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  • Abdallah, J., et al. (författare)
  • Measurements of CP-conserving trilinear gauge boson couplings WWV (V gamma, Z) in e(+)e(-) collisions at LEP2
  • 2010
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 66:1-2, s. 35-56
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The data taken by DELPHI at centre-of-mass energies between 189 and 209 GeV are used to place limits on the CP-conserving trilinear gauge boson couplings Delta g(1)(Z), lambda(gamma) and Delta k(gamma) associated to W+W- and single W production at LEP2. Using data from the jjl nu, jjjj, jjX and lX final states, where j,l and X represent a jet, a lepton and missing four-momentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: Delta g(1)(Z) =-0.025-(+0.033)(0.030,), lambda(gamma) = 0.002(-0.035)(+0.035) and Delta k(gamma) = 0.024(-0.081)(+0.077). Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by DELPHI.</p>
  • Abdallah, J., et al. (författare)
  • Search for one large extra dimension with the DELPHI detector at LEP
  • 2009
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 60:1, s. 17-23
  • Tidskriftsartikel (refereegranskat)abstract
    • Single photons detected by the DELPHI experiment at LEP2 in the years 1997-2000 are reanalysed to investigate the existence of a single extra dimension in a modified ADD scenario with slightly warped large extra dimensions. The data collected at centre-of-mass energies between 180 and 209 GeV for an integrated luminosity of similar to 650 pb(-1) agree with the predictions of the Standard Model and allow a limit to be set on graviton emission in one large extra dimension. The limit obtained on the fundamental mass scale M-D is 1.69 TeV/c(2) at 95% CL, with an expected limit of 1.71 TeV/c(2).
  • 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.
  • Abdallah, J., et al. (författare)
  • Study of the dependence of direct soft photon production on the jet characteristics in hadronic Z (0) decays
  • 2010
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 67:3-4, s. 343-366
  • Tidskriftsartikel (refereegranskat)abstract
    • An analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behavior to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.
  • Abdallah, J., et al. (författare)
  • Study of triple-gauge-boson couplings ZZZ, ZZ gamma and Z gamma gamma at LEP
  • 2007
  • Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 51:3, s. 525-542
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Neutral triple-gauge-boson couplings ZZZ, ZZγ and Zγγ have been studied with the DELPHI detector using data at energies between 183 and 208 GeV. Limits are derived on these couplings from an analysis of the reactions e<sup>+</sup>e<sup>-</sup>→Zγ, using data from the final states γff̄, with f=q or ν, from e<sup>+</sup>e<sup>-</sup>→ZZ, using data from the four-fermion final states qq̄qq̄, qq̄μ<sup>+</sup>μ<sup>-</sup>, qq̄e<sup>+</sup>e<sup>-</sup>, qq̄νν̄, μ<sup>+</sup>μ<sup>-</sup>νν̄ and e<sup>+</sup>e<sup>-</sup>νν̄, and from e<sup>+</sup>e<sup>-</sup>→Zγ<sup>*</sup>, in which the final state γ is off mass-shell, using data from the four-fermion final states qq̄e<sup>+</sup>e<sup>-</sup> and qq̄μ<sup>+</sup>μ<sup>-</sup>. No evidence for the presence of such couplings is observed, in agreement with the predictions of the Standard Model.</p>
  • Abat, E., et al. (författare)
  • A layer correlation technique for pion energy calibration at the 2004 ATLAS Combined Beam Test
  • 2011
  • Ingår i: Journal of Instrumentation. - IOP Publishing. - 1748-0221. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by between 11% and 25% compared to the resolution at the electromagnetic scale.
  • Abat, E., et al. (författare)
  • Combined performance studies for electrons at the 2004 ATLAS combined test-beam
  • 2010
  • Ingår i: Journal of Instrumentation. - IOP Publishing. - 1748-0221. ; 5
  • Tidskriftsartikel (refereegranskat)abstract
    • In 2004 at the ATLAS (A Toroidal LHC ApparatuS) combined test beam, one slice of the ATLAS barrel detector (including an Inner Detector set-up and the Liquid Argon calorimeter) was exposed to particles from the H8 SPS beam line at CERN. It was the first occasion to test the combined electron performance of ATLAS. This paper presents results obtained for the momentum measurement p with the Inner Detector and for the performance of the electron measurement with the LAr calorimeter (energy E linearity and resolution) in the presence of a magnetic field in the Inner Detector for momenta ranging from 20 GeV/c to 100 GeV/c. Furthermore the particle identification capabilities of the Transition Radiation Tracker, Bremsstrahlungs-recovery algorithms relying on the LAr calorimeter and results obtained for the E/p ratio and a way how to extract scale parameters will be discussed.
  • Abat, E., et al. (författare)
  • Photon reconstruction in the ATLAS Inner Detector and Liquid Argon Barrel Calorimeter at the 2004 Combined Test Beam
  • 2011
  • Ingår i: Journal of Instrumentation. - IOP Publishing. - 1748-0221. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • The reconstruction of photons in the ATLAS detector is studied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS detector was exposed to beams of particles of known energy at the CERN SPS. The results presented show significant differences in the longitudinal development of the electromagnetic shower between converted and unconverted photons as well as in the total measured energy. The potential to use the reconstructed converted photons as a means to precisely map the material of the tracker in front of the electromagnetic calorimeter is also considered. All results obtained are compared with a detailed Monte-Carlo simulation of the test-beam setup which is based on the same simulation and reconstruction tools as those used for the ATLAS detector itself.
  • 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>
  • 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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