A "dark matter hunter" dissects cosmic rays

Co-led by the University of Geneva, the DAMPE mission, a dark matter detector in space, published its first scientific results. 

Never detected, dark matter is nevertheless considered as an important element for understanding and studying many phenomena in the Universe. The DAMPE (DArk Matter Particle Explorer) mission, initiated in 2012 by the Chinese Academy of Sciences (CAS) in collaboration with the University of Geneva (UNIGE) and the National Institute of Nuclear Physics of Italy (INFN), has the mission to discover its trace. Its first scientific results are published in the journal Nature. The data collected by the satellite reveal the distribution of the particles of the cosmic rays according to their energy: the lower the measured energy, the more the particles are numerous, and vice versa. But what should have been a regular curve actually shows an unexplained break in the high energy range, around 0.9 TeV, from which particles are less numerous than expected. Understanding this "spectrum break" could allow us to go back to the source that emitted these particles. And among the possible sources are the annihilation or the disintegration of dark matter.

DAMPE, China's first astronomical satellite, was launched from the Jiuquan Satellite Launch Center in Orbit on December 17, 2015. DAMPE is the result of a collaboration of more than a hundred scientists, technicians and students from nine institutes in China, Switzerland and Italy. The team of Professor Xin Wu, from the Physics Section of the Faculty of Science of UNIGE, in collaboration with Italian scientists from the National Institute of Nuclear Physics (INFN) in Italy (Bari, Lecce and Perugia) , designed part of this satellite: the Silicon Tungsten Tracker (STK). It permits the detection of the traces of particles which traveling through DAMPE, in order to understand the origin and the nature of the dark matter.

A Spectrum rupture detected with unprecedented precision

During its first 18 months of scientific operation, DAMPE has detected 1.5 million electrons and positrons, the antiparticle of the electron, from cosmic ray, up to very high energy range, a few Teraelectronvolt (TeV),  with a very low background noise. DAMPE has made a direct measurement of a break, ie a decrease in particle flux, in the spectrum of electrons and positrons at an energy of about 0.9 TeV. This very precise measurement complements other anomalies already observed and considerably reduces the researchers' field of investigation; it makes it possible to fine tune the models explaining the behavior of flows, and thus to define more precisely the possible sources. 

New data will soon enable a more precise measurement of the spectrum of electrons and positrons of cosmic rays, up to an energy two times higher. Scientists will also be able to explore the spectral features potentially generated by the annihilation and disintegration of dark matter particles or by nearby astrophysical sources, such as neutron stars spinning very fast on themselves and emitting radiations. "But these first data already represent a great advance and could suggest a connection between the observed anomalies and the disintegration of dark matter," Xin Wu explains.

Contact : Xin Wu, Xin.Wu(at)unige.ch, +41 22 379 62 72