The Color Of Antihydrogen Seen At Most Precise Measurement Of Antimatter Ever

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The ALPHA experiment at CERN has measured with the highest precision a light-induced transition in an atom of antihydrogen, making this the most precise direct measurement of antimatter ever made. The study is the culmination of 30 years of research into the nature of antimatter by CERN.

Electrons in atoms can jump from one orbital to a higher energy orbital when shooting around photons and they emit light at specific wavelengths (color) when jumping back down. These are called spectral lines. The spectral lines of hydrogen, which is the most common element in the universe, are already known to a precision of a few parts in a quadrillion (1015).

Similar measurements for antihydrogen has not been as easy to obtain due to several factors, chiefly among which there’s the pesky habit of antimatter’s annihilation whenever it comes into contact with regular matter. But researchers at CERN persisted and have now been able to obtain the frequency of the transition between the lowest-energy state and the first excited state at a precision of a few parts per trillion. The results, published in Nature, are 100 times better than the previous ALPHA estimate.

“This measurement completely blows the previous best measurement out of the water. Our last publication on this property of antihydrogen in 2016 looked at the same property of antihydrogen, the spectra from its lowest energy state,” Joseph McKenna, detector, machine learning and data analysis expert for ALPHA, told IFLScience. “To measure the color of antihydrogen with a precision of one part in a trillion is a huge step towards understanding our universe.”

Obtaining and studying antihydrogen is not easy. Researchers with ALPHA need to use antiprotons from CERN’s antiproton decelerator and bind them with positrons (the anti-electrons) emitted by a sodium-22 source. Afterward, they are placed in a magnetic trap that prevents them coming into contact with matter and annihilating. The researchers then shine a laser on these atoms, so that the positron can jump to a higher orbital.

By studying antimatter physicists hope to answer a fundamental question about the universe; why everything we see is made of matter. According to the Standard Model of particle physics, which describes all particles and their interactions, matter and antimatter should behave exactly in the same way. Clearly, something favored matter over antimatter, and researchers are hoping to find such a discrepancy in some of the properties in antihydrogen. No such luck in this case. The antihydrogen measurement is in great agreement with the hydrogen measurement.

“Our major goal is to see if there is any difference in the properties of hydrogen and antihydrogen, and compare the matter and antimatter world. Any differences could lead to an understanding why we are made of matter rather than antimatter,” Mckenna added.  

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