New report lays out what kids should know about science

July 29, 2011 | 12:13 pm

This looks like it is quite a departure from previous reports.

The idea of having a framework that spells out what we want kids to know about science is new. Previously there was something called the National Science Education Standards, which was drawn up by the Academy about 15 years ago. But every state created its own standards, and how they decided what parts of the national standards were in and what parts were out was different in every state.

Now because 44 states and the District of Columbia have adopted common standards in math and language arts, there’s beginning to be a demand for a similar thing to happen in science.

So this is the first step of a two-step process. The Academy is doing the framework, and a non-profit organization called Achieve, working with a small group of states, will develop standards that multiple states will choose to adopt if they wish.

What’s the advantage of having common standards?

Well, for example, right now every state has to pay to develop tests for assessing students’ knowledge based on different standards, so test developers are really getting paid multiple times for doing very similar work. It would be better to put that investment into developing more sophisticated kinds of tests that actually measure what it is you want the students to know and be able to do, rather than measure whether they’ve memorized a list of facts. Same thing with the development of curriculum and textbooks. So there are some economies of scale, in a sense.

How different is this from what kids are learning in school today?

It depends on the school. It depends on the teacher. There’s nothing in this framework that hasn’t been done, but there’s probably no classroom that’s doing it all.

The current national education standards push for science as inquiry. And because inquiry has a whole different set of meanings to different people, the understanding that students should be doing science to learn science has sometimes been overwhelmed by the notion that that was just messing around, and that children really needed to be learning facts.

What the research on learning shows is that students learn better when they have a context in which to put those facts, where the facts are developed in a coherent fashion and where they get to understand what science is by engaging in scientific practices.

So we spell out very explicitly the practices of science we think students should be doing. That is quite a departure. That’s a list that has some pieces in it that very few classrooms are doing today.

For instance?

For example engaging students seriously in arguing from evidence – so students are the ones drawing the conclusions and saying how does this evidence support or not support a particular explanation that was given for what’s going on. Another one is using models. Scientists when they’re studying a particular system always have in mind a model for that system that helps them compare and develop their ideas. Let’s take atomic theory of gases. You have the model of a gas as a set of spheres bouncing around in space. It’s a simplification because atoms are not spheres, but you can derive many properties of gases from that model and it gives an understanding of a gas even before you get to the idea of what is an atom or what is a molecule.

Having children explicitly make and discuss models for the things they’re being told about science helps them really capture the ideas as their own. The evidence shows it is important.

I was really struck by that because one of the things the public often doesn’t understand is that all these arguments among scientists – first they say one thing and then they say another – are really an important part of the process.

Absolutely. That’s what we want students to understand, that developing the explanation is what science is doing. And when you get to a certain point of understanding you have one explanation, and when you learn some more you have a more complex explanation, a more sophisticated explanation. The explanations evolve. A classic example I give is that Newton’s laws are not wrong, but they begin to be seen as approximate as you learn the next stage and understand relativity.

The report also recommends encouraging students to ask questions, and developing that ability.

Finding the question that is just beyond what you know, and that is ready to be answered with what you know and what you can now do, is key to science, and it’s key to learning science. Clearly students need guidance to get interested in an area where we want them to be learning something. But once they’re learning something, proceeding in the context of the questions students are asking, rather than a predetermined “this is what you should know,” works better because it’s capturing their interest and engaging them in the process more closely.

The report mentions how kids learn at different levels of development.

What the research shows is that kids learn better if information is coherent – if it takes into account their prior conceptions.

Take the structure of matter. Kids come with some ideas about that. They understand liquids and solids in some way. They may not have any concept of gases, but that comes later. So you develop the language and concept of matter – the idea that different substances have different properties, and that those properties depend on what they’re made of, and what they’re made of is some kind of particles. In each grade you’re working with the knowledge that’s already been developed at the previous stage and building on it, and helping them change their own mental concepts. That change of mental construct takes doing some things as well as being told some things.

For instance, if you put a liter of water and a liter of alcohol together, you don’t get two liters of liquid. The two liquids interpenetrate, and together take up a tiny bit less space. That’s very surprising to most kids, indeed even to most adults. But if you put a liter of sand and a liter of rocks together, you don’t get two liters of stuff either, because the sand fills in and goes between the rocks. So using a concrete example of something they can see to help them understand something that they can’t see is part of how you change their mental concept. Finding those examples and presenting them to kids is an important part of teaching science.

How does the development of the Internet figure into this framework?

That is part of the reason for stressing scientific practice, right? You will notice one of the practices is collecting, evaluating and presenting information. That’s reading and writing, but it’s also Internet searching and giving slide presentations and communicating in other ways. The evaluating piece is critical, because people do have so much access to so much information, and some of it is very good information and some of it is junk. A student needs to be able to say ok, if I’m looking for scientific information how do I judge if this is a good source or a bad source? How do I know what I trust and what I don’t trust?

That skill needs to be explicitly developed in the science classroom. The students need to be encouraged to go out and find information, but then helped to learn the skills they need in order to do that effectively.

The framework also talks about having students drawing out their ideas, which is the quintessential thing scientists do when they’re trying to explain something.

That’s a piece of the puzzle. Every scientist gives you a diagram or something that makes concrete what they’re thinking. That’s modeling, one of practices we expect students to do, too, all the time.

Does the framework draw any lessons from international comparisons of student performance in science?

The criticism of the US curriculum today is there’s just so much stuff in there that kids don’t get to see how it all fits together. The countries that do best in the international comparisons tend to be the countries that have a more coherent development of fewer major ideas over time, and a clear idea that learning more vocabulary isn’t adding depth. They teach kids how to think about a problem rather than learning a lot of Latin names for parts of the cell. How to think about cells and how they function is more important.

When we just memorize things we have no real understanding of, all of us tend to forget them.

How did you come up with the list of core ideas for each area of science?

We had a set of criteria for what constitutes a core idea for science learning. It’s not just what are the core ideas of the discipline, but what are the core ideas of the discipline that are important for students to learn about in K-12? For example in physical science, the core ideas are matter and energy and forces and interactions; those are the ones everyone would expect. But then another one is waves and their relationship to information technology. That’s for kids to understand that physics and chemistry have applications, and understand how these things play out in things they see in their everyday life.

Similarly, the last idea under earth science is the Earth and human activity; that has things like natural hazards but also human impacts on the planet. Both of those are important for kids to understand.

You also include engineering and technology.

For the same reason. Having a subgroup called engineering, technology and the applications of science is to stress the applications of science. One of the ways kids can develop and demonstrate their understanding of science is by designing something that applies that knowledge. So doing engineering design is a learning practice for students just as arguing from evidence is, or making models.

How much public feedback did you get?

The committee started in January and had its first meeting for public comment in July 2010.

There were about 2,000 people who responded on the website, and also there were a large number of focus groups that we organized – groups of people who would be engaged in using this material, for example the National Science Teachers Association and AAPT, the American Association of Physics Teachers. The Council of State Science Supervisors had three regional meetings where they brought people in from multiple states to discuss and review and give us feedback. Then we really revised a lot, so the document that came out last week is the same in many features, but different in many details from the one that was circulated a year ago.

We knew we had a primitive draft and it needed work. But that work was much more effectively done because we got input from the field.

Are there any aspects of the material that may be controversial?

The standards based on this framework will certainly include evolution, and they will also include climate change. Both of those things are, at least by some people, considered controversial, although scientifically they’re not controversial. As the Academy we can say scientifically that this is what the science says and this is what students should know, and the standards will be written based on that. Then the states will have to decide what they do about adopting them.

In the current political climate there’s a lot of debate about what should happen in education at the national versus the state or local level.

It’s important that these are not federal standards. The National Academy is a non-governmental body, and this framework development was funded by the Carnegie Corporation of New York, another non-governmental body. This work is being done for the states. The development of standards will involve the states – it’s not being done by federal government and pushed to the states.

There still is some political resistance to the whole movement toward common standards. But 44 states have decided they want common standards in math and language arts, so we’re hoping there will be nearly that number for the standards based on this framework.

What happens from here?

The framework is pointing in a direction, and it will probably take some time before everything is in place for the system to arrive in the place described by this framework. The system has many parts – for instance curriculum materials, the tests that students and, to a great extent today, their teachers are assessed by, what the teacher is doing in the classroom, and teacher professional development and teacher preparation. This is a guide for the evolution of all those pieces.

The non-profit, Achieve, will select about six states from the ones that apply and work with those states as kind of a test bed as they develop over the next year a set of standards based on this document. Once there is a set of standards, states will choose whether or not to adopt them. Curriculum developers will be developing curriculum materials that match those standards.

Basically since I retired a year ago January this has been my full-time job, and to some extent will continue to be as I try to guide how this plays out in various areas of assessment, curriculum, materials and teacher professional development. I’m already being asked by people in all those areas to come talk to them about what this is about and how can they help realize it. I tell people this is my retirement career.

 

Glennda Chui

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Antiproton mass measured with unprecedented precision

July 28, 2011 | 7:39 am

Scientists in the Japanese-European ASACUSA experiment at CERN reported today that they have measured the mass of the antiproton with nearly the same accuracy as scientists have measured the mass of its partner particle, the proton.

This will help scientists seeking to understand why our universe is dominated by matter when the big bang is thought to have created matter and antimatter in equal amounts.

The ASACUSA measurement reached a precision just below one part per billion. They found the ratio between the masses of the antiproton and the electron to be 1,836.1526736(23), in which the numbers in parentheses are the uncertainties on the last two digits.

“Imagine measuring the weight of the Eiffel tower,” said Masaki Hori, a project leader in the ASACUSA collaboration. “The accuracy we’ve achieved here is roughly equivalent to making that measurement to within less than the weight of a sparrow perched on top. Next time it will be a feather.”

From the CERN press release:

Ordinary protons constitute about half of the world around us, ourselves included. With so many protons around it would be natural to assume that the proton mass should be measurable to greater accuracy than that of antiprotons. After today’s result, this remains true but only just. In future experiments, ASACUSA expects to improve the accuracy of the antiproton mass measurement to far better than that for the proton. Any difference between the mass of protons and antiprotons would be a signal for new physics, indicating that the laws of nature could be different for matter and antimatter.

To make the measurement, scientists trapped antiprotons in helium atoms. When trapped in an atom of helium, an antiproton replaces an electron, occupying its orbital with about the same binding energy. Scientists fired a pair of laser beams at these atoms, destabilizing them and sending the antiprotons crashing into the helium nuclei to be annihilated. Scientists could interpret the mass of the antiproton compared to that of the electron by comparing the different laser frequencies that would cause this destabilization.

Scientists on ASACUSA conducted a similar experiment in 2006 using a single laser beam. However, they found the beam caused the atoms to jiggle around, hurting the accuracy of their measurement. The additional beam served to cancel out the jiggling effect.

Read the press release or read the article in Nature.

Kathryn Grim

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Tevatron experiments close in on Higgs particle

July 27, 2011 | 10:10 am

Scientists of the CDF and DZero collaborations at Fermilab continue to increase the sensitivity of their Tevatron experiments to the Higgs particle and narrow the range in which the particle seems to be hiding. At the European Physical Society conference in Grenoble, Fermilab physicist Eric James reported today that together the CDF and DZero experiments now can exclude the existence of a Higgs particle in the 100-108 and the 156-177 GeV/c² mass ranges, expanding exclusion ranges that the two experiments had reported in March 2011.

Last Friday, the ATLAS and CMS experiments at the European center for particle physics, CERN, reported their first exclusion regions. The two experiments exclude a Higgs particle with a mass of about 150 to 450 GeV/c², confirming the Tevatron exclusion range and extending it to higher masses that are beyond the reach of the Tevatron. Even larger Higgs masses are excluded on theoretical grounds.

This leaves a narrow window for the Higgs particle, and the Tevatron experiments are on track to collect enough data by the end of September 2011 to close this window if the Higgs particle does not exist.

James reported that the Tevatron experiments are steadily becoming more sensitive to Higgs processes that the LHC experiments will not be able to measure for some time. In particular, the Tevatron experiments can look for the decay of a Higgs particle into a pair of bottom and anti-bottom quark which are the dominant, hard-to-detect decay mode of the Higgs particle. In contrast, the ATLAS and CMS experiments currently focus on the search for the decay of a Higgs particle into a pair of W bosons, which then decay into lighter particles.

The LHC experiments reported at the EPS conference an excess of Higgs-like events in the 120-150 GeV/c² mass region at about the 2-sigma level. The Tevatron experiments have seen a small, 1-sigma excess of Higgs-like events in this region for a couple of years. A 3-sigma level is considered evidence for a new result, but particle physicists prefer a 5-sigma level to claim a discovery. More data and better analyses are necessary to determine whether these excesses are due to a Higgs particle, some new phenomena or random data fluctuations.

In early July, before the announcement of the latest Tevatron and LHC results, a global analysis of particle physics data by the GFitter group indicated that, in the simplest Higgs model, the Higgs particle should have a mass between approximately 115 and 137 GeV/c².

“To have confidence in having found the Higgs particle that theory predicts, you need to analyze the various ways it interacts with other particles,” said Giovanni Punzi, co-spokesperson of the CDF experiment. “If there really is a Higgs boson hiding in this region, you should be able to find its decay into a bottom-anti-bottom pair. Otherwise, the result could be a statistical fluctuation, or some different particle lurking in your data.”

The CDF and DZero experiments will continue to take data until the Tevatron shuts down at the end of September.

“The search for the Higgs particle in its bottom and anti-bottom quark decay mode really has been the strength of the Tevatron,” said Dmitri Denisov, DZero co-spokesperson.

“With the additional data and further improvements in our analysis tools, we expect to be sensitive to the Higgs particle for the entire mass range that has not yet been excluded. We should be able to exclude the Higgs particle or see first hints of its existence in early 2012.”

The details of the CDF and DZero analysis are described in this note, which will be posted later today, as well as submitted to the arXiv.

Kurt Riesselmann

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More than one way to search for SUSY

July 26, 2011 | 11:44 am

Experiments at the Large Hadron Collider have yet to find signs of supersymmetric particles, scientists announced at the European Physical Society conference this week in Grenoble.

But physicists will significantly improve their knowledge of SUSY in the coming year through indirect methods, which could include the discovery of the Higgs boson.

“For supersymmetry, this is a decisive moment in time,” said theorist Lars Bergstrom of Stockholm University.

Supersymmetry is a model that solves some significant problems of the Standard Model of particle physics. SUSY doubles the zoo of elementary particles by adding a partner for each of the particles we already know. It handily relates different types of particles in the Standard Model and offers an appealing candidate for dark matter. So far, scientists have found no evidence of SUSY particles at the LHC.

It’s looking bad for the simplest models of supersymmetry. Scientists at the LHC have been chipping away at two basic SUSY theories since they began analyzing data in 2010. But dozens of other models are still in the running, and scientists have more than one way to test them.

Discovering the mass of the Higgs boson, which scientists could do by next year, will reveal something about the likelihood that supersymmetry exists. Members of the ATLAS and CMS collaborations both displayed at the EPS conference tiny hints of a Higgs boson with a mass within the interval of 115-150 GeV.

To mesh well with the simplest models of supersymmetry, the Higgs would need to have a mass lower than 130 GeV, Bergstrom said. If its mass were more than 140, even the more complicated models of supersymmetry would fall out of favor.

“If it were higher than 140 GeV, you would have to twist things in weird ways to make supersymmetry work,” Bergstrom said. He added, “But one should never underestimate theorists.”

Scientists will also know more about SUSY by next year through improved studies of rare decays, which supersymmetric particles could influence.

Scientists from the CDF collaboration at the Tevatron and the CMS and LHCb collaborations at the LHC announced results in a study of the decay of a bottom-strange meson into two muons. According to the Standard Model, this decay should happen extremely rarely. However, if heavier, unseen particles exist, they could spur this decay to happen more frequently.

“This decay is one of the most powerful indirect searches for new physics,” said Guido Tonelli, spokesperson of the CMS experiment.

The CDF experiment saw the mesons decay onto a pair of muons more often than expected but only by a small amount with limited statistical significance. CDF scientists plan to update their result using 20-30 percent more data by next year.

“By then the LHC experiments will probably write the book on this, though,” said Rob Roser, spokesperson for the CDF experiment. “And that’s good; that’s what they’re supposed to do.”

The CMS and LHCb experiments did not see the same effect, but so far they do not have enough data to give a final verdict. They hope to have triple the data by next year.

In these types of decays, the heavier the unseen particles are, the less influence they have. It could be that the experiments do not see much of an effect because the particles causing the decay are extremely massive.

This could spell trouble for supersymmetry, Tonelli said. “The heavier they become, the more difficult it is to explain supersymmetry,” he said. “Above a certain mass it makes no sense.”

It could also be that the particles affecting the decay are not supersymmetric but rather something different. And it could be that nothing is affecting the decay at all.

The LHCb experiment, which was made to do this kind of physics, is looking into about six of these types of decays. Other accelerator experiments are looking into some of these as well.

The many versions of SUSY make it almost impossible to completely rule out, but physicists are spreading as wide as they can in their search.

Kathryn Grim

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DZero announces top quark asymmetry result, questions theory

July 25, 2011 | 11:49 am

This story first appeared on July 25 in Fermilab Today.

A new result from Fermilab’s DZero experiment was announced Saturday at the European Physical Society conference in Grenoble, France, studying the production of the top quark and its antimatter counterpart, the antitop quark, in proton-antiproton collisions. This result, called top quark forward and backward asymmetry, shows that the top quark travels more often in the direction of the incoming proton, whereas the anti-top quark follows the direction of the antiproton. This large asymmetry, which was unexpected, is consistent with a result reported earlier in the year and recently updated by Fermilab’s CDF collaboration.

The result means that there is a discrepancy between the data and a theory of the Standard Model that predicts the Tevatron detectors should see no such preference of the top and anti-op directions. Similar asymmetries observed in the production of muon and antimuon pairs about 30 years ago were a first step in the discovery of the Z boson.

When discrepancies such as this exist, it can indicate one of several things: an anomaly in the data, new physics at work or that the theories may need adjustment. In this case, DZero collaborators believe that the theory needs to be amended.

“The central value of the result is consistent with what CDF sees. The excess seems to be higher than the theory predicts. But we’ve taken our analysis one step further to give a possible interpretation of what is happening,” said Stefan Soldner-Rembold, DZero experiment co-spokesperson.

New physics is an attractive idea, explained DZero co-spokesperson Dmitri Denisov, but before you can look at that, you have to rule out other things first.

Finding that data doesn’t always fit with the prominent theory is something that physicists occasionally experience. Denisov explained that Tevatron physicists are running into this situation now because they have a larger data set, which enables them to look at more complex phenomena, which are more challenging to analyze.

In this case, DZero’s challenging analysis used 5.4 inverse femtobarns of data to measure the symmetry of how top quarks come out of collisions, either in the direction the beam of protons is moving (forward) or the direction of the antiproton beam (backward). Their result found a (19.6±6.5) percent asymmetry, similar to the (15.8±7.5) percent asymmetry CDF reported in January. The result is at a 2.4 sigma level, where a 3 sigma result is statistically relevant. CDF also announced over the weekend an update to their result using a different decay channel. The CDF collaboration’s updated result is (20.1±6.7) percent at about a 3 sigma level.

Douglas Orbaker, a DZero collaborator from the University of Rochester, will present the DZero result at a special Wine and Cheese lecture at 2:30 p.m. Monday, July 25, in One West. The talk will be available via streaming video.

Rhianna Wisniewski

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Higgs buzz at summer physics conference 

July 22, 2011 | 2:25 pm

Physicists could be on their way to discovering the Higgs boson, if it exists, by next year. Scientists in two experiments at the Large Hadron Collider pleasantly surprised attendees at the European Physical Society conference this afternoon by both showing small hints of what could be the prized particle in the same area.

“This is what we expect to find on the road to the Higgs,” said Gigi Rolandi, physics coordinator for the CMS experiment.

Both experiments found excesses in the 130-150 GeV mass region. But the excesses did not have enough statistical significance to count as evidence of the Higgs.

If the Higgs really is lurking in this region, it is still in reach of experiments at Fermilab’s Tevatron. Although the accelerator will shut down for good at the end of September, Fermilab’s CDF and DZero experiments will continue to collect data up until that point and to improve their analyses.

“This should give us the sensitivity to make a new statement about the 114-180 mass range,” said Rob Roser, CDF co-spokesperson. Read more about the differences between Higgs searches at the Tevatron and at the LHC here.

The CDF and DZero experiments announced expanded exclusions in the search for their specialty, the low-mass Higgs, this morning. On Wednesday, the two experiments will announce their combined Higgs results.

Scientists measure statistical significance in units called sigma, written as the Greek letter σ. These high-energy experiments usually require 3σ  level of confidence, about 99.7 percent certainty, to claim they’ve seen evidence of something. They need 5σ to claim a discovery. The ATLAS experiment reported excesses at confidence levels between 2 and 2.8σ, and the CMS experiment found similar excesses at close to 3σ.

After the two experiments combine their results — a mathematical process much more arduous than simple addition — they could find themselves on new ground. They hope to do this in the next few months, at the latest by the winter conferences, said Kyle Cranmer, an assistant professor at New York University who presented the results for the ATLAS collaboration.

“The fact that these two experiments with different issues, different approaches and different modeling found similar results leads you to believe it might not be just a fluke,” Cranmer said. “This is what it would look like if it were real.”

If the accelerator and the detectors continue to function as impressively as they have been, ATLAS and CMS should be able to at least double their data by the end of the year, increasing their reach. This could flatten the excesses if they turn out to be mere statistical fluctuations. Both experiments have seen bumps come and go as they’ve gone through their data, as have experiments before them.

“DZero has seen these kinds of effects vanish,” said Sebastien Greder of Institut Pluridisciplinaire Hubert Curien in Strasbourg, who presented DZero’s Higgs results.

The excesses could also be hints of new physics other than the Higgs. Whatever the case, scientists have made huge strides in ruling out places the Higgs could be hiding.

The ATLAS collaboration ruled out two areas, 155-190 GeV and 295-450 GeV, with a 95 percent confidence level. Similarly, the CMS collaboration excluded the ranges from 149-206 GeV and 300-440 GeV, plus three short segments in between, with the same confidence.

“We have excluded regions of mass not explored before by the Tevatron,” said Fabiola Gianotti, spokesperson for the ATLAS experiment. “The area where it can be has gotten narrower and narrower.”

The hunt continues.

Kathryn Grim

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How to find the Higgs particle; first Higgs search results from LHC and Tevatron

July 22, 2011 | 12:01 am

Editor’s note: story updated at noon CDT on July 22: The LHC experiments reported at the EPS meeting a tantalizing excess of Higgs-like events, short of claiming a discovery, but very intriguing nevertheless. See the Higgs search at the LHC section further below for more information on these results.

Experiments at Fermi National Accelerator Laboratory and the European particle physics center, CERN, are zooming in on the final remaining mass region where the Higgs particle might be lurking. Over the next seven days, Fermilab’s CDF and DZero collaborations and CERN’s ATLAS and CMS collaborations will announce their latest Higgs search results at the High-Energy Physics conference of the European Physical Society.

Scientists at Fermilab and CERN employ very similar methods to create the Higgs: accelerate particles to high energy using the world’s most powerful accelerators, the Tevatron (1 TeV beam energy) and the Large Hadron Collider (3.5 TeV), smash the particles together, and sift through the large number of new particles emerging from these collisions. But to find a Higgs particle among the many particles created, the teams of scientists are focusing on different signals (see below).

If the Higgs particle exists and has the properties predicted by the simplest Higgs model, named after Scottish physicist Peter Higgs, then the colliders at Fermilab and CERN already must have produced Higgs particles. But finding the tell-tale sign of a Higgs boson among all other particle signatures is like searching for a drop of ink in an ocean. Only if the accelerators produce more and more collisions do scientists stand a chance of finding enough evidence for the Higgs particle.

Where to look

The Higgs mechanism, developed in the 1960s by several independent groups of theorists, explains why some fundamental particles have mass and others don’t. Its mathematical framework fits perfectly into one of the most successful theories in science: the Standard Model of elementary particles and forces.

Experimenters sifting through data from one experiment after another have come up empty-handed; instead they have ruled out larger and larger swaths of potential Higgs territory. An analysis by the GFitter group of precision measurements and the direct and indirect constraints on the Higgs mass indicates that, in the simplest Higgs model, the Higgs particle should have a mass between approximately 115 and 137 billion electron volts (GeV)/c², or about 100 times the mass of a proton.

Higgs search at the Tevatron

At Fermilab’s Tevatron, scientists attempt to produce Higgs particles by smashing together protons and antiprotons, composite particles that comprise elementary building blocks. When a proton and antiproton hit each other at high energy, scientists observe the collisions and interactions of these components, such as quarks, antiquarks and gluons. Those subatomic collisions transform energy into new particles that can be heavier than the protons themselves, as predicted by Einstein’s famous equation E=mc².

Tevatron scientists have carried out detailed simulations of such collisions and found that the best chance for producing, say, a 120-GeV Higgs boson at the Tevatron are quark-antiquark collisions that create a high-energy W boson (see graphic). This W boson has a chance to spend its extra energy to generate a short-lived Higgs boson. The W boson and the Higgs boson would then decay into lighter particles that can be caught and identified by the CDF and DZero particle detectors, which surround the two proton-antiproton collision points of the Tevatron.

According to the Standard Model, such a 120-GeV Higgs boson will decay 68 percent of the time into a bottom quark and anti-bottom quark. But other collision processes and particle decays also produce bottom and anti-bottom quarks. Identifying an excess of these particles due to the decay of the Higgs boson is the best chance for Tevatron scientists to discover or rule out a Standard Model Higgs.

At the EPS conference, CDF and DZero will report (see press release) that, for the first time, the two collaborations have successfully applied well-established techniques used to search for the Higgs boson to observe extremely rare collisions that produce pairs of heavy bosons (WW or WZ) that decay into heavy quarks. This well-known process closely mimics the production of a W boson and a Higgs particle, with the Higgs decaying into a bottom quark and antiquark.

Higgs search at the LHC

At the LHC, located on the French-Swiss border, scientists smash protons into protons. Because the LHC operates at higher collision energies than the Tevatron, each collision produces on average many more particles than a collision at the Tevatron. In particular, the LHC floods its particle detectors with bottom and anti-bottom quarks created by many different types of subatomic processes. Hence it becomes more difficult than at the Tevatron to find this particular “ink in the ocean”—an excess of bottom and anti-bottom quarks in the LHC data due to the Higgs particle.

At the EPS conference, the ATLAS scientists showed that they should have been able to exclude a Higgs boson with mass between 130 and 200 GeV/c², but instead the collaboration saw an excess of events in the 130 to 155 GeV/c² range, as reported by ATLAS physicist Jon Butterworth in his blog at the Guardian. It could be a fluctuation, but it could also be the first hint of a Higgs signal. Geoff Brumfiel writes for Nature News that the CMS experiment also sees an excess in the 130 to 150 GeV/c² range. (CMS physicist Tommaso Dorigo has posted the relevant CMS Higgs search plots in his blog.) Combined, the two LHC experiments should have enough data by the end of this summer to say whether this excess is real or not. The Tevatron experiments are getting close to being sensitive to a Higgs particle near 150 GeV as well. Here is the new DZero result: the dotted line, which indicates sensitivity, is approaching 1 near 150 GeV, but the solid line, which is the actual observation, is significantly below 1, yet it differs from the expectation only at the 1 to 1.5 sigma level. Bottom line: DZero scientists cannot exclude a Higgs boson in this range. And here is the new CDF result: Again, for a Higgs mass of about 150 GeV/c², the sensitivity approaches 1, and the observed Higgs constraints agree well with the expectations. (Note that DZero shows 1-sensitivity and CDF shows sensitivity; that’s why the CDF curve is above 1.) On Wednesday, July 27, CDF and DZero will present their combined results for this mass range at the EPS conference. The sensitivity of the combined CDF and DZero results will be even closer to 1 at 150 GeV/c².

For a light Higgs boson, LHC scientists focus on a very different Higgs production and decay process, complementary to the Higgs search at the Tevatron. Detailed simulations of high-energy proton-proton collisions have shown that the best chance to catch, say, a 120-GeV Standard Model Higgs particle at the LHC is to look for a Higgs boson emerging from the collision of two gluons, followed by its decay into two high-energy gamma rays (see second graphic). This is an extremely rare process since the Higgs boson doesn’t interact directly with the massless gluons and gamma rays. Instead, the Higgs production and decay occur through intermediate, massive quark-antiquark loops, which can temporarily appear in subatomic processes, in accordance with the laws of quantum mechanics. The intermediate loop, however, makes this process much rarer to occur. In particular, the decay of a 120-GeV Standard Model Higgs boson into two gamma rays happens only once out of 500 times. Hence LHC scientists will need to gather a sufficiently large number of proton-proton collisions to observe this process.

Why do physicists think that the Higgs particle exists?

The discovery in the 1980s of heavy, force-carrying particles, known as W and Z bosons, confirmed crucial predictions made by the Standard Model and the simplest Higgs model. Since then, further discoveries and precision measurements of particle interactions have confirmed the validity of the Standard Model many times. It now seems almost impossible to explain the wealth of particle data without the Higgs mechanism. But one crucial ingredient of this fabulous particle recipe—the Higgs boson itself—has remained at large. Does it exist? How heavy is it? Does it interact with quarks and other massive particles as expected? These questions will keep scientists busy for years to come.

Want to learn more about what the Higgs particle is and how it gives mass to some particles? Watch this 3-minute video.

Kurt Riesselmann

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Wealth of particle physics data yields numerous results for EPS conference

July 21, 2011 | 12:11 pm

Fermilab’s Tevatron particle collider is nearing the end of its lifetime, but results from its two collider experiments are nowhere close to dwindling. Members of the CDF and DZero collaborations at Fermilab will present a record number of results at this month’s European Physical Society conference on High-Energy Physics, which begins on July 21 in Grenoble, France.

Collaborators from the CMS experiment at the LHC will also present numerous results following a successful start to the LHC running in 2011. Fermilab is the host laboratory for the U.S. group participating in the CMS experiment and plays a major role in the operation of the detector and the analysis of the experiment’s collision data.

Fermilab’s MINOS experiment will present its result on the transformation of muon neutrinos into electron neutrinos, which constrained a measurement reported earlier by the Japanese T2K experiment.

Results from CDF will include the first observation of a new, heavy relative of the neutron as well as a first indication of the extremely rare decay of particles containing a bottom and a strange quark into two muons. This might shed light on the existence of yet unknown particles. DZero will present an update on a tantalizing hint of a new type of matter-antimatter asymmetry and present numerous measurements of properties of the top quark, the heaviest known elementary particle. Both CDF and DZero will provide updates on their search for the Higgs boson, which, if it exists, will explain why some elementary particles have mass and others don’t.

CDF and DZero spokespersons attribute the rush of new results to several things, including the record size of the data set produced by the Tevatron collider, and the improved data analysis techniques developed and employed by hundreds of scientists and the friendly competition with physicists working at the Large Hadron Collider, who are sifting through a quickly growing set of LHC data.

“As the majority of our expected Tevatron data is now available and as the LHC data set begins to grow significantly, our collaborators are starting to put results out quickly,” said DZero co-spokesperson Stefan Soldner-Rembold.

To date, CDF has analyzed more than 8 inverse femtobarns of collision data while DZero has scrutinized up to 9 inverse femtobarns. The collaborations anticipate accumulating a total of 10 and 11 inverse femtobarns of data, respectively, by the time the Tevatron shuts down at the end of September. One inverse femtobarn represents about 50 trillion proton-antiproton collisions at the Tevatron.

The steadily increasing data sets at the Tevatron have boosted the number of papers submitted by the CDF and DZero collaborations for publication. At a little more than six months through the year, both collaborations have published more than 60 papers between them and are on track to publish more papers in a single year than any year in the history of the Tevatron experiments. The number of publications produced will grow through 2012 and beyond as scientists will use better analysis techniques to squeeze more information out of their unique data sets.

More information about these and other particle physics results will be presented at the EPS conference. The EPS organizers will hold a press conference on Monday, July 25.

Rhianna Wisniewski

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Fermilab experiment discovers a heavy relative of the neutron

July 20, 2011 | 5:13 pm

Fermilab issued the following press release on July 20.

Scientists of the CDF collaboration at the Department of Energy’s Fermi National Accelerator Laboratory announced the observation of a new particle, the neutral Xi-sub-b (Ξ_b⁰). This particle contains three quarks: a strange quark, an up quark and a bottom quark (s-u-b). While its existence was predicted by the Standard Model, the observation of the neutral Xi-sub-b is significant because it strengthens our understanding of how quarks form matter. Fermilab physicist Pat Lukens, a member of the CDF collaboration, presented the discovery at Fermilab on Wednesday, July 20.

The neutral Xi-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 (two up quarks and a down quark) and the neutron (two down quarks and an up quark). The neutral Xi-sub-b belongs to the family of bottom baryons, which are about six times heavier than the proton and neutron because they all contain a heavy bottom quark. The particles are produced only in high-energy collisions, and are rare and very difficult to observe.

Although Fermilab’s Tevatron particle collider is not a dedicated bottom quark factory, sophisticated particle detectors and trillions of proton-antiproton collisions have made it a haven for discovering and studying almost all of the known bottom baryons. Experiments at the Tevatron discovered the Sigma-sub-b baryons (Σ_b and Σ_b*) in 2006, observed the Xi-b-minus baryon (Ξ_b^-) in 2007, and found the Omega-sub-b (Ω_b^-) in 2009. The lightest bottom baryon, the Lambda-sub-b (Λ_b), was discovered at CERN. Measuring the properties of all these particles allows scientists to test and improve models of how quarks interact at close distances via the strong nuclear force, as explained by the theory of quantum chromodynamics (QCD). Scientists at Fermilab and other DOE national laboratories use powerful computers to simulate quark interactions and understand the properties of particles comprised of quarks.

Once produced, the neutral Xi-sub-b travels a fraction of a millimeter before it decays into lighter particles. These particles then decay again into even lighter particles. Physicists rely on the details of this series of decays to identify the initial particle. The complex decay pattern of the neutral Xi-sub-b has made the observation of this particle significantly more challenging than that of its charged sibling (Ξ_b^-). Combing through almost 500 trillion proton-antiproton collisions produced by Fermilab’s Tevatron particle collider, the CDF collaboration isolated 25 examples in which the particles emerging from a collision revealed the distinctive signature of the neutral Xi-sub-b. The analysis established the discovery at a level of 7 sigma. Scientists consider 5 sigma the threshold for discoveries.

CDF also re-observed the already known charged version of the neutral Xi-sub-b in a never before observed decay, which served as an independent cross-check of the analysis. The newly analyzed data samples offer possibilities for further discoveries.

The CDF collaboration submitted a paper that summarizes the details of its Xi-sub-b discovery to the journal Physical Review Letters. It will be available on the arXiv preprint server on July 20, 2011.

CDF is an international experiment of about 500 physicists from 58 institutions in 15 countries. It is supported by the U.S. Department of Energy, the National Science Foundation and a number of international funding agencies.

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

 

Rhianna Wisniewski

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Iowa State physicist to test next-generation neutrino detector for major experiment

July 19, 2011 | 4:01 pm

Iowa State issued the following press release on July 15.

Hundreds of physicists from around the world are making plans to shoot the world’s most intense beam of neutrinos from Illinois, underground through Iowa, all the way to a former gold mine in South Dakota. And Iowa State University’s Mayly Sanchez is part of the research team.

Sanchez, an assistant professor of physics and astronomy, is working to develop the next generation of detectors to pick up the trail of neutrinos, subatomic particles that are among the most abundant in the universe and normally race through matter without leaving a trace.

“Advances in material sciences are allowing us to make photodetectors that are larger, cheaper, better,” said Sanchez. “They’ll have a larger surface area and be better able to measure points in space with better timing. The question is, can we make a better experiment?”

Sanchez’s work is supported by a five-year, $709,000 grant from the National Science Foundation‘s Faculty Early Career Development Program. The early career grants support junior faculty identified as teacher-scholars through outstanding research, excellent education and the integration of education and research.

The grant allows Sanchez to contribute to the proposed Long Baseline Neutrino Experiment – a $900 million collaboration of 300-plus researchers led by the Fermi, Brookhaven and Los Alamos national laboratories of the U.S. Department of Energy. The experiment would send a neutrino beam 800 miles – that’s the long baseline – from the Fermi National Accelerator Laboratory in Batavia, Ill., to the Homestake Mine in Lead, S.D., to see how the neutrinos change over distance.

Sanchez is working to develop photodetectors for a proposed neutrino water Cherenkov detector as big as a 20-story building.

The detector would be built deep underground at the Homestake Mine. The detector is designed to spot Cherenkov light, the blue glow emitted when a charged particle passes through matter faster than light. Passing light is possible because matter – that’s water in the case of these detectors – slows light more than subatomic particles.

Neutrino physicists surround huge pools of water with sensitive photodetectors to find any Cherenkov light emitted when chargeless neutrinos hit hydrogen and oxygen atoms and throw off charged electrons and muons. Current detectors use 10- to 12-inch photodetectors that cost $1,500 each.

Because the long baseline experiment will need 45,000 photodetectors, the size and expense of current technology has physicists looking for a different kind of photodetector. Sanchez is working with researchers at Argonne National Laboratory in Argonne, Ill., to develop and test photodetectors that take advantage of materials and nanotechnology advancements.

As part of the project, Sanchez expects to establish a photodetector testing laboratory on the Iowa State campus. She’ll also lead the group working to calibrate the photodetectors as they’re developed. Iowa State graduate student Tian Xin and undergraduate Abhishek Vemuri are also working on the project.

“We’re trying to demonstrate that you can use these new photodetectors and improve the physics capabilities,” Sanchez said.

The Department of Energy’s long baseline experiment is designed to answer some fundamental questions of physics: What role did neutrinos play in the evolution of the universe? Why do we live in a universe dominated by matter? Why do neutrinos have masses smaller than other subatomic particles? And what are the masses of the three kinds or neutrinos – the electron, muon and tau?

Sanchez is a veteran of neutrino experiments, working on the MINOS and NOvA experiments designed to study neutrinos sent from Fermilab to detectors in northern Minnesota.

It’s a scientific and engineering challenge to probe the mysteries of neutrino physics.

“The challenge is the probability of neutrinos reacting with matter is really, really small,” Sanchez said. “And so we need really, really large detectors and very intense beams of neutrinos.”

But, she said, “Neutrino physics is very exciting. That’s the reason I’m doing this.”

 

Guest author

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