BaBar's hunt for an exotic Higgs particle

July 7, 2009 | 1:31 pm

BaBar scientists hunting for the light Higgs boson include: (clockwise from back left) Arafat Gabareen Mokhtar, Arthur Snyder, Erik Petigura, Yury Kolomensky, and Hojeong Kim. (Photo by Nicholas Bock.)

The BaBar collaboration submitted two papers to Physical Review Letters last month, both searching for hypothetical light-mass Higgs bosons, the particles suspected of giving objects their mass. While the Large Hadron Collider at CERN will search for a heavy-mass Higgs that lies outside the BaBar experiment’s energy range, other theories predict another, lighter Higgs within BaBar’s reach. Both papers found no evidence of a low-mass Higgs in the BaBar data set.

“While it would have been very exciting to find a low-mass Higgs, the BaBar results are still important for the particle physics community,” says Yury Kolomensky of U.C. Berkeley and Lawrence Berkeley National Laboratory. “A negative result can rule out some Higgs theories, which is positive progress. If and when the Higgs is discovered, we will need to understand the underlying theory. Do we live in a world where a single Higgs boson is responsible for the generation of the mass of all particles, or is there more variety in nature?”

“The concept of mass is one of the most intuitive ideas in physics, since it is present in everyday human experience,” writes Erik Petigura, a junior physics major at U.C. Berkeley. “Yet the fundamental nature of mass remains one of the great mysteries [of science].” Petigura’s words open the first of the two journal articles, on which he is a collaborator.

Scientists believe that Higgs bosons cluster around other particles, giving them mass. Imagine a party where guests stand randomly distributed about the room. When the guest of honor arrives, the guests clump around her, giving her more inertia and making it harder for her to move once she starts to slow down. The Higgs bosons behave like these partygoers, surrounding particles and giving them mass. The Standard Model of particle physics predicts the existence of a particle like the Higgs boson, and has successfully described most known particle physics phenomena. Yet the Higgs boson, the last essential ingredient of the Standard Model, remains undiscovered.

Alternative theories exist, and are often based on new observations in astrophysics such as the properties of the mysterious dark matter. Scientists are drawn to them because they may be able to solve some of the unsatisfactory features in the Standard Model, such as the need to fine tune some parameters to make them match the values observed in nature. Some of these theories propose that several Higgs bosons may exist, with one of them having a lighter mass and lower energy than predicted by the Standard Model.

The BaBar experiment has produced vast numbers of particles called Upsilon mesons in different “resonances,” or states: Y(2S), Y(3S), and Y(4S). According to some models, a light Higgs boson, A0, might be produced when the Y(2S) or Y(3S) mesons decay, emitting a photon. From there, A0 would also decay and scientists would search for products it leaves behind. Because so little is known about the theoretical A0, including its mass, it is important to search for it in as many ways as possible. One of the papers submitted by the BaBar collaboration last month details the search for the decay of a light-mass Higgs boson into a pair of muons, with research led by Petigura, Kolomensky and SLAC physicist Hojeong Kim. The second paper reports a related search for the Higgs decaying into tau-lepton pairs, with research led by SLAC physicists Arafat Gabareen Mokhtar and Arthur Snyder. Tau leptons are heavier than muons, so the two teams searched for the A0 in slightly different mass ranges.

The search involved painstaking separation of the potential signal candidates from millions of the unwanted background events, careful calibration of the detector properties and a scan of a wide range of A0 masses. After about a year of work by both groups, the results are in: no light Higgs.

Not yet, anyway. While the BaBar analysis was exhaustive, a light Higgs may still have slipped through a loophole. Nature may have made these decay processes barely visible with BaBar’s data samples. The BaBar collaboration plans to improve the sensitivity of both the muon and tau analyses with additional data sets from different upsilon resonances. It’s also possible that the light Higgs decays into something other than muons or taus. Additional searches are planned to look for Higgs decays into hadrons, another type of subatomic particle, as well as “invisible” decays of A0 that produce particles that do not interact with the detector. These processes still leave behind photons that the researchers can then search for.

If these efforts yield no discoveries, the theories that propose the light Higgs will be re-evaluated or discarded. The theoretical and astrophysical problems these theories attempted to solve will have to be addressed with new ideas. BaBar will then pass the torch to their colleagues at the Large Hadron Collider, which is expected to start again this October. In the Super B Factories, proposed to be built in Italy and Japan, would also increase dataset sizes by orders of magnitude, and could look for the hints of the Higgs in even more rare processes. The hunt for the Higgs continues…

SLAC Today, July 7, 2009

Calla Cofield

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Revolutionary neutral-current discovery honored 36 years later

July 7, 2009 | 8:00 am

In a room at a German university a physicist went through his daily routine. He walked down a line of bubble-chamber photo scanners.  He leafed through the piles of particle-interaction photos the scanners had recorded.

Bubble-chamber photo of first leptonic neutral current event, found in Aachen. Courtesy Jorge Morfin.

One image caught his eye.

Soon another physicist was called over to look, and another. The excitement was palpable. By evening, everyone in the Aachen group — and, soon thereafter, everyone in the rest of the Gargamelle collaboration — knew particle physics would never be the same.

“It actually provided the experimental foundation for what we now call the Standard Model,” says Harry Weerts, recounting the observation of the first neutral current event in 1972 – a single electron scattering.

 Jorge Morfin, also on the team searching for this leptonic event, agrees. “Seldom has a single interaction had such a dramatic impact on particle physics” he says. 

 Weak neutral current interactions are similar to electromagnetism. They occur through the exchange of neutral particles.  The Gargamelle bubble chamber had been set up to observe neutrinos, which leave no tracks in bubble-chamber fluid but can be seen indirectly through their interactions with other particles as they pass through. It was one of those interactions, in which a neutrino scatters a single electron, that directly revealed the presence of the weak neutral current.   Ten years later, experiments at CERN discovered the Z, the particle associated with weak neutral currents.

The single picture of the single electron found by the Aachen group would drive the collaboration to confirm the observation with a larger, more complicated hadronic study that involved events with and without muons and more than one million bubble-chamber images.

In 1973 the collaboration published a paper that would become one of two discovery cornerstones for the electroweak force theory. This theory postulates that at very high energies, two of the four fundamental forces of nature – the weak force, which is responsible for radioactive decay, and the electromagnetic force, which is responsible for electric and magnetic interactions – become one.

More than three decades later, at a July 20 conference in Krakow, Poland, the Gargamelle collaboration will receive the European Physical Society High Energy and Particle Physics Prize for discovering the weak neutral current. The men who first predicted weak neutral currents won the Nobel Prize in 1979. 

The Gargamelle discovery was the first time that more than one or two physicists stood out as key players in a discovery.  The 55 physicists who authored the paper, which some have called the most important discovery made by CERN scientists so far,  came from working groups in Germany, Belgium, Italy, France and England, all using a neutrino beam based at CERN. 

Professor Fabio Zwirner, a member of the EPS-HEPP Board, called the award “long overdue.”

From observation to discovery:

The road to discovery was nearly as unusual as the road to recognition.

Former Gargamelle collaboration members and the first bubble chamber photos of neutral current interactions. Jorge Morfin holds the leptonic event and Harry Weerts holds one of the hadronic events.

In the winter of 1972, when the neutral current search team in Aachen, Germany, which included Morfin and Weerts, found the first hint the neutral current existed – the single electron event –  the theory behind it was only a few years old. A strong bias that this type of interaction shouldn’t exist was just starting to fade.

The research team had received the fateful photo by chance, after the event photos were divided among universities. 

“We called it our Christmas present,” says Morfin. The team worked for months trying to rule out the possibility that the event was caused by background and not a new discovery.

Subsequently, Gargamelle was racing the HPWF (Harvard, Pennsylvania, Wisconsin, Fermilab) experiment at Fermilab to discover hadronic neutral currents. The race was dubbed “alternating neutral currents” for the announcements of “we found it, no we didn’t, etc., ” Morfin says.

The entire Gargamelle collaboration kicked into high gear, compiling event data and analysis from all members, until the discovery was doubt proof, culminating in a 1973 publication.

“CERN and Fermilab both had the evidence, but we were trying to convince ourselves that what we were seeing wasn’t background neutrons,” Morfin says. “We finally were convinced there were no other explanations that would fit the data. The energy and spatial distribution of the muon-less events were not consistent with neutrons.”

Forging a legacy and a bond:

Four of the living collaborators currently work in the United States: Morfin at Fermi National Laboratory, Weerts at Argonne National Laboratory, Robert Palmer at Brookhaven National Laboratory and William “Jack” Fry at the University of Wisconsin-Madison, where he is a professor emeritus.

“Our committee rewards a milestone experimental discovery in the physics of elementary interactions,” said Professor Stefan Pokorski, from the University of Warsaw, in a press release. He called the discovery ”a benchmark to full understanding of the phenomenon of radioactivity, observed more than a hundred years ago by Henri Becquerel, Marie and Pierre Curie and Ernest Rutherford.”

The discovery, made in a 12-cubic-meter liquid Freon bubble chamber, created a foundation for future experiments, including the NuTev experiment at Fermilab that looked at the neutrino ratio of neutral currents to charged currents and the searches for the Higgs boson at Fermilab’s Tevatron and CERN’s Large Hadron Collider, which could round out the understanding of the electroweak interaction.

“This was a very exciting time,” Weerts says. “What this does is it binds people together for a lifetime. As a group, you feel that you accomplished something great.”

Read more about the historic discovery in this AAPPS Bulletin article. And in this review of the discovery. 

View a CERN film about the construction and operation of this giant bubble chamber here.

View past  EPS HEPP prize winners here.

Tona Kunz

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“Beyond our wildest dreams”: Fermi scope bags 16 gamma-ray-only pulsars

July 6, 2009 | 12:34 pm

This all-sky map shows the positions and names of 16 new pulsars (yellow) and eight millisecond pulsars (magenta) studied using Fermi's LAT. (Image: NASA)

After only one year of operation, the Fermi Gamma-ray Space Telescope has already outperformed researchers’ best expectations. In two papers published in the July 2 edition of Science Express, the researchers reported a new class of pulsar and evidence that helps explain how gamma-ray emission occurs.

The team examined 300 sites of gamma-ray radiation for the study, using data collected by FGST’s Large Area Telescope between August 2008 and January 2009 along with data collected by a predecessor, the Energetic Gamma Ray Experiment Telescope. Within these sites they were able to identify 16 new gamma-ray only pulsars.

The LAT, one of the two main instruments on FGST, was assembled at SLAC National Accelerator Laboratory. The SLAC Instrument Science Operations Center processes all data from the LAT, converting the raw information into a form that scientists can analyze.

“With Fermi we are really opening the window on the possibility of discovering a new class of pulsars, using gamma-ray emissions,” said LAT Analysis Coordinator Nicola Omodei, who is visiting SLAC this year from the physics lab INFN in Pisa. “We basically saw something that no one has seen before.”

Pulsars are fast-spinning neutron stars: super-dense stellar remnants left in the wake of supernovae. As the neutron stars spin, they emit radio waves from their poles that sweep across the universe like giant searchlights. Radio telescopes on Earth or in orbit can detect the pulsars if the beam crosses the Earth’s path.

So far, more than 1800 pulsars have been identified by scanning the galaxy for radio waves. In some cases, though, the radio waves can’t be seen. Fermi first demonstrated this in October 2008, when researchers announced the identification of the first gamma-ray only pulsar.

“Before launch, some predicted that Fermi might uncover a handful of new pulsars during its mission,” University of California, Santa Cruz Astronomer Marcus Ziegler said. “To discover 16 in its first five months of operation is really beyond our wildest dreams.”

The results also provide insight on how gamma-ray emissions arise. Where radio waves emissions are thought to arise from the poles of a neutron star, the results suggest that gamma rays might originate as far as 300 miles from the star’s surface.

Researchers were also able to use the data to closer examine unique objects called millisecond pulsars.

Normally, pulsars lose energy as they spin. As they lose energy, they slow down and stop emitting radiation. But if these aging neutron stars are in close proximity to other stars, something interesting happens: the neutron star’s enormous density causes it to accrete material from its neighbors, increasing its mass and restarting its spin.

For reasons that aren’t yet clear, these rejuvenated pulsars can spin even faster than their younger brethren. They spin so fast, in fact, that they can complete anywhere from 100 to 1000 full rotations every second.

Before the Fermi gamma-ray telescope, the mechanism of how these millisecond pulsars emitted energy was unclear. But comparing the emission spectrum of the millisecond pulsars to those of gamma-ray only pulsars, researchers found that they were nearly identical.

“Before Fermi launched, it wasn’t clear that pulsars with millisecond periods could emit gamma-rays at all,” said Lucas Guillemot at the Center for Nuclear Studies in Gradigna, near Bordeaux, France. “Now we know that they do. It’s also clear that, despite their differences, both normal and millisecond pulsars share similar mechanisms for emitting gamma-rays.”

NASA has a press release here.

Nicholas Bock, SLAC Today

Symmetry Intern

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A milestone for ArgoNeuT

July 3, 2009 | 5:00 am

A screen capture of ArgoNeuT's first neutrino interaction event.

The Argon Neutrino Teststand, or ArgoNeuT, has seen its first neutrino–the first one observed by a liquid argon detector in the United States.

ArgoNeuT is named for the Argonauts, a brave band of mythical explorers led by Jason in search of the Golden Fleece; this makes for many fine nautical metaphors and puns.  This liquid-argon technology may offer a cheaper, more efficient way to capture neutrinos, mysterious particles that may hold the key to why the universe is made of matter, and therefore to why we exist; for details, see this feature in the August 2008 issue of the magazine.

Subsequent updates reported ArgoNeuT’s first observations of cosmic rays–an important step in testing and calibrating the detector–and the lowering of the detector into a Fermilab tunnel 350 feet below ground, where it’s shielded from those same troublesome rays.

Now here’s the latest, from Wednesday’s Fermilab Today:

“Liquid-argon detectors can achieve high accuracy in determining the type of particle interaction. Because of this, they are very good at rejecting background events. These detectors can also get the same measurements as much larger detectors that use different technologies,” said Brian Page, a graduate student at Michigan State University who works on ArgoNeuT.

ArgoNeuT, a small, 175-liter, liquid-argon-filled detector, sits upstream of the MINOS detector in the neutrino beamline. Neutrinos from the NuMI beamline enter the ArgoNeuT detector chamber and interact with argon atoms. The interactions produce light and charged particles, which continue to travel through the argon and knock electrons loose. A wire plane attracts these electrons, which induce electrical signals. The data collected helps scientists reconstruct a 3-D image of the original interaction event.

Scientists lowered the experiment, commissioned in 2008, into a detector hall in January 2009. It was filled with liquid argon this May, and saw the first interactions on May 27.

“Seeing the neutrino interactions is another step towards showing us that we can build these detectors for the long baseline neutrino oscillation program at the proposed Deep Underground Science and Engineering Laboratory,” said Bonnie Fleming, ArgoNeuT spokesperson.

All we can say is: Smooth sailing!

Glennda Chui

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Data-taking dress rehearsal proves world's largest computing grid is ready for LHC restart

July 1, 2009 | 2:38 pm

The Worldwide LHC ComputingGrid is gearing up to handle the massive amount of data expected shortly after the restart of the Large Hadron Collider.

Read how CERN is preparing to take record-setting amounts of data in this Interactions press release.

And read in the press release below how Brookhaven National Laboratory and Fermi National Accelerator Laboratory will lead the US portion of the data distribution.

Tape storage at Brookhaven National Laboratory's Tier-1 Computing Center. Photo Courtesy of BNL.

BATAVIA, IL and UPTON, NY–The world’s largest computing grid has passed its most comprehensive tests to date in anticipation of the restart of the world’s most powerful particle accelerator, the Large Hadron Collider (LHC). The successful dress rehearsal proves that the Worldwide LHC Computing Grid (WLCG) is ready to analyze and manage real data from the massive machine. The United States is a vital partner in the development and operation of the WLCG, with 15 universities and three US Department of Energy (DOE) national laboratories from 11 states contributing to the project.

The full-scale test, collectively called the Scale Test of the Experimental Program 2009 (STEP09), demonstrates the ability of the WLCG to efficiently navigate data collected from the LHC’s intense collisions at CERN, in Geneva, Switzerland, all the way through a multi-layered management process that culminates at laboratories and universities around the world. When the LHC resumes operations this fall, the WLCG will handle more than 15 million gigabytes of data every year.

Although there have been several large-scale WLCG data-processing tests in the past, STEP09, which was completed on June 15, was the first to simultaneously test all of the key elements of the process.

“Unlike previous challenges, which were dedicated testing periods, STEP09 was a production activity that closely matches the types of workload that we can expect during LHC data taking. It was a demonstration not only of the readiness of experiments, sites and services but also the operations and support procedures and infrastructures,” said CERN’s Ian Bird, leader of the WLCG project.

Cables at Fermilab's Grid Computing Center. Photo Courtesy Fermilab.

Once LHC data have been collected at CERN, dedicated optical fiber networks distribute the data to 11 major “Tier-1″ computer centers in Europe, North America and Asia, including those at DOE’s Brookhaven National Laboratory in New York and Fermi National Accelerator Laboratory in Illinois. From these, data are dispatched to more than 140 “Tier-2″ centers around the world, including 12 in the United States. It will be at the Tier-2 and Tier-3 centers that physicists will analyze data from the LHC experiments–ATLAS, CMS, ALICE, and LHCb–leading to new discoveries. Support for the Tier-2 and Tier-3 centers is provided by the DOE Office of Science and the National Science Foundation.

“In order to really prove our readiness at close-to-real-life circumstances, we have to carry out data replication, data reprocessing, data analysis, and event simulation all at the same time and all at the expected scale for data taking,” said Michael Ernst, director of Brookhaven National Laboratory’s Tier-1 Computing Center. “That’s what made STEP09 unique.”

The result was “wildly successful,” Ernst said, adding that the US distributed computing facility for the ATLAS experiment completed 150,000 analysis jobs at an efficiency of 94 percent.

A key goal of the test was gauging the analysis capabilities of the Tier 2 and Tier 3 computing centers. During STEP09’s 13-day run, seven US Tier 2 centers for the CMS experiment, and four US CMS Tier 3 centers, performed around 225,000 successful analysis jobs.

“We knew from past tests that we wanted to improve certain areas,” said Oliver Gutsche, the Fermilab physicist who led the effort for the CMS experiment. “This test was especially useful because we learned how the infrastructure behaves under heavy load from all four LHC experiments. We now know that we are ready for collisions.”

US contributions to the WLCG are coordinated through the Open Science Grid (OSG), a national computing infrastructure for science. OSG not only contributes computing power for LHC data needs, but also for projects in many other scientific fields including biology, nanotechnology, medicine and climate science.

“This is another significant step to demonstrating that shared infrastructures can be used by multiple high-throughput science communities simultaneously,” said Ruth Pordes, executive director of the Open Science Grid Consortium. “ATLAS and CMS are not only proving the usability of OSG, but contributing to maturing national distributed facilities in the US for other sciences.”

Physicists in the United States and around the world will sift through the LHC data in search of tiny signals that will lead to discoveries about the nature of the physical universe. Through their distributed computing infrastructures, these physicists also help other scientific researchers increase their use of computing and storage for broader discovery.

Read the full press release here.

Tona Kunz

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World Science Festival: Time Since Einstein

July 1, 2009 | 7:31 am

There was a strong science vibe in New York City as the World Science Festival rang in its third year. Founded by string theorist and author Brian Greene and  journalist Tracy Day, the festival hosted forty events over four days that sold out at various locations throughout the city.

“Time, I think, is a little bit like love,” began moderator John Hockenberry. “It’s accessible to all of us; it is intuitively experienced by all of us in the same way; yet it retains its mystery at whatever level you weigh in on it. It is a mysterious force that we all can experience and share.” And so Hockenberry opened the panel discussion at the World Science Festival titled “Time Since Einstein.” The award-winning journalist nearly slaps his audience awake with his booming voice and dramatic inflection, and by the end of the talk you just want to chat with him for hours.

The panel members were enough to make this science nerd drool: physicists George Ellis, Roger Penrose, Sean Carroll, and Fotini Markopoulou-Kalamara, who were joined by the two very physics-savvy philosophers David Albert and Michael Heller. The panel had its work cut out for it, given the task to cover everything we’ve learned and begun to question about time since the relativity revolution incited by Einstein. By the end, my friend and I wondered, “Would someone with no physics background think these people knew an incredible amount about time, or nothing at all?” And really, both are true. For as much as we’ve learned since Einstein, we’ve only found more to wonder about.

What is time? No, really, what is it? A dimension of space-time, says relativity, but is it physical? Or just mental? Why does it seem to move forward and not back? Does the universe acknowledge the arrow of time that we experience? How big is time? Does our notion of “now” have any validity? Is time quantized? And are the answers to these questions within the grasp of physics?

Einstein revolutionized our notion of time, and experimental evidence has since shown that time is in fact relative; it depends on where you are and how you are moving. Time was once the stage on which events occurred, but after Einstein, it became a player on the stage, equally influenced by the other players. “Our notion of time is very physical,” says Markopoulou-Kalamara. She’s referring to the fact that our concept of time often relies on physical cues, such as something we heard or saw. So is time just a series of events or changes in spatial dimensions? Einstein linked space and time into the dimension of space-time, and now scientists wonder if they can ever untangle the two. The nature of time, like many of physics’ most confounding issues, is explored on both the largest and the smallest scales we know of.

The notion of time plays different roles in general relativity and quantum mechanics. Markopoulou-Kalamara is at the forefront of the pursuit to link the two. She has worked in the development of loop quantum gravity, an alternative to string theory, and she is also developing models of space-time that account for the flow of time. While quantum mechanics suggests that the future is not planned, we don’t know if it equals a spontaneous present where we can chose our actions. Following this thread, she had this back and forth with Hockenberry:

Hockenberry: Can there be a non-deterministic future that actually exists?
Markopoulou-Kalamara: This is the conflict between the two theories–general relativity and quantum theory. So in general relativity, yes, it is deterministic. You never have to choose anything, everything is chosen for you.
H: Which is depressing. (laughs from the audience)
M-K:…Or freeing. (more laughs and some applause.) But in quantum mechanics that’s not true.
H: Which is…liberating or depressing?
M-K: Depends.

Einstein, a member of the elite group that shaped quantum mechanics, took a deterministic view; maybe he thought an intrinsically probabilistic universe was too frightening. Quantum mechanics doesn’t guarantee free will, but does it prove that the future is distinct from the past? George Ellis says that it does.

“There are many theoretical physicists who think the flow of time is an illusion,” he says. “And I think that’s a great mistake…according to quantum physics you don’t know the outcome of events until they happen. We know what happened in the past, there’s a time called the present when things are happening, and there’s a time in the future which is not yet determined. That’s my view on it, which is not a very widely supported one.”

A professor emeritus of applied mathematics at the University of Capetown, Ellis is the co-author with Stephen Hawking of The Large Scale Structure of Space Time, and investigates the physical foundations of the flow of time. He notes that subatomic particles, in the form of cosmic rays, affected the formation of life on this planet beginning four billion years ago. Even if we knew everything there was to know about the Earth then, we couldn’t have predicted the way things would turn out. Doesn’t that imply a distinct future?

Time on the quantum scale also challenges our notion of the present. One audience member asked if “now” really exists; can we take a picture of this moment and make it distinct? To totally freeze this moment would mean to collapse the wave functions of many things which would otherwise have been left as probabilites. In some ways, “now” is not definite.

The notion that time moves forward is something we humans can’t escape. As Carroll pointed out, if you’re out in space you might get confused about up and down, but you wouldn’t get confused about the past and the present (unless  you got a severe case of space madness). But most of the laws of physics are untouched by that notion–they are time symmetric, meaning if you run them backwards they look the same as they do running forward. A few rare particle experiments, however, done at CERN and Fermilab, have demonstrated a time asymmetry. The second law of thermodynamics is another heavy hitter for the idea of an arrow of time. The second law states that in a closed system things get more random; one can scramble an egg but not unscramble it. Entropy will always increase, and moving backwards in time would violate that.

Carroll, a senior research associate at the California Institute of Technology, is the author of the upcoming From Eternity to Here, a book about cosmology and the arrow of time. Always good for an elegant and enlightening talk despite the great complexity of his own research, he discussed the question “How long does time go?”:

“Scientists have gotten used to the idea that when people ask us ‘What happened before the big bang?’ we give St. Augustine’s answer: we say there was no such thing as before the big bang. But in very recent times, beyond Einstein, we’re realizing that we have absolutely no justification for saying that that’s true. We have to move beyond Einstein to understand what happened at the big bang. And the answer might be that the universe came into existence at the big bang; there’s nothing before. Or it might not. There could be something before the big bang….Cosmologists, people who are working on quantum gravity, are very interested in what we’ve learned since Einstein to answer these questions and go back and answer St. Augustine’s question.”

Ellis adds that Einstein also hated the idea of a beginning of time. It does seem rather odd that something with a very distinct beginning would simply have no end, or to think that even 14 billion years after the big bang (if the universe is infinite) we are still infinitesimally close to the beginning.

It seems the discussion of time swings quickly between the largest scale and the smallest scale. Discussion of the ultimate length of time begs the question, is time quantized? Can we break it up into packets like photons and quarks? Markopoulou-Kalamara says it depends on your notion of time. In terms of the geometric notion of time, as in the time dimension of a space-time, she says yes; she believes it has to break down. But if you’re referring to time as change, something that has happened, “I doubt it,” she says. Ellis adds that quantization of time may have to confront something like Zeno’s paradox of infinite halves:

“If you look between my fingers, the question is how many points are between there. And in some views of physics there’s not just an infinite number of points, there’s an uncountable infinity of points in between. I don’t believe it. I believe there’s got to be a discrete number of points. The same thing happens if I were to say one…two. How many points were between there and there? Was there an uncountable infinity of points? I don’t think so. I think there was a discrete number of time events between that point and that point.”

So, what is time?

“Change,” says Markopoulou-Kalamara.

“I would have to prepare a two-semester course,” says Heller.

Ellis:  ”It’s what clocks measure.”

Hockenberry closed with “The coming of wisdom with time,” by W.B. Yeats:

Though leaves are many, the root is one;
Through all the lying days of my youth
I swayed my leaves and flowers in the sun;
Now I may wither into the truth.

Calla Cofield

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Researchers find evidence for the origin of cosmic rays

June 30, 2009 | 7:00 am

Studies of supernova remnant RCW 86 have revealed the origin of cosmic rays. (Image courtesy of ESO/E. Helder and NASA/Chandra.)

An international team of researchers has discovered strong evidence that extremely energetic cosmic rays are born in supernova remnants.

“Cosmic rays constantly bombard the earth’s atmosphere but, until now, we didn’t have proof of where in our galaxy they originated,” said co-author Stefan Funk of the Kavli Institute for Particle Astrophysics and Cosmology at SLAC National Accelerator Laboratory. “That’s because cosmic rays are almost entirely made of protons, which as charged particles are bent by magnetic forces as they travel to Earth. So we can’t just trace a straight line back to know where they originated, like we can with light.”

Instead, the researchers traced the sources of cosmic rays by indirect means.

In a paper published last week in Science Express, the researchers describe measurements made with the European Southern Observatory’s Very Large Telescope and NASA’s Chandra X-ray Observatory. These measurements, of a star that exploded in the year A.D. 185, compare the temperature of the gas immediately behind the shockwave created by the stellar explosion with the speed of the shockwave itself. If the energy of the stellar explosion was converted solely into heat and motion, these two measurements should have been directly related by a very well-known and well-tested equation. Yet when the researchers plugged their measurements into the equation, it didn’t balance. Something else was being energized by the explosion.

“When a star explodes in what we call a supernova, a large part of the explosion energy is used for accelerating some particles up to extremely high energies,” said co-author Eveline Helder of the Astronomical Institute Utrecht in the Netherlands. “The energy that is used for particle acceleration is at the expense of heating the gas, which is therefore much colder than theory predicts.”

The researchers concluded that the missing energy goes into accelerating protons to nearly the speed of light-creating the cosmic rays that continually pummel our solar system, creating flashes of light behind the eyelids of astronauts and causing glitches in electronic components on Earth.

“Our observations reveal the smoking gun,” said Helder.

This story was first published in SLAC Today on June 30, 2009.

Kelen Tuttle

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Fermilab's CDF observes Omega-sub-b baryon

June 29, 2009 | 2:43 pm

This press release was issued by Fermilab today.

Once produced, the Omega-sub-b (Ωb) particle travels about a third of a millimeter before it disintegrates into two intermediate particles called J/Psi (J/ψ) and Omega-minus (Ω-). The J/Psi then promptly decays into a pair of muons. The Omega-minus baryon, on the other hand, can travel several centimeters and occasionally be measured in the CDF silicon vertex detector. The particle decays into an unstable particle called a Lambda (Λ) baryon along with a long-lived kaon particle (K). The Lambda baryon, which has no electric charge, also can travel several centimeters prior to decaying into a proton (p) and a pion (π). Credit: CDF collaboration.

At a recent physics seminar at the Department of Energy’s Fermi National Accelerator Laboratory, Fermilab physicist Pat Lukens of the CDF experiment announced the observation of a new particle, the Omega-sub-b (Ω_b). The particle contains three quarks, two strange quarks and a bottom quark (s-s-b). It is an exotic relative of the much more common proton and has about six times the proton’s mass.

The discovery of this “doubly strange” particle, predicted by the Standard Model, is significant because it strengthens physicists’ confidence in their understanding of how quarks form matter–and because it conflicts with a 2008 result announced by CDF’s sister experiment, DZero.

The Omega-sub-b is the latest entry in the “periodic table of baryons.” Baryons are particles formed of three quarks, the most common examples being the proton and neutron. The Tevatron particle accelerator at Fermilab is unique in its ability to produce baryons containing the b quark, and the large data samples now available after many years of successful running enable experimenters to find and study these rare particles.  The observation opens a new window for scientists to investigate its properties and better understand this rare object.

Combing through almost half a quadrillion (1000 billion) proton-antiproton collisions produced by Fermilab’s Tevatron particle collider, the CDF collaboration isolated 16 examples in which the particles emerging from a collision revealed the distinctive signature of the Omega-sub-b. Once produced, the Omega-sub-b travels a few millimeters before it decays into lighter particles. This decay, mediated by the weak force, occurs in about a trillionth of a second.

Late in 2008, DZero, the sister experiment to CDF, announced its own observation of the Omega-sub-b based on a smaller sample of Tevatron data.  Interestingly, the new CDF observation announced here is in direct conflict with the earlier DZero result.  The CDF physicists measured the Omega-sub-b mass to be 6054.4±6.8(stat.) ±0.9(syst.) GeV/c² , compared to DZero’s 6.165 ± 0.016 GeV/c². These two experimental results are statistically inconsistent with each other leaving scientists from both experiments wondering whether they are measuring the same particle.  Furthermore, the experiments observed different rates of production of this particle. Perhaps most interesting is that neither experiment sees a hint of evidence for the particle at the other’s measured value.

Although the latest result announced by CDF agrees with theoretical expectation for the Omega-sub-b both in the measured production rate and in the mass value, further investigation is needed to solve the puzzle of these conflicting results.

The Omega-sub-b discovery follows the observation of the Cascade-b-minus baryon (Ξ_b), first observed at the Tevatron in 2007, and two types of Sigma-sub-b baryons (Σ_b), discovered at the Tevatron in 2006.

The CDF collaboration submitted a paper that summarizes the details of its discovery to the journal Physical Review D.

Kurt Riesselmann

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Steven Chu's energy challenge

June 26, 2009 | 5:44 pm

Secretary of Energy Steven Chu speaking at SLAC on Friday morning. Photo: Brad Plummer, SLAC.

Update: A video of Chu’s nearly two-hour talk is now available on SLAC Today.  Here are links to coverage of the talk in the Contra Costa Times and Palo Alto Online.

Speaking to a crowd of more than 800 this morning at SLAC National Accelerator Laboratory, Secretary of Energy Steven Chu urged researchers to confront what he called “the energy challenge.”

“For the first time in history, science has shown humans altering the destiny of our planet in a meaningful way,” he said. “We have to try to enlist some of the very best intellectual horsepower to deal with this.”

In a wide-ranging speech that touched on worldwide emissions, climbing global temperatures, changing precipitation patterns, increasing atmospheric carbon dioxide concentrations, and the rising sea level, Chu demonstrated how the energy challenge cuts across many areas and is intensely tied to our economic prosperity.

“But there’s reason for hope,” he said. “Scientists by their very nature have to be very optimistic… We can fix this.”

Pointing to historical examples of research easing global problems-including the invention of artificial fertilizer, which helped set off the so-called “green revolution”-Chu expressed his belief that science research would again come to the world’s aid.

“It was scientific discoveries that enabled the world to feed itself,” Chu said. Now, he continued, scientific discoveries can increase energy efficiency and develop improved means of generating clean energy.

“There are lots of really exciting things that people at SLAC can think about,” he said. “Research can spur incredible intellectual achievement. And in the field of energy, I think we can do some really great science. A physicist or applied mathematician can really start to drool at these problems.”

Chu, who received the 1997 Nobel Prize in Physics for his work in cooling and trapping atoms with laser light, is a former chair of the Stanford University physics department. Prior to becoming Secretary of Energy, he was a professor of physics and molecular and cellular biology at the University of California, Berkeley, and the director of the Lawrence Berkeley National Laboratory.

Kelen Tuttle

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Crews dig in at NOvA site

June 26, 2009 | 10:30 am

The crew will blast through 50 feet of rock at the NOvA site to accommodate the detector facility.

Construction crews began digging at the future site of the NOvA detector facility in Ash River, Minn., on June 1.

The American Reinvestment and Recovery Act provided funds for the civil construction project.

Fifteen workers from Hoover Construction, a subcontractor of Adolfson & Peterson Construction, have been clearing the top layer of dirt and developing the roads at the site.

“It’s pretty much earth work now,” said Davin “Buddy” Juusola, senior project manager for Adolfson & Peterson. But once the dirt is cleared, the construction crew will face the Canadian Shield, a mass of 2.7 billion-year-old Precambrian rock that stretches 3 million square miles across Canada and dips into a small northern edge of the U.S.

Crews from Adolfson & Peterson often work with rock, but blasting at the NOvA site will present a unique challenge, said Juusola, who has worked with the construction company for nine years.

The crew will blast down 50 feet to accommodate the NuMI Off-Axis Electron Neutrino Appearance, NOvA, detector facility. The laboratory will house a 15,000-ton particle detector that physicists will use to study a beam of neutrinos originating at Fermilab.

Members of the crew have talked to local residents about the project, Juusola said. “They seem very excited. They’re very receptive to it.”

The appeal goes beyond an interest in the science. Local supplier Seppi Brothers Concrete Products, based in Virginia, Minn., will provide concrete for the site, and other businesses will likely become involved.

Juusola said this will be his first experience building a laboratory.

“There are not too many neutrino labs built,” he said. “It’s very unique, which makes it exciting. It’s a nice project to have on your resume.”

This story first appeared in Fermilab Today on June 26, 2009.

Kathryn Grim

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