| 31. |
- Abdallah, J, et al.
(författare)
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Photon events with missing energy in e(+)e(-) collisions at root s=130 to 209 GeV
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 38:4, s. 395-411
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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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| 32. |
- Abdallah, J., et al.
(författare)
-
Single intermediate vector boson production in e(+)e(-) collisions at root s=183-209 GeV
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 45:2, s. 273-289
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Tidskriftsartikel (refereegranskat)abstract
- The production of single charged and neutral intermediate vector bosons in e(+)e(-) collisions has been studied in the data collected by the DELPHI experiment at LEP at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 640 pb(-1). The measured cross-sections for the reactions, determined in limited kinematic regions, are in agreement with the Standard Model predictions.
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| 33. |
- Abdallah, J, et al.
(författare)
-
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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| 34. |
- Abdallah, J, et al.
(författare)
-
Determination of heavy quark non-perturbative parametersfrom spectral moments in semileptonic B decays
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 45:1, s. 35-59
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Tidskriftsartikel (refereegranskat)abstract
- Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of vertical bar V-cb vertical bar from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: m(b)(1 GeV) = 4.591 +/- 0.062 +/- 0.039 +/- 0.005 GeV/c(2), m(c)(1 GeV) = 1.170 +/- 0.093 +/- 0.055 +/- 0.005 GeV/c(2), m(pi)(2) (1 GeV) = 0.399 +/- 0.048 +/- 0.034 +/- 0.087 GeV2, (p) over tilde (3)(D) = 0.053 +/- 0.017 +/- 0.011 +/- 0.026 GeV3, and include corrections at order 1/m(b)(3). Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of vertical bar V-cb vertical bar is obtained: vertical bar V-cb vertical bar = 0.0421 x (1 +/- 0.014 (meas center dot) +/- 0.014 (fit) +/- 0.015 (th center dot)).
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| 35. |
- Abdallah, J, et al.
(författare)
-
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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| 36. |
- Abdallah, J, et al.
(författare)
-
Search for eta(b) in two-photon collisions at LEP II with the DELPHI detector
- 2006
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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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| 37. |
- Abdallah, J, et al.
(författare)
-
Production of Xi(0)(c) and Xi(b) in Z decays and lifetime measurement of Xi(b)
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:44, s. 299-309
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Tidskriftsartikel (refereegranskat)abstract
- The charmed strange baryon Xi(c)(0) was searched for in the decay channel Xi(c)(0) -> Xi(-)pi(+), and the beauty strange baryon Xi(b) in the inclusive channel Xi(b) -> Xi(-)l(-)(nu) over barX, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992-1995. The Xi(-) was reconstructed through the decay AT, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Xi(c)(0) and Xi(b) selection. The production rates were measured to be f(Xi c)(0) x BR(Xi(c)(0) -> Xi(-)pi(+) = (4.7 +/- 1.4(stat.) +/- 1.1(syst.)) x 10(-4) per hadronic Z decay, and BR(b -> Xi(b))xBR(Xi(b) -> Xi(-)l(-)X) = (3.0 +/- 1.0(stat.) +/- 0.3(syst.)) x 10(-4) for each lepton species (electron or muon). The lifetime of the Xi(b) baryon was measured to be tau(Xi b) = 1.45(-0.43)(+0.55)(stat.)+/- 0.13(syst.) ps. A combination with the previous DELPHI lifetime measurement gives tau(Xi b) = 1.48(-0.31)(+0.40)(stat.)+/- 0.12(syst.) ps.
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| 38. |
- Abdallah, J, et al.
(författare)
-
Charged particle multiplicity in three-jet events and two-gluon systems
- 2005
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:44, s. 311-331
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Tidskriftsartikel (refereegranskat)abstract
- The charged particle multiplicity in hadronic three-jet events from Z decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio C-A/C-F with the result C-A/C-F = 2.261 +/- 0.014(stat). +/- 0.036(exp). +/- 0-066(theo). in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios r = N-gg(s)/Ng (g) over bar (s) of the gluon and quark multiplicities and r((1)) = N'(gg)(s)/N'g (g) over bar (s) of their derivatives are compared with perturbative calculations. While a good agreement between calculations and data is observed for r((1)), larger deviations are found for r indicating that non-perturbative effects are more important for r than for r((1)).
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