ALPHA is an international collaboration based at CERN, and whose aim is stable trapping of 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.
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