Experimental study of resonance states in ${}^7\mathrm{H}$ and ${}^6\mathrm{H}$

The ${}^7\mathrm{H}$ and ${}^6\mathrm{H}$ nuclear systems were investigated via transfer reactions with a ${}^8\mathrm{He}$ beam at $15.4A$ MeV impinging in a ${}^{12}\mathrm{C}$ target. The experimental setup allowed a complete reconstruction of the reaction kinematics with the MAYA gas detector, based on the active-target concept, where the carbon atoms of the filling isobutane played also the role of reaction target. The ${}^7\mathrm{H}$ resonance was observed at $0.{57}_{-0.21}^{+0.42}$ MeV above the ${}^3\mathrm{H}+4n$ threshold with a width of $0.{09}_{-0.06}^{+0.94}$ MeV. The ${}^6\mathrm{H}$ system was formed at $2.{91}_{-0.95}^{+0.85}$ MeV with a resonance width of $1.{52}_{-0.35}^{+1.77}$ MeV. These results show the availability of nuclear structure information well outside the bounding limits, resulting in an extraordinary input to improve the present models and understanding of nuclear matter.

Figure 1

Experimental setup. Two drift chambers, in front of the MAYA detector, monitor the beam particles. The reactions occur in the volume filled with ${\mathrm{C}}_4{\mathrm{H}}_{10}$ gas. A $5\times 5$ matrix of CsI detectors is placed at the back side for detecting light particles. A small metal cup is used to stop the beam.

Figure 2

Construction of charge profile. The figure shows an area of the segmented cathode with a particle trace, represented by the grey crossing line. The numbers in the pads correspond to the charge collected. Those pads with the maxima of charge collected along the selected axis of symmetry are signalled in dark grey. The total charge collected in each row along this axis is used to build the charge profile depicted in the upper part of the figure. The inset shows the punctual charge induction with the connected points, and its projection in a row of pads with a dashed line.

Figure 3

Simulation of (a) starting and (b) ending points of energy loss profile. The energy loss along the trajectory is schematically described by the solid line. The connected points correspond to the convolution of the energy loss with the distribution of induction from a punctual charge. The dashed line builds the charge profile with the projection of the charge distribution in a row of pads.

Figure 4

Kinematics of ${}^7\mathrm{H}$ and ${}^6\mathrm{H}$ production. (a) Scattering angle of ${}^7\mathrm{H}$ (solid line) and ${}^6\mathrm{H}$ (dashed line) respect to recoils ${}^{13}\mathrm{N}$ and ${}^{14}\mathrm{N}$ in laboratory. (b) Kinematics of recoils ${}^{13}\mathrm{N}$ (solid line) and ${}^{14}\mathrm{N}$ (dashed line). The grey area corresponds to the geometrical coverage of MAYA in both panels.

Figure 5

Identification of light scattering particles in CsI. The total energy in the CsI detectors is plotted versus the fast component of the signals. (a) shows the identification of $Z=1$ isotopes. The solid line shows a selection where high energy tritons involved in $1p\text{−}\mathit{xn}$ transfer reactions are expected. (b) Identification of $Z⩾2$ isotopes.

Figure 6

Recoil nitrogen identification. The selection of nitrogen among other recoil species is shown in a spectrum of range/charge ratio. The carbon isotopes region is fitted to a Gaussian shape for reference. The grey histogram shows the distribution when conditioned by tritium identification in one of the CsI detectors.

Figure 7

Excitation energy distributions calculated under the assumptions of (a) ${}^5\mathrm{H}$, (b) ${}^6\mathrm{H}$, and (c) ${}^7\mathrm{H}$ production channels. The grey histograms in the ${}^5\mathrm{H}$ and ${}^6\mathrm{H}$ channels correspond to those events lying in the regions where the resonances were already observed in previous experiments. The grey histogram in the ${}^7\mathrm{H}$ corresponds to those events identified as ${}^7\mathrm{H}$ production. See text for details.

Figure 8

Phase-space calculation. (a) The six-body (solid line) and three-body (dashed line) calculated phase-space are plotted over the excitation energy distribution associated with ${}^7\mathrm{H}$ production. (b) The six-body phase-space from $1p$ transfer (solid) and five-body phase-space from $1p\text{−}1n$ transfer (dashed line) are plotted over the excitation energy distribution associated with ${}^6\mathrm{H}$ production.

Figure 9

Determination of maximum likelihood. The likelihood as a function of the energy and width of the resonance is plotted for (a) ${}^7\mathrm{H}$ and (b) ${}^6\mathrm{H}$. The white lines correspond to the energy and width at the maximum likelihood in both cases.

Figure 10

Excitation energy distribution for the identified (a) ${}^7\mathrm{H}$ and (b) ${}^6\mathrm{H}$ events. The solid function is the Breit-Wigner distribution resulting from the fit to the experimental events. The data is represented with the empty histograms, merely as a guide to the eye, with a 2.5 MeV binning corresponding to the average estimated uncertainty.