Showing posts with label fermilab. Show all posts
Showing posts with label fermilab. Show all posts

Tuesday, November 9, 2010

Talking weak sauce at the NASW luncheon.

It was almost like kindergarden. One by one, decked out with our nametags and matching knapsacks, each of us chose a boxed lunch and filed into the classroom. There we sat, in a circle, waiting for the woman whose job it was that day to teach us something new. But when Dr. Bonnie Fleming of Yale University arrived, it wasn't a group of five year olds that she stood before; instead, it was a small group of science journalists from around the country, all gathered there to eat, relax, and listen to the latest news in neutrino physics.

"Neutrino physics is a field with many great stories," Fleming began. She then went on to explain that one of the most well-known of these stories is that of flavor oscillation. As it turns out, neutrinos have a sort of quantum mechanical ADD. Rather than sticking with one identity, neutrinos tend to change states spontaneously over the course of their travels. An electron neutrino may suddenly become a tau neutrino, and then a muon neutrino, and then a tau neutrino once more long before you or I have had the chance to ask, "what the- ?"

Regardless of flavor, however, all neutrinos have been said to interact via the same fundamental force: the weak force. As we sat dutifully munching on our sandwiches, Dr. Fleming invited each of us to lay one of our palms on the table and count to three. During that short time, she explained, over a trillion neutrinos had passed through every one of our outstretched hands. Indeed, a neutrino could pass straight through 200 Earths before having any appreciative chance of hitting anything. Physicists call it the "weak" force for a reason.

However, new research at Fermilab has suggested that there may be a fourth, even lazier type of neutrino - one that, unlike its electron, muon and tau counterparts, interacts via the gravitational force rather than the weak force. Perhaps surprisingly, gravity is actually the weakest of the four fundamental forces. If you're not convinced, just rub a balloon against your hair, stick it to the wall, and rest easily in the knowledge that you have just overcome the gravitational influence of the entire planet. Gravity's unbelievable frailty would make directly detecting the alleged new flavor of neutrino, dubbed the sterile neutrino, one of the most daunting tasks yet undertaken by the particle physics community. As it is, neutrinos are notoriously difficult to pin down. "We can only detect their flavor by whatever charged lepton they turn into," said Fleming.

As if neutrinos weren't hard enough to wrap your head around. Rather than exhaust myself by asking any more questions, I just sat there, ate my cookie, and let Dr. Fleming do rest of the talking.

Monday, August 16, 2010

Particle physics theory plays God, creates the universe.

For eons, human beings have wondered how we came to be. Physics provides a simple answer: in the early universe, there was more matter than antimatter. You see, when equal parts matter and antimatter meet, they annihilate each other. The slight overabundance of the former 13.7 billion years ago explains why there is a universe at all, and why all the "stuff" we see in it is made out of matter instead of antimatter. Although this is a fairly agreed-upon theory, it begs yet another question: why was there an excess of matter? For years, scientists have cited a phenomenon called CP violation that predicts such an excess; however, CP violation does not predict enough of an excess to match present-day observations. Now, a group at Fermilab's Tevatron claims that they have found yet another instance of CP violation that could help to fill the observational gap.

Fermilab, home of the Tevatron. Image courtesy of Renzo Borgatti.

CP violation postulates that certain particles can transform into both their associated antiparticles and particles that exhibit a mirror-image symmetry, or an opposite "handedness". The former type of inversion is called charge conjugation violation, while the latter is called parity violation. CP violation is one of the Sakharov conditions, three rules that detail what must have occurred during the first short moments following the Big Bang in order for the universe to appear as it does today. The new instance of CP violation was found during an experiment involving a type of neutral B meson. These B mesons each consist of two quarks: an anti-bottom quark and a strange quark. During the experiment, B mesons transformed into anti-B mesons, which consist of a bottom quark and either an anti-strange quark or an anti-down quark. Each of these different "flavors" of quark is unstable in isolation, and decays into a different kind of particle.

The Tevatron experiment yielded an excess of positively charged muons, which only result from the decay of anti-bottom quarks. Since anti-bottom quarks are only found in B mesons and not anti-B mesons, this particular instance of CP violation seems to indicate an excess of matter over antimatter: the exact result the team was seeking. The results of this experiment will soon be retested at multiple detectors around the world, including CDF at Fermilab and the ATLAS and LHC-b detectors at CERN. Until then, the jury is out on whether CP violation can account for the very small matter of our human existence.

Wednesday, July 14, 2010

Rogue physicist stokes the Higgs rumor mill.

For the past week, the physics community has been buzzing about a recent blog post written by Tommaso Dorigo, a member of Fermilab's CDF team. In it, he claimed to have heard "from two different, possibly independent sources" that the infamous Higgs boson may have been detected at the Tevatron within the three-sigma statistical level of confidence (99.73%). The Tevatron is the second most powerful particle accelerator in the world (behind the LHC at CERN) and is located at Fermilab in Illinois. This discovery would be huge news, as the Higgs is one of the most elusive and sought-after entities in modern particle physics.

The Standard Model hangs on discovery of the mysterious Higgs boson.
Image courtesy of Fermilab.

Particle accelerators such as the Tevatron and the LHC were built to probe the Standard Model of particle physics. The Standard Model (see above) describes three of the four forces of nature: Electromagnetism, and the Strong and Weak forces. Gravity is left out, as is the mechanism by which objects in the universe acquire mass. This latter mystery is where the Higgs boson comes in. Although physicists know how most particles interact in order to give rise to such properties as radioactivity and light emission, no one knows where the property of mass comes from. In 1960, Peter Higgs came up with the idea of a field that permeates all of space, much like the electromagnetic field; but instead of gathering electromagnetic energy from photons in this field, particles traveling through the Higgs field would be granted mass by Higgs bosons.

At the moment, Fermilab is denying that any such discovery has been made. On July 12, scientists posted the following via the FermilabToday Twitter account: "Let's settle this: the rumors spread by one fame-seeking blogger are just rumors. That's it." Ouch. Keep in mind, however, that this is the same group who announced they had a 50% chance of detecting the Higgs particle this year. We'll just have to wait and see.