The mystery of antimatter
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The discovery of a particle with curious properties in August 1932 was probably the first time a piece of antimatter was found in nature. At that time, a particle detector called cloud chamber, where an incoming particle would leave a trail of drops was being used to record particles. In the presence of a magnetic field, particles would curve in opposite directions depending on their charge. Carl Andersen, a physicist from Caltech in the USA, when working with cosmic rays, found a track in the cloud chamber which was opposite in direction to the ones caused by the electron. Carl called it a positron which seemed to be very similar to the electron except for the charge.
This particle had been actually anticipated by the scientific community. In 1897, J J Thomson discovered the electron, a negative charged particle. In 1928, the great theorist Paul Dirac published the famous Dirac equation, which allowed electrons to have both positive charge and negative energy. While for sometime, he thought that proton could be that particle, three years later he predicted the particle would be an antielectron with all qualities same as electron but with a positive charge. Paul and Carl and got the Nobel Prize for the prediction and the discovery in 1933 and 1936, respectively. Thus, it was accepted that all particles should have antiparticles.
A fundamental concept
In the postulation and discovery of the positron, physicists were enunciating a fundamental concept that equal amount of matter and antimatter should be present in the Universe. Paul had also postulated that when matter and antimatter combine, they would annihilate each other, resulting in the creation of energy which would present itself in the form of high energy photons like gamma rays.
The energy of one of the first big particle accelerators Bevatron was tuned specifically to produce antiprotons. It started functioning in 1954. After one year of the experiment, and sifting through nearly two million particle events, the group had detected 38 particles with same mass as proton but with negative charge. This research also fetched the Nobel Prize for the discovery of antiproton.
Neutral particles also have antiparticles. For example, neutron and antineutron have differing signs for their magnetic moment. Just as hydrogen atom has a proton in the centre and an electron in the outer ring, antihydrogen atom would have antiproton in the centre and a positron in the outer ring.
The preponderance of matter over antimatter has been a mystery of nature. If these had been in the same proportion, the Universe, as we know, would not have come into existence. Somewhere in the initial stages of the Big Bang, due to certain processes, we have an asymmetric universe. However, there is the possibility that there are some regions of the Universe where antimatter dominates. Thus, how much antimatter exists is one of the fundamental questions of the origin and nature of the Universe. Another important question is about the possible difference between matter and antimatter. There have been two interesting experiments addressing these questions in the last few months.
First is the AMS (Alpha Magnetic Spectrometer) experiment located on the International Space Station, which looks for primary antiprotons in cosmic rays. Its aim, according to its spokesman, Nobel Prize winner Samuel Ting, is “to search for phenomena that so far we have not had the imagination or the technology to discover!” The standard picture is that antiprotons are produced in collisions of cosmic ray protons with nuclei in interstellar matter. New results from the experiment presented in mid-April disagree with current models of antiproton production.
The ratio of antiprotons to protons has been obtained across a wide energy range and the experiment finds that this proportion does not decrease at higher energies as predicted, but stays almost constant. Earlier, the same group had found an anomalous result for the proportion of positrons to electrons, a higher fraction than expected, but it could be invoking conventional physics. The authors believe that dark matter could be producing these antiprotons but only more data can give a better understanding of the results.
The second experiment seeks to find possible differences between matter and antimatter. While they can differ, for example, in the way they decay, other fundamental properties, such as the absolute value of their electric charges and masses are predicted to be exactly equal. It is with this aim that an experiment called Baryon Antibaryon Symmetry Experiment (BASE) conducted in CERN laboratory in Geneva started some time ago. The experiment looks for precise comparison of the charge-to-mass ratio of the proton to that of the antiproton.
The new result, the result of an intense 35-day experiment with 13,000 measurements, shows no difference between the proton and the antiproton. They state, “We found that the charge-to-mass ratio is identical to 69 parts per thousand billion, supporting a fundamental symmetry between matter and antimatter.”
Any difference between the charge-to-mass ratio of protons and antiprotons, however small, would break a fundamental symmetry law, a difference that would constitute a dramatic challenge to the basic concepts of particle physics.
This particle had been actually anticipated by the scientific community. In 1897, J J Thomson discovered the electron, a negative charged particle. In 1928, the great theorist Paul Dirac published the famous Dirac equation, which allowed electrons to have both positive charge and negative energy. While for sometime, he thought that proton could be that particle, three years later he predicted the particle would be an antielectron with all qualities same as electron but with a positive charge. Paul and Carl and got the Nobel Prize for the prediction and the discovery in 1933 and 1936, respectively. Thus, it was accepted that all particles should have antiparticles.
A fundamental concept
In the postulation and discovery of the positron, physicists were enunciating a fundamental concept that equal amount of matter and antimatter should be present in the Universe. Paul had also postulated that when matter and antimatter combine, they would annihilate each other, resulting in the creation of energy which would present itself in the form of high energy photons like gamma rays.
The energy of one of the first big particle accelerators Bevatron was tuned specifically to produce antiprotons. It started functioning in 1954. After one year of the experiment, and sifting through nearly two million particle events, the group had detected 38 particles with same mass as proton but with negative charge. This research also fetched the Nobel Prize for the discovery of antiproton.
Neutral particles also have antiparticles. For example, neutron and antineutron have differing signs for their magnetic moment. Just as hydrogen atom has a proton in the centre and an electron in the outer ring, antihydrogen atom would have antiproton in the centre and a positron in the outer ring.
The preponderance of matter over antimatter has been a mystery of nature. If these had been in the same proportion, the Universe, as we know, would not have come into existence. Somewhere in the initial stages of the Big Bang, due to certain processes, we have an asymmetric universe. However, there is the possibility that there are some regions of the Universe where antimatter dominates. Thus, how much antimatter exists is one of the fundamental questions of the origin and nature of the Universe. Another important question is about the possible difference between matter and antimatter. There have been two interesting experiments addressing these questions in the last few months.
First is the AMS (Alpha Magnetic Spectrometer) experiment located on the International Space Station, which looks for primary antiprotons in cosmic rays. Its aim, according to its spokesman, Nobel Prize winner Samuel Ting, is “to search for phenomena that so far we have not had the imagination or the technology to discover!” The standard picture is that antiprotons are produced in collisions of cosmic ray protons with nuclei in interstellar matter. New results from the experiment presented in mid-April disagree with current models of antiproton production.
The ratio of antiprotons to protons has been obtained across a wide energy range and the experiment finds that this proportion does not decrease at higher energies as predicted, but stays almost constant. Earlier, the same group had found an anomalous result for the proportion of positrons to electrons, a higher fraction than expected, but it could be invoking conventional physics. The authors believe that dark matter could be producing these antiprotons but only more data can give a better understanding of the results.
The second experiment seeks to find possible differences between matter and antimatter. While they can differ, for example, in the way they decay, other fundamental properties, such as the absolute value of their electric charges and masses are predicted to be exactly equal. It is with this aim that an experiment called Baryon Antibaryon Symmetry Experiment (BASE) conducted in CERN laboratory in Geneva started some time ago. The experiment looks for precise comparison of the charge-to-mass ratio of the proton to that of the antiproton.
The new result, the result of an intense 35-day experiment with 13,000 measurements, shows no difference between the proton and the antiproton. They state, “We found that the charge-to-mass ratio is identical to 69 parts per thousand billion, supporting a fundamental symmetry between matter and antimatter.”
Any difference between the charge-to-mass ratio of protons and antiprotons, however small, would break a fundamental symmetry law, a difference that would constitute a dramatic challenge to the basic concepts of particle physics.