| 11. |
- Abadie, J., et al.
(författare)
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Upper limits on a stochastic gravitational-wave background using LIGO and Virgo interferometers at 600-1000 Hz
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:12
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Tidskriftsartikel (refereegranskat)abstract
- A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600-1000 Hz, we obtained a 95% upper limit on the amplitude of Omega(GW)(f) = Omega(3)(f/900 Hz)(3), of Omega(3) < 0.32, assuming a value of the Hubble parameter of h(100) = 0.71. These new limits are a factor of seven better than the previous best in this frequency band.
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| 12. |
- Abadie, J., et al.
(författare)
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Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
- 2012
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 539
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Tidskriftsartikel (refereegranskat)abstract
- Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of wide-field telescopes.
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| 13. |
- Abadie, J., et al.
(författare)
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Search for gravitational waves from intermediate mass binary black holes
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:10
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100-450 M-circle dot and with the component mass ratios between 1: and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 M-circle dot, for nonspinning sources, the rate density upper limit is 0.13 per Mpc(3) per Myr at the 90% confidence level.
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| 14. |
- Abadie, J., et al.
(författare)
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All-sky search for periodic gravitational waves in the full S5 LIGO data
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on an all-sky search for periodic gravitational waves in the frequency band 50-800 Hz and with the frequency time derivative in the range of 0 through -6 x 10(-9) Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10x increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150 Hz our upper limit on worst-case linearly polarized strain amplitude h(0) is 1 x 10(-24), while at the high end of our frequency range we achieve a worst-case upper limit of 3.8 x 10(-24) for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational-wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long-period binary companion.
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| 15. |
- Abadie, J., et al.
(författare)
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Search for gravitational waves from low mass compact binary coalescence in LIGO's sixth science run and Virgo's science runs 2 and 3
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 85:8
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Tidskriftsartikel (refereegranskat)abstract
- We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M(circle dot); this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron star-black hole, and binary black hole systems are 1.3 x 10(-4), 3.1 x 10(-5), and 6.4 x 10(-6) Mpc(-3) yr(-1), respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.
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| 16. |
- Düllmann, Ch. E., et al.
(författare)
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Production and Decay of Element 114: High Cross Sections and the New Nucleus 277Hs
- 2010
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Ingår i: Physical Review Letters. - 1079-7114. ; 104:25
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Tidskriftsartikel (refereegranskat)abstract
- The fusion-evaporation reaction 244Pu(48Ca, 3-4n)288,289114 was studied at the new gas-filled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of 288,289114. At a compound nucleus excitation energy of E* = 39.8-43.9 MeV, the 4n evaporation channel cross section was 9.8(-3.1)(+3.9) pb. At E* = 36.1-39.5 MeV, that of the 3n evaporation channel was 8.0-(+7.4)(4.5) pb. In one of the 3n evaporation channel decay chains, a previously unobserved alpha branch in 281Ds was observed ( probability to be of random origin from background: 0.1%). This alpha decay populated the new nucleus 277Hs, which decayed by spontaneous fission after a lifetime of 4.5 ms.
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| 17. |
- Gates, J. M., et al.
(författare)
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First Superheavy Element Experiments at the GSI Recoil Separator TASCA: The Production and Decay of Element 114 in the 244Pu(48Ca,3-4n) Reaction
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 83:5
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Tidskriftsartikel (refereegranskat)abstract
- Experiments with the new recoil separator, Transactinide Separator and Chemistry Apparatus (TASCA), at the GSI were performed by using beams of Ca-48 to irradiate targets of Pb206-208, which led to the production of No252-254 isotopes. These studies allowed for evaluation of the performance of TASCA when coupled to a new detector and electronics system. By following these studies, the isotopes of element 114 ((288-291)114) were produced in irradiations of Pu-244 targets with Ca-48 beams at compound nucleus excitation energies around 41.7 and 37.5 MeV, demonstrating TASCA's ability to perform experiments with picobarn-level cross sections. A total of 15 decay chains were observed and were assigned to the decay of 288-291114. A new a-decay branch in (281)Ds was observed, leading to the new nucleus (277)Hs.
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| 18. |
- Yakushev, A., et al.
(författare)
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Superheavy Element Flerovium (Element 114) Is a Volatile Metal
- 2014
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 53:3, s. 1624-1629
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of superheavy elements (Z ≥ 104) and their chemical properties are dominated by relativistic effects. Recently two superheavy elements were recognized by the IUPAC and named flerovium (Fl, Z = 114) and livermorium (Lv, Z = 116). Fl is the heaviest element with which chemical experiments were performed. Here, we report on experiments that help answering the long-standing question whether Fl behaves rather like a noble gas or like a metal.
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| 19. |
- Graeger, R., et al.
(författare)
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Experimental Study of the 238U(36S,3-5n)269-271Hs Reaction Leading to the Observation of 270Hs
- 2010
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 81:6
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Tidskriftsartikel (refereegranskat)abstract
- The deformed doubly magic nucleus (270)Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg-26+Cm-248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of (270)Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca-48+Ra-226 and S-36+U-238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction S-36+U-238 that are similar to those of the Mg-26+Cm-248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S-36+U-238 and the observation of (270)Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8(-0.7)(+2.6) pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg-26+Cm-248 reaction at similar excitation energy.
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| 20. |
- Hild, K., et al.
(författare)
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Dominance of the first excitation step for magnetic circular dichroism in near-threshold two-photon photoemission
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:1, s. 014426-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic circular dichroism (MCD) in near-threshold photoemission is measured for a perpendicularly magnetized Cs/Co/Pt(111) film with work function adjusted by Cs adsorption. For one-photon photoemission (1PPE) the MCD asymmetry is recorded at a fixed photon energy of h nu = 3.06 eV and varying work function Phi. The asymmetry shows a nonmonotonous behavior in dependence of the excess energy h nu-Phi with a maximum value of A(1PPE) = 6.2 % at Phi = 2.45 eV. The measurement explores the first excitation step of a former two-photon photoemission (2PPE) measurement with A(2PPE) = 8.4% demonstrating that in 2PPE from Co(111) the first excitation step is the dominant asymmetry-generating process. An energy-dependent measurement in 2PPE at reduced work function (Phi approximate to 3 eV) yields a constant asymmetry of about 17% in the photon energy range between h nu = 1.53-1.66 eV. It reveals that for Co(111) the involvement of a real intermediate state is crucial for enlarged MCD asymmetries. Both results are discussed in the framework of direct interband transitions in directions deviating from the direction of normal electron emission Gamma-L. The 1PPE measurement is in reasonable agreement with calculations on the basis of this model. This reveals that an ab initio calculation considering all directions of excitation with an additional restriction in energy due to the existence of the sample work function in the photoemission process adequately describes MCD asymmetries in near-threshold photoemission.
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