A simulation of a lead ion collision in ALICE. Credit: CERN
CERN: Most precise measurement of mass and charge of Light Nuclei and Snti-Nuclei. Why did anti-matter disappear almost completely from our universe, whereas matter did not? Scientists are attempting to solve this mystery at the European research institute at CERN. Now they published the most precise measurement of the properties of light atomic nuclei and anti-nuclei ever made.
At the LHC, researchers let lead nuclei and protons collide at the highest beam energies to date. The temperatures created are 100,000X higher than those in the center of the Sun. “A state is created that is very similar to the one after the Big Bang,” explains Prof Laura Fabbietti. The quark-gluon-plasma (QGP) probably formed 1 microsecond after the Big Bang when the universe was expanding at great speed. The QGP produced in the laboratory is stable only for a fraction of a second, but in this short time, they can look back into the past of the universe.
According to CPT theorem (charge, parity, time), there is a fundamental symmetry between particles and antiparticles in our Universe. ie there should be no difference between our Universe and one where all particles are exchanged with antiparticles (and vice versa), if the Universe is also inverted in time and space. There must be a difference nevertheless, since CPT says that equal quantities of matter and antimatter should have been produced during the Big Bang. When particles and antiparticles meet, they annihilate each another. However, nowadays we almost only observe particles – there must therefore have been an imbalance.
Physicists are looking for a violation of the CPT theorem which would help to explain the existing matter-antimatter asymmetry. “ALICE is attempting to find a difference by means of high-precision measurements of the properties of particles and their antiparticles which are produced in particle collisions at the LHC,” explains Dahms. In the current study, they investigated mass-to-charge ratio of He-3 nuclei and He-2 nuclei and their respective antiparticles. Charge and mass are determined by measuring the particle traces and particle’s specific energy loss within gas detector TPC (Time Projection Chamber), heart of the ALICE detector system.
“At the moment we are able to record 500 collisions per second,” explains Fabbietti. “Soon it should be 50,000 collisions per second.” The TUM groups are working on an upgrade of the TPC read out. The existing multi-wire chambers are being replaced by state of the art GEM foils that provide better spatial resolution as well. http://www.tum.de/en/about-tum/news/press-releases/short/article/32586/
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