LHC experiments dive into the quark gluon plasma

May 23, 2011 | 3:03 pm

Experiments at the Large Hadron Collider have begun to prove their worth among scientists who study the quark gluon plasma, a hot soup of unbound particles theorists say made up the universe just after the big bang.

The highest peak on the graph shows the production of tightly bound upsilons in both proton-proton and heavy-ion collisions. The bumps outlined in dotted blue show the production of the two other upsilon states in proton-proton collisions, while the red line shows the same production in heavy-ion collisions.

This week at Quark Matter 2011, scientists from LHC are sharing the results of their experiments, which have elevated studies of the QGP to a whole new energy level. Their observations of how particles react to the plasma have given them new hints as to its temperature and the strength of its influence.

“It’s a very exciting time,” said Brookhaven National Laboratory physicist Peter Steinberg of the ATLAS collaboration. “Now that we’ve all shown our hands, we’re going to start comparing results.”

Scientists from the CMS experiment gained new insights from the studies of particles called upsilons. An upsilon is a bound state of a bottom quark and its antiparticle. Upsilons come in three basic bound states, each almost identical to the next except for the strength of the bond between its quarks.

During most of the year, scientists at the LHC collide protons in their detectors. But for one month, they take a break from the usual fare to collide heavy ions. Heavy ion collisions have the ability to create quark gluon plasma.

Scientists on the CMS experiment at the LHC compared the production of the three states of upsilons in both types of collisions. Heavy-ion collisions seemed to produce a smaller fraction of lightly bound upsilons than proton-proton collisions. This could be because the less tightly bound upsilons break up in the heat of the quark gluon plasma, but not the most tightly bound ones.

The fact that only some types of upsilons melt apart in the QGP gives scientists a great tool for divining the temperature of the plasma. They can calculate the energies at which the different states would break apart. They know from experiment that the QGP is hotter than the breaking points of the weakest two states but cooler than that of the strongest one.

“Temperature is one of the most fundamental parameters,” said MIT scientist Bolek Wyslouch of the CMS collaboration. “Once you know that, you can look at other things.”

Scientists on the ALICE, ATLAS and CMS experiments have studied the interactions of other particles with the QGP. J/psi particles also seem to break up in the quark gluon plasma, but they only come in one easily measurable bound state. Photons and Z bosons do not interact strongly and so seem unaffected by the quark gluon plasma.

Another phenomenon scientists are using to reveal the secrets of the quark gluon plasma is jet quenching. Particle collisions often produce sprays of particles that fly away from the interaction point in opposite directions. Scientists looked that these back-to-back jets created in the quark gluon plasma and found that many of them were imbalanced. The jets on the side with a greater density of the plasma shrank significantly before shooting out the other side, apparently sapped of their energy by the QGP.

Scientists at Brookhaven National Laboratory previously studied jet quenching at the RHIC accelerator. This year, the ATLAS and CMS experiments were able to study jets in finer detail. This is because the particles in jets created in LHC collisions have greater energy and because the detectors at LHC experiments cover more area around the collision point than those at RHIC. The ALICE experiment will be able to do the same later this year, now that its new calorimeter is in place.

“LHC experiments have taken a giant step toward understanding the properties of the quark gluon plasma,” said Yale physicist John Harris of the ALICE experiment. “To me that just jumped out at the conference. We’ve made a quantum leap.”

Read the CERN press release.

Kathryn Grim

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May 2011 issue of symmetry available

May 19, 2011 | 1:20 pm

The new issue of symmetry focuses on what may be the ultimate killer app for particle physics technology — the light source.  These large, versatile machines harvest the light given off by accelerating particles and wield it, Swiss-Army-knife fashion, to perform all sorts of research — materials, energy, biology, drug discovery, you name it.

In “Shedding Light,” Lori Ann White traces light sources from their humble origins in the 1970s — when experiments took place in little sheds grafted onto accelerator rings used for particle physics experiments — to the explosion of research taking place today and the latest light source technology, the free-electron laser.

John Galayda describes the “beautiful combination” of physics, technology, creativity and practical applications that drew him into light source work; Herman Winick explains synchrotron radiation in 60 seconds; and the symmetry logbook takes a look at early light source experiments on protein structure in a Sears garden shed at SLAC.

Plus:

– The inside buzz on the Long Baseline Neutrino Experiment: It takes a hive to pull off a big project like this one

– Why the standoffish attitude of noble elements appeals to hunters of dark matter and neutrinos

– Hammering nails with a banana:  A science festival attracts a million people to Washington, DC

– Far-flung parts for the Dark Energy Camera come together in Chile 

– How particle accelerators help keep baby bottoms dry

As always, a pdf of the issue is available for download.

Glennda Chui

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Endeavour launch lifts search for dark matter, antimatter to new heights

May 16, 2011 | 8:54 am

This morning the Endeavour launched from the Florida coast on its final mission. The NASA shuttle will deliver to the International Space Station the largest physics experiment to blast into space, the Alpha Magnetic Spectrometer.

AMS-02 will allow scientists to study highly energetic subatomic particles outside Earth’s atmosphere to search for signs of dark matter and primordial antimatter, or antimatter created during the big bang. Fifty-six institutions from 16 countries take part in the AMS-02 collaboration.

Read more about the experiment.

Kathryn Grim

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New movie with far-fetched “Big Bang” scenario released today

May 13, 2011 | 9:57 am

The Big Bang, a sci-fi particle physics inspired film, opens today.

Picture this: The abandoned underground tunnels for what would have been the world’s largest particle accelerator get taken over by a billionaire/physicist duo that plans to recreate the Big Bang and bring about the end of the world as we know it.

Sound like great movie fodder? Director Tony Krantz certainly thought so. It’s the basis of his new movie, The Big Bang, a neo-noir thriller which comes out in theatres today (view the trailer online. Caution: Not safe for work).

According to the movie synopsis, a Los Angeles private eye (Antonio Banderas) is on a hunt to find a Russian boxer’s stripper ex-girlfriend. Along the way he meets some interesting characters, including a particle physics-obsessed waitress, played by Autumn Reeser, and the folks who are intent on destroying the world. It all sounds very complicated.

Now don’t you worry, all you physicists and folks out there who appreciate good science. I see you scratching your head with a confused look on your face. And understandably so, as the particle physics scenario put forth in this movie is not feasible at all.

But is that really a bad thing?

“Well, obviously it’s not sound science,” said Jennifer Ouellette, science writer and former director of the Science & Entertainment Exchange. “People hear ‘recreate the Big Bang’ and they think ‘Explosion!’ and that’s actually a function of them not really understanding what the Big Bang was, that it happens at very tiny, small sub-atomic scales.”

Although she hasn’t seen the movie yet, she had a thing or two to say about the issue of mangled science in films. While serving on the Science & Entertainment Exchange, she worked to bring more accurate science to Hollywood.

You have to bear in mind that the story is first and foremost, and “any science that’s in there has to be in service to the story,” she said.

This means you can’t expect Hollywood directors to jump at the chance to provide detailed explanations for the scientific concepts put forth in the movie.

But neither can you expect them to refrain from embellishing the science, even to the point of it being completely wrong, completely… fictional (that’s why it’s called science fiction).

Some scientists fall off the rocker when they see bad science on the big screen. But Ouellette thinks we need not respond this way.

“You can sit there and shake your finger and cluck your tongue and say this is really bad for science,” she said. “Or you can say, ‘This gives us a great opportunity, we can write blog posts, we can give talks, we can show clips in our classrooms from this movie and get a good laugh and talk about why that’s not so.’”

Fanciful science found in movies can also inspire young children to explore the wonders of science as they grow up, which can lead to future scientific advances, Ouellette said.

“Science inspires sci-fi writers and movie makers, and they in turn write these futuristic, creative takes,” she explained. “Then budding young scientists see those and grow up and want to invent those devices. It’s a very nice symbiotic relationship when it works.”

Okay, but couldn’t that be accomplished by using true science? I mean, there are people out there that will walk away from this movie thinking that high-energy particle physicists are out to destroy the world.

“The bottom line is that what [movie makers] ultimately are going to care about, and what audiences care about is characters and emotional resonance and good story,” Ouellette said.

And while, yes, it would great if the science presented in movies were at least somewhat accurate (or at least didn’t make us cringe), “good science is not why we go to the movies,” she added.

Good point.

So if you’re looking for a movie that accurately portrays what high-energy particle colliders can accomplish for society, you’re going to want to pass on this one.

But if you’re looking for a neo-noir racy sci-fi thriller with some fanciful particle physics ideas mixed in, (which could lead to nerdy science talk amongst friends), then it may be worth your while!

See what others have to say about the movie here.

– Christine Herman

Symmetry Intern

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Earthquake damage and recovery report from Japan’s KEK

May 12, 2011 | 4:04 pm

In a column published Monday, KEK Director General Atsuto Suzuki offers an overview of damage from the March 11 earthquake to the laboratory’s campuses in Tsukuba and Tokai and outlines a repair and recovery plan.  Although both sites are more than 300 km from the epicenter, the quake was so powerful — a 9 on the magnitude scale — that the shaking caused significant damage, he wrote:

In the Tsukuba-campus, components of accelerators, detectors and peripheral became detached and fell to the ground or collided with each other. Infrastructures such as the substation to receive and distribute electric power from outside, water reservoir tanks and campus roads were also damaged. Their functions have already been partially restored with quick-fix repairs. The tsunami did not affect J-PARC although it did penetrate somewhat beyond the beach area. However, there is serious subsidence and cracks have appeared in the surrounding roads, with a partial collapse of the accelerator/detector buildings. Fortunately, there has been no observed serious damage to the accelerator and detector devices located underground.

His report includes a map and details of the damage at both sites, as well as a recovery timeline, and concludes:  

Thanks to your strong and continuous encouragement, we are moving from the inspection phase to the recovery phase. All the KEK staff are maintaining their tenacious efforts not just to restore KEK, but to create a new KEK. Once again, I would like to thank you for your support.

Glennda Chui

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Why did the chicken cross the road?

May 4, 2011 | 9:40 am

Why did the chicken cross the road? Joseph Liken's answer takes the classic joke to a whole new dimension.

To escape from the wormhole that leads to the black hole of course.

That’s the answer that Joseph Likens, a second-grader at the John F. Kennedy Elementary School in Brewster, New York, provided for a classroom assignment, taking the classic joke to a whole new dimension.

Every spring, Lorna Rubin, a library media specialist at the JFK Elementary School, uses the book, “Why did the chicken cross the road?” to teach children about creative interpretation. Illustrated by 14 different children’s artists, the story presents a collection of jokes that answer the classic chicken question.

“We talk about each artist’s interpretation, and then the children come up with their own answers,” Rubin said. “So far, Joseph has been the only student I’ve had do something with black holes.”

In keeping with the spirit, we did some digging of our own and found a plethora of physics-related answers to the age old question:

(We apologize in advance for the corny nature of the following jokes. Remember, we are a particle physics magazine.)

Q: Why did the quantum chicken cross the road?

A: It was already on both sides of the road!

Q: Why did the graduate student cross the road?

A: He was writing his dissertation on the chicken.

Q: Why did the chicken cross the Mobius strip?

A: To get to the same side.

Q: Why did the chicken cross the road?

Occam: It was the simplest way to get to the other side.

Q: Why did the chicken cross the road?

Newton: Chickens at rest tend to stay at rest, chickens in motion tend to cross roads.

Q: Why did the chicken cross the road?

Einstein: Whether the chicken crossed the road or the road crossed the chicken depends on your frame of reference.

For more physics jokes with a chicken theme, visit http://www.physics.harvard.edu/academics/undergrad/chickenroad.html

Elizabeth Clements

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Keep it simple, SUSY

May 3, 2011 | 3:49 pm

This CMS event display from October 2010 captured a collision that produced very energetic jets - showers of particles that leave energy deposits in the detectors - and an exceptional amount of missing energy, represented by the blue line at the bottom left. Experimentalists and theorists are continuing to analyze collision events such as this one in search of new physics.(Image courtesy CMS/CERN.)

Experimentalists at the Large Hadron Collider recently proved effective a simple, new method of looking for evidence of supersymmetry. The method addresses a challenge particle physicists often face in looking for new particles and processes: They can manifest themselves in a multitude of ways.

How new physics will reveal itself is anybody’s guess. It’s a bit like the game Plinko on “The Price is Right” – contestants drop a token at the top of a pegboard and watch hopefully as it zigzags toward a slot at the bottom that may or may not contain a prize. If the game is played enough times, the token is likely to retrace some of the same routes, but occasionally it will take an unexpected path to the prize.

And so it goes at the LHC. Energy from proton collisions transforms into a handful of massive particles, which can decay in seemingly endless ways to any number of final particles. Collide enough protons and eventually the rarest particles will appear among the commonly produced ones.

“The set of possibilities for finding new physics is so large that it can be overwhelming,” said theoretical physicist Jay Wacker from SLAC National Accelerator Laboratory in California. “We’re trying to go about systematically exploring all of these possibilities. We want to make sure no stone is left unturned.”

Using the first round of data taken in 2010, LHC experimentalists sifted through several billion collisions looking for rare signatures that could represent supersymmetry. They looked where theory stated that these signatures were most likely to appear – the tokens that took a particular path down the pegboard and ended up in a certain slot on the bottom – and came up empty-handed.

The experimental groups are still looking for supersymmetry under different conditions, but it would take far too long to analyze every possible combination of initial particles, decay paths and final particles. To solve this problem, a group of theorists came up with a way to look for supersymmetry in the widest area possible.

Wacker and his colleagues designed a search that is sensitive to a number of different particle signatures that appear in the aftermath of a high-energy proton collision. The goal, he said, was to come up with the easiest way to cover the most possible areas where new physics might pop up.

The search looks at a class of events called jets plus missing energy – proton collisions that result in a shower of hadronic particles plus a stable, neutral particle that escapes detection – and ignores events that show signs of electrons or muons.

Both the theorists and the experimentalists looked only at the pile of tokens that landed in a particular slot at the bottom of the Plinko board. While the experimentalists had a set of guidelines about how the tokens should have gotten there and excluded any tokens that didn’t follow the rules, the theorists didn’t care as much about that. They were primarily concerned with the mass of the initial particles, the mass of the final particles and the ratio between them.

When the initial massive particles decay into lighter ones, the total energy must be conserved. Sometimes this energy goes missing; if the missing energy adds up to a certain amount, it could mean that a supersymmetric particle carried it away without being detected.

“These models are really nice because they allow us to think in terms of particles, not abstract parameters,” said CMS deputy spokesperson Joseph Incandela, from the University of California, Santa Barbara. “As particle physicists, we like that.”

The theorists’ approach also does not consider each individual possibility, but rather a few combinations of particle masses, decay paths and missing energy ranges that are a well-rounded representation of all the possibilities.

From the set, Wacker’s group proposed two dozen model signatures, each of which describes the masses and behaviors of a set of particles corresponding to a spot within the search region. The ATLAS group applied these models to their SUSY search.

“The good news is that they work,” said ATLAS physicist Zach Marshall, who helped test the search strategy against the 2010 LHC data. “We were basically asking, ‘If the signature really did look like that, would we have seen it last year?’ And the answer is that we can exclude many of those points.”

The models not only verify last year’s searches, they also help to optimize them. The groups now have a better understanding of potentially missed supersymmetry signatures and can state much more clearly the mass limits on particles, Marshall explains. What’s more, the models extend even beyond the constraints set by the experiments and are sensitive to many different supersymmetry theories.

“They essentially broke down a very important class of supersymmetry models and found the common denominators,” Incandela said. After certain limits are set with these simple models, scientists will gradually add more variables back into the equation. This will narrow down the number of potential new physics events and will help scientists to get a better handle on what they see in the detectors.

Both the CMS and ATLAS experiments will use the search again as they collect and analyze data from the 2011 run. Meanwhile, the theorists are working to expand these models and apply them to other slots at the bottom of the Plinko board.

“These models created a search more extensive than what has been used, and with reasonable efficacy,” Wacker said. “But this is just the first step in showing what kinds of new physics the LHC is sensitive to.”

Lauren Rugani

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Fermilab moves forward with testing components for a muon collider

May 2, 2011 | 9:59 am

This story first appeared in Fermilab Today on May 2.

The MuCool Test Area hall viewed from the downstream end of the magnet looking toward the beamline. The beam absorber and collimators are visible in the foreground and the beamline in the background. Photo: Yagmur Torun, Accelerator Research Center.A decade ago, a muon collider was considered nearly impossible. Now, scientists at Fermilab’s MuCool Test Area are a step closer to testing some critical components for such an accelerator.

In February, the MTA, located near the southern end of Fermilab’s linear accelerator, received its first beam of particles. The new beamline will allow scientists to test equipment for muon cooling, a critical part of development for future muon colliders.

“The beam entered the center of the hall last week,” said MTA coordinator Yagmur Torun. “We’re making great progress.”

The new beamline from the linac to the MTA was made possible by the External Beamlines Department.

“We’re very happy to see the new beam reach the MTA,” said External Beamlines Department Head Craig Moore. “This achievement was years in the making, and the team worked hard to develop and install the shielding and safety components necessary for the new beam.”

The path to building a muon collider is a difficult one. Muons, the electron’s heavy cousins, are unstable and decay in two millionths of a second.

Scientists can create large numbers of muons by steering a proton beam into a target of dense liquid. Once the muons are created, magnets send them in the right direction. At this stage, the muons are still too diffuse to create useful collisions.

At the MTA, scientists are exploring methods to cool muons and corral them into dense beams for high-luminosity collisions. One proposed method, known as ionization cooling, would focus muons into a laser-like beam by forcing them through a series of magnets and absorbers filled with liquid hydrogen. The hydrogen slows the muons and absorbs their energy, while the magnetic fields narrow the beam. This process has to take place quickly, before the muons decay into electrons and neutrinos.

This ionization cooling method is necessary for the success of a future muon collider, said Alan Bross, co-spokesperson for the Muon Collider collaboration. With the new beam to the MTA, experimenters can soon put this method to the test. Bross expects to see crucial results from MuCool in the next four months.

For more information on research and design for a muon collider, check out this article in symmetry magazine.

— Cynthia Horwitz

Guest author

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