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Antimatter Angst: The Universe Shouldn’t Exist

veil-nebby — The Veil Nebula as seen by Hubble. Because it looks cool (NASA, ESA, Hubble Heritage Team)

The universe shouldn’t exist, according to new ultra-precise measurements of anti-protons.

But the fact that I’m typing this article and you’re reading it, however, suggests that we are here, so something must be awry with our understanding of the physics the universe is governed by.

The universe is the embodiment of an epic battle between matter and antimatter that occurred immediately after the Big Bang, 13.82 billion years ago. Evidently, matter won — because there are galaxies, stars, planets, you, me, hamsters, long walks on sandy beaches and beer — but how matter won is one of the biggest mysteries hanging over physics.

It is predicted that equal amounts of matter and antimatter were produced in the primordial universe (a basic prediction by the Standard Model of physics), but if that’s the case, all matter in the universe should have been annihilated when it came into contact with its antimatter counterpart — a Big Bang followed by a big disappointment.

This physics conundrum focuses on the idea that all particles have their antimatter twin with the same quantum numbers, only the exact opposite. Protons have anti-protons, electrons have positrons, neutrinos have anti-neutrinos etc.; a beautiful example of symmetry in the quantum world. But should one of these quantum numbers be very slightly different between matter and antimatter particles, it might explain why matter became the dominant “stuff” of the universe.

So, in an attempt to measure one of the quantum states of particles, physicists of CERN’s Baryon–Antibaryon Symmetry Experiment (BASE), located near Geneva, Switzerland, have made the most precise measurement of the anti-proton’s magnetic moment. BASE is a complex piece of hardware that can precisely measure the magnetic moments of protons and anti-protons in an attempt to detect an extremely small difference between the two. Should there be a difference, this might explain why matter is more dominant than antimatter.

However, this latest measurement of the magnetic moment of anti-protons has revealed that the magnetic moments of both protons and anti-protons are exactly the same to a record-breaking level of precision. In fact, the anti-proton measurement is even more precise than our measurements of the magnetic moment of a proton — a stunning feat considering how difficult anti-protons are to study.

“It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator,” said physicist Christian Smorra in a CERN statement. The Antiproton Decelerator is a machine that can capture antiparticles (created from particle collisions that occur at CERN’s Proton Synchrotron) and funnel them to other experiments, like BASE.

Antimatter is very tricky to observe and measure. Should these antiparticles come into contact with particles, they annihilate — you can’t simply shove a bunch of anti-protons into a flask and expect them to play nice. So, to prevent antimatter from making contact with matter, physicists have to create magnetic vacuum “traps” that can quarantine anti-protons from touching matter, thereby allowing further study.

A major area of research has been to develop ever more sophisticated magnetic traps; the slightest imperfections in a trap’s magnetic field containing the antimatter can allow particles to leak. The more perfect the magnetic field, the less chance there is of leakage and the longer antimatter remains levitating away from matter. Over the years, physicists have achieved longer and longer antimatter containment records.

In this new study, published in the journal Nature on Oct. 18, researchers used a combination of two cryogenically-cooled Penning traps that held anti-protons in place for a record-breaking 405 days. In that time they were able to apply another magnetic field to the antimatter, forcing quantum jumps in the particles’ spin. By doing this, they could measure their magnetic moments to astonishing accuracy.

According to their study, anti-protons have a magnetic moment of −2.792847344142 μ_N (where μ_N is the nuclear magneton, a physical constant). The proton’s magnetic moment is 2.7928473509 μ_N, almost exactly the same — the slight difference is well within the experiment’s error margin. As a consequence, if there’s a difference between the magnetic moment of protons and anti-protons, it must be much smaller than the experiment can currently detect.

These tiny measurements have huge — you could say: universal — implications.

“All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” added Smorra. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.”

Now the plan is to improve methods of capturing antimatter particles, pushing BASE to even higher precision, to see if there really is an asymmetry in magnetic moment between protons and anti-protons. If there’s not, well, physicists will need to find their asymmetry elsewhere.

Peter Higgs Discovers Higgs Boson… in the Mail!

Dr Peter Higgs holds his very own Higgs boson (©Particle Zoo/Peter Higgs) — Peter Higgs holds his very own Higgs boson (©Particle Zoo/Peter Higgs)

In October, something very special happened to me. There, on the doorstep, a Higgs boson sat, waiting to be picked up and unwrapped from his packaging (and yes, I can confirm, he is a he).

Of course, he wasn’t the same Higgs boson physicists at the Large Hadron Collider (LHC) were looking for, he was a Higgs boson plushie from Julie Peason’s Particle Zoo.

Since that day, Higgsy (as I affectionately call him) has been sitting on my desk, watching me write, whilst holding down a stack of papers when I have my office window open.

Yesterday, I received some more good news via email from my friend Julie, the Particle Zookeeper. The particle physicist whom the Higgs boson is named after has also discovered his very own Higgs boson… at his home in Scotland!
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Higgs Boson Discovered on Doorstep

You don’t need the Large Hadron Collider to discover the Higgs boson after all…

The moment of discovery. It turns out Higgsy is a little shy.

This evening I went outside to investigate a noise. On opening the door I saw a small box lying awkwardly on its side against a flower pot. A little confused (as there was no knock on the door to say there was a delivery), I picked the small package. The box was heavy. I gave it a shake. Something was rolling around in there. It didn’t make a sound.

On opening the box I couldn’t believe my eyes. There he was, hiding under styrofoam packaging, neatly wrapped in a clear plastic bag, the one particle EVERYONE wants to meet… the Higgs boson!

Far from being smug, the little guy was actually pretty shy and was reluctant to leave the comfort of his box. After a brief chat I assured him that he was safe from particle physicists wanting to see him spontaneously decay…

As you might have guessed, I didn’t discover a real Higgs particle on my doorstep (although we all know that it must be full of them… theoretically anyhow). My Higgs boson plushie has just travelled from the caring hands of its creator, Particle Zookeeper Julie Peasley…
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What is the Higgs Boson?

Artist rendition of Higgs bosons generated after a particle collision. Created for Niels Bohr institute by artist-in-residence Mette Høst

Billions of Euros have been ploughed into the construction of the largest experiment known in the history of mankind. The Large Hadron Collider (officially due to be “switched on” September 10th 2008) will eventually create proton-proton collision energies near the 14 TeV mark by the end of this decade. This is all highly impressive; already the applications of the LHC appear to be endless, probing smaller and smaller scales with bigger and bigger energies. But how did the LHC secure all that funding? After all, the most expensive piece of lab equipment must be built with a purpose? Although the aims are varied and far-reaching, the LHC has one key task to achieve: Discover the Higgs Boson, the world’s most sought-after particle. If discovered, key theories in particle physics and quantum dynamics will be proven. If it isn’t found by the LHC, perhaps our theories are wrong, and our view of the Universe needs to be revolutionized… or the LHC needs to be more powerful.

Either way, the LHC will revolutionize all facets of physics. But what is the Higgs boson? And why in the hell is it so important?

I’ve read many very interesting articles about the Higgs boson and what its discovery will do for mankind. However, many of these texts are very hard to understand by non-specialists, particularly by the guys-at-the-top (i.e. the politicians who approve vast amounts of funding for physics experiments). The LHC physicists obviously did a very good job on Europe’s leaders so this gargantuan particle accelerator could secure billions of euros/dollars/pounds to be built.

There is a classic physics-politics outreach example that has become synonymous with LHC funding. On trying to acquire UK funding for the LHC project in 1993, physicists had to derive a way of explaining what the Higgs boson was to the UK Science Minister, William Waldegrave. This quasi-political example is wonderfully described by David J. Miller; Bryan Cox also discusses the same occasion in this outstanding TED lecture.

What is the Higgs boson? The Short Answer
Predicted by the Standard Model of particle physics, the Higgs boson is a particle that carries the Higgs field. The Higgs field is theorized to permeate through the entire Universe. As a massless particle passes through the Higgs field, it accumulates it, and the particle gains mass. Therefore, should the Higgs boson be discovered, we’ll know why matter has mass.

What is the Higgs boson? The Long Answer
Firstly we must know what the “Standard Model” is. In quantum physics, there are basically six types of quarks, six types of leptons (all 12 are collectively known as “fermions”) and four bosons. Quarks are the building blocks of all hadrons in the Universe (they are contained inside common hadrons like protons and neutrons) and they can never exist as a single entity in nature. The “glue” that holds hadrons together (thus bonding quarks together) is governed by the “strong force,” a powerful force which acts over very small distances (nucleon-scales). The strong force is delivered by one of the four bosons called the “gluon.” When two quarks combine to form a hadron, the resulting particle is called a “meson“; when three combine, the resulting particle is called a “baryon.”

The Standard Model. Including 6 quarks, 6 leptons and four bosons. Source: http://tinyurl.com/6z3tb3

In addition to six quarks in the Standard Model, we have six leptons. The electron, muon and tau particles plus their neutrinos; the electron neutrino, muon neutrino and tau neutrino. Add to this the four bosons: photon (electromagnetic force), W and Z bosons (weak force) and gluons (strong force), we have all the components of the Standard Model.

However, there’s something missing. What about gravity? Although very weak on quantum scales, this fundamental force cannot be explained by the Standard Model. The gravitational force is mediated by the hypothetical particle, the graviton.

The Higgs Field
The Standard Model has its shortcomings (such as the non-inclusion of the graviton) but ultimately it has elegantly described many fundamental properties of the quantum and cosmological universe. However, we need to find a way of describing how these Standard Model particles have (and indeed, have no) mass.

Permeating through all the theoretical calculations of the Standard Model is the “Higgs field.” It is predicted to exist, giving quarks and gluons their large masses; but also giving photons and neutrinos little or no mass. The Higgs field forms the basic underlying structure of the Universe; it has to, otherwise “mass” would not exist (if the Universe is indeed governed by the Standard Model).

People evenly distributed in a room, akin to the Higgs field (CERN)

As a particle travels through the Higgs field (which can be thought of as a 3D lattice filling the Universe, from the vacuum of space to the centre of stars), it causes a distortion in the field. As it moves, the particle will cause the Higgs field to cluster around the particle. The more clustering there is, the more mass the particle will accumulate. Going back to David J. Miller’s 1993 quasi-political description of the Higgs field, his analogy of the number of people attracted to a powerful politician rings very similar to what actually happens in the Higgs field as a particle passes through it (see the cartoon left and below).

Using the cartoon of Margaret Thatcher, ex-UK Prime Minister, entering a crowded room, suddenly makes sense. As Thatcher enters the room, although the people are evenly distributed across the floor, Thatcher will soon start accumulating delegates wanting to talk to her as she tries to walk. This effect is seen all the time when paparazzi accumulate around a celebrity here in Los Angeles; the longer the celeb walks within the “paparazzi field,” more photographers and reporters accumulate.

Then Thatcher enters the room, people gather, mass increases (CERN)

Pretty obvious so far. The Thatcher analogy worked really well in 1993 and the paparazzi analogy works well today. But, critically, what happens when the individual accumulates all these people (i.e. increase mass)? If they are able to travel at the same speed across the room, the whole ensemble will have greater momentum, thus will be harder to slow down.

The Higgs Boson
So going back to our otherwise massless particle travelling through the Higgs field, as it does so, it distorts the surrounding field, causing it to bunch up around the particle, thus giving it mass and therefore momentum. Observations of the weak force (exchanged by the W and Z particles) cannot be explained without the inclusion of the Higgs field.

OK, so we have a “Higgs field,” where does the “Higgs boson” come into it? The Higgs particle is simply the boson that carries the Higgs field. So if we were to dissect a particle (like colliding it inside a particle accelerator), we’d see a Higgs boson carrying the Higgs field. This boson can be called a Higgs particle. If the Higgs particle is just an enhancement in the Higgs field, there could be many different “types” of Higgs particles, of varying energies.

British particle physicist Peter Higgs (as seen in the 1960s), Higgs boson namesake and lead researcher on the Higgs mechanism (Peter Tuffy)

This is where the LHC comes in. We know that the Higgs boson governs the amount of mass a particle can have. It is therefore by definition “massive.” The more massive a particle, the more energy it has (i.e. E = mc²), so in an effort to isolate the Higgs particle, we need a highly energetic collision. Previous particle accelerator experiments have not turned up evidence for the Higgs boson, but this null result sets a lower limit on the mass of the Higgs boson. This currently holds at a rest-mass energy of 114 GeV (meaning the lower limit for the Higgs boson will be greater than 114 GeV). It is hoped that the high energy collisions possible by the LHC will confirm that the Higgs exists at higher masses (predicted in the mass range of 0.1-1 TeV).

So why is the Higgs boson important?
The Higgs boson is the last remaining particle of the Standard Model that has not been observed; all the other fermions and bosons have been proven to exist through experiment. If the LHC does focus enough energy to generate an observable Higgs boson with a mass over 114 GeV, the Standard Model will be complete and we’ll know why matter has mass. Then we will be working on validating the possibility of supersymmetry and string theory… but we’ll leave that for another day…

But does the Higgs boson give hadrons the ability to feel pain? I doubt it…

Special thanks to regular Astroengine reader Hannah from São Paulo, Brazil for suggesting this article, I hope it went to some way of explaining the general nature of the Higgs boson…