Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNew Narrow $N(1685)$ and $N(1726)$? Remarks on the Interpretation of the Neutron Anomaly as an Interference Phenomenon
61
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Different interpretations of narrow structures at $Wsim 1.68$ and $Wsim 1.72$ GeV observed in several reactions are discussed. It is questionable whether interference phenomena could explain the whole complex of experimental findings. More probable hypotheses would be the existence of one or two narrow resonances $N(1685)$ and $N(1726)$ and/or the sub-threshold virtual $KSigma$ and $omega p$ production (cusps).
rate research
Read More
Observation of a narrow structure at $Wsim 1.68$ GeV in the excitation functions of some photon- and pion-induced reactions may signal a new narrow isospin-1/2 $N(1685)$ resonance. New data on the $gamma N to pi eta N$ reactions from GRAAL seems to reveal the signals of both $N^+(1685)$ and $N^0(1685)$ resonances.
The first study of quasi-free Compton scattering on the neutron in the energy range of $E_{gamma}=0.75 - 1.5$ GeV is presented. The data reveals a narrow peak at $Wsim 1.685$ GeV. This result, being considered in conjunction with the recent evidence for a narrow structure at $Wsim 1.68$GeV in the $eta$ photoproduction on the neutron, suggests the existence of a new nucleon resonance with unusual properties: the mass $Msim 1.685$GeV, the narrow width $Gamma leq 30$MeV, and the much stronger photoexcitation on the neutron than on the proton.
Revised analysis of $Sigma$ beam asymmetry for $eta$ photoproduction on the free proton reveals a resonant structure at $Wsim 1.69$ GeV. Comparison of experimental data with multipole decomposition based on the E429 solution of the SAID partial wave analysis and including narrow states, suggests a narrow ($Gamma leq 15$ MeV) resonance. Possible candidates are $P_{11}$, $P_{13}$, or $D_{13}$ resonances. The result is considered in conjunction with the recent evidence for a bump-like structure at $Wsim 1.67 - 1.68$ GeV in quasi-free $eta$ photoproduction on the neutron.
Discrepancies from in-beam and in-bottle type experiments measuring the neutron lifetime are on the 4$sigma$ standard deviation level. In a recent publication Fornal and Grinstein proposed that the puzzle could be solved if the neutron would decay on the one percent level via a dark decay mode, one possible branch being $n rightarrow chi + e^+ e^-$. With data from the perkeoII experiment we set limits on the branching fraction and exclude a one percent contribution for $95,%$ of the allowed mass range for the dark matter particle.
We have performed high precision measurements of the zero-energy neutron scattering amplitudes of gas phase molecular hydrogen, deuterium, and $^{3}$He using neutron interferometry. We find $b_{mathit{np}}=(-3.7384 pm 0.0020)$ fmcite{Schoen03}, $b_{mathit{nd}}=(6.6649 pm 0.0040)$ fmcite{Black03,Schoen03}, and $b_{n^{3}textrm{He}} = (5.8572 pm 0.0072)$ fmcite{Huffman04}. When combined with the previous world data, properly corrected for small multiple scattering, radiative corrections, and local field effects from the theory of neutron optics and combined by the prescriptions of the Particle Data Group, the zero-energy scattering amplitudes are: $b_{mathit{np}}=(-3.7389 pm 0.0010)$ fm, $b_{mathit{nd}}=(6.6683 pm 0.0030)$ fm, and $b_{n^{3}textrm{He}} = (5.853 pm .007)$ fm. The precision of these measurements is now high enough to severely constrain NN few-body models. The n-d and n-$^{3}$He coherent neutron scattering amplitudes are both now in disagreement with the best current theories. The new values can be used as input for precision calculations of few body processes. This precision data is sensitive to small effects such as nuclear three-body forces, charge-symmetry breaking in the strong interaction, and residual electromagnetic effects not yet fully included in current models.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
