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Register a new userSearch for a Possible Spontaneous Emission of Muons from Heavy Nuclei
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Authors
M. Giorgini
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A search for an exotic natural radioactivity of lead nuclei, using nuclear emulsion sheets as detector, is described. We discuss the experimental set-up of a test performed at the Gran Sasso National Laboratory (Italy), the event simulation, data analysis and preliminary results.
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We describe a possible search for muonic radioactivity from lead nuclei using the base elements (bricks composed by lead and nuclear emulsion sheets) of the long-baseline OPERA neutrino experiment. We present the results of a Monte Carlo simulation concerning the expected event topologies and estimates of the background events. Using few bricks, we could reach a good sensitivity level.
The possible occurence of highly deformed configurations is investigated in the $^{40}$Ca and $^{56}$Ni di-nuclear systems as formed in the $^{28}$Si + $^{12}$C and $^{28}$Si + $^{28}$Si reactions, respectively, by using the properties of emitted light charged particles. Inclusive as well as exclusive data of the heavy fragments (A $geq$ 6) and their associated light charged particles (p, d, t, and $alpha$-particles) have been collected at the IReS Strasbourg VIVITRON Tandem facility with two bombarding energies $E_{lab}(^{28}$Si) = 112 and 180 MeV by using the ICARE charged particle multidetector array, which consists of nearly 40 telescopes. The measured energy spectra, velocity distributions, in-plane and out-of-plane angular correlations are analysed by Monte Carlo CASCADE statistical-model calculations using a consistent set of parameters with spin-dependent level densities. Although significant deformation effects at high spin are needed, the remaining disagreement observed in the $^{28}$Si + $^{12}$C reaction for the S evaporation residue suggests an unexpected large unstable $^{8}$Be cluster emission of a binary nature.
A large $mu^-$ polarization was achieved in muonic Bi atoms with the help of the strong hyperfine field in a polarized nuclear target. Using $^{209}$Bi nuclei polarized to ($59pm9$)% in ferromagnetic BiMn, we observed a $mu$-$e$ decay asymmetry of ($13.1pm3.9$)%, which gives $mu^-$ polarization per nuclear polarization equal to $-1.07pm 0.35$. This value is almost consistent with $-0.792$ calculated for nuclei with spin $I= frac{9}{2}$ and a positive magnetic moment under the assumption that the hyperfine interaction becomes effective in the lowest muonic states.
We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, $phi_{V_5} = [2.8pm,4.6(stat.)pm,4.0(sys.)]times 10^{-5}~mbox{rad/m}$ is consistent with zero. This result improves the upper bounds on the neutron-matter coupling $g_{A}^{2}$ from such an interaction by about three orders of magnitude for force ranges in the mm-$mu$m regime.
This paper reports the first observation of the Jacobi shape transition in $^{31}$P using high energy $gamma$-rays from the decay of giant dipole resonance (GDR) as a probe. The measured GDR spectrum in the decay of $^{31}$P shows a distinct low energy component around 10 MeV, which is a clear signature of Coriolis splitting in a highly deformed rotating nucleus. Interestingly, a self-conjugate $alpha$-cluster nucleus $^{28}$Si, populated at similar initial excitation energy and angular momentum, exhibits a vastly different GDR line shape. Even though the angular momentum of the compound nucleus $^{28}$Si is higher than the critical angular momentum required for the Jacobi shape transition, the GDR lineshape is akin to a prolate deformed nucleus. Considering the present results for $^{28}$Si and similar observation recently reported in $^{32}$S, it is proposed that the nuclear orbiting phenomenon exhibited by $alpha$-cluster nuclei hinders the Jacobi shape transition. The present experimental results suggest a possibility to investigate the nuclear orbiting phenomenon using high energy $gamma$-rays as a probe.
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