Study of ultra-narrow dibaryon states during the interaction of nucleons of intermediate energies with few-nucleon systems

INR RAS - Study of ultra-narrow dibaryon states in the interaction of nucleons of intermediate energies with systems with few nucleons.

For several years, the Moscow Meson Factory of the Institute for Nuclear Research (INR RAS) has been searching for ultra-narrow dibaryons - six-quark systems with a mass less than 2MN+mp, the decay of which into two nucleons is prohibited by the Pauli principle. Ultranarrow dibaryons can be produced during the interaction of nucleons of intermediate energy with systems with few nucleons and must decay through an electromagnetic channel. Moreover, heavy particles from the decay of a super-narrow dibaryon fly out in a narrow angular cone. This feature of ultra-narrow dibaryons is the basis for the method of their experimental study using the TAMS two-arm multidetector scintillation spectrometer, which consists of measuring the spectrum of missing masses when registering a scattered nucleon in coincidence with heavy particles from the decay of the dibaryon. This method allows a special choice of kinematic conditions to suppress the non-resonant background by several orders of magnitude and register the birth of ultra-narrow dibaryons at a level of ~100 nb/(sr MeV) and determine their quantum numbers from the angular distribution of heavy particles from the decay of dibaryons.

Using the TAMS spectrometer, a search for ultra-narrow dibaryons in the pd->p1X reaction was carried out in the mass range (1876-1945) MeV/c2 at a linear accelerator proton beam energy of 305 MeV. As a result of the experiment, three narrow peaks at 1904, 1926 and 1942 MeV/c2 with widths equal to the experimental resolution were discovered in the spectrum of the missing masses Mx with high confidence (SD=6-7). Analysis of the experimental X decay spectra shows that the main contribution to the detected resonances comes from processes with the X -> γ pn decay channel. This, as well as the measured angular distributions of protons from resonance decays, indicate that they can most likely be interpreted as isovector dibaryon states with spin 1.

In the future, at the TAMS facility it is planned to continue the experimental study of ultra-narrow dibaryon states during the interaction of nucleons of intermediate energy with few-nucleon systems in order to obtain new information about their parameters: masses, widths, quantum numbers and decay modes. To do this, it is proposed to study, using proton and neutron beams, the charge exchange reactions pd -> nX and nd -> pX, in which only isovector dibaryon states can be excited. The use of T and 3He targets increases the probability of the formation of ultranarrow dibaryons in the reactions pT -> dX, p3He -> dX, nT -> dX, n3He -> dX.

Using the TAMS installation, it is also possible to study spin-isospin excitations in the charge exchange reactions pT -> n3He* and n3He -> pT*, p3He -> nX+, nT->pX- in order to search for high-isospin excited states in few-nucleon systems. The search for high-isospin excited states is also possible in the reactions pd -> πT*, nd -> π-3He *, pd -> π-X+, nd -> π+X- using a charged pion spectrometer created and tested on a proton beam.

An experiment is also being developed to search for ultra-narrow dibaryons in the pd -> p1pnγ reaction using a petawatt laser facility for proton acceleration (ELI-NP facility). In the experiment, it is expected to obtain a secondary beam of protons with an average intensity of ~ 2.6 1014 cm-2 s-1 during the interaction of laser-plasma radiation with the target. It is planned to register a scattered proton as well as a proton and a neutron from the decay of a dibaryon in coincidence. To detect protons, it is proposed to use two magnetic spectrometers equipped with multi-wire cameras. To measure neutron energy, it is proposed to use a system of new detectors based on layers of 10B and wire chambers. We plan to study the missing mass with a resolution of less than 1 MeV without detecting a photon.