1,586 research outputs found

### Mass--dependence of the Lambda hypernuclear decay widths

Two different approaches have been employed for the evaluation of the decay
widths of Lambda-hypernuclei (ranging from $^5_{\Lambda}$He to
$^{208}_{\Lambda}$Pb) with the polarization propagator method. In ref.[1], the
two-nucleon stimulated non-mesonic decay, $\Lambda NN\to NNN$, has been
parameterized phenomenologically by means of data on the pion-nucleus optical
potential. The other approach [2] consisted in a fully microscopic description
of the non-mesonic decays through the first order approximation of the
so-called bosonic-loop-expansion. Both calculations reproduce, with
approximately the same accuracy, the experimental decay rates for the whole
range of mass numbers considered.Comment: 4 pages, 2 figures. Talk presented at HYP2000, Torino, 23-27 Oct.
2000. To appear in the proceedings (Nucl. Phys. A

### Weak Decay of Hypernuclei

The focus of these Lectures is on the weak decay modes of hypernuclei, with
special attention to Lambda-hypernuclei. The subject involves many fields of
modern theoretical and experimental physics, from nuclear structure to the
fundamental constituents of matter and their interactions. The various weak
decay modes of Lambda-hypernuclei are described: the mesonic mode and the
non-mesonic ones. The latter are the dominant decay channels of medium--heavy
hypernuclei, where, on the contrary, the mesonic decay is disfavoured by Pauli
blocking effect on the outgoing nucleon. In particular, one can distinguish
between one-body and two-body induced decays. Theoretical models employed to
evaluate the (partial and total) decay widths of hypernuclei are illustrated,
and their results compared with existing experimental data. Open problems and
recent achievements are extensively discussed, in particular the determination
of the ratio Gamma_n/Gamma_p, possible tests of the Delta I=1/2 rule in
non-mesonic decays and the puzzling asymmetric non-mesonic decay of polarized
hypernuclei.Comment: 59 pages, 13 figures Lectures given at the International School of
Physics "Enrico Fermi" Course on: HADRON PHYSICS, Varenna (Lake Como), June
22nd - July 2nd, 200

### Hydrostatic pressure to trigger and assist magnetic transitions: baromagnetic refrigeration

The possible application of the barocaloric effect to produce solid state
refrigerators is a topic of interest in the field of applied physics. In this
work, we present experimental data about the influence of external pressure on
the magnetic properties of a manganite with phase separation. Using the Jahn
Teller effect associated with the presence of the charge ordering we were able
to follow the transition to the ferromagnetic state induced by pressure. We
also demonstrated that external pressure can assist the ferromagnetic state,
decreasing the magnetic field necessary to generate the magnetic transition.Comment: Acepted to be published in Applied Physics Letter

### On the role of ground state correlations in hypernuclear non-mesonic weak decay

The contribution of ground state correlations (GSC) to the non--mesonic weak
decay of $^{12}_\Lambda$C and other medium to heavy hypernuclei is studied
within a nuclear matter formalism implemented in a local density approximation.
We adopt a weak transition potential including the exchange of the complete
octets of pseudoscalar and vector mesons as well as a residual strong
interaction modeled on the Bonn potential. Leading GSC contributions, at first
order in the residual strong interaction, are introduced on the same footing
for all isospin channels of one-- and two--nucleon induced decays. Together
with fermion antisymmetrization, GSC turn out to be important for an accurate
determination of the decay widths. Besides opening the two--nucleon stimulated
decay channels, for $^{12}_\Lambda$C GSC are responsible for 14% of the rate
$\Gamma_1$ while increasing the $\Gamma_{n}/\Gamma_{p}$ ratio by 4%. Our final
results for $^{12}_\Lambda$C are: $\Gamma_{\rm NM}=0.98$,
$\Gamma_{n}/\Gamma_{p}=0.34$ and $\Gamma_2/\Gamma_{\rm NM}=0.26$. The
saturation property of $\Gamma_{\rm NM}$ with increasing hypernuclear mass
number is clearly observed. The agreement with data of our predictions for
$\Gamma_{\rm NM}$, $\Gamma_n/\Gamma_p$ and $\Gamma_2$ is rather good.Comment: 32 pages, 9 figure

### Minimum Detection Efficiencies for a Loophole-Free Bell-type Test

We discuss the problem of finding the most favorable conditions for closing
the detection loophole in a test of local realism with a Bell inequality. For a
generic non-maximally entangled two-qubit state and two alternative measurement
bases we apply Hardy's proof of non-locality without inequality and derive an
Eberhard-like inequality. For an infinity of non-maximally entangled states we
find that it is possible to refute local realism by requiring perfect detection
efficiency for only one of the two measurements: the test is free from the
detection loophole for any value of the detection efficiency corresponding to
the other measurement. The maximum tolerable noise in a loophole-free test is
also evaluated.Comment: 4 pages, 2 figure

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