Scientists at CERN take Anti-Matter for a Sunday Drive, and just what is Anti-Matter anyway.

We’ve all heard about anti-matter. We’ve been told that anti-matter is made up of anti-particles which are some weird mirror images of familiar particles like the electron or proton. We’ve also know that whenever a particle and its anti-particle come in contact they annihilate each other leaving only a burst of energy.

I know that anti-matter seems like the stuff of science fiction, after all doesn’t the starship Enterprise in Star Trek have matter / anti-matter engines. Anti-matter isn’t real, it’s just some strange theory that Einstein or some other physicist thought up, right?

It’s true that the English physicist Paul Dirac predicted the existence of anti-matter in 1926 as he was trying to mathematically combine Einstein’s special theory of relativity with quantum mechanics. What Dirac’s calculations told him was that for every kind of particle there should be another particle, having the same mass but the opposite charge. Even Dirac wasn’t certain what to make of his own prediction.

It was only six years later in 1932 however that the first picture of an anti-particle was taken by the American physicist Carl Anderson who was doing research on the cosmic ray particles striking our planet from outer space. That first evidence of the reality of anti-matter is shown below in a picture made in what is known as a cloud chamber.

First Photograph of an Anti-Particle taken by Carl Anderson (Credit: Public Domain)

Since the time of Dirac and Anderson physicists have continued to study anti-matter in cosmic rays. Not only that but they have also used their high-energy atom smashers; we call them particle accelerators nowadays, to actually manufacture anti-matter.

How do they manufacture anti-matter you ask? Well if a particle and anti-particle annihilate each other leaving only energy, then energy can be separated into a particle and its particular anti-particle. Out of the debris that comes from collisions in particle accelerators we have found the anti-particle of nearly every known particle. The photon of light is an exception because it is actually its own anti-particle! Below is an image taken of the products of some of these collisions along with a breakdown of what is happening.

Bubble Chamber Photograph from CERN (left) along with analysis of interactions (Credit: CERN)

Handling the anti-matter is obviously a delicate task but slowly scientists are learning how to confine charged anti-particles in a vacuum bottle with a magnetic field that keeps the particles from even touching the bottle’s walls. Using such a magnetic bottle the physicists at CERN now plan for the first time to transport anti-protons from the labouratory where they were produced to another labouratory at the CERN facility.

You see the physicists working on the PUMA experiment (that’s the anti-Proton Unstable Matter Annihilation experiment) are studying the structure of Protons and Neutrons in large, unstable nuclei. The researchers working on PUMA intend to use the anti-protons as probes that can tell them a great deal about the arrangement of the protons and neutrons in the nuclei that they study.

You remember from high school that the nucleus of every atom is made up of protons and neutrons. You may also recall that the lighter, more stable nuclei like Carbon-12 have six protons and six neutrons, an equal number of each. However large unstable nuclei like Uranium have more neutrons, 146 than protons 92 and physicists want to learn the details of how the different particles arrange themselves.

Now an anti-proton will annihilate a proton but it will also react with a neutron in a different way so observing the reactions will paint a picture of the structure of the target nucleus. The planned setup for the PUMA experiments is shown in the image below.

Outline of PUMA experiment at CERN (Credit: Nature)

There are still a lot of things we don’t know about anti-matter and scientists will continue to study these mirror particles for years to come. However it is a measure of how much we’ve learned that we are now using anti-matter to study other phenomenon.


America’s Science Decline: Part 3, Our Forgotten Atom Smashers

This is the third in a series of posts discussing what I see as the decline of Science in the United States. In part two of this series I talked about how for more than a century the United States built ever larger and larger telescopes, the largest in the World. I spoke of how those instruments made some of the most important discoveries in the history of science. I ended that post by pointing out that America no longer possessed the World’s largest telescope. I described how our largest scopes now had been built back in the 1990s and that while Europe and the rest of the World were planning to build the next generation of telescopes the United States was not.

This week I’m going to tell a very similar story about the scientific instruments that allow scientists to see the smallest objects in the Universe. I’m talking about the particle accelerators, the Atom Smashers with which we study the fundamental building blocks of creation.

The first scientist to smash one kind of particle into another was the Englishman Ernest Rutherford, who aimed the alpha particles from radioactive Uranium at a thin film of gold atoms. The scattering pattern from those alpha particles revealed the basic structure of the atom as a dense nucleus surrounded by a cloud of electrons.

Now Rutherford only aimed his alpha particles, collimated is the technical term. He couldn’t increase their energy in any way but other scientists soon began looking for techniques to do just that. Attempting to build instruments that would accelerate sub-atomic particles and use those particles to probe deeper and deeper into the atom.

The first really practical such atom smasher was the cyclotron, developed by Ernest Lawrence at the University of California at Berkeley in 1932. To understand the operation of the cyclotron, and particle accelerators in general, refer to the picture below.

Workings of a Cyclotron (Public Domain)

In a cyclotron charged particles, usually protons, are confined to move in circular orbits by a large external magnetic field. The size of the orbit is determined by the velocity / energy of the charged particle. The particles orbit inside two metal “D”s that are connected to a high voltage oscillator that gives one of the “D”s a positive voltage and the other a negative voltage with the voltages flipping back and forth at very high frequency.

The positively charged protons are repelled by the positive “D” and attracted to the negative “D”, but by the time they get to the correct side the voltage has flipped causing the protons to fly back and forth, gaining energy with each orbit. The increasing energy increases the size of the orbit until the protons reach the outer edge of the “D”s where they are extracted and fired at a target being studied.

The “D”s in Lawrence’s first instrument measured only 11 inches (28cm) across and could only accelerate the protons to an energy of 1.2MeV. (An eV is an electron volt, it stands for the amount of energy that an electron will gain as it crosses a potential of 1 Volt. an MeV is a million eVs, GeV is a billion eVs and TeV is a trillion)

In the years that followed Lawrence built progressively more powerful instruments including a 184 inch (467cm) device that was used during the development of the atomic bomb to study the separation of uranium isotopes.

In the 1950s a new design of accelerators was developed where the strength of the confining magnetic field was synchronized to the energy of the accelerated particles. These accelerators were christened synchrotrons and they continued to grow in size and energy. The Bevatron, still at UC Berkeley succeeded in producing the first the anti-protons and anti-neutrons while the Cosmotron at Brookhaven National Laboratory on Long Island discovered the Delta particle and produced the first artificial mesons. The picture below shows the Bevatron at Berkeley.

The Bevatron Particle Accelerator (Public Domain)

The rest of the world just couldn’t keep up. The US just kept building the most powerful instruments and making all the discoveries. In 1960 Brookhaven got a new 33Gev machine called the Alternating Gradient Synchrotron, which is still making important discoveries today. In 1983 a brand new facility was opened outside Chicago called Fermilab with an accelerator ring over one and a third mile (2.2km) in diameter. The instrument named the Tevatron because it not only accelerated protons to over a TeV but it also accelerated anti-protons in the opposite direction and studied the collisions between them. The discoveries made by American Atom Smashers formed the basis of what physicists call ‘The Standard Model’. In 1995 the Top quark was discovered at Fermilab, the last elementary particle to be discovered at an American facility.

At almost the same time the US congress cancelled the next great American accelerator, the Superconducting Super Collider or SSC, whose ring would have been over 17 miles (27.7km) in diameter and whose total energy would have reached 40TeV.

Instead the Europeans have taken the lead with their Large Hadron Collider (LHC) at CERN. This is the instrument that finally discovered the Higgs boson in 2013 with its 8.6 km ring (5.4miles) and energy of 13Tev. It is worth keeping in mind that America’s SSC would have been completed earlier than Europe’s LHC and still been more powerful if the politicians had not fought over a deficit that they’ve pretty much ignored since then anyway. And now even the Tevatron at Fermilab has been shut down over budget concerns.

Europe meanwhile is pressing on. There are plans under development at CERN for an even bigger, more powerful machine. Called the Future Circular Collider it will have a ring 32 km (20 miles) in diameter and a top energy of 100Tev. So therefore it will be Europe that in the next decades will lead the search for physics beyond the standard model.

In my next post I’ll conclude my discussion of how the United States is losing its once predominant position in Science.

Post Script: Even as I was writing this post the Physicists at CERN have announced the discovery of a new particle! Now this is not a new fundamental particle but rather the first composite particle with two heavy quarks. Worse yet, Fermilab had published data over ten years ago indicating the possible existence of this particle but the Tevatron was not quite powerful enough to meet the tight requirements needed to officially announce a discovery.