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	Friday, July 17, 2015

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Something goes bump in the data

The CMS and ATLAS experiments at the LHC see something mysterious, but it's too soon to pop the Champagne. Photo: Maximilien Brice, CERN

An unexpected bump in data gathered during the first run of the Large Hadron Collider is stirring the curiosity of scientists on the two general-purpose LHC experiments, ATLAS and CMS.

CMS first reported the bump in July 2014. But because it was small and insignificant, they dismissed it as a statistical fluke. Recently ATLAS confirmed that they also see a bump in roughly the same place, and this time it's bigger and stronger.

"Both ATLAS and CMS are developing new search techniques that are greatly improving our ability to search for new particles," says Ayana Arce, an assistant professor of physics at Duke University. "We can look for new physics in ways we couldn't before."

Unlike the pronounced peak that recently led to the discovery of pentaquarks, these two studies are in their nascent stages. And scientists aren't quite sure what they're seeing yet … or if they're seeing anything at all.

If this bump matures into a sharp peak during the second run of the LHC, it could indicate the existence of a new heavy particle with 2000 times the mass of a proton. The discovery of a new and unpredicted particle would revolutionize our understanding of the laws of nature. But first, scientists have to rule out false leads.

"It's like trying to pick up a radio station," says theoretical physicist Bogdan Dobrescu of Fermi National Accelerator Laboratory who co-authored a paper on the bump in CMS and ATLAS data. "As you tune the dial, you think you're beginning to hear voices through the static, but you can't understand what they're saying, so you keep tuning until you hear a clear voice."

—Katie Elyce Jones and Sarah Charley

In Brief

Rock the LHC finalist voting closes July 19

View the finalist videos.

The last day to vote for finalists in the Rock the LHC video contest is Sunday, July 19. The winner will receive a trip for two from anywhere in the continental United States to Chicago and a tour of Fermilab.

Learn more at the Rock the LHC website.

Photo of the Day

Mothra-to-be

This polyphemus moth, spotted outside Wilson Hall, is as big as the palm of your hand. Photo: Aaron Sauers, OPTT

In the News

Fermilab's new proposed experiment

From Naperville Community Television, July 10, 2015

They're called neutrinos, the most abundant particles produced by the universe. In fact, at any given time, trillions of them run through your body. But surprisingly, scientists don't know much about them.

To take a closer look at these tiny particles, they actually have to be sent far away. That's just what those at Fermilab in Batavia are working to do.

"We've selected a site at the Sanford Underground Research Facility in Lead, South Dakota, which is about 800 miles from Fermilab and we want to use that longer baseline to study additional properties of neutrinos," said Elaine McCluskey, Project Manager for the Long-Baseline Neutrino Facility.

Watch the 3-minute video

In the News

Pentaquarks: LHC has discovered an exotic particle

From Discovery News, July 14, 2015

Now that the Large Hadron Collider (LHC) is smashing protons together at record energies, physicists are hoping to discover new and exotic particles emerge from the collisions. But there are a few unsolved mysteries surrounding different configurations of known subatomic particles that still have to be wrapped up.

And today, CERN announced the discovery of the "pentaquark" — a collection of five quarks bound together to form an exotic state of matter, a particle that has been theorized for some time but other experiments have had a hard time nailing down a true detection.

Frontier Science Result: MINERvA

Neutrinos in nuclei: studying group effects of interactions

This plot shows the ratio for iron (top) and lead (bottom) for neutrino deep inelastic scattering cross sections versus the fractional momentum of the struck quarks (Bjorken-x) for MINERvA data (black points) and the prediction (red line).

Para una versión en español, haga clic aquí. Para a versão em português, clique aqui. Pour une version en français, cliquez ici.

Physics is a holistic science in which we consider not only the individual parts but also how these parts combine into groups. Nucleons, or protons and neutrons, combine in groups to form atomic nuclei. The differences between how free nucleons behave and how nucleons inside a nucleus (bound nucleons) behave are called nuclear effects.

In the past, scientists have measured nuclear effects using beams of high-energy electrons. These high-energy beams allow electrons to interact with the quarks contained inside nucleons and nuclei, an interaction called deep inelastic scattering, or DIS. Scientists can now also bombard nuclei with neutrinos, which can also induce deep inelastic scattering. Studying these interactions can help us understand the behavior of quarks.

Using a beam of neutrinos, MINERvA has performed the first neutrino DIS analysis in the energy range of 5 to 50 GeV. Neutrinos and electrons interact with quarks within the nucleus differently; we do not expect nuclear effects in neutrino DIS will be the same as electron DIS.

MINERvA observes DIS interactions by measuring the cross section, or probability, of a neutrino interacting with quarks inside bound nucleons as a function of a property called Bjorken-x. Bjorken-x is proportional to the momentum of the quark that was stuck inside the nucleon.

MINERvA took data on neutrino interactions with carbon, iron and lead nuclei. We compared these data to a theoretical model that assumes the nuclear effects for both neutrino and electron interactions are the same.

We found that the data did not agree with the assumption in the lowest Bjorken-x values (0.1 to 0.2 — see figures) for lead. Further, the cross section for lead at those values differs significantly from those for carbon or iron. We say that the nuclear effect is enhanced in that region for lead.

This enhancement was seen in a previous MINERvA inclusive analysis that considered all kinds of interactions together — without singling out deep inelastic scattering.

In contrast, the model in the largest Bjorken-x range (0.4 to 0.75) agrees very well with data. This is intriguing, since the cause of nuclear effects in this region is not well understood. Whatever underlying physics governs behavior in this region, it appears to be the same for neutrinos and electrons.

This information is very valuable in building new models of this mysterious effect. Understanding these effects are a priority for MINERvA and will be studied more extensively using data we are currently collecting, taken at higher energies and higher statistics. This data will be invaluable in resolving the theoretical puzzles at large and small Bjorken-x.

—Joel Mousseau, University of Florida

These results were presented by the author at a recent Joint Experimental-Theoretical Physics Seminar. Mousseau's presentation is available online.

Joel Mousseau of the University of Florida presented this result at a recent Joint Experimental-Theoretical Physics Seminar.

In the News

The cosmos and dark matter

From Hark!, July 8, 2015

Space. The Origins of the Universe. Black Holes. Dark Matter. It's seemingly impossible to tire of discussing the timeless question of how we got here. Sometimes we tackle this topic from a spiritual viewpoint, or we entertain a metaphysical talk. But more likely we turn to our friends in academia, specifically those who study cosmology.

Two of the leading scientists on cosmology and dark matter, in particular, are Drs. Michael Turner (who coined the term) and Don Lincoln, both affiliated with Fermilab. Turner has long been the head of Kavli Institute for Cosmological Physics at the University of Chicago. Lincoln is a guest professor of high energy physics at Notre Dame in addition to his regular post as a senior physicist at Fermilab and also work on the Large Hadron Collider at Cern, on which he's written another fantastic book.

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