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1.
  • Abreu, P., et al. (författare)
  • Measurement of the gluon fragmentation function and a comparison of the scaling violation in gluon and quark jets
  • 2000
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 13:4, s. 573-589
  • 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..
2.
  • Abreu, P., et al. (författare)
  • Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
  • 2001
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 19:1, s. 15-28
  • 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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3.
  • Abreu, P., et al. (författare)
  • Search for sleptons in e+e- collisions at √s = 183 to 189 GeV
  • 2001
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 19:1, s. 29-42
  • 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.
4.
  • Abdallah, J., et al. (författare)
  • A measurement of the tau hadronic branching ratios
  • 2006
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 46:1, s. 1-26
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The exclusive and semi-exclusive branching ratios of the tau lepton hadronic decay modes (h(-)upsilon(tau), h(-)pi(0)upsilon(tau), h(-)pi(0)pi(0)upsilon(tau), h(-) &gt;= 2 pi(0)nu(tau), 2h(-)h(+)upsilon(tau), 2h(-)h(+)&gt;= 2 pi(0)upsilon(tau), 3h(-)2h(+)upsilon(tau) and 3h(-)2h(+) &gt;= 1 pi(0)upsilon(tau)) were measured with data from the DELPHI detector at LEP.</p>
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5.
  • Abdallah, J., et al. (författare)
  • A study of b(b)over-bar production in e(+)e(-) collisions at root s=130-207 GeV
  • 2009
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 60:1, s. 1-15
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Measurements are presented of R-b, the ratio of the b (b) over bar cross-section to the q (q) over bar cross-section in e(+)e(-) collisions, and the forward-backward asymmetry A(FB)(b) at twelve energy points in the range root s = 130-207 GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.</p>
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6.
  • Abdallah, J., et al. (författare)
  • A study of the b-quark fragmentation function with the DELPHI detector at LEP I and an averaged distribution obtained at the Z Pole
  • 2011
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 71:2, s. 1557
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The nature of b-quark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying b-hadrons, E-B(weak). The average value of x(B)(weak) = E-B(weak)/E-beam is measured to be 0.699 +/- 0.011. The resulting x(B)(weak) distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of b-hadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA 6.156 from DELPHI data: a = 1.84(-0.21)(+0.23) and b = 0.642(-0.063)(+0.073) GeV-2, with a correlation factor rho = 92.2%. Combining the data on the b-quark fragmentation distributions with those obtained at the Z peak by ALEPH, OPAL and SLD, the average value of x(B)(weak) is found to be 0.7092 +/- 0.0025 and the non-perturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a = 1.48(-0.10)(+0.11) and b = 0.509(-0.023)(+0.024) GeV-2, with a correlation factor rho = 92.6%.</p>
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7.
  • Abdallah, J., et al. (författare)
  • Investigation of colour reconnection in WW events with the DELPHI detector at LEP-2
  • 2007
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 51:2, s. 249-269
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>In the reaction e(+)e(-) -&gt; WW -&gt; (q(1) (q) over bar (2))(q(3)(q) over bar (4)) the usual hadronization models treat the colour singlets q(1)(q) over bar (2) and q(3)(q) over bar (4) coming from two W bosons independently. However, since the. nal state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This e. ect is known as colour reconnection. In this article the results of the investigation of colour reconnection e. ects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle. ow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its. parameter most compatible with the data was found to be: (SK)-S-kappa-I = 2.2(-1.3) (+2.5) corresponding to the probability of reconnection P-reco to be in the range 0.31 &lt; P-reco &lt; 0.68 at 68% confidence level with its best value at 0.52.</p>
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8.
  • Abdallah, J., et al. (författare)
  • Masses, lifetimes and production rates of Xi(-) and Xi(+) at LEP 1
  • 2006
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 639:3-4, s. 179-191
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Measurements of the Xi(-) and (Xi) over bar (+) masses, mass differences, lifetimes and lifetime differences are presented. The (Xi) over bar (+) sample used is much larger than those used previously for such measurements. In addition, the S production rates in Z -&gt; b (b) over bar and Z -&gt; q (q) over bar events are compared and the position xi* of the maximum of the distribution in Z -&gt; q (q) over bar events is measured.</p>
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9.
  • Abdallah, J., et al. (författare)
  • Measurement of the electron structure function F-2(e) at LEP energies
  • 2014
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 737, s. 39-47
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The hadronic part of the electron structure function F-2(e) has been measured for the first time, using e(+)e(-) data collected by the DELPHI experiment at LEP, at centre-of-mass energies of root s = 91.2-209.5 GeV. The data analysis is simpler than that of the measurement of the photon structure function. The electron structure function F-2(e) data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the contribution of large target photon virtualities is significant. The data presented can serve as a cross-check of the photon structure function F-2(gamma) analyses and help in refining existing parameterisations.</p>
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10.
  • Abdallah, J., et al. (författare)
  • Measurement of the mass and width of the W boson in e(+) e(-) collisions at root s=161-209 GeV
  • 2008
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 55:1, s. 1-38
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996-2000). The data sample has an integrated luminosity of 660 pb(-1) and was collected over a range of centre-of-mass energies from 161 to 209 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W- -&gt; l (nu) over bar (l) and W+W- -&gt; q (q) over bar'(q) over barq'channels. The W mass result for the combined data set is M-W = 80.336 +/- 0.055(Stat.) +/- 0.028(Syst.) +/- 0.025(FSI) +/- 0.009(LEP) GeV/c(2) , where FSI represents the uncertainty due to final state interaction effects in the q (q) over bar'(q) over barq' channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is Gamma(W) = 2.404 +/- 0.140(Stat.) +/- 0.077(Syst.) +/- 0.065(FSI) GeV/c(2). These results supersede all values previously published by the DELPHI collaboration.</p>
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