448 research outputs found
Inclusive pion double charge exchange on O-16 above the delta resonance
The forward inclusive pion double charge exchange reaction,
^{16}O(pi^-,pi^+)X, at T_0 = 0.50 and 0.75 GeV has been studied in the
kinematical region where an additional pion production is forbidden by
energy-momentum conservation. The experiment was performed with the SKS
spectrometer at KEK PS. The measured ratio of double charge exchange
cross-section for these energies dsigma(0.50 GeV)/dOmega / dsigma(0.75
GeV)/dOmega = 1.7 +/- 0.2, disagrees with the value of 7.2 predicted within the
conventional sequential single charge exchange mechanism. Possible reasons for
the disagreement are discussed in connection with the Glauber inelastic
rescatterings.Comment: 4 pages, 5 figure
Orbital eccentricities of binary systems with a former AGB star
Many binary stellar systems in which the primary star is beyond the
asymptotic giant branch (AGB) evolutionary phase show significant orbital
eccentricities whereas current binary interaction models predict their orbits
to be circularised. We analyse how the orbital parameters in a system are
modified under mass loss and mass exchange among its binary components and
propose a model for enhanced mass-loss from the AGB star due to tidal
interaction with its companion, which allows a smooth transition between the
wind and Roche-lobe overflow mass-loss regimes. We explicitly follow its effect
along the orbit on the change of eccentricity and orbital semi-major axis, as
well as the effect of accretion by the companion. We calculate timescales for
the variation of these orbital parameters and compare them to the tidal
circularisation timescale. We find that in many cases, due to the enhanced mass
loss of the AGB component at orbital phases closer to the periastron, the net
eccentricity growth rate in one orbit is comparable to the rate of tidal
circularisation. We show that with this eccentricity enhancing mechanism it is
possible to reproduce the orbital period and eccentricity of the Sirius system,
which under the standard assumptions of binary interaction is expected to be
circularised. We also show that this mechanism may provide an explanation for
the eccentricities of most barium star systems, which are expected to be
circularised due to tidal dissipation. By proposing a tidally enhanced model of
mass loss from AGB stars we find a mechanism which efficiently works against
the tidal circularisation of the orbit, which explains the significant
eccentricities observed in binary systems containing a white dwarf and a less
evolved companion, such as Sirius and systems with barium stars.Comment: 9 pages, 5 figures, accepted for publication in Astronomy and
Astrophysics on 24th of October of 200
The HypHI project: Hypernuclear spectroscopy with stable heavy ion beams and rare isotope beams at GSI and FAIR
The HypHI collaboration aims to perform a precise hypernuclear spectroscopy
with stable heavy ion beams and rare isotope beams at GSI and fAIR in order to
study hypernuclei at extreme isospin, especially neutron rich hypernuclei to
look insight hyperon-nucleon interactions in the neutron rich medium, and
hypernuclear magnetic moments to investigate baryon properties in the nuclei.
We are currently preparing for the first experiment with Li and C
beams at 2 AGeV to demonstrate the feasibility of a precise hypernuclear
spectroscopy by identifying H, H and
He. The first physics experiment on these hypernuclei is
planned for 2009. In the present document, an overview of the HypHI project and
the details of this first experiment will be discussed.Comment: 5 pages, 2 figures, French-Japanese symposium 2008, Paris (France
Measurement of the decay width of He
We have precisely measured decay width of \5LHe and
demonstrated significantly larger - overlap than expected
from the central repulsion - potential, which is derived from
YNG \Lambda$-nucleon interaction.Comment: 4 pages, 3 figure
Proton asymmetry in non-mesonic weak decay of light hypernuclei
We have obtained the decay asymmetry parameters in non-mesonic weak decay of
polarized Lambda-hypernuclei by measuring the proton asymmetry. The polarized
Lambda-hypernuclei, 5_Lambda-He, 12_Lambda-C, and 11_Lambda-B, were produced in
high statistics via the (pi^+,k^+) reaction at 1.05 GeV/c in the forward
angles. Preliminary analysis shows that the decay asymmetry parameters are very
small for these s-shell and p-shell hypernuclei.Comment: 4pages, 4figures, International Conference on Hypernuclear and
Strange Particle Physics (HYP2003
Early phase observations of extremely luminous Type Ia Supernova 2009dc
We present early phase observations in optical and near-infrared wavelengths
for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate
of the light curve is , which is one of the
slowest among SNe Ia. The peak -band absolute magnitude is mag even if the host extinction is mag. It reaches
mag for the host extinction of mag as
inferred from the observed Na {\sc i} D line absorption in the host. Our
-band photometry shows that the SN is one of the most luminous SNe Ia
also in near-infrared wavelengths. These results indicate that SN 2009dc
belongs to the most luminous class of SNe Ia, like SN 2003fg and SN 2006gz. We
estimate the ejected Ni mass of \Msun for no host
extinction case (or 1.6 0.4 M for the host extinction of
mag). The C {\sc ii} 6580 absorption line keeps visible
until a week after maximum, which diminished in SN 2006gz before its maximum
brightness. The line velocity of Si {\sc ii} 6355 is about 8000 km
s around the maximum, being considerably slower than that of SN 2006gz,
while comparable to that of SN 2003fg. The velocity of the C {\sc ii} line is
almost comparable to that of the Si {\sc ii}. The presence of the carbon line
suggests that thick unburned C+O layers remain after the explosion. SN 2009dc
is a plausible candidate of the super-Chandrasekhar mass SNe Ia
Gamma-Ray Spectroscopy of O and N Hypernuclei via the O reaction
he bound-state level structures of the O and
N hypernuclei were studied by -ray spectroscopy using
a germanium detector array (Hyperball) via the O ()
reaction. A level scheme for O was determined from the
observation of three -ray transitions from the doublet of states
(,) at MeV to the ground-state doublet (,). The
N hypernuclei were produced via proton emission from unbound
states in O . Three -rays were observed and the
lifetime of the state in N was measured by the
Doppler shift attenuation method. By comparing the experimental results with
shell-model calculations, the spin-dependence of the interaction is
discussed. In particular, the measured O ground-state doublet
spacing of 26.4 1.6 0.5 keV determines a small but nonzero strength
of the tensor interaction.Comment: 22 pages, 17 figure
pi^0 decay branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei
We precisely measured pi^0 branching ratios of 5_Lambda-He and 12_Lambda-C
hypernuclei produced via (pi^+,k^+) reaction. Using these pi^0 branching ratios
with the pi^- branching ratios and the lifetimes, we obtained the pi^0 decay
widths and the non-mesonic weak decay widths at high statistics with the
accuracy of ~5 % (stat) for both hypernuclei.Comment: 4pages, 4figures, International Conference on Hypernuclear and
Strange Particle Physics (HYP2003
Exclusive Measurement of the Nonmesonic Weak Decay of ^{5}_{\Lambda}He Hypernucleus
We performed a coincidence measurement of two nucleons emitted from the
nonmesonic weak decay (NMWD) of ^{5}_{\Lambda}He formed via the
^{6}Li(\pi^+,K^+) reaction. The energies of two nucleons and the pair number
distributions in the opening angle between them were measured. In both np and
nn pairs, we observed a clean back-to-back correlation coming from the two-body
decay of \Lambda p --> n p and \Lambda n --> n n, respectively. The ratio of
the nucleon pair numbers was N_{nn}/N_{np}=0.45 \pm 0.11(stat)\pm 0.03(syst) in
the kinematic region of cos(theta_{NN}) < -0.8. Since each decay mode was
exclusively detected, the measured ratio should be close to the ratio of
\Gamma(\Lambda p --> np)/\Gamma(\Lambda n --> nn).
The ratio is consistent with recent theoretical calculations based on the
heavy meson/direct quark exchange picture.Comment: Submitted to Phys. Rev. lett., 4 pages, 3 figure
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