March 7, 2012
The Ever-expanding Hunt For The Elusive Higgs
Scientists working at the US Tevatron particle collider near Batavia, Illinois on Wednesday said they have found the strongest evidence yet for the existence of the elusive “God particle.”
They said their experiments mirror those from the Large Hadron Collider (LHC) in Europe that have narrowed the range where the Higgs boson particle could be hiding. The Higgs Boson is the missing link in the standard model of physics and is believed to be what gives objects mass, though scientists have never been able to confirm its existence.The Tevatron scientists, based at Fermilab, announced their findings at the annual Rencontres de Moriond conference in La Thuile, Italy on Wednesday.
Analyzing data from some 500 trillion subatomic particle collisions designed to emulate conditions right after the Big Bang when the universe was formed, the Tevatron team produced around 1,000 Higgs particles over more than ten years of work.
Tevatron became operational in 1983 and was the world´s premier particle smasher for nearly twenty years before being shutdown in 2011 due to budget constraints. However, the massive amount of data that was amassed during that time has scientists pouring over that data, and they say they have come up with some fascinating hints into the possible existence of the “God particle.”
“Unfortunately, this hint is not significant enough to conclude that the Higgs boson exists,” said Rob Roser, a physicist at Fermilab, in explaining the findings at the Italian conference, according to Andrew Stern of Reuters. The image scientists have of the short-lived Higgs particles, which almost immediately decay into other particles, is still slightly “fuzzy,” he added.
What makes the Tevatron find most compelling is that the LHC in Geneva has found a suggestive hint within its data at roughly the same mass that US scientists at Tevatron have found, especially where the LHC is being used for a radically different experiment. While the LHC collides protons together, the Tevatron used protons and their antimatter counterpart, antiprotons.
Both experiments hunt for the Higgs by looking at what those high-energy particles decay into. But at Tevatron, the data are from the production of bottom quarks and their counterparts bottom antiquarks. The LHC experiments primarily search for the production of the light particles known as photons.
“It´s a different accelerator, different detectors and a different decay channel,” Roser told Jason Palmer of BBC News. “It adds to the picture, and it´s starting to make a compelling case. But we can´t make quite as bold a statement as we would like.”
“I just wish either one of us just had more data right now,” he said. “It´s frustrating”
Tony Weidberg, a University of Oxford physicist who works at the LHC´s Atlas detector, said the Tevatron results are consistent with the idea of a comparatively “light” Higgs boson.
“It´s interesting because it´s another little hint,” Weidberg told BBC News. “It makes it a little bit more likely that we´re going to end the year with a discovery rather than an exclusion.”
The probability that what physicists detected at Tevatron is not a Higgs boson but instead a statistical fluke was 1 in 250, which is near the threshold of 1 in 740 that physics has set to establish proof of the particle´s existence.
The hunt for the Higgs boson has been significant. British scientist Peter Higgs first theorized the Higgs field in the 1960s as the way that matter obtained mass after the universe was created during the Big Bang. According to his theory, it was the agent that made the stars, planets and life possible by giving mass to most elementary particles.
Discovery of the Higgs boson would also complete Einstein´s Standard Model of Physics. If the Higgs boson does not exist, scientists would then have to search elsewhere for how particles gained mass.
“The end game is approaching in the hunt for the Higgs boson,” Jim Siegrist, Department of Energy associate director of science for high energy physics, told the AFP news agency. “This is an important milestone for the Tevatron experiments, and demonstrates the continuing importance of independent measurements in the quest to understand the building blocks of nature.”
Physicists from the CDF and DZero collaborations at Fermi National Accelerator Laboratory in Illinois said in a statement that their data “might be interpreted as coming from a Higgs boson with a mass in the region of 115 to 135 GeV (gigaelectronvolts).”
Those results are similar to what the world´s largest particle accelerator, LHC, found in their results. Their experiments have shown a likely range for the Higgs boson between 115 to 127 GeV.
GeV is the standard measure for the mass of sub-atomic particles. One GeV is roughly equivalent to the mass of a proton.
Pier Oddone, director at Fermilab, said he was excited with the progress made in the hunt for the Higgs boson. He noted that scientists from around the world have combed through hundreds of trillions of proton-antiproton collisions.
“There is still much work ahead before the scientific community can say for sure whether the Higgs boson exists,” added Dmitri Denisov, DZero co-spokesman and physicist at Fermilab. “Based on these exciting hints, we are working as quickly as possible to further improve our analysis methods and squeeze the last ounce out of Tevatron data.”
But not everyone is convinced the findings point to the elusive Higgs boson.
“The ℠Higgsteria´ surrounding the excess of [bottom] quarks in the Tevatron is certainly suggestive of a Higgs but we could still just be seeing the cruel hand of statistical fluctuations or better still the indications of something unexpected and more prosaic than the Higgs,” Mark Lancaster, a physicist at University College London who works on the Tevatron´s CDF experiment, told Alok Jha of The Guardian.
The Higgs mechanism was only one solution to the equation of how fundamental particles get their mass, he said. Mass could also be the result of the interactions predicted by a theory called Technicolor, which proposes the existence of different, also yet to be discovered, particles.
The observed results may be down to random fluctuations or a systematic error in the way the Tevatron detectors model and interpret the particle collisions, said Stefan SÃ¶ldner-Rembold of the University of Manchester, who works on the DZero experiment. But many factors would have had to “come together and conspire in a very strange way.”
“There´s so many hints from the LHC and the Tevatron, they all point in the same direction,” he told The Guardian. “Unless there's some conspiracy going on in nature, it all looks like it´s the Higgs boson.”
The LHC will need to gather much more data in the coming months and years before scientists are able to either confirm or deny the existence of the Higgs boson.
Roser said the Tevatron data is almost all used up. “We´ll do a few more experiments and try to have a final answer in June.”
Image Caption: The Tevatron typically produces about 10 million proton-antiproton collisions per second. Each collision produces hundreds of particles. About 200 collisions per second are recorded at each detector for further analysis. Credit: Fermilab
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