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Archive for June, 2011

This column by Mike Lamm, head of Fermilab’s Magnet Systems Department and Mu2e Level 2 Manager for Solenoids, first appeared in Fermilab Today May 25.

For the past 18 months, the Technical Division magnet program has been working on the development of several complex magnets for Mu2e (pronounced mew-2-e), one of the flagship experiments of Fermilab’s Intensity Frontier program. A few weeks ago, we achieved an important milestone when our detailed, conceptual design for the Mu2e magnets passed a three-day Director’s Technical Design Review of the entire project.

The Mu2e experiment will provide a strong test for beyond the Standard Model theories. Mu2e will look for the predicted but not-yet-observed direct conversion of a muon into an electron, a process known as charged lepton flavor violation. We know that all quarks can change flavor, such as a charm quark turning into an up quark, and we have recently learned that leptons without charge can change flavor too, such as a muon neutrino transforming into an electron neutrino. Hence we suspect that charged leptons such as muons might be able to likewise change flavor by directly converting into an electron. If they do, it will be a very rare process, and its discovery will require a special beamline and particle detector.

The Mu2e experiment will smash an intense beam of protons from Fermilab’s Booster accelerator into a gold target to produce lots of low-energy muons. A magnet known as the production solenoid will slow and collect these particles (see graphic). A transport solenoid will guide the muons through the S-shaped chicane that weeds out unwanted particles. Then the muons will be captured in an aluminum target. If and when a muon converts to an electron within the target, an electron detector within a detector solenoid will identify the emerging electron.

The production solenoid and detector solenoid resemble the superconducting solenoid magnets currently used in Tevatron and LHC experiments, but with additional requirements. The production solenoid must achieve 5 Tesla, or 100,000 times the earth’s magnetic field–the highest central magnetic field of any solenoid in particle physics. Its coils will experience 170 tons of force during operation, or the weight of four fully loaded 18-wheeler trucks. The detector solenoid will be comparable in diameter to the massive ATLAS central solenoid at the LHC, but will be longer, with a total length of more than 11 meters. It will store about the same amount of energy as the ATLAS solenoid, but will feature a more uniform magnetic field.

The transport solenoid will be like nothing else ever built. Because of its complex S-shape its superconducting coils will experience strong forces and torques that will pull in opposite directions when the adjacent coils are forced to power down during an operational hiccup known as a quench. This made its design very challenging.

With the detailed, conceptual design of the Mu2e magnets approved and almost complete, we are moving one step closer to building this experiment, and one step closer to a better understanding of our universe.

Related information:


While most labs managed to dodge a bullet mor(what really looked like a giant bomb) in the 2011 budget. There are still many problems coming. Announced Thursday and reported on the Courier News and this blog that Fermilab will seek to reduce its staff by 5% through a voluntary program.

With the ending of the Tevatron program in September this doesn’t come as too much of a surprise, however it doesn’t do much to boost morale around the lab. In fact, even though much of the talk is on the future experiments like Long Baseline Neutrino Experiment (LBNE), Mu2e (website), and the future of Project X (website) there can’t help but be a sense of loss for many scientist working there.

For me, trying desperately to finish my thesis on work at CDF and looking for post-docs that might keep me in the Chicago land area, pieces of news about the shrinking of the lab only causes me to take pause and check to see if going down this path is the best for me.

The little support and almost no excitement coming from a budget strapped government towards science makes it hard for a young researcher to keep a stiff upper lip and look to the future with too much optimism .

Oh well, more focus on thesis and hopefully when I lift my head there will be a good position on an interesting and well funded experiment to work on.


We’ve been discussing the Higgs (its interactions, its role in particle mass, and its vacuum expectation value) as part of our ongoing series on understanding the Standard Model with Feynman diagrams. Now I’d like to take a post to discuss a very subtle feature of the Standard Model: its chiral structure and the meaning of “mass.” This post is a little bit different in character from the others, but it goes over some very subtle features of particle physics and I would really like to explain them carefully because they’re important for understanding the entire scaffolding of the Standard Model.

My goal is to explain the sense in which the Standard Model is “chiral” and what that means. In order to do this, we’ll first learn about a related idea, helicity, which is related to a particle’s spin. We’ll then use this as an intuitive step to understanding the more abstract notion of chirality, and then see how masses affect chiral theories and what this all has to do with the Higgs.


Fact: every matter particle (electrons, quarks, etc.) is spinning, i.e. each matter particle carries some intrinsic angular momentum.

Let me make the caveat that this spin is an inherently quantum mechanical property of fundamental particles! There’s really no classical sense in which there’s a little sphere spinning like a top. Nevertheless, this turns out to be a useful cartoon picture of what’s going on:

This is our spinning particle. The red arrow indicates the direction of the particle’s spin. The gray arrow indicates the direction that the particle is moving. I’ve drawn a face on the particle just to show it spinning.

The red arrow (indicating spin) and the gray arrow (indicating direction of motion) defines an orientation, or a handedness. The particular particle above is “right-handed” because it’s the same orientation as your right hand: if your thumb points in the direction of the gray arrow, then your fingers wrap in the direction of the red arrow. Physicists call this “handedness” the helicity of a particle.

To be clear, we can also draw the right-handed particle moving in the opposite direction (to the left):

Note that the direction of the spin (the red arrow) also had to change. You can confirm that if you point your thumb in the opposite direction, your fingers will also wrap in the opposite direction.

Sounds good? Okay, now we can also imagine a particle that is left-handed (or “left helicity”). For reference here’s a depiction of a left-handed particle moving in each direction; to help distinguish between left- and right-handed spins, I’ve given left-handed particles a blue arrow:

[Confirm that these two particles are different from the red-arrowed particles!]

An observation: note that if you only flip the direction of the gray arrow, you end up with a particle with the opposite handedness. This is precisely the reason why the person staring back at you in the mirror is left-handed (if you are right-handed)!

Thus far we’re restricting ourselves to matter particles (fermions). There’s a similar story for force particles (gauge bosons), but there’s an additional twist that will deserve special attention. The Higgs boson is another special case since it doesn’t have spin, but this actually ties into the gauge boson story.

Once we specify that we have a particular type of fermion, say an electron, we automatically have a left-helicity and a right-helicity version.

Helicity, Relativity, and Mass

Now let’s start to think about the meaning of mass. There are a lot of ways to think about mass. For example, it is perhaps most intuitive to associate mass with how ‘heavy’ a particle is. We’ll take a different point of view that is inspired by special relativity.

A massless particle (like the photon) travels at the speed of light and you can never catch up to it. There is no “rest frame” in which a massless particle is at rest. The analogy for this is driving on the freeway: if you are driving at the same speed as the car in the lane next to you, then it appears as if the car next to you is not moving (relative to you). Just replace the car with a particle.

On the other hand, a massive particle travels at less than the speed of light so that you can (in principle) match its velocity so that the particle is at rest relative to you. In fact, you can move faster than a massive particle so that it looks like the particle is traveling in the opposite direction (this flips the direction of the gray arrow). Note that the direction of its spin (the red arrow) does not change! However, we already noted that flipping only the particle’s direction—and not its spin—changes the particle’s helicity:

Here we’ve drawn the particle with a blue arrow because it has gone from being right-handed to left-handed. Clearly this is the same particle: all that we’ve done is gone to a different reference frame and principles of special relativity say that any reference frame is valid.

Okay, so here’s the point so far: mass is a something that tells us whether or not helicity is an “intrinsic” property of the particle. If a particle is massless, then its helicity has a fixed value in all reference frames. On the other hand, if a particle has any mass, then helicity is not an intrinsic property since different observers (in valid reference frames) can measure different values for the helicity (left- or right-helicity). So even though helicity is something which is easy to visualize, it is not a “fundamental” property of most particles.

Now a good question to ask is: Is there some property of a particle related to the helicity which is intrinsic to the particle? In other words, is there some property which

  1. is equivalent to helicity in the massless limit
  2. is something which all observers in valid reference frames would measure to be the same for a given particle.

The good news is that such a property exists, it is called chirality. The bad news is that it’s a bit more abstract. However, this is where a lot of the subtlety of the Standard Model lives, and I think it’s best to just go through it carefully.


Chirality and helicity are very closely related ideas. Just as we say that a particle can have left- or right-handed helicity, we also say that a particle can have left- or right-handed chirality. As we said above, for massless particles the chirality and helicity are the same. A massless left-chiral particle also has left-helicity.

However, a massive particle has a specific chirality. A massive left-chiral particle may have either left- or right-helicity depending on your reference frame relative to the particle. In all reference frames the particle will still be left-chiral, no matter what helicity it is.

Unfortunately, chirality is a bit trickier to define. It is an inherently quantum mechanical sense in which a particle is left- or right-handed. For now let us focus on fermions, which are “spin one-half.” Recall that this means that if you rotate an electron by 360 degrees, you don’t get the same quantum mechanical state: you get the same state up to a minus sign! This minus sign is related to quantum interference. A fermion’s chirality tells you how it gets to this minus sign in terms of a complex number:

What happens when you rotate a left- vs right-chiral fermion 360 degree about its direction of motion. Both particles pick up a -1, but the left-chiral fermion goes one way around the complex plane, while the right-chiral fermion goes the other way. The circle on the right represents the complex phase of the particle’s quantum state; as we rotate a particle, the value of the phase moves along the circle. Rotating the particle 360 degrees only brings you halfway around the circle in a direction that depends on the chirality of the fermion.

The physical meaning of this is the phase of the particle’s wavefunction. When you rotate a fermion, its quantum wavefunction is shifted in a way that depends on the fermion’s chirality:

Rotating a fermion shifts its quantum wavefunction. Left- and right-chiral fermions are shifted in opposite directions. This is a purely quantum phenomenon.

We don’t have to worry too much about the meaning of this quantum mechanical phase shift. The point is that chirality is related in a “deep” way to the particle’s inherent quantum properties. We’ll see below that this notion of chirality has more dramatic effects when we introduce mass.

Some technical remarks: The broad procedure being outlined in the last two sections can be understood in terms of group theory. What we claim is that massive and massless particles transform under different [unitary] representations of the Poincaré group. The notion of fermion chirality refers to the two types of spin-1/2 representations of the Poincaré group. In the brief discussion above, I tried to explain the difference by looking at the effect of a rotation about the z-axis, which is generated by ±σ3/2.

The take home message here is that particles with different chiralities are really different particles. If we have a particle with left-handed helicity, then we know that there should also be a version of the particle with right-handed helicity. On the other hand, a particle with left-handed chirality needn’t have a right-chiral partner. (But it will certainly furnish both helicities either way.) Bear with me on this, because this is really where the magic of the Higgs shows up in the Standard Model.

Chiral theories

[6/20/11: the following 2 paragraphs were edited and augmented slightly for better clarity. Thanks to Bjorn and Jack C. for comments. 4/8/17: corrected “right-chiral positron” to “left-chiral positron” and analogously for anti-positrons; further clarification to text and images; thanks to Martha Lindeman, Ph.D.]

One of the funny features of the Standard Model is that it is a chiral theory, which means that left-chiral and right-chiral particles behave differently. In particular, the W bosons will only talk to electrons (left-chiral electrons and right-chiral anti-electrons) and refuses to talk to positrons (left-chiral positrons and right-chiral anti-positrons). You should stop and think about this for a moment: nature discriminates between left- and right-chiral particles! (Of course, biologists are already very familiar with this from the ‘chirality’ of amino acids.)

Note that Nature is still, in some sense, symmetric with respect to left- and right-helicity. In the case where everything is massless, the chirality and helicity of a particle are the same. The W will couple to both a left- and right-helicity particles: the electron and anti-electron. However, it still ignores the positrons. In other words, the W will couple to a charge -1 left-handed particle (the electron), but does not couple to a charge -1 right-handed particle (the anti-positron). This is a very subtle point!

Technical remark: the difference between chirality and helicity is one of the very subtle points when one is first learning field theory. The mathematical difference can be seen just by looking at the form of the helicity and chirality operators. Intuitively, helicity is something which can be directly measured (by looking at angular momentum) whereas chirality is associated with the transformation under the Lorentz group (e.g. the quantum mechanical phase under a rotation).

In order to really drive this point home, let me reintroduce two particles to you: the electron and the “anti-positron.” We often say that the positron is the anti-partner of the electron, so shouldn’t these two particles be the same? No! The real story is actually more subtle—though some of this depends on what people mean by ‘positron,’ here we are making a useful, if unconventional, definition. The electron is a left-chiral particle while the positron is a right-chiral particle. Both have electric charge -1, but they are two completely different particles.

Electrons (left-chiral) and anti-positrons (right-chiral) have the same electric charge but are two completely different particles, as evidenced by the positron’s mustache.

How different are these particles? The electron can couple to a neutrino through the W-boson, while the anti-positron cannot. Why does the W only talk to the (left-chiral) electron? That’s just the way the Standard Model is constructed; the left-chiral electron is charged under the weak force whereas the right-chiral anti-positron is not. So let us be clear: the electron and the anti-positron are not the same particle! Even though they both have the same charge, they have different chirality and the electron can talk to a W, whereas the anti-positron cannot.

For now let us assume that all of these particles are massless so that these chirality states can be identified with their helicity states. Further, at this stage, the electron has its own anti-particle (an “anti-electron”) which has right-chirality which couples to the W boson. The anti-positron also has a different antiparticle which we call the positron (the same as an “anti-anti-positron”) and has left-chirality but does not couple to the W boson. We thus have a total of four particles (plus the four with opposite helicities):

The electron, anti-electron, anti-positron, and positron.

Technical remark: the left- & right-helicity electrons and left- & right-helicity anti-positrons are the four components of the Dirac spinor for the object which we normally call the electron (in the mass basis). Similarly, the left- & right-helicity anti-electrons and left- & right-helicity positrons for the conjugate Dirac spinor which represents what we normally call the positron (in the mass basis).

Important summary: [6/20/11: added this section to address some lingering confusion; thanks to David and James from CV, and Steve. 6/29: Thanks to Rainer for pointing out a mistake in 3 and 4 below (‘left’ and ‘right’ were swapped).] We’re bending the usual nomenclature for pedagogical reasons—the things which we are calling the “electron” and “positron” (and their anti-partners) are not the “physical” electron in, say, the Hydrogen atom. We will see below how these two ideas are connected. Thus far, the key point is that there are four distinct particles:

  1. Electron: left-chiral, charge -1, can interact with the W
  2. Anti-electron: right-chiral, charge +1, can interact with the W
  3. Positron: left-chiral, charge +1, cannot interact with the W
  4. Anti-positron: right-chiral, charge -1, cannot interact with the W.

We’re using names “electron” and “positron” to distinguish between the particles which couple to the W and those that don’t. The conventional language in particle physics is to call these the left-handed (chirality) electron and the right-handed (chirality) electron. But I wanted to use a different notation to emphasize that these are not related to one another by parity (space inversion, or reversing angular momentum).

Masses mix different particles!

Now here’s the magical step: masses cause different particles to “mix” with one another.

Recall that we explained that mass could be understood as a particle “bumping up against the Higgs boson’s vacuum expectation value (vev).” We drew crosses in the fermion lines of Feynman diagrams to represent a particle interacting with the Higgs vev, where each cross is really a truncated Higgs line. Let us now show explicitly what particles are appearing in these diagrams:

An “electron” propagating in space and interacting with the Higgs field. Note that the Higgs-induced mass term connects an electron with an anti-positron. This means that the two types of particles are exhibiting quantum mixing.

[6/25: this paragraph added for clarity] Note that in this picture the blue arrow represents helicity (it is conserved), whereas the mustache (or non-mustache) represents chirality. The mass insertions flip chirality, but maintain helicity.

This is very important; two completely different particles (the electron and the anti-positron) are swapping back and forth. What does this mean? The physical thing which is propagating through space is a mixture of the two particles. When you observe the particle at one point, it may be an electron, but if you observe it a moment later, the very same particle might manifest itself as an anti-positron! This should sound very familiar, it’s the exact same story as neutrino mixing (or, similarly, meson mixing).

Let us call this propagating particle is a “physical electron.” The mass-basis-electron can either be an electron or an anti-positron when you observe it; it is a quantum mixture of both. The W boson only interacts with the “physical electron” through its electron component and does not interact with the anti-positron component. Similarly, we can define a “physical positron” which is the mixture of the positron and anti-electron. Now I need to clarify the language a bit. When people usually refer to an electron, what they really mean is the mass-basis-electron, not the “electron which interacts with W.” It’s easiest to see this as a picture:

The “physical electron” (what most people mean when they say “electron”) is a combination of an electron and an anti-positron. Note that the electron and the anti-positron have different interactions (e.g. the electron can interact with the W boson); the physical electron inherits the interactions of both particles.

Note that we can now say that the “physical electron” and the “physical positron” are antiparticles of one another. This is clear since the two particles which combine to make up a physical electron are the antiparticles of the two particles which combine to make up the physical positron. Further, let me pause to remark that in all of the above discussion, one could have replaced the electron and positron with any other Standard Model matter particle (except the neutrino, see below). [The electron and positron are handy examples because the positron has a name other than anti-electron, which would have introduced language ambiguities.]

Technical remarks: To match to the parlance used in particle physics:

  1. The “electron” (interacts with the W) is called eL, or the left-chiral electron
  2. The “anti-positron” (does not interact with the W) is called eR, or the right-chiral electron.  [6/25: corrected and updated, thanks to those who left comments about this] Note that I very carefully said that this is a right-chiral electron, not a right-helicity electron. In order to conserve angular momentum, the helicities of the eL and eR have to match. This means that one of these particles has opposite helicity and chirality—and this is the whole point of distinguishing helicity from chirality!
  3. The “physical electron” is usually just called the electron, e, or mass-basis electron

The analogy to flavor mixing should be taken literally. These are different particles that can propagate into one another in exactly the same way that different flavors are different particles that propagate into one another. Note that the mixing angle is controlled by the ratio of the energy to the mass and is 45 degrees in the non-relativistic limit. [6/22: thanks to Rainer P. for correcting me on this.] Also, the “physical electron” now contains twice the physical degrees of freedom as the electron and anti-positron. This is just the observation that a Dirac mass combines two 2-component Weyl spinors into a 4-component Dirac spinor.

When one first learns quantum field theory, one usually glosses over all of these details because one can work directly in the mass basis where all fermions are Dirac spinors and all mass insertions are re-summed in the propagators. However, the chiral structure of the Standard Model is telling us that the underlying theory is written in terms of two-component [chiral] Weyl spinors and the Higgs induces the mixing into Dirac spinors. For those that want to learn the two-component formalism in gory detail, I strongly recommend the recent review by Dreiner, Haber, and Martin.

What this all has to do with the Higgs

We have now learned that masses are responsible for mixing between different types of particles. The mass terms combine two a priori particles (electron and anti-positron) into a single particle (physical electron). [See a very old post where I tried—I think unsuccessfully—to convey similar ideas.] The reason why we’ve gone through this entire rigmarole is to say that ordinarily, two unrelated particles don’t want to be mixed up into one another.

The reason for this is that particles can only mix if they carry the same quantum properties. You’ll note, for example, that the electron and the anti-positron both had the same electric charge (-1). It would have been impossible for the electron and anti-electron to mix because they have different electric charges. However, the electron carries a weak charge because it couples to the W boson, whereas the anti-positron carries no weak charge. Thus these two particles should not be able to mix. In highfalutin language, one might say that this mass term is prohibited by “gauge invariance,” where the word “gauge” refers to the W as a gauge boson. This is a consequence of the Standard Model being a chiral theory.

The reason why this unlikely mixing is allowed is because of the Higgs vev. The Higgs carries weak charge. When it obtains a vacuum expectation value, it “breaks” the conservation of weak charge and allows the electron to mix with the anti-positron, even though they have different weak charges. Or, in other words, the vacuum expectation value of the Higgs “soaks up” the difference in weak charge between the electron and anti-positron.

So now the mystery of the Higgs boson continues. First we said that the Higgs somehow gives particle masses. We then said that these masses are generated by the Higgs vacuum expectation value. In this post we took a detour to explain what this mass really does and got a glimpse of why the Higgs vev was necessary to allow this mass. The next step is to finally address how this Higgs managed to obtain a vacuum expectation value, and what it means that it “breaks” weak charge. This phenomenon is called electroweak symmetry breaking, and is one of the primary motivations for theories of new physics beyond the Standard Model.

Addendum: Majorana masses

Okay, this is somewhat outside of our main discussion, but I feel obligated to mention it. The kind of fermion mass that we discussed above is called a Dirac mass. This is a type of mass that connects two different particles (electron and anti-positron). It is also possible to have a mass that connects two of the same kind of particle, this is called a Majorana mass. This type of mass is forbidden for particles that have any type of charge. For example, an electron and an anti-electron cannot mix because they have opposite electric charge, as we discussed above. There is, however, one type of matter particle in the Standard Model which does not carry any charge: the neutrino! (Neutrinos do carry weak charge, but this is “soaked up” by the Higgs vev.)

Within the Standard Model, Majorana masses are special for neutrinos. They mix neutrinos with anti-neutrinos so that the “physical neutrino” is its own antiparticle. (In fancy language, we’d say the neutrino is a Majorana fermion, or is described by a Weyl spinor rather than a Dirac spinor.) It is also possible for the neutrino to have both a Majorana and a Dirac mass. (The latter would require additional “mustached” neutrinos to play the role of the positron.) This would have some interesting consequences. As we suggested above, the Dirac mass is associated with the non-conservation of weak charge due to the Higgs, thus Dirac masses are typically “small.” (Nature doesn’t like it when things which ought to be conserved are not.)  Majorana masses, on the other hand, do not cause any charge non-conservation and can be arbitrarily large. The “see-saw” between these two masses can lead to a natural explanation for why neutrinos are so much lighter than the other Standard Model fermions, though for the moment this is a conjecture which is outside of the range of present experiments.


— by Nigel S. Lockyer, Director

The Canadian Association of Physicists (CAP) met last week in St. John’s, Newfoundland (a huge island it turns out), off the most eastern part of Canada. Newfoundland-Labrador (NL) (one of 10 Canadian provinces…joined the federation in March 31, 1949) is remote with a ruggedly beautiful coastline and—at this time of year—cool, rainy, and foggy. NL is famous for icebergs floating by the coast, pods of whales, schools of capelins, and millions of sea birds. Check out the maps, weather, and iceberg tracking.

Capelin fish.

A capelin is the fish the whales eat. They come to shore to spawn in June and July, followed by the whales, and everyone in town benefits, except of course the capelins. Looks like a “lycoptera” to me.

Rolf-Dieter Heuer, DG of CERN, attended the first day of the meeting and gave a public lecture in the evening to the conference delegates, university students, and local citizens. Standing-room only in an auditirium for at least 1,000!  It was a superb and captivating lecture for physicists outside of particle physics and for the public alike. Rolf is a tremendous spokesperson for CERN and particle physics.   During his daytime itinerary, Rolf participated in several sessions and panel discussions where he spoke passionately about the opportunity for Canada to work with CERN more closely as one of the first “associate members” from overseas.

One of the CAP meeting highlights was the T2K result, which reported a 2.5 sigma effect on theta-13, an angle that measures the degree to which flavours “1” and “3” of neutrinos change back and forth into one another. This result, if it holds, has major implications for the next-generation long-baseline neutrino experiments being discussed around the world. It is possible decisions will take place about proceeding to search for CP violation in the neutrino sector in the next 5 years…a billion dollar program wherever it is built.

Another conference highlight was the inaugural award of the CAP-TRIUMF Medal for Subatomic Physics named after Erich W. Vogt, one of the founders of TRIUMF and an early director of the laboratory.  Professor Vogt travelled to Newfoundland for the conference specifically for the purpose of handing the medal to David Sinclair (a professor at Carleton and a senior research scientist at TRIUMF) for his contributions to the SNO experiment.  It was a special moment as David acknowledged that he’d always seen Erich as a mentor.

Although most of the conference was work, we did get a few minutes to go outside and look around.  Touring the local historical sites was fun. Almost everyone visited Signal Hill (site of the first radio transmission across the Atlantic) and Cape Spear, the most eastern point in Canada. Cape Spear has the second oldest lighthouse in Canada. The tour, given by a young woman from Labrador (the first person I have met from Labrador), was fascinating. The lighthouse had been run for seven generations by the same family….yes seven. They hired a technician to keep the lighthouse maintenance up to snuff and to rewind the clockwork mechanism every three hours. This individual lived in a small room in the lighthouse, next to his minimal work shop.  The room was so cold in winter that our Labrador tour guide said the “contents of the pisspot froze” (FYI — “piss” is an acceptable word in haute-Canada).  I also learned about the big technological advance in lamps: when the wick on oil lamps was upgraded to be cylindrical rather than flat and a fluted glass chimney was attached. The round wick improved oxygen flow and most importantly increased light output versus a candle by a factor of seven and eliminated the smoke and hence the need to clean the glass chimneys and Fresnel lense so often. The Swiss physicist Argand is credited with this innovation in 1781.

Barrerl of sperm-whale oil.

The whales they caught provided the oil for the lamps. Barrels of sperm whale oil were stored next to the maintenance man’s bedroom and his piss-pot.

The final topic to share is the controversy over the Canadian sealing industry, strongly supported in NL. If you are inclined, check out http://www.ifaw.org/ifaw_canada_english/ or for the other side of the argument see http://speeches.empireclub.org/61890/data?n=20

I’ll remember this trip because I watched the Vancouver Canucks lose the seventh game of the Stanley Cup to Boston in a local St. John’s bar, a piss…, made worse by all the local Boston fans!  (just kidding)  It was a privilege to have our team in the finals.



J-PARC announced that the international T2K collaboration have
observed, for the first time, an indication of a neutrino oscillation
from a muon neutrino to an electron neutrino. Please see J-PARC press
release for detail.






Neutrinos could tell us why matter formed in the early universe.

The Japan-based experiment T2K Tuesday gave scores of U.S. particle hunters a license to ready their detectors and take aim at the biggest question in the universe: How everything we see came to exist.

“It’s our hunting license,” said Fermilab physicist and University of Rochester professor Kevin McFarland, who works on T2K and neutrino experiments at Fermilab.

The observation by T2K affects what the Fermilab neutrino experiments NOvA and the proposed Long Baseline Neutrino Experiment, LBNE, can expect to discover and how quickly. It also makes the experiment McFarland serves as co-spokesman on, MINERvA, more important than ever in the international neutrino-research field.

Physicists working with T2K recorded six muon neutrinos changing into electron neutrinos across a long distance, a transformation called theta 13 in physics circles. Physicists had predicted that they should observe only 1.5 of these transformations as background events rather than the six they did observe, so the probability of the existence of an electron neutrino appearance is estimated to be 99.3 percent. While the T2K observation doesn’t rise to the level of “discovery” in the science community, it is far enough beyond the expected statistical error bar to make people shout for joy and start revising plans for their own particle hunts.

“Because neutrino science is so hard, scientist don’t get a lot of exciting days,” McFarland said the day of the T2K announcement. “But this is a very exciting day.”

The T2K observation also was statistically large enough that it quells a long-standing fear that this transformation would be statistically too small, much less than one percent, to observe. At that level, modern technology wouldn’t be able to use the observation as a stepping stone to move to the next research phase in figure out how matter came to dominate antimatter in the universe.

The quarry:

Something, possibly neutrinos, tipped the scales to have more matter than antimatter in the universe allowing for life. Credit: symmetry magazine

Physics predicts that the three types of neutrino particles can change back and forth into one another across long distances. Previous solar and reactor neutrino experiments had observed two types doing just that, but the third switch – muon neutrino into electron neutrino – had remained elusive.

T2K’s recording of this transformation, the first of its kind, means that physicists will have the tools to track down the next two potential discoveries on the path to the ultimate trophy. After the Big Bang, equal amounts of matter and antimatter should have annihilated each other leaving nothing but free-floating energy. But we’re here and antimatter isn’t, so that didn’t happen. Something tipped the scales in matter’s favor, allowing particles to join together and form planets, plants and people. Physicists think neutrinos could be that tipping-point particle.

Following the tracks:

The first step in finding out if they are right is T2K’s observation. Plugging this observation into the research equation, physicists on NOvA, an experiment under construction in Minnesota, will be able to tease out the details of what is called the neutrino mass hierarchy. The pattern of this hierarchy essentially will tell physicist if neutrinos behave like other particles, in a pattern of light, heavy and very heavy, or neutrinos behave oddly in a pattern of light, heavy and heavy.

This pattern of masses is important to know because it provides a clue to help physicists understand what causes neutrinos to have masses that are so much lighter than other particles and why neutrinos aren’t massless as predicted by the Standard Model, the playbook for how the world works at the subatomic level.

Physicists think the origins of neutrino masses are closely tied to subatomic processes that took place right after the big bang. Determining which neutrino types are heaviest and lightest—the neutrino mass ordering—is a first step toward revealing these processes. Credit: symmetry magazine

NOvA is ideally situated to do discern this pattern because its particle beam will travel three times as farther than T2K’s, allowing researchers see how the material in the Earth alters the change from muon to electron neutrinos. T2K’s observation of half a dozen muon neutrino to electron neutrino changes points to the relatively high rate of the change, so NOvA should have a lot of data to work with to speed up the discovery of the mass hierarchy.

Step three is combining what NOvA learns about the mass hierarchy with more precise data from the LBNE experiment to look for differences in the neutrino and antineutrino probabilities of changing from muon to electron neutrino types. After accounting for the effect of the earth and the mass hierarchy, any remaining difference would point to a fundamental difference between matter and antimatter neutrinos. Differences between matter and anti-matter are nearly non-existent in nature and these differences are precious clues about why matter dominated antimatter to survive in today’s universe.

The three types of neutrinos mix across long distances enabling physicists to see them to change type if the distance is long enough. Credit: symmetry magazine

LBNE, proposed for South Dakota, sits even farther away from the Fermilab neutrino source, making it well-suited to make this comparison of antineutrinos, which are rarer and harder to detect than neutrinos. T2K’s observation of a large change signal means LBNE will have better statistics to create precise comparisons.
The level of precision could mean the difference between getting an answer or not, depending on how subtle the difference is between neutrinos and antineutrinos.

Bringing out the rifle scope:

Short-baseline experiments can’t compete in the hunt for why matter dominated antimatter, which requires tracking neutrinos across great distances, but they can provide the precision measurements that work like a rifle scope for the particle hunters. MINERvA at Fermilab and the neutrino reactor experiments Daya Bay in China and Double Chooz in France will provide the data to allow NOvA and LBNE to zoom in on the minute details of mass hierarchy and how neutrinos change types.

The reactor-based experiments with detectors near to neutrino spewing reactors were designed to be experts at finding the neutrino change T2K found. Ideally, they will find a cleaner neutrino transformation signal, without the data complications, such as the effects of Earth material on the transformation that come with T2K and NOvA being multi-purpose experiments. Cleaner reactor experiment measurements provide a baseline for the measurements of NOvA and LBNE.

MINERvA will provide data to help NOvA and LBNE map the type and amount of background events that can obscure their search. This will enable physicists to put the trophy deer-like potential discovery in their analysis cross-hairs and discount the imposter trees and hunters dressed in brown that cloud the view of their data. While MINERvA was built for this job and currently aids neutrino experiments across the globe, including T2K, with this variable-removing research information, T2K’s observation makes MINERvA’s unique skill more important. The large T2K signal means a lot of data and the ability to do precision analysis if MINERvA can tell researchers what variables to discount.

“There is always an exchange of data, and one experiment builds on another,” McFarland says.

Previously data from the MINOS experiment at Fermilab told T2K how to tune the energy of its particle beam. Now T2K is returning the favor with an observation that will help Fermilab experiments.

“Experiments building on one another,” he says, “that is what makes it exciting.”

Related information:

Symmetry breaking: Japan’s T2K experiment observes electrion neutrino appearance


In Honour of Bob Moore (1935-2011)

— By Byron Jennings, Theorist and Project Coordinator

A few years ago I published an article on how science works in Physics in Canada. Since I failed philosophy in university, I refuse to call it philosophy of science. The response was like the advertising slogan for Keith’s India Pale Ale (a Nova Scotian brew): “Those that like it, like it a lot”. One of the letters I received on the paper came from Bob Moore, a colleague from my McGill days. He indeed liked it a lot. However he did point out one aspect of the how science works that I had overlooked. The paper was already getting rather lengthy, and the usual comment was not that I left things out but had put too much in.

Now, Bob was a Newfoundlander or Newfie for short. Like many Newfies he had the gift to tell a good story. Thus I considered it the ultimate compliment when he said on reading parts of my paper, “I could have written that.” What I had left out, he noted, was the idea that scientists are more like gamblers or bookies than priests (the holders of eternal truths) or Gnostics (processors of secrete knowledge). Bob sent me an essay he had written on the topic which I will now summarize and mangle.

Consider the thesis that reindeer can fly. How do we test that idea? Well, take some reindeer to the top of a tall building and push them off. There goes Dasher; Splat, Dancer: Splat, … Blitzen: Splat. Ok, have we falsified the thesis that reindeer can fly? No we have only shown that those reindeer in that particular instance did not fly. Perhaps they could but choose not to. Perhaps they could not but there are others that could. We have proven nothing but only given another example of the Duhem-Quine thesis that any potential falsification can be gotten around. Bob’s point was that we were really asking the wrong question. The correct question is: How would you bet on Rudolph?

In this uncertain world, the role of science is much like that of bookies—to set the odds of what will happen, not to discover eternal truths. Will the sun rise tomorrow? Highly probable. Will the LHC discover the Higgs boson? Likely. Will Vancouver ever win the Stanley Cup? Unlikely. (Toronto? Forget it.) Can reindeer fly? Very unlikely. In a very real sense all we ever do in science to determine probability.

So why is science so successful? Because, as any professional gambler knows, playing by the odds gets you more wins than not playing by the odds. Playing by hunches and hoping you luck out will “work” occasionally, but not in the long run. And if you play against the laws of physics, the odds against lucking out can be very long. The odds that the atomic fine structure constant is between 0.00729735242 and 0.00729735271 are estimated to be about a billion to one. And the odds for the conservation of momentum in physics are so high as to be incalculable—but not infinite. Some physicists think that the law could break down in the extreme gravitational field of a neutron star orbiting a black hole.

For scientists that have to deal with things as complex as the health and attitudes of human beings, the odds can be hard to determine. Yet for our health and wellbeing it is often important to try to do so. Not doing so leads to false beliefs and superstitions, like using apricot pits to cure cancer. The most ludicrous I have heard of is a hockey player who before each game dipped his stick in a toilet bowl. Perhaps the Vancouver Canuks should have tried that. (ah, perhaps they did!).

Beliefs, such as the power of laetrile to cure cancer and the aphrodisiacal power of ground rhinoceros horn can be detrimental to our health and wellbeing, and certainly to the rhinoceroses. So when someone tells you about a study that shows evidence of flying saucers, or of mental telepathy, or that apricot seeds can cure cancer, practice a little “I come from Missouri” and ask “How much do you want to bet?”

However, in addition to death and taxes, one other thing is certain: We will miss Bob’s humour, newfie stories, and insights. Good-bye old friend, so long.





Under the sky, Paris.

Thursday, June 16th, 2011








–by Nigel S. Lockyer, Director

Scientists from the China Institute of Atomic Energy (CIAE) and the National Science Foundation of China (NSFC) visited TRIUMF this past week (Tuesday, June 7) and gave me an unusual and exotic gift. I received a fossil of a fish—a herring-like fish!

This present seems well above average.  My first thought was about how they had carried the present thousands of miles, since they were coming from NSF in Washington, DC, and Brookhaven National Lab in the USA. The fossil was encased in a frame the size of a small book with a glass cover. The fossil was of Lycoptera, a fish that existed in China and that part of the world during the Jurassic period (200 million to 145 million years ago). This was the period of dinosaurs, reptiles, first birds, and, yes, fish. It was a time when atmospheric CO2 was 900 ppm, as opposed to present levels of about 390 ppm and the world was hot, on average three degrees Celsius above today’s temperatures…. a very different place from today (I hope).  Erudite papers suggest the Lycoptera is a member of the Leptolepidae family (“Delicate Scales”), an appealing name to me as a particle physicist (reminds me of the leptoquark…also a fossil, but from the beginnings of the Universe).

"Photocopy" of the Lycoptera fish fossil

The NSFC visitors indicated they expected Chinese science investments to grow by 20% per year.  One consequence of that is China now has plans for three rare-isotope beam facilities. Wow!  Finally, let me say we thanked our Chinese visitors by presenting them with six high quality ballpoint pens with TRIUMF, Vancouver BC, emblazoned on the side.