CERN opens dazzling new public exhibition

June 30, 2010 | 1:58 pm

Inside Universe of Particles (image courtesy of CERN).

It’s like stepping into a science fiction film: Eerie blue and green lighting; spherical white chairs with black cushions; touch-operated computer information stations; a full-wall projection of stars and galaxies; and a calming voice coming over a loudspeaker and asking, “Why are we here?”

If the architectural firm behind the new exhibition, Atelier Bruckner, wanted to get their audience excited about science, they have certainly succeeded. The new CERN public exhibition Universe of Particles will make a fantastic starting point for lab visitors. In dramatic fashion, it presents them with the big, exciting questions that CERN scientists would like to answer, like “What is dark energy?” and “What will be the fate of our universe?”  These questions alone will inspire excitement in many people, but the design group has used a dramatic setting to ramp up visitors’ excitement. Like a good sci-fi flick, it ignites the feeling of excitement that comes with the start of a great adventure.

The Interactive Globe features information about facilities working with CERN world wide.

From the entrance of the room, visitors notice what appears to be a large globe, standing over four feet high. But an up-close view shows that the massive ball is blank, until a projection from above turns it into a globe of the Earth. As visitors spin the globe (technically referred to as the Interactive Ball), the light projection keeps up and reveals a complete map of our planet, but with the addition of circular markers that open up to reveal information about each country’s participation at CERN. Hit a button to change the rolling display to a timeline of CERN’s history. A few other display screens use the same projection-based, touch sensitive technology that makes you feel like you’re playing with a giant iPhone.

To get away from the crowd for a moment, visitors can sink into chairs cut from white spheres, creating a small cave-like setting. Select a language, and a speaker begins to explain the search for the cause of the matter/antimatter asymmetry or the basis for string theory. Display cases, also cut out of futuristic white spheres, feature a few artifacts of physics like the first World Wide Web server and parts from old detectors.

The Globe (image courtesy of CERN).

About every half hour, the lights dim even more, and a soothing voice from above begins to narrate a visual presentation about the great universal questions that CERN science seeks to answer. The projection plays on one segment of the curved wall, and on a large angled surface in the middle of the room. When the show ends, a projection on the slanted surfaces plays recreations of particle collisions.

The new exhibit rests inside the most recognizable building at CERN, The Globe (although it is technically not on the CERN campus, but directly across the street from the main entrance). The Globe of Science and Innovation is a 130-foot-wide, 88-foot-tall sphere made of five types of timber, making it a natural carbon sink. It was built for an exhibition in Hanover, Switzerland, as a symbol of sustainable building. Two walking ramps spiral up the outside of The Globe from the ground floor (where the exhibition is located), and another walking ramp connects the two floors from the inside.  The second floor is a high-ceilinged room with exposed wood walls. CERN uses the space for some press conferences and public events. The bottom half is now dedicated to the exhibit center, along with the hallway winding down on the inside, which features posters explaining the big bang.

During the audio visual presentation inside Universe of Particles (image courtesy of CERN).

Rolex sponsored the entirety of the exhibition hall, and Jacques Baur, Associate Director and Head of Research for the company, spoke at a press event for the new exhibition last week. Baur emphasized just how impressed he was with the detectors he saw at CERN and the work going on there. He discussed how the exhibit falls under Rolex’s philosophy of philanthropy, particularly toward science.

Universe of Particles is open to the public starting July 1, 2010.

Calla Cofield

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CMS Exotica hotline leads hunt for exotic particles

June 24, 2010 | 1:59 pm

Strangers in the dark: they meet, make contact, and break away with force, careless of what they leave behind. At midnight each night, snapshots of these frenzied chance encounters are collected for curious eyes. In the morning, those onlookers reconstruct the story that each image tells, tracing the mysterious paths born from a fateful meeting.

This is the CMS exotica hotline, and no, it’s not a 900 number.

Those snapshots are event displays, pictorial descriptions of proton collisions in the CMS detector, selected from the previous 24 hours. Every morning, 10 CMS collaborators volunteer to review between 20 and 100 hotline displays to get a sneak-peek at the latest data. By picking out the most unusual events first, CMS physicists hope to learn more about how the detector is functioning and spot exotic physics.

Exotic physics is the physics that breaks rules and defies expectations. This is the realm beyond the Standard Model and even beyond supersymmetry —the domain of the unstable and excited, the string balls, black holes, and extra dimensions. The CMS group devoted to seeking out these events is called the exotica group, and the hotline supports their search.

Every morning, CMS collaborator Tulika Bose of Boston University, a lead developer of the hotline, scans event displays to parse potential physics from peculiar equipment signals. She explains that the hotline offers an open-minded way of developing new search criteria for exotic events.

“New physics at the LHC may have none of the characteristics that our search groups are looking for, so this helps cover the area of the unknown,” Bose says.

The concept is not without controversy. Event displays are traditionally created only after extensive analyses suggest an event deserves a closer look. The exotica hotline, in a sense, works backwards, using a graphic display before numerical analysis.

“The hotline is not to replace the analysis,” says Massimiliano Chiorboli, a CMS collaborator who co-designed the software for the exotica hotline. “CMS is a very big community and a lot of people are working on analysis. We want to provide more information to those analysts and show the community when we recognize something special.”

The inspiration for the project comes from a previous CERN experiment on the Super Proton Synchrotron. In the ’80s, the UA1 experiment’s control room kept a bell that collaborators would ring at the first hint of a special event. A similar early warning system was later used by experiments at DESY’s HERA and Fermilab’s Tevatron collider. This inspired Chiorboli, of the University of Catania and INFN, and CERN’s Maurizio Pierini to develop a similar system to alert their collaborators.

At midnight each night, Chiorboli and Pierini’s program collects express-stream events from the previous day. The express-stream data is a subset of the total collected CMS data, assembled and reconstructed into recognizable physics events for those who need to quickly check the detector’s condition. Displays for the hotline are filtered to include only the most convincing and interesting events.

Around 9 a.m., the hotline software sends an automated e-mail summarizing select displays. The 10 volunteers who receive this e-mail come from all areas of the collaboration. They critically examine the hotline to decipher what they see. Volunteers are also on the lookout for strange events that could be misleading or distracting in later analysis.

Thus far, the hotline has called attention to unusual detector signals and rare but familiar physics, such as Z and W bosons. That makes this an ideal time to fine-tune the hotline’s filters, a task that Alexey Ferapontov of Brown University, who looks for exotic multi-jet events, assists.

“The exotica hotline cannot be treated as an analysis, but it gives us valuable experience,” Ferapontov says. “The whole CMS collaboration can profit from this and there is always the possibility that we find something really new and unseen before. This makes participation very fun!”

The exotica hotline offers new thrills to CMS collaborators in their physics searches—and what’s more, they won’t get in trouble for watching at work.

by Daisy Yuhas

Symmetry Intern

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Possible multiple Higgs role in matter-antimatter balance gets a blessing

June 22, 2010 | 6:10 pm

The idea that a preference in meson decays for matter over antimatter could point to a whole world of unseen particles, including multiple Higgs bosons, just got a blessing.

Physical Review Letters this week accepted a paper titled “CP violation in B_s mixing from heavy Higgs exchange”, or in layman terms, “Supersymmetric Higgs bosons may tilt the matter-antimatter balance” . The paper should appear in the journal shortly. PRL is considered by many the top clearing house for original papers about particle physics results and theories. Acceptance in the journal means the paper passed review by peers in the field, akin to the peer review that occurs for doctors in the Journal of the American Medical Association.

symmetry wrote in “Could DZero result point to multiple Higgses?” on June 4 about the preprint of this paper, written by a trio of Fermilab theorists, before it had passed peer review.

The Higgs boson, whether one or many, is thought to exist as an energy-type field that imparts all other particles with their mass as they pass through it. Mass allows particles to  join together to form the visible  structures in the universe.

While this theory paper points out that a multiple Higgs scenerio is one of several possible interpretations of the May DZero asymmetry result, the multiple Higgs idea is what has piqued interest by media including a National Geographic “God Particle May Be Five Distinct Particles, New Evidence Shows” and a BBC article “US experiment hints at ‘multiple God particles’.” Nobel Prize winner Leon Lederman, a Fermilab physicist, dubbed the Higgs particle the “God Particle” in his book by the same name, though the moniker has limited acceptance within the academic physics world.

A plenary talk of this paper given at the Planck 2010International Conference held at CERN didn’t draw criticism but the idea recently has drawn fire from physicist bloggers questioning the theory and the DZero result that it interprets. An excerpt from a June 18 update of the symmetry story that looked at the debate:

Complexity also breeds debate, and sometimes rumors. In particular, two rumors seem to have gained traction: that CDF already did a comparable study to DZero’s that negates the DZero claim of a 1 percent predisposition of muons over antimuons, and that CDF  for technical reasons cannot conduct an analysis that could confirm or deny the result.

First, did CDF already rule out the DZero result? No …

… This brings up the second rumor: Can CDF cross check the DZero result? Yes

So stay tuned…

Tona Kunz

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CERN Council opens the door to greater integration

June 21, 2010 | 11:56 am

This release was issued on June 18, 2010, by CERN.

At its 155th session [Friday], the CERN Council strongly congratulated the Laboratory on the excellent performance of the LHC since its start-up for physics on 30 March this year. Council also opened the door to greater integration in particle physics when it unanimously adopted the recommendations of a working group set up in 2008 to examine the role of the Organization in the light of increasing globalization in particle physics.

The key points agreed at today’s meeting are that:

- All states shall be eligible for Membership, irrespective of their geographical location;
- A new Associate Membership status is to be introduced to allow non-Member States to establish or intensify their institutional links with the Organization;
- Associate Membership shall also serve as the obligatory pre-stage to Membership;
- The existing Observer status will be phased out for States, but retained for International Organizations;
- International co-operation agreements and protocols will be retained.

Applications for Membership from Cyprus, Israel, Serbia, Slovenia and Turkey have already been received by the CERN Council, and are undergoing technical verification. At future meetings, Council will determine how to apply the new arrangements to these States.

“This is a milestone in CERN’s history and a giant leap for particle physics”, said Michel Spiro, President of the CERN Council. “It recognizes the increasing globalization of the field, and the important role played by CERN on the world stage.”

“Particle physics is becoming increasingly integrated at the global level,” said CERN Director General Rolf Heuer. “Today’s decision contributes to creating the conditions that will enable CERN to play a full role in any future facility wherever in the world it might be.”

In other business, Council recognized that further work is necessary on the Organization’s medium term plan, in order to maintain a vibrant research programme through a period of financial austerity, and endorsed CERN’s new Code of Conduct.

“CERN’s new code of conduct enshrines the core values of this Organization,” said Spiro, “integrity, commitment, professionalism, creativity and diversity – which taken together add up to excellence.”

Full details of the new Membership arrangements are available in Council document CERN/2918.

Press Release

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MiniBooNE results suggest antineutrinos act differently

June 18, 2010 | 12:41 pm

A comparison of the energy spectrum for MiniBooNE electron neutrino (top) and antineutrino (bottom) candidates. The MiniBooNE experiment has found that antineutrinos, which should follow the same rules as neutrinos, might oscillate in a slightly different way. Data is shown in blue points and compared to expected backgrounds. Data is taken with 6.5x1020 (neutrino beam) and 5.7x1020 (antineutrino beam) protons delivered to the MiniBooNE target. Statistical errors are shown on the data points, while systematic uncertainties are plotted on the background.

Neutrinos, the ubiquitous daughters of the weak interaction, start their universe-traversing lives as one of three varieties: ν_e, ν_μ, or ν_τ. However, like ghosts with an identity crisis, these phantasmal particles find themselves constantly morphing from one variety to another, or oscillating, as they propagate on their long journeys.

Now the MiniBooNE experiment has found that antineutrinos, which should follow the same rules as neutrinos, might oscillate in a slightly different way. The results seem to favor a much-debated antineutrino result obtained by the Liquid Scintillator Neutrino Detector experiment in 1990.

The MiniBooNE experiment studies these oscillations by creating intense beams of muon neutrinos and antineutrinos, and directing them at an 800-ton sphere filled with mineral oil and located a half a kilometer away from the beam’s source. The vast majority of these particles pass through the detector unscathed; however, a few unlucky voyagers pass too close to a carbon nucleus. The neutrinos, or antineutrinos, interact with carbon nuclei, giving scientists a glimpse of the particles’ true identities.

MiniBooNE counts how many muon antineutrinos oscillate into electron antineutrinos over a relatively short distance. A 1990 result from the LSND experiment at Los Alamos, which used a beam of muon antineutrinos, reported electron antineutrinos appearing about 0.25 percent of the time. The result is difficult for scientists to reconcile in a world with only three active neutrinos.

Earlier this week, after nearly three years of running in antineutrino mode, MiniBooNE collaborators announced that they had obtained a result consistent with the findings from LSND. In fact, analyzing the data in the context of a standard two neutrino mixing model favors an LSND-like signal at a 99.4 percent confidence level. However, model-independent tests show there is still a three percent chance that background fluctutations could mimic the data. While this new result is intriguing, a confirmation of LSND will require more data.

Interpretations of the latest MiniBooNE results are complicated due to an apparent difference between the way neutrinos and antineutrinos behave. In a prior analysis based on four years of running with a beam of muon neutrinos, the MiniBooNE experiment did not observe significant evidence for muon neutrinos oscillating to electron neutrinos in the energy range expected under the simplest models for explaining the LSND result. However, an excess was observed at lower neutrino energies (below 475 MeV) at a 3 sigma significance that remains unexplained.

Interestingly, the MINOS results announced earlier this week also raises the question as to whether neutrinos and antineutrinos behave differently.

The MiniBooNE experiment continues to acquire data, and scientists on the project are hoping to nearly double the antineutrino statistics before the experiment finishes acquiring data within the next two years. Future experiments, such as MicroBooNE or BooNE, a proposal to build a second MiniBooNE detector at a near location, could help to shed more light on these results.

This story first appeared in Fermilab Today on June 18, 2010.

Rhianna Wisniewski

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Three nerds walk into a bar…

June 15, 2010 | 9:46 am

Forty-odd Chicagoans gathered in a bar on June 3, not to watch the Blackhawks in the Stanley Cup finals, but to hear Jason St. John talk about particle colliders, the Standard Model and how the Large Hadron Collider won’t be the end of us all.

His lecture was part of Chicago’s inaugural Nerd Nite, a monthly series of informal talks intended to educate and entertain the community’s “lay nerds,” as St. John describes them, while they kick back with beers and martinis.

It was a far cry from the Ben Stein chalk talk that many have in mind when picturing physics presentations.

“He totally turned that upside-down,” says attendee Maurice Ball of the Mechanical Support Department in the Accelerator Division at Fermilab.

“Not that many people know quantum field theory or how to calculate branching ratios … but it’s not that hard conceptually,” says St. John, who helped organize the event.

As it turns out, it made for great Nerd Nite material.

Inside the California Clipper, an old-fashioned lounge in Chicago’s Humboldt Park neighborhood, St. John, who works on the CMS experiment at the LHC, took the mic in front of a largely graduate-student crowd. His aim was to unpack a topic that, while attracting a good deal of hoopla, is little understood by the public: the subatomic realm. With as much humor as studied consideration, he examined the controversy that made the LHC a hot news item a year ago – its reputation in some circles as an instrument of the world’s annihilation.

Conceding that it isn’t clear how to calculate how often proton collisions will produce black holes – which is why there’s controversy in the first place, he says – St. John laid out the physical arguments against the likelihood of a doomsday scenario in a way that was accessible to people who may have been hearing the term Planck scale for the first time.

“It was stuff I’d heard a hundred times before, but he explained it in a way that made you go ‘Oh, okay!’” Ball says.

Halley Brown, a scientist working on the CDF experiment at Fermilab, agrees. “I think the audience was kind of excited to hear an explanation that they could understand,” she says.

After the black hole lesson, St. John moved on to the science of high-energy physics. A cartoon of a proton beam collision – a big hit with the audience – led to a lively lesson in proton structure, the four fundamental forces, the rules governing the interactions between particles and what matter is and isn’t.

“Then I could show them Feynman diagrams that looked like animals: penguin diagrams, and others that look like dogs,” St. John says.

“St. John can explain a very complicated topic to … regular ‘civilians’ and make it exciting, funny and intriguing,” Ball says, noting that St. John created an environment where people could just blurt out questions.

St. John’s talk anchored an evening of three lectures, the first entitled “Parasitic Birds, Sex, Lies, and Dinosaurs.” A second lecture about 19th century Shakers had audience members singing a hymn in chorus.

As for St. John’s presentation, “It made me proud to be a part of this whole high-energy thing,” Ball says.

Nerd Nite began in Boston in 2003 and has since spread to Austin, Washington D.C., New York City and San Francisco.

Check out the event’s Web page.

by Leah Hesla

Guest author

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New measurements from Fermilab’s MINOS experiment suggest a difference in a key property of neutrinos and antineutrinos

June 14, 2010 | 12:24 pm

The oscillations of antineutrinos depend on two parameters: the square of the antineutrino mass difference, Δm2, and the antineutrino mixing angle, sin22θ (shown in red). MINOS has found Δm2 = 0.0034 ± 0.0004 eV2. The MINOS neutrino results are show in blue for comparison. Theorists expected the values for neutrinos and antineutrinos to be the same.

Scientists of the MINOS experiment at the Department of Energy’s Fermi National Accelerator laboratory today (June 14) announced the world’s most precise measurement to date of the parameters that govern antineutrino oscillations, the back-and-forth transformations of antineutrinos from one type to another. This result provides information about the difference in mass between different antineutrino types. The measurement showed an unexpected variance in the values for neutrinos and antineutrinos. This mass difference parameter, called Δm² (“delta m squared”), is smaller by approximately 40 percent for neutrinos than for antineutrinos.

However, there is a still a five percent probability that Δm² is actually the same for neutrinos and antineutrinos. With such a level of uncertainty, MINOS physicists need more data and analysis to know for certain if the variance is real.

Neutrinos and antineutrinos behave differently in many respects, but the MINOS results, presented today at the Neutrino 2010 conference in Athens, Greece, and in a seminar at Fermilab, are the first observation of a potential fundamental difference that established physical theory could not explain.

“Everything we know up to now about neutrinos would tell you that our measured mass difference parameters should be very similar for neutrinos and antineutrinos,” said MINOS co-spokesperson Rob Plunkett. “If this result holds up, it would signal a fundamentally new property of the neutrino-antineutrino system. The implications of this difference for the physics of the universe would be profound.”

The NUMI beam is capable of producing intense beams of either antineutrinos or neutrinos. This capability allowed the experimenters to measure the unexpected mass difference parameters. The measurement also relies on the unique characteristics of the MINOS detector, particularly its magnetic field, which allows the detector to separate the positively and negatively charged muons resulting from interactions of antineutrinos and neutrinos, respectively. MINOS scientists have also updated their measurement of the standard oscillation parameters for muon neutrinos, providing an extremely precise value of Δm2.

Muon antineutrinos are produced in a beam originating in Fermilab’s Main Injector. The antineutrinos’ extremely rare interactions with matter allow most of them to pass through the Earth unperturbed. A small number, however, interact in the MINOS detector, located 735 km away from Fermilab in Soudan, Minnesota. During their journey, which lasts 2.5 milliseconds, the particles oscillate in a process governed by a difference between their mass states.

“We do know that a difference of this size in the behavior of neutrinos and antineutrinos could not be explained by current theory,” said MINOS co-spokesperson Jenny Thomas. “While the neutrinos and antineutrinos do behave differently on their journey through the Earth, the Standard Model predicts the effect is immeasurably small in the MINOS experiment. Clearly, more antineutrino running is essential to clarify whether this effect is just due to a statistical fluctuation.”

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

Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated under contract by Fermi Research Alliance, LLC.

View the press release

Rhianna Wisniewski

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Rewriting textbooks and remeasuring the particle data booklet at the LHC

June 14, 2010 | 6:07 am

A pi-zero particle decay, as seen by the ALICE detector at the LHC. Image credit ALICE Collaboration

Textbooks were being rewritten during last week’s Physics at LHC conference.

“I was sitting in the session, listening to the ALICE talk by Andrea Dainese from Padova on Wednesday morning, and suddenly I knew: I could replace all the textbook bubble-chamber pictures from the sixties in my lectures,” said DESY’s Thomas Naumann, a member of the ATLAS collaboration.

Naumann’s revelation was sparked by an image showing a neutral pion decaying into two photons that then convert into two electron-positron pairs in the the ALICE inner tracker. Generations of physicists have learned about the history and characteristics of neutral pions, also called pi zero particles, in their undergraduate classes and textbooks. Until now, the decay of a pi zero particles was always illustrated with a picture from a 1950s- or 1960s-era bubble chamber experiment.

Pi zeros aren’t rare; in fact their decays are responsible for most of the photons seen in the LHC detectors. They are used as standard candles to calibrate detectors, which is why every student of particle physics has to know them inside out.  They’re also one of the many known particles being rediscovered by particle physicists using the first LHC collision data.

Theorist Hitoshi Murayama's prediction for a page in the PDG in 2016.

The particle physicist’s bible, the booklet published by the Particle Data Group or PDG, played an important role at the Physics at LHC conference. It contains tables with all the possible data for all existing and hypothetical particles, such as their mass, charge, flavor, lifetime and decay modes. LHC physicists are rediscovering the known particle families from strange through charm, and bottom through (hopefully soon) top, and in a matter of weeks they have almost reached the statistical precision currently listed in the PDG for many measurements.

The known particles aren’t the only ones being reassessed; theoretical physicists are also hard at work refining their predictions about particles and their behavior. In his talk, theorist Hitoshi Murayama of Japan’s Institute for the Physics and Mathematics of the Universe showed his vision of what the PDG could look like in a few years. A slide from his talk—originally called ‘Theories of Beyond the Standard Model Physics’ but renamed “How stupid theorists are and Why LHC matters”—features a page from the PDG in 2016.

by Barbara Warmbein

Guest author

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Drinking data from a fire hose at the LHC

June 11, 2010 | 1:21 pm

This article first appeared June 11 in Fermilab Today.

With 2 1/2 months of running the Large Hadron Collider’s CMS experiment under our belts, our mid-range goals have evolved. Initially we were happy to record any interactions at a collision energy of 7 trillion electron volts. However, it’s important to recall that the beam energy is only one of the important parameters in a particle collider. A second critical parameter is the brightness of the beams, and, in the first few weeks of running, the brightness of the beams was tiny. Under these circumstances, the number of collisions per second was quite modest, and we could record every collision that occurred.

The amount of beam delivered has increased enormously. In the month and a half (45 days) since beginning operations, the amount of beam delivered is more than 10,000 times what we saw on the first day.

However, the beam brightness has steadily increased over the past two and a half months. It currently takes a minute to see as many collisions as we used to see in a day. Very soon, the same number of collisions will take seconds. Those of us of a certain age might remember the old I Love Lucy episode in which she and Ethel wrap candy. It starts out easily, but the rate quickly increases until they can no longer handle it and chaos ensues. This is essentially the situation in which the CMS detector collaborators find themselves.

Of course, this was anticipated. Today’s thousands of collisions per second are a far cry from the designed 800,000,000 collisions per second. To cope with the deluge, CMS designed an extensive trigger system. As the torrent of collisions occurs in the center of the detector, carefully designed electronics inspect them all and select those that are most likely to include a discovery. The LHC is now delivering enough beam that we must utilize the trigger system to record only a portion of the collisions.

This is a unique time in the lifetime of an experiment. About every week, the amount of beam delivered by the LHC doubles. With our trigger electronics doing their job, we look forward to seeing our data set grow in leaps and bounds.

by Don Lincoln

Guest author

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Scientists present first “bread-and-butter” results from LHC collisions

June 8, 2010 | 8:50 am

One slide from CMS spokesperson Guido Tonelli's presentation, showing a preview of the results to be presented by members of the CMS collaboration at "Physics at LHC."

It’s been just over two months since the first high-energy proton collisions took place in the Large Hadron Collider, and scientists from the LHC experiments have been working feverishly to analyze the data now pouring from their detectors. The results of these first analyses using real LHC data are being presented this week at the “Physics at LHC” conference. The conference, taking place at the DESY laboratory in Hamburg, Germany, is the first in this summer’s series of international particle physics conferences.

LHC scientists have not yet found the Higgs boson, nor any hints of supersymmetric particles; these discoveries require much more collision data than has yet been collected. But nevertheless there is excitement among the 270 conference participants, who have been waiting years–in some cases decades–for the first proton-proton collisions at the LHC. With these data, particle physicists are doing what they call “bread-and-butter” physics: rediscovering the Standard Model.

The Standard Model of particle physics is the best theory that physicists currently have to describe the building blocks of the universe. With the exception of the discovery of the Higgs boson, the model has been very precisely measured at other particle accelerators and can thus be used as a touchstone to see if the LHC detectors work properly. Physicists also repeat Standard Model measurements to verify that their simulated data correspond to real data. The simulated data, also known as Monte Carlo data, will play a critical role in future discoveries.

The spokespeople of all four major LHC experiments–ALICE, ATLAS, CMS and LHCb–kicked off the first day of the conference by presenting results from their experiments since the first low-energy collisions in November 2009. All four spokespeople reported that the detectors work exceptionally well, have been able to record most of the collisions provided by the LHC, and that the known Standard Model is emerging beautifully in all of them. The CMS collaboration, for example, has caught the J/ψ particle 1,230 times.

“In other experiments I suffered a lot and for a long time to reach this point,” recounted CMS spokesperson Guido Tonelli. “At the LHC we get there in a few weeks. Amazing.” Tonelli was similarly proud of the detector’s performance in a process that hunts for secondary decays of beauty quarks, called b tagging. “There were people who thought it would be years before sophisticated techniques like b tagging could be used.”

With their detector recording an uptime of 90 percent, and good agreement between Monte Carlo data and real collisions, the members of the ATLAS collaboration are also having fun rediscovering the Standard Model. ATLAS spokesperson Fabiola Gianotti pointed out that the production of W and Z bosons had been previously measured, “but never before in proton-proton collisions.” ATLAS has submitted a total of six million jobs to the Worldwide LHC Computing Grid, with a total of 45 billion events analyzed.

Just as happy with their new collision data is the LHCb collaboration. Because of its salami-like slices (rather than the onion-like layers of the other three major LHC experiments) LHCb could not use cosmic rays to check and align its subdetectors. Precise detector alignment is crucial for experiments that are measuring the decays and paths of fundamental particles, thus the first collisions were especially important for LHCb, said spokesperson Andrey Golutvin. Similarly, spokesperson Jurgen Schukraft reported that ALICE detector is now now aligned and “literally in good shape.”

Bread and butter have never tasted so sweet.

The rest of the week will bring more results from the LHC experiments, so stay tuned to Symmetry Breaking for an update, or view the conference agenda to watch recorded videos or view slides from previous presentations.

by Barbara Warmbein

Guest author

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