After several years of nail-biting delays and breakdowns, the Large Hadron Collider, one of the few science experiments to become a household name, got underway in March of 2010. The search for the Higgs boson, the elusive “God particle” that would resolve several problems in the Standard Model of particle physics, was front-page news.
But in the last 18 months, as the LHC has scanned through various energies, the Higgs has not showed itself. And at a conference in Mumbai on August 22, CERN scientists revealed news that set the physics community humming: in the energies so far explored, there’s a 95% probability that the Higgs doesn’t exist. Amir Azcel, writing in a guest blog at Scientific American, explains these numbers, considers the tumult in particle physics that will occur should the Higgs prove no more than theoretical, and asks whether Stephen Hawking has just won his infamous bet against the Higgs:
A few years ago, celebrated British physicist Stephen Hawking was widely reported in the press to have placed a provocative public bet that the LHC (along with all particle accelerators that preceded it) would never find the Higgs boson, the so-called “God particle” believed responsible for having imbued massive particles with their mass when the universe was very young.
Read more at Scientific American.
Image courtesy of CERN
As a younger stronger particle smasher, the Large Hadron Collider can turn even baby steps into new records. Over this past weekend, the LHC beat another personal best–colliding its most protons yet at 10,000 particle collisions per second (about double its earlier rate). Physicists believe this is a crucial step on the collider’s hunt for new physics.
In November of 2009, the LHC collided its first protons as it started its quest to find the suspected mass-giving particle known as the Higgs Boson. The collider is still running at half of its designed maximum energy, but after this weekend, the number of particles per bunch traveling in the ring is just what physicists had planned. This is essential, says CERN physicist John Ellis:
“Protons are complicated particles, they’ve got quarks, [and other small particles], and colliding them is like colliding two garbage cans and watching carrots come out…. The more collisions we get, the closer we get to supersymmetry, dark matter, the Higgs boson and other types of new physics.” [BBC]
Here are some basics:
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If the Higgs boson is the “God Particle,” then some particle physicists just turned polytheistic. To explain a recent experiment, they wonder if five Higgs bosons give our universe mass instead of one.
Last month, we discussed a curious experiment at the Tevatron particle accelerator at Fermilab near Chicago. Colliding protons and antiprotons, the Tevratron’s DZero group found more matter than antimatter.
This agrees well with common sense–if the Big Bang had really churned out equal amounts of matter and antimatter, the particles would have annihilated each other, and we wouldn’t be here. Unfortunately, the physics for this matter favoritism doesn’t make sense.
For one, it requires some fudging to fit the Standard Model, the organizing theory for particle physics. This might seem sad since we were so close to finishing the Standard Model up, with the Higgs filling the last cage in physicists’ particle zoo:
For those who believe the Standard Model is nearly complete, the discovery of the Higgs boson–a theoretical particle that imparts mass to all the other particles–would close out the final chapter. But for others who think that undiscovered physics properties exist–so-called new physics–a sequel to the Standard Model is needed. [Symmetry]
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Long hyped as the largest science experiment ever built, the Large Hadron Collider now has a world record for doing something: accelerating particles with more energy than any accelerator ever has.
On Sunday evening, at 6:44 p.m. eastern time in the United States, engineers at the Switzerland-based accelerator increased the energy of this “pilot beam”, reaching 1.18 trillion electron volts…. The previous record of 0.98 trillion electron volts has been held by the Tevatron accelerator since 2001 [BBC News].
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Hackers. Leaking liquid helium caused by a faulty connection. International ridicule. And to top it all off, aerial attack by a wayward baguette. Yes, it’s safe to say that things haven’t gone according to plan at the Large Hadron Collider in the last 14 months, but the world’s largest particle smasher is finally—finally!—back online after its Friday restart, with proton beams circulating through this huge underground ring.
The first time protons circled the collider, on Sept. 10, 2008, the event was celebrated with Champagne and midnight pajama parties around the world. But the festivities were cut short a few days later when an electrical connection between a pair of the collider’s giant superconducting electromagnets vaporized [The New York Times].
The initial enthusiasm, it seems, was rather premature—scientists analysis of the failed connection revealed many more that probably couldn’t handle the strain of the energy needed to re-create conditions similar to the Big Bang. During 14 months of repairs dozens of giant superconducting magnets that accelerate particles at the speed of light had to be replaced [BBC News].
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Particle physicists have ruled out one of the possible remaining hiding places of the Higgs boson, bringing them one step closer to finding the slippery subatomic particle–or, conceivably, to ruling out its existence.
Physicists believe that the Higgs particle interacts with some other particles, like the W and Z bosons, to give them mass. The standard quip about the Higgs is that it is the “God Particle” — it is everywhere but remains frustratingly elusive. Confirming the Higgs would fill a huge gap in the so-called Standard Model, the theory that summarizes our present knowledge of particles [AFP].
The new results, from the Tevatron particle accelerator at the Fermi National Accelerator Laboratory, narrow down the range of masses where the Higgs boson may be found. Physicist Craig Blocker explains that particle accelerators smash particles together and then sift through the debris produced, looking for particles with certain masses. Previous collider experiments had placed a lower bound of 114 giga-electron volts (GeV), a measure that can be used for particle mass, on the Higgs, and theoretical calculations require it to be less than 185 GeV. The new Fermilab results, from its Tevatron collider, rule out a Higgs mass between 160 and 170 GeV…. “If the Higgs had a mass in this fairly narrow range” of 160 to 170 GeV, he says, “we should have seen it, we had a good chance to see it” [Scientific American].
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After all the excitement and anticipation surrounding the Large Hadron Collider‘s launch last September, its first few months have been an anticlimactic cascade of disappointments. When a fault shut down the subatomic particle collider just nine days after the first beam of protons whizzed around its 17-mile track, officials at first said it would take several weeks to repair. Then they revised that estimate, saying it wouldn’t be fixed until spring of 2009–and then that changed to summer of 2009. Now, officials say that repairs won’t be finished before September, at the earliest.
To appease impatient high-energy physicists, the laboratory will probably run the machine (albeit at reduced powers) for a ten-month stretch from November until the autumn of 2010 [Nature News]. Officials at CERN, the European agency that runs the collider, hadn’t planned to run it through the winters when electricity costs are higher; they estimate that this appeasement will cost them an extra $10.5 million for electricity.
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The standard model of physics got it right when it predicted where the mass of ordinary matter comes from, according to a massive new computational effort. Particle physics explains that the bulk of atoms is made up of protons and neutrons, which are themselves composed of smaller particles known as quarks, which in turn are bound by gluons. The odd thing is this: the mass of gluons is zero and the mass of quarks [accounts for] only five percent. Where, therefore, is the missing 95 percent? [AFP]
The answer, according to theory, is that the energy from the interactions between quarks and gluons accounts for the excess mass (because as Einstein‘s famous E=mc² equation proved, energy and mass are equivalent). Gluons are the carriers of the strong nuclear force that binds three quarks together to form one proton or neutron; these gluons are constantly popping into existence and disappearing again. The energy of these vacuum fluctuations has to be included in the total mass of the proton and neutron [New Scientist]. The new study finally crunched the numbers on how much energy is created in these fluctuations and confirmed the theory, but it took a supercomputer over a year to do so.
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Today at 10 a.m. Swiss time, researchers fired up the Large Hadron Collider (LHC), successfully sending a stream of protons all the way around a 17-mile track for the first time. The enormous collider has been eagerly anticipated by physicists, who hope the device will answer questions about the behavior of subatomic particles and reveal secrets of the universe, but some people have also worried (needlessly, physicists say) that its unprecedented experiments will cause the world to end. For all that hype, the action today was somewhat anticlimatic: Two white dots flashed on a computer screen indicating that the protons reached the final point of the world’s largest particle collider [AP].
As many scientists have pointed out, today’s test run didn’t involve any actual collisions; those will come later when particles shoot around the track in both directions and smash into each other. Therefore today’s event could never have produced any breathtaking results, it was simply intended to test the equipment.
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After 15 years of construction, the world’s largest particle accelerator is warmed up, fully tested, and ready to rumble. The Large Hadron Collider will go into operation on September 10th, and researchers are celebrating every step towards that momentous day. Last weekend, physicists popped champagne to toast the results of a test in which beams of protons were sent barreling into a massive block of concrete, causing the protons to fragment into smaller particles. Researchers have also successfully sent test batches of protons part-way around the collider’s 17-mile circular track.
The Large Hadron Collider represents the science world’s latest, greatest attempt to smash its way into the mysteries of the universe: Beams of protons will eventually collide with the energy of two bullet trains – spawning sprays of subatomic debris that are certain to lead to new discoveries…. One experiment at the LHC, known as ALICE, seeks to re-create the conditions that existed just an instant after the big bang that gave rise to the universe as we know it. [The collider's] researchers want to understand why matter won out over antimatter after the creation of the cosmos [MSNBC].
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