| 1. |
- Abdallah, J, et al.
(author)
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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
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:3, s. 307-324
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Journal article (peer-reviewed)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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| 2. |
- Abdallah, J, et al.
(author)
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A precise measurement of the tau lifetime
- 2004
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 36:3, s. 283-296
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Journal article (peer-reviewed)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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| 3. |
- Abdallah, J, et al.
(author)
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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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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 29:3, s. 285-312
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Journal article (peer-reviewed)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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| 4. |
- Abdallah, J, et al.
(author)
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Determination of the e(+)e(-)->gamma gamma(gamma) cross-section at LEP 2
- 2004
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 37:4, s. 405-419
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Journal article (peer-reviewed)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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| 5. |
- Abdallah, J, et al.
(author)
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Final results from DELPHI on the searches for SM and MSSM neutral Higgs bosons
- 2004
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 32:2, s. 145-183
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Journal article (peer-reviewed)abstract
- These final results from DELPHI searches for the Standard Model (SM) Higgs boson, together with benchmark scans of the Minimal Supersymmetric Standard Model (MSSM) neutral Higgs bosons, used data taken at centre-of-mass energies between 200 and 209 GeV with a total integrated luminosity of 224 pb(-1). The data from 192 to 202 GeV are reanalysed with improved b-tagging for MSSM final states decaying to four b-quarks. The 95% confidence level lower mass bound on the Standard Model Higgs boson is 114.1 GeV/c(2). Limits are also given on the lightest scalar and pseudo-scalar Higgs bosons of the MSSM.
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| 6. |
- Abdallah, J, et al.
(author)
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Measurement of the e(+)e(-)-> W+W- gamma cross-section and limits on anomalous quartic gauge couplings with DELPHI
- 2003
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 31:2, s. 139-147
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Journal article (peer-reviewed)abstract
- W(+)W(-)gamma production at LEP2 is studied using data collected with the DELPHI detector at centre-of-mass energies between 189 GeV and 209 GeV, corresponding to an integrated luminosity of about 600 pb(-1). Cross-sections are measured for the production of W+W- with a hard, central and isolated photon in the final state, and are found to be compatible with the Standard Model prediction. The photon energy spectra are used to derive limits on anomalous contributions to the W(+)W(-)Z(o)gamma and W(+)W(-)gammagamma vertices.
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| 7. |
- Abdallah, J, et al.
(author)
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Measurement of the forward-backward asymmetries of e(+)e(-)-> Z -> b(b)over-bar and e(+)e(-)-> Z -> c(c)over-bar using prompt leptons
- 2004
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 109-125
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Journal article (peer-reviewed)abstract
- The forward-backward asymmetries of the processes e(+) e(-) --> Z --> b (b) over bar and e(+)e(-) --> Z --> c (c) over bar were measured from a sample of hadronic Z decays collected by the DELPHI experiment between 1993 and 1995. Enriched samples of b (b) over bar and c (c) over bar events were obtained using lifetime information. The tagging of b and c quarks in these samples was based on the semileptonic decay channels b/c --> X + mu and b/c --> X + e combined with charge flow information from the hemisphere opposite to the lepton. Combining the A(FB)(b (b) over bar) and A(FB)(c (c) over bar) measurements presented in this paper with published results based on 1991 and 1992 DELPHI data samples, the following pole asymmetries were obtained: A(FB)(0,b) = 0.1021 +/- 0.0052 (stat) +/- 0.0024 (syst) A(FB)(0,c) = 0.0728 +/- 0.0086 (stat) +/- 0.0063 (syst) The effective value of the weak mixing angle derived from these measurements is sin(2) theta(W,eff)(lept) = 0.23170 +/- 0.00097.
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| 8. |
- Abdallah, J, et al.
(author)
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Measurement of the W-pair production cross-section and W branching ratios in e(+)e(-) collisions at root s=161-209 GeV
- 2004
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 127-144
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Journal article (peer-reviewed)abstract
- These final results on e(+) e(-) W+ W- production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |V-cs| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.
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| 9. |
- Abdallah, J, et al.
(author)
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Measurement of vertical bar Vcb vertical bar using the semileptonic decay (B)d(0))over-bar -> D*+l(-)(nu)over-barl
- 2004
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:2, s. 213-232
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Journal article (peer-reviewed)abstract
- Data from Z decays in DELPHI have been searched for <(B-d(o))over bar> --> D*+ l(-) (ν) over bar (l) with the D*+ decaying to D(0)pi(+) and D-0 --> K(-)pi(+), K(-)pi(+)pi(+)pi(-) or K- pi(+)(pi(0)). These events are used to measure the CKM matrix element V-cb and the form factor slope, rho(A1)(2): F-D*(1) V-cb = 0.0392 +/- 0.0018 +/- 0.0023; rho(A1)(2) = 1.32 +/- 0.15 +/- 0.33 corresponding to a branching fraction: BR(<(B-d(0))over bar> --> D(*+)l(-)(ν) over bar (l)) = (5.90 +/- 0.22 +/- 0.50)%. Combining these and previous DELPHI measurements gives: FD*(1)V-cb = 0.0377 +/- 0.0011 +/- 0.0019, rho(A1)(2) = 1.39 +/- 0.10 +/- 0.33 and BR(<(B-d(0))over bar> --> D(*+)l(-)(ν) over bar (l)) = (5.39 +/- 0.11 +/- 0.34)% Using F-D*(1) = 0.91 +/- 0.04, yields: V-cb = 0.0414 +/- 0.0012(stat.) +/- 0.0021(syst.) +/- 0.0018 (theory). The b-quark semileptonic branching fraction into a D*+ emitted from higher mass charmed excited states has also been measured to be: BR(b --> D*+ Xl(-)(ν) over bar (l)) = (0.67 +/- 0.08 +/- 0.10)%.
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| 10. |
- Abdallah, J, et al.
(author)
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Search for an LSP gluino at LEP with the DELPHI detector
- 2003
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 26:4, s. 505-525
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Journal article (peer-reviewed)abstract
- In some supersymmetric models, the gluino ((g) over tilde) is predicted to be light and stable. In that case, it would hadronize to form R-hadrons. In these models, the missing energy signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved. Therefore, such a gluino is not constrained by hadron collider results, which looked for the decay (g) over tilde --> q (q) over bar(χ) over tilde (0)(1). Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for q (q) over bar(gg) over tilde events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c(2) is excluded at the 95% confidence level in these models. Then, R-hadrons produced in the squark decays were searched for in the data collected by DELPHI at the centre-of-mass energies of 189 to 208 GeV, corresponding to an overall integrated luminosity of 609 pb(-1). The observed number of events is in agreement with the Standard Model predictions. Limits at 95% confidence level are derived on the squark masses from the excluded regions in the plane (m((q) over tilde1),m((g) over bar)): m((t) over tilde1) > 90 GeV/c(2) and m((b) over tilde1) > 96 GeV/c(2) for purely left squarks. m((t) over tilde1) > 87 GeV/c(2) and m((b) over tilde1) > 82 GeV/c(2) independent of the mixing angle.
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