New Tevatron collider result may help explain the matter-antimatter asymmetry in the universe

June 30, 2011 | 9:27 am

About a year ago, the DZero collaboration at Fermilab published  a tantalizing result in which the universe unexpectedly showed a preference for matter over antimatter. Now the collaboration has more data, and the evidence for this effect has grown stronger.

The result is extremely exciting: The question of why our universe should exist solely of matter is one of the burning scientific questions of our time. Theory predicts that matter and antimatter was made in equal quantities. If something hadn’t slightly favored matter over antimatter, our universe would consist of a bath of photons and little else. Matter wouldn’t exist.

The Standard Model predicts a value near zero for one of the parameters that is associated with the difference between the production of muons and antimuons in B meson decays. The DZero results from 2010 and 2011 differ from zero and are consistent with each other. The vertical bars of the measurements indicate their uncertainty.

The 2010 measurement looked at muons and antimuons emerging from the decays of neutral mesons containing bottom quarks, which is a source that scientists have long expected to be a fruitful place to study the behavior of matter and antimatter under high-energy conditions. DZero scientists found a 1 percent difference between the production of pairs of muons and pairs of antimuons in B meson decays at Fermilab’s Tevatron collider. Like all measurements, that measurement had an uncertainty associated with it. Specifically, there was about a 0.07 percent chance that the measurement could come from a random fluctuation of the data recorded. That’s a tiny probability, but since DZero makes thousands of measurements, scientists expect to see the occasional rare fluctuation that turns out to be nothing.

During the last year, the DZero collaboration has taken more data and refined its analysis techniques. In addition, other scientists have raised questions and requested additional cross-checks. One concern was whether the muons and antimuons are actually coming from the decay of B mesons, rather than some other source.

Now, after incorporating almost 50 percent more data and dozens of cross-checks, DZero scientists are even more confident in the strength of their result. The probability that the observed effect is from a random fluctuation has dropped quite a bit and now is only 0.005 percent. DZero scientists will present the details of their analysis in a seminar geared toward particle physicists later today.

Scientists are a cautious bunch and require a high level of certainty to claim a discovery. For a measurement of the level of certainty achieved in the summer of 2010, particle physicists claim that they have evidence for an unexpected phenomenon. A claim of discovery requires a higher level of certainty.

If the earlier measurement were a fluctuation, scientists would expect the uncertainty of the new result to grow, not get smaller. Instead, the improvement is exactly what scientists expect if the effect is real. But the uncertainty associated with the new result is still too high to claim a discovery. For a discovery, particle physicists require an uncertainty of less than 0.00005 percent.

The new result suggests that DZero is hot on the trail of a crucial clue in one of the defining questions of all time: Why are we here at all?

- Don Lincoln

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Fermilab experiment weighs in on neutrino mystery

June 24, 2011 | 4:55 pm

Step by step, physicists are moving closer to understanding the evolution of our universe.  Neutrinos — among the most abundant particles in the universe –  could have played a critical role in the unfolding of the universe right after the big bang. They are strong candidates for explaining why the big bang produced more matter than antimatter, leading to the universe as it exists today.

Scientists of the MINOS experiment at the Department of Energy’s Fermi National Accelerator Laboratory announced today the results from a search for a rare phenomenon, the transformation of muon neutrinos into electron neutrinos. If this type of neutrino transformation did not exist, neutrinos would not break the matter-antimatter symmetry, and a lot of scientists would be scratching their heads and wonder what else could have caused the dominance of matter of antimatter in our universe.

The MINOS result is consistent with and significantly constrains a measurement reported 10 days ago by the Japanese T2K experiment, which announced an indication of this type of transformation.

The observation of electron neutrino-like events allows MINOS scientists to extract information about a quantity called sin2 2θ13. If muon neutrinos don’t transform into electron neutrinos, sin2 2θ13 is zero. The new MINOS result constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. Credit: Fermilab

The Main Injector Neutrino Oscillation Search (MINOS) at Fermilab recorded a total of 62 electron neutrino-like events. If muon neutrinos do not transform into electron neutrinos, then MINOS should have seen only 49 events. The experiment should have seen 71 events if neutrinos transform as often as suggested by recent results from the Tokai-to-Kamioka (T2K) experiment in Japan. The two experiments use different methods and analysis techniques to look for this rare transformation.

To measure the transformation of muon neutrinos into other neutrinos, the MINOS experiment sends a muon neutrino beam 450 miles (735 kilometers) through the earth from the Main Injector accelerator at Fermilab to a 5,400-ton neutrino detector, located half a mile underground in the Soudan Underground Laboratory in northern Minnesota.  The experiment uses two almost identical detectors: the detector at Fermilab is used to check the purity of the muon neutrino beam, and the detector at Soudan looks for electron and muon neutrinos. The neutrinos’ trip from Fermilab to Soudan takes about one four hundredths of a second, giving the neutrinos enough time to change their identities.

For more than a decade, scientists have seen evidence that the three known types of neutrinos can morph into each other. Experiments have found that muon neutrinos disappear, with some of the best measurements provided by the MINOS experiment. Scientists think that a large fraction of these muon neutrinos transform into tau neutrinos, which so far have been very hard to detect, and they suspect that a tiny fraction transform into electron neutrinos.

The observation of electron neutrino-like events in the detector in Soudan allows MINOS scientists to extract information about a quantity called sin² 2 theta-13 (pronounced sine squared two theta one three). If muon neutrinos don’t transform into electron neutrinos, this quantity is zero. The range allowed by the latest MINOS measurement overlaps with but is narrower than the T2K range. MINOS constrains this quantity to a range between 0 and 0.12, improving on results it obtained with smaller data sets in 2009 and 2010. The T2K range for sin² 2 theta-13 is between 0.03 and 0.28.

“MINOS is expected to be more sensitive to the transformation with the amount of data that both experiments have,” said Fermilab physicist Robert Plunkett, co-spokesperson for the MINOS experiment. “It seems that nature has chosen a value for sin² 2 theta-13 that likely is in the lower part of the T2K allowed range. More work and more data are really needed to confirm both these measurements.”

The MINOS measurement is the latest step in a worldwide effort to learn more about neutrinos. MINOS will continue to collect data until February 2012. The T2K experiment was interrupted in March when the severe earth quake in Japan damaged the muon neutrino source for T2K. Scientists expect to resume operations of the experiment at the end of the year. Three nuclear-reactor based neutrino experiments, which use different techniques to measure sin² 2 theta-13, are in the process of starting up.

The MINOS far detector is located in a cavern half a mile underground in the Soudan Underground Laboratory in Minnesota. The collaboration records about 1,000 neutrinos per year. A tiny fraction of them seem to be electron neutrinos. Photo: Peter Ginter

“Science usually proceeds in small steps rather than sudden, big discoveries, and this certainly has been true for neutrino research,” said Jenny Thomas from University College London, co-spokesperson for the MINOS experiment. “If the transformation from muon neutrinos to electron neutrinos occurs at a large enough rate, future experiments  should find out whether nature has given us two light neutrinos and one heavy neutrino, or vice versa. This is really the next big thing in neutrino physics.”

A large value of sin² 2 theta-13 is welcome news for the worldwide neutrino physics community and a boon for the NOvA neutrino experiment, under construction at Fermilab. The experiment is designed to determine the neutrino mass hierarchy. It will find out whether there are one light and two heavy neutrinos, or whether there are two light neutrinos and a heavy one. Together with several nuclear physics experiments, such as EXO and Majorana, NOvA will help scientists determine what early-universe theories are the most viable ones.

To measure directly the matter-antimatter asymmetry hidden among the neutrino transformations, scientists have proposed the Long-Baseline Neutrino Experiment. It would send neutrinos on a 1,300-kilometer trip from Fermilab to a detector in South Dakota. This would give muon neutrinos more time to transform into other neutrinos than any other experiment. It would give scientists the best shot at observing whether neutrinos break the matter-antimatter symmetry and by how much. For more information about MINOS, NOvA and LBNE, visit the Fermilab neutrino website:
http://www.fnal.gov/pub/science/experiments/intensity/

The MINOS experiment involves more than 140 scientists, engineers, technical specialists and students from 30 institutions, including universities and national laboratories, in five countries: Brazil, Greece, Poland, the United Kingdom and the United States. Funding comes from: the Department of Energy Office of Science and the National Science Foundation in the U.S., the Science and Technology Facilities Council in the U.K; the University of Minnesota in the U.S.; the University of Athens in Greece; and Brazil’s Foundation for Research Support of the State of São Paulo (FAPESP) and National Council of Scientific and Technological Development (CNPq).

Kurt Riesselmann

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An Ear for Science: The Particle Physics Wind Chime

June 23, 2011 | 3:12 pm

Like particle physicists the world over, Stanford’s Matt Bellis is always looking for ways to share his research with the public. “I had the idea of the BaBar detector as an instrument,” Bellis said, but not one played by human hands. It would be played by the particles gusting through it, like wind through a wind chime. Read the full article that SLAC published on June 23 about Bellis and his particle physics wind chime:

Matt Bellis stands in front of a projected image from his Particle Physics Windchime, to which he has added visualization capabilities. (Photo by Brad Plummer.)

Stanford physicist Matt Bellis deals in the infinitesimal. As a member of the BaBar collaboration based at SLAC, he studies what happens when an electron and a positron collide at certain energies. Electrons and positrons have opposite electrical charges, but in all other respects – including mass – they are exactly the same, and they are very small.

As a result, Bellis inhabits a world of visualizations.  Animations, graphs, computer-drawn images, Bellis uses them all to try to picture the scene when a particle that weighs about 9×10^-31 kg – that’s a nine multiplied by a zero-point-thirty more zeros and a 1 – slams into another particle exactly the same size. Granted, in a realm where mass and energy intertwine the particles travel at speeds that give them a little more oomph, but that doesn’t change the fact that no one will ever actually see this – except through the magic of special effects.

Like particle physicists the world over, Bellis is forced to improvise ways to share his research with the public, using whatever  comes to hand. He’s animated bristling spheres of particle tracks in sophisticated vector graphics – complete with cool soundtracks. He’s illustrated fundamental relationships between different particle types with Google Docs. Bellis has developed a whole toolbox of methods to help him explain particle physics. Until recently, however, all the tools in his toolbox were visual.

A trained musician, Bellis came up with the idea of rendering the results of particle collisions as sounds. The process of rendering data into sound is known in general as “sonification.” Bellis wanted to sonify data from BaBar.

“I had the idea of the BaBar detector as an instrument,” Bellis said, but not one played by human hands. It would be played by the particles gusting through it, like wind through a wind chime.

“Think of it,” Bellis said.  “The wind itself makes no sound. You hear the wind if it rustles the leaves in a tree. The motion of the wind itself doesn’t necessarily make a sound. The wind has to interact with something to make noise.” In the same way, “When you have these particles that pass through the detector, they send it ringing, resonating in some way.”

Thus was born the idea of the Particle Physics Windchime: A computer application that could take particle physics data such as particle type, momentum, distance from a fixed point, and so on, and turn it into sound.

Last November, at the urging of ex-SLACer and event co-organizer David Harris, Bellis took his idea to Science Hack Day SF [http://sciencehackday.com/], where enthusiastic programmers, web designers, science fans and self-professed geeks gathered for the express purpose of spending 24 intense hours “hacking together” the basics of several science-related computer applications.

Bellis rounded up an interested group of Science Hack Day attendees, laid his idea before them, and turned them loose on simulated BaBar data. That weekend, they developed the kernel of the Particle Physics Windchime. According to Bellis, his cadre of coders – not all of whom had a background in science – got swept up in the physics of the colliding particles and how to portray them, sonically speaking. By the time the group presented Version 0.1 of the Particle Physics Windchime, they could define some simple relationships such as the energy of a particle to the volume of the sound representing it, or the angle of a particle track to the original electron-positron beam with the pitch of the sound representing the particle.

“We actually won the People’s Choice Award” at Science Hack Day, Bellis said, along with the award for Best Use of Data. But what Bellis said he found most interesting about the experience is how involved his team became in particle physics during the course of building the Windchime, and the interest shown by the audience during his team’s final presentation.

“I wanted to create the Particle Physics Windchime partly because I thought it was a cool idea, and partly because I wanted to see if there’s something new we can learn from the data,” Bellis said. “Is there something I can hear in the data that I can’t see or that a computer can’t pick up? Will it add to an intuitive understanding of the data?” While at Science Hack Day he learned that other particle physicists were thinking along much the same lines – members of the ATLAS group at the Large Hadron Collider had been sonifying LHC data, with the results available on the LHCsound website. All this served to bolster his belief that a sound-based teaching tool could help interest a lay audience in particle physics.

“Science should be something society is involved in,” he said. For example, the project he’s working on, BaBar, investigated a fundamental imbalance in the way the universe works – the triumph of matter over antimatter. The implications of this imbalance “are so profound that particle physics cannot be just for particle physicists,” Bellis said. “This cannot be just for a few thousand people to understand. We have to find ways to explain it to anybody who wants to know what we’re doing, no matter how obscure, no matter how difficult.”

This responsibility is not news to the BaBar collaboration. Now that data-taking is over and collaboration members are busy crunching numbers, an effort to preserve the data for future users is under way, Bellis said. “One of the arguments for preserving well-understood data sets is using them for education and outreach,” he explained. “Kindergarten through 12, college, training new people.” But he readily admits that explaining even well-understood particle physics data is hard. According to Bellis, he thinks particle physicists may be able to use the Windchime to learn about communicating with the public.

The path from idea to reality has not always been smooth. The demands of research leave Bellis little time to continue developing the Windchime, and to progress to the point of having a robust, easily-customized tool that anyone could play with will take time and resources Bellis currently doesn’t have. One option he’d like to try is continuing with the collaborative model of Science Hack Day, in a sense.  “I welcome people who are interested to pitch in,” Bellis said. Even if the particle physics doesn’t sink in, just working on the Windchime would be educational. “This is a killer app for all ages to learn programming.”

In the meantime, Bellis will continue to tinker with the Windchime as time allows. He said he’s also eager to introduce it to audiences of all types. And when Bellis says “all types,” he means it:  “If I get a gig at a coffeehouse somewhere where I play B-meson music out to a crowd, I will consider this all a success.”

- Lori Ann White

Related Links

• Download the Particle Physics Windchime
• SLAC Experimental Seminar, June 28 featuring Bellis discussing the Particle Physics Windchime
• Mustang Physics podcast featuring Bellis
• BBC interview (Fast forward to the 20:50 mark to listen to the Science Hack Day story.)
• LHCsound blog

Symmetry Intern

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Pledges of Support Keep Mideast SESAME Project on Track

June 22, 2011 | 9:54 am

SLAC first published this story on June 20, 2011.

The SESAME Microtron Particle Accelerator. Photo courtesy SESAME.

The latest report on SESAME, a synchrotron light source that will be the first big international science center in the Middle East, says it is progressing both technically and financially on the road to its scheduled opening in 2015. At the May 30–31 meeting of the SESAME Council, member nations pledged both money and in-kind donations to help bridge a $35 million budget gap that stands in the way of completing the project and putting it into operation.

The status update comes in a press release from UNESCO, the United Nations Educational, Scientific and Cultural Organization, under whose auspices the research center was established.

SESAME stands for Synchrotron-light for Experimental Science and Applications in the Middle East. Many people from many countries have come together to make the project a reality, but the one who started it all was Herman Winick, a physicist at SLAC National Accelerator Laboratory.

When he learned in 1997 that a lab in Berlin was planning to scrap a synchrotron called BESSY I, Winick proposed recycling it instead as the centerpiece of the first synchrotron light source—and the first major international science center—in the Middle East. Working with Gus Voss of Germany’s DESY laboratory, he began to plan an upgraded facility that would draw scientists from all over the region, including countries that are politically at odds, for training and research, serving as a beacon of cooperation and progress. The project is modeled after CERN, the European particle physics center, which brought European scientists together in the aftermath of World War II. Current members of the SESAME Council are Bahrain, Cyprus, Egypt, Iran, Israel, Jordan, Pakistan, the Palestinian Authority and Turkey. Sir Chris Llewellyn-Smith, former Director-General of CERN, is the council president.

The Mideast needs a synchrotron light source “because it is a center of scientific excellence,” said Mukhles Sowwan, a Palestinian physicist from Al-Quds University in East Jerusalem who specializes in nanotechnology; he has been doing research at SLAC as a visiting professor since September 2010. The SESAME facility will provide powerful beams of X-rays for advanced research in a wide variety of scientific fields, including biology, chemistry, and earth, environmental and energy science. SESAME “will do good science, and eventually this will lead to more interaction between scientists of different countries” and promote peace in the region, Sowwan said: “Imagine Israelis working with Iranians, and Palestinians with Israelis, Jordanians with Turks. It’s amazing.”

He added that the project’s location in Jordan, on land donated by the Jordanian government, should allow researchers from the nine member countries to travel relatively freely between SESAME and their home institutions. And the first-class research opportunities available there will allow students to train locally, helping to reverse the brain drain that has seen many of the region’s best scientists leave to pursue careers abroad. In a new brochure, Sowwan and other Middle Eastern scientists describe the impact that SESAME has already had and is expected to have when research begins there.

SESAME has come a long way since Winick’s initial proposal. With the help of supporters and scientists from a number of nations, as well as from UNESCO and the International Atomic Energy Agency, the BESSY I injector system is being upgraded and installed in the SESAME building, which was donated by Jordan. It will inject electrons into a new 2.5 GeV main storage ring with a circumference of 436 feet. Electrons racing around the ring at nearly the speed of light will give off intense X-ray light, which will flow into beamlines filled with equipment where the experiments will take place. Construction of the ring is expected to start soon.

Five of those beamlines have been donated by the United Kingdom, and a number of labs in the United States and Europe are also providing gear. Two of the three major US equipment donations came from SLAC: a permanent-magnet undulator from the lab’s PEP storage ring, which was decommissioned in the late 1980s, and a double crystal X-ray monochromator, which selects specific wavelengths of X-rays for particular experiments.  The third piece, a permanent-magnet wiggler, came from Lawrence Berkeley National Laboratory.

In addition, about $300,000 in funding from the US Department of Energy’s Office of Basic Energy Sciences has allowed about 25 researchers from the Middle East to come to SLAC and other US synchrotron labs for research and training, Winick said—a vital part of building the base of expertise needed to run the new facility.

Earlier this month, the US Liaison Committee for IUPAP, the International Union for Pure and Applied Physics, agreed to provide additional travel support for SESAME researchers, instructors and students. And the project recently received its first substantial support from a private foundation—a $100,000 training grant from the Richard Lounsbery Foundation. These are just the latest in a series of contributions for travel and training from many sources, including the Japanese Society for the Promotion of Science, foundations, companies, professional scientific societies such as the American Physical Society, and synchrotron radiationlaboratories around the world.

Related Links

• “SESAME,” symmetry magazine
• “Science and peace,” commentary by Herman Winick
• “Middle East accelerator project approaches barrier” symmetrybreaking
• The SESAME website, which includes a downloadable brochure

Glennda Chui

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Tribute to Rosalyn Sussman Yalow, Nobel medical physicist

June 21, 2011 | 1:05 pm

Dr. Rosalyn Yalow. Image courtesy of Nobelprize.org.

Dr. Rosalyn Sussman Yalow, who passed away last month on May 30, was a mother, wife, educator, and dedicated medical physicist.  She received the Nobel Prize  in Medicine in 1977 while working for the Veterans Administration Hospital in New York for her contributions to the development of radioimmunoassays of peptide hormones. Today scientists utilize this technology to further diagnostics in the medical field for cancer research and Type II diabetes.  If this technique had not been developed by Dr. Yalow and Dr. Solomon Berson, her longtime collaborator, it would have taken longer for the other scientists that followed in their footsteps to achieve their own accomplishments.  The Scientific Community recognized Dr. Yalow with many awards:  the Albert Lasker Basic Medical Research Award; A. Cressy Morrison Award in Natural Sciences of the N.Y. Academy of Sciences; Scientific Achievement Award of the American Medical Association; Koch Award of the Endocrine Society; Gairdner Foundation International Award; American College of Physicians Award for distinguished contributions in science as related to medicine; Eli Lilly Award of the American Diabetes Association; First William S. Middleton Medical Research Award of the VA and five honorary doctorates. Dr. Yalow was only the second woman to earn a Nobel Prize in Medicine. She served as an inspiration for women scientists in the field today, and I would like to personally say, “Thank you.”

Editor’s note: For more information about Dr. Yalow, read her autobiography and the obituary in the New York Times.

- Linda Sue Purcell-Taylor, Fermi National Accelerator Laboratory

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Japanese neutrino observation a boon for U.S. physics

June 17, 2011 | 2:54 pm

Quantum Diaries first published this story on June 17.

Neutrinos could tell us why matter formed in the early universe.

The Japan-based experiment T2K Tuesday gave scores of U.S. particle hunters a license to ready their detectors and take aim at the biggest question in the universe: How everything we see came to exist.

“It’s our hunting license,” said Fermilab physicist and University of Rochester professor Kevin McFarland, who works on T2K and neutrino experiments at Fermilab.

The observation by T2K affects what the Fermilab neutrino experiments NOvA and the proposed Long Baseline Neutrino Experiment, LBNE, can expect to discover and how quickly. It also makes the experiment McFarland serves as co-spokesman on, MINERvA, more important than ever in the international neutrino-research field.

Physicists working with T2K recorded six muon neutrinos changing into electron neutrinos across a long distance, a transformation called theta 13 in physics circles. Physicists had predicted that they should observe only 1.5 of these transformations as background events rather than the six they did observe, so the probability of the existence of an electron neutrino appearance is estimated to be 99.3 percent. While the T2K observation doesn’t rise to the level of “discovery” in the science community, it is far enough beyond the expected statistical error bar to make people shout for joy and start revising plans for their own particle hunts.

“Because neutrino science is so hard, scientist don’t get a lot of exciting days,” McFarland said the day of the T2K announcement. “But this is a very exciting day.”

Something, possibly neutrinos, tipped the scales to have more matter than antimatter in the universe allowing for life. Credit: symmetry magazine

The T2K observation also was statistically large enough that it quells a long-standing fear that this transformation would be statistically too small, much less than one percent, to observe. At that level, modern technology wouldn’t be able to use the observation as a stepping stone to move to the next research phase in figure out how matter came to dominate antimatter in the universe.

The quarry:

Physics predicts that the three types of neutrino particles can change back and forth into one another across long distances. Previous solar and reactor neutrino experiments had observed two types doing just that, but the third switch – muon neutrino into electron neutrino – had remained elusive.

T2K’s recording of this transformation, the first of its kind, means that physicists will have the tools to track down the next two potential discoveries on the path to the ultimate trophy.

After the Big Bang, equal amounts of matter and antimatter should have annihilated each other leaving nothing but free-floating energy. But we’re here and antimatter isn’t, so that didn’t happen. Something tipped the scales in matter’s favor, allowing particles to join together and form planets, plants and people. Physicists think neutrinos could be that tipping-point particle.

Following the tracks:

Physicists think the origins of neutrino masses are closely tied to subatomic processes that took place right after the big bang. Determining which neutrino types are heaviest and lightest—the neutrino mass ordering—is a first step toward revealing these processes. Credit: symmetry magazine

The first step in finding out if they are right is T2K’s observation. Plugging this observation into the research equation, physicists on NOvA, an experiment under construction in Minnesota, will be able to tease out the details of what is called the neutrino mass hierarchy. The pattern of this hierarchy essentially will tell physicist if neutrinos behave like other particles, in a pattern of light, heavy and very heavy, or neutrinos behave oddly in a pattern of light, heavy and heavy.

This pattern of masses is important to know because it provides a clue to help physicists understand what causes neutrinos to have masses that are so much lighter than other particles and why neutrinos aren’t massless as predicted by the Standard Model, the playbook for how the world works at the subatomic level.

NOvA is ideally situated to do this because its particle beam will travel three times farther than T2K’s, allowing researchers see how the material in the Earth alters the change from muon to electron neutrinos. T2K’s observation of half a dozen muon neutrino to electron neutrino changes points to the relatively high rate of the change, so NOvA should have a lot of data to work with to speed up the discovery of the mass hierarchy.

Step three is combining what NOvA learns about the mass hierarchy with more precise data from the LBNE experiment to look for differences in the neutrino and antineutrino probabilities of changing from muon to electron neutrino types. After accounting for the effect of the earth and the mass hierarchy, any remaining difference would point to a fundamental difference between matter and antimatter neutrinos. Differences between matter and anti-matter are nearly non-existent in nature and these differences are precious clues about why matter dominated antimatter to survive in today’s universe.

LBNE, proposed for South Dakota, sits even farther away from the Fermilab neutrino source, making it well-suited to make this comparison of antineutrinos, which are rarer and harder to detect than neutrinos. T2K’s observation of a large change signal means LBNE will have better statistics to create precise comparisons.

The level of precision could mean the difference between getting an answer or not, depending on how subtle the difference is between neutrinos and antineutrinos.

Bringing out the scope:

Short-baseline experiments can’t compete in the hunt for why matter dominated antimatter, which requires tracking neutrinos across great distances, but they can provide the precision measurements that work like a rifle scope for the particle hunters.

The three types of neutrinos mix across long distances enabling physicists to see them to change type if the distance is long enough. Credit: symmetry magazine

MINERvA at Fermilab and the neutrino reactor experiments Daya Bay in China and Double Chooz in France will provide the data to allow NOvA and LBNE to zoom in on the minute details of mass hierarchy and how neutrinos change types.

The reactor-based experiments with detectors near to neutrino spewing reactors were designed to be experts at finding the neutrino change T2K found. Ideally, they will find a cleaner neutrino transformation signal, without the data complications, such as the effects of Earth material on the transformation that come with T2K and NOvA being multi-purpose experiments. Cleaner reactor experiment measurements provide a baseline for the measurements of NOvA and LBNE.

MINERvA will provide data to help NOvA and LBNE map the type and amount of background events that can obscure their search. This will enable physicists to put the trophy deer-like potential discovery in their analysis cross-hairs and discount the imposter trees and hunters dressed in brown that cloud the view of their data. While MINERvA was built for this job and currently aids neutrino experiments across the globe, including T2K, with this variable-removing research information, T2K’s observation makes MINERvA’s unique skill more important. The large T2K signal means a lot of data and the ability to do precision analysis if MINERvA can tell researchers what variables to discount.

“There is always an exchange of data, and one experiment builds on another,” McFarland says.

Previously data from the MINOS experiment at Fermilab told T2K how to tune the energy of its particle beam. Now T2K is returning the favor with an observation that will help Fermilab experiments.

“Experiments building on one another,” he says, “that is what makes it exciting.”

Related information:

http://www.symmetrymagazine.org/breaking/2011/06/15/japans-t2k-experiment-observes-electron-neutrino-appearance/

Tona Kunz

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LHC experiments reach record data milestone

June 17, 2011 | 9:09 am

The ATLAS and CMS experiments have both accumulated 1 inverse femtobarn of data, an important milestone for both experiments. Image courtesy of CERN.

As of this week, the Large Hadron Collider has delivered 1 inverse femtobarn of integrated luminosity to ATLAS and CMS, two of the four experimental stations housed along the ring. This means the detectors will have gathered data from about 70 trillion proton-proton collisions. For comparison, the experiments collected just 45 inverse picobarns in all of 2010; 1 inverse femtobarn is equal to one thousand inverse picobarns.

Accelerator scientists promised 1 inverse femtobarn for the entire 2011 run, but met their goal just a few months after collisions began in March. The groups could see several more inverse femtobarns by the end of the year.

Scientists wasted no time analyzing the first few hundred inverse picobarns and announced their findings at the Physics at LHC conference last week. With five times more data than they had in 2010, researchers have been able to set more stringent limits on new physics. They haven’t observed anything new just yet but are beginning to explore uncharted territory.

“We spent 2010 rediscovering the Standard Model,” said Richard Hawkings, the deputy physics coordinator for the ATLAS experiment. “In 2011, we will push our detectors to the limit and make more precise measurements.”

Experimentalists have increased the sensitivity of the detectors to Standard Model processes, the events that account for much of the background signal in the hunt for new physics. Making the most precise measurements of these events could lead to an indirect hint of something new.

The LHC has delivered an integrated luminosity of one inverse femtobarn, nearly all of which has been recorded by the experiments. Image courtesy CERN

For example, the number of single top quarks scientists have spotted agrees well with what is predicted by the Standard Model, but with the new data they can begin to study the behavior between the top quark and the other, lighter quarks.

Despite finding no direct evidence of new physics, Hawkings says they have made significant inroads toward a discovery. “We’re closing in on supersymmetry,” he said. The data suggest that some of the theorized superparticles must have masses greater than 1 TeV, which narrows the window for observation. “We’ve looked through a lot of the space where supersymmetry could have been found, but there are still more corners to explore,” Hawkings said.

With only a few hundred inverse picobarns parsed at the time of the conference, LHC researchers weren’t able to match the Tevatron’s limits on the Higgs boson, though they have made some headway studying potential Higgs events that decay into two photons. Now that the experiments have received an integrated luminosity of 1 inverse femtobarn, researchers will have plenty more data to analyze before the European Physical Society and Lepton-Photon conferences this summer.

“The field is wide open for surprises, hints, speculations and false alarms,” Hawkings said. “We really need to see a hint of something new so we know what we can exclude and what we need to pursue further. But I really hope we get to see the first hint of the Higgs boson this year.”

Lauren Rugani

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TAUWER aims for cosmic heights

June 16, 2011 | 2:25 pm

The origin of ultra-high-energy cosmic rays is a question that makes it onto many top-unsolved-problems-in-physics lists.

The TAUWER experiment looks at particle showers that originate from tau neutrinos that take short paths through the earth (inset). An ideal site to observe these events is a mountain bowl. Image courtesy of Maurizio Iori.

The math says that these particles, which carry in excess of 10¹⁹ electron volts, or eV,  from somewhere in outer space, are far too energetic not to have interacted themselves out of existence before reaching the earth. And yet every year scientists see evidence in the earth’s atmosphere of a handful of these particles, which have several million times the energy of the protons being collided at the Large Hadron Collider.

Scientists are proposing a new experiment, called TAUWER, that would look to tau neutrinos to remove some of the mystery from these strange, over-stimulated cosmic rays.

“The question is, how do they get this energy?” says James Russ, TAUWER collaborator and professor of physics at Carnegie Mellon University. “We don’t know what the mechanism is.”

One idea for the mechanism is a rapid rebounding between plasma shock waves. In places such as those near black holes, where charged matter builds to extreme densities, protons may be ricocheting back and forth between shock wave fronts, accelerating and gathering energy over billions of years. Then one day the proton may escape and come to earth in the form of an ultra-high-energy cosmic ray or UHECR.

If these UHECRs are indeed protons escaped from star systems, they’ll reveal their existence, through a series of interactions, by producing ultra-high-energy neutrinos, neutrinos with energies greater than 10¹⁶ eV—over a billion times more energetic than those produced by supernovas.

TAUWER detectors would examine the particle showers brought on by these neutrinos’ interaction with the earth. The resulting energy measurements of the tau neutrinos could give scientists information about their conjectured parents, the UHECR protons.

“The neutrinos’ energy spectrum tells you about the nature of the protons’ acceleration,” Russ said. “That’s why it’s an interesting measurement to make.”

Collaborators are interested in particular in tau neutrinos – one of three known types – because of the high chance they’ll end up propagating particle showers that their detectors can see.

Rough layout scheme of TAUWER detectors on a mountainside. The straight blue line represents a tau lepton emerging from the earth. The white lines represent shower tracks from the tau lepton decay. Image courtesy of Maurizio Iori.

TAUWER isn’t the only program that’s using neutrinos to get to cosmic rays. The IceCube experiment at the South Pole looks for lower-energy neutrinos as they barrel through the length of the earth’s diameter with energies of up to 10¹⁶ eV. IceCube experimenters are currently busy with creative new schemes to extend their energy reach.

TAUWER picks up where the present IceCube design leaves off. Neutrinos with higher energies may not be able to make it from one end of the planet to the other since they’ll very likely be derailed by the rock in the earth. But if the trip through the earth is short enough, they can still make their way out.

TAUWER detectors would turn their attention particles that fly through short slices of the planet, about 1/13 the diameter of the earth. The neutrinos could, for example, enter San Francisco Bay and, a thousand kilometers later, exit Salt Lake. During these split-second trips through the earth, the ultra-high-energy neutrinos’ interaction with the rock would be close enough to the earth’s surface that its offspring, a tau lepton (a heavy cousin of the electron) could still push its way from beneath the ground into the air. TAUWER detectors, pointed at some angle toward the earth, will see the 1-kilometer-radius particle shower that springs from the tau lepton’s connection with the atmosphere.

The detectors, which have a very high pointing accuracy, can then pick out the direction of the UHECR that started it all. And with enough tau neutrino data, the UHECR phenomenon could very well lose its place on the top-unsolved-problems list – a good thing.

The Pierre Auger experiment in Argentina has also been on a quest to catch glimpses of UHECRs by way of tau neutrinos, but using very different methods. Auger detectors look for UHECRs that come uninterrupted from the sky. TAUWER detectors, on the other hand, would watch the ground to find tau neutrinos that come from below. Russ imagines TAUWER detectors searching for neutrino events from the height of a mountainside. The collaboration is scouting mountain bowls, sites where mountain ridges surround level stretches of land, in Europe, Mexico, and the US.

“A mountain bowl has the lovely feature that it screens horizontal cosmic rays, which are one background source,” Russ said. “You’re sitting on a mountain range that’s looking down on a nice flat space for neutrinos to come up through.”

The collaboration is currently testing a handful of detectors. Once the experiment is running full speed ahead, they’ll run 2,500 small detectors, each about as tall and wide as a CD case. Grouped in fours and spaced about 70 meters apart, the detectors will help map the energy spectrum of tau neutrinos that plow through the earth.

TAUWER collaborators are currently based at Carnegie Mellon University, Sapienza University of Rome and two Turkish institutions in the Bolu and Kars provinces. The TAUWER name is a nod both to the tau neutrino and to the aluminum frames – towers – that support the experiment’s instruments.

“By next summer, we should be ready to find more interested people who want to take on the ice and snow of a mountain environment to help make things work,” Russ said.

Leah Hesla

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String theory may hold answers about quark-gluon plasma

June 15, 2011 | 2:36 pm

String theorists describe the physics of black holes in five-dimensional spacetime. They found that these five-dimensional objects provide a good approximation of the quark-gluon plasma in one fewer dimension, a relationship similar to the one between a three-dimensional object and its two-dimensional shadow. Image: SLAC National Accelerator Laboratory

Recreating the conditions present just after the Big Bang has given experimentalists a glimpse into how the universe formed. Now, scientists have begun to see striking similarities between the properties of the early universe and a theory that aims to unite gravity with quantum mechanics, a long-standing goal for physicists.

“Combining calculations from experiments and theories could help us capture some universal characteristic of nature,” said MIT theoretical physicist Krishna Rajagopal, who discussed these possibilities at the recent Quark Matter conference in Annecy, France.

One millionth of a second after the Big Bang, the universe was a hot, dense sea of freely roaming particles called quarks and gluons. As the universe rapidly cooled, the particles joined together to form protons and neutrons, and the unique state of matter known as quark-gluon plasma disappeared.

In recent years, scientists have reproduced the quark-gluon plasma by smashing together heavy ions – first with gold nuclei at the Relativistic Heavy Ion Collider, and then with heavier lead ions at the Large Hadron Collider in 2010. The energy from the collisions at the LHC is nearly 14 times higher than those at RHIC, and produces temperatures more than 100,000 times hotter than the center of the sun, enough to melt the protons and neutrons from the ions down to their quark and gluon components.

The quark-gluon plasma created inside the experiments disappears almost instantaneously – billions of times faster than it did in the early universe – as the quarks and gluons reassemble into composite particles. These particles then fly into the surrounding detectors. Researchers study them to glean information about the quark-gluon plasma.

For example, in 2005 RHIC scientists discovered that the quark-gluon plasma didn’t behave like a gas of particles traveling randomly, but rather as a nearly perfect liquid. All the particles moved with a strong sense of coordination, much like a school of fish seems to move as a single object even though individual fish may be darting around in different directions.

Although researchers have since learned a great deal about the plasma, the collective movement among the quarks and gluons continues to be a stumbling block for explaining the behavior of the exotic fluid. The tools that normally describe particles and interactions on a subatomic scale don’t work, and physicists have set out to find a better measuring stick.

“We have to figure out how to get from understanding single particles to understanding the medium as a whole,” said CERN theoretical physicist Urs Wiedemann. Surprisingly, the answer may come from string theory.

Strung together

String theory is a hypothetical description of nature that accommodates both gravity and the quantum physics that describe the other three fundamental forces: electromagnetism and the strong and weak nuclear forces. Traditionally, gravity and quantum physics don’t play well together, but string theory uses extra dimensions of space to reconcile the two.

Theorists found that the mathematics of certain quantum theories and that of objects described by gravity in one extra dimension, such as black holes, look remarkably similar. Physicists are taking advantage of this duality by translating problems from the quark-gluon plasma into the language of gravity, where the equations become much simpler. Although the translation can’t provide precise calculations, solving a problem in one realm can give valuable insights into the other.

“On the theory side, black hole physics looks the same as quark-gluon plasma physics,” said physicist David Mateos, an ICREA research professor at the University of Barcelona in Spain, who also presented his work at the conference. “The fact that the same theory can be used to describe physics with gravity and physics without gravity is truly fascinating.”

String theory provides good approximations for certain properties of the quark-gluon plasma, such as its extremely low viscosity – the fact that it can flow without experiencing much resistance – or how certain particles are affected as they travel through the dense liquid.

“String theory is like a gift to us,” Rajagopal said. “We’re challenged with understanding the quark-gluon plasma as a liquid, and while string theory doesn’t give us precision, it can help us get a feel for the shape of the subject.”

Ultimately, physicists hope to understand how quarks and gluons bind together inside the fluid to form new particles, and what causes them to stay confined. Gravity-based explanations from string theory can also be used to describe phenomena that exhibit strong interactions similar to the quark-gluon plasma, such as superconductivity or supercold atomic gases.

In turn, experimental validations of these approximations could show how string theory best represents nature and point theorists toward avenues to explore further, Weidemann said. “But for now, string theory is just a useful tool for solving a current theory of reality.”

Lauren Rugani

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Japan’s T2K experiment observes candidates for electron neutrino appearance

June 15, 2011 | 10:04 am

The T2K experiment has detected six candidate events for oscillations of muon neutrinos into electron neutrinos. In this graphic, each colored dot shows the light detected when an electron neutrino hit a water molecule inside the Super-Kamiokande detector and created an electron that led to the emission of Cerenkov light.that allows scientists to better understand a phenomenon known as neutrino oscillations. For a long time scientists have suspected that the three known types of neutrinos can morph into each other. Several experiments previously found neutrinos to disappear.

The T2K experiment in Japan has observed six particle events that indicate the oscillation of muon neutrinos into electron neutrinos, a long-sought signal that allows scientists to better understand a phenomenon known as neutrino oscillations. For a long time scientists have suspected that the three known types of neutrinos can morph into each other. Several experiments previously found neutrinos to disappear.

The T2K experiment is the first experiment to report candidate events for the appearance of electron neutrinos in a muon neutrino beam. The experiment analyses a muon neutrino beam that travels 295 kilometers through the earth from the Japan Proton Accelerator Research Complex (J-PARC) to the 50,000-ton Super-Kamiokande neutrino detector.

Based on the analysis of the data collected by the T2K experiment between January 2010 and March 11, 2011, when the experiment was interrupted due to the magnitude 9 earthquake in eastern Japan, scientists found 88 neutrino events that were detected by the Super-Kamiokande detector. Among these 88 events, they identified six candidate events as electron neutrino interactions.

“Congratulations to our Japanese colleagues for their excellent work,” said Fermilab’s Rob Plunkett, co-spokesperson for the MINOS neutrino experiment. “This is a major accomplishment of the T2K program.”

The T2K result indicates that the last unknown neutrino mixing angle, called theta-13, is non-zero, with a significance of 2.5 sigma. If theta-13 were zero, the T2K experiment should only have found one or two electron neutrino events.

The T2K experiment sends a beam of muon neutrinos from the J-PARC facility 295 kilometers through the earth to the Super-Kamiokande neutrino detector. A near detector measures the purity of the muon neutrino beam, and the Super-K detector looks for the appearance of electron neutrinos due to neutrino oscillations.

The result is good news for the Fermilab neutrino program.

“This is a great result for NOvA,” said Mark Messier, of Indiana University and co-spokesperson of the NOvA neutrino experiment under construction at Fermilab. “It means that NOvA will be able to solve the question of the neutrino mass ordering, a question that no other neutrino experiment in operation or under construction can address. NOvA will let us know whether there are one light and two heavy neutrinos, or whether there are two light neutrinos and a heavy one.”

In addition, a non-zero value of theta-13 opens up the possibility that neutrinos violate the matter-antimatter symmetry and could be the reason that matter dominates over antimatter in our universe, a phenomenon that has puzzled scientists for a long time. The proposed Long-Baseline Neutrino Experiment is designed to look for this effect.

“This is a great time for neutrino physics,” Messier said.

Read the T2K press release

Kurt Riesselmann

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