Source: Nanfang Daily 2013-04-09 A08
Written by: Lei Yu
Translated by: Wang Chun, Liang Wenjie
Proofread by: Professor He Zhenhui
Edited by: Wang Dongmei

Under the leadership of Chinese-American physicist and Nobel laureate Samuel C. C. Ting, the research team of a large-scale particle physics experiment, the Alpha Magnetic Spectrometer (AMS) Collaboration published its first physics result in Physical Review Letters on April 5, 2013.

The reporter learned yesterday that among the authors of this recently published paper were 18 teachers and students from Sun Yat-sen University (SYSU) who took part in the AMS Experiment. SYSU teachers and students involved in the experiment told the reporter of Nanfang Daily that in the next few years, Professor Samuel C. C. Ting and the AMS team would be highly possible to find important evidence to prove the existence of dark matter.

Current achievements
Precision calculation of unprecedented 6.8 million electrons

AMS is the most powerful and sensitive particle detector ever deployed in space. One of its main tasks was to search for dark matter in the universe. On May 16, 2011, as the final mission, the space shuttle Endeavor sent “AMS 02” to the International Space Station (ISS).

It is reported that known matter only takes up about 4% of the composition of the universe, while dark matter is 6 times that much, but for a long time, scientists haven’t found the evidence of its existence.

Since its installment on the exterior of ISS on May 19, 2011, AMS has measured more than 30 billion cosmic rays at energies up to trillions of (10¹²) electron volts. Its permanent magnet and array of precision particle detectors collect and identify charged cosmic rays passing through AMS from outer space. Over its long duration mission on ISS, AMS will record signals from 16 billion cosmic rays every year and transmit them to Earth for analysis by the AMS Collaboration.

According to Professor He Zhenhui from the School of Physics & Engineering of Sun Yat-sen University, who took part in the AMS Experiment, AMS analyzed 25 billion primary cosmic ray events in the initial 18 months since its launch. “Of these, we identified an unprecedented number of 6.8 million electrons and their antiparticles, positrons.” He said that the first paper is the result of the precision study of the 6.8 million particles observed in the energy range of 0.5 to 350 GeV.

"Our result is consistent with the theory that dark matter particles may annihilate by colliding and finally produce electrons and positrons." However, Professor He Zhenhui also expressed that, this cannot fully prove the theory, and more data are required for the study — the data reported is only one tenth of the total expected.

Calculating astronomical figure
1,000 CPUs calculate continuously for a whole month

AMS Experiment is a major international scientific project undertaken by more than 500 scientists from over 16 countries and regions. Sun Yat-sen University participated in it since 2003 and undertook a key technology part. Besides, SYSU engaged in experiment data processing and analysis.

"Data processing and analysis are as important as AMS detector construction,” said Weng Zhili, a PhD student of SYSU who has participated in data reconstruction and analysis of the paper. We can know whether dark matter exists or not only after data analysis is completed. AMS statistical analysis is carried out by two independent groups. Each group consists of scientists from several countries who “find fault” with each other, and eventually reach a consensus in order to ensure the accuracy of the results.

Weng Zhili is a 2010 PhD student from the School of Physics & Engineering of Sun Yat-sen University. SYSU has sent three PhD students to AMS Collaboration in succession, among them Weng Zhili is the lucky one who collaborate with Samuel C. C. Ting’s team to do AMS data analysis. In 2009, as an MSc student, he was selected to work in the AMS Operation Center of the European Organization for Nuclear Research (CERN) in Geneva.

25 billion events, 6.8 million electrons, how can we calculate and analyze these overwhelming numbers? “This is not an easy job.” Weng Zhili made a vivid analogy: for the 18 months’ data reconstruction, we need about 1,000 desktop computers with 2.4GHz CPU to run continuously for a whole month.

Weng Zhili said that the life and work in Geneva was stressful. “Mr. Samuel C. C. Ting is very strict, and he never allows even one single mistake in the experiment.” Apart from this, the most pressing thing is to race with time: if the results were not out, he could not graduate from his PhD program on time.

Fortunately, the first experiment result of AMS was released recently. Weng Zhili was able to come back to SYSU for his doctoral dissertation defence.

Highly Praise
Samuel C. C. Ting wrote a letter to SYSU praising its outstanding contributions

Li Ping, Deputy Secretary of SYSU Party Committee, witnessed the whole process of SYSU’s participation in the AMS Experiment. She said that actually there are nearly 70 teachers and students who have taken part in the AMS-TTCS construction. Among them, 30 people have made major contributions, including 18 teachers and students in the authors of the paper.

SYSU takes part in the key technology of the project, and for the first time in the world has developed the thermal control system for AMS tracker, which is used in complex space environment to ensure the tracker’s temperature evenly distributed and stable. Li Ping said that, through participating in the AMS project, SYSU has learned and accumulated abundant experience in the development and management of large-scale international collaborative projects, and improved the overall ability to undertake top level international research projects. During this period, SYSU has published 21 relevant papers in domestic and international journals and 20 conference papers.

Recently, Mr. Samuel C. C. Ting wrote a letter to Professor Xu Ningsheng, President of Sun Yat-sen University, and highly praised the important contributions made by SYSU. “AMS incessantly records and collects billions of events every day. SYSU has made outstanding contributions to the development and assembly of AMS, and has been supporting the monitoring of AMS in orbit to ensure the smooth operation of the experiment.” Samuel C. C. Ting said that the first paper of AMS was published on April 5, 2013, and has received attention from the scientists and the media in many countries; “SYSU has made important contributions to the success of the AMS Experiment.”

Weng Zhili also told the reporter that Chinese scientists will continue to carry out data analysis and physics research. Although it may take several years to ultimately disclose the puzzle of the existence of dark matter, there is no doubt that this achievement is of great significance for the development of physics.