Evidence of the existence of the six-quark component of the deuteron in the energy spectra of photons emitted in proton-deuteron collisions

Abstract

We present evidence of the existence of the six-quark component of the deuteron ($d_{6q}$) found in the experimental photon energy spectra of the proton deuteron bremsstrahlung measured at the proton incident energy of 200 MeV by the Grenoble group and of 195 MeV by the Michigan state group. A comparison of these spectra with the theoretically predicted ones revealed that the experimental spectra significantly exceed the theoretical ones. We show that the excess of photons in the experimental spectra was caused by contributions of new mechanisms for the photon production in $pd$ collisions, which are due to the existence of $d_{6q}$. The mechanisms comprise the process $p+d_{6q}\to p^\prime+d_{6q}^\star$, where $p^\prime$ is the scattered proton and $d_{6q}^\star$ is the $d_{6q}$ excited state, which has the total energy below the threshold for its decay by pion emission and the quantum numbers forbidden for the $NN$ system, that experiences then either the radiative decay $d_{6q}^\star\to p+n+\gamma$ or $d_{6q}^\star\to d+\gamma$. By assuming that $d_{6q}^\star$ is the $NN$-decoupled dibaryon $d_1^\star (1956)$, we calculated the expected contribution of these mechanisms to the most precisely measured energy spectrum of photons emitted at $90^0$ for an incident proton energy of 195 MeV. After a simple subtraction of this contribution from the experimental spectrum, we found that the experimetally and theoretically predicted spectra are in good agreement.