| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Abreu, P, et al.
(författare)
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A measurement of alpha(s) from the scaling violation in e(+)e(-) annihilation
- 1997
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 398:1-2, s. 194-206
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z(0) decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at e
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Abreu, P, et al.
(författare)
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A precise measurement of the B-d(0) meson lifetime using a new technique
- 1997
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Ingår i: ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. - : SPRINGER VERLAG. - 0170-9739. ; 74:1, s. 19-32
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z(0) decays, a measurement of the <(B-d(0))over bar> meson lifetime, based on the inclusive reconstruction of 3520 +/- 150 semileptonic decays of the type <(B-d(
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| 10. |
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| 11. |
- Abreu, P, et al.
(författare)
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A search for eta '(c) production in photon-photon fusion at LEP
- 1998
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 441:1-4, s. 479-490
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A search for the production of the eta(c)' meson, the first radial excitation of the ground state of charmonium eta(c)(2980), in the photon-photon fusion reaction at LEP has been performed using the data collected by the DELPHI detector during 1992-1996.
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| 12. |
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| 13. |
- Abreu, P, et al.
(författare)
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A study of the hadronic resonance structure in the decay tau -> 3 pi nu(tau)
- 1998
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 426:3-4, s. 411-427
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The hadronic structure of the decay of the tau lepton to three charged particles, tau --> 3 pi nu(tau), is studied using data collected by the DELPHI detector at LEP between 1992 and 1995. The invariant mass of the 3 pi system, m(3 pi), is fitted using th
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| 14. |
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| 15. |
- Abreu, P, et al.
(författare)
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An upper limit for Br(Z(0)->ggg) from symmetric 3-jet Z(0) hadronic decays
- 1996
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 389:2, s. 405-415
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- An upper limit for BR(Z(0) --> 3g) is obtained from a correlation method, which distinguishes statistically between quark and gluon jets by using the difference in their charged particle multiplicity distributions. From the sample of threefold symmetric t
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| 16. |
- ABREU, P, et al.
(författare)
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B-ASTERISK PRODUCTION IN Z-DECAYS
- 1995
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Ingår i: ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. ; 68:3
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 17. |
- Abreu, P, et al.
(författare)
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Charged particle multiplicity in e(+)e(-) interactions at root s=130 GeV
- 1996
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 372:1-2, s. 172-180
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be [n(ch)] = 23.84 +/- 0.51(stat) +/- 0.52(syst), When compared to lower energy data, the value measured is
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| 18. |
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| 19. |
- Abreu, P, et al.
(författare)
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Cross-sections and leptonic forward-backward asymmetries from the Z(0) running of LEP
- 2000
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Ingår i: EUROPEAN PHYSICAL JOURNAL C. - : SPRINGER-VERLAG. - 1434-6044. ; 16:3, s. 371-405
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Tidskriftsartikel (refereegranskat)abstract
- During 1993 and 1995 LEP was run at 3 energies near the Z(0) peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP operated only at the Z(0) peak. In total DELPHI accumulated data corresponding to an integrat
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| 20. |
- Abreu, P, et al.
(författare)
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Determination of the average lifetime of b-baryons
- 1996
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Ingår i: ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. - : SPRINGER VERLAG. - 0170-9739. ; 71:2, s. 199-210
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The average lifetime of b-baryons has been studied using 3 x 10(6) hadronic Z(0) decays collected by the DELPHI detector at LEP. Three methods have been used, based on the measurement of different observables: the proper decay time distribution of 206 ver
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| 21. |
- Abreu, P, et al.
(författare)
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Determination of vertical bar V-cb vertical bar from the semileptonic decay B-0->D*(-)l(+)nu
- 1996
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Ingår i: ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. - : SPRINGER VERLAG. - 0170-9739. ; 71:4, s. 539-553
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Semileptonic decays B --> D*(-)l(+)nu X were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*(-)pi(+) states was performed and t
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| 22. |
- Abreu, P, et al.
(författare)
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First evidence for a charm radial excitation, D-*'
- 1998
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 426:1-2, s. 231-242
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Using D*+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66 +/- 14(stat.) events is observed in the D(*+)pi(+)pi(-) final state with a mass of 2637 +/- 2(stat.) +/- 6(syst.) MeV/c(2) and a full width smaller than 15 MeV/c(2)
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| 23. |
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| 24. |
- Abreu, P, et al.
(författare)
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First measurement of f'(2)(1525) production in Z(0) hadronic decays
- 1996
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 379:1-4, s. 309-318
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The inclusive production of the f(2)'(1525) in hadronic Z(0) decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f(2)'(1525) --> K+K-. The av
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| 25. |
- Abreu, P, et al.
(författare)
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Identified particles in quark and gluon jets
- 1997
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Ingår i: PHYSICS LETTERS B. - : ELSEVIER SCIENCE BV. - 0370-2693. ; 401:1-2, s. 118-130
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K+, K-0, p, Lambda and their antiparticles in gluon and quark jets.
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