Jefferson Lab’s rules for achieving spotless cavities

November 29, 2010 | 10:00 am

This story first appeared in ILC Newsline on November 18, 2010.

Depending on your household’s rules of cleaning, you may have learned about a “right way” to wash dishes: keep dishwater clean for as long as you can, cleaning glasses first, then silverware, then plates. Save the dirtiest wares, pots and pans, for last.

A research team at Jefferson Lab has developed its own detailed set of rules for optimal cleaning. Team members have been working on a regimen for removing imperfections and impurities from superconducting radiofrequency (SRF) niobium cavities. Their procedures, they believe, have helped create cavities that could exceed [International Linear Collider] 2010 performance benchmarks.

The ILC cavity community has achieved a 35-megavolt-per-metre gradient with a 50% probability, or yield, for cavities produced by experienced vendors, using standard cavity preparation techniques at DESY and Jefferson Lab. That’s right on target with the ILC R&D 2010 goal, the achievement of which was announced in the 4 November Director’s Corner.

“Right now, Jefferson Lab is pretty much doing the best work for production cavities for an accelerator,” said Camille Ginsburg, who is Fermilab’s nine-cell SRF cavity coordinator.

The Jefferson Lab team, led by Rongli Geng, recently presented the results, based on very limited statistics, demonstrating achievement of 35 megavolt-per-metre gradient with an even higher yield of 90%. If that figure bears out with further tests, it would demonstrate achievement of the 2012 ILC goal.

Scientists believe that the success is due in part to their precise prescription to rid the cavity of dust, wipe out imperfections on its surface and purge gases that could inhibit conductivity. Their research has resulted in the formulation of a cocktail of voltages, temperatures, pressures and bake times to produce the cleanest possible cavity.

“With this optimisation, you not only increase the yield, you push the gradient,” said Geng. “Our data show that the practical gradient limit for real nine-cell cavities can be pushed to 40 megavolts per metre.” Higher yields and gradients mean lower costs for a linear collider.

The operation begins with a process called electropolishing. A metal rod is carefully inserted into the cavity, whose inner wall is partially immersed in acid. A voltage is applied between the rod and the cavity, prompting the acid to zap bumps in the wall, which could be defects caused by fabrication or parts of a rough surface. The process shaves about a 120-micron layer off the wall, smoothing it.

Geng’s team optimised their electropolishing recipe for SRF cavities, originally developed by Siemens. That recipe is carefully developed to polish, but not etch, the inner cavity walls. Scientists determined that the wall temperature near the cavity’s equator should be between 30 and 35 °C for a first, bulk electropolish and between 25 and 30 °C for a second, gentler one. They also recommended a voltage of 14.5 volts between the metal rod and the cavity.

The formula appears to be doing the job.

“Electropolishing is the technique that got us up to 35 megavolts per metre,” said Ginsburg.

Following the initial electropolish, the cavity is brushed and wiped down to remove anything that may have been deposited in its nooks and crannies. It’s then put through a detergent rinse, another process to clean the hardware, and yet another rinse to remove the particulates introduced by that process.

By this point, it’s unlikely any dust will turn up in a white glove test.

The effects of dust and metal bumps can impede a particle’s trip down the cavity, but those aren’t the only possible culprits. Hydrogen gas, introduced into the cavity wall during the electropolish, weakens the inner layer’s conductivity. It has to go, and scientists found that baking the cavity at a temperature above 600 °C chases the gas away.

Actual baking temperatures vary at different labs. For example, 800 °C has been a standard temperature at DESY for some time.

Though hydrogen degassing is not new, previous treatments at Jefferson Lab dictated that the cavity be baked at a lower temperature, 600 °C, for about 10 hours. Not only did that eat up valuable time, it also turned out to be rather incompatible with the metal’s particular mechanical properties. By changing the Jefferson Lab baking procedure to 800 °C for two hours, degassing is a snap and leaves cavities more favorable for mechanical adjustments.

“We decided to make this a standard heat treatment for ILC cavity-processing at Jefferson Lab,” said Geng. “At the same time, we’re pursuing a better understanding of the relationship between the heat treatment temperature and material properties.”

The Jefferson Lab team was rigorous in linking a cavity-polishing and cavity-cleaning process to a resulting cavity behavior. Incorporating those responses into a feedback loop of data, researchers make changes to details in the cleaning processes — upping the temperature here, lowering the pressure there. Every improvement takes them one step closer to an optimal cavity. They’ve worked to create an effective, repeatable procedure that others can adopt.

Their research has built on related work in industry and at Cornell University, DESY, Fermilab and KEK.

“I anticipate all this wonderful work will be in industry and in the ILC, and our job is to create an example to show it’s possible,” said Geng. “Our final goal is to make this knowledge available not only to sister labs but also to industry.”

Leah Hesla

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New insight into primordial universe from the LHC

November 26, 2010 | 10:04 am

CERN announced today that the ATLAS experiment has published its first measurements from lead-ion collisions.  The measurement, of a phenomenon called jet quenching, opens up a new era in the ability of scientists to probe the behavior of the hot, dense matter–the quark gluon plasma–that existed microseconds after the Big Bang.

The publication of the ATLAS paper comes three weeks after the first lead-ion collisions in the LHC, and one week after the ALICE experiment published its first two measurements of different properties of lead-ion collisions. Scientists from the CMS experiment have confirmed that they also see the jet quenching effect in their data, and will publish their result in the coming weeks.

Jets are sprays of particles that fly out from high-energy collisions of particles like protons or lead ions. When protons or lead ions collide at high energies, what really collides are their component particles: quarks and gluons. Since nature has made it impossible for quarks or gluons to exist in isolation, as they move away from the point of collision they immediately turn into a narrow cascade, or jet, of particles.

Jets are a common sight in collisions of protons at the LHC, usually appearing in pairs as narrow cones of particles heading away in opposite directions from the collision point. They are equally common in collisions of lead ions, but with a twist. The ATLAS measurement showed that the more “head-on” the collisions of lead ions, the more unbalanced the energies of the jets streaming out in opposite directions from the collision point. While one jet may still appear as a narrow cone of particles, the second jet has a much lower energy, and the narrow cone of particles has become much more diffused.

This is the phenomenon of jet quenching, first observed indirectly in 2003 by experiments at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider. In the years since, scientists have theorized that the quenching effect occurs when quarks scatter and lose energy as they travel through the quark gluon plasma. Depending on where the pairs of quarks are created and their paths out of the plasma, they may lose different amounts of energy. In the extreme case, where the jets are produced near the surface, one jet may escape unscathed while the other jet travels through the bulk of the plasma losing a large fraction of its energy.

Precisely measuring jets as they emerge from heavy-ion collisions thus provides an excellent tool to probe the quark gluon plasma itself, about which relatively little is known. But the indirect measurements of jet quenching possible at RHIC severely limited scientists’ ability to explain exactly what was happening to the jets as they passed through the plasma. ATLAS has shown in its publication today that direct measurements of jet quenching are possible at the LHC, and that the phenomenon is even stronger than expected from the RHIC results.

“This result, the fact that the interactions are so strong, was completely unexpected,” says Brian Cole from Columbia University, who led the ATLAS analysis. The effect is so strong at the LHC that scientists in both the ATLAS and CMS experiments were able to see it with their own eyes as they looked at event displays on computer monitors. “We also see that the jets remain exactly back-to-back, even when they’re quenched. This is startling, and was the kind of insight we didn’t get at RHIC.”

ATLAS and CMS are able to directly measure jet quenching for two reasons. First, the higher collision energy at the LHC  means that jets have enough energy to make it out of the collision zone and into the particle detectors. Second, unlike the RHIC detectors, the ATLAS and CMS detectors capture almost all of the particles that stream outward from the collision point, and are sophisticated enough to record all of the particles that make up a jet.

“In ATLAS the jets have nowhere to hide,” says Peter Steinberg from Brookhaven National Laboratory, co-leader of the heavy ion physics group within ATLAS. “We see one jet that’s a sharp cone, and debris in the other direction that seems to originate from the recoiling jet. It’s analogous to comparing a drop of ink falling in air, and in water. In one case the drop goes straight ahead and in the other it diffuses and spreads as it interacts with the water, but in either case nothing is lost.”

But scientists, including Cole, caution that this is just another step in a process that will span years and perhaps decades, as scientists seek to understand exactly how quarks and gluons interact within the plasma. But with the knowledge in hand that the jet quenching effect is strong at the LHC, and the ability to directly measure the phenomenon, scientists from ATLAS, CMS and ALICE will forge ahead with more analysis using more lead-ion collision data. Theoretical physicists will turn to the task of interpreting the new measurements, all with the goal of learning more about the behavior of the universe’s fundamental particles and forces.

The ATLAS result has been accepted for publication by the journal Physical Review Letters, and a draft is available on the CERN document server.

Katie Yurkewicz

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Undergrads take particle physics research to the ocean and D.C.

November 24, 2010 | 10:00 am

When you’ve weathered four months aboard a ship that’s been through a storm so severe it knocks the cabinets off the walls, asking for money from your senator is no big deal.

So a trio of university students from Wisconsin weren’t nervous when they got the chance to join the April pilgrimage of undergraduate science students to Washington D.C.

Spring is an especially busy time on Capitol Hill. Before every election primary, members of Congress and would-be legislators campaign to be November’s nominee, expounding on their records of service and drumming up funds. And every April students descend on Washington with a zeal befitting stumping season. They aren’t looking for ballot votes, but they are rallying for a piece of the budget pie. Their message is clear: Undergraduate research is a great cause.  

“We just laid it out for the legislators and said, ‘We’re living, breathing examples of why giving money to undergraduate research is beneficial not only to individuals, but to communities, states, our country even,’” said Samantha Jakel, now at University of Wisconsin-Madison. 

Jakel, along with Drew Anderson and Kyle Jero of University of Wisconsin-River Falls, presented their research at the annual Washington, D.C., conference Posters on the Hill. Their science poster summarized their contribution to a neutrino detection collaboration called IceCube. The forum, sponsored by the Council on Undergraduate Research, gave 75 undergraduates from 50 different institutions the chance to discuss their research with legislators, thank them for their support and talk up the importance of sustained funding.   

The Wisconsin crew had an array of anecdotes and lessons learned firsthand to back up their bid for money.

Symmetry magazine reported in October on the trio’s trip last winter from Sweden to Antarctica on a ship as they monitored the particle detector on board with them. Earth’s magnetic field gradually intensifies between the equator and poles, permitting only particles above a particular energy into the atmosphere based on geographic location. With this knowledge, the students collected data necessary to calibrate the low-energy range of the IceTop detector. This detector, currently being installed in the Antarctic ice, will help calibrate the larger IceCube detector.

The students and their advisor James Madsen, a professor of physics at UW-River Falls, met with Wisconsin’s legislators, including Sen. Russ Feingold and staffers from the offices of Sen. Herb Kohl and representatives Dave Obey and Paul Ryan. They also met with a riveted Rep. Ron Kind, who had to be dragged away from the students’ poster to submit a vote.

“Representative Kind actually talked to the students for quite a while,” Madsen said. “He’s been quite supportive of continued funding to double the NSF budget; that was really encouraging to see.” As for Sen. Feingold, he engages with the students, Madsen said. “He’ll ask, ‘What do you tell people is the reason you’re doing this research?’”

When the senator asked, the students had their answers ready.

“Physics isn’t about turning in assignments and taking tests,” Jero said. It’s about being able to do something on your own. It’s about learning how to ask the questions yourself instead of having questions asked of you.”

Jakel’s stint on the ship showed her the value of undergraduate research.

“Before I started this, I didn’t think you could really work doing research and work with real data,” Jakel said. “My impression of the whole thing was that you had an internship; you learned stuff, but you didn’t really get to do anything hands-on.”

But participants at Posters on the Hill would like legislators to know that this isn’t and shouldn’t be the case.

“I think that’s the bottom line. These things have value beyond the individual experience, and there are multiplying effects as people hear about these things,” Madsen said. “While the legislators may be signing a bill that looks like a bunch of numbers, these are real experiences that happen.”

Learn more about the students’ project at http://www2.uwrf.edu/icecube/.

Leah Hesla

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SLAC and Stanford extend partnership another 33 years

November 23, 2010 | 10:00 am

This story first appeared in SLAC Today on November 18, 2010, under the headline “A New Lease for an Evolving Partnership.”

When asked how long a lifetime the proposed linear accelerator at Stanford would have, SLAC founding Director Pief Panofsky reportedly replied, “About 10 years or so, unless somebody has a bright idea, which someone here usually does.”

Nearly 50 years and countless bright ideas later, SLAC and its linear accelerator are still going strong. Despite Panofsky’s short-term quip, Stanford and what was then the Atomic Energy Commission set up a 50-year agreement, in which the university would provide its land to the government for free and operate the laboratory on behalf of the AEC. Recently, Stanford and the AEC’s successor, the Department of Energy, agreed to extend this relationship for another 33 years.

The idea for a two-mile linear accelerator sprang from a group of Stanford physicists, including Panofsky, around 1956. They envisioned a machine that would let them hunt for the most fundamental building blocks of the universe, one that required more than 50 times the energy of the 220-foot electron accelerator already housed in a university laboratory. Because of the project’s massive price tag—which at $114 million was nearly twice that of Stanford’s endowment at the time—Panofsky knew it would require government funding.

In 1957, the group sent a 100-page proposal to three government agencies, hopeful that one of them might be able to support the project. Of the National Science Foundation, the Office of the Secretary of Defense for Research and Engineering, and the U.S. Atomic Energy Commission, the AEC was deemed the most appropriate to take it on.

Negotiations between Stanford and the AEC went on for several years, on topics such as the site of the accelerator, who would oversee the construction, and how the lab would operate once experiments were under way. Stanford offered to let the AEC use its land free of charge, but wanted to maintain its own research program. The facility would also be open to qualified researchers outside the university, and results from all of the experiments would freely be published. Finally, in 1962, five years after the proposal, the two institutions signed a contract.

These original agreements were forged primarily between the AEC and the Stanford Board of Trustees. The board then set up a network of groups and individuals to manage the research and administrative programs at the laboratory. They assigned operating responsibilities to the president of Stanford, who in turn delegated them to the director of SLAC. A team of associate directors would oversee the day-to-day functions of the various divisions within the lab.

There were also several independent committees that communicated among the three partners. A program advisory committee provided advice on scientific programs to the SLAC director. Another committee advised the Stanford president on the scientific policies at SLAC, which were then forwarded to the AEC. In addition, a university coordinating committee advised the president regarding affairs between SLAC and the university, and an AEC site office was established at SLAC to serve as a liaison between the lab, the university and the federal government.

Many of these relationships are still in place today, but have evolved to reflect SLAC’s place in the national laboratory system. SLAC now operates under the Office of Science within the Department of Energy, as a multi-program laboratory aligned with the larger DOE mission. There is still a site office at SLAC, now run by the DOE, where current manager Paul Golan works closely with the lab and university.

“I’m like the umpire,” Golan said. “I make sure the game is played fairly and that the rules are followed.” But he can sometimes act like a first-base coach too, providing direction and feedback on the operations, safety and infrastructure at the lab.

Stanford has established a Board of Overseers to review SLAC operations and send an annual assurance letter to the DOE, which describes how well the lab is performing and includes assessments of risks and mitigations.

The university’s official representative to the government is Bill Madia, who oversees the day-to-day operations of the contract. He said he ensures that both Stanford and the DOE meet the conditions of the contract, follow safety protocols and are generally “heading in the right direction.” He works regularly with SLAC Director Persis Drell and Stanford President John Hennessey, discussing the long-term direction and goals of the lab.

“Because of the broad scientific footprint of the Linac Coherent Light Source, there is an expanded interest on campus to work with SLAC,” Madia said. The latest adaptation of SLAC’s two-mile linear accelerator, the LCLS has a working lifetime of about 30 years, not including the proposed LCLS-II facilities. Stanford and the DOE agreed on the new, 33-year lease term to allow SLAC, Stanford and the DOE enough time to complete the mission.

The new lease had to be updated to reflect five decades of change in the legal and political landscapes, especially regarding state and federal environmental laws. The basic premise of the original lease was that the government could use the land for the lifetime of the lab, but it must return it in the same condition it was in when Stanford first gave it to the government.

“Today, environmental laws and regulations are much more specific,” Madia said. Although the land cannot be restored to its undeveloped state, it must be returned without financial impairments or contamination in the soil, groundwater or air that would restrict Stanford’s ability to use the land for other purposes in the future.

The new lease also allows future extension of the relationship for as long as Stanford and the DOE see the arrangement as mutually beneficial—which leaves plenty of time to come up with the next bright idea.

– Lauren Rugani

Symmetry Intern

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A camera’s odyssey

November 22, 2010 | 10:00 am

This story first appeared in Fermilab Today on November 17, 2010.

In comparison to scouring the universe for elusory dark energy, transporting a fragile, multi-ton, one-of-a-kind camera from the windswept Illinois prairie to the barren mountaintop of Cerro Tololo in the Chilean Andes is a simple feat. By any other comparison, though, it’s a massive undertaking.

Since 2004, the Dark Energy Survey collaboration has worked at Fermilab on constructing a large 570-megapixel camera that will take snapshots of the night sky to search for dark energy. Scientists believe dark energy is causing the expansion of the universe to speed up. Parts of the Dark Energy Camera are already fully operational, and the DES collaborators are beginning to ship them one by one to Cerro Tololo Inter-American Observatory in Chile through the rest of the year. There, scientists will attach the camera to an existing telescope.

Many of the camera’s components have already traveled from far-off lands, including England, Germany, Spain and Italy to Fermilab, but they have even farther to go. The first piece of DECam recently arrived at Cerro Tololo after a long, complicated journey over land and sea.

At noon on Sept. 16, two semi-trucks carrying empty shipping containers arrived at Fermilab to pick up the disassembled F/8 handler, the heavy apparatus that installs and removes a 1-ton mirror from the front of the camera. The F/8 mirror, already at CTIO, will allow researchers to direct celestial light into the telescope’s other experiments when not using DECam. Its

handler was carefully packaged into wooden crates and then into the shipping containers for the month-long journey. After the short jaunt to Chicago aboard the semis, the two 10-ton containers were loaded onto a 50-car train bound for Elizabeth, NJ. From there, the cargo was transferred back onto semis, driven to New York Harbor, and placed in storage for the next week to await the arrival of their transport ship, Kiel Express.

“It was cool to watch the F/8 handler loaded into containers just like other stuff that’s going around the world,” said Brenna Flaugher, DECam project manager. “It reminded me of the scene at the end of ‘Raiders of the Lost Ark’ where it goes into a box that looks like all the other boxes, but somehow they managed to get the right boxes to Chile.”

The Kiel Express departed New York for its journey around the southeastern United States on Sept. 28. Cruising at about 10 knots (11 mph), it reached the Panamá Canal on Oct. 5. When it sailed into Manzanillo International Terminal, one of the world’s busiest container shipping ports, dockworkers immediately offloaded the entire ship and randomly subjected its crates to high security measures, including X-ray scans and drug-sniffing dogs.

From here, said George Bressani, export coordinator for the German shipping company DB Schenker, the cargo was loaded onto a smaller vessel, Bahia Laura, for the second half of its trip. It sailed through the Pacific Ocean to Santiago without delay, arriving at the port of Valparaiso on Oct. 16.

As part of a federally-funded operation, DES collaborators worked with other organizations to make arrangements to fast-track the shipment through Chilean customs, said Edilia Cerda, Santiago operations manager for the Association of Universities for Research in Astronomy (AURA). On Oct. 18, the crates were free to be loaded onto semis to begin the seven hour drive up to the Cerro Tololo International Observatory, which sits at 7,000 feet above sea level in the Andes. The dusty dirt road, Cerda said, is well maintained and the semis with their heavy loads had no trouble reaching the top. At the top of the desert mountain, observatory crews stored the F/8 carefully. It will be installed in January, before the rest of DECam arrives.

“It looks great there,” Flaugher said. “We’re very happy and relieved that it arrived intact.”

For more information on the Dark Energy Camera, visit http://www.darkenergysurvey.org/

-Sara Reardon

Symmetry Intern

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ALICE experiment announces first results from LHC’s lead-ion collisions

November 18, 2010 | 5:50 am

Scientists from the ALICE experiment at CERN’s Large Hadron Collider have publicly revealed the first measurements from the world’s highest energy heavy-ion collisions. In two papers posted today to the arXiv.org website, the collaboration describes two characteristics of the collisions: the number of particles produced from the most head-on collisions; and, for more glancing blows, the flow of the system of two colliding nuclei.

Both measurements serve to rule out some theories about how the universe behaves at its most fundamental, despite being based on a relatively small number of collisions collected in the first few days of LHC running with lead-ion beams.

In the first measurement, scientists counted the charged particles that were produced from a few thousand of the most central lead-ion collisions—those where the lead nuclei hit each other head-on. The result showed that about 18,000 particles are produced from collisions of lead ions, which is about 2.2 times more particles than produced in similar collisions of gold ions at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider.

With the LHC’s lead-ion collisions taking place at more than 13 times the energy of RHIC’s gold-ion collisions, predicting a big increase in the number of particles produced would seem to be a no-brainer. Surprisingly, however, the opposite was true. The majority of theories predicted a number lower than that measured by ALICE, because of a strange property of the world of quarks and gluons, the fundamental particles that make up a lead nucleus.

“Imagine you have a magnifying glass strong enough to be able to look at a lead nucleus,” explains Yale University’s John Harris, a member of the ALICE experiment.  “When you look at the nucleus with the lower magnification, you will see three quarks and a few gluons. As you increase the magnification, you will see the same number of quarks but more and more gluons. When colliding at the higher energies of LHC, we are probing smaller sizes and distances as with the magnifying glass, and there the gluons will play a big role in what happens.”

Among theorists who work to describe what happens in these collisions, one school of thought said that there was an upper limit on how many gluons could be packed into a certain area. So at some point the number of gluons interacting—colliding—with each other would be saturated, and no more particles would be produced. But the measurement published today by ALICE shows that, if that limit exists, it’s not yet been reached at the LHC.

In the second measurement, ALICE scientists looked at events where the lead nuclei didn’t collide head-on, but instead hit each other slightly off-center. By using the ALICE detector to measure properties of particles emitted from these collisions, scientists measured how the system created when the two nuclei collide–the quark gluon plasma–flows.

The type of flow, called elliptic, has also been measured at RHIC and is related to the strength of the interaction between the quarks and gluons within nuclei. Measurements of the elliptic flow at RHIC experiments led to the surprising finding that the quark gluon plasma formed when two gold nuclei collide appears to flow like a “nearly perfect” liquid with almost no viscosity.

“The important thing about any fluid is its viscosity—its resistance to flow,” says ALICE scientist Peter Jacobs from Lawrence Berkeley National Laboratory. “If the particles in the fluid have a high probability of interacting with each other, the fluid has low viscosity, and vice versa. At RHIC we saw that a model with very low viscosity seems to describe the measured elliptic flow very well.”

The new ALICE measurement shows that the elliptic flow in LHC collisions is higher than at RHIC, but Jacobs cautions that it’s too early to translate that measurement into a statement about the viscosity of the quark gluon plasma formed at the LHC.

“Our measurement of elliptic flow is final, but it will take much more discussion with theorists before we know what that means in terms of viscosity,” he adds.

But one thing is already known – a number of theories have been ruled out that predicted that the quark gluon plasma created at the LHC would flow more like a gas.

“We can say that the system definitely flows like a liquid,” says Harris.

Both papers have been submitted to the journal Physical Review Letters.

Katie Yurkewicz

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Antimatter atoms produced and trapped at CERN

November 17, 2010 | 4:14 pm

This release was issued November 17, 2010, by the InterAction Collaboration.

The ALPHA experiment at CERN has taken an important step forward in developing techniques to understand one of the Universe’s open questions: is there a difference between matter and antimatter? In a paper published in Nature today, the collaboration shows that it has successfully produced and trapped atoms of antihydrogen.

This development opens the path to new ways of making detailed measurements of antihydrogen, which will in turn allow scientists to compare matter and antimatter.

Antimatter – or the lack of it – remains one of the biggest mysteries of science. Matter and its counterpart are identical except for opposite charge, and they annihilate when they meet. At the Big Bang, matter and antimatter should have been produced in equal amounts. However, we know that our world is made up of matter: antimatter seems to have disappeared. To find out what has happened to it, scientists employ a range of methods to investigate whether a tiny difference in the properties of matter and antimatter could point towards an explanation.

One of these methods is to take one of the best-known systems in physics, the hydrogen atom, which is made of one proton and one electron, and check whether its antimatter counterpart, antihydrogen, consisting of an antiproton and a positron, behaves in the same way. CERN is the only laboratory in the world with a dedicated low-energy antiproton facility where this research can be carried out.

The antihydrogen programme goes back a long way. In 1995, the first nine atoms of man-made antihydrogen were produced at CERN. Then, in 2002, the ATHENA and ATRAP experiments showed that it was possible to produce antihydrogen in large quantities, opening up the possibility of conducting detailed studies. The new result from ALPHA is the latest step in this journey.

Antihydrogen atoms are produced in a vacuum at CERN, but are nevertheless surrounded by normal matter. Because matter and antimatter annihilate when they meet, the antihydrogen atoms have a very short life expectancy. This can be extended, however, by using strong and complex magnetic fields to trap them and thus prevent them from coming into contact with matter.
The ALPHA experiment has shown that it is possible to hold on to atoms of antihydrogen in this way for about a tenth of a second: easily long enough to study them. Of the many thousands of antiatoms the experiment has created, ALPHA’s latest paper reports that 38 have been trapped for long enough to study.

“For reasons that no one yet understands, nature ruled out antimatter. It is thus very rewarding, and a bit overwhelming, to look at the ALPHA device and know that it contains stable, neutral atoms of antimatter,” said Jeffrey Hangst of Aarhus University, Denmark, spokesman of the ALPHA collaboration. “This inspires us to work that much harder to see if antimatter holds some secret.”

In another recent development in CERN’s antimatter programme, the ASACUSA experiment has demonstrated a new technique for producing antihydrogen atoms. In a paper soon to appear in Physical Review Letters, the collaboration reports success in producing antihydrogen in a so-called Cusp trap, an essential precursor to making a beam. ASACUSA plans to develop this technique to the point at which beams of sufficient intensity will survive for long enough to be studied.

“With two alternative methods of producing and eventually studying antihydrogen, antimatter will not be able to hide its properties from us much longer,” said Yasunori Yamazaki of Japan’s RIKEN research centre and a member of the ASACUSA collaboration. “There’s still some way to go, but we’re very happy to see how well this technique works.”

“These are significant steps in antimatter research,” said CERN Director General Rolf Heuer, “and an important part of the very broad research programme at CERN.”

Full information about the ASACUSA approach will be made available when the paper is published.

Press Release

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People in physics: George Redlinger and the search for SUSY

November 17, 2010 | 12:00 pm

This story first appeared in @brookhaven Today on November 1, 2010.

Ask George Redlinger about his car’s license plate — which reads “SUSY DM” — and he’ll be delighted to explain it to you.

“I like the ambiguity,” he said. “SUSY DM could be a woman named Susan advertising her Doctor of Management or her interest in Dungeons and Dragons.”

SUSY DM, however, is no lady.

Google “SUSY DM” and the first thing to appear is supersymmetric (SUSY) dark matter (DM). This is a logical choice for Redlinger, co-coordinator of the supersymmetry search group on the ATLAS experiment. With Pascal Pralavorio of the Marseilles Center for Particle Physics in France, he oversees experimental groups searching for SUSY at the Large Hadron Collider (LHC) at CERN.

Symmetry is beautiful — especially to physicists. In physics, space and time are governed by three principles of symmetry: translational, rotational, and time translation symmetry. In essence, these maintain that the laws of physics are the same everywhere in the universe, in every direction, and throughout time.

By the mid-1960′s, these three symmetries were theorized to be the only possible symmetries of space and time. Supersymmetry is a loophole to this theorem, extending space-time symmetry into the dimension of spin, a quantum mechanical property related to the magnetic charge of fundamental particles.

“You extend the symmetry and when you do this, some profound things happen. You’re now able to make a connection between the theories of general relativity, which apply to space and time, and quantum mechanics,” Redlinger said. “That’s the Holy Grail of modern physics.”

Supersymmetry posits that all particles have a superpartner related by its spin. These superpartners are the objects of SUSY searches and what Redlinger’s three search groups look for evidence of with the ATLAS detector.

The first group looks for red herrings. They characterize all of the known particles and processes that resemble the decay of theorized superpartners and could trip up the other two groups.

The second and third groups look for evidence of superpartners, but each has a different tactic. One searches with the assumption that these particles will leave direct evidence of their presence in the detector, while the other is on the lookout for particles that do not. In the latter case, physicists infer the presence of invisible particles through an imbalance in momentum as they decay into other particles.

So what does it mean if physicists find superpartners in the ATLAS detector?

“For me, the most exciting thing would be finding this new symmetry. It’s something that would totally shake up the field,” Redlinger said.

SUSY could also be the key to other physics puzzles.

Those invisible superpartners might be the elusive dark matter that physicists have attempted to pin down for decades. In addition, supersymmetry could be used to explain the mass of the Higgs boson, a long-sought particle central to the LHC program. Supersymmetry might even unify our understanding of nature’s fundamental forces, much like the late 19th century realization that electricity and magnetism were manifestations of the same electromagnetic force.

With the possible exception of a few hints from Brookhaven’s Muon g-2 experiment however, no experimental evidence of supersymmetry has been found in roughly three decades of searching. Yet physicists keep looking.

“Supersymmetry is such a beautiful idea that, to paraphrase Einstein, it would be a shame if nature did not take advantage of it,” he said. “Even if we don’t find supersymmetry at the LHC, I would still think it’s out there. We’re just missing something important about how it relates to today’s universe.”

Redlinger first came to BNL in the 1990’s, while collaborating with Canadian laboratory TRIUMF in the search for rare kaon decay. The search techniques, which he conducted at BNL’s Alternating Gradient Synchrotron, had much in common with SUSY search techniques. It was BNL theorist Frank Paige who hooked Redlinger onto the SUSY search after he joined the ATLAS experiment in 2005.

Redlinger received his bachelor’s degree in physics from Johns Hopkins University and pursued graduate work at the University of Chicago, conducting research at Fermilab’s Tevatron accelerator.

For Redlinger, who was a graduate student during the Tevatron’s first collisions 25 years ago, the first collisions at the LHC have a curious air of déjà vu about them.

“I remember professors telling me when the Tevatron’s collisions started that this was it,” he said. “We were going to find the Higgs boson, supersymmetry, all of these things that now we’re saying we’ll find at the LHC.”

Now, he is more aware than ever of how tantalizingly close they might be to discovery. If superpartners exist at a mass just a little bit greater than what the Tevatron has attained, the data from the LHC may already contain signs of SUSY.

“There’s a chance that we’ll be lucky,” he said. “We’ve already collected a huge amount of data and we’re working furiously.”

– Daisy Yuhas

Guest author

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Fermilab takes fun to DC

November 16, 2010 | 10:00 am

This story first appeared in Fermilab Today on November 12, 2010.

A group of preteen girls entered the Fermilab exhibit tent on the Washington, D.C., Mall and pushed forward to stare at the numbers whizzing by on an electronic counter. 6,000. 6,015. Their foreheads crinkled.

Adrian Mead, a high school senior, spoke directly to the girls.

“It’s counting the number of cosmic ray muons that go through the two detectors in a short time,” he said, pointing to a laptop-sized block covered in electrical tape with PVC pipe and wires sticking out of it. He marked off a space with his fingers that was smaller than a postage stamp. “There are thousands going through an area like this right now.”

The girls leaned forward to get a closer look.

Interactivity — and often an air of mystery — marked most of the more than 1,500 exhibits and 75 stage shows that took over the National Mall in late October for the first U.S. Science and Engineering Festival. Fermilab and 350 of the nation’s leading science and engineering organizations joined together in the hopes of engaging the nation in the wonders of science and inspiring youth to consider scientific careers. To meet the needs of a competitive global economy, science and engineering jobs in the U.S. have grown at twice the rate of the American workforce as a whole, reported the National Science Board.

Mead plans to pursue a career in mathematics, though he said that he’s really attracted to the gee-whiz-type facts that populate particle physics. He told the girls that the invisible muon particles the detector counts — cascading remnants of the energy of the sun — are all around them. He also told them that his friends in his Oakton High School science class made the detector to make the particles visible to the computer. He held off on telling them billions pass through their body each second. “I didn’t want to make them cry,” he said.

He got a lot of questions from the crowd that often measured three deep at the Fermilab booth about how the detector works. If he didn’t know an answer, he simply turned to one of the scientists working the exhibits around him or the Education Office staff. They filled in the blanks about how particle physics experiments build high-tech versions of this type of detector to look for dark matter and even the Higgs boson. They also explained how the national QuarkNet program provides schools such as Mead’s with these detectors to let students get a hands-on feel for science and share data with schools across the globe. Several teachers took notes.

“Not all principals know this stuff exists,” said Pam Greyer, who organizes science courses with middle and high school teachers in Chicago. “Our kids graduate, and there’s a huge piece of the world they are missing.”

These types of hands-on festivals give children and parents a chance to develop an appreciation for science, which can encourage them to seek other avenues for learning, she said.

For those who weren’t new to science, the festival offered a chance to expand their knowledge about modern science, such as particle physics, rarely found outside of college textbooks.

Game-like exhibits made the introduction to the topics easy. A U-shaped track let visitors ram steel balls together to learn about how energy gets exchanged during collisions, just as occurs with protons and antiprotons that collide in Fermilab’s Tevatron accelerator. Shooting balls down a table at hidden targets demonstrated how scientists must use probability calculations to determine the diameter of the target, similar to the way scientists probe a nucleus.

Those who wanted to put a face on science got a chance to visit with Nobel Laureate Leon Lederman or TV personality Bill Nye the Science Guy, whom Mead wandered off to find.

“He got me interested in science when I was a kid,” he said.

Maybe one of the festival visitors will say the same thing about Mead one day.

Photos by Reidar Hahn, Fermilab

Tona Kunz

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LHC basics: What we can learn from lead-ion collisions

November 12, 2010 | 10:22 am

The LHC has been smashing lead ions since Sunday, and physicists from the ALICE, ATLAS and CMS experiments are working around the clock to analyze the aftermath of these heavy-ion collisions at record energies and temperatures.* Last week we walked you through the process of creating, accelerating and colliding lead ions. Now we’ll talk about the big question: Why spend one month each year colliding heavy ions in the LHC?

The building blocks and mini ‘big bangs’

To understand why physicists around the world study heavy-ion collisions, we need to review some basic particle physics and discuss what happens when two nuclei collide at ultra-high energies.

First, the basics. Everything you see around you is composed of atoms, which are themselves composed of protons and neutrons bound together in an atomic nucleus, surrounded by a cloud of electrons. Electrons are one of the basic building blocks of matter, but protons and neutrons are not—they are in turn composed of elementary particles called quarks.

The strong force binds quarks inside composite particles, such as protons, via other elementary particles called gluons. Thus lead nuclei, which are made up of protons and neutrons, are really composed of many quarks and gluons.

When two lead nuclei slam into each other at high enough energies, they form a fireball of hot, dense matter. The temperatures created in the fireball are so great that they ‘melt’ the protons and neutrons. The result is a state of matter called the quark gluon plasma, in which quarks and gluons roam freely. The QGP exists for only an instant before the fireball expands and cools to the point where quarks and gluons once again form composite particles.

The LHC is not the first accelerator to create QGP. CERN announced indirect evidence for the “new state of matter” in 2000, a result of experiments in the 1980s and 1990s at the Super Proton Synchrotron (now used as the injector for the LHC). Next up was Brookhaven National Laboratory’s Relativistic Heavy Ion Collider. In 2005 scientists from the RHIC experiments tentatively claimed the creation of a QGP in collisions of gold nuclei. Physicists at the LHC are now studying collisions of lead nuclei—and the properties of the QGP that should be produced in those collisions—at energies more than 13 times higher than at RHIC.

From bang to being—why we care

Physicists believe that the universe was filled with QGP millionths of a second after the big bang, until it expanded and cooled enough for the very first composite particles to form. This process is mirrored at very small scales in heavy-ion collisions, allowing scientists to study in the laboratory one of the early stages of the universe’s evolution. By creating millions of QGPs over the next month, scientists will learn more about how the basic building blocks of matter—quarks and gluons—come together to form particles, which in turn form all the matter in the universe.

One specific area of interest for LHC physicists is confinement. It appears to be impossible to observe quarks and gluons in isolation. Outside the quark gluon plasma, they are always confined within composite particles. The exact mechanism that causes this confinement is unknown. Without confinement, none of the composite particles that make up the world around us exist. So pinning down aspects of this mechanism is critical to understanding how matter evolved into the form it has today.

QGP will also be used to study the mystery of mass. Physicists are eagerly hunting for the Higgs boson in proton collision data, but finding the Higgs would only explain how the elementary particles such as quarks get their masses.  Another unsolved puzzle is where most of the mass of a proton or neutron comes from. Protons and neutrons are made up of three quarks each, but adding up the masses of the three quarks only accounts for about 1 percent of the proton or neutron mass. Physicists hope to find clues to the missing 99 percent in the behavior of the QGP.

One step at a time

Even with higher-energy collisions and more sophisticated detectors than ever before, LHC scientists won’t solve all the mysteries of quark confinement or the proton’s missing mass. But with only five days’ worth of data collected, physicists in the ALICE, ATLAS and CMS experiments are already working feverishly to produce the first new QGP measurements that will improve our understanding of the strong force.

With the very first data, physicists will study the heavy-ion collision environment at the highest energies ever produced in the laboratory. Some of the very first measurements to be published from the ALICE, ATLAS and CMS experiments with lead-ion collision data will describe the number of particles produced in such collisions, which will confirm or rule out various theoretical predictions.

With a bit more data, scientists will measure the “flow” of the QGP. In 2005 the physics community was surprised by RHIC physicists’ announcement that the QGP created in gold-ion collisions behaved like a liquid rather than a gas. Scientists don’t yet know—but will very soon—whether the QGP created in these higher-energy lead-ion collisions will flow like a liquid or will act more like a gas.

With even more data, physicists will measure the behavior of certain types of particles as they travel through the QGP. Physicists at RHIC have shown that certain particles are suppressed as they move through the QGP, which shows that the plasma interacts very strongly with these particles. The higher energies at the LHC and the more sensitive particle detectors will allow a greater number and variety of particles to be measured.

The ALICE experiment published its first paper using proton collision data mere days after the first collisions in November 2009, so the first papers with measurements from the LHC’s lead-ion collisions should be popping up in physics journals very soon.

* A note about temperatures
If you’ve been reading the news reports on the first lead-ion collisions at CERN, you will have seen scientists and journalists claiming that LHC collisions will create temperatures anywhere from 100,000 to 1 million times hotter than in the center of the sun. Here’s an attempt to set the record straight.

• Based on measurements made at previous accelerators, the temperature at which a quark gluon plasma is created is about 100,000 times hotter than the sun’s core temperature. Above this temperature quarks and gluons are no longer confined inside other particles. (The sun’s core temperature is about 20 million Kelvin, equal to about 36 million degrees Fahrenheit.)
• At RHIC, physicists discovered that the temperature generated in the very first instant after two gold ions collide was up to 2.5 times higher than that necessary to create the quark-gluon plasma – about 250,000 times higher than the sun’s core temperature.
• This month’s lead-ion collisions at the LHC will take place at energies more than 13 times higher than at RHIC. Physicists estimate that these collisions could create temperatures up to twice as high as at RHIC, thus about 500,000 times the sun’s core temperature. When the LHC eventually runs at design energy, the temperatures could rise even higher.

Katie Yurkewicz

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