| 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. |
- Öhrwall, Gunnar, et al.
(författare)
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The electronic structure of free water clusters probed by Auger electron spectroscopy
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123, s. 054310-
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Tidskriftsartikel (refereegranskat)abstract
- (H2O)(N) clusters generated in a supersonic expansion source with N similar to 1000 were core ionized by synchrotron radiation, giving rise to core-level photoelectron and Auger electron spectra (AES), free from charging effects. The AES is interpreted as being intermediate between the molecular and solid water spectra showing broadened bands as well as a significant shoulder at high kinetic energy. Qualitative considerations as well as ab initio calculations explain this shoulder to be due to delocalized final states in which the two valence holes are mostly located at different water molecules. The ab initio calculations show that valence hole configurations with both valence holes at the core-ionized water molecule are admixed to these final states and give rise to their intensity in the AES. Density-functional investigations of model systems for the doubly ionized final states-the water dimer and a 20-molecule water cluster-were performed to analyze the localization of the two valence holes in the electronic ground states. Whereas these holes are preferentially located at the same water molecule in the dimer, they are delocalized in the cluster showing a preference of the holes for surface molecules. The calculated double-ionization potential of the cluster (22.1 eV) is in reasonable agreement with the low-energy limit of the delocalized hole shoulder in the AES.
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| 3. |
- Abu-samha, M, et al.
(författare)
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Lineshapes in carbon 1s photoelectron spectra of methanol clusters
- 2006
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 8:21, s. 2473-2482
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Tidskriftsartikel (refereegranskat)abstract
- A general protocol for theoretical modeling of inner-shell photoelectron spectra of molecular clusters is presented and applied to C1s spectra of oligomers and medium-sized clusters of methanol. The protocol employs molecular dynamics for obtaining cluster geometries and a polarizable force field for computing site-specific chemical shifts in ionization energy and linewidth. Comparisons to spectra computed from first-principle theories are used to establish the accuracy of the proposed force field approach. The model is used to analyze the C1s photoelectron spectrum of medium-sized clusters in terms of surface and bulk contributions. By treating the surface-to-bulk ratio as an adjustable parameter, satisfactory fits are obtained to experimental C1s spectra of a beam of methanol clusters.
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| 4. |
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| 5. |
- Lindblad, A, et al.
(författare)
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Postcollision interaction in noble gas clusters: Observation of differences in surface and bulk line shapes
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:21
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Tidskriftsartikel (refereegranskat)abstract
- The surface and bulk components of the x-ray photoelectron spectra of free noble gas clusters are shown to display differences in the influence of postcollision interaction between the photoelectron and the Auger electron on the spectral line shape; the bulk component is observed to be less affected than the surface and atomic parts of the spectra. A model for postcollision interaction in nonmetallic solids and clusters is also provided which takes the polarization screening into account. Core-level photoelectron spectra of Ar, Kr, and Xe have been recorded to verify the dependence of the postcollision interaction effect on the polarizability of the sample.
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| 6. |
- Lindblad, A, et al.
(författare)
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The far from equilibrium structure of argon clusters doped with krypton or xenon
- 2006
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 8:16, s. 1899-1905
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Tidskriftsartikel (refereegranskat)abstract
- Heterogeneous clusters created by doping Ar host clusters with Kr or Xe are shown to have radically different structures from the mixed clusters of the same type created by co-expansion of Ar-Kr or Ar-Xe gas mixtures. In contrast to the co-expansion case, the doped mixed clusters can be produced with Kr or Xe on the surface and Ar in the bulk. With the doping technique it is thus possible to control the surface composition of a specific cluster. A study of the cluster properties as a function of the doping pressure is also reported for the case of Ar clusters doped with Xe. The clusters have been studied by means of synchrotron radiation based X-ray photoelectron spectroscopy.
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| 7. |
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| 8. |
- Lundwall, M, et al.
(författare)
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Enhanced surface sensitivity in AES relative to XPS observed in free argon clusters
- 2005
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 594:1-3, s. 12-19
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Tidskriftsartikel (refereegranskat)abstract
- The surface-to-bulk intensity ratio in Auger electron spectra has been studied in comparison with core-level photoelectron spectra using free argon clusters of sizes ranging over two orders of magnitude. Enhanced surface sensitivity is observed in L2,3M2,3M2.3 Auger electron spectra compared to 2p photoelectron spectra where electrons of similar kinetic energies were recorded. This is discussed in terms of the effective attenuation length of the electrons.
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| 9. |
- Lundwall, M., et al.
(författare)
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Preferential site occupancy of krypton atoms on free argon-cluster surfaces
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:1
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Tidskriftsartikel (refereegranskat)abstract
- Argon clusters have been doped with krypton atoms in a pick-up setup and investigated by means of ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The width of the krypton surface feature in the XPS spectra from mixed krypton/argon clusters has been studied and found to be narrower than in the case of homogeneous krypton clusters. By considering known spectral broadening mechanisms of the cluster features and the electron binding energy shift of the cluster surface feature relative to the atomic signal, we conclude that krypton ad-atoms preferentially occupy high-coordination surface sites on the argon host-cluster. (c) 2006 American Institute of Physics.
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| 10. |
- Lundwall, M., et al.
(författare)
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Shell-dependent core-level chemical shifts observed in free xenon clusters
- 2006
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:24, s. 5225-5235
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron and Auger electron spectra following Xe-3d and Xe-4d ionization of free xenon clusters have been measured using synchrotron radiation. The atom-to-surface and atom-to-bulk binding energy shifts found in the Xe-3d and the subsequent M5N4,5N4,5 Auger decay are about 15% larger than those observed in the Xe-4d and N4,5O2,3O2,3 measurements. This experimental result is also considered theoretically.
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