| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Aaron, F. D., et al.
(författare)
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Multi-leptons with high transverse momentum at HERA
- 2009
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :10
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Tidskriftsartikel (refereegranskat)abstract
- Events with at least two high transverse momentum leptons (electrons or muons) are studied using the H1 and ZEUS detectors at HERA with an integrated luminosity of 0.94 fb(-1). The observed numbers of events are in general agreement with the Standard Model predictions. Seven di- and tri-lepton events are observed in e(+)p collision data with a scalar sum of the lepton transverse momenta above 100 GeV while 1.94 +/- 0.17 events are expected. Such events are not observed in e(-)p collisions for which 1.19 +/- 0.12 are predicted. Total visible and differential di-electron and di-muon photoproduction cross sections are extracted in a restricted phase space dominated by photon-photon collisions.
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| 3. |
- Abdallah, J., et al.
(författare)
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Study of double-tagged gamma gamma events at LEPII
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 46:3, s. 559-568
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Tidskriftsartikel (refereegranskat)abstract
- Double-tagged interactions of photons with virtualities Q(2) between 10 GeV2 and 200 GeV2 are studied with the data collected by DELPHI at LEPII from 1998 to 2000, corresponding to an integrated luminosity of 550 pb(-1). The gamma*gamma* -> mu(+)mu(-) data agree with QED predictions. The cross-section of the reaction gamma*gamma* -> hadrons is measured and compared to the LO and NLO BFKL calculations.
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| 4. |
- Abdallah, J., et al.
(författare)
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A determination of the centre-of-mass energy at LEP2 using radiative two-fermion events
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 46:2, s. 295-305
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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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| 5. |
- Abdallah, J., et al.
(författare)
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Determination of the b quark mass at the M-Z scale with the DELPHI detector at LEP
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 46:3, s. 569-583
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of the normalized three-jet rate of b quark events with respect to light quarks events (light = l equivalent to u, d, s) has been performed using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are found to agree with theoretical predictions treating mass corrections at next-to-leading order. Measurements of the b quark mass have also been performed for both the b pole mass: M-b and the b running mass: m(b)(M-Z). Data are found to be better described when using the running mass. The measurement yields: m(b)(M-Z) = 2.85 +/- 0.18(stat) +/- 0.13(exp) +/- 0.19(had) +/- 0.12(theo) GeV/c(2). for the CAMBRIDGE algorithm. This result is the most precise measurement of the b mass derived from a high energy process. When compared to other b mass determinations by experiments at lower energy scales, this value agrees with the prediction of quantum chromodynamics for the energy evolution of the running mass. The mass measurement is equivalent to a test of the flavour independence of the strong coupling constant with an accuracy of 7 parts per thousand.
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| 6. |
- Aaron, F. D., et al.
(författare)
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Measurement of isolated photon production in deep-inelastic scattering at HERA
- 2008
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 54:3, s. 371-387
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Tidskriftsartikel (refereegranskat)abstract
- The production of isolated photons in deep-inelastic scattering ep -> e gamma X is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared 4 < Q(2)< 150 GeV2 and a mass of the hadronic system W-X > 50 GeV. The analysis is based on a total integrated luminosity of 227 pb(-1). The production cross section of isolated photons with a transverse energy in the range 3 < E-T(gamma)< 10 GeV and pseudorapidity range -1.2
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| 7. |
- Aaron, F. D., et al.
(författare)
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Three- and four-jet production at low x at HERA
- 2008
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 54:3, s. 389-409
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Tidskriftsartikel (refereegranskat)abstract
- Three- and four-jet production is measured in deep-inelastic ep scattering at low x and Q(2) with the H1 detector using an integrated luminosity of 44.2 pb(-1). Several phase space regions are selected for the three-jet analysis in order to study the underlying parton dynamics from global topologies to the more restrictive regions of forward jets close to the proton direction. The measurements of cross sections for events with at least three jets are compared to fixed order QCD predictions of O(alpha(2)(s)) and O(alpha(3)(s)) and with Monte Carlo simulation programs where higher order effects are approximated by parton showers. A good overall description is provided by the O(alpha(3)(s)) calculation. Too few events are predicted at the lowest x similar to 10(-4), especially for topologies with two forward jets. This hints to large contributions at low x from initial state radiation of gluons close to the proton direction and unordered in transverse momentum. The Monte Carlo program in which gluon radiation is generated by the colour dipole model gives a good description of both the three- and the four-jet data in absolute normalisation and shape.
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| 8. |
- Abdallah, J, et al.
(författare)
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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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| 9. |
- Abdallah, J., et al.
(författare)
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Di-jet production in gamma gamma collisions at LEP2
- 2008
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:58, s. 531-541
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Abdallah, J, et al.
(författare)
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Flavour independent searchesfor hadronically decaying neutral Higgs bosons
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 44:2, s. 147-159
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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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