A new bottomonium particle makes its debut

March 31, 2011 | 4:35 pm

The November 08 issue of symmetry told the tale of the BaBar experiment’s last experimental hurrah– the quest to find a particle called eta sub b, the lowest-energy member of the bottomonium family. (Our reporter even scored an exclusive interview with the particle itself!)  Now the saga continues, as scientists report the results of their search for another member of the bottomonia in data from BaBar and Belle. This story first appeared in the March 31, 2011 issue of SLAC Today:

Data collected by the BaBar experiment during its final months of operation in 2008 point to a new member of the “bottomonium” family of subatomic particles. BaBar collaboration member and SLAC physicist Valentina Santoro presented the results on behalf of the collaboration last month at the Lake Louise Winter Institute, a yearly conference held at Lake Louise, Alberta, Canada. The discovery adds another piece to physicists’ model of the so-called “strong” force, which binds subatomic particles into larger chunks of matter.

In 2008, members of the BaBar collaboration announced they’d discovered the lowest-energy bottomonium particle, called ηb (pronounced eta-sub-b). A subsequent BaBar study confirmed the finding in 2009. Continued examination of the final BaBar data set has now revealed another particle of the bottomonium family, called the hb (h sub b).

Several variants of bottomonium—a bottom quark bound to a bottom anti-quark—have been predicted and a number have now been observed, the first more than thirty years ago. But many of the predicted states remain unobserved. Each one discovered offers a valuable window into quantum chromodynamics, or QCD, explained BaBar Physics Analysis Coordinator Steve Robertson. QCD is the theory of the strong force that binds quarks into the protons and neutrons that make up atomic nuclei (and ultimately us). It’s an important part of the Standard Model, currently the best theory physicists have to explain matter, energy, and how the two interact.

“Since [bottomonium particles] are held together by the strong force interactions, studying the particles is a good way to study the strong force,” Robertson explained. However, studying them isn’t easy. The strong force, though effectively limited in distance to lengths that span an atomic nucleus, is strong. Individual quarks have never been isolated, and all bottomonium particles are unstable and decay rapidly into lighter, less exotic particles. That means particle physicists must study them indirectly, by taking the final products of a particle collision, after any bottomonia have decayed away, and tracing back along the processes required to create these decay products. In this way, they can determine the nature of the particle at the beginning of that chain of particle decays. It’s somewhat akin to running a film backward to watch shards of porcelain on the kitchen floor rise into the air and reassemble themselves into a tea cup on a table.

The BaBar researchers combed through data from more than 120 million electron–positron collisions to find their shards. They also narrowed the possibilities for how the hb particle is created, and confirmed theoretical predictions of its mass.

Less than two weeks after Santoro presented the results, a group of researchers from Belle, a collaboration based at the KEK facility in Japan, announced their observation of the hb particle while studying a completely different and somewhat unexpected decay process. Figuratively speaking, the Belle researchers watched the same pile of porcelain shards reassemble into a coffee mug.

Lori Ann White

Guest author

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Rare particle decays could indicate presence of new physics

March 30, 2011 | 12:07 pm

Physicists at the LHCb experiment at the Large Hadron Collider recently reported the first observations of a new way that particles called B_s mesons decay into other particles. Studying this particular decay could provide clues as to why the universe is made up of matter rather than antimatter.

Collaboration members stand in front of the LHCb detector.

Equal amounts of matter and antimatter existed in the earliest stages of the universe. But when a matter particle comes in contact with its antimatter counterpart, the two annihilate one another and leave behind pure energy. In principle, all the matter and antimatter in the universe should have annihilated. But matter managed to survive, and scientists are seeking to explain why.

B mesons could hold the answer. Although they don’t exist naturally, they can be created easily in high-energy particle collisions. They contain a bottom antiquark and either an up, down, charm or strange quark. A peculiar trait of some B mesons is that they spontaneously transform into their own antiparticles and back before decaying into new particles. Last year, researchers at Fermilab discovered that certain B mesons decayed into matter particles 1 percent more often than they decayed into antimatter particles, which could account for the imbalance in the universe.

The cause of the imbalance could be the meddling of an unseen, heavier particle, one that physicists have never observed.

“New physics can influence the way B mesons decay,” said LHCb physicist Steve Blusk from Syracuse University. “What we’re trying to do is effectively measure this interference.”

Previous experiments have observed B mesons switching between matter and antimatter with good precision. With higher collision energies and up to 40 times as much data, LHCb could narrow down the uncertainties in existing data and finally explain the mechanism behind the oscillations.

If the culprit is a new particle too massive to be seen at the LHC, it could be observed through its indirect effect on B meson decays. Studying the decays will help scientists understand the forces acting behind the scenes that result in B mesons decaying to matter more than antimatter.

In a paper published this week in Physics Letters B, the LHCb group describes a new decay mode of one particular B meson, B_s (pronounced B-sub-s), which contains a bottom antiquark and a strange quark. After being created in the wake of a proton-proton collision, B_s mesons can decay into a J/psi particle (a charm quark bound to a charm antiquark) and an f₀ (a strange quark bound to a strange antiquark). These particles then decay further, leaving trajectories inside the detector for the researchers to observe.

By studying the difference between the way the B_s meson and its antiparticle decay to this
particular final state, the group can measure the interference between new physics and the Standard Model. If these effects are quite large, as earlier data suggests, LHCb researchers could discover new physics in the data recorded this year.

“At the very least, this will establish that the Standard Model is not the end of the road,” Blusk said.

Lauren Rugani

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The Daya Bay Neutrino Experiment: On Track to Completion

March 29, 2011 | 9:52 am

The Daya Bay Reactor Neutrino Experiment brings Chinese and American scientists together with colleagues from Russia, Taiwan, and the Czech Republic to investigate perhaps the most important unanswered question relating to the phenomenon of neutrino oscillation. What they find will bear on some of the most intriguing questions in basic physics. How much do different kinds of neutrinos weigh? And which kind is the heaviest?

By weighing neutrinos, scientists hope to learn how electrons and their cousins, muons and tau particles, came into existence in the moments after the big bang. The answers could explain why there is more matter than antimatter in the universe – and indeed why there is any matter at all.

Clues to neutrino mass lie in measuring how one “flavor” of neutrino changes into another. (Electron neutrinos, muon neutrinos, and tau neutrinos, the three flavors, are named after the leptons with which each is associated.) The crucial value, written θ13, is a term known as “neutrino mixing angle theta one three” – and the Daya Bay experiment is intended to measure it to within a few degrees.

Yifang Wang of Beijing’s Institute of High Energy Physics and Kam-Biu Luk of Lawrence Berkeley National Laboratory, a professor of physics at the University of California at Berkeley, are Daya Bay’s scientific co-spokespersons. Berkeley Lab’s Bill Edwards is the U.S. Project and Operations Manager.

This tour of the experimental site, with photographs by Berkeley Lab’s Roy Kaltschmidt, shows how the researchers hope to trap enough neutrinos to answer their questions.

- Paul Preuss

Guest author

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Buzz Aldrin visits the LHC

March 25, 2011 | 3:31 pm

One of the few people in history to walk on the moon recently became one of the few people in the world to push a big red button in the control center at the Large Hadron Collider. During a visit to CERN on March 1, American astronaut Buzz Aldrin was allowed to dump the beam at the LHC.

Aldrin was in town for an event at CERN’s Globe of Science and Innovation and took advantage of the opportunity to get a behind-the-scenes tour of the lab. Before he left, he stopped to chat about his impressions of CERN and large scientific missions in general.

“We’re always dealing with trying to explore a little bit further,” he said. “I suspect we’re only scratching the surface.”

Lauren Rugani

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Of sports cars, the Higgs, and Poppa Neutrino

March 23, 2011 | 4:01 pm

Bumbling around the Web, you can’t help but notice that pop culture references to particle physics pop up everywhere.  Dark energy is not just a mysterious force that accelerates the expansion of the universe;  it’s  an evil vibe, a video game company and a gaming weapon (typical gamer exchange: “Any 1 know what Dark Energy is for?” “you get it after last zhul raid.”)  Ditto the Higgs boson, as in this Wall Street Journal  review of the 2012 McLaren MP4-12C sports car describing it as 

…crazy light, a mere 3,279 pounds. There’s a kind of sheer depravity of physics going on here, a larceny of inertial mass, as if the car had been scoured of its Higgs bosons.

(Technically, of course, things don’t contain Higgs bosons;  see an explanation here.  But the reference made me smile.)

But long before the current particle physics craze got going there was Poppa Neutrino, aka David Pearlman, who died in January at the age of 77.

An obituary in the New York Times obituary describes him as

… an itinerant philosopher, adventurer and environmentalist … who founded his own church, crossed the Atlantic on a raft made from scrap and invented a theoretically unstoppable football strategy…. He had no fixed abode but had spent the last two years in Burlington, Vt., building and testing a new raft on Lake Champlain that he planned to sail around the globe.

The article — long, full of surprises, well worth a read — describes how Pearlman chose the name Poppa Neutrino 27 years ago after recovering from a serious illness brought on by a dog bite.  He felt reborn, and felt a kinship with the elusive, fast-moving, fundamental particle.

One of the legacies of this fascinating and eccentric gentleman is The Flying Neutrinos, a jazz band he founded with his wife in the 1980s; it’s now led by his daughter, Ingrid Lucia, and just one of a number of physics-inflected bands and songs that add zing to pop culture.

Glennda Chui

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Interesting effect at the Tevatron hints at new physics

March 18, 2011 | 9:00 am

Fermilab's Wilson Hall in the shape of a t, the symbol for the top quark.

Scientists at the Large Hadron Collider may be on the verge of discovering a new particle, according to mounting evidence from experiments at Fermilab’s Tevatron.

Judging by its behavior, it’s not the Higgs.

Scientists are finding signs of new physics through the study of a particle Fermilab physicists discovered at the Tevatron, the top quark.

When top quarks and their anti-particles, anti-top quarks, are created in particle collisions at the Tevatron, detectors note the direction in which they fly. Theory predicts that the particles will favor one direction slightly over the other, traveling that way about 5 percent of the time more.

However, in studies by the DZero collaboration and the CDF collaboration, the particles seemed to be picky 15 percent of the time. Top quarks went forward and anti-top quarks went backward. This month, the CDF collaboration announced results with an even larger asymmetry.

They also recently released a study in which top quarks and their partners showed this unexpected behavior almost half of the time in collisions above a certain energy.

“It’s really challenging for us to construct a convincing theory to explain this,” said theorist Susanne Westhoff, who presented on the subject at the Rencontres de Moriond conference on Wednesday. “All of the proposed explanations involve a new particle.”

Scientists think the cause of the unexpected asymmetry could be the interference of an undiscovered particle, one just heavy enough to go undetected by the Tevatron. If that’s true, experiments at the recently restarted Large Hadron Collider may be just weeks from collecting enough data to find it.

The Higgs particle would not have this kind of effect, said physicist Fabrizio Margaroli, CDF top quark group leader, who presented the experimental results at the conference.

In particle colliders, energy converts to mass to create heavy particles that haven’t been around in abundance in nature since moments after the big bang. The more energy a collider has, the more massive particles it can create. Scientists search for particles with certain masses by studying collisions with the corresponding energy.

If a new particle is affecting top and anti-top quark production, scientists should see greater effects in collisions closer to the energy at which the new particle is created. CDF physicists saw just that. In collisions above 450 GeV, top and anti-top quarks favored one direction over the other 48 percent of the time.

The Tevatron experiments did not have quite enough confidence in the measurements considering collisions at any energy to call what they saw evidence of a deviation from the expected. However, the study of collisions above 450 GeV is statistically significant enough to make the cut.

“At this point, things become really interesting,” Margaroli said. “People have a reason to be curious.”

The CDF and DZero experiments expect to announce updated results by this summer. If their findings are similar, the combined evidence from the two experiments could tell scientists with 99.9999 percent certainty that what they’re seeing is no fluke; new physics are most likely afoot.

Kathryn Grim

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Report on damage at Japan’s KEK

March 17, 2011 | 1:37 pm

Fallen ATF2 shield blocks

Our hearts  go out to the people of Japan who are suffering in the continuing disaster there. We’ll bring you updates on Japanese physics facilities and their people as they become available. 

This report from Rika Takahashi ran in today’s ILC Newsline:

As many people in the world already know, Japan is currently dealing with its worst disaster: Japan’s biggest earthquake on record and the fourth largest in history. Thousands of lives have been lost. Tens of thousands people are forced to evacuate and live without basic necessities. Hundreds of thousands are still missing.

KEK laboratory in Tsukuba is also dealing with the situation, and established an earthquake emergency response team headed by director general Atsuto Suzuki on 11 March upon arrival of the earthquake. Because of the power outage, detailed investigations into damages have not yet been conducted. However, some damage to the buildings and facilities has already been identified based on a glance-over inspection.

“The ILC-related facilities at KEK sustained considerable damages, especially at ATF (Accelerator Test Facility), which suffered severe damages,” said Seiya Yamaguchi, head of the Linear Collider Project Office at KEK. Many cracks on the building surfaces have been observed, and some window glasses were destroyed. Some of the cables and concrete shield blocks fell down. “The ATF linear accelerator suffered considerable damages. We will need a length of time to fully recover from the incident,” said Yamaguchi.

KEK reported that the operation of all accelerators and experimental devices operations were stopped immediately after the first shake, and confirmed employees were safe from radiation and that there was no hazard to the environment. There are no reports of casualties on either the Tsukuba or Tokai campuses. All users and collaborators who stayed at the Tsukuba and Tokai campuses were confirmed safe, and those who were at the Tokai campus have either moved to the dormitory at the Tsukuba campus or have returned to their homes.

Staff at KEK have received many e-mails from colleagues all over the world concerning the circumstances of the laboratory, which include warm encouraging words such as those from Taiwan:

 Japan has endured many hard times in the past and has proven to the world that miracles exist. We wish the earthquake never happened. Nevertheless, facing the heartbreaking tragedy today, it only makes Japan a stronger nation and united as ever.

KEK staff are endeavouring to understand the extent of the damage and how to actively address the situation. “Our first priority is to restore the facilities and reopen the lab. We sincerely appreciate everyone’s understanding and cooperation,” said Suzuki.

Akira Yamamoto, GDE project manager, also expressed his hope for the future of KEK. “We are deeply thankful for the many e-mails and warm words we have received from many global collaborators around the world,” he said. “We have been much encouraged and have received the energy needed to overcome this very difficult situation. We seek all possibilities for moving forward. We would hope to continue and extend our global team effort for the ILC.”

Further reporting will appear in a future issue of ILC NewsLine.

Rika Takahashi

Guest author

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LHC set to gain major ground in Higgs search

March 16, 2011 | 6:32 am

This plot shows the confidence with which the CMS collaboration should be able to observe the Higgs with different amounts of collision data. Image courtesy of the CMS Collaboration.

The Standard Model Higgs is running out of places to hide, fast.

LHC experiments will reduce the range in which it could be lurking by about 80 percent by the end of this year, according to projections.

That’s if the LHC meets minimum expectations by collecting 1 inverse femtobarn of data in 2011.

If the CMS and ATLAS experiments collect 5 inverse femtobarns of data, which they hope to do by the end of 2012, they will either see signs of the Standard Model Higgs or know with 95 percent certainty that the model is wrong. If they can collect twice that much, or 10 inverse femtobarns, experiments will be able to claim either discovery or nonexistence of the Higgs across the majority of its expected mass range.

“We are entering a very exciting time in physics,” said physicist Vivek Sharma, Higgs search leader for the CMS experiment, at the Rencontres de Moriond conference on Monday.

Scientists theorize the Higgs boson is the reason particles have mass. Funny thing is, physicists don’t know how much mass the Higgs itself has. But they have a good idea what the Higgs would look like if they created it with a particle collider, so they’re trying to make Higgs particles of different masses.

It won’t be enough to catch just one Higgs event. When physicists find a new particle, they use statistics to be sure they’re really seeing the thing they’re after. Once scientists have enough data, they can determine whether they have seen signs of the Higgs in a certain mass range or whether they can cross that area off of the map.

Physicists measure particle masses in units of energy called giga-electron volts, or GeV. They do this because, according to Einstein, energy is the same as mass multiplied by a constant, the speed of light squared. When high-energy particles collide in a particle accelerator, energy converts briefly to mass, creating new particles.

“The larger energy you have, the more massive particles you can create,” Sharma said. That’s why the LHC, which accelerates beams of protons up to 3.5 TeV and will eventually accelerate them to 7 TeV, can summon heavier particles than the Tevatron, which accelerates particle beams to about 1 TeV.

This plot shows the ATLAS collaboration's projected ability to rule out Higgs bosons of different masses by the end of 2011. Wherever a line dips below the dotted line at 1, ATLAS will be able to exclude the Higgs at that mass. Image courtesy of the ATLAS Collaboration.

The Standard Model (or Standard Model-like) Higgs mass range LHC experiments use falls between 114-600 GeV. Tevatron experiments have already ruled out the range between 158-173 GeV with a certainty of 95 percent. According to projections, LHC experiments should rule out the range between 120-530 GeV with the same certainty after each collecting 1 inverse femtobarn of data. This will reduce the portion of the Standard Model Higgs mass range in which experiments have not ruled out the Higgs with 95 percent certainty by about 80 percent.

“But we are not just in the business of excluding the Higgs,” Sharma said. “We are in the business of discovering it.”

Since physicists’ searches involve statistics, their results are expressed in degrees of certainty. They measure that certainty in units called sigma, represented as the Greek letter σ.

In this case, a result with a 3σ level of certainty is 99.7 percent sure to be correct. If scientists have 3σ certainty that they’ve found a new particle, they say they’ve found evidence of that particle. Results with a 5σ level of certainty are 99.9999 percent sure to be correct. If scientists have 5σ certainty that they’ve found a new particle, they consider that a discovery.

Recording just 1 inverse femtobarn of data, the minimum expected in 2011, the ATLAS and CMS experiments will be able to see evidence of the Higgs if it’s hiding in a mass range spanning an impressive 340 GeV, between 135 and 475 GeV, and will be able to discover the Higgs if it’s between 152 and 175.

This is a huge leap forward, but scientists hope to do even better. The more data the CMS and ATLAS experiments collect, the more sensitive they will be to excluding, finding signs of or discovering the Higgs.

Kathryn Grim

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Fermilab supports Japanese colleagues and friends, sees evidence of quake

March 15, 2011 | 1:41 pm

Editor’s note: We at symmetry magazine extend our deepest condolences and support to all those affected by the tragic events that occurred in Japan. Collaboration between the U.S. and Japanese particle physics communities goes back decades. Our thoughts remain with our Japanese colleagues and friends.

This story first appeared in Quantum Diaries on March 15.

When the 8.9-magnitude earthquake struck Japan last week, Fermilab felt the jolt emotionally and physically.

This screen image from the Tevatron main control room shows how the earthquake in Japan March 11 affects superconducting quadrupole magnets in the accelerator tunnel.

Accelerator operators in the main control room of the Tevatron saw the heart-rate-monitor-style tracking system for the more than 1,000 superconducting magnets go into cardiac arrest. This signaled the forward and backward pitch and side-to-side roll of the 4- ton, 20-foot-long magnets buried underground.

And that meant somewhere, something very bad had happened.

The monitor readings came from sensors called tiltmeters on underground magnets that steer particles around the four-mile Tevatron ring. They record vibrations too tiny for people at the laboratory to feel, including seismic waves from earthquakes thousands of miles away. The last time the magnets rocked like that was in 2010 when a 7-magnitude quake struck Haiti. The Tevatron also recorded a 2007 quake in Mexico, a 2006 quake in New Zealand, and earthquakes that triggered deadly tsunamis in Sumatra in 2005 and Indonesia in 2004. In all, the Tevatron has felt disaster more than 20 times.

A December 2010 symmetry magazine article explains how physicists first noticed the Tevatron’s super sensitivity, and how they work to make sure it doesn’t  interrupt the laboratory’s multi-million-dollar research efforts.

For accelerator operators, learning that the computer sqiggles signaled a quake in  Japan was an emotional blow. Fermilab
has a long and fruitful history of working with Japanese physicists and institutions. Japanese scientists have been involved with Fermilab from about the beginning of the experimental program in the early 1970s and became key members of the Tevatron’s CDF collaboration in the early 1980s.  Many Fermilab scientists, engineers and technicians have friends in Japan, from Japan or have worked at its high-energy physics laboratory, KEK, or JPARC, the high-energy accelerator complex.

In 2010, the most recent data available, Fermilab had 80 visiting researchers from Japanese institutions spread throughout the country, including the areas hardest hit by the earthquake and tsunami. Those scientists are valuable members of several experiments, particularly the CDF collaboration and the accelerator research program.  In all likelihood, the Japanese contribute even more to Fermilab’s research program because the also work at the laboratory as users from non-Japanese institutions, but a statistic on the number of those users is unavailable.

Tona Kunz

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Speedy single top sighting at the LHC

March 15, 2011 | 4:34 am

CMS scientists observed an excess in their data consistent with the production of single top quarks after combining just a couple of variables. Image courtesy of the CMS Collaboration.

For the first time, scientists at the Large Hadron Collider have spotted single top quark production.

It took Fermilab scientists at the Tevatron more than 13 years to observe the particle in its solo state after they discovered it paired with its antiparticle in 1995. The CMS experiment teased signs of the single top out of 36 inverse picobarns of collision data, roughly what Tevatron experiments collect over three days.

“We were surprised we saw it so soon,” said CMS physicist Philip Coleman Harris, who announced the accomplishment on Monday at the Rencontres de Moriond conference. The ATLAS experiment also made public impressive limits on the single top quark.

Scientists took the news as one of many signs that experiments at the LHC are prepared to make great strides in the coming years.

Energy makes all the difference. Rare single top quarks appear buried in background particles in collisions at the Tevatron, which have a center-of-mass energy of about 2 TeV. The LHC’s center-of-mass energy in 2010 was more than three times that high, at 7 TeV. At that energy, the production gap between the number of single top quarks and the number of background particles widens significantly, making them much easier to pick from the pack.

CMS scientists also found evidence of the single top quark through a multivariate analysis using 37 variables. Image courtesy of the CMS Collaboration.

At the Tevatron, the CDF and DZero experiments shook single top quarks from their data through a multivariate process, in which scientists combine data about dozens of variables in an algorithm to infer new information. At the LHC, CMS needed to look at only two variables. This simpler search gives scientists a new understanding of what they’ve found, said CMS Physics Coordinator Gigi Rolandi.

“When you have fewer variables, you understand the search better,” he said. “You can see if it shows the right behavior. A multivariate search is less intuitive.”

The CMS collaboration also found the single top quark using a multivariate search. But it’s the additional success of the simpler search that gives scientists the most hope for future hunting for new physics.

Kathryn Grim

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