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From symmetry

Waiting for supernova

Catching a nearby supernova would be a once-in-a-lifetime experience that could give scientists a glimpse into physics they could never recreate on Earth. Image: Sandbox Studio with Shawna X

Thousands of years ago, when a stargazer noticed a bright, new speck in the sky, one that wasn't there the night before, he likely would have been mystified. For early astronomers, stars were eternal, appearing faithfully on the dark firmament night after night since the beginning of time. What message might the gods be sending by throwing this newcomer into the familiar pattern?

"If stars developed on a faster time scale, then people might have been able to figure out sooner, 'Gee, they're not just points painted on the ceiling,'" says John Beacom, a physicist at The Ohio State University. "They didn't know how to decode it when a new star appeared, and they couldn't guess it was a star exploding."

Nowadays physicists not only are aware of these celestial explosions, they eagerly await the next one to happen nearby. An exploding star's intense conditions could provide us with a glimpse of physics that we could never recreate on Earth.

Supernovae are not rare. Every second, a few stars in the universe expire as supernovae. But it's a big universe, and in our own Milky Way, only two or three go off every hundred years, scientists estimate. The last observed supernova went off in the Large Magellanic Cloud, just outside the Milky Way at a distance of 163,000 light-years from Earth. That was seen in 1987. The last observed supernova in our own galaxy was Kepler's Star, spotted in 1604. It was 20,000 light-years away.

Supernovae come in two types. One type of supernova is born when two white dwarfs merge or when, in a binary star system consisting of a white dwarf and another type of star, the white dwarf accretes too much material from the other. The overwhelming mass of the merged star compresses it to the point that the resulting heat ignites a thermonuclear runaway.

Read more

Leah Hesla

Photo of the Day

Happy Independence Day

Julie Kurnat's latest chalk drawing reminds us to have a happy 4th of July! Image: Julie Kurnat, TD
In the News

CMS closes major chapter of Higgs measurements

From CMS, July 3, 2014

Since the discovery of a Higgs boson by the CMS and ATLAS Collaborations in 2012, physicists at the LHC have been making intense efforts to measure this new particle's properties. The Standard Model Higgs boson is the particle associated with an all-pervading field that is believed to impart mass to fundamental particles via the Brout-Englert-Higgs mechanism. Awaited for decades, the 2012 observation was a historical milestone for the LHC and led to the award of the 2013 Nobel Prize in Physics to Peter Higgs and Fran├žois Englert. An open question arising from the discovery is whether the new particle is the one of the Standard Model — or a different one, perhaps just one of many types of Higgs bosons waiting to be found. Since the particle's discovery, physicists at the LHC have been making intense efforts to answer this question.

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In the News

Could antigravity explain away dark matter and dark energy?

From Motherboard, July 1, 2014

There are a few big placeholders in our understanding of the universe: dark energy, dark matter, gravitational waves. These are the names of things that should exist with certain general properties in order for our most cherished notion(s) of the universe not to collapse, but their precise nature is as yet undetermined.

It all feels a bit precarious, as proving the nonexistence of any of these concepts might put other, more certain notions into question, like the constancy of the gravitational force throughout the universe. And while we have these big blanks blacking out vast regions of understanding, we have something like the opposite in antimatter: we can see it readily in labs and in nature, but we don't have the immense cosmic blank to fit it into. One should exist out there, but we don't see it. The universe seems to be composed almost entirely of regular matter.

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Frontier Science Result: DZero

If the top is lopsided, will the bottom be also?

A proton and antiproton collision may produce a top or bottom quark in the forward direction, as shown. The situation in which the directions of the produced quark and antiquark are swapped is known as production in the backwards direction.

Disponible en español

Some of the most attention-drawing results from the Tevatron have been the recent ones about a certain asymmetry in the production of top quark pairs. When a proton collides with an antiproton, they can produce a top quark and a top antiquark, and the direction of the top quark tends to be along the direction of the proton. This result, depicted above, should happen more often than the case where the top quark is produced moving in the direction of the initial antiproton. How much more often? The so-called forward case is predicted to happen somewhere between 5 and 13 percent more often than the backward case.

Initial measurements of this asymmetry in 2008 came out somewhat higher than this expectation. Later measurements, taken using more data, are closer to the prediction, but we want to be quite sure that we understand what is happening in this kind of collision. In particular, because a top quark is so massive, there is some possibility that it has new interactions with as-yet-unseen particles that might change this asymmetry. So an obvious thing to do is to look at the forward-backward asymmetry with another quark that is thought not to have new physics associated with its production.

That other quark would be the bottom quark, the first of the two quarks discovered here at Fermilab. The bottom quark is much less massive than the top quark and has been very extensively studied.

The DZero collaboration has measured the forward-backward asymmetry of the production of bottom quark-antiquark pairs. In order to make the measurement easier, we looked at a very specific case of what happens to these quarks after they are produced. We looked at the case in which the bottom quark paired with an up antiquark to make a particle called B- that then decayed into two specific particles: a J/Ψ and a K-. The reason to look for this particular decay pattern is that the J/Ψ itself is easy to see; it decays to a very distinctive pair of muons.

The result is that the forward-backward production asymmetry for the production of bottom quark-antiquark pairs is -0.27 ± 0.45 percent. That is essentially zero. The prediction is fairly close to zero too: The prediction was 1.12 ± 0.77 percent. The agreement between these numbers supports the original assertion that there might not be new physics in bottom quark production. And so it seems that the bottom isn't lopsided after all!

Leo Bellantoni

These DZero members all made significant contributions to this result.
Every member of DZero contributes to the success of the collaboration. Here are (many) of the members of the DZero collaboration, gathered for their last summer workshop here at Fermilab in June.

Today's New Announcements

Fermilab prairie plant survey - July 12, July 23, Aug. 9

Lecture Series - Technology for Advanced Neural Prostheses - July 11

On-site housing requests for fall 2014 and spring 2015 due July 14

Register for the C++ Fermilab software school - Aug. 4-8

New updates available for Mac computers

FermiWorks training for managers with direct reports

Construction work at Main Ring Road and AZero

Outdoor soccer

Scottish country dancing Tuesday evenings in Ramsey Auditorium

International folk dancing Thursday evenings in Ramsey Auditorium

Fermi Days at Six Flags Great America

Employee Appreciation Day at Hollywood Palms Cinema