| 1. |
- Abazov, V. M., et al.
(författare)
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Search for a heavy resonance decaying into a Z plus jet final state in p(p)over-bar collisions at root s=1.96 TeV using the D0 detector
- 2006
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998 .- 1550-2368. ; 74:1, s. 011104-
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Tidskriftsartikel (refereegranskat)abstract
- We have searched for a heavy resonance decaying into a Z+jet final state in p (p) over bar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370 pb(-1). We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.
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| 2. |
- Abazov, V. M., et al.
(författare)
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The upgraded DO detector
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 565:2, s. 463-537
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Tidskriftsartikel (refereegranskat)abstract
- The DO experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid -argon calorimeters and central muon detector, remaining from Run 1, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DO.
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| 3. |
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| 4. |
- Andersson, P., et al.
(författare)
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Selective detection of C-13 by laser photodetachment mass spectrometry
- 2008
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 266:16, s. 3667-3673
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we demonstrate how laser photodetachment mass spectrometry (LPMS) can be used to selectively detect C-13(-) ions in the presence of C-12(-) ions in a low energy ion beam. An isotopically enriched beam of carbon ions consisting of equal amounts of C-13(-) and 12C- ions was extracted from an ion source. The ions interacted with a laser beam in a collinear geometry over a distance of 70 cm. Residual atoms produced in the photodetachment process were detected in a neutral particle detector placed downstream of the collinear interaction region. By making use of the Doppler effect we were able to selectively photodetach C-13(-) ions. The number of detected C-13 atoms was 13 times larger than the number of detected C-12 atoms. The population of the excited, weakly bound D-2 excited state of the C- ion was depleted by the use of a second laser. This significantly reduced the background accompanying the signal arising from the photodetachment of the S-4 ground state C- ion. Different applications of the LPMS method will be discussed in the paper.
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| 5. |
- Bahati, E. M., et al.
(författare)
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Electron-impact dissociation of CD3+ and CH3+ ions producing CD2+, CH+ and C+ fragment ions
- 2009
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 79:5, s. 52703-
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Tidskriftsartikel (refereegranskat)abstract
- Using a crossed electron-ion beams method, we measured absolute cross sections for electron-impact dissociation of the CD3+ molecular ions producing CD2+ fragment ions and CH3+ ions yielding CH+ and C+ fragment ions over a collision energy range from a few eV up to 100 eV. The total experimental uncertainties are about 12% at the maximum of the curves of cross sections (peak of the cross section for the CH+ channel). The obtained results suggest important roles played by predissociation of bound states in the production of both the CH+ and C+ fragment ions. Good agreement is found with other results reported for the CH+ fragment, but some differences are found for the CD2+ and C+ fragments.
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| 6. |
- Bhardwaj, R. D., et al.
(författare)
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Neocortical neurogenesis in humans is restricted to development.
- 2006
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424. ; 103:33, s. 12564-8
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Tidskriftsartikel (refereegranskat)abstract
- Stem cells generate neurons in discrete regions in the postnatal mammalian brain. However, the extent of neurogenesis in the adult human brain has been difficult to establish. We have taken advantage of the integration of (14)C, generated by nuclear bomb tests during the Cold War, in DNA to establish the age of neurons in the major areas of the human cerebral neocortex. Together with the analysis of the neocortex from patients who received BrdU, which integrates in the DNA of dividing cells, our results demonstrate that, whereas nonneuronal cells turn over, neurons in the human cerebral neocortex are not generated in adulthood at detectable levels but are generated perinatally.
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| 7. |
- Collins, G F, et al.
(författare)
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Electron-impact fragmentation of Cl-2(-)
- 2005
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:4, s. 042708-
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Tidskriftsartikel (refereegranskat)abstract
- A merged beam technique has been used to investigate the fragmentation of the Cl-2(-) ion in collisions with electrons over an energy range of 0-200 eV. We have measured absolute cross sections for detachment, detachment plus dissociation and dissociation processes. Over the energy range studied, the dominant breakup mechanism is dissociation. Dissociation is relatively enhanced in the e(-)+Cl-2(-) collision system due to the suppression of the normally dominant detachment process, as a result of the large difference between the equilibrium internuclear distances of the Cl-2 and Cl-2(-) ground state potential curves. A prominent structure is observed just above the threshold in the Cl-+Cl+e(-) dissociation channel. It is proposed that the structure is a resonance associated with production and rapid decay of an excited state of the doubly charged Cl-2(-) ion. A plausible mechanism for production of the di-anionic state based on an excitation plus capture process is suggested.
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| 8. |
- Ehlerding, A., et al.
(författare)
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The dissociative recombination of fluorocarbon ions III : CF2+ and CF3
- 2006
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:4, s. 805-812
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Tidskriftsartikel (refereegranskat)abstract
- Cross sections and branching ratios are presented for the dissociative recombination of the CF2+ and C-3(+) ions with electrons. It is found that the channel producing CF + F is dominant for the reaction with CF2+ and the production of CF2 + F is dominant for the reaction with CF3+. The cross sections for these two ions are very similar.
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| 9. |
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| 10. |
- Fogle, M., et al.
(författare)
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Electron-impact ionization of Be-like CIII, NIV, and OV
- 2008
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 175:2, s. 543-556
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Tidskriftsartikel (refereegranskat)abstract
- We present recent measurements of absolute electron-impact ionization cross sections for Be-like C III, N IV, and O V forming Li- like C IV, N V, and O VI. The measurements were taken using the crossed-beams apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation method was used to independently measure the metastable fractions present in the ion beams. The measured ionization cross sections were compared with calculations using the R-matrix with pseudostates and distorted-wave theoretical methods. Best agreement is found with the R-matrix with pseudostates cross sections results that account for the metastable fractions inferred from the gas attenuation measurements. We present a set of recommended rate coefficients for electron-impact single ionization from the ground state and metastable term of each ion.
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