| 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. |
- Abdallah, J, et al.
(författare)
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Charged particle multiplicity in three-jet events and two-gluon systems
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:44, s. 311-331
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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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| 3. |
- Abdallah, J, et al.
(författare)
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Coherent soft particle production in Z decays into three jets
- 2005
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 605:1-2, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy particle production perpendicular to the event plane in three-jet events produced in Z decays in e(+)e(-) annihilation is measured and compared to that perpendicular to the event axis in two-jet events. The topology dependence of the hadron production ratio is found to agree with a leading-order QCD prediction. This agreement and especially the need for the presence of a destructive interference term gives evidence for the coherent nature of gluon radiation. Hadron production in three-jet events is found to be directly proportional to a single topological scale function of the inter-jet angles. The slope of the dependence of the multiplicity with respect to the topological scale was measured to be 2.211 +/- 0.014(stat.) +/- 0.053(syst.) in good agreement with the expectation given by the colour-factor ratio C-A/C-F = 9/4. This result strongly supports the assumption of local parton-hadron duality, LPHD, at low hadron momentum.
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| 4. |
- 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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| 5. |
- Abdallah, J, et al.
(författare)
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Production of Xi(0)(c) and Xi(b) in Z decays and lifetime measurement of Xi(b)
- 2005
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; C:44, s. 299-309
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Tidskriftsartikel (refereegranskat)abstract
- The charmed strange baryon Xi(c)(0) was searched for in the decay channel Xi(c)(0) -> Xi(-)pi(+), and the beauty strange baryon Xi(b) in the inclusive channel Xi(b) -> Xi(-)l(-)(nu) over barX, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992-1995. The Xi(-) was reconstructed through the decay AT, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Xi(c)(0) and Xi(b) selection. The production rates were measured to be f(Xi c)(0) x BR(Xi(c)(0) -> Xi(-)pi(+) = (4.7 +/- 1.4(stat.) +/- 1.1(syst.)) x 10(-4) per hadronic Z decay, and BR(b -> Xi(b))xBR(Xi(b) -> Xi(-)l(-)X) = (3.0 +/- 1.0(stat.) +/- 0.3(syst.)) x 10(-4) for each lepton species (electron or muon). The lifetime of the Xi(b) baryon was measured to be tau(Xi b) = 1.45(-0.43)(+0.55)(stat.)+/- 0.13(syst.) ps. A combination with the previous DELPHI lifetime measurement gives tau(Xi b) = 1.48(-0.31)(+0.40)(stat.)+/- 0.12(syst.) ps.
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| 6. |
- Abdallah, J, et al.
(författare)
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Search for eta(b) in two-photon collisions at LEP II with the DELPHI detector
- 2006
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 634:4, s. 340-346
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Tidskriftsartikel (refereegranskat)abstract
- The pseudoscalar meson eta(b) has been searched for in two-photon interactions at LEP II. The data sample corresponds to a total integrated luminosity of 617 pb(-1) at centre-of-mass energies ranging from 161 to 209 GeV. Upper limits at a confidence level of 95% on the product Gamma(gamma gamma) (eta(b)) x BR(eta(b)) are 190, 470 and 660 eV/c(2) for the eta(b) decaying into 4, 6 and 8 charged particles, respectively.
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| 7. |
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| 8. |
- Chen, P.Y., et al.
(författare)
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Synthesis design of artificial magnetic metamaterials using a genetic algorithm
- 2008
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Ingår i: Optics Express. - 1094-4087. ; 16:17, s. 12806-12818
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a genetic algorithm (GA) as one branch of artificial intelligence (AI) for the optimization-design of the artificial magnetic metamaterial whose structure is automatically generated by computer through the filling element methodology. A representative design example, metamaterials with permeability of negative unity, is investigated and the optimized structures found by the GA are presented. It is also demonstrated that our approach is effective for the synthesis of functional magnetic and electric metamaterials with optimal structures. This GA-based optimization-design technique shows great versatility and applicability in the design of functional metamaterials. © 2008 Optical Society of America.
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| 9. |
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| 10. |
- Tångring, Ivar, 1978, et al.
(författare)
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1.58 µm InGaAs quantum well laser on GaAs
- 2007
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Ingår i: Applied Physics Letters. ; 91, s. 221101-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the 1.58 µm emission at room temperature from a metamorphic In0.6Ga0.4As quantum well laser grown on GaAs by molecular beam epitaxy. The large lattice mismatch was accommodated through growth of a linearly graded buffer layer to create a high quality virtual In0.32Ga0.68As substrate. Careful growth optimization ensured good optical and structural qualities. For a 1250×50 µm2 broad area laser, a minimum threshold current density of 490 A/cm2 was achieved under pulsed operation. This result indicates that metamorphic InGaAs quantum wells can be an alternative approach for 1.55 µm GaAs-based lasers.
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| 11. |
- Tångring, Ivar, 1978, et al.
(författare)
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Molecular beam epitaxy growth of A 1.58 μm InGaAs quantum well laser on GaAs
- 2008
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Ingår i: Conference Proceedings - International Conference on Indium Phosphide and Related Materials. - 1092-8669. - 9781424422593
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Konferensbidrag (refereegranskat)abstract
- We demonstrate how MBE growth parameters can be optimized to produce a metamorphic InGaAs QW laser emitting in the 1.55 ?m range. Different techniques to suppress roughening while maintaining low threading dislocation densities are evaluated. Finally, we demonstrate a 50×1250 ?m 2 broad area FabryPerot laser that produces pulsed lasing with a threshold current density of 490 A/cm2 and a wavelength of 1.58 ?m at room temperature.
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| 12. |
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| 13. |
- Laruelle, G. G., et al.
(författare)
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Anthropogenic perturbations of the silicon cycle at the global scale: Key role of the land-ocean transition
- 2009
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 23
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Forskningsöversikt (refereegranskat)abstract
- Silicon (Si), in the form of dissolved silicate (DSi), is a key nutrient in marine and continental ecosystems. DSi is taken up by organisms to produce structural elements (e.g., shells and phytoliths) composed of amorphous biogenic silica (bSiO(2)). A global mass balance model of the biologically active part of the modern Si cycle is derived on the basis of a systematic review of existing data regarding terrestrial and oceanic production fluxes, reservoir sizes, and residence times for DSi and bSiO(2). The model demonstrates the high sensitivity of biogeochemical Si cycling in the coastal zone to anthropogenic pressures, such as river damming and global temperature rise. As a result, further significant changes in the production and recycling of bSiO(2) in the coastal zone are to be expected over the course of this century.
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| 14. |
- Cheng, M.H., et al.
(författare)
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Growth and characterization of Ge nanostructures selectively grown on patterned Si
- 2008
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Ingår i: Thin Solid Films. - : Elsevier Science B.V., Amsterdam.. - 0040-6090 .- 1879-2731. ; 517:1, s. 57-61
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Tidskriftsartikel (refereegranskat)abstract
- By utilizing different distribution of strain fields around the edges of oxide, which are dominated by a series of sizes of oxide-patterned windows, long-range ordered self-assembly Ge nanostructures, such as nano-rings, nano-disks and nano-dots, were selectively grown by ultra high vacuum chemical vapor deposition (UHV-CVD) on Si (001) substrates. High-resolution double-crystal symmetrical omega/2 theta scans and two-dimensional reciprocal space mapping (2D-RSM) technologies employing the triple axis X-ray diffractometry have been used to evaluate the quality and strain status of as-deposited as well as in-situ annealed Ge nanostructures. Furthermore, we also compare the quality and strain status of Ge epilayers grown on planar unpatterned Si substrates. It was found that the quality of all Ge epitaxial structures is improved after in-situ annealing process and the quality of Ge nano-disk structures is better than that of Ge epilayers; on planar unpatterned Si substrates, because oxide sidewalls are effective dislocation sinks. We also noted that the degree of relaxation for as-deposited Ge epilayers on planar unpatterned Si substrates is less than that for as-deposited Ge nano-disk structures. After in-situ annealing process,all Ge epitaxial structures are almost at full relaxation whatever Ge epitaxial structures grew on patterned or unpatterned Si substrates.
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| 15. |
- Karim, Amir, 1976-, et al.
(författare)
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Photoluminescence Studies of Sn Quantum Dots in Si Grown by MBE
- 2005
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 27:5, s. 836-840
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Tidskriftsartikel (refereegranskat)abstract
- A few nanometer thick SnxSi1−x layers with x 0.1 grown on silicon (1 0 0) surfaces can be used to form tin (α-Sn) quantum dots as a result of heat treatment of such structures up to 800 °C. These quantum dots with a well-defined shape are expected to be a candidate for obtaining a low-energy direct band gap structure in Si. Absorption measurements reported by Ragan et al. have shown the onset of absorption at 0.27 eV indicating that the MBE-grown α-Sn quantum dots could be used, e.g. in infrared detectors or emitters. We have performed low temperature photoluminescence (PL) studies of some of the structures produced in this first study and observed no emission peak near 0.27 eV. The PL spectra are instead characterised by a broadband emission in the range 0.7–1 eV. Furthermore there are narrow features that have previously been described as the 789 meV C–O band and 1018 meV W or I1 band. The broad emission at 0.7–1 eV is attributed to the presence of defects introduced by the grown layers, which have suppressed the emission peaks related to the substrate as well. We have also grown α-Sn quantum dot samples on Si (1 0 0) substrates with very low doping concentrations. These samples show PL spectra with Si-substrate related peaks and a relatively lower broad feature at 0.7–1 eV. However, no emission was observed near 0.27 eV.
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| 16. |
- Lynch, S.A., et al.
(författare)
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Toward silicon-based lasers for terahertz sources
- 2006
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 12:6, s. 1570-1577
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Tidskriftsartikel (refereegranskat)abstract
- Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried suicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser. © 2006 IEEE.
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