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Antimatter

wikipedia article on antimatter

We have performed several calculations that provide data for experiments that have made antihydrogen. The focus of our current calculations is on processes that will control whether the antihydrogen can be trapped. See a review article (F. Robicheaux, "Atomic processes in antihydrogen experiments: a theoretical and computational perspective," J. Phys. B 41, 192001 (2008). PDF (369 kB)) about our understanding of atomic processes in these experiments.

We are part of the ALPHA collaboration which includes groupus from over 10 countries. The experiment is performed at CERN. The eventual goal is to perform spectroscopy on antihydrogen to compare with the same process in hydrogen. Currently, the 1s-2s frequency is known to 14 significant digits. There would be profound implications for our understanding of fundamental physical laws if there were to be any difference in the spectra of antihydrogen compared to hydrogen.

The goal of trapping antihydrogen is the last necessary stage before performing spectroscopy experiments. This is a difficult undertaking because the trapping well will not be able to hold atoms with energy greater than about 1/2 K. The well depth is about 10,000 times smaller than the starting energies of the charged particles.

Our role in the collaboration is to perform calculations to understand the basic processes in the ALPHA apparatus. This helps in trying to pick the most likely schemes for making cold antihydrogen. Below is a brief description of results in three recent publications.



G. B. Andresen, et al (ALPHA collaboration), "Trapped antihydrogen," Nature 468, 673 (2010). PDF (946 kB) (Many online articles)

This was the first report of trapped antihydrogen.



This image shows a schematic of the trap (upper image) and the electric potentials which trap the antiprotons and positrons before they are combined to form antihydrogen.



The trapped antihydrogen were detected by quenching the magnetic fields from the octupole and mirror coils. The image above shows where (along the trap axis) and when the antihydrogen annihilated on the walls of the trap after the quench. The solid symbols are the experimental data. The dots are from our calculations. The upper plot shows calculated data for trapped antihydrogen. The lower plot shows calculated data for trapped antiprotons. The agreement in the upper plot and disagreement in the lower plot rules out mirror trapped antiprotons and confirms the trapping of antihydrogen.




G. B. Andresen, et al (ALPHA collaboration), "Confinement of antihydrogen for 1,000 seconds," Nature Physics 7, 558 (2011). PDF (1260 kB) (Many online articles)

This was the first report that trapped antihydrogen could be confined for times long enough (more than 15 minutes) to be able to perform experiments on them.


This image shows the measured trapping rate as a function of how long we waited between the formation of the antihydrogen and the time of the quench. The upper graph shows the the trapping rate is nearly independent of the hold time. The lower graph shows the results are statistically significant out to 1000 seconds which is longer than 15 minutes.




C. Amole, et al (ALPHA collaboration), "An experimental limit on the charge of antihydrogen," Nature Comm. 5, 4955 (2014). PDF (793 kB)

This was the first report on the limits of the antihydrogen charge.



This image shows that the position of the antihydrogen annihilation was performed with the electric potential giving either a left or right pushing electric field. The measured hit positions of the antihydrogen for the two different potentials is the lowest plot. An uncharged antihydrogen should give an unbiased hit distribution.



This image shows the calculations for uncharged and two slightly charged antihydrogen in units of the proton charge. This gives an idea of the sensitivity of the measurement.



Five Recent Publications

C. Ahmadi, et al (ALPHA collaboration), "An improved limit on the charge of antihydrogen from stochastic acceleration," Nature 529, 373 (2016). PDF (641 kB)

C. Amole, et al (ALPHA collaboration), "An experimental limit on the charge of antihydrogen," Nature Comm. 5, 4955 (2014). PDF (793 kB)

P. Hamilton, A. Zhmoginov, F. Robicheaux, J. Fajans, J.S. Wurtele, and H. Muller, "Antimatter interferometry for gravity measurements," Phys. Rev. Lett. 112, 121102 (2014). PDF (730 kB) News and commentary, Physics World

C. Amole, et al (ALPHA collaboration), "Description and first application of a new technique to measure the gravitational mass of antihydrogen," Nature Comm. 4, 1785 (2013). PDF (873 kB)

C. Amole, et al (ALPHA collaboration), "Resonant quantum transitions in trapped antihydrogen atoms," Nature 483, 439 (2012). proofs PDF (623 kB)


Francis Image

robichf[at]purdue.edu
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