| 41. |
- Abdallah, J, et al.
(författare)
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Flavour independent searchesfor hadronically decaying neutral Higgs bosons
- 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. 147-159
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes flavour independent searches for hadronically decaying neutral Higgs bosons in the data collected by the DELPHI experiment at LEP, at centre-of-mass energies between 189 and 209 GeV. The collected data-set corresponds to an integrated luminosity of around 610 pb(-1). The e(+)e(-) -> hA and e(+)e(-) -> hZand processes are considered, with direct Higgs boson decays into hadrons. No evidence for Higgs boson production is found, and cross-section limits are set as a function of the Higgs boson masses. No explicit assumptions are made on the underlying physics beyond the Standard Model, allowing interpretation of the data in a large class of models.
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| 42. |
- Abdallah, J, et al.
(författare)
-
Inclusive single-particle production in two-photon collisions at LEP II with the DELPHI detector
- 2009
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 678:5, s. 444-449
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Tidskriftsartikel (refereegranskat)abstract
- A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle p(T) distribution and the differential charged hadrons d sigma/dp(T) cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results. (C) 2009 Elsevier B.V. All rights reserved.
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| 43. |
- Abdallah, J, et al.
(författare)
-
Measurement of the energy dependence of hadronic jet rates and the strong coupling alpha(s) from the four-jet rate with the DELPHI detector at LEP
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 413-426
-
Tidskriftsartikel (refereegranskat)abstract
- Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 GeV to 209 GeV are selected, their jet rates are determined and compared to predictions of four different event generators. One of them is the recently developed APACIC++ generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure alpha(s) in the next-to-leading-order approximation yielding alpha(s)(M-Z(2)) = 0.1175 +/- 0.0030. The running of alpha(s) determined by using four-jet events has been tested. The logarithmic energy slope is measured to be dalpha(s)(-1)/d log E-cm = 1.14 +/- 0.36. Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI alpha(s) measurements using event shape distributions.
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| 44. |
- Abdallah, J, et al.
(författare)
-
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
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 109-125
-
Tidskriftsartikel (refereegranskat)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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| 45. |
- Abdallah, J, et al.
(författare)
-
Measurement of the W-pair production cross-section and W branching ratios in e(+)e(-) collisions at root s=161-209 GeV
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 34:2, s. 127-144
-
Tidskriftsartikel (refereegranskat)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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| 46. |
- Abdallah, J, et al.
(författare)
-
Measurement of vertical bar Vcb vertical bar using the semileptonic decay (B)d(0))over-bar -> D*+l(-)(nu)over-barl
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 33:2, s. 213-232
-
Tidskriftsartikel (refereegranskat)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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| 47. |
- Abdallah, J, et al.
(författare)
-
Observation of the muon inner bremsstrahlung at LEP1
- 2008
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:57, s. 499-514
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Tidskriftsartikel (refereegranskat)abstract
- Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2< E-gamma <= 1 GeV and transverse momentum with respect to the parent muon p(T) < 40 MeV/c, and 1< E-gamma <= 10 GeV and pT < 80 MeV/c. A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic Z(0) decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06 +/- 0.12 +/- 0.07 in the photon energy range 0.2< E-gamma <= 1 GeV and 1.04 +/- 0.09 +/- 0.12 in the photon energy range 1< E-gamma <= 10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.
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| 48. |
- Abdallah, J, et al.
(författare)
-
Photon events with missing energy in e(+)e(-) collisions at root s=130 to 209 GeV
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 395-411
-
Tidskriftsartikel (refereegranskat)abstract
- The production of single- and multi-photon events has been studied in the reaction e(+) e(-) --> gamma(gamma) + invisible particles. The data collected with the DELPHI detector during the years 1999 and 2000 at centre-of-mass energies between 191 GeV and 209 GeV was combined with earlier data to search for phenomena beyond the Standard Model. The measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the Standard Model processes was used to set limits on new physics. Both model-independent searches and searches for new processes predicted by supersymmetric and extra-dimensional models have been made. Limits on new non-standard model interactions between neutrinos and electrons were also determined.
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| 49. |
- Abdallah, J, et al.
(författare)
-
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
-
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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| 50. |
- Abdallah, J, et al.
(författare)
-
Search for B-s(0)-(B-s(0))over-bar oscillations in DELPHI using high-p(t) leptons
- 2004
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 35:1, s. 35-52
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Tidskriftsartikel (refereegranskat)abstract
- Oscillations in the B-s(0)- <(B-s(0))over bar> system were studied in events selected from about 4.3 million hadronic Z(0) decays registered by DELPHI between 1992 and 2000. This paper presents updates of two published analyses ([11, 12]). The first analysis, which utilizes leptons emitted with large momentum transverse to a jet, was improved by means of a better algorithm for the vertex reconstuction and a new algorithm for flavour-tagging at production time. The second analysis, which utilizes D-s-lepton events, was improved by optimizing the treatment of proper time resolution. No signal of B-s(0) oscillations was observed and limits on the mass difference between the physical B-s(0) states were obtained to be: Deltam(s)>8.0 ps-1 at the 95% C.L. with a sensitivity of Deltam(s)= 9.1 ps(-1) in the high p(t) lepton analysis and Deltam(s)>4.9 ps(-1) at the 95% C.L. with a sensitivity of Deltam(s)=8.6 ps(-1) in the D-s-lepton analysis. Previously published results on these analyses are superseded. The combination of these results with those obtained in other independent analyses previously performed in DELPHI (D-s-hadron, exclusive B-s(0), inclusive vertex) gives: Deltam(s)>8.5 ps(-1) at the 95% C.L. with a sensitivity of Deltam(s)=12.0 ps(-1).
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