Higgs Boson, Understanding The Buzz


The European Organization for Nuclear Research, CERN, will be holding a news seminar the morning of July 4 in order to announce new results from the ATLAS and CMS experiments. Based at the Large Hadron Collider (LHC) these two experiments are searching for the elusive Higgs boson particle.

Both of the research teams are working down to the deadline in order to finish analyzing their new data and decide what exactly they can say 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.”

Just last December, after the LHC had shut down its operations for the winter, both ATLAS and CMS “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, “[i]n 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.”

So why can’t they be certain? And what exactly is a Higgs boson? And why is it important?

“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.”

According to the theory, “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.”

The Standard Model isn’t able to predict the mass of the Higgs itself though. Apparently, that’s something that can only be learned from experimenting.

“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.”

“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, who was recently the Data Preparation Coordinator for ATLAS, says that knowing what to look for is the key. “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.”

“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, the head of 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.”

The U.S. participation in the ATLAS and CMS experiments at CERN numbers considerably over 1,500 people, and that’s not including the contributions made to other experiments and to 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.”



If the discovery is announced at CERN’s conference on July 4, it will really just be the discovery of hints and flashes about its nature and 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.”

Source: DOE/Lawrence Berkeley National Laboratory
Image Credits: DOE/Lawrence Berkeley National Laboratory; ATLAS/CERN

  1. Narotam Lathia

    Reproduced from Asian Voice (UK)
    “The discovery of the hitherto elusive Higgs boson or its subatomic kin ­ the popular “God particle“­ set India alight.
    Reams of print told us the story of the shy and retiring Professor Peter Higgs, now a venerable 83, and the theory he had fathered way back in the 1960s as a 37year-old physicist at the Edinburgh University. Confirmation of its existence, said CERN’s German Director General Rolf-Dieter Heuer, had increased man’s understanding of the universe by 4 per cent, its remaining mysteries, a daunting 96 per cent, still to be plumbed. The hugely ambitious CERN project buried under the Alps between France and Switzerland, is Europeanled but its outreach is global, with scientists from around the world participating in its ground-breaking researches in physics and cosmology. These stretch the human mind to its limits, so it was heartening to read of the Indian involvement in this amazing adventure. Japan and India represent the largest Asian presence in CERN, complementing the finest brains of North America, Russia, not to speak of Europe itself.

    There was much excitement at Kolkata’s Saha Institute of Nuclear Physics, whose scientists had made their own special contribution to the work of CERN. There were also contributions from the Tata Institute of Fundamental Research (TIFR) in Mumbai and Bangalore’s College of Science, a reminder of the distance India has travelled since independence in advanced science and engineering. For this the country’s owes a deep debt of gratitude to the pioneering vision of Homi Bhabha and Jawaharlal Nehru. One reason for the Kolkata’s celebration was the fact that the term boson is named after one its great sons, Satyendra Nath Bose, by none other than Albert Einstein. Their collaboration in what is today known as the Bose-Einstein statistics (one of two classes of subatomicparticles that laid the basis of quantam mechanics). Bose, like his distinguished Kolkata contemporary, the astrophysicist Megnad Saha, and their eminent senior Jagadish Bose, may have been elected Fellows of the Royal Society (FRS) in their time, but the accolade of the Nobel prize eluded all three, as did the Nobel Peace prize Mahatma Gandhi, but not Henry Kissinger who, in a fairer world, would surely have been indicted for crimes against humanity. Amit Chaudhuri, author of two jewelled fragments of autobiography and works of English literary criticism, remarked in a piece in The Guardian (July 3) that Indian scientists, in particular, were best advised to set up base in America if they harboured ambitions for the coveted Nobel. For the popular Western imagination India is largely unknown territory: exotic, poverty-ridden, disasterprone, mysterious and distant.

    Is Sweden’s Nobel Committee weighed down by the white man’s burden?”

  2. Narotam Lathia

    Higgs Boson and Gods’ particle Discovery of Higgs Boson is gigantic step for humanity in quantum and sub atomic field.

    Contribution of present Indian scientists from SINP-Bengal, Tata Institute for Nuclear Reasearch and Bhabha Atomic Research Centres, Chandigadh, and Bhubaneshwar is acknowledged by CERN, European counterpart for Large Hadron Collider Project.

    Following Indian names will and should be honoured in discovery of God particle: Satyendranath Bose, Suchendra Dutta, Meghnad Saha, Subroto Sarkar, Satyaki Bhattacharya, Manjeet Kaur and team etc. Indian newspapers must draw world attention to these Indian scientists to oppose casual dropping of the word “Bose“, thus erasing the real source. UK and USA media naming Higgs Boson as Higgs PARTICLE, must be opposed.

    The name Higgs denotes effort by Peter Higgs and Boson denotes Satyendranath Bose whose work was endorsed by Albert Einstine in 1920, and formed basis of Higg’s theories in 1960.

  3. Anadish Kumar Pal

    A proof out of compulsion to go on. However, falling short of ‘discovery’ to weave on with the virtual collision threads the Emperor’s New Clothes. What do they know about the reason behind ‘big bang’ and the preponderance of the proton and the electron? Nothing. Forget about knowing the reason behind baryonic asymmetry!

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