ALPHA is an international collaboration based at CERN, and who is working with trapped antihydrogen atoms, the antimatter counterpart of the simplest atom, hydrogen. By precise comparisons of hydrogen and antihydrogen, the experiment hopes to study fundamental symmetries between matter and antimatter.


Artist's impression of a cloud of trapped antihydrogen atoms (Chukman So)

Our latest breakthrough, the first observation of the 1S-2S transition in trapped antihydrogen has been published in Nature and is the first time a spectral line has been observed in antihydrogen. This builds on years of work, developing techniques to manipulate super-cold antiprotons and positrons, create trapped antihydrogen and detect the very few atoms that are available to the experiment. It is another crucial step towards precision comparisons of antihydrogen and hydrogen. 

Directly measuring if there are any differences between the antimatter partners may help us understand why our Universe is made almost entirely of matter, even though matter and antimatter should have been produced in equal quanitites in the Big Bang.

In our experiment, we trapped antihydrogen atoms in our magnetic trap and illuminated them with laser light with a wavelength close to 243nm. In one series of runs, we tuned the light so that it is in resonance with the 1S-2S transition in hydrogen, and in a second series, so that it was detuned by 200 kHz. Interactions between the laser and the trapped atoms should cause atoms to be lost from the trap. 

In each run, after 600s of illumination, we counted the number of atoms left in the trap using our annihilation imaging detector. When the laser was tuned to resonance, we observed 67 atoms in 11 runs; when the laser was detuned, we counted 159 atoms in the same number of runs. We also searched for signs of the atoms annihilating as they left the trap while the laser illuminated. When the laser was on-resonance, we observed 79 events that pass our criteria for inclusion, and 27 when off-resonance. Both of these comparisons help us conclude that the on-resonance laser light is interacting with the antihydrogen atoms via their 1S-2S transition.

This first result implies that the 1S-2S transition in hydrogen and antihydrogen are not too different, and the next steps are to measure the transition's lineshape and increase the precision of the measurement. Watch out for more exciting results over the next few years!

This item in the news!

The 2016 run is over

06 Dec 2016

We've shut down for 2016 - see you next year!


ELENA, a new ring that will slow the Antiproton Decelerator's antiprotons down even further has now finished construction and is entering the commissioning phase. Read about it here and check out the timelapse video of the construction below. For more information, read the CERN Courier article or visit the ELENA project website.

We're looking forward to receiving antiprotons from ELENA after the next long shutdown at CERN!

Some members of the Canadian group at ALPHA

The Canadian group contributes accross the spectrum of ALPHA's work, but particularly in the areas of electronics and analysis for the annihilation detector, and the development of the microwave system for measuring antihydrogen's ground-state structure. The design and construction of ALPHA-2's atom-trap cryostat was also led by Canadian institutes.

The full Canadian team at ALPHA is Nathan Evetts, Andrea Gutierrez, Prof. Walter Hardy, Mario Michan, Prof. Takamasa Momose, Sarah Seif El Nasr (University of British Columbia), Dr. Timothy Friesen, Dr. Richard Hydomako, Prof. Robert Thompson (University of Calgary), Mohammad Ashkezari, Ryan Dunlop, Prof. Mike Hayden (Simon Fraser University), Dr. Makoto C. Fujiwara, Dr. David Gill, Leonid Kurchaninov, Konstantin Olchanski, Prof. Art Olin, Dr. James Storey, Dr. Simone Stracka (TRIUMF), Chanpreet Amole, Andrea Capra, Prof. Scott Menary (York University).

Prof. John C. Polyani, the  Nobel-prize winning chemist for whom the prize is named, welcomed the award, saying

‘’Throughout my career colleagues have assured me that the universe should not exist. Creation produced equal amounts of matter and anti-matter; they should have annihilated one another. Today's prizewinners give us hope that the universe may yet be saved. They have kept anti-matter away from matter for a full 15 minutes. The universe is older than that, so our prizewinners will be back on this stage. Meanwhile we congratulate NSERC for bravely recognizing the best and most basic research, and we applaud our prizewinners for adding an important milestone to the history of science.’’

Physicists have long wondered if the gravitational interaction between antimatter and matter might be different than that between matter and itself. Do atoms made of antimatter, like antihydrogen, fall at a different rate to those made of matter, or might they even fall up -- antigravity? There are many arguments that make the case that the interaction must be the same, but no-one has ever observed what an anti-atom does in a gravitational field - until now.

Today, the ALPHA Collaboration has published results in Nature Communications placing the first experimental limits on the ratio of the graviational and inertial masses of antihydrogen (the ratio is very close to one for hydrogen). We observed the times and positions at which 434 trapped antihydrogen atoms escaped our magnetic trap, and searched for the influence of a gravitational force. Based on our data, we can exclude the possibility that the gravitiational mass of antihydrogen is more than 110 times its inertial mass, or that it falls upwards with a gravitational mass more than 65 times its inertial mass.

Our results far from settle the question of antimatter gravity. But they open the way towards higher-precision measurments in the future, using the same technique, but more, and colder trapped antihydrogen atoms, and a better understanding of the systematic effects in our apparatus.

Read the paper on Nature Communications at http://dx.doi.org/10.1038/ncomms2787

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