| 1. |
- 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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| 2. |
- Kelly, J. J., et al.
(författare)
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Recoil polarization measurements for neutral pion electroproduction at Q(2)=1(GeV/c)(2) near the Delta resonance
- 2007
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 75:2
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Tidskriftsartikel (refereegranskat)abstract
- We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q(2)=1.0 (GeV/c)(2) in 10 bins of 1.17 <= W <= 1.35 GeV across the Delta resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near the physical mass, W=M-Delta approximate to 1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W > M-Delta. We performed a multipole analysis that adjusts suitable subsets of center dot(pi)<= 2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent-there is very little sensitivity to the choice of baseline model or truncation scheme. By contrast, truncation errors in the traditional Legendre analysis of N ->Delta quadrupole ratios are not negligible. Parabolic fits to the W dependence around M-Delta for the multiple analysis gives values for Re(S1+/M1+)=(-6.61 +/- 0.18)% and Re(E1+/M1+)=(-2.87 +/- 0.19)% for the p pi(0) channel at W=1.232 GeV and Q(2)=1.0 (GeV/c)(2) that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+)=(+7.1 +/- 0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe.
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| 3. |
- Jallow, Muminatou, et al.
(författare)
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Genome-wide and fine-resolution association analysis of malaria in West Africa.
- 2009
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; , s. 657-665
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Tidskriftsartikel (refereegranskat)abstract
- We report a genome-wide association (GWA) study of severe malaria in The Gambia. The initial GWA scan included 2,500 children genotyped on the Affymetrix 500K GeneChip, and a replication study included 3,400 children. We used this to examine the performance of GWA methods in Africa. We found considerable population stratification, and also that signals of association at known malaria resistance loci were greatly attenuated owing to weak linkage disequilibrium (LD). To investigate possible solutions to the problem of low LD, we focused on the HbS locus, sequencing this region of the genome in 62 Gambian individuals and then using these data to conduct multipoint imputation in the GWA samples. This increased the signal of association, from P = 4 x 10(-7) to P = 4 x 10(-14), with the peak of the signal located precisely at the HbS causal variant. Our findings provide proof of principle that fine-resolution multipoint imputation, based on population-specific sequencing data, can substantially boost authentic GWA signals and enable fine mapping of causal variants in African populations.
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| 4. |
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| 5. |
- Atalla, E, et al.
(författare)
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An all-digital ΣΔ--frequency discriminator of arbitrary order
- 2006
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Ingår i: IEEE International Symposium on Circuits and Systems, ISCAS 2006. Proceedings.. - 0780393899
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose an all-digital frequency synthesizer architecture, based on an all-digital ΣΔ-frequency discriminator. The new all-digital synthesizer is compared to previously published work. The architecture of the ΣΔ-frequency discriminator is verified using behavioral simulation.
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| 6. |
- de Walle, J. V., et al.
(författare)
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Coulomb excitation of the N=50 nucleus Zn-80
- 2008
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Ingår i: AIP Conference Proceedings. - 1551-7616 .- 0094-243X. ; 1012, s. 291-295 453
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Konferensbidrag (refereegranskat)abstract
- Neutron rich Zinc isotopes, including the N=50 nucleus Zn-80, were produced and post-accelerated at the Radioactive Ion Beam (RIB) facility REX-ISOLDE (CERN). Low-energy Coulomb excitation was induced on these isotopes after post-acceleration, yielding B(E2) strengths to the first excited 2(+) states. For the first time, an excited state in Zn-80 was observed and the 2(1)(+) state in Zn-78 was established. The measured B(E2,2(1)(+) -> 0(1)(+)) values are compared to two sets of large scale shell model calculations. Both calculations reproduce the observed B(E2) systematics for the full Zinc isotopic chain. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni-78.
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| 7. |
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| 8. |
- Van de Walle, J., et al.
(författare)
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Coulomb excitation of neutron-rich Zn isotopes: First observation of the 2(1)(+) state in Zn-80
- 2007
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Ingår i: Physical Review Letters. - 1079-7114. ; 99:14
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)(+) state in Zn-78 could be firmly established and for the first time the 2(+)-> 0(1)(+) transition in Zn-80 was observed at 1492(1) keV. B(E2,2(1)(+)-> 0(1)(+)) values were extracted for Zn-74,Zn-76,Zn-78,Zn-80 and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, Zn-80 is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni-78.
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| 9. |
- Van de Walle, J., et al.
(författare)
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Low-energy Coulomb excitation of neutron-rich zinc isotopes
- 2009
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:1
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Tidskriftsartikel (refereegranskat)abstract
- At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2, 2(1)(+)-> 0(1)(+)) values in Zn74-80, B(E2, 4(1)(+)-> 2(1)(+)) values in Zn-74,Zn-76 and the determination of the energy of the first excited 2(1)(+) states in Zn-78,Zn-80. The zinc isotopes were produced by high-energy proton- (A = 74, 76, 80) and neutron-(A = 78) induced fission of U-238, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondary target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N = 50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.
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| 10. |
- Walle, J. Van de, et al.
(författare)
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Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the 2[sub 1][sup +] State in [sup 80]Zn
- 2007
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Ingår i: Physical Review Letters. ; 99:14, s. 142501-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 21+ state in 78Zn could be firmly established and for the first time the 2+-->01+ transition in 80Zn was observed at 1492(1) keV. B(E2,21+-->01+) values were extracted for 74,76,78,80Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni.
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