symmetry breaking » 2011

The twelve days of winter break: particle physics edition

December 22, 2011 | 9:00 am

As symmetry breaking closes down for its long winter’s nap, please enjoy (or at least put up with) a badly adapted holiday song and the chance to reflect on a fascinating year in particle physics:

The Twelve Days of Winter Break: Particle Physics Edition

On the first day of winter break, I saw in symmetry…
possible Higgs (but not discovery).

Higgs seminar. Photo: CERN

On the second day of winter break, I saw in symmetry…
faster-than-light neutrinos
and possible Higgs (but not discovery).

Speeding. Photo: Paul Townsend

On the third day of winter break, I saw in symmetry…
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Wilson Hall as a t. Photo: Fermilab.

On the fourth day of winter break, I saw in symmetry…
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Endeavor. Photo: NASA.

On the fifth day of winter break, I saw in symmetry…
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Lego ATLAS. Photo: Sascha Mehlhase

On the sixth day of winter break, I saw in symmetry…
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs with sigmas under three.

CDF bump. Image: CDF.

On the seventh day of winter break, I saw in symmetry…
CP violation
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

LHCb detector. Photo: CERN.

On the eighth day of winter break, I saw in symmetry…
one Muppet a-meeping
CP violation
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Still image from Muppets movie trailer.

On the ninth day of winter break, I saw in symmetry…
Tevatron retiring
one Muppet a-meeping
CP violation
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Tevatron ring. Photo: Fermilab.

On the tenth day of winter break, I saw in symmetry…
six neutrinos oscillating
Tevatron retiring
one Muppet a-meeping
CP violation
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Image from T2K experiment.

On the eleventh day of winter break, I saw in symmetry…
just-discovered baryons
six neutrinos oscillating
Tevatron retiring
one Muppet a-meeping
CP violation
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and possible Higgs (but not discovery).

Baryons. Image: Fermilab.

On the twelfth day of winter break, I saw in symmetry…
antimatter ATRAP-ing
just-discovered baryons
six neutrinos oscillating
Tevatron retiring
one Muppet a-meeping
CP violation
CDF a-bumping
10,000 Legos
one launching shuttle
top quark asymmetry
faster-than-light neutrinos
and a verdict on Higgs by 2013.

ATRAP experiment. Photo: CERN.

Happy holidays, everyone! See you next year!

Kathryn Grim

1 Comment »

Happy 10th Birthday, WLCG!

December 21, 2011 | 4:00 pm

Computing center, photo courtesy of CERN.

This story appeared today in iSGTW.

Amid all the hype and excitement of the new physics being announced from experiments at the Large Hadron Collider in 2011, there was another, little known, cause for celebration: the anniversary of the Worldwide LHC Computing Grid (WLCG).

It was 10 years ago, in September 2001, that the huge computing grid was conceived of and approved by the CERN council, in order to handle the large volumes of data expected by the LHC. By March 2002, a plan of action had formed.

And, now that the LHC is up and running, “the biggest achievement,” said Ian Bird, the head of the WLCG at CERN, in Geneva, Switzerland, “is that is works so well and so early in the life of LHC.”

Data pours out of each of the four detectors at a ripping pace – the ATLAS detector alone produces about one petabyte per second (or 1,000,000 GB per second), and a farm of processors pares back the data, filtering out the majority of it, until 300 MB per second is chosen to be stored on the grid. One copy of the data is kept at CERN (Tier 0), while another copy of the data is transferred and shared between the 11 major computing centers (Tier 1).

“The most amazing thing is that we can actually handle this kind of data,” said Bird. “Data rates today are much higher than anything we ever planned for during a normal year of data taking.”

As well as the sheer volume of data, the WLCG has also faced the unique challenges of computationally intensive simulations, and the fact that the 8,000 or so physicists involved in the projects must be able to access the data from their home institutions around the world.

“The grid is pretty much the only way that the masses of data produced by the collider can be processed. Without it, the LHC would be an elaborate performance art project on the French-Swiss border,” wrote Geoff Brumfield in a Nature blog, following his valiant attempt to follow a single piece of data through the grid (“Down the Petabyte Highway” published January 2011).

While the WLCG computing grid is successfully handling the data today, 10 years ago, while preparations for the Large Hadron Collider were well underway, there was a hole in the funding bucket. The computing resources required to handle the avalanche of LHC data had been left behind as preparations were made for the collider.
A hole in the funding bucket

“Computing wasn’t included in the original costs of the LHC,” Les Robertson, who was the head of the computing grid from 2002 – 2008, told iSGTW in 2008.

This decision left a big hole in funding for IT crucial to the ultimate success of the LHC.“We clearly required computing,” said Robertson, “but the original idea was that it could be handled by other people.”

But by 2001, these “other people” had not stepped forward. “There was no funding at CERN or elsewhere,” Robertson said. “A single organization could never find the money to do it.”

“Early on, it became evident that, for various reasons, placing all of the computing and storage power at CERN to satisfy all the [computing] needs would not be possible. First, the infrastructure of the CERN computing facility could not scale to the required level without significant investments in a power and cooling infrastructure many times larger than what was available at the time,” Ian Bird said.

And in 2001, “CERN’s dramatic advance in computing capacity is urgent,” the press release read.
A dramatic advance in computing capacity

There were two phases to the WLCG. From 2002 to 2005, staff at CERN and collaborating institutes around the world developed prototypes, which would eventually be incorporated into the system. Then, from 2006, the LHC Computing Grid formally became a worldwide collaboration (the Worldwide LCG – WLCG), and computing centers around the world were connected to CERN to help store data and provide computing power. Throughout its lifetime, the WLCG has worked closely with large-scale grid projects such as EGEE (Enabling Grids for E-sciencE), and more recently EGI (European Grid Initiative), funded by the European Commission, and OSG (Open Science Grid) funded the National Science Foundation in the USA. Today, EGI and OSG not only support high energy physics, but a variety of other science experiments and simulations as well.

Using the grid for real computation began as early 2003, with the experiments using it to run simulations. And since 2004 a series of data and service challenges were performed (see timeline, below), to test things such as reliability of data transfers.

“The grid’s performance during the first two years of LHC running has been impressive and has enabled very rapid production of physics results,” Bird said. Data flow and hybrid clouds The first model of distributed computing, proposed in 1999 and called the MONARC model, was the model on which all the experiments originally based their own computing model. But this model was much more complicated than it has to be today, according to Bird. This complexity was added because it was thought that the weakest link in the chain would be the networks linking together all the computing centers and allowing for fast, reliable data transfer. Today, computing models are more likely to see extensive data flows between Tier 2 and Tier 3 centres.

As well as a new model for data flow, other future challenges include the use of multicore and other CPU types, the replacement of certain components of grid middleware with more standard software and the use of virtualization. And the use of cloud computing is a matter of “when, not if” Bird said.

“The LHC computing environment will outlive the accelerator itself, but it will evolve along with technology and is likely to become very different over the next few years,” Bird said.

– Jaqui Hayes

Guest author

No Comments »

U.S. ships world’s largest digital camera to Chile

December 20, 2011 | 9:00 am

Completed imager of the DES camera. Photo by Fermilab.

The following article ran in the Fermilab blog on Quantum Diaries on Dec. 12.

A four-ton digital camera landed safely in Chile [this month] on its way to making history by enabling the world’s largest galaxy survey, starting next year. Getting the camera there was a worldwide feat of technology and transportation prowess.

Doing big science, such as building the Dark Energy Camera, takes big effort and big cooperation. Building and installing one of the world’s largest digital cameras to conduct the most extensive galaxy survey to date as part of the Dark Energy Survey [PDF] experiment required scientists and manufacturers from across the globe. Researchers from more than 26 institutions enlisted the help of 129 companies in the United States and about half a dozen in foreign countries to fabricate the often one-of-a-kind components for the camera.

Most components for the camera migrated to the Department of Energy’s Fermilab for testing and assembly, as seen in this timelapse video, before being shipped to the four-meter Blanco telescope in the remote Chilean mountains. The journey required help from planes, trains, trucks and boats to traverse continents and oceans, and ended with an 11-hour drive to a mountaintop.

The DES’s combination of survey area and depth will far surpass what has come before and provide researchers for the first time with four search techniques in one powerful instrument. To find clues to the characteristics of dark energy and why the expansion of the universe is accelerating, DES will trace the history of the expanding universe roughly three-quarters of the way back to the time of the big bang.

During five years of operation, starting in 2012, the 570-megapixel camera will create in-depth color images of one-eighth of the sky, or 5000 square degrees, to measure 100,000 galaxy clusters, 4,000 supernovae, and an estimated 300 million distant galaxies, about 10 million times fainter than the dimmest star you can see from Earth with the naked eye. It will yield the largest 3-D map of the cosmic web of large-scale structures in the universe.

Tona Kunz

No Comments »

A cheaper way to purify liquid argon for neutrino experiments

December 19, 2011 | 9:00 am

The Liquid Argon Purity Demonstrator at Fermilab could help scientists cut costs for future neutrino experiments. Photo by Terry Tope

Fermilab Today published this story on Dec. 16.

Today’s high-end experiments are pushing scientists to invent new technologies to meet the demands of the next generation of physics. These innovations, however, must be balanced with creative cost-saving strategies. One expense currently under evaluation is the construction of liquid argon tanks, which play a vital role in sensitive neutrino experiments.

When neutrinos reach an experiment tank full of liquid argon, they interact with the nuclei in the argon and produce charged particles. Those particles spawn electrons that then drift toward an array of wire detectors. The distance the electrons drift, along with arrival information gathered from the wires, provides scientists with a detailed 3D reconstruction of the event.

In order to reduce the chance of those electrons interacting with other particles, the liquid argon should have the highest purity possible, with oxygen contamination levels that are only 100 parts per trillion. To achieve this level of purity, scientists often evacuate a tank to remove oxygen and water vapor before filling it with liquid argon. Making a tank that can withstand the complicated evacuation process is very expensive, as is the equipment to perform the evacuation.

Fermilab physicists Brian Rebel and Rob Plunkett, along with mechanical engineer Terry Tope, have led an effort over the last two years to design a new method to cut these costs. The innovative Liquid Argon Purity Demonstrator (LAPD) they engineered is the first system without evacuation that can achieve the necessary electron lifetimes for long drift distances.

The purification process begins with argon gas flowing into a tank that will eventually hold up to 30 tons of liquid argon. This pushes out ambient air. The gas is then recirculated throughout the entire system to further reduce contamination levels, while a heater dries the internal surfaces. When the desired purity level is achieved, Rebel and his team add liquid argon.

With a full tank, the recirculation begins. The liquid is pumped from the bottom of the tank through a maze of pipes and instruments, which include filters for separating water, oxygen and particulates from the argon. Eventually, the liquid returns to the bottom of the tank to restart the process. After eight hours, an entire tank volume is recirculated.

Insulation wrapped around the tank is part of a cryogenic cooling system that maintains a consistent low temperature of minus 186 degrees Celsius, keeping the argon in a liquid state.

“The real trick is this has never been done before,” Rebel said. “There’s nothing like this.”

The bigger a tank is, the more neutrino interactions it can record. But the monetary tradeoff in building an evacuation-based vessel often limits the size of the tank and of the detector, compromising the capabilities of the experiment.

In large experiments, the LAPD system would have to recirculate the liquid argon to gain a level of purity high enough for 40 percent of the electrons to travel at least 2.5 meters to the readout wires without attaching to any positive ions within the argon. Electrons need 1.5 milliseconds to travel this distance, but a longer lifetime is necessary for minimizing electron losses.

As of late November, LAPD has consistently documented electron lifetimes of three milliseconds, easily meeting the team’s goal. This means contamination in the tank has been successfully reduced to just 100 parts per trillion of oxygen.

“We are very happy with the results,” Rebel said. “We couldn’t have achieved them without the hard work of the people who contributed to the project.”

- Brad Hooker

Symmetry Intern

No Comments »

Fermilab to build Illinois Accelerator Research Center

December 16, 2011 | 2:25 pm

From left: Bob Kephart, IARC Project Director; Jim Siegrist, associate director of the Office of Science for the Office of High Energy Physics; Michael Weis, DOE Fermilab site manager for the Office of Science; William Brinkman, director of the Office of Science for the DOE; Pier Oddone, Fermilab director; Warren Ribley, director of the Illinois Department of Commerce and Economic Opportunity; Linda Holmes, Illinois state senator; and Michael Fortner, Illinois state representative. Image by Reidar Hahn, Fermilab

Fermi National Accelerator Laboratory issued the following press release today.

Batavia, Ill. – A new accelerator research facility being built at Fermi National Accelerator Laboratory will bolster Illinois’ reputation as a technology hub and foster job creation.

The Illinois Accelerator Research Center (IARC) at the Department of Energy’s Fermilab will provide a state-of-the-art facility for research, development and industrialization of particle accelerator technology. The design and construction of IARC is jointly funded by DOE and the State of Illinois.

“In Illinois we understand the importance of investing in cutting edge technologies, which not only boost our economy, but also secure our role as a major competitor in the global marketplace,” said Governor Quinn. “The best minds in the world are right here, and today we are investing in our future by ensuring that the latest groundbreaking particle research activities will continue to come from Illinois.”

A major focus of IARC will be to develop partnerships with private industry for the commercial and industrial application of accelerator technology for energy and the environment, medicine, industry, national security and discovery science. IARC will also offer unique advanced educational opportunities to a new generation of Illinois engineers and scientists and attract top scientists from around the world.

Located in the heart of the industrial area of the Fermilab campus, IARC will house 42,000 square feet of technical, office and educational space for scientists and engineers from Fermilab, DOE’s Argonne National Laboratory, local universities and industrial partners.

“The IARC facility will help fuel innovation by developing advanced technologies, strengthening ties with industry and training the scientists of tomorrow,” said Dr. William F. Brinkman, Director of DOE’s Office of Science, one of the speakers at today’s groundbreaking. “The Department of Energy welcomes the opportunity to partner with the State of Illinois and looks forward to seeing IARC come to fruition.”

Press Release

No Comments »

First physics experiments soon to move into former Homestake mine

December 15, 2011 | 6:40 am

Rick Labahn, project engineer (left) and Ben Sayler, director of education and outreach at Sanford Lab, check out the almost-finished Davis Cavern, located about a mile underground in the former Homestake mine. Photo by Matt Kapust, Sanford Underground Laboratory

Construction of a 12,000-square-foot research campus a mile underground is nearing completion in the Black Hills of South Dakota, and scientists will begin to move the first physics experiments underground this spring.

“We’re on schedule for occupancy in March 2012, but it’s quite a little process,” said Project Engineer Rick Labahn, understating the complexity of his job.

Labahn is directing the outfitting of the Davis Campus, which comprises two large underground halls at the 4,850-foot level of the Sanford Underground Laboratory in the former Homestake gold mine. Early next spring researchers will begin installing two experiments there—both of them at the leading edge of 21st-century physics. The Large Underground Xenon experiment, which already is taking test run data in a building on the surface, aims to become the world’s most sensitive detector to look for a mysterious substance called dark matter. Thought to comprise 80 percent of all the matter in the universe, dark matter remains undetected so far. The second experiment, the Majorana Demonstrator, will search for one of the rarest forms of radioactive decays—neutrinoless double-beta decay. Majorana could help determine whether subatomic particles called neutrinos can act as their own anti-particles, a discovery that could help physicists better explain how the universe evolved.

The site of the Davis Campus already is a landmark in neutrino physics. It’s named for the late Ray Davis, a nuclear chemist who in the mid-1960s designed a pioneering experiment to detect neutrinos produced in the sun. Davis put his neutrino detector 4,850 feet underground to shield it from the noise of cosmic radiation, and his research earned him a share of the Nobel Prize for physics in 2002. Homestake closed in 2003, but in 2007 the South Dakota Science and Technology Authority began reopening the mine for a range of experiments that require shielding from cosmic radiation.

Sanford Lab technicians, many of them former Homestake miners, have enlarged the original Davis Cavern, which is now 60 feet long by 30 feet wide by 40 feet tall. The LUX experiment will be installed there. They’ve also excavated a new underground hall, the Transition Cavern—135 feet long by 50 feet wide by 17 feet tall—where the Majorana experiment will be installed.

The Transition Cavern will be equipped with showers for people and a “cart wash” for equipment. Everyone and everything entering the Davis Campus must be as free as possible of contaminants. Outside the clean area, a third cavern has been excavated for mechanical infrastructure such as air conditioning, an electrical substation and emergency generators.

The area of the Davis Campus is bigger than four tennis courts, and almost every square inch of that space is spoken for by the infrastructure and equipment needed to run LUX and Majorana. Most of that materiel is being lowered down Homestake’s Yates Shaft on two work decks, each of them 4 feet wide by 12-feet deep. When completed, the cargo will have included:

2,000 cubic yards of gravel

525 cubic yards of concrete

29 tons of steel rebar

13,000 cement blocks

75,000 pounds of rectangular ducts

80,000 pounds of spiral ducts

30 miles of wiring

7 miles of electrical conduit

320 light fixtures

68 frames and doors

Items too big for the work decks—such as a batch plant for mixing concrete and 32-foot steel beams for construction of the LUX lab—are slung beneath the decks and lowered to the 4850 Level in a step-by-step process developed during decades of underground mining.

The Transition Cavern, 135 feet long by 50 feet wide, will host the Majorana experiment and will be equipped with showers for people and equipment to keep the research campus as free as possible of contaminants. Photo by Matt Kapust, Sanford Underground Laboratory

A local contractor, Ainsworth-Benning Construction of Spearfish, S.D., is outfitting the $8 million campus. This nine-month phase of the project began in July. By early December, all of the concrete floors had been poured, about half of the block walls had been built and installation of ductwork had begun. This month contractors will install the second-story steel deck for the LUX experiment and a 71,600-gallon stainless-steel water tank that will protect the LUX detector from background gamma radiation and stray neutrons.

“The progress has been extraordinary,” LUX physicist Rick Gaitskell of Brown University said during a recent inspection trip to the 4850 Level. The heart of the LUX detector is a titanium cryostat that will hold more than 770 pounds of liquid xenon, cooled to a minus 170 degrees F. Photomultiplier tubes and an electrical wire grid in the detector will register photons and electrons kicked out when dark-matter particles collide with xenon atoms. The LUX detector already has been assembled in a surface lab and filled with liquid xenon for a test run that will last several weeks.

“The whole thing is coming together very nicely,” said Gaitskell’s colleague, Case Western Reserve physicist Tom Shutt. “We’re learning the detector on the surface. When we fire it up next year, underground, it should be the world’s most sensitive dark matter detector.”

The Majorana team already is underground, electroforming the world’s purest copper in a temporary cleanroom on the 4850 Level, just over half a mile from the Transition Cavern.

“We’re pushing very hard so we can hit the ground running when we move into the Transition Cavern,” Majorana spokesperson Steve Elliott of Los Alamos National Laboratory said. The team has manufactured more than 20 percent of the 5,000 pounds of radiation-free copper that will shield the experiment and hold in place the enriched germanium crystals used to look for neutrinoless double-beta decay. “I was very impressed with how the outfitting is going,” Majorana Principal Investigator John Wilkerson of the University of North Carolina said after a visit to the 4850 Level. The Majorana Demonstrator will test detector technology in preparation for a larger, next-generation experiment.

South Dakota has committed nearly $130 million to the Sanford Underground Laboratory, including a $70 million donation from philanthropist T. Denny Sanford. Meanwhile, the Department of Energy is weighing how to use the Sanford Lab’s great depth for long-term projects, such as a proposed partnership with Fermilab to build the Long-Baseline Neutrino Experiment. The expanded DOE project, known as the Sanford Underground Research Facility, SURF, could provide research opportunities for decades.

- Bill Harlan, Sanford Underground Laboratory

Guest author

2 Comments »

Kicking cancer with carbon ions

December 14, 2011 | 7:15 am

Hadron therapy patients receive treatment in this room at CNAO in Italy. Image courtesy of CNAO

Medical physics is getting heavier. Shooting intense beams of protons into tumors to destroy them while leaving nearby tissues largely unharmed has been in vogue since the ’60s. Globally, however, many centers offering such beam-based cancer treatment, known as hadron therapy, are looking to more massive carbon ions for their unique therapeutic promise. These particles are sometimes able to eradicate tumors that have become resistant to all other forms of radiation.

One interested center is CNAO, an Italian acronym that stands for the National Centre for Oncological Hadron Therapy. On Sept. 22 the facility finished treating its first cancer patient with proton beams and plans to be ready for carbon-ion beams by mid-2012.

“You don’t build such a giant center just for protons,” CNAO technical director Sandro Rossi said. When all the magnets needed to steer the large carbon ions from the hospital’s basement accelerator to the patient are installed, the apparatus will weigh between 1,000 and 2,000 tons. Rossi expects that, in the next decade or so, when the facility is fully operational, 80 percent of its treatments will be with carbon ions, the rest with protons.

The design for the synchrotron accelerator now used at CNAO originated in a study done at CERN from 1995 to 2000. The European laboratory then provided help with key systems of the machine, and experts still share their advice as needed, though none are employed by the medical center.

Both protons and carbon ions offer precision and damage-control advantages over other radiation therapy. Traditional radiation therapy and chemotherapy target a greater portion of the body than hadron therapy, leading to undesirable extra damage and side effects. Due to an energy distribution known as the Bragg peak, protons and carbon ions can be made to deliver the bulk of their impact at a particular depth within tissues: Tumors are pounded while surrounding tissues are largely left alone. Proton beams are so precise that they are often used when tumors lie close to vital organs and surgery is too risky an option.

This synchrotron accelerator provides particles for hadron therapy at CNAO. Image courtesy of CNAO

But while protons may only damage one strand of DNA in a tumor cell, eventually causing its death, carbon ions cripple both strands in the double helix. Thus the heavier carbon ions make a more potent beam and have a better chance to kill cells traditional methods haven’t been able to.

Still, clinical tests of carbon ion therapy remain scanty. Only 6,000 to 7,000 patients in history have been treated this way, which is few in terms of medical statistics for such a procedure, Rossi said. Japan, the world leader in carbon ion treatment, is responsible for more than 90 percent of these patients. Rossi expects that CNAO will begin regular treatments with proton beams at the end of next year and with carbon ion beams some months later, after more trials are complete.

Meanwhile in the U.S., the Mayo Clinic broke ground on its second proton beam facility in Arizona on Tuesday. Only nine other proton centers in the nation are currently operational, though seven more are in development.

“Right now we’re just trying to get our heads around the protons,” said Chair of Radiation Oncology at the Mayo Clinic in Arizona Steven E. Schild about the Arizona facility. No carbon ion treatment centers exist yet in the U.S., though Schild said they’ve been thinking of adding that technology at the Mayo Clinic.

While hadron therapy is the most promising form of radiation available, he can’t be positive this is the future of cancer treatment, he said. “We’ll see.”

Part of Schild and other U.S. proton pioneers’ research will involve cost-benefit analysis of such beam centers, including those that use carbon ions, to see if the initial expenses are ultimately outweighed by the decrease in complications, secondary effects and tumor recurrence using this method. “What you want to accomplish is the greatest good for the most people,” he said.

Amy Dusto

No Comments »

Possible signs of the Higgs remain in latest analyses

December 13, 2011 | 8:41 am

CERN Director-General Rolf Heuer, ATLAS Spokesperson Fabiola Gianotti and CMS Spokesperson Guido Tonelli stand before a packed auditorium to present the latest results in the search for the Higgs boson. Image: CERN

Fermi National Accelerator Laboratory and Brookhaven National Laboratory jointly issued the following press release today.

Two experiments at the Large Hadron Collider have nearly eliminated the space in which the Higgs boson could dwell, scientists announced in a seminar held at CERN today. However, the ATLAS and CMS experiments see modest excesses in their data that could soon uncover the famous missing piece of the physics puzzle.

The experiments revealed the latest results as part of their regular report to the CERN Council, which provides oversight for the laboratory near Geneva, Switzerland.

Theorists have predicted that some subatomic particles gain mass by interacting with other particles called Higgs bosons. The Higgs boson is the only undiscovered part of the Standard Model of physics, which describes the basic building blocks of matter and their interactions.

The experiments’ main conclusion is that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 116-130 GeV by the ATLAS experiment, and 115-127 GeV by CMS. Tantalizing hints have been seen by both experiments in this mass region, but these are not yet strong enough to claim a discovery.

Higgs bosons, if they exist, are short-lived and can decay in many different ways. Just as a vending machine might return the same amount of change using different combinations of coins, the Higgs can decay into different combinations of particles. Discovery relies on observing statistically significant excesses of the particles into which they decay rather than observing the Higgs itself. Both ATLAS and CMS have analyzed several decay channels, and the experiments see small excesses in the low mass region that has not yet been excluded.

Taken individually, none of these excesses is any more statistically significant than rolling a die and coming up with two sixes in a row. What is interesting is that there are multiple independent measurements pointing to the region of 124 to 126 GeV. It’s far too early to say whether ATLAS and CMS have discovered the Higgs boson, but these updated results are generating a lot of interest in the particle physics community.

Hundreds of scientists from U.S. universities and institutions are heavily involved in the search for the Higgs boson at LHC experiments, said CMS physicist Boaz Klima of the Department of Energy’s Fermi National Accelerator Laboratory near Chicago. “U.S. scientists are definitely in the thick of things in all aspects and at all levels,” he said.

More than 1,600 scientists, students, engineers and technicians from more than 90 U.S. universities and five U.S. national laboratories take part in the CMS and ATLAS experiments, the vast majority via an ultra-high broadband network that delivers LHC data to researchers at universities and national laboratories across the nation. The Department of Energy’s Office of Science and the National Science Foundation provide support for U.S. participation in these experiments. Fermi National Accelerator Laboratory is the host laboratory for the U.S. contingent on the CMS experiment, while Brookhaven National Laboratory hosts the U.S. ATLAS collaboration.

Over the coming months, both the CMS and ATLAS experiments will focus on refining their analyses in time for the winter particle physics conferences in March. The experiments will resume taking data in spring 2012.

“We’ve now analyzed all or most of the data taken in 2011 in some of the most important Higgs search analyses,” said ATLAS physicist Rik Yoshida of Argonne National Laboratory near Chicago. “I think everybody’s very surprised and pleased at the pace of progress.”

Higgs-hunting scientists on experiments at U.S. particle accelerator the Tevatron will also present results in March.

Discovering the type of Higgs boson predicted in the Standard Model would confirm a theory first put forward in the 1960s.

Even if the experiments find a particle where they expect to find the Higgs, it will take more analysis and more data to prove it is a Standard Model Higgs. If scientists found subtle departures from the Standard Model in the particle’s behavior, this would point to the presence of new physics, linked to theories that go beyond the Standard Model. Observing a non-Standard Model Higgs, currently beyond the reach of the LHC experiments with the data they’ve recorded so far, would immediately open the door to new physics.

Another possibility, discovering the absence of a Standard Model Higgs, would point to new physics at the LHC’s full design energy, set to be achieved after 2014. Whether ATLAS and CMS show over the coming months that the Standard Model Higgs boson exists or not, the LHC program is closing in on new discoveries.

Press Release

1 Comment »

A new book plays on the mystery of physics machines

December 9, 2011 | 10:53 am

Underground and closed off from visitors, experiments in particle physics often hide, rather than flaunt, the exotic and intricate machines that seem more at home in a science fiction blockbuster. No space shuttles, rockets or rovers wow visitors at today’s physics laboratories. The tried and true conduit from the underground to the outside world remains in most part the camera.

Polarized electron source, Bates Linear Accelerator Center, MIT, Massachusetts, 2007. Photo: Stanley Greenberg

In his new book, “Time Machines,” New York-based photographer Stanley Greenberg immersed himself within physics machinery to capture the cannon-like CMS detector before installation at the LHC, the frigid lifelessness surrounding the ICECUBE Neutrino Observatory in Antarctica and the Frankenstein mystique of Fermilab’s Cockroft-Walton accelerator. Greenberg’s book assembles 80 rich, black-and-white photos that distill from the complex machines a space-age style and individual personalities – preserving a romanticism free of scientific overload.

“Their massive cement blocks, multi-story electronics, and miles of circumference dwarf their human makers as intestines of tubes and wires converge Leviathan-like into the ultimate probe of the tiniest and the most hidden secrets of the vast universe,” writes David Cassidy in his imaginative, yet informative, introduction to “Time Machines.”

In his previous works, Greenberg, who is no stranger to towering structures, delved into sub-city tunnels, toured waterfront shipyards and scaled the skeletons of burgeoning buildings. He then left his home in New York City on a five-year quest to photograph the infrastructure and equipment of the most advanced high-energy and nuclear physics laboratories.

“It’s an almost completely hidden kind of world,” Greenberg said. “That’s always been an attraction to me – the places people can’t go.”

Assuming access to laboratories to be a challenge, Greenberg instead discovered open doors and smiling scientists, who often invited him before he asked.

Drawn by sweeping patterns that slice across his lens and massive structures that hemorrhage off the pages of his book, Greenberg has, for the most part, let the reader’s mind simply admire the machinery and wander what roles these strange instruments would fill.

“There are parts you see that will hopefully become metaphors for the whole,” Greenberg said.

While the book does briefly explain the experiments in the introduction and appendix, this is not a science book – it is a celebration of science.

What’s left out of the book are hundreds of old negatives from an era when bubble chambers were ubiquitous in the field. Greenberg collected and borrowed these abstract portraits of particles in the hope of one day displaying them in a gallery.

The collection in this book is simply one selection of weird and complex experiments from across physics history. Yet each otherworldly machine by being framed within a photograph is frozen in its own unique and immutable time.

All travel for the book was funded by the Alfred P. Sloan Foundation, and the NSF Artists and Writers Program funded Greenberg’s trip to the South Pole.

Brad Hooker

No Comments »

Freeing positronium from their dangling bonds

December 7, 2011 | 10:10 am

Last summer David Cassidy, a scientist at the University of California, Riverside, was busy using silicon to study positronium formation when his team noticed that the positronium, sitting on the silicon surface, didn’t behave as it should have.

Setup for positronium formation with silicon at the University of California, Riverside. Image: David Cassidy

As the silicon was heated, the amount of positronium leaving the surface increased, as expected. What was surprising, however, was the fact that, even as the silicon’s temperature was hiked up, the energy of the positronium atoms being ejected from the surface didn’t increase along with it.

The positronium emission energy had nothing to do with the material’s temperature.

“The positronium energy wasn’t changing, which doesn’t make any sense if you think it’s coming from a thermal distribution, because it should obviously get hotter if you heat the target up,” Cassidy says. “That’s how we found out that something different was going on.”

Positronium is an electron-positron pair. It survives for tens of nanoseconds before the two particles annihilate each other.

In the typical recipe, positrons stuck on the surface of some material grab hold of an electron, forming positronium. If the material is heated, the positronium gets a thermal kick and leaves the surface, with an energy that depends on the temperature. The temperature dependence of thermal positronium can be easily measured.

But the positronium in the UC Riverside silicon setup was falling off the material spontaneously.

“It’s metastable, sitting there on the edge of a cliff,” says Allen Mills, head of Cassidy’s group.

What appeared to be pushing it off the cliff was not the heat itself, but a consequence of the rise in temperature: the movement of the electrons in the surface material. As the temperature goes up, the electrons, with positrons clinging to them, move differently. When the arrangement of the positronium is just right, it flies off.

“Our idea was that it has a transient existence that can be thermally activated by moving some electrons from somewhere to somewhere else,” Mills says.

Or, in other words, posits Cassidy, “It’s really the electronic activation that you’re looking at, not the positronium emission.”

That the positronium flies off with a fixed energy means that it’s in a fixed energy state when it’s sitting on the surface. If you can control the state it’s in, you can control the energy with which it’s emitted.

“It’s only held at the surface because it’s not in the right arrangement to leave,” Mills says. “It has to make arrangements, call a babysitter and stuff, to fall off spontaneously.”

The team decided to heat silicon with a laser, bringing electrons to the surface in a controlled way, readying them for take-off. With a laser, they could control the electron population and manipulate their energy states.

Using a laser also enables researchers to activate the electrons in the material without having to heat it up, meaning that positronium production doesn’t have to be restricted to materials at hotter temperatures, which is typically the case. Being able to efficiently generate positronium at low temperatures opens up new experimental arenas. Cryogenic traps, for example, are not well suited to positronium experiments that require a metal at 1000 kelvins.

Mills and Cassidy are no strangers to positronium. They were the first to observe di-positronium, a two-positronium molecule, and had made plenty of it, not in silicon, but in porous films where the positronium molecules would hang out in the little voids dotting the film.

The move from porous films to the silicon made sense. Silicon, a semiconductor, is widely used in the tech industry. But beyond its use in broader applications, it turned out it was useful as part of a kind of positronium factory. For one, it’s resilient and easy to maintain. Metals, by contrast, require constant cleaning. And where the porous films, which are insulators, can not only become damaged at low temperatures but also, by nature, build up charge and discourage electron movement, silicon doesn’t. Its conducting electrons are easy for any off-the-shelf laser to bring to the surface.

“It might be a really handy way around those problems,” Cassidy said. “You don’t need any fancy lasers to create the positronium.”

Both Mills and Cassidy emphasize that their guesses as to exactly what’s happening at the silicon surface are just that – hypotheses. As the discovery happened by chance, they hadn’t planned on following the thread of this strange non-correlation between positronium energy and temperature, but they’d love to hear what others might have to say about it.

“I’d really like some theorists to weigh in on this and tell us precisely what’s going on,” Cassidy says. “There are a lot of details related to how the electrons are getting into these particular phases, what those states are and how they interact with each other – all that stuff that somebody more theoretically minded could help with.”

Leah Hesla

No Comments »

« Previous Entries