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DOE OSTI · 2204694

Invariant-mass spectroscopy in projectile fragmentation reactions

Charity, R. J.·Sobotka, L. G.
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Abstract

The fragmentation of a projectile into a number of pieces can lead to the creation of many resonances in different nuclei. We discuss application of the invariant-mass method to the products from such reactions to find some of the most exotic resonances located furthest beyond the proton drip line. We show examples from fragmentation of a fast 13 O beam including the production of the newly identified 9 N resonance. In extracting resonance parameters from invariant-mass spectra, accurate estimates of the background from nonresonant prompt protons are needed. These prompt protons are correlated with the resonances due to long-range Coulomb interactions and will suppress events when resonance decay products and the prompt protons have small invariant masses. The shape of this background is especially important in determining the widths of wide resonances typically found at the edge of the chart of nuclides. An event-mixing recipe is proposed to describe this background, where the mixed events have reduced weighting for the smaller invariant masses to account for the effect of the Coulomb final-state interactions. The weighting is based on the measured correlations of heavier hydrogen isotopes with the resonances or the projectile residues. We also show that the relative magnitude of the background can be reduced in some cases by selecting events where the resonance decay products are accompanied by a deuteron or triton cluster. Here, the deuteron and triton clusters are largely not products of resonant decay and thus events with an accompanying cluster are associated with fewer background protons than events without them. The width of the 5/2¯ state in 9 C with the new background prescription was found to be consistent with the value obtained using proton elastic scattering on 8 B. Improved values for the widths of 10 C, 10,11 N, and 12 O resonances were also obtained using the new background prescription.

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6 ≤ A ≤ 1973 NUCLEAR PHYSICS AND RADIATION PHYSICSBreakup reactionsEnergy levelsLifetimes & widthsNuclear fragmentationNuclear reactionsNuclear spin & parityNuclear structure & decaysProton emissionRare & new isotopes

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BibTeXRIS

Charity, R. J., Sobotka, L. G.. 2023-10-27. Invariant-mass spectroscopy in projectile fragmentation reactions. https://doi.org/10.1103/physrevc.108.044318

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