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1.
  • Abdallah, J., et al. (författare)
  • Search for a fourth generation b '-quark at LEP-II at root s=196-209GeV
  • 2007
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 50:3, s. 507-518
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A search for the pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb(-1). No evidence for a signal was found. Upper limits on BR(b'-&gt; bZ) and BR(b'-&gt; bZ) were obtained for b' masses ranging from 96 to 103 GeV/c(2) stop. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of R-CKM=vertical bar V-cb(') /V-tb'V-tb vertical bar there V-cb', V-tb' and V-tb are elements of the extended CKM matrix.</p>
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2.
  • Abdallah, J, et al. (författare)
  • Correlations between polarisation states of W particles in the reaction e(-)e(+)-&gt; W-W+ at LEP2 energies 189-209 GeV
  • 2009
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 63:4, s. 611-623
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>In a study of the reaction e(-)e(+)-&gt; W-W+ with the DELPHI detector, the probabilities of the two W particles occurring in the joint polarisation states transverse-transverse (T T), longitudinal-transverse plus transverse-longitudinal (LT) and longitudinal-longitudinal (LL) have been determined using the final states WW -&gt; lvq (q) over bar (l = e, mu). The two-particle joint polarisation probabilities, i.e. the spin density matrix elements rho T T, rho LT, rho LL, are measured as functions of the W- production angle, theta(W-), at an average reaction energy of 198.2 GeV. Averaged over all cos.W-, the following joint probabilities are obtained: (rho) over barT T = (67 +/- 8)%, (rho) over barL T = (30 +/- 8)%, (rho) over barL T = (3 +/- 7)%. These results are in agreement with the Standard Model predictions of 63.0%, 28.9% and 8.1%, respectively. The related polarisation cross-sections sigma(TT), sigma(LT) and sigma(LL) are also presented.</p>
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3.
  • Abdallah, J., et al. (författare)
  • Evidence for an excess of soft photons in hadronic decays of Z(0)
  • 2006
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 47:2, s. 273-294
  • Tidskriftsartikel (refereegranskat)abstract
    • Soft photons inside hadronic jets converted in front of the DELPHI main tracker (TPC) in events of qq disintegrations of the Z(0) were studied in the kinematic range 0.2 < E-y < I GeV and transverse momentum with respect to the closest jet direction P-T < 80 MeV/c. A clear excess of photons in the experimental data as compared to the Monte Carlo predictions is observed. This excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/- 0.27) x 10(-3) gamma/jet in the specified kinematic region, while the expected level of the inner hadronic bremsstrahlung (which is not included in the Monte Carlo) is (0.340 +/- 0.001 +/- 0.038) X 10(-3) gamma/jet. The ratio of the excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8), which is similar in strength to the anomalous soft photon signal observed in fixed target experiments with hadronic beams.
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4.
  • Abdallah, J, et al. (författare)
  • Inclusive single-particle production in two-photon collisions at LEP II with the DELPHI detector
  • 2009
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 678:5, s. 444-449
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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.</p>
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5.
  • Abdallah, J., et al. (författare)
  • Measurement of the tau lepton polarisation at LEP2
  • 2008
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 659:1-2, s. 65-73
  • Tidskriftsartikel (refereegranskat)abstract
    • A first measurement of the average polarisation P-tau of tau leptons produced in e(+)e(-) annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value P-tau = -0.164 +/- 0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV. (c) 2007 Elsevier B.V. All rights reserved.
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6.
  • Abdallah, J, et al. (författare)
  • Observation of the muon inner bremsstrahlung at LEP1
  • 2008
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 57:3, s. 499-514
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>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&lt; E-gamma &lt;= 1 GeV and transverse momentum with respect to the parent muon p(T) &lt; 40 MeV/c, and 1&lt; E-gamma &lt;= 10 GeV and pT &lt; 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&lt; E-gamma &lt;= 1 GeV and 1.04 +/- 0.09 +/- 0.12 in the photon energy range 1&lt; E-gamma &lt;= 10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.</p>
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7.
  • Abdallah, J., et al. (författare)
  • Search for a fourth generation b '-quark at LEP-II at root s=196-209GeV
  • 2007
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 50:3, s. 507-518
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for the pair production of fourth generation b'-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb(-1). No evidence for a signal was found. Upper limits on BR(b'-> bZ) and BR(b'-> bZ) were obtained for b' masses ranging from 96 to 103 GeV/c(2) stop. These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of R-CKM=vertical bar V-cb(') /V-tb'V-tb vertical bar there V-cb', V-tb' and V-tb are elements of the extended CKM matrix.
  •  
8.
  • Abdallah, J., et al. (författare)
  • Search for pentaquarks in the hadronic decays of the Z boson with the DELPHI detector at LEP
  • 2007
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 653:2-4, s. 151-160
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The quark model does not exclude states composed of more than three quarks, like pentaquark systems. Controversial evidence for such states has been published in the last years, in particular: for a strange pentaquark Theta(1540)(+); for a double-strange state, the Xi(1862)(--), subsequently called Phi(1860)--; and for a charmed state, the Theta(c)(3100)(0). If confirmed, a full pentaquark family might exist; such pentaquark states could be produced in e(+)e(-) annihilations near the Z energy. In this Letter a search for pentaquarks is described using the DELPHI detector at LEP, characterized by powerful particle identification sub-systems crucial in the separation of the signal from the background for these states. At 95% CL, upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N-Theta+ x Br(Theta(+) -&gt; pK(S)(0)) &lt; 5.1 x 10(-4), N Theta++ &lt; 1.6 x 10(-3), N Phi(1860)-- x Br((P(1860)-- -&gt; Xi(-)pi(-)) &lt; 2.9 x 10(-4), N-Theta c(3100)0 x Br(Theta(c)(3100)(0) -&gt; D*(+)p) &lt; 8.8 x 10(-4).</p>
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9.
  • Abdallah, J., et al. (författare)
  • Search for single top quark production via contact interactions at LEP2
  • 2011
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 71:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Single top quark production via four-fermion contact interactions associated to flavour-changing neutral currents was searched for in data taken by the DELPHI detector at LEP2. The data were accumulated at centre-of-mass energies ranging from 189 to 209 GeV, with an integrated luminosity of 598.1 pb(-1). No evidence for a signal was found. Limits on the energy scale Lambda, were set for scalar-, vector- and tensor-like coupling scenarios.
10.
  • Abdallah, J., et al. (författare)
  • Search for single top quark production via contact interactions at LEP2
  • 2011
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 71:2, s. 1555
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Single top quark production via four-fermion contact interactions associated to flavour-changing neutral currents was searched for in data taken by the DELPHI detector at LEP2. The data were accumulated at centre-of-mass energies ranging from 189 to 209 GeV, with an integrated luminosity of 598.1 pb(-1). No evidence for a signal was found. Limits on the energy scale Lambda, were set for scalar-, vector- and tensor-like coupling scenarios.</p>
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