Abstract
In the present Letter we investigate π0π0 and π±π0 photoproduction off complex nuclei at incident beam energies of 400–460 MeV. Simulations of two pion photoproduction on protons and nuclei are performed by means of a semi-classical BUU transport model including a full coupled-channel treatment of the final state interactions. Elastic scattering of the final state pions with the nucleons in the surrounding nuclear medium is found to yield a downward shift of the ππ invariant mass distribution. We show that the target mass dependence of the π0π0 invariant mass spectrum as measured by the TAPS Collaboration can be explained without introducing medium effects beyond absorption and quasi-elastic scattering of the final state particles. On the other hand, we find considerable discrepancies with the data in the π±π0 channel, which are not understood.
Highlights
In the present paper we investigate π0π0 and π±π0 photoproduction off complex nuclei at incident beam energies of 400 − 460 MeV
Since the chiral order parameter qq is expected to decrease by about 30% already at normal nuclear matter density [1, 2, 3, 4], any in-medium change due to the dropping quark condensate should in principle be observable in photonuclear reactions. The conjecture that such a partial restoration of chiral symmetry causes a softening and narrowing of the σ meson as the chiral partner of the pion in the nuclear medium [5, 6] has led to the idea of measuring the π0π0 invariant mass distribution near the 2π threshold in photon induced reactions on nuclei [7]
Measuring a threshold enhancement of the π0π0 invariant mass spectrum might serve as a signal for the partial restoration of chiral symmetry inside nuclei and, give information about one of the most fundamental features of QCD
Summary
In the present paper we investigate π0π0 and π±π0 photoproduction off complex nuclei at incident beam energies of 400 − 460 MeV. The final state interactions (FSI) of the pions with the nucleons in the surrounding nuclear medium have been treated as purely absorptive by means of a Glauber-type damping factor calculated along straight line trajectories.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
