| 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. |
- Abat, E., et al.
(författare)
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Study of the response of the ATLAS central calorimeter to pions of energies from 3 to 9 GeV
- 2009
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002 .- 1872-9576. ; 607:2, s. 372-386
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Tidskriftsartikel (refereegranskat)abstract
- A fully instrumented slice of the ATLAS central detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. in this paper, the response of the central calorimeters to pions with energies in the range between 3 and 9 GeV is presented. The linearity and the resolution of the combined calorimetry (electromagnetic and hadronic calorimeters) was measured and compared to the prediction of a detector simulation program using the toolkit Geant 4. (C) 2009 Elsevier B.V. All rights reserved.
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| 3. |
- Aktas, A, et al.
(författare)
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A determination of electroweak parameters at HERA
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 632:1, s. 35-42
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Tidskriftsartikel (refereegranskat)abstract
- Using the deep inelastic e(+) p and e(-) p charged and neutral current scattering cross sections previously published, a combined electroweak and QCD analysis is performed to determine electroweak parameters accounting for their correlation with parton distributions. The data used have been collected by the HI experiment in 1994-2000 and correspond to an integrated luminosity of 117.2 pb(-1). A measurement is obtained of the W propagator mass in charged current ep scattering. The weak mixing angle sin(2)theta w is determined in the on-mass-shell renormalisation scheme. A first measurement at HERA is made of the light quark weak couplings to the Z(0) boson and a possible contribution of right-handed isospin components to the weak couplings is investigated. (c) 2005 Elsevier B.V. All rights reserved.
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| 4. |
- Aktas, A, et al.
(författare)
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A direct search for stable magnetic monopoles produced in positron-proton collisions at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 41, s. 133-141
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Tidskriftsartikel (refereegranskat)abstract
- A direct search has been made for magnetic monopoles produced in e(+)p collisions at a centre of mass energy of 300 GeV at HERA. The beam pipe surrounding the interaction region in 1995-1997 was investigated using a SQUID magnetometer to look for stopped magnetic monopoles. During this time an integrated luminosity of 62 pb(-1) was delivered. No magnetic monopoles were observed and charge and mass dependent upper limits on the e(+)p production cross section are set.
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| 5. |
- Aktas, A., et al.
(författare)
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Forward jet production in deep inelastic scattering at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:1, s. 27-42
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Tidskriftsartikel (refereegranskat)abstract
- The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken scaling variable (xB(j)) and as triple differential cross sections d3 sigma/dx(Bj)dQ(2)dp(t)(,jet)(2), where Q(2) is the four momentum transfer squared and p(t)(,iet)(2) is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets. The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models.
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| 6. |
- Aktas, A, et al.
(författare)
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Measurement of Fc(c)over-bar(2) and Fb(b)over-bar(2) at low Q(2) and x using the H1 vertex detector at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 45:1, s. 23-33
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Tidskriftsartikel (refereegranskat)abstract
- Measurements are presented of inclusive charm and beauty cross sections in e(+)p collisions at HERA for values of photon virtuality 12 <= Q(2) = 60 GeV2 and of the Bjorken scaling variable 0.0002 <= x <= 0.005. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. Values for the structure functions F-2(cc) and F-2(bb) are obtained. This is the first measurement of F-2(bb) in this kinematic range. The results are found to be compatible with the predictions of perturbative quantum chromodynamics and with previous measurements of F-2(cc).
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| 7. |
- Aktas, A., et al.
(författare)
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Elastic J/psi production at HERA
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 46:3, s. 585-603
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Tidskriftsartikel (refereegranskat)abstract
- Cross sections for elastic production of J/psi mesons in photoproduction and electroproduction are measured in electron proton collisions at HERA using an integrated luminosity of 55 pb(-1). Results are presented for photon virtualities Q(2) up to 80 GeV2. The dependence on the photon-proton centre of mass energy W-gamma p is analysed in the range 40 <= W-gamma p <= 305 GeV in photoproduction and 40 <= W-gamma p <= 160 GeV in electroproduction. The W-gamma p dependences of the cross sections do not change significantly with Q(2) and can be described by models based on perturbative QCD. Within such models, the data show a high sensitivity to the gluon density of the proton in the domain of low Bjorken x and low Q(2). Differential cross sections d sigma/dt, where t is the squared four-momentum transfer at the proton vertex, are measured in the range vertical bar t vertical bar < 1.2 GeV2 as functions of W-gamma p and Q(2). Effective Pomeron trajectories are determined for photoproduction and electroproduction. The J/psi production and decay angular distributions are consistent with s-channel helicity conservation. The ratio of the cross sections for longitudinally and transversely polarised photons is measured as a function of Q(2) and is found to be described by perturbative QCD based models.
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| 8. |
- Aktas, A, et al.
(författare)
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Measurement of charm and beauty photoproduction at HERA using D*mu correlations
- 2005
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 621:1-2, s. 56-71
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of charm and beauty photoproduction at the electron proton collider HERA is presented based on the simultaneous detection of a D*(+/-) meson and a muon. The correlation between the D* meson and the muon serves to separate the charm and beauty contributions and the analysis provides comparable sensitivity to both. The total and differential experimental cross sections are compared to LO and NLO QCD calculations. The measured charm cross section is in good agreement with QCD predictions including higher order effects while the beauty cross section is higher.
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| 9. |
- Aktas, A, et al.
(författare)
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Measurement of deeply virtual Compton scattering at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 44:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- A measurement is presented of elastic deeply virtual Compton scattering gamma* p -> gamma p made using e(+) p collision data corresponding to a luminosity of 46.5 pb(-1), taken with the H1 detector at HERA. The cross section is measured as a function of the photon virtuality, Q(2), the invariant mass of the gamma* p system, W, and for the first time, differentially in the squared momentum transfer at the proton vertex, t, in the kinematic range 2 < Q(2) < 80 GeV2, 30 < W < 140 GeV and vertical bar t vertical bar < 1 GeV2. QCD based calculations at next-to-leading order using generalized parton distributions can describe the data, as can colour dipole model predictions.
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| 10. |
- Aktas, A, et al.
(författare)
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Measurement of F-2(c(c)over-bar) and F-2(b(b)over-bar) at high Q(2) using the H1 vertex detector at HERA
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 40:3, s. 349-359
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Tidskriftsartikel (refereegranskat)abstract
- Measurements are presented of inclusive charm and beauty cross sections in e(+)p collisions at HERA for values of photon virtuality Q(2) > 150 GeV2 and of inelasticity 0.1 < y < 0.7. The charm and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. The data are divided into four regions in Q(2) and Bjorken x, and values for the structure functions F-2(c (c) over bar) and F-2(b (b) over bar) are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.
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