Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Understanding What’s Up With the Higgs Boson

29.06.2012
Berkeley Lab scientists, major contributors to the ATLAS experiment at the Large Hadron Collider, explain what the excitement is about
CERN, the European Organization for Nuclear Research headquartered in Geneva, Switzerland, will hold a seminar early in the morning on July 4 to announce the latest results from ATLAS and CMS, two major experiments at the Large Hadron Collider (LHC) that are searching for the Higgs boson. Both experimental teams are working down to the wire to finish analyzing their data, and to determine exactly what can be said about what they’ve found.

“We do not yet know what will be shown on July 4th,” says Ian Hinchliffe, a theoretical physicist in the Physics Division at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), who heads the Lab’s participation in the ATLAS experiment. “I have seen many conjectures on the blogs about what will be shown: these are idle speculation. Things are moving very fast this week, and it’s an exciting time at CERN. Many years of hard work are coming to fruition.”

Last December, not long after the LHC had shut down for the winter, ATLAS and CMS both reported slight excesses over background of two kinds of signals consistent with the expected signature of a Higgs boson. The LHC started running again at a higher energy this spring, and, says Hinchliffe, “In that short time we’ve already doubled the data. But even if both experiments were to confirm what they saw last year with new data, no one can be certain that it is the Higgs.”

Why can’t they know? And what’s a Higgs boson anyway?

Why particles have mass

A Higgs boson is an excitation – a fleeting, grainy representation – of the Higgs field, which extends throughout space and gives all other particles their mass.

At the instant of the big bang, everything was the same as everything else, a state of symmetry that lasted no time and was immediately broken. Particles of matter called fermions emerged from the sea of energy (mass and energy being interchangeable), including quarks and electrons that would much later form atoms. Along with them came force-carrying particles called bosons to rule how they all were related. All had different masses – sometimes wildly different masses.

Using the concepts of a Higgs field and Higgs boson, the Standard Model explains why quarks, protons, electrons, photons, and a wide-ranging zoo of other particles have the specific masses they do. Oddly, however, the Standard Model can’t predict the mass of the Higgs itself. That will only be learned from experiment.

It will be far from simple to know when the Higgs has actually been found. Any particle that packs as much energy as the Higgs lasts only a miniscule fraction of a second before it falls apart into other particles, each with lower energy, and these fall apart into still lower-energy particles, finally leaving a set that ATLAS or CMS can see or infer. According to the Standard Model, the Higgs can decay by half a dozen different patterns of tracks, or channels.

The probability of each path varies. For example, there’s a low probability that a Higgs with mass equivalent to 100 billion electron volts (100 GeV) of energy would decay into a pair of W bosons, carriers of the weak interaction. Yet if its mass were 170 GeV, the probability of its decaying by that channel would be very high.

But earlier measurements, including those made last year at the LHC and at Fermilab’s Tevatron, have already excluded many possible masses for a Standard Model Higgs. Of the narrowing possibilities, the hints that ATLAS and CMS saw in 2011 were in the neighborhood of 125 or 126 GeV.

The two channels involved, called the two-photon channel and the four-lepton channel for short, are certainly not the most likely decay routes, says Beate Heinemann of Berkeley Lab’s Physics Division, who is also a professor in UC Berkeley’s Department of Physics. “The probability that a 125-GeV Higgs would decay into two gamma rays is about two tenths of one percent, and the likelihood that it would decay into four muons or electrons is even smaller.”

Finding the music in the noise

Background noise is the key. Even though the two-photon and four-lepton channels have a low probability, they are relatively free of noise from particle debris that obscures evidence of other channels. More probable routes for the decay of a Higgs with mass near 125 GeV would be to a bottom quark and antibottom quark, or a pair of W bosons, or a pair of tau particles, but all these are much harder to detect.

Heinemann, recently the Data Preparation Coordinator for ATLAS, says knowing what to look for is crucial. “Bunches of protons cross through each other 20 million times a second inside the ATLAS detector, with an average of 20 collisions at each crossing.” Electronic filters automatically cull the events to 100,000 per second of possible interest. Sophisticated software further reduces the cull to a few hundred events per second that are recorded and stored for later study. Says Heinemann, “We try to keep everything anyone can think of that might be interesting.”

The products of data reduction are colorful diagrams of spectacular sprays of particles from proton-proton collisions, recorded by the concentric layers of detectors that ATLAS wraps around the beam line. What makes the diagrams so intricate and precise begins in the Inner Detector, largely designed and built at Berkeley Lab, as was much of the filtering and sifting hardware and software.

A simulation of the two-photon channel shows what ATLAS sees when the decay of a Higgs boson results in the production of two gamma rays. The blue beads indicate intermediate massive particles, and the bright green rods are the gamma-ray tracks. While the two-photon channel is the least likely Higgs decay, it is easier to observe than others with even noisier backgrounds.

ATLAS’s innermost detector consists of three barrels, the diameter of the outermost equalling 24 centimeters (less than 10 inches), plus three disks; 80 million pixels cover an area of 1.7 square meters (18 square feet). Particle tracks are followed through three layers of pixels, initiating precise measurement of each event.

“The LHC produces far more particles per collision than any accelerator before it. Not confusing them requires finer granularity and finer resolution, which means many more detector elements close to the beam,” says Murdock “Gil” Gilchriese, who headed the Berkeley Lab group that worked on the ATLAS Inner Detector.

The very heart of ATLAS is a pixel detector consisting of 80 million tiny silicon rectangles 50 microns (millionths of a meter) wide and 400 microns long, each connected to its own electronics – many millions of transistors bathed in the most intense radiation an accelerator has ever produced.

At CERN, U.S. participation in the ATLAS and CMS experiments alone numbers well over 1,500 people, not to mention significant U.S. contributions to other experiments and the accelerator itself. Fermilab hosts the U.S. participation in CMS, and Brookhaven National Laboratory is the U.S. host for ATLAS.

“About 20 percent of the ATLAS collaboration comes from the U.S.,” says Heinemann, “and one of the largest contingents is from Berkeley Lab, many of us in key positions. For example, Kevin Einsweiler, who led the ATLAS pixel project, is currently ATLAS’s Physics Coordinator, guiding analysis of the data. Michael Barnett has long held the post of Outreach Coordinator. At any given time we may also have 10 students and 10 postdocs working on ATLAS. There are a lot of us, and much of the time many of us are on the job at CERN.”

Whatever news comes out of CERN in the wee hours of the morning on July 4, hints and indications so far are just the beginning of the search to pin down the Higgs and learn its characteristics. The Higgs search commences a long voyage of discovery into a realm of unexplored physics, of supersymmetry, dark matter, miniature black holes, extra dimensions of space – and other, unanticipated wonders that defy prediction.


For further information contact:
Ian Hinchliffe, head of Berkeley Lab participation in ATLAS, i_hinchliffe@lbl.gov, 510-486-4487
Beate Heinemann, Berkeley Lab staff scientist and professor of physics at UC Berkeley, bheheinemann@lbl.gov, 510-486-7538
Natalie Roe, Director of Berkeley Lab’s Physics Division, naroe@lbl.gov, 510-486-6380

More about ATLAS is at http://atlas.ch/

Wikipedia’s discussion of the Higgs is at http://en.wikipedia.org/wiki/Higgs_boson

More about quarks, neutrinos, antimatter, extra dimensions, dark matter, accelerators, detectors, and other fascinating aspects of particle physics can be found in the Particle Adventure at http://www.particleadventure.org/index.html

The U.S. Department of Energy’s Office of Science and the National Science Foundation provide support for U.S. participation in the Large Hadron Collider and its major experiments. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

Paul Preuss | EurekAlert!
Further information:
http://www.lbl.gov

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Stretchable biofuel cells extract energy from sweat to power wearable devices

22.08.2017 | Power and Electrical Engineering

New technique to treating mitral valve diseases: First patient data

22.08.2017 | Medical Engineering

IVAM Marketing Prize recognizes convincing technology marketing for the tenth time

22.08.2017 | Awards Funding

VideoLinks
B2B-VideoLinks
More VideoLinks >>>