Basic Science

Major Progress Scored on Heavy Ion Research Facility

CAS scientists have made significant headway in the development on Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring (HIRFL-CSR), a national mega-science project built by the CAS Institute of Modern Physics (IMP) in Lanzhou, capital of northwest China's Gansu Province. On Oct. 7, the stored beam current intensity at the experimental ring of HIRFL-CSR surpassed its design standards, making new records in terms of ion types, and maximum energy range and beam intensity among the similar systems in the world.

As introduced, the construction of HIRFL-CSR started formally in December 1999. It consists of a main ring (CSRm), an experimental ring (CSRe), beam transportation lines, radioactive ion beam (RIB) separator, experimental probing devices, HIREL improvement and construction and installation projects. CSRm has a circumference of 161 meters with an acceleration energy up to 900MeV/u(12C6+) and 400MeV/u(238U72+) to the highest extent. CSRe has a circumference of 129 meters with an acceleration energy up to 600MeV/u (12C6+) and 400MeV/u(238U90+) to the highest extent. The beam transportation lines are 473 in the total length. The magnet is 1,451 tons in weight. The total power for the electric source of the magnet is 8,234 kilovolt-ampere. The facility covers a floor area of around 17,000 ㎡.

Recent Progress Made in Heavy Ion Collision Study

A heavy ion reaction research team headed by Ma Yugang, Research Fellow from the Shanghai Institute of Applied Physics, CAS, has presented with assistance from their American partners the first measurements of the Φ-meson elliptic flow (v2 (pT )) and high statistics pT distributions for different centralities from sqrt(S_NN) = 200 GeV Au+Au collisions at RHIC. Chen Jinhui, a doctorate student from the Institute, and S. Blyth, a visiting student from the Lawrence Berkeley National Laboratory in U.S., discovered in the RHIC/STAR experiment that in minimum bias collisions the v2 of the Φ meson is consistent with the trend observed for mesons. The ratio of the yields of the ? to those of the Φ as a function of transverse momentum is consistent with a model based on the recombination of thermal s quarks up to pT ~4 GeV/c, but disagrees at higher momenta. The nuclear modification factor (RCP) of Φ follows the trend observed in the KOS mesons rather than in Λ baryons, supporting baryon-meson scaling. Since Φ-mesons are made via coalescence of seemingly thermalized s quarks in central Au+Au collisions, the observations imply hot and dense matter with partonic collectivity has been formed at RHIC. Their feat high in academic significance provides valuable information concerning the shaping of quark-gluon plasma. The relevant paper entitled “Partonic Flow and Φ-Meson Production in Au+Au Collisions at sqrt (S_NN)=200 GeV” has been reported in Physical Review Letters (99, 112301 (2007)).

Construction for Neutrino Experiment Triggered

On Oct. 13, the ground-breaking ceremony for the Daya Reactor Neutrino Experiment, China's single largest international collaboration in basic science as well as the biggest one between US and China, was held at Daya Bay Nuclear Power Base in Shenzhen. Bai Chunli, Executive Vice President of CAS, Cheng Jinpei, Vice Minister of Science and Technology，Shen Wenqing, Vice Minister of the National Natural Science Foundation, Zhong Yangsheng, Vice Governor of Guangdong Province and He Yu, General Manager of the Guangdong Nuclear Power Group and other senior officials and guests were present at the ceremony. There are about 190 researchers from 34 institutions of six countries, who have been involved in the Daya Experiment, such as China (including Hong Kong, Taiwan), US, Russia, etc. It is expected that the construction of the tunnel and the experiment hall will be completed within two years. The assembly and testing of the detector will be finished within one year, and the first data-taking with final configuration in late 2010. It is estimated that the physical objectives will be achieved in three years.