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1.
  • 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. - 1434-6044. ; 44:3, s. 311-331
  • 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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2.
  • Abdallah, J., et al. (författare)
  • A measurement of the tau hadronic branching ratios
  • 2006
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 46:1, s. 1-26
  • Tidskriftsartikel (refereegranskat)abstract
    • 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(-) >= 2 pi(0)nu(tau), 2h(-)h(+)upsilon(tau), 2h(-)h(+)>= 2 pi(0)upsilon(tau), 3h(-)2h(+)upsilon(tau) and 3h(-)2h(+) >= 1 pi(0)upsilon(tau)) were measured with data from the DELPHI detector at LEP.
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3.
  • Abdallah, J, et al. (författare)
  • Bose-Einstein correlations in W+W- events at LEP2
  • 2005
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 44:2, s. 161-174
  • Tidskriftsartikel (refereegranskat)abstract
    • Bose-Einstein correlations (BEC) between final state particles in the reaction e(+)e(-) -> W+ W- -> q(1)(q(2)) over barq(3)(q(4)over bar>) over bar) have been studied. Data corresponding to a total integrated luminosity of 550 pb(-1), recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties.
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4.
  • 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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5.
  • Abdallah, J., et al. (författare)
  • Search for excited leptons in e(+)e(-) collisions at root s=189-209 GeV
  • 2006
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 46:2, s. 277-293
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for excited lepton production in e(+)e(-) collisions was performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies ranging from 189 GeV to 209 GeV, corresponding to an integrated luminosity of approximately 600 pb(-1). No evidence for excited lepton production was found. In searches for pair-produced excited leptons, lower mass limits were established in the range 94-103 GeV/c(2), depending on the channel and model assumptions. In searches for singly-produced excited leptons, upper limits on the parameter f/Lambda were established as a function of the mass.
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6.
  • Abdallah, J, et al. (författare)
  • Flavour independent searchesfor hadronically decaying neutral Higgs bosons
  • 2005
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 44:2, s. 147-159
  • 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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7.
  • Abdallah, J., et al. (författare)
  • A determination of the centre-of-mass energy at LEP2 using radiative two-fermion events
  • 2006
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 46:2, s. 295-305
  • Tidskriftsartikel (refereegranskat)abstract
    • Using e(+)e(-) -> mu(+)mu(-)(gamma) and e(+)e(-) -> q (q) over bar(gamma) events radiative to the Z pole, DELPHI has determined the centre-of-mass energy, root s, using energy and momentum constraint methods. The results are expressed as deviations from the nominal LEP centre-of-mass energy, measured using other techniques. The results are found to be compatible with the LEP Energy Working Group estimates for a combination of the 1997 to 2000 data sets.
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8.
  • Abdallah, J..., et al. (författare)
  • Higgs boson searches in CP-conserving and CP-violating MSSM scenarios with the DELPHI detector
  • 2008
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 54:1, s. 1-35
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents the final interpretation of the results from DELPHI on the searches for Higgs bosons in the minimal supersymmetric extension of the Standard Model (MSSM). A few representative scenarios are considered, that include CP conservation and explicit CP violation in the Higgs sector. The experimental results encompass the searches for neutral Higgs bosons at LEP1 and LEP2 in final states as expected in the MSSM, as well as LEP2 searches for charged Higgs bosons and for neutral Higgs bosons decaying into hadrons independent of the quark flavour. The data reveal no significant excess with respect to background expectations. The results are translated into excluded regions of the parameter space in the various scenarios. In the CP-conserving case, these lead to limits on the masses of the lightest scalar and pseudoscalar Higgs bosons, h and A, and on tan beta. The dependence of these limits on the top quark mass is discussed. Allowing for CP violation reduces the experimental sensitivity to Higgs bosons. It is shown that this effect depends strongly on the values of the parameters responsible for CP violation in the Higgs sector.
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9.
  • 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. - 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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10.
  • 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. - 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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