The origin of the universe is one of the fundamental puzzles that scientists devote themselves to. The “Big Bang” theory predicts that the universe was created from an explosion with extremely high energy density at time birth. A few micro-seconds after that a hot and dense matter formed with quark and gluon isolated, which is the new matter state that scientists search for in the collider. This new matter state is so-called Quark-Gluon Plasma (QGP). Looking for the evidences of the QGP existence is the most important goal.

ZHANG Yifei, associate professor from State Key Laboratory of Particle Detection and Electronics at USTC, collaborated with Dr. DONG Xin from LBNL and STAR Collaboration, observed the D⁰ meson nuclear modifications from 800 million events in Au+Au collisions at RHIC. This work provide experimental evidence that charm quark lose energy in a hot and dense nuclear matter and the D⁰ meson is hadronized from quark coalescence with a charm and an anti-up quark isolated in this kind of matter. This supports the QGP, formed in the early stage of the universe, has been created in the collider. This work is published online at Phys. Rev. Lett. 113, 142301, 2014.

ZHANG Yifei, TANG Zebo and GUO Yi from USTC, collaborated with SINAP, BNL and LBNL, achieved another important result in di-lepton production measurement. The results are published at Phys. Rev. Lett. 113, 022301, 2014.

Fig.1: D⁰ meson nuclear modification factor, the enhancement at low pT is from quark coalescence and suppression at high pT is from quark energy loss.

This work is supported by the NNSFC and the MoST of China (973 program).

(School of Physical Sciences)