Higgs territory continues to shrink

March 13, 2009 | 9:16 am

The CDF and DZero experiments at the Fermi National Accelerator Laboratory have excluded a significant fraction of the allowed Higgs mass range established by earlier measurements. But they have not yet caught a glimpse of the elusive particle.

Scientists knew from previous measurements that the Higgs boson must weigh between 114 and 185 GeV/c²-the units that scientists use to measure the mass of particles. The new Fermilab result carves out a section in the middle of this range: the Higgs boson cannot have a mass in between 160 and 170 GeV/c²-if it exists at all.

Scientists from the CDF and DZero collaborations at DOE

The Higgs particle is the last missing piece in the theoretical framework known as the Standard Model of particles and their interactions. According to the Standard Model, the Higgs boson explains why some elementary particles have mass and others do not. Thousands of measurements at particle experiments around the world have led to the Standard Model over the last forty years, and precision measurements have confirmed it again and again. However, the Higgs particle-a keystone-keeps eluding detection.

The first observation of the Higgs particle is also one of the many scientific goals of the Large Hadron Collider experiments at CERN, which plans to record its first collisions before the end of this year.  The LHC will make particles collide more often and with greater energy than the Tevatron collider at Fermilab, but physicists familiar with the LHC expect that the first scientific results will not be available until the end of 2010.

In the mean time, the Tevatron might produce the first evidence for the Higgs.

“Fermilab’s Tevatron collider typically produces about ten million collisions per second,” said DZero co-spokesperson Darien Wood, of Northeastern University. “The Standard Model predicts how many times a year we should expect to see the Higgs boson in our detector, and how often we should see particle signals that can mimic a Higgs. By refining our analysis techniques and by collecting more and more data, the true Higgs signal, if it exists, will sooner or later emerge.”

The Tevatron collider at Fermilab, four miles in circumference, accelerates protons and antiprotons close to the speed of light and makes them collide.

To increase their chances of finding the Higgs boson, the CDF and DZero scientists combine the results from their separate analyses, effectively doubling the data available.

“A particle collision at the Tevatron collider can produce a Higgs boson in many different ways, and the Higgs particle can then decay into various particles,” said CDF co-spokesperson Rob Roser, of Fermilab. “Each experiment examines more and more possibilities. Combining all of them, we hope to see a first hint of the Higgs particle.”

In the last two years the Tevatron has performed exceptionally well, and the 25-year-old machine continues to set numerous performance records, increasing the number of proton-antiproton collisions it produces. By the end of 2010, the Tevatron experiments will have recorded three times the number of collisions that scientists have used for the current analysis.

“We’re looking forward to further Tevatron constraints on the Higgs mass,” says Dennis Kovar, associate director of the Office of Science for High Energy Physics at the U.S. Department of Energy, which owns and funds Fermilab.

Watch a 2-minute video of Barbara Alvarez giving a tour of the CDF experiment and its search for the Higgs particle.

Watch a 2-minute video of Michael Kirby in the DZero control room, where he explains the on-going analysis of collision data in search of the Higgs particle.

Kurt Riesselmann

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What will it be? Fermilab announces new Higgs results Friday

March 12, 2009 | 3:32 pm

Update: News story about results here.

This week, particle physicists from around the world are gathering in Europe for a conference known as the Rencontres de Moriond. Conference organizers seem to have saved the biggest news for last.

This Friday, scientists from the CDF and DZero experiments at Fermilab in Batavia, Illinois, will present their latest results on the search for the elusive Higgs boson. New Scientist and Newsweek already reported on the conference, but the results from the direct search for the Higgs particle are still a top secret. On Friday morning, at 8 a.m. CDT, Fermilab will post the new constraints on the Higgs particle on its homepage: http://www.fnal.gov/

Finding the Higgs is no easy task. Just look at the discovery that the CDF and DZero collaborations announced less than a week ago: single top quark production. An amazing feat in its own right, the discovery also showed that the Fermilab Higgs hunters may finally have the tools to find–if it exists–the particle that explains the origin of mass. Time will tell.

Particle collisions at the Tevatron collider at Fermilab produce single top quarks about as often as they produce pairs of top quarks. The difference in observing them: 14 years. Fermilab announced the discovery of top pairs–the first sighting of top quarks–in 1995. The announcement for the discovery of single tops happened March 9.

Fast forward to the Higgs: it is even more difficult to detect than a single top, scientists say. The collisions that produce a Higgs particle and a single top quark have other particle processes in common that can mimic the signal. Worse, the single top is itself a background process that needs to be distinguished from the Higgs particle.

The Standard Model, the theoretical framework that explains the interactions of subatomic particles, predicts the existence of the Higgs boson. Searches at the Large Electron Positron collider at the European laboratory CERN established that the Higgs boson must weigh more than 114 GeV/c^2 (the scientific units for the tiny, tiny mass of a particle). Calculations of quantum effects involving the Higgs boson require its mass to be less than 185 GeV/c^2. (The New Scientist article has a really nice explanation.)

The Tevatron experiments are now sensitive enough to begin testing the range in between. Tomorrow we’ll see what Higgs masses they can exclude so far.

What will it be?

Kurt Riesselmann

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Can basic research bring renewable energies to scale?

March 12, 2009 | 9:13 am

The public is heaping pressure on the new presidential administration to increase renewable, domestic sources of energy. But the efforts of politicians and policy makers may amount to very little if science can’t catch up. Right now, our global energy future may rest in the hands of basic research scientists.

At the 2009 AAAS meeting, a session titled “Basic Research for Energy Security: A Call To Action,” featured speakers who drove home the idea that improving current alternative energy technologies—including silicon solar cells and lithium ion batteries—simply won’t be enough to solve the energy crisis. Instead, basic research scientists need to develop new technologies that are cheaper, more efficient, and fit for mass deployment.

“We’re going to need more than political will,” said Nathan Lewis of the California Institute of Technology, speaking about new technologies in solar panels. “We’re going need R&D and technology to get this to scale. Because the scale of energy is enormous, and therefore what works in your back yard or on your roof doesn’t apply to scaling globally, unless it’s very cheap and very amenable to mass deployment.”

Lewis estimates that to fully supply the US with solar energy by 2050, we would need to install solar panels on one million homes a day, every day, for the next forty years. Right now, the most ambitious plan of this kind is in California, where the government plans to put solar panels on one million homes over ten years. But not enough silicon is produced in the world each year to create that many solar cells. Many other solar cell materials would also fall short. To achieve even a portion of this goal requires variety and versatility.

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Calla Cofield

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W boson squeezes Higgs particle

March 11, 2009 | 12:53 pm

The W boson will help to corner the elusive Higgs particle. And photographer Robert Tilden has a photo to prove it.

The W boson is squeezing the Higgs boson: plush toys by artist Julie Peasley, photo by Robert Tilden.

The DZero collaboration at the Department of Energy’s Fermilab has achieved the world’s most precise measurement of the mass of the W boson by a single experiment. Combined with other measurements, the reduced uncertainty of the W boson mass will lead to stricter bounds on the mass of the elusive Higgs boson.

This inspired Tilden, a software engineer at Northwestern University and photographer, to create a photo of the W boson squeezing the Higgs boson in a vise. Artist Julie Peasley created the plush toys representing the particles, and they are available for sale on http://www.particlezoo.net/

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Kurt Riesselmann

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Fermi Gamma-ray Space Telescope reveals sky map and top-ten source list

March 11, 2009 | 8:01 am

This view from NASA's Fermi Gamma-ray Space Telescope is the deepest and best-resolved portrait of the gamma-ray sky to date. The image shows how the sky appears at energies more than 150 million times greater than that of visible light. Among the signatures of bright pulsars and active galaxies is something familiar--a faint path traced by the sun. Credit: NASA/DOE/Fermi LAT Collaboration

The Fermi Gamma-ray Space Telescope, a joint mission of NASA, the US Department of Energy, and international partners, today released a three-month sky-map of the gamma-ray sky and a list of the ten most interesting gamma-ray sources they have observed.

NASA’s press release and top-ten list (below) reveal a new perspective on the gamma-ray sky, highlighting interesting objects both within the galaxy and outside.

Here is what NASA has to say:

A new map combining nearly three months of data from NASA’s Fermi Gamma-ray Space Telescope is giving astronomers an unprecedented look at the high-energy cosmos. To Fermi’s eyes, the universe is ablaze with gamma rays from sources ranging from within the solar system to galaxies billions of light-years away.

“Fermi has given us a deeper and better-resolved view of the gamma-ray sky than any previous space mission,” said Peter Michelson, the lead scientist for the spacecraft’s Large Area Telescope (LAT) at Stanford University, Calif. “We’re watching flares from supermassive black holes in distant galaxies and seeing pulsars, high-mass binary systems, and even a globular cluster in our own.”

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David Harris

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Catching cosmic rays half a world away

March 10, 2009 | 5:00 am

There’s more than one way to study particle physics. You can use huge human-made accelerators such as the Tevatron at Fermilab. Or you can rely on nature to supply you with its tiniest constituents for research.

Tapping nature’s supply of cosmic rays is one of the oldest forms of particle physics research but the Pierre Auger Observatory in Argentina gives it a modern twist with cutting-edge technology, including the world’s largest array of detectors and solar panels powering them.

Angela Olinto, University of Chicago astronomy and astrophysics professor, said the chance to find out about the birth of the universe and the opportunity to work in a field with a long history drew her to the study of cosmic rays and the Pierre Auger collaboration. Olinto captivated an audience of about 500 people at Fermilab on Feb. 27 for a lecture on the Pierre Auger Observatory.

“The birth of particle physics is closely tied to cosmic rays,” she said.

Cosmic rays may provide a window into exotic, undiscovered particles or explain dark matter, the mysterious, invisible matter thought to influence the motion and structure of galaxies.

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Fermilab collider experiments discover rare single top quark

March 9, 2009 | 9:13 am

Scientists at the Department of Energy’s Fermilab have observed a new subatomic process. In particle collisions produced by the Tevatron collider, currently the world’s most powerful operating particle accelerator, two teams of scientists found single top quarks. The discovery has significance for the ongoing search for the Higgs particle.

Previously, top quarks had only been observed when produced by the strong nuclear force. That interaction leads to the production of pairs of top quarks. The production of single top quarks, which involves the weak nuclear force and happens almost as often as the strong force production, is harder to identify experimentally. Now, scientists working on the CDF and DZero collider experiments at Fermilab achieved this feat, almost 14 years to the day of the top quark discovery at Fermilab in 1995.

A single top quark candidate event recorded by the DZero collaboration. The top quark decayed into a bottom quark, a muon, and a neutrino.

Searching for single-top production makes finding a needle in a haystack look easy. Only one in every 20 billion proton-antiproton collisions produces a single top quark. Even worse, the signal of these rare occurrences is easily mimicked by other “background” processes that occur at much higher rates.

“Observation of the single top quark production is an important milestone for the Tevatron program,” says Dennis Kovar, associate director of the DOE Office of Science for High Energy Physics. ”The highly sensitive and successful analysis is an important step in the search for the Higgs.”

Discovering the single top quark production presents challenges similar to the Higgs boson search in the need to extract an extremely small signal from a very large background. Advanced analysis techniques pioneered for the single top discovery are now in use for the Higgs boson search at Fermilab. In addition, the single top and the Higgs signals have backgrounds in common, and collisions that produce single top quarks can mimic collisions events that create a Higgs particle.

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Kurt Riesselmann

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Steps toward an analytical proton

March 6, 2009 | 2:35 pm

SLAC theoretical physicist Stan Brodsky. (Photo by Lauren Schenkman.)

SLAC National Accelerator Laboratory theoretical physicist Stan Brodsky and University of Costa Rica physicist Guy de Téramond have found a simple equation describing the behavior of the subatomic particles within the proton. Their paper “Light-Front Holography: A First Approximation to QCD“, published in the February 27 issue of Physical Review Letters, is an important step in SLAC’s long history of investigations into the quantum mechanical world of the proton.

“A better understanding of the structure of the proton has traditionally been one of the main goals of SLAC physics,” Brodsky said. “How is it made up, at the fundamental level? That’s one of our main driving points at SLAC, and, in fact, in the whole field of high energy physics and nuclear physics.”

The SLAC tradition dates back to the 1960s, when Richard Taylor, Henry Kendall, and Jerome Friedman used SLAC’s linear accelerator to shoot high-energy electrons at the protons and neutrons in a liquid hydrogen target. The experiments confirmed a prediction of a young SLAC theorist named James Bjorken–the apparently fundamental protons and neutrons were made up of smaller particles called quarks. The discovery earned Taylor and his collaborators the 1990 Nobel Prize in physics.

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LHC weekly update: March 6, 2009

March 6, 2009 | 11:36 am

This week at the LHC, the third sector to be warmed up due to a suspected faulty magnet splice is now at room temperature, and removal of the magnet in question is underway. A prototype for a new anchoring system for another type of LHC magnet is now being tested in the tunnel. If successful, the system would prevent collateral damage to magnets were another large helium leak to occur.

CERN also reports that its Enhanced Quench Protection system for the LHC was favorably reviewed last week by a panel of outside experts. The system, to be installed before the LHC restart later this year, will identify and protect against the type of problem that led to last September’s incident.

Technical details from the CERN Bulletin.

Katie Yurkewicz

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IceCube season completed with record result

March 5, 2009 | 1:31 pm

This story originally appeared in DESY inFORM, the in-house publication of the DESY laboratory in Hamburg, Germany.

The drilling station in the foreground melts holes into the ice that are 2.5 kilometers long and house the IceCube strings. Photo courtesy of DESY.

Nineteen and fifty-nine: taken together these numbers give the year DESY was founded. They will be with us through all this anniversary year. But they also play a special role in the just-finished season of the Antarctic neutrino telescope IceCube: 19 IceCube strings have been deployed this Antarctic summer–as many as ever before–propelling the total number of strings to 59. When IceCube will be completed in January 2011, it will consist of 86 strings. These are six more than originally planned because we will integrate a small sub-detector called “Deep Core” into IceCube.

The sub-detector is tailored to detect neutrinos below the nominal IceCube threshold of roughly 50 giga-electronvolts. Each string carries 60 Digital Optical Modules (DOM)–highly sensitive light sensors in pressure-resistant glass spheres. The spheres are lowered into holes melted into the polar ice crust with pressurized hot water, down to depths between 1450 and 2450 metres, where they freeze in.

At the end of the construction phase, a full cubic kilometer of ice will be equipped with DOMs. In the extremely transparent ice, they “see” the light emitted by charged particles produced by high-energy cosmic neutrinos. Neutrinos may transmit information from cosmic regions from which no light but only the extremely elusive neutrinos can escape.

Schematic of the IceCube detector with AMANDA and Deep Core. IceCube has a volume of one cubic kilometer. Deep Core

A substantial amount of IceCube components and know-how comes from DESY: almost a quarter of altogether five thousand IceCube DOMs were assembled in Zeuthen and tested in a deep-freeze chamber over several weeks. Meanwhile, the final 233 of the DOMs produced in Zeuthen were shipped to Antarctica and are now waiting for their installation in the coming two Antarctic summer seasons. Moreover, DESY delivered the magnetic shielding and suspension elements for all DOMs. DESY also designed and tested the front-end electronics at the surface, which manages the entire communication with the DOMs. By now, DESY has delivered all components for the IceCube assembly–in total compliance with the planned time and budget limit.

Have we already “seen something”? Yes–nearly ten thousand neutrinos! However, their number, energy, and angular distribution are compatible with the assumption that their origin is not extraterrestrial but that they are almost completely originating from collisions of charged cosmic particles with the Earth’s atmosphere. We wouldn’t be particle physicists if we didn’t use this largest statistic worldwide of “atmospheric neutrinos” to investigate interesting questions of particle physics; nevertheless, we haven’t yet reached our main goal: the clear evidence for extra-terrestrial neutrinos. This could change very soon.

The sensitivity we have reached after one year with a quarter of the IceCube detector complete (22 strings, data of 2007) is already twice as high as that from seven years of data taking with the predecessor detector AMANDA. This is a real step into new territories, and the coming years will yield another factor of 20 to 30. The identification of high-energy extraterrestrial neutrinos could solve one of the most exciting questions of astrophysics: what are the sources of “cosmic rays”? What is the origin of protons, light and heavy atomic nuclei which constantly bombard the Earth’s atmosphere, some of them reaching energies more than a million times higher than the LHC beam energy?

Cosmic rays were first recorded in 1912 by the Austrian physicist Viktor Hess, so only three years are left to the hundredth anniversary of this discovery. Wouldn’t it be fantastic if we were able to solve the secret before that date?

By Christian Spiering

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