|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!
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!
Members of the ALPHA Collaboration from Canada were recently awarded the NSERC John C. Polanyi Award for their contributions to ALPHA's sucesses in trapping and measuring antihydrogen atoms. The award honours an individual or team whose Canadian-based research has led to a recent outstanding advance in the natural sciences or engineering.
|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
Right now everyone at ALPHA is busy assembly the ALPHA-2 apparatust, the sucessor to ALPHA. The most recent parts to arrive have been the atom-trap cryostat built in TRIUMF in Vancouver, and the new superconducting solenoid, built by Oxford Instruments in the UK and financed by the Danish Carlsberg Foundation. They join the catching trap, designed by the Cockcroft Institute and the existing positron accumulator from ALPHA to make up the complete chain of apparatus being used in ALPHA-2.
The first antiprotons were caught last night in the new ALPHA2 catching trap, the first component of the next generation of the ALPHA experiment to be installed. This is the representation of the first 'hot dump' -- where we release the captured antiprotons, allowing them to annihilate on the surrounding apparatus. The annihilation converts the antiprotons into high-energy charged particles, which are counted by detectors surrounding the apparatus. Because we detect the annihilations at the same time as we release the trap, we can be sure that the antiprotons have been captured in the trap. Read more about the Penning trap in How ALPHA works.
The catching trap, designed in collaboration with staff at the Daresbury Laboratory and the Cockcroft Institute in the UK, will be responsible for cooling 5MeV antiprotons from the AD, and supplying them on demand to the ALPHA2 atom trap, which will be installed later this year. Construction has been taking place at the AD for the last month, and even though there's a long way to go before the apparatus achieves its full potential, this is a big milestone for us at ALPHA.
The construction team at CERN
Once you've trapped antihydrogen what do you do? You measure it! That's just what we've done. Published in Nature, we report the first resonant quantum transitions in antihydrogen atoms. We've used microwave radiation to change the internal state of the atom, from one which can be kept in our trap, to one that is kicked out. This process depends on the frequency of the microwave radiation and the magnetic field in the trap, so by changing both of these, we demonstrated that we had enough control and sensitivity to sucessfully carry out the experiment. This is by no means easy, as antihydrogen is not found in nature, but must be prepared in our apparatus from antiprotons made in the Antiproton Decelerator, and positrons from a radioactive source, Even more, it must have low enough energy to remain trapped in the magnetic fields making up our trap. Here's an animation describing how we do our measurement.
Eventually, we will use this technique to compare the structure of antihydrogen and hydrogen atoms, to search for difference between matter and antimatter, but In this first experiment, we do not yet have enough precision to test these fundamental symmetries. This is important, as the Universe has shown a preference for matter over antimatter as it has evolved, but so far, no measurements can explain why this came about. If matter and antimatter were truely identical, the Universe as we know it could not have come about. The next step at ALPHA is to construct an apparatus that will allow us to make these more precise measurements, using both microwave radiation, and laser light.
We've been waiting a long time for this result, so we're really happy -- the CERN People documentary has been following us through the process -- check out the first video here.
Our new octupole is being made at Brookhaven National Laboratory - here's a video that they've sent us of the work in progress.
The superconducting wire is laid down by a machine-controlled head, and bonded in place as it goes. The new octupole will be welded into the ALPHA-2 cryostat and comissioned at CERN this summer. Thanks to the BNL Superconductng Magnet Division for making this video for us.