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Register a new userObservation of Anomalous Internal Pair Creation in $^8$Be: A Possible Signature of a Light, Neutral Boson
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Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV state ($J^pi=1^+$, $T=1$) $rightarrow$ ground state ($J^pi=0^+$, $T=0$) and the isoscalar magnetic dipole 18.15 MeV ($J^pi=1^+$, $T=0$) state $rightarrow$ ground state transitions in $^{8}$Be. Significant deviation from the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of $> 5sigma$. This observation might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70$pm0.35 $ (stat)$pm 0.5 $ (sys) MeV$/c^2$ and $J^pi = 1^+$ was created.
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According to classical electrodynamics, sunlight that is passed through an iron layer can be detected with the naked eye only if the thickness of the layer is less than 170nm. However, in an old experiment, August Kundt was able to see the sunlight with the naked eye even when it had passed an iron layer with thickness greater than 200nm. To explain this observation, we propose a second kind of light which was introduced in a different context by Abdus Salam. A tabletop experiment can verify this possibility.
An inelastic $alpha$-scattering experiment on the unstable $N=Z$, doubly-magic $^{56}$Ni nucleus was performed in inverse kinematics at an incident energy of 50 A.MeV at GANIL. High multiplicity for $alpha$-particle emission was observed within the limited phase-space of the experimental setup. This observation cannot be explained by means of the statistical-decay model. The ideal classical gas model at $kT$ = 0.4 MeV reproduces fairly well the experimental momentum distribution and the observed multiplicity of $alpha$ particles corresponds to an excitation energy around 96 MeV. The method of distributed $malpha$-decay ensembles is in agreement with the experimental results if we assume that the $alpha$-gas state in $^{56}$Ni exists at around $113^{+15}_{-17}$ MeV. These results suggest that there may exist an exotic state consisting of many $alpha$ particles at the excitation energy of $113^{+15}_{-17}$ MeV.
We have observed a bimodal behaviour of the distribution of the asymmetry between the charges of the two heaviest products resulting from the decay of the quasi-projectile released in binary Xe+Sn and Au+Au collisions from 60 to 100 MeV/u. Event sorting has been achieved through the transverse energy of light charged particles emitted on the quasi-target side, thus avoiding artificial correlations between the bimodality signal and the sorting variable. Bimodality is observed for intermediate impact parameters for which the quasi-projectile is identified. A simulation shows that the deexcitation step rather than the geometry of the collision appears responsible for the bimodal behaviour. The influence of mid-rapidity emission has been verified. The two bumps of the bimodal distribution correspond to different excitation energies and similar temperatures. It is also shown that it is possible to correlate the bimodality signal with a change in the distribution of the heaviest fragment charge and a peak in potential energy fluctuations. All together, this set of data is coherent with what would be expected in a finite system if the corresponding system in the thermodynamic limit exhibits a first order phase transition.
Nuclear track emulsion is exposed to 1.2 A $^9$C GeV nuclei. Pairs of 2$^3$He nuclei having unusually narrow opening angles are observed in channel $^9$C $rightarrow$ 3$^3$He pointing to the possible 2$^3$He resonance near the production threshold.
A double-$Lambda$ hypernucleus, ${}_{LambdaLambda}mathrm{Be}$, was observed by the J-PARC E07 collaboration in nuclear emulsions tagged by the $(K^{-},K^{+})$ reaction. This event was interpreted as a production and decay of $ {}_{LambdaLambda}^{;10}mathrm{Be}$, ${}_{LambdaLambda}^{;11}mathrm{Be}$, or ${}_{LambdaLambda}^{;12}mathrm{Be}^{*}$ via $Xi^{-}$ capture in ${}^{16}mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $Lambda$ hyperons$,$($B_{LambdaLambda}$) of these double-$Lambda$ hypernuclei are obtained to be $15.05 pm 0.11,mathrm{MeV}$, $19.07 pm 0.11,mathrm{MeV}$, and $13.68 pm 0.11,mathrm{MeV}$, respectively. Based on the kinematic fitting, ${}_{LambdaLambda}^{;11}mathrm{Be}$ is the most likely explanation for the observed event.
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