Bacon took a different track and extracted something different from the study of Aristotle. This something different was an early version of the scientific method. He applied mathematics to describe observations and advocated using observation to test models. Bacon described a repeating cycle of observation, hypothesis, experimentation, and the need for independent verification.  Bacon was largely ignored and, unlike Aquinas, was not declared a saint. Galileo Galilei (1564 – 1642), if not directly influenced by Bacon, was in many ways following his tradition, both in his use of mathematics and in stressing the importance of observations. The difference between Aquinas and Bacon is the contrast between the appeal to authority and the finding out for oneself. In this contest, the appeal to authority lost rather decisively, but it was a long tough fight. People generally prefer a given answer, even if it is wrong, to the tough process of extracting the correct answer.

In spite of all that, appeal to authority is frequently necessary. The legal system in most democracies, for example, is based on the idea of appeal to authority. The parliament may make the laws but it is the courts that decide on what they mean.  Frequently, the courts even have the authority to override laws based on the constitution. This is true in many countries but most famously in the United States of America. In these countries, what the Supreme Court says, is the law. What a law actually means is commonly a matter of interpretation as evidenced by split decisions where one judge holds one opinion and another judge the opposite. Perhaps the interpretations are even arbitrary as they sometimes change over time despite the authority given to precedence. But a decision is required and there is no objective criteria, so the majority rules.

Now, it is worth commenting that that laws of nature and laws of man are completely different beasts and it is unfortunate that they are given the same name. The so called laws of nature are descriptive. They describe regularities that have been observed in nature.  They have no prescriptive value. In contrast, the laws of man are prescriptive, not descriptive. Certainly, the laws against smoking marijuana are not descriptive in British Columbia, neither were the laws against drinking during US prohibition. The laws describe what the government thinks should happen with prescribed punishments for those who disobey. However, there is no penalty for breaking the law of gravity because, as far as we know, it can’t be done. If someone actually did it, it would cease to be a law and there would be a Nobel Prize, not a penalty.  Like the laws of man, the laws of God—for example, the Ten Commandments—are prescriptive, not descriptive, with penalties given for breaking them. You can break the law of man and the laws of God, but not the laws of physics.

In science, things are different than in the courts of law. In the latter, we are concerned with the meaning of a law that some group of people have written. This, by its very nature, has a subjective component. In science, we are trying to discover regularities in how the universe operates. In this, we have the two objective criteria: parsimony and the ability to make correct predictions for observations. As pointed out in the previous post, idolizing a person is a mistake, even if that person is Isaac Newton. Appeal to observation trumps appeal to a human authority, but in the short term, even in science, appeal to a human authority is often necessary. Life is too short and the amount to know too large to discover it all for oneself. Thus, one relies on authorities. I consult the literature rather than trying to do experiments myself. We consult other people for expertise that we do not have ourselves. We rely on the collective wisdom of the community as reflected in the published literature. When we require decisions, we must rely on the proximate authorities of peers in a process called peer review. This process is relied on to maintain the collective wisdom and will be discussed in more detail in the next post.  In the meantime, we conclude this post by paraphrasing William Lyon McKenzie King[1] (1874 –1950): Appeal to authority if necessary but not necessarily appeal to authority.

Additional posts in this series will appear most Friday afternoons at 3:30 pm Vancouver time. To receive a reminder follow me on Twitter: @musquod.

One of the latest creations is YETS: Year End Technical Stop, referring to the period between the end of the heavy ion run on 7 December 2011 and the restart of LHC operations due to begin next week with hardware commissioning leading ultimately to pp collisions in April. So what to physicists do during YETS? A lot as it turns out!

One of the major activities is how to cope with the projected instantaneous luminosity of 7e33 (per cm**2 per s). This luminosity will likely come with a 50 nanosecond beam structure (the time between collisions) as was used in 2011. This means that the average number of pp interactions per triggered readout will be about 35, the one you tried to select with the trigger, plus many more piled on top of it. This affects trigger rates and thresholds, background conditions, and the algorithms used in the physics analysis. In addition, we shall likely run at 8 TeV total energy (compared to 7 last year). These new expected conditions are being simulated, a process requiring a huge amount of physicist manpower and computing resources. The results are carefully scrutinized in collaboration-wide meetings. That is the “glory” activity.

Besides the glory work, there is also a huge amount of technical service work, both hardware and software. At CMS in Point 5 (P5) we have observed beam-induced pressure spikes (rise and fall) in the vacuum. The pumping required for recovery is using up the supply of non evaporable getter (NEG) needed to achieve ultrahigh vacuum (UHV). The UHV in turn is needed to ensure that the beams do not abort which nearly happened last year. A huge effort was launched to radiograph the region in question to see if the same problems of drooping radio frequency (RF) fingers are present as has been observed in other sectors. An electrical discharge from the RF fingers can possibly cause the UHV spikes. Also at P5 work will be done on the zero degree calorimeter (ZDC), the Centauro And Strange Object Research (CASTOR) detector (not to be confused with CERN Advanced Storage Manager), the cathode strip chamber (CSC), the restive plate chamber (RPC) and the drift tube (DT) muon detectors which are accessible without opening the yoke of CMS. In addition, there is maintenance of the water cooling and rewiring of the magnet circuit breaker.

Each of the CMS subsystems has work to do as evident by a recent a trip into the P5 pit. The detailed activities of the pixel (PX), silicon tracker (TK), electromagnetic calorimeter (ECAL), and muon (MU) subdetectors are beyond the scope of this blog. I can give you some idea of what is going on with the hadron calorimeter (HCAL), where a bit of the details are fresh in my mind.

The HCAL activities are quite intense. Detector channel-by-channel gains, the numbers that are needed to convert electrical signals into absolute energy units can vary with time for a variety of reasons (e.g. radiation damage) and need periodic updating. This information has to go into the look up tables (LUTs) that are used by the electronics to provide TPGs (trigger primitive generation) which are in turn used by the level-1 hardware trigger to select events. If these numbers in the LUTs are slightly off, then the energy threshold that we think we are selecting is off target which is very bad because trigger rates vary exponentially with energy.

The HCAL uses 32 optical S-LINKs (where the S stands for simple, although I don’t remember anything simple about getting it to work) to send the data to DAQ computers. My group at Boston designed and built the front end driver (FED) electronics that collects and transmits the data on these links. The data transmission involves a complex buffering and feedback system so that the data flow can be throttled without crashing in case something goes wrong. The data flow reached its design value of 2 kBytes per link per event at the end of 2011 so we are going to reduce the payload by eliminating some redundant data bits which were previously useful for commissioning the detector but are no longer needed. This will allow us to comfortably handle the expected increase in event size due to increased pileup. Also 4 of our boards developed dynamic random access memory (DRAM) problems after a sudden power failure which took up two days of my time at CERN to inventory spares, isolate the affected DRAMS, and arrange for repairs.

The HCAL computers at P5 are running 32 bit Scientific Linux CERN (SLC4, another nested acronym). While we enjoyed the stability of this release over a number of years, it will no longer be supported by CERN after February 2012.  These computers are being upgraded (as I write this!) to 64 bit SLC5.

The HF calorimeters will have their photomultiplier tubes (PMTs) replaced in the LS1. We would like to do measurements with a few new PMTs in order to study performance stability and aging in the colliding beam environment. This activity requires building and testing new high-voltage (HV) distribution printed circuit boards (PCBs). The HV PCBs require testing and installation in the current HF read out boxes (ROBOXs) while there is still access to the detector.

Our group at Boston in also involved with designing electronics needed for the HCAL upgrade, the first part of which will take place in the first long shutdown (LS1). The new electronics is based on micro telecommunications computing architecture (uTCA). In Boston we have built a uTCA advanced mezzanine card for the unique slot number 13 (AMC13). This card will distribute the LHC clock signals needed for trigger timing and control (TTC) as well as serve as the FED. We plan to test these cards during the 2012 run. To prepare for these tests we have installed an AMC13 card in the central DAQ (cDAQ) lab which can transmit data on optical fibers to a multi optical link (MOL) card which exists in the form of a personal computer interface (PCI) card that can be readily attached to a computer. I addition, to be able to perform the readout tests with the new electronics without interrupting the physics data flow, we have installed optical splitters on the HCAL front end digital signals for a portion of the detector, parts of the HCAL barrel (HB), HCAL end cap (HE), and HCAL forward (HF), so that one path can be used for physics data and the other path for uTCA tests.

I can assure you that the activities in parts of CMS are (almost) as intense as during physics runs. There has been a lot to do!

I once met a secretary in California, the land of innovative thinkers, who was exposed to physics through typing exams, that could not understand why students thought physics was so hard. She thought each letter always stood for the same thing and once you learned them you were pretty much set. I am not sure she believed me when I told her there weren’t enough letters to go around. Same thing with acronyms. A quick search for CMS will include: Center for Medicare & Medicaid Services (a nested acronym), Content Management System, Chicago Manual of Style, Chronic Mountain Sickness, Central Middle School, City Montessori School, Charlotte Motor Speedway, Comparative Media Studies, Central Management Services, Convention on Migratory Species, Correctional Medical Services, College Music Society, Colorado Medical Society, Cytoplasmic Male Sterility, Certified Master Safecracker, Cryptographic Message Syntax, Code Morphing Software, Council for the Mathematical Sciences, Court of Master Sommeliers, and my own favorite, a neighborhood landscaper Chris Mark & Sons, of which am proud owner of one of their shirts.

And for those against acronym abuse, you can buy an AAAAA T-shirt (maybe I will too):

Thanks to Kathryn Grim for suggesting a blog about what goes on at an LHC experiment during shutdown.

We’d many more events over 2012 if the LHC simply kept running the way it already was at the end of the year. That’s because for most of the year, the luminosity was increasing over and over as the LHC folks added more proton bunches and focused them better. But we expect that the LHC will do better, starting close to last year’s peak, and then pushing to ever-higher luminosities. The worst-case we are preparing for is perhaps twice as much luminosity as we had at the end of last year.

But wait, why did I say “worst-case”?

Well, actually, it will give us the most interesting events we can get and the best shot at officially finding the Higgs this year. But increased luminosity also gives more events in every bunch crossing, most of which are boring, and most of which get in the way. This makes it a real challenge to prepare for 2012 if you’re working on the trigger, because have to sift quickly through events with more and more extra stuff (called “pileup”). As it happens, that’s exactly what I’m working on.

Let me explain a bit more of the challenge. One of the triggers I’m becoming responsible for is trying to find collisions containing a Higgs decaying to a bottom quark and anti-bottom quark and a W boson decaying to an electron and neutrino. If we just look for an electron — the easiest thing to trigger on — then we get too many events. The easy choice is to ask only for higher-energy electrons, but beyond a certain points we start missing the events we’re looking for! So instead, we ask for the other things in the event: the two jets from the Higgs, and the missing energy from the invisible neutrino. But now, with more and more extra collisions, we have random jets added in, and random fluctuations that contribute to the missing energy. We are more and more likely to get the extra jets and missing energy we ask for even though there isn’t much missing energy or a “Higgs-like” pair of jets in the core event! As a result, the event rate for the trigger we want can become too high.

How do we deal with this? Well, there are a few choices:

1. Increase the amount of momentum required for the electron (again!)
2. Increase the amount of missing energy required
3. Increase the minimum energy of the jets being required
4. Get smarter about how you count jets, by trying to be sure that they come from the main collision rather than one of the extras
5. Check specifically if the jets come from bottom quarks
6. Find some way to allocate more bandwidth to the trigger

There’s a cost for every option. Increasing energies means we lose some events we might have wanted to collect — which means that even though the LHC has produced more Higgs bosons, it’s counterbalanced by us seeing fewer of the ones that were there. Being “smarter” about the jets means more time spent by our trigger processing software on this trigger, when it has lots of other things to look at. Asking for bottom quarks not only takes more processing, it also means the trigger can’t be shared with as many other analyses. And allocating more bandwidth means we’d have to delay processing or cut elsewhere.

And for all the options, there’s simply more work. But we have to deal with the potential for extra collisions as well as we can. In the end, the LHC collecting much more data is really the best-case scenerio.

Science is complex. There’s no getting around that. But it’s essential that everyone engage constructively with it. That’s particularly true of the political and business leaders in Davos, whose decisions on science-based subjects can influence everything from the well being of our children to the future of the planet. It’s vital that those decisions are taken from an informed position and on rational grounds.

The challenge that science faces is that we live in a world where it’s de rigueur to know your Shakespeare, Molière or Goethe, but quite all right to be proudly ignorant of Faraday, Pasteur or Einstein. It hasn’t always been that way, and it doesn’t have to be that way. But right now, there’s a trend in society towards scientific apathy, and even antagonism. This is dangerous for us all and it’s incumbent on the scientific community to address the issue.

There was a time not so long ago when science was a fully integrated part of society, discussed in the same breath as football matches and front-page news. In the early part of the 20^th century, news of Einstein’s advances were accompanied by cartoons in the press, and as recently as the 1960s science grabbed the popular imagination, thanks largely to NASA’s Apollo programme. But the moon shots bucked a trend of increasing distance between science and society, which is leaving society ill equipped to make the science-based decisions it needs to make.

Among the biggest challenges to society today are climate change and energy. Both are highly complex political and scientific issues. The climate is changing. There’s no doubt about that, and it is equally incontrovertible that human activity has something to do with it. Yet in the public sphere, the debate still rages on. Similarly, it’s a simple fact that renewable energy does not currently have the capacity to supply the increasing demands of the world.  That’s not to say that renewables do not have a place. Of course they do, and that place will grow with time. But the current timescale for delivery is longer than that for demand. Is society equipped to make the difficult decisions that need to be made on issues of global importance such as this? In my opinion, we’re far from it.

On the personal level, there’s a range of issues that leave people confused and forced to take ill-informed decisions that can literally have life-or-death consequences. Take mad cow disease, scares over the MMR vaccine, and the safety of mobile phones, for example.

Of course, at CERN, we’ve had our own experience of this phenomenon. When starting up the LHC in 2008, the world was in the grip of black hole fever. According to a small handful of people, our flagship accelerator would create a black hole that would devour the Earth. The idea went viral on social media, and was also widely reported in the mainstream media, many of which conveniently left the normal journalistic code of ethics to one side as they explored the comic possibilities of the story. Unfortunately, science has left society alone for too long, and many people were unable to see the funny side. There were even stories of schools being closed for the day to allow children to be with their parents, just in case. And all this was based largely on the testimony of a man who, when asked about his concerns on television, explained that the LHC would either destroy the Universe or it would not, therefore the probability for disaster was one in two.  If this were not so tragic, it would be laughable.

What can science do about it? In my opinion, a great deal.  At the institutional level, things are changing.  The recently created Blavatnik School of Government at Oxford University includes science as an obligatory part of its course on public policy, to cite just one example. We need to use exciting science projects like the LHC to engage people with science, not just through the science pages, but also in new ways such as the arts residency programme we recently launched at CERN. And scientists in positions of influence need to use that influence to shape political debate in the world’s Capitals and in places like Davos.

Broad engagement has been our approach at CERN for a number of years, seizing the opportunity offered by the visibility of the LHC to engage more fully with everyone from decision makers to our neighbours and the general public. As a result we’re seeing our science being covered responsibly, and once again we’re seeing people talking about it along with football and front-page news. Sometimes the stories are not exactly what we’d like to see, but what’s important is that people are talking about science.

When the LHC started up, and the world continued to exist, at least one newspaper boldly declared that the LHC would be the new Apollo, set to engage a whole generation with science. While I take such headlines with a healthy pinch of salt, they do make good reading. More recently, another newspaper declared that physics has the X-factor, that elusive quality that makes it part of the zeitgeist.

Science as a whole needs to capitalise on this, to ensure that the LHC is not science’s one-hit-wonder, and that engagement with society is sustained. As scientists, we owe the world this, helping people to master the complexity of their own science-based lives. Twelve months from now, I’ll be taking this message back to Davos.

Rolf Heuer

Now, compare that to how we go about getting our data in particle physics experiments. Back in the day, you definitely had to know the exact directory and exact file names of the dataset that you wanted to analyze, and then carefully type that into your computer programs. A single typo could destroy hours or days of computing effort. We’ve largely gotten past that — we have better technology for file catalogues, such that you can just specify the name of a dataset, and all the file names will be looked up for you. But we are still largely constrained by “data locality,” the requirement that your analysis program must be running on a computer in the same room as the computer that has the disk with your data on it. This constraint leads to a variety of optimization problems. What if a dataset gets popular all of a sudden — are there enough processing resources in the right place to handle the demand? Can you get more copies out to the bigger processing centers quickly? Are you then under-using other centers and letting CPU cycles go idle? If you want to run on a given dataset, you might know which computing sites have that data, but how do you know which has the most available resources right now? And finally, what if data at a site gets corrupted? Will all the jobs running in that computer room start failing? Needless to say this doesn’t sound like YouTube at all.

I and some colleagues are working on a project that tries to change this. We’ve called it “Any Data, Anytime, Anywhere,” as our goal is to make it as easy to access LHC data as it is to access a YouTube video. At the heart of the system is a “redirector,” a system that serves as a giant index of files that reside at computing sites all over the country. A computer program asks the redirector for a file, the redirector finds an optimal source for the file, and the program then reads the file from that source, without the user having to know where the file actually is. That means that the source could be thousands of miles away, and the only way for the remote reading to be efficient is for it to be nearly as fast as reading from a computer in the same room, so some effort has gone into making that happen. Once you have removed the data locality requirement, all sorts of things are possible. If a file is corrupt at one site, it could introduce a fallback mechanism so that a read failure results in an attempt to get the same file through the redirector instead. If a particular site gets overloaded with jobs, we could start to migrate them to a less busy site, even if that site doesn’t actually have the data that the jobs want; they can be obtained through the redirector instead. That could lead to a better global balancing of supply and demand for resources. While we imagine that it’s computers at CMS institutions that will be reading the data, there’s nothing to stop any computer anywhere from reading the data, even if it is not part of CMS. That could really fulfill the promise of grid computing — if we can borrow a computer for a few hours, we can use it to analyze CMS data even if that computer starts out knowing nothing about CMS. It also gives us a straightforward way to use cloud-computing resources, if that were to turn out to be cost effective.

And on top of all that, what stops this from being limited to the LHC? Many disciplines have large datasets that need to be analyzed by distributed teams of scientists. In principle, they could use the same infrastructure. We’re hoping that this technology could eventually be used across the sciences and even into emerging fields like digital humanities. If that were to happen, then researchers from all sorts of disciplines could consider themselves Easy Readers, at least as far as their data is concerned.

I have always considered it strange that philosophy places such importance on reading the works of long dead people—Aristotle, Descartes, etc. In science, Newton’s ideas trumped those of both Aristotle and Descartes, yet very few scientists today read Newton’s works. His ideas have been taken, clarified, reworked, and simplified. The same thing applies to the scientific writings of other great and long dead scientists. Nothing is gained by going to the older sources. Science advances and the older writings lose their pedagogical value. This is because in science, the ultimate authority is not a person, but observation.

A given person may play an important role but there is always someone else close on his heels. Natural selection was first suggested, not by Darwin, but by Patrick Matthew (1790 – 1874) in 1831 and perhaps by others even earlier. Alfred Russell Wallace’s (1823 – 1913) and Darwin’s works were presented together to the Linnean Society in July 1858[2].  And so it goes: Henri Poincaré (1854 – 1912) and Hendrik Lorentz (1853 – 1928) were nipping at Einstein’s heels when he published his work on special relativity.  Someone gets priority, but it is observation that ultimately should be given the credit for new models.

When the ultimate role of observation is forgotten, science stagnates. Take, for example, British physics after Isaac Newton (1642 – 1727). It fell behind the progress on the continent because the British physicists were too enamoured of Newton. But the most egregious example is Aristotle (384 BC – 322 BC). The adoration of Aristotle delayed the development of knowledge for close to two millennia.  Galileo and his critic, Fortunio Liceti (1577 – 1657), disputed about which was the better Aristotelian, as if this was the crucial issue. Even today, post-docs all too frequently worry about what the supervisor means rather than thinking for themselves: But he is a great man, so his remark must be significant[3]. Actually he puts on his pants on one leg at a time like anyone else.

Then there is the related problem of rejecting results due to their origins, or the associated ideology. The most notorious example is the Nazi rejection of non-Aryan science; for example, relativity because Einstein was a Jew. One sees a similar thing in politics where ideas are rejected as being socialist, fascist, atheist, Islamic, Christian, or un-American thus avoiding the real issues of the validity of the idea: Darwinism[4] is atheistic hence it must be condemned. Yeah?  And your mother wears army boots.

In science, people are considered great because of the greatness of the models they develop or the experimental results they obtained. In religion, it is the other way around. Religions are considered great based on the greatness of their founder. Jesus Christ is central to Christianity: and if Christ has not been raised, then our preaching is vain, your faith also is vain (1 Corinthians 15:14). Islam is based on the idea: There is no God but Allah and Mohammad is his prophet. Many other major religions (or philosophies of life) are founded on one person: Moses (Judaism), Buddha (Buddhism), Confucius (Confucianism), Lao Tzu (Taoism), Guru Nanak (Sikhism), Zoroaster (Zoroastrianism), Bahá’u’lláh (Bahá’í Faith) and Joseph Smith (Mormonism).  Even at an operational level, certain people have an elevated position and are considered authorities: for example, the Pope in the Catholic Church, or the Grand Ayatollahs in Shi’ite Islam. Because of the basic difference between science and religion, an attack on a founder of a religion is an attack on its core, while an attack on a scientist is an irrelevancy. If Joseph Smith (1805 – 1844) was a fraud, then Mormonism collapses. Yet nothing in evolution depends on Darwin, nor anything in classical mechanics on Newton. But we can understand the upset of the Islamic community when Mohammad is denigrated: it is an attack on their whole religious framework which depends on Mohammad’s unique role.

The difference in the role of the individual in science and religion is due to their different epistemologies. In science, everything is public—both the observations and the models built on them. In contradistinction, the inspiration or revelation of religion is inherently private, a point noted by Saint Thomas Aquinas (1225 – 1274). You too can check Einstein’s calculations or Eddington’s experiment; you do not have to rely on either Einstein or Eddington. Now it may take years of work and a lot of money, but in principle it can be done. But you cannot similarly check the claims of Jesus’s divinity, even with years of study, but must take it on faith or as the result of private revelation.

Unlike in science, in religion, old is better than new. If a physical manuscript of St. Paul’s writing dating from the first century were discovered, it would have a profound effect on Christianity. But a whole suitcase of newly discover works in Newton’s or Darwin’s handwriting would have no effect on the progress of science. This is because religion is based on following the teachings of the inspired leader, while science is based on observation.

Additional posts in this series will appear most Friday afternoons at 3:30 pm Vancouver time. To receive a reminder follow me on Twitter: @musquod.

Surprisingly, the answer to “How does an electron-positron collider produce quarks if neither particle contains any?” all begins with the inconspicuous photon.

No Firefox, I Swear “Hadronization” is a Real Word.

As far as the history of quantum physics is concerned, the discovery that all light is fundamentally composed of very small particles called photons is a pretty big deal. The discovery allows us to have a very real and tangible description of how light and electrons actually interact, i.e., through the absorption or emission of photon by electrons.

Figure 1: Feynman diagrams demonstrating how electrons (denoted by e^-) can accelerate (change direction of motion) by (a) absorbing or (b) emitting a photon (denoted by the Greek letter gamma: γ).

The usefulness of recognizing light as being made up many, many photons is kicked up a few notches with the discovery of anti-particles during the 1930s, and in particular the anti-electron, or positron as it is popularly called. In summary, a particle’s anti-particle partner is an identical copy of the particle but all of its charges (like electric, weak, & color!) are the opposite. Consequentially, since positrons (e⁺) are so similar to electrons (e^-) their interactions with light are described just as easily.

Figure 2: Feynman diagrams demonstrating how positrons (e⁺) can accelerate (change direction of motion) by (a) absorbing or (b) emitting a photon (γ). Note: positrons are moving from left to right; the arrow’s direction simply implies that the positron is an anti-particle.

Then came Quantum Electrodynamics, a.k.a. QED, which gives us the rules for flipping, twisting, and combining these diagrams in order to describe all kinds of other real, physical phenomena. Instead of electrons interacting with photons (or positrons with photons), what if we wanted to describe electrons interacting with positrons? Well, one way is if an electron exchanges a photon with a positron.

Figure 3: A Feynman diagram demonstrating the exchange of a photon (γ) between an electrons (e^-)  and a positron (e⁺). Both the electron and positron are traveling from the left to the right. Additionally, not explicitly distinguishing between whether the electron is emitting or absorbing is intentional.

And now for the grand process that is the basis of all particle colliders throughout the entire brief* history of the Universe. According to electrodynamics, there is another way electrons and positrons can both interact with a photon. Namely, an electron and positron can annihilate into a photon and the photon can then pair-produce into a new electron and positron pair!

Figure 4: A Feynman diagram demonstrating  an annihilation of an electrons (e^-)  and a positron (e⁺) into a photon (γ) that then produces an e⁺e^- pair. Note: All particles depicted travel from left to right.

However, electrons and positrons is not the only particle-anti-particle pair that can annihilate into photons, and hence be pair-produced by photons. You also have muons, which are identical to electrons in every way except that it is 200 times heavier than the electron. Given enough energy, a photon can pair-produce a muon and anti-muon just as easily as it can an electron and positron.

Figure 5: A Feynman diagram demonstrating  an annihilation of an electrons (e^-)  and a positron (e⁺) into a photon (γ) that then produces a muon (μ^-) and anti-muon(μ⁺) pair.

But there is no reason why we need to limit ourselves only to particles that have no color charge, i.e., not charged under the Strong nuclear force. Take a bottom-type quark for example. A bottom quark has an electric charge of -1/3 elementary units; a weak (isospin) charge of -1/2; and its color charge can be red, blue, or green. The anti-bottom quark therefore has an electric charge of +1/3 elementary units; a weak (isospin) charge of +1/2; and its color charge can be anti-red, anti-blue, or anti-green. Since the two have non-zero electric charges, it can be pair-produced by a photon, too.

Figure 6: A Feynman diagram demonstrating  an annihilation of an electrons (e^-)  and a positron (e⁺) into a photon (γ) that then produces a bottom quark (b) and anti-bottom quark (b) pair.

On top of that, since the Strong nuclear force is, well, really strong, either the bottom quark or the anti-bottom quark can very easily emit or absorb a gluon!

Figure 7: A Feynman diagram demonstrating  an annihilation of an electrons (e^-)  and a positron (e⁺) into a photon (γ) that produces a bottom quark (b) and anti-bottom quark (b) pair, which then radiate gluons (blue).

In electrodynamics, photons (γ) are emitted or absorbed whenever an electrically charged particle changes it direction of motion. And since the gluon in chromodynamics plays the same role as the photon in electrodynamics, a gluon is emitted or absorbed whenever  a “colorfully” charged particle changes its direction of motion. We can absolutely take this analogy a step further: gluons are able to pair-produce, just like photons.

Figure 8: A Feynman diagram demonstrating  an annihilation of an electrons (e^-)  and a positron (e⁺) into a photon (γ) that produces a bottom quark (b) and anti-bottom quark (b) pair. These quarks then radiate gluons (blue), which finally pair-produce into quarks.

At the end of the day, however, we have to include the effects of the Weak nuclear force. This is because electrons and quarks have what are called “weak (isospin) charges”. Firstly, there is the massive Z boson (Z), which acts and behaves much like the photon; that is to say, an electron and positron can annihilate into a Z boson. Secondly, there is the slightly lighter but still very massive W boson (W), which can be radiated from quarks much like gluons, just to a lesser extent. Phenomenally, both Weak bosons can decay into quarks and form semi-stable, multi-quark systems called hadrons. The formation of hadrons is, unsurprisingly, called hadronization. Two such examples are the the π meson (pronounced: pie mez-on)  or the J/ψ meson (pronounced: jay-sigh mezon). (See this other QD article for more about hadrons.)

Figure 9: A Feynman diagram demonstrating  an annihilation of an electrons (e^-)  and a positron (e⁺) into a photon (γ) or a Z boson (Z) that produces a bottom quark (b) and anti-bottom quark (b) pair. These quarks then radiate gluons (blue) and a W boson (W), both of which finally pair-produce into semi-stable multi-quark systems known as hadrons (J/ψ and π).

In summary, when electrons and positrons annihilate, they will produce a photon or a Z boson. In either case, the resultant particle is allowed to decay into quarks, which can radiate additional gluons and W bosons. The gluons and W boson will then form hadrons. My friend Geoffry, that is how how you can produce quarks and hadrons from electron-positron colliders.

Now go! Discuss and ask questions.

Happy Colliding

- richard (@bravelittlemuon)

* The Universe’s age is measured to be about 13.69 billion years. The mean life of a proton is longer than 2.1 x 10²⁹ years, which is more than 15,000,000,000,000,000,000 times the age of the Universe. Yeah, I know it sounds absurd but it is true.

Belle PlusはKEK、奈良女子大学、奈良教育大学理数教育研究センターが共催している、高校生を対象とした研究体験型のサイエンスキャンプです。研究者に直接指導を受けながら素粒子物理学に関する実習や解析を行い、最終的に研究発表を行うもので、実際に研究者が行っている研究活動の流れを体験することができます。平成18年度よりBelle実験グループが中心となって実施しており、今年度で5回目の開催となります。

今回は、「B-Lab班」、「ワイヤーチェンバー班」、「霧箱班」、「理論班」の４つの班に分かれて実習を行いました。その他にもKEKの施設の見学や素粒子に関する講義、放射線についてのサイエンスカフェが開かれるなど盛りだくさんの内容となりました。最後の日には研究発表会が行われ、高校生同士で活発に質疑応答する様子が見られました。

高校生からは「将来研究者になりたい」「自分が興味を持っている事柄を、同じく興味を持つ他の人と共有できたので、とても良かった」といった感想が聞かれました。Belle Plusでの経験や共に議論した仲間達との繋がりを大切にしながら、素粒子物理学に対する興味関心がさらに高まればいいなと思います。

Belle Plus2011についての詳しい活動内容は以下をご覧ください。

Belle PlusのHP 活動報告　http://belle.kek.jp/b-camp/report.html

高エネルギー加速器研究機構 トピックス記事 http://www.kek.jp/ja/NewsRoom/Release/20120127130000/

Here is an unusual contest: participants are asked to communicate their work or interest in a 3-minute speech delivered to a general audience. In return, they get training from professionals (science communicators and media people), get invited to a Masterclass and can even make it to the finals at the Cheltenham Science Festival in the United Kingdom. The contestants are judged by professional scientists on their content, clarity and charisma. The goal is to detect the new voices for science and to find communicators able to captivate their audience.

It started in 2005 at the Cheltenham Science Festival. In 2007, the British Council adopted this competition as one of its flagship science engagement projects first in South East Europe for a pilot project, then expanding in 2010 to include 14 countries from Europe, Asia and Africa. Check out if there is a competition near you. You can also get help to host your own event.

On February 4, CERN will be hosting the Swiss semi-finals, with the finals to be held in Zurich on March 30. Anybody working or studying in Switzerland can participate. You can register up to the day of the event itself. Every one is also invited to attend the competition, which will start at 15:00 in CERN Globe of Innovation.

Don’t miss Tom Whyntie’s winning performance at the 2009 finals. Tom is a Ph.D student working on the CMS experiment at CERN. This is the most convincing speech you might ever heard about the importance of nothing.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.

The Globe of Innovation, CERN expositions and visitors center

Cette compétition est assez inhabituelle: les participant-e-s ont trois minutes pour décrire leur recherche ou un sujet qui les intéresse devant une audience tout-public. En retour, ils et elles  reçoivent une formation donnée par des professionnel-le-s en communication et sont invité-es à participer à une « Masterclass ». Les finalistes iront au Cheltenham Science Festival au Royaume-Uni. Le jury est composé de scientifiques et gens des médias.

Les participant-e-s seront jugés sur leur clarté, le contenu et leur charisme. Le but est de repérer ceux et celles qui sauront captiver leur auditoire et qui pourraient devenir les nouvelles voix de la science.

L’idée est née au Festival des Sciences de Cheltenham en 2005 et grâce à l’implication du British Council, l’événement a vite évolué d’un premier projet pilote dans le sud ouest de l’Europe pour atteindre 14 pays d’Europe, d’Asie et d’Afrique. Vérifiez pour voir si une compétition se tient près de chez vous. Vous pouvez même obtenir de l’aide pour lancer votre propre compétition.

Le 4 février, le CERN accueillera les demi-finales suisses. La finale aura lieu à Zurich le 30 mars. Toute personne travaillant ou étudiant en Suisse peut participer. On peut s’inscrire jusqu’au 4 février. Le public est aussi invité à assister à la compétition dès 15:00 au Globe de l’Innovation du CERN.

Ne manquez pas la performance du grand gagnant de 2009, Tom Whyntie. Tom est étudiant au doctorat et fait sa recherche au CERN sur l’expérience CMS. Vous ne trouverez pas discours plus convaincant sur l’importance de rien.

Pauline Gagnon

Pour être averti-e lors de la parution de nouveaux blogs, suivez-moi sur Twitter: @GagnonPauline ou par e-mail en ajoutant votre nom à cette liste de distribution

Le Globe de l’Innovation du CERN, centre d’expositions et de visites

Those who followed me on Twitter (@aidanatcern) may have already seen some of the wonderful images of aurorae. There are dedicated webcams that capture the night sky, and you can see some sample images at the Aurora Webcam archive.

Aurora over Alaska (wikimedia)

When charged particles accelerate or decelerate, or recombine in pairs, they emit electromagnetic radiation, and it is this radiation that we see in the aurora. The color of the light depends on the wavelength of the radiation, and the intensity of the light depends on how much radiation is emitted. That means that there is always an aurora above us, but if the energy of the radiation is too low, or the intensity is too weak, we won’t see anything. Once we know how to interpret the light we can learn something about the radiation that is emitted. Usually we see a variety of colors in an aurora and each color corresponds to a different wavelength, so if we can see a region of the sky that is all one color, we know that the wavelength (and hence the energy, ignoring the effects of aberration) must be the same. That means we can “map” the sky and find contours of wavelength.

Since the particles are accelerating, there must be something that causes the acceleration. The Earth’s core is made of (among other materials) molten iron. The rotation of the Earth means that this core is also rotating, and a rotating fluid magnetic medium creates a magnetic dipole, giving the Earth magnetic North and South poles. These poles are aligned near the geographic North and South poles of the Earth, but not exactly. (In fact, magnetic North and South keep moving and from time to time they even swap places. The exact mechanism behind this is not yet fully understood, but geological records show it happens every few hundred thousand years. Simulations suggest that the rotating magnetic fluid is a chaotic system, so the reversals occur at stochastic, or random, intervals of time.)

The sun produces a stream of particles, known as the solar wind, and they create their own electromagnetic field. The two fields, from the Earth and the sun, interact and they force charged particles in the upper atmosphere along curved paths. As the particles move along these paths they accelerate, decelerate and recombine, and that is what produces the aurorae. The most recent increase in magnetic activity can be traced back to a huge coronal mass ejection that arrived from the sun. This video shows the arrival of the flare:

The effect looks impressive, but don’t be scared, solar winds like this are perfectly harmless. Far bigger winds have hit the Earth in the past few billions years and life has continued to flourish in spite of them. Life has adapted to the Earth’s magnetic field and this field protects us from the high energy particles.

It turns out that while looking up at the night sky is a beautiful and moving experience in itself, it is also important to particle physicists. Some of the most important discoveries in the last century came from a different phenomena, cosmic rays. Cosmic rays are very high energy particles (usually protons) that travel huge interstellar distances and rain down on the Earth in much the same way that the solar wind does. They interact with the upper atmosphere to create cascades of particles, and usually the muons are the only detectable particles that reach sea level. Interactions of these cosmic rays gave rise to the discovery of the muon (“Who ordered that?!”), the pion and the kaon, the lightest forms of mesonic matter. It was around this time that large scale accelerators were developed, and we found hundreds of new mesons and baryons. Cosmic rays gave us a very small glimpse into a rich “zoo” of particles that has occupied physicists ever since.

Eventually, when we have exhausted our ability to accelerate particles to higher energies we might need to rely on cosmic rays again. There are proposals to develop ground based detectors to study the interactions of extremely high energy particles from outer space. Those particles have the potential to reach energy regimes we can only dream of at the moment. (Incidentally, this is one of the ways that we know for sure that the LHC cannot destroy the world. The universe creates much more energetic particles than we could ever hope to create in our accelerators, and since the universe seems to be in one piece we can conclude that the LHC is safe on Earth!)

An aurora from above (Expedition 28 on board the International Space Station)

If you’re fortunate enough to see an aurora then take a few moments to think about the huge forces at work, the vast distances involved, and how the colors tell us so much about how the Earth and solar wind behave. It really is one of the most beautiful phenomena in the universe.

This article first appeared in Fermilab Today on Jan. 24.

Despite the biting cold and snow, scientists and Fermilab personnel gathered outside to break ground for Fermilab’s new Liquid Argon Test Facility. The facility, expected to be completed spring 2013, will house liquid-argon based experiments.

Scientists have speculated since the 1980s that liquid argon could be used as a crash pad for high-energy neutrinos and have subsequently constructed several liquid-argon neutrino detectors; the largest and most prominent being ICARUS, the Imaging Cosmic And Rare Underground Signals, detector in Italy. The design of the new MicroBooNE experiment improves upon technology developed for ICARUS and will allow scientists to observe neutrinos with greater precision and resolution.

Regina Rameika is the project manager for the construction of the MicroBooNE detector.

“The MicroBooNE detector that will first use this facility is smaller than ICARUS, but incorporates some advanced designs,” Rameika said.

MicroBooNE will use liquid argon as a target for neutrinos generated in the Booster neutrino beam. When the neutrinos hit the argon nuclei, they generate showers of charged particles that then drift to an electrical detector. The purer the argon, the further the particles are able to drift. MicroBooNE will use ultrapure argon to maximize the distance these particles drift. This model is more efficient, cost effective, and has the potential to be scaled-up to a much larger size than previous detectors.

The MicroBooNE experiment will provide another layer of data for using the Booster neutrino beam. Not only will scientists be able to observe particles with the existing MiniBooNE detector, but now they will be able to measure neutrinos from the Booster neutrino beam with a second, higher-resolution detector.

“The MicroBooNE experiment will be focused on understanding some anomalies observed in the data from the MiniBooNE experiment,” Rameika said. This project will also provide valuable insight into different designs for liquid-argon detectors that could be located in the LArTF once MicroBooNE is complete.

—Sarah Charley

Fermilab’s iconic Wilson Hall can be seen in the background as visitors inspect savanna restoration efforts. Credit: Fermilab Natural Areas.

Editor’s note: One of the bonuses of Fermilab having much of its scientific infrastructure underground is that it allows for a wealth of open space on the 6,800-acre campus. Fermilab and volunteers from  neighboring communities use that space to create havens of restored native habitats to help wildlife flourish. So far, more than 1,100 acres have been restored. Savannas are just one example of these restoration efforts.

The highly endangered oak savanna was once one of the most common vegetation types in the Midwest. Grant money from the DuPage Community Foundation is helping to save this natural gem for hikers and animals by supporting restoration efforts at Fermi National Accelerator Laboratory.

In December, the Foundation awarded $7,500 for oak savanna restoration to Fermilab Natural Areas, a not-for-profit organization consisting of volunteers from the Chicagoland area.

The money will help protect a 35-acre savanna remnant in the center of Fermilab, which straddles the border of Kane and DuPage counties.

The restored savannah will create a tool for educating school and community groups about Illinois’ environmental past and the need for conservation. The savanna also should attract more wildlife to the area. Many infrequently seen species of insects and birds, such as the red-headed woodpecker, thrive in oak savannas.

The multi-phase restoration effort planned to start this winter will include removal of invasive species of trees and shrubs, prescribed burning, enrichment of the flora and monitoring. The project continues a long history of stewardship of environmental resources at Fermilab, which has led to the restoration of more than 1,100 acres of prairie, woodland, grassland and wetland.

“However, this restoration would not be possible without the injection of supplemental funding from organizations such as the DuPage Community Foundation to the Fermilab Natural Areas,” said Rod Walton, Fermilab ecologist.

Farming and development has taken its toll on the environment, leaving less than one-tenth of one percent of the native landscape of Illinois intact. Groups such as Fermilab Natural Areas are restoring the balance.

“The restoration of Illinois’s oak savannas allows children to see that landscape that greeted Illinois settlers,” Walton said. “It also secures a healthy future for the area by creating a diverse habitat.”

About FNA:

Fermilab Natural Areas (FNA) is a volunteer organization located in DuPage and Kane counties at Fermilab, dedicated to involving local community in restoring and conserving the natural environment at Fermilab. Established in 2006, FNA has a membership of more than 80 volunteers, whose activities are concentrated on conservation of the 10 square miles of largely open land at the facility owned by the U.S. Department of Energy and operated by Fermi Research Alliance, LLC. For further information regarding Fermilab Natural Areas, visit the website: http://www.fermilabnaturalareas.org/.

(these minutephysics pieces are quite good!)

So, ANITA is the balloon-borne experiment mentioned in the video and of which I am a collaborator. But folks at IceCube claim that’s the world’s largest neutrino detector. And that’s a project I also work on. Furthermore, I was just at the South Pole working on a new neutrino detector called ARA (the Askaryan Radio Array) which has been mentioned as the largest neutrino detector in the world, even when only partially constructed. (See arxiv for a good ARA summary.)

So what’s the truth? Well, as in so many different endeavors, it comes down to the definition of largest. Or largest in what sense.

IceCube: This is an instrumented volume of a full cubic kilometer. Made up of over five thousand individual digital optical modules (DOMs) it is certainly the largest instrumented volume in the world. It uses the Cherenkov effect of neutrino-induced shower particles in the optically clear ice to image the shower and hence the neutrino.

ANITA: During an ANITA balloon flight, the payload observes a simply astonishing, more than a million square kilometers at a time. Only for certain narrow angular ranges can events form in the ice, refract through the surface and reach the balloon floating at 120,000 feet, but it is the largest observed area. This uses the Askaryan Effect which is a Cherenkov-like radio pulse emission from showers in dense materials.

ARA: The full ARA will cover hundreds of cubic kilometers of ice, but will have just 37 stations, each with four strings of four antennas. A much larger volume than IceCube, but much more sparsely instrumented due to the better attenuation length of radio than optical photons in the cold polar ice. The engineering test station that has been running since January 2011 has the largest volumetric acceptance of any neutrino detector in the world, several cubic kilometers. This also uses the radio technique.

So, largest neutrino detector in the world? Depends on your definition.

Read more about them: ANITA, IceCube on Facebook, Ice Cube on Facebook, ARA homepage, other radio neutrino efforts…RICE, ARIANNA, SalSA …

The problem with the uncertainty principle is similar. This principle states that we cannot simultaneously measure the position and motion of a particle. Now, classically, the state of a particle is given by its location and motion (i.e. it’s momentum). Quantum mechanically, the state is given by the wave function or, if you prefer, by a distribution in the location-motion space[1]. Now the problem is not that the location and motion cannot be measured simultaneously but that the particle does not simultaneous have a well-defined position and motion since its state is given by a distribution. This causes realists, at least classical realists, to have fits. In quantum mechanics, the position is only known when it is directly measured, ie properties of the system only exist when they are being looked at. This is a distinctly antirealist point of view. Again, this is trying to force a classical framework on a quantum system. If anything is real in quantum systems, it is wave functions, not individual observables. But see below.

Quantum mechanics is definitely weird; it goes against our common sense, our intuition. The main problem is that, while classical mechanics is deterministic, quantum mechanics is probabilistic. To see why this is a problem, consider the classical-probability problem of rolling a dice. I roll a fair dice. The chance of it being 2 is 1/6; similarly for any value from 1 to 6. Now once I look at the dice the probability distribution collapses. Let’s say, I see a 2. The probability is now 1 that the value is 2 and zero for the other values. But for Alice who has not seen me check, the probabilities are still all 1/6. I now tell her that the number is even. This collapse her probability distribution so that it is 1/3 for 2,4,6 and zero for 1,3,5. Now for Bob, who did not hear me telling Alice, the probabilities are still 1/6 for each of the numbers. Two important points arise from this. First, classical probabilities change discontinuously when measurements are made and, second, classical probabilities depend not just on the system but on the observer, ie probabilities are observer dependant.

We should expect the same quantum mechanically. We should expect measurements to discontinuously change the probability distribution and the probability distribution to be observer dependent. The first is certainly true. Quantum mechanical measurements cause the wave function to collapse and consequently the probability distribution[2] also collapses. The second is not commonly realized or accepted, but it should be. The idea that the wave function is a property of the quantum system plus observer, not the quantum system in isolation, is not new. Indeed, it is a variant of the original Copenhagen interpretation of quantum mechanics. But frequently, it is denied. When this is done, one is usually forced to the conclusion that the mind or consciousness plays a large and mysterious role in the measurement process. Making the wave function, or the state description, observer dependent avoids this problem.  The wave function is then just the information the observer has about the quantum system. As Niels Bohr (1885 – 1962), one of the founders of quantum mechanics, said: It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.

Let us consider the wave function collapse in more detail. Consider an entanglement experiment. The idea is to have a system emit two particles such that if we know the properties of one, the properties of the other are also known. One of the two emitted particles is measured by Bob and the other by Alice.[3] Now, Alice is lazy so she has her particle transported to her home laboratory. She also knows that once Bob has done his measurement, she does not have to measure her particle but only has to call Bob to get the answer. Bob is also lazy, but he does go the lab and, if he feels like it, does the measurement and faithfully records it in his log book. One day when Alice calls, she gets no answer. It turns out Bob has died between the time he would have made the measurement and when he would have recorded it in his lab book. Now Alice is very upset. Not that Bob has died—she never liked him anyway—but that she does not know if the momentous event of the wave function collapse has happened or not. Her particle has not arrived at her home yet, but there is no experiment she can do on it to determine if the wave function has collapsed or not. The universe may have split into many worlds but she can never know! Of course, if the wave function is a property of the observer-quantum system, there is no problem.  The information Bob had on the wave function was lost when Bob died and Alice’s wave function is as it always was. Nothing to see here, move along.

So what is the interpretation of quantum mechanics? An important part seems to be that wave functions are the information the observer has on the quantum system, and is not a property of the quantum system alone. If you do not like that, well there is always instrumentalism,[4] i.e. shut up and calculate.

Additional posts in this series will appear most Friday afternoons at 3:30 pm Vancouver time. To receive a reminder follow me on Twitter: @musquod.