| 1. |
- Schonning, K., et al.
(author)
-
The pd -> He-3 eta pi(0) reaction at T-p=1450 MeV CELSIUS/WASA Collaboration
- 2010
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 685:1, s. 33-37
-
Journal article (peer-reviewed)abstract
- The cross section for the pd -> He-3 eta pi(0) reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring. The He-3 was detected in coincidence with four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Delta(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant mass distributions Of all three pairs of final particles are well reproduced by a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the pi(0) momentum in the He-3 pi(0) system.
|
|
| 2. |
- Knowles, Sarah C L, et al.
(author)
-
Molecular epidemiology of malaria prevalence and parasitaemia in a wild bird population.
- 2011
-
In: Molecular Ecology. - 0962-1083. ; 20, s. 1062-1076
-
Journal article (peer-reviewed)abstract
- Avian malaria (Plasmodium spp.) and other blood parasitic infections of birds constitute increasingly popular model systems in ecological and evolutionary host-parasite studies. Field studies of these parasites commonly use two traits in hypothesis testing: infection status (or prevalence at the population level) and parasitaemia, yet the causes of variation in these traits remain poorly understood. Here, we use quantitative PCR to investigate fine-scale environmental and host predictors of malaria infection status and parasitaemia in a large 4-year data set from a well-characterized population of blue tits (Cyanistes caeruleus). We also examine the temporal dynamics of both traits within individuals. Both infection status and parasitaemia showed marked temporal and spatial variation within this population. However, spatiotemporal patterns of prevalence and parasitaemia were non-parallel, suggesting that different biological processes underpin variation in these two traits at this scale. Infection probability and parasitaemia both increased with host age, and parasitaemia was higher in individuals investing more in reproduction (those with larger clutch sizes). Several local environmental characteristics predicted parasitaemia, including food availability, altitude, and distance from the woodland edge. Although infection status and parasitaemia were somewhat repeatable within individuals, infections were clearly dynamic: patent infections frequently disappeared from the bloodstream, with up to 26% being lost between years, and parasitaemia also fluctuated within individuals across years in a pattern that mirrored annual population-level changes. Overall, these findings highlight the ecological complexity of avian malaria infections in natural populations, while providing valuable insight into the fundamental biology of this system that will increase its utility as a model host-parasite system.
|
|
| 3. |
- Petrén, Henrik, et al.
(author)
-
eta-meson production in proton-proton collisions at excess energies of 40 and 72 MeV
- 2010
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 82:5, s. 055206-
-
Journal article (peer-reviewed)abstract
- The production of eta mesons in proton-proton collisions has been studied using the WASA detector at the CELSIUS storage ring at excess energies of Q = 40 MeV and Q = 72 MeV. The eta was detected through its 2 gamma decay in a near-4 pi electromagnetic calorimeter, whereas the protons were measured by a combination of straw chambers and plastic scintillator planes in the forward hemisphere. About 6.9 x 10(4) and 9.3 x 10(4) events were found at Q = 40 MeV and Q = 72 MeV, respectively, with background contributions of less than 5%. A simple parametrization of the production cross section in terms of low partial waves was used to evaluate the acceptance corrections. Strong evidence was found for the influence of higher partial waves. The Dalitz plots show the presence of p waves in both the pp and the eta {pp} systems and the angular distributions of the eta in the center-of-mass frame suggest the influence of d-wave eta mesons.
|
|
| 4. |
- Schönning, Karin, et al.
(author)
-
The pd →3Heηπ0 reaction at Tp = 1450 MeV
- 2010
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 685:1, s. 33-37
-
Journal article (peer-reviewed)abstract
- The cross section for the pd→3Heηπ0 reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring and detecting one 3He and four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Δ(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant masses of all three pairs of final particles are well reproduce dby a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the π0 momentum in the 3He π0 system.
|
|
| 5. |
- Fäldt, Göran, et al.
(author)
-
Estimation of the ratio of the pn -> pn pi(0)pi(0)/pn -> d pi(0)pi(0) cross sections
- 2011
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 701:5, s. 619-622
-
Journal article (peer-reviewed)abstract
- Evidence has recently been presented for the existence of a dibaryon of mass 2380 MeV/c(2) and width 70 MeV/c(2), which decays strongly into the d pi(0)pi(0) channel [M. Bashkanov, et al., Phys. Rev. Lett. 102 (2009) 052301; P. Adlarson, et al., arXiv:1104.0123]. The decay rate of such a hypothesised dibaryon into the {pn}i=0 pi(0)pi(0) channel is estimated in a weakly model-dependent way by using final state interaction theory. It is shown that, if the resonance exists, it should show up as strongly in this channel as in d pi(0)pi(0). The sum of the two decay modes would saturate most of the inelasticity predicted in the relevant partial waves in the 2380 MeV/c(2) region.
|
|
| 6. |
- Johansson, Arne, et al.
(author)
-
Measurement and analysis of the pp -> pp gamma action at 310 MeV
- 2011
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 83:5, s. 054001-
-
Journal article (peer-reviewed)abstract
- The pp -> pp gamma reaction has been studied at a beam energy of 310 MeV by detecting both final protons at the PROMICE-WASA facility and identifying the photon through the resulting missing-mass peak. The photon angular distribution in the center-of-mass system and those of the proton-proton relative momentum with respect to the beam direction and to that of the recoil photon were determined reliably up to a final pp excitation energy of E-pp similar to 30 MeV. Except for very small E-pp values, the behavior of these distributions with excitation energy is well reproduced by a new refined model of the hard bremsstrahlung process. The model reproduces absolutely the total cross section and its energy dependence to within the experimental and theoretical uncertainties.
|
|
