several hundred GeV2/c4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function Fγ 2. Azimuthal correlations are used to obtain information on additional structure functions, Fγ A and Fγ B, which originate from interference terms of the scattering amplitudes. The measured ratios Fγ A/Fγ 2 and FγB/Fγ 2 are significantly different from zero and consistent with QED predictions.
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| 26. |
- Abreu, P., et al.
(författare)
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Search for sleptons in e+e- collisions at √s = 183 to 189 GeV
- 2001
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 29-42
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Tidskriftsartikel (refereegranskat)abstract
- Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb-1 have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (ℓ̃ → ℓx̃), producing acoplanar lepton pairs plus missing energy, and the cascade decay (ℓ → ℓx̃0 2 → ℓγx̃0 1), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are mẽ ≤ 87 GeV/c2, mμ̃ ≤ 80 GeV/c2 and mτ̃ 75 GeV/c2, respectively, for values of μ=-200 GeV/c2 and tanβ=1.5.
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| 27. |
- Abdesselam, A., et al.
(författare)
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Engineering for the ATLAS SemiConductor Tracker (SCT) end-cap
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS SemiConductor Tracker (SCT) is a silicon-strip tracking detector which forms part of the ATLAS inner detector. The SCT is designed to track charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC) at CERN at an energy of 14 TeV. The tracker is made up of a central barrel and two identical end-caps. The barrel contains 2112 silicon modules, while each end-cap contains 988 modules. The overall tracking performance depends not only on the intrinsic measurement precision of the modules but also on the characteristics of the whole assembly, in particular, the stability and the total material budget. This paper describes the engineering design and construction of the SCT end-caps, which are required to support mechanically the silicon modules, supply services to them and provide a suitable environment within the inner detector. Critical engineering choices are highlighted and innovative solutions are presented - these will be of interest to other builders of large-scale tracking detectors. The SCT end-caps will be fully connected at the start of 2008. Further commissioning will continue, to be ready for proton-proton collision data in 2008.
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| 28. |
- Ederle, Joerg, et al.
(författare)
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Carotid artery stenting compared with endarterectomy in patients with symptomatic carotid stenosis (International Carotid Stenting Study): an interim analysis of a randomised controlled trial
- 2010
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Ingår i: The Lancet. - 1474-547X. ; 375:9719, s. 985-997
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Tidskriftsartikel (refereegranskat)abstract
- Background Stents are an alternative treatment to carotid endarterectomy for symptomatic carotid stenosis, but previous trials have not established equivalent safety and efficacy. We compared the safety of carotid artery stenting with that of carotid endarterectomy. Methods The International Carotid Stenting Study (ICSS) is a multicentre, international, randomised controlled trial with blinded adjudication of outcomes. Patients with recently symptomatic carotid artery stenosis were randomly assigned in a 1:1 ratio to receive carotid artery stenting or carotid endarterectomy. Randomisation was by telephone call or fax to a central computerised service and was stratified by centre with minimisation for sex, age, contralateral occlusion, and side of the randomised artery. Patients and investigators were not masked to treatment assignment. Patients were followed up by independent clinicians not directly involved in delivering the randomised treatment. The primary outcome measure of the trial is the 3-year rate of fatal or disabling stroke in any territory, which has not been analysed yet. The main outcome measure for the interim safety analysis was the 120-day rate of stroke, death, or procedural myocardial infarction. Analysis was by intention to treat (ITT). This study is registered, number ISRCTN25337470. Findings The trial enrolled 1713 patients (stenting group, n=855; endarterectomy group, n=858). Two patients in the stenting group and one in the endarterectomy group withdrew immediately after randomisation, and were not included in the ITT analysis. Between randomisation and 120 days, there were 34 (Kaplan-Meier estimate 4.0%) events of disabling stroke or death in the stenting group compared with 27 (3.2%) events in the endarterectomy group (hazard ratio [HR] 1.28, 95% CI 0.77-2.11). The incidence of stroke, death, or procedural myocardial infarction was 8.5% in the stenting group compared with 5.2% in the endarterectomy group (72 vs 44 events; HR 1.69, 1.16-2.45, p=0.006), Risks of any stroke (65 vs 35 events; HR 1.92, 1.27-2.89) and all-cause death (19 vs seven events; HR 2.76, 1.16-6.56) were higher in the stenting group than in the endarterectomy group. Three procedural myocardial infarctions were recorded in the stenting group, all of which were fatal, compared with four, all non-fatal, in the endarterectomy group. There was one event of cranial nerve palsy in the stenting group compared with 45 in the endarterectomy group. There were also fewer haematomas of any severity in the stenting group than in the endarterectomy group (31 vs 50 events; p=0.0197). Interpretation Completion of long-term follow-up is needed to establish the efficacy of carotid artery stenting compared with endarterectomy. In the meantime, carotid endarterectomy should remain the treatment of choice for patients suitable for surgery.
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| 29. |
- Abdesselam, A., et al.
(författare)
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The barrel modules of the ATLAS semiconductor tracker
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 568:2, s. 642-671
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Tidskriftsartikel (refereegranskat)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.
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| 30. |
- Abdallah, J, et al.
(författare)
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Search for single top production via FCNC at LEP at root s=189-208 GeV
- 2004
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 590:1-2, s. 21-34
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Tidskriftsartikel (refereegranskat)abstract
- A search for single top production (e(+)e(-) --> t (c) over bar) via flavour changing neutral currents (FCNC) was performed using the data taken by the DELPHI detector at LEP2. The data analyzed have been accumulated at center-of-mass energies ranging from 189 to 208 GeV. Limits at 95% confidence level were obtained on the anomalous coupling parameters kappa(gamma) and kappa(Z). (C) 2004 Published by Elsevier B.V.
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| 31. |
- Abdallah, J, et al.
(författare)
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Search for eta(b) in two-photon collisions at LEP II with the DELPHI detector
- 2006
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 634:4, s. 340-346
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Tidskriftsartikel (refereegranskat)abstract
- The pseudoscalar meson eta(b) has been searched for in two-photon interactions at LEP II. The data sample corresponds to a total integrated luminosity of 617 pb(-1) at centre-of-mass energies ranging from 161 to 209 GeV. Upper limits at a confidence level of 95% on the product Gamma(gamma gamma) (eta(b)) x BR(eta(b)) are 190, 470 and 660 eV/c(2) for the eta(b) decaying into 4, 6 and 8 charged particles, respectively.
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| 32. |
- Abdallah, J, et al.
(författare)
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Inclusive b decays to wrong sign charmed mesons
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 561:1-2, s. 26-40
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Tidskriftsartikel (refereegranskat)abstract
- The production of wrong sign charmed mesons b --> (D) over bar X-(s), D-(s) = (D-0, D+, D-s), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995. Charmed mesons in Z --> b (b) over bar events are exclusively reconstructed by searching for the decays D-0 --> K(-)pi(+), D+ --> K(-)pi(+)pi(+) and D-s(+) --> phipi(+) --> K(+)K(-)pi(+). The wrong sign contribution is extracted by using two discriminant variables: the charge of the b-quark at decay time, estimated from the charges of identified particles, and the momentum of the charmed meson in the rest frame of the b-hadron. The inclusive branching fractions of b-hadrons into wrong sign charm mesons are measured to be: B(b --> (D) over bar X-0) + B(b --> D-X) = (9.3 +/- 1.7(stat) +/- 1.3(syst) +/- 0.4(B))%, B(b --> Ds-X) = (10.1 +/- 1.0(stat) +/- 0.6(syst) +/- 2.8(B))% where the first error is statistical, the second and third errors are systematic. (C) 2003 Published by Elsevier Science B.V.
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| 33. |
- Abdallah, J, et al.
(författare)
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Coherent soft particle production in Z decays into three jets
- 2005
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 605:1-2, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy particle production perpendicular to the event plane in three-jet events produced in Z decays in e(+)e(-) annihilation is measured and compared to that perpendicular to the event axis in two-jet events. The topology dependence of the hadron production ratio is found to agree with a leading-order QCD prediction. This agreement and especially the need for the presence of a destructive interference term gives evidence for the coherent nature of gluon radiation. Hadron production in three-jet events is found to be directly proportional to a single topological scale function of the inter-jet angles. The slope of the dependence of the multiplicity with respect to the topological scale was measured to be 2.211 +/- 0.014(stat.) +/- 0.053(syst.) in good agreement with the expectation given by the colour-factor ratio C-A/C-F = 9/4. This result strongly supports the assumption of local parton-hadron duality, LPHD, at low hadron momentum.
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| 34. |
- Abdallah, J, et al.
(författare)
-
Measurement of inclusive f(1) (1285) and f(1) (1420) production in Z decays with the DELPHI detector
- 2003
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 569:3-4, s. 129-139
-
Tidskriftsartikel (refereegranskat)abstract
- DELPHI results are presented on the inclusive production of two (K(K) over bar π)(0) states in the mass region 1.2-1.6 GeV/c(2) in hadronic Z decays at LEP I. The measured masses (widths) are 1274 +/- 6 MeV/c(2) (29 +/- 12 MeV/c(2)) and 1426 +/- 6 MeV/c(2) (51 +/- 14 MeV/c(2)), respectively. A partial-wave analysis of the (K(K) over bar π)(0) system shows that the first peak is consistent with the I-G (J(PC)) = 0(+)(1(++))/(0(-+))a(0)(980)pi and the second with the I-G (J(PC)) = 0(+)(1(++))K*(892)(K) over bar + c.c. assignments. The total hadronic production rates per hadronic Z decay are (0.165 +/- 0.051) and (0.056 +/- 0.012), respectively. These measurements are consistent with the two states being the f(1) (1285) and f(1) (1420) mesons. (C) 2003 Published by Elsevier B.V.
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| 35. |
- Abdallah, J, et al.
(författare)
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Rapidity-alignment and p(T) compensation of particle pairs in hadronic Z(0) decays
- 2002
-
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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| 36. |
- Abdallah, J., et al.
(författare)
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Search for a fourth generation b '-quark at LEP-II at root s=196-209GeV
- 2007
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 50:3, s. 507-518
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Tidskriftsartikel (refereegranskat)abstract
- A search for the pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb(-1). No evidence for a signal was found. Upper limits on BR(b'-> bZ) and BR(b'-> bZ) were obtained for b' masses ranging from 96 to 103 GeV/c(2) stop. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of R-CKM=vertical bar V-cb(') /V-tb'V-tb vertical bar there V-cb', V-tb' and V-tb are elements of the extended CKM matrix.
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| 37. |
- Abdallah, J, et al.
(författare)
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Search for charged Higgs bosons in e(+)e(-) collisions root s=189-202 GeV
- 2002
-
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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| 38. |
- Abdallah, J, et al.
(författare)
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Search for doubly charged Higgs bosons at LEP2
- 2003
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 552:3-4, s. 127-137
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Tidskriftsartikel (refereegranskat)abstract
- A search for pair-produced doubly charged Higgs bosons has been performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies between 189 and 209 GeV. No excess is observed in the data with respect to the Standard Model background. A lower limit for the mass of 97.3 GeV/c(2) at the 95% confidence level has been set for doubly charged Higgs bosons in left-right symmetric models for any value of the Yukawa coupling between the Higgs bosons and the tau leptons. (C) 2002 Published by Elsevier Science B.V.
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| 39. |
- 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
-
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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| 40. |
- 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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| 41. |
- Abdallah, J., et al.
(författare)
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Study of multi-muon bundles in cosmic ray showers detected with the DELPHI detector at LEP
- 2007
-
Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 28:3, s. 273-286
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Tidskriftsartikel (refereegranskat)abstract
- The DELPHI detector at LEP has been used to measure multi-muon bundles originating from cosmic ray interactions with air. The cosmic events were recorded in "parasitic mode" between individual e(+)e(-) interactions and the total live time of this data taking is equivalent to 1.6 x 10(6) s. The DELPHI apparatus is located about 100 m underground and the 84 metres rock overburden imposes a cutoff of about 52 GeV/c on muon momenta. The data from the large volume Hadron Calorimeter allowed the muon multiplicity of 54,201 events to be reconstructed. The resulting muon multiplicity distribution is compared with the prediction of the Monte Carlo simulation based on CORSIKA/QGSJETOI. The model fails to describe the abundance of high multiplicity events. The impact of QGSJET internal parameters on the results is also studied.
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| 42. |
- 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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| 43. |
- Abdallah, J, et al.
(författare)
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A precise measurement of the B+, B-0 and mean b-hadron lifetime with the DELPHI detector at LEP I
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:3, s. 307-324
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Tidskriftsartikel (refereegranskat)abstract
- Final results from the DELPHI Collaboration on the lifetime of B+ and B-0 mesons and the mean b-hadron lifetime, are presented using the data collected at the Z(0) peak in 1994 and 1995. Elaborate, inclusive, secondary vertexing methods have been employed to ensure a b-hadron reconstruction with good efficiency. To separate samples of B+ and B-0 mesons, high performance neural network techniques are used that achieve very high purity signals. The results obtained are: tau(B+) = 1.624+/-0.014 (stat)+/-0.018 (syst) ps tau(B)0 = 1.531+/-0.021 (stat)+/-0.031 (syst) ps tau(B+)/tau(B)0 = 1.060+/-0.021 (stat)+/-0.024 (syst) and for the average b-hadron lifetime: taub/tau(B)0 = 1.570+/-0.005 (stat)+/-0.008 (syst) ps.
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| 44. |
- Abdallah, J, et al.
(författare)
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A precise measurement of the tau lifetime
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 36:3, s. 283-296
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Tidskriftsartikel (refereegranskat)abstract
- The tau lepton lifetime has been measured with the e(+) e(-) --> tau(+) tau(-) events collected by the DELPHI detector at LEP in the years 1991 - 1995. Three different methods have been exploited, using both one-prong and three-prong tau decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave tau(tau) ( 1 prong) = 291.8 +/- 2.3(stat) +/- 1.5(sys) fs. A third measurement using taus which decayed to three charged particles yielded tau(tau) (3 prong) = 288.6 +/- 2.4(stat) +/- 1.3(sys) fs. These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be tau(tau) = 290.9 +/- 1.4(stat) +/- 1.0(sys) fs.
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| 45. |
- Abdallah, J, et al.
(författare)
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A study of the energy evolution of event shape distributions and their means with the DELPHI detector at LEP
- 2003
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 29:3, s. 285-312
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Tidskriftsartikel (refereegranskat)abstract
- Infrared and collinear safe event shape distributions and their mean values are determined in e(+)e(-) collisions at centre-of-mass energies between 45 and 202GeV. A phenomenological analysis based on power correction models including hadron mass effects for both differential distributions and mean values is presented. Using power corrections, alpha(s) is extracted from the mean values and shapes. In an alternative approach, renormalisation group invariance (RGI) is used as an explicit constraint, leading to a consistent description of mean values without the need for sizeable power corrections. The QCD beta-function is precisely measured using this approach. From the DELPHI data on Thrust, including data from low energy experiments, one finds beta(0) = 7.86 +/- 0.32 for the one loop coefficient of the beta-function or, assuming QCD, n(f) = 4.75 +/- 0.44 for the number of active flavours. These values agree well with the QCD expectation of beta(0) = 7.67 and n(f) 5. A direct measurement of the full logarithmic energy slope excludes light gluinos with a mass below 5GeV.
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| 46. |
- Abdallah, J, et al.
(författare)
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Bose-Einstein correlations in W+W- events at LEP2
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 44:2, s. 161-174
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Tidskriftsartikel (refereegranskat)abstract
- Bose-Einstein correlations (BEC) between final state particles in the reaction e(+)e(-) -> W+ W- -> q(1)(q(2)) over barq(3)(q(4)over bar>) over bar) have been studied. Data corresponding to a total integrated luminosity of 550 pb(-1), recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties.
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| 47. |
- Abdallah, J, et al.
(författare)
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Correlations between polarisation states of W particles in the reaction e(-)e(+)-> W-W+ at LEP2 energies 189-209 GeV
- 2009
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 63:4, s. 611-623
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Tidskriftsartikel (refereegranskat)abstract
- In a study of the reaction e(-)e(+)-> W-W+ with the DELPHI detector, the probabilities of the two W particles occurring in the joint polarisation states transverse-transverse (T T), longitudinal-transverse plus transverse-longitudinal (LT) and longitudinal-longitudinal (LL) have been determined using the final states WW -> lvq (q) over bar (l = e, mu). The two-particle joint polarisation probabilities, i.e. the spin density matrix elements rho T T, rho LT, rho LL, are measured as functions of the W- production angle, theta(W-), at an average reaction energy of 198.2 GeV. Averaged over all cos.W-, the following joint probabilities are obtained: (rho) over barT T = (67 +/- 8)%, (rho) over barL T = (30 +/- 8)%, (rho) over barL T = (3 +/- 7)%. These results are in agreement with the Standard Model predictions of 63.0%, 28.9% and 8.1%, respectively. The related polarisation cross-sections sigma(TT), sigma(LT) and sigma(LL) are also presented.
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| 48. |
- Abdallah, J, et al.
(författare)
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Determination of A(FB)(b) at the Z pole using inclusive charge reconstruction and lifetime tagging
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 40:1, s. 1-25
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Tidskriftsartikel (refereegranskat)abstract
- A novel high precision method measures the b-quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000. An enhanced impact parameter tag provides a high purity b sample. For event hemispheres with a reconstructed secondary vertex the charge of the corresponding quark or anti-quark is determined using a neural network which combines in an optimal way the full available charge information from the vertex charge, the jet charge and from identified leptons and hadrons. The probability of correctly identifying b-quarks and anti-quarks is measured on the data themselves comparing the rates of double hemisphere tagged like-sign and unlike-sign events. The b-quark forward-backward asymmetry is determined from the differential asymmetry, taking small corrections due to hemisphere correlations and background contributions into account. The results for different centre-of-mass energies are: A(FB)(b) ( 89.449 GeV) = 0.0637 +/- 0.0143( stat.) +/- 0.0017( syst.), A(FB)(b) ( 91.231 GeV) = 0.0958 +/- 0.0032( stat.) +/- 0.0014( syst.), A(FB)(b) ( 92.990 GeV) = 0.1041 +/- 0.0115( stat.) +/- 0.0024( syst.). Combining these results yields the b-quark pole asymmetry A(FB)(b0) = 0.0972 +/- 0.0030( stat.) +/- 0.0014( syst.).
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| 49. |
- Abdallah, J, et al.
(författare)
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Determination of the e(+)e(-)->gamma gamma(gamma) cross-section at LEP 2
- 2004
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 37:4, s. 405-419
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Tidskriftsartikel (refereegranskat)abstract
- A test of the benchmark QED process e(+) e(-) -->gammagamma(gamma) is reported, using the data collected with the DELPHI detector at LEP 2. The data analysed were recorded at centre-of-mass energies ranging from 161 GeV to 208 GeV and correspond to a total integrated luminosity of 656.4 pb(-1). The Born cross-section for the process e(+) e(-)-->gammagamma(gamma) was determined, confirming the validity of QED at the highest energies ever attained in electron-positron collisions. Lower limits on the parameters of a number of possible deviations from QED, predicted within theoretical frameworks expressing physics beyond the Standard Model, were derived.
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| 50. |
- Abdallah, J., et al.
(författare)
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Di-jet production in gamma gamma collisions at LEP2
- 2008
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:58, s. 531-541
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Tidskriftsartikel (refereegranskat)
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