Higgs boson solutionby Rebecca Priestley
Are physicists closing in on the elusive Higgs boson or is a surprise in store?
Particle physics used to be easy. There were atoms, inside which energetic electrons whizzed around a nucleus made up of protons and neutrons. Today’s elementary particles are quarks and leptons and bosons and fermions; there are up versions and down versions, charged versions and neutral versions.
But together, the many subatomic particles discovered in recent decades are not enough to explain what physicists call the “standard model”, a theory that squares away pretty much everything about the constituent parts of the known universe … except why particles have mass.
Enter the Higgs boson. This theoretical particle – the missing piece of the puzzle – was predicted by physicist Peter Higgs in 1964. Higgs’s idea was that the universe contains an as yet undiscovered field. Interaction with what is now called the Higgs field gives particles their mass and would explain why some particles have high mass (that is, are heavy) and some particles have almost no mass.
But despite all the recent talk about the Higgs boson – the physical manifestation of an excited Higgs field – no one yet knows if it even exists. Or rather, if it ever existed. “Higgs bosons would not naturally exist in the universe today,” says David Krofcheck, a physicist from the University of Auckland. “Everything in the known universe is too cold.”
Physicists, therefore, have the challenge of searching for a theoretical particle that may have briefly existed immediately after the Big Bang that created the universe. In 2009 the European Organisation for Nuclear Research (CERN) began operating the Large Hadron Collider (LHC) primarily to search for the elusive particle.
This underground particle accelerator, with a circumference of 27km, boosts protons to high speeds, smashes them together, and uses sophisticated detectors to see what results from the high-speed, high-temperature collisions that mimic conditions one-thousandth of a billionth of a second after the Big Bang.
A boson is an elementary particle of the same type as the photon. Theoretical bosons include the Higgs and gravitons. Physicists have predicted that any Higgs bosons created by the LHC would immediately decay into one of several precise combinations of quarks, leptons and gamma rays, and that is what the detectors are searching for. Working backwards from any combinations of particles detected in the LHC collisions allows the calculation of the mass of the Higgs boson.
Early experiments, by the LHC and other particle accelerators, confirmed masses at which the Higgs boson does not exist. That narrowed the range of possible masses at which it might be found, and has allowed further experiments to be more focused. Last December CERN reported that two of its experiments had revealed “tantalising hints” of a new particle with a mass between 115 and 130GeV (a proton, in comparison, has a mass of 1GeV).
So how significant is this result? “The hints from CERN are extremely exciting but the recent announcement is not a confirmed discovery,” says Krofcheck, who has just returned from five months at CERN, playing devil’s advocate with a group of physicists “whose questions the data analysts must satisfy before they can make their results public”.
So far, although peaks have been seen at 125GeV, the results are not conclusive. The next round of proton-proton collisions will start in March, with the goal, says Krofcheck, of “accumulating more data to eliminate the statistical uncertainty in the current results”.
Krofcheck is excited about the possibility that what they are seeing is the Higgs boson. “If the promising signals from CERN do not vanish as mere statistical fluctuations in 2012, then I think we can feel that we are still on the right track, but we should always be open for surprises.”
What if the final results rule out the Higgs boson? “This would be a huge surprise and secretly we hope this might happen,” Professor Stefan Söldner-Rembold, head of the particle physics group at the University of Manchester, told the media in December. “If this is the case, there must be something else that takes the role of the ‘standard’ Higgs particle, perhaps a family of several Higgs particles or something even more exotic. The unexpected is always the most exciting.”
Question: Denis Lander of Christchurch asks: "Why do all animals sleep, when the dangers might appear to outweigh the advantages of reduced metabolic demands? And why do old humans recapitulate the sleep patterns of infants?"
Answer: Karyn O'Keeffe, research fellow at Massey University's sleep/wake research centre, says we can't do without shut-eye. "Animals die without it. Sleep in mammals likely plays a vital role in brain and body energy conservation, learning, memory and development. Studies in humans also suggest sleep may play a role in metabolism, cardiac health, mental health and immune function. Smaller animals often sleep for longer than larger animals. The sleeping environment also changes with animal size to maximise safety. Smaller animals tend to sleep in warm nest-like environments, whereas larger animals often sleep in herds with some of the animals keeping an eye-out. A fascinating adaptation in marine mammals, which have no warm, safe place to sleep, allows them to have certain stages of sleep only in one brain hemisphere at a time. There is a common misperception that sleep in older adults is similar to infant sleep. Infant sleep is very different to adult sleep in terms of sleep stages, sleep structure and sleep timing. There is a gradual, and often slight, reduction in the amount of slow wave (deep) sleep and REM sleep across adulthood, but few changes after 60 years of age. Importantly, older adults need the same amount of sleep as younger adults. However, older adults have much more fragmented sleep. Sleep in older adults is, therefore, quite often unrefreshing and older adults may try to catch up on sleep by napping during the day."
Question: "Before I went to Antarctica I was warned my camera batteries would drain faster in the cold. Take a small camera and keep it warm in a pocket, I was advised. But why? How does temperature affect battery operation?"
Answer: I put this question to Shaun Hendy, deputy director of the MacDiarmid Centre for Advanced Materials and Nanotechnology. "When you've got a battery sitting in your camera," explains Hendy, "you've got an electrical circuit. Electrons flow around your camera from the negative to the positive terminals on the battery. To complete the circuit, there is a flow of ions – atoms that have lost electrons – in the opposite direction to the electrons through the battery. So why is it affected by temperature? Well, temperature is really the jiggling motion of atoms. If it's hot those atoms are jiggling around a lot and will travel easily through the battery. If it's cold, it's a bit like moving through treacle – they slow down and it is harder to get across the battery. So if you've got your lithium ion battery in Antarctica at 0°C, its performance might drop by 30-40%. Because you're trying to maintain the current in your camera, that will drain the battery of easily available lithium ions quite quickly and your battery will go flat. But by warming the battery up again, you can reactivate it – it will start working again and you'll get more life out of it."
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