Researchers observe enhanced yield ratio between strange and nonstrange open-charm mesons

The researchers from the University of Science and Technology of China (USTC), together with international collaborators, observed an obvious enhancement in the yield ratio between strange (Ds^±) and nonstrange (D⁰) open-charm mesons compared to PYTHIA simulations for p + p collisions. This study was published in Physical Review Letters on August 26.

Significant enhancement of Ds^±/D⁰ yield ratio. (Image by STAR Collaboration)

It has been widely acknowledged that the temperature and energy densities were extremely high shortly after the Big Bang that created the universe. Under such circumstances, quark-gluon plasma (QGP) in which quarks and gluons constrained by hadrons became the degrees of freedom, was formed. The Ds^± consists of a charm quark and a strange antiquark, and the D⁰ is made of a charm quark and a light antiquark.

In this study, the Relativistic Heavy Ion Collider (RHIC), the first machine in the world capable of colliding heavy ions at relativistic speeds, helped researchers create conditions close to the Big Bang.

The measurement of Ds^±/D⁰ based on the Au + Au collisions at a center-of-mass energy of 200 GeV which were collected by the STAR experiment showed notable enhancement compared to the values of PYTHIA simulations of p + p collisions. The results verified the composition of Ds^± and D⁰.

This study ensures the coalescence hadronization mechanism of charm quarks through the formation of open-charm hadrons and shows the leading role QGP plays in Ds^±-meson production.