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Posts Tagged ‘history’

This article appeared in Fermilab Today on Sept. 5, 2014.

This aerial view shows the Neutrino Area under construction in May 1971. The 15-foot bubble chamber, pictured on the left, would later be moved to the present-day location of Lab D.  Photo: Fermilab

This aerial view shows the Neutrino Area under construction in May 1971. The 15-foot bubble chamber, pictured on the left, would later be moved to the present-day location of Lab B. Photo: Fermilab

It was called Target Station C. One of three stations north of Wilson Hall at the end of beamlines extending from the Main Ring (later replaced by the Tevatron), Target Station C was assigned to experiments that would require high beam intensities for investigating neutrino interactions, according to a 1968 design report.

Within a few years, Target Station C was officially renamed the Neutrino Area. It was the first named fixed-target area and the first to be fully operational. Neutrinos and the Intensity Frontier had an early relationship with Fermilab. But why is it resurfacing now?

“The experimental program is driven by the current state of knowledge, and that’s always changing,” said Jeffrey Appel, a retired Fermilab physicist and assistant laboratory director who started research at the lab in 1972.

When Appel first arrived, there was intense interest in neutrinos because the weak force was poorly understood, and neutral currents were still a controversial idea. Fermilab joined forces with many institutions both in and outside the United States, and throughout the 1970s and early 1980s, neutrinos generated from protons in the Main Ring crashed through a 15-foot bubble chamber filled with super-heated liquid hydrogen. Other experiments running in parallel recorded neutrino interactions in iron and scintillator.

“The goal was to look for the W and Z produced in neutrino interactions,” said Appel. “So the priority for getting the beam up first and the priority for getting the detectors built and installed was on that program in those days.”

It turns out that the W and Z bosons are too massive to have been produced this way and had to wait to be discovered at colliding-beam experiments. As soon as the Tevatron was ready for colliding beams in 1985, the transition began at Fermilab from fixed-target areas to high-energy particle colliding.

More recent revelations have shown that neutrinos have mass. These findings have raised new questions that need answers. In 1988, plans were laid to add the Main Injector to the Fermilab campus, partly to boost the capabilities of the Tevatron, but also, according to one report, because “intense beams of neutral kaons and neutrinos would provide a unique facility for CP violation and neutrino oscillation experiments.”

Although neutrino research was a smaller fraction of the lab’s program during Tevatron operations, it was far from dormant. Two great accomplishments in neutrino research occurred in this time period: One was the most precise neutrino measurement of the strength of the weak interaction by the NuTeV experiment. The other was when the DONUT experiment achieved its goal of making the first direct observation of the tau neutrino in 2000.

“In the ’90s most evidence of neutrinos changing flavors was coming from natural sources. But this inspired a whole new generation of accelerator-based neutrino experiments,” said Deborah Harris, co-spokesperson for the MINERvA neutrino experiment. “That’s when Fermilab changed gears to make lower-energy but very intense neutrino beams that were uniquely suited for oscillation physics.”

In partnership with institutions around the globe, Fermilab began planning and building a suite of neutrino experiments. MiniBooNE and MINOS started running in the early 2000s and MINERvA started in 2010. MicroBooNE and NOvA are starting their runs this year.

Now the lab is working with other institutions to establish a Long-Baseline Neutrino Facility at the laboratory and advance its short-baseline neutrino research program. As Fermilab strengthens its international partnerships in all its neutrino experiments, it is also working to position itself as the home of the world’s forefront neutrino research.

“The combination of the completion of the Tevatron program and the new questions about neutrinos means that it’s an opportune time to redefine the focus of Fermilab,” Appel explained.

“Everybody says: ‘It’s not like the old days,’ and it’s always true,” Appel said. “Experiments are bigger and more expensive, but people are just as excited about what they’re doing.”

He added, “It’s different now but just as exciting, if not more so.”

Troy Rummler

Special thanks go to Fermilab archivists Valerie Higgins and Adrienne Kolb for helping navigate Fermilab’s many resources on early neutrino research at the laboratory.

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J/ψ

Wednesday, August 6th, 2014

The particle with two names: The J/ψ Vector Meson. Again, under 500 words.

jpsi_NOVA

Trident decay of J/Psi Credit: SLAC/NOVA

Hi All,

The J/ψ (or J/psi) is a very special particle. Its discovery was announced in 1974 independently by two groups: one lead by Samuel Ting at Brookhaven National Laboratory (BNL) in New York and the second lead by Burton Richter at Standford Linear Accelerator Center (SLAC) in California. J/ψ is special because it established the quark model as a credible description of nature. Having been invented by Gell-Man and Zweig as a bookkeeping tool, it was not until Glashow, Iliopoulos and Maiani (GIM) that the concept of quarks as real particles was taken seriously. GIM predicted that if quarks were real, then they should come in pairs, like the  up and down quarks. Candidates for the up, down, and strange were identified, but there was no partner for the strange quark. J/ψ was the key.

ting-group-335px_BNL

Samuel Ting and his BNL team. Credit: BNL

Like the proton or an atom, the J/ψ is a composite particle. This means that J/ψ is made of smaller, more elementary particles. Specifically, it is a bound state of  one charm quark and one anticharm quark. Since it is made of quarks, it is a “hadron“. But since it is made of exactly one quark and one antiquark, it is specifically a “meson.” Experimentally, we have learned that the  J/ψ has an intrinsic angular momentum (spin) of 1ħ (same as the photon), and call it a “vector meson.” We infer that the charm and anticharm, which are both spin ½ħ, are aligned in the same direction (½ħ + ½ħ = 1ħ). The J/ψ must also be electrically neutral because charm and anticharm quarks have equal but opposite electric charges.

richter_SLAC

Burton Richter following the announcement of co-winning the 1976 Nobel Prize. Credit: SLAC

At 3.1 GeV/c², the J/ψ is a about three times heavier than the proton and about three-quarters the mass of the bottom quark. However, because so few hadrons are lighter than it, the J/ψ possesses a remarkable feature: it decays 10% of the time to charged leptons, like an electron-positron pair. By conservation of energy, it is forbidden to decay to heavier hadrons. Because there are so few  J/ψ decay modes, it is appears as a very narrow peak in experiments. In fact, the particle’s mass and width are so well-known that experiments like ATLAS and CMS use them as calibration markers.

Credit: CMS

Drell-Yan spectrum data at 7 TeV LHC Credit: CMS

The J/ψ meson is one of the coolest things in the particle zoo. It is a hadronic bound state that decays into charged leptons. It shares the same quantum numbers as the photon and Z boson, so it appears as a Drell-Yan processes. It established the quark model, and is critical to new discoveries because of its use as a calibration tool. In my opinion, not too shabby.

Happy colliding.

Richard (@BraveLittleMuon)

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Many years ago when I was in a grade-eight math class, I was sitting looking out the windows at the dinosaurs playing. Ok, despite what my daughter thinks, I am not quite that old. What I was looking at was planes circling around in the distance. It turns out that a plane had crashed. It was a Handley Page HPR-7 Herald 211 operated by Eastern Provincial Airlines and all eight people on board were killed.  Now, it is sometimes claimed that science cannot explain the past. It’s even argued that historical sciences like paleontology, archeology, and cosmology, somehow use different methods of discovering the past, than say, determining the reason of a plane crash and that is again different from the method for discovering the laws of nature.  In reality, the methods are all the same.

I suppose, in response to the plane crash, people could have sat around and made predictions for future plane crashes but instead they used science to try to discover the past—what had caused the plane to crash. In this case it turned out to not be so difficult. The Aviation Safety Network describes the cause thus: Failure of corroded skin area along the bottom centre line of the aircraft beneath stringer No.32 which resulted in structural failure of the fuselage and aerial disintegration. This was found out by a metallographic examination which provided clear evidence of stress corrosion in the aluminum alloy. The planes of this type that were remaining in service were repaired to prevent them from crashing as well.

The approach to understanding why the Eastern Provincial Airline’s plane had crashed followed a similar approach to any other plane crash: you analyse the debris, gather records from the black box and whatever other information is available, and construct a model for what happened. You test the model by making predictions for future observations; for example, that corrosion will be found on other planes of the same type.  This sounds very much like the standard scientific method as proposed originally by Roger Bacon (1220 – 1292) and followed by scientists ever since: observe, hypothesize, test, rehypothesize, and repeat as necessary.

The same technique is used for any reconstruction of the past, be it plane crashes, the cause of Napoleon’s death, archeology, paleontology, evolution, and cosmology. The cause of Napoleon’s death is quite interesting as an exercise in forensic science. The original cause of death was suggested to be gastric cancer. But that is too mundane a cause of death for such an august figure. So the conspiracy advocates went to work and suggested he was poisoned by arsenic. How to test? Easy look for arsenic in samples of hair. Well, that was done and arsenic was found. Case closed? Not quite. Were there other sources of arsenic than deliberate poisoning? Yes, the wall paper in his room had arsenic in it. Also further investigation revealed that he had been exposed to arsenic long before he went to St. Helena.  In support of the caner hypothesis his father also died of stomach cancer.  The current consensus is that the original diagnosis was correct. He died of stomach cancer. But notice the play of events: hypothesis—arsenic poisoning, testing—look for arsenic in hair samples, refine hypothesis—check for other sources of arsenic, etc. We can see here the classic process of science being played out in reconstructing the past.

We can continue this technique into the more distant past: When did humans evolve? Why did the dinosaurs die out? How did the earth form? How did the solar system form? What if anything preceded the big bang? All of these questions can be tackled using the standard methods of science. Observations of present tell us about the past, counting tree ring tells us when the tree started to grow.

The interplay between what might be called natural history and natural laws is very intricate. We must interpret the past in order to extract the natural laws and use the natural laws to interpret the past. All our models of science have, explicitly or implicitly, both an historical and a law component. In testing a model for how the universe works—ie to develop the laws—we conduct an experiment. Once the experiment is finished, it becomes history and interpreting it is historical science.  For example, why did the OPERA experiment claim to see faster than light propagation for neutrinos? Or is the bump seen in searches for the Higgs boson real or an artifact of the detector? Those investigations are as much forensic science as trying to decide why Napoleon died or the dinosaurs went extinct.  Thus, all science is historical and sometimes, quite explicitly. Einstein abandoned the cosmological constant based on an alternate model for the history of the universe, namely that it is expanding rather than static.

So, we have science as a unified whole, encompassing the past, present, and future; the natural laws entangled with the natural history. But what about the dinosaurs I did not see out of the math-room windows? We can be quite sure they did not exist at that time and that Fred Flintstone did not have one as a pet (a saber-toothed pussy cat is another story). The study of evolution is much like that for plane crashes. You study the debris, in the case of evolution that “debris” includes fossils and the current distribution of species.  Consider the fossil Tiktaalik roseae, a tetrapod-like fish or a fish-like tetrapod, that was found a few years ago.  One can engage in futile semantic arguments about whether it is a fish, or a tetrapod, or a missing link, or whether it is the work of the devil. However, the significant point is that a striking prediction has been confirmed by a peer-reviewed observation. Using evolution, a model of fossil formation, and a model of the earth’s geology, a prediction was made that a certain type of fossil would be found in a certain type of rock. Tiktaalik roseae dramatically fulfilled that prediction and provides information on the fish-tetrapod transition.

The cause of plane crashes, Napoleon’s death, evolution, and the extinction of dinosaurs can all be explored by using the same empirically-constrained model-building techniques as the rest of science.  There is only one scientific method.

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