LHC Has Found a Bump: Exotic Physics or Just Noise?
As the year draws to a close and the Large Hadron Collider prepares for a winter break, a tantalizing hint of new physics surfaces in particle collision data.
Science at the Large Hadron Collider is starting to wind down ahead of a scheduled winter break after carrying out experiments at record-breaking energies. Needless to say, these are exciting times; physicists are in an unknown realm of discovery where physics ideas beyond the Standard Model are being tested. And this week, LHC scientists announced something peculiar in two of the collider's experiments.
But this "something peculiar" could just be a glitch in the data. Or maybe it's not. Regardless, a tiny "bump" in datasets from two detectors has caused a buzz.
Conditions of the Big Bang Before we go neck-deep into what the LHC has (or, more likely, hasn't) found, we need to quickly understand how the largest experiment ever devised my humankind discovers new particles and new forces.
On Dec. 15, LHC collaborators met at CERN (the European Organization for Nuclear Research), the laboratory that manages the LHC located just outside Geneva, Switzerland. This was the first major meeting since the particle accelerator was upgraded earlier this year to accommodate higher energy collisions - a new phase called "Run 2″. The LHC is now accelerating particles around its 17-mile circumference ring of supercooled electromagnets at 13 teraelectronvolts (TeV) - an energy nearly double that of the energies physicists used to discover the Higgs boson in 2012.
Around the ring of electromagnets, several experiments are housed. These experiments are huge, building-sized detectors that are highly sensitive to finding particles that are generated after two counter-rotating "beams" of hadrons (such as protons or heavy ions, like lead nuclei) are forced to collide. These counter-rotating beams are traveling at relativistic speeds, so when they smash into one another, for the briefest of moments, the conditions that the universe hasn't seen since the Big Bang are created.
The Big Bang is the genesis of the universe; all energy in the universe was unleashed from an infinitely dense singularity nearly 14 billion years ago. From this energy, as the universe cooled, a zoo of subatomic particles condensed to form the matter we know and love in the modern universe.
By recreating the conditions of the Big Bang in the LHC, physicists are able to peel back time and see for a very brief moment what primordial particles can be created by Nature, thereby testing physics theories on what particles are possible in our universe. In the case of the Higgs boson, physicists needed huge energies to produce the massive particle - "weighing in" at a mass of 125 gigaelectronvolts (GeV). The discovery of the Higgs confirmed that the Standard Model of physics (a quantum recipe book of sorts) correctly described all known particles and forces in the cosmos.
A Mysterious Bump?
Physics didn't simply "end" with the confirmation of the Higgs, however. Many mysteries remain, not least why gravity was ominously not invited to the Standard Model party. Now physicists are looking beyond the Standard Model for answers - a realm known as "exotic physics." It is in this realm that physicists hope to reveal evidence for dark matter particles, extra-dimensions, the possibility of supersymmetry, the hypothetical graviton and other stuff that we haven't even thought of yet.
So, inside the same two LHC experiments that made the Higgs boson discovery in 2012 comes a signal that, albeit weak, has caused a minor stir.
Now that the LHC is smashing particles together at the highest energies ever attained, there's hope that we may start glimpsing some exotic physics that, so far, are only hypothetical ideas. Like a photographic film that slowly collects photons to produce a photograph, the LHC's detectors must carry out months or years of experiments to develop a clear picture. As we're only a few months into this high energy experimental run, any results or signals will likely be blurry, but according to Run 2 preliminary results from the CMS and ATLAS detectors, a very slight bump in energy at around 750 GeV has been spotted. What could it be?
"We've been working round-the-clock to understand and triple-check our numbers, and (Dec. 15) was the culmination of the year's worth of work by thousands of people," said particle physicist James Beacham, a post-doctoral research fellow with the Ohio State University, in an interview with Discovery News.
Beacham is based at CERN and working on the ATLAS experiment to seek out "diphoton" signals in the huge quantities of data flowing from the massive detector.
Basically, when new particles are produced by high energy collisions, like the Higgs boson, they tend to decay very quickly. As they decay, they produce other particles that may be detected by LHC experiments.
The signature of this signal can reveal a fingerprint of the particle that decayed - in this case the excess could be caused by pairs of photons (diphotons) with an energy of 750 GeV. After more and more data are collected from billions and billions of collisions, small and unexpected bumps in collision data may start to rise from the noise, above what would be predicted by the Standard Model. These bumps are known as "excesses" and they can signal the production of new and exotic particles.
"The diphoton search, the one that has the most significant excess, is interesting because it could possibly discover things like exotic Higgs bosons or gravitons (the as-yet-undiscovered particles of gravity)," said Beacham. "Both of these discoveries would be revolutionary, because they'd be concrete evidence of physics beyond-the-Standard-Model, something we've never seen."
The size of the bump is indeed tiny and may well wash away as more collision data is added, but the thing that makes this statistically tiny event interesting is that another detector, the CMS, has also detected a tiny signal in exactly the same 750 GeV energy range.
Although the signal is most likely noise at this early stage, physicists will of course be hoping for something exotic. But as cautioned by LHC physicists, even if this signal does turn out to be real, it could represent the presence of something decidedly un-exotic, like a more massive Higgs boson.
More Data Needed As interesting as these matching bumps may be, it's only the tiniest of hints that there's something really there and Beacham is very clear, pointing out that the take home message is that "we need more data."
"When we saw this tiny hill in the diphoton mass spectrum in ATLAS we're like, 'Hmmmmm...' and then we instantly started poking it with our most ruthless experimental sticks, as usual, to see if it would withstand scrutiny. After poking and prodding (e.g., ruling out detector problems, multiple-checking the statistical methods) it was still there. But, again, the 'it' is just a slight uptick that, statistically, is just a hint," he said. "We will have to remain on the edges of our seats for a few more months to years."
His LHC colleagues agree: "It's interesting because we did not expect it, and both experiments are seeing something in roughly the same place," Jim Olsen, of Princeton University who works on the CMS detector, told Symmetry Magazine. "However, it's not a discovery. It could be the first spark of a discovery, but we need more data before we know what it means -- if it means anything at all."
Beacham is hopeful that we'll have significantly more data by next summer that could either strengthen this particular bump or flatten it out. High-energy physics is as much about statistics as it is building the most powerful particle colliders on the planet - deciphering signals needs to be statistically robust and this particular CMS/ATLAS excess only registers at the 2σ ("2 sigma") level. For something to be called a "discovery" the signal needs to hit 5σ, basically the "gold standard." Currently, this bump is considered nothing more than a statistical wiggle, but the fact that 2 detectors are seeing something rise out of the fog of collision data could be more than a coincidence.
So for now, we wait for the LHC to continue its job of colliding particles, spewing a firehose of data ripe for analysis. But first, a pause for LHC physicists to get some rest in the run-up to Christmas.
"CERN shuts down for the winter break in a few days, and I think a lot of us who've been breaking our necks playing with our new, shiny 13 TeV data (small bump or no) will sleep for a week," said Beacham.
For more details behind the CERN meeting on Dec. 15, check out the organization's news release.
A computer rendering of a 13 TeV collision recorded by the CMS experiment, including jets of particles that can be measured to reveal the presence of new physics in the LHC.
Did you own a toy race-car track as a child? Ever crash your model trains into one another just to see what happened? If you did, then congratulations, you already know some of the basic principles behind the Large Hadron Collider (LHC). Built by the European Organization for Nuclear Research (CERN), the 27-kilometer tunnel buried in the Swiss countryside exists to smash particle beams into each other at velocities approaching the speed of light. The idea is to use the resulting data to better understand the structure and origins of the universe. We're talking heavy questions and even heavier answers. Perhaps it's understandable that some critics, conspiracy theorists, crackpots and (alleged) time travelers might fear something more substantial than the Higgs boson particle. In this article, we'll run through some of the more popular misconceptions about the LHC and how little you have to fear about it causing the end of the world as we know it.
5. CERN Is Making an Antimatter Bomb
The Dan Brown detective novel (and movie adaptation) "Angels and Demons" centers on a plot to steal an antimatter bomb from CERN and blow up the Vatican with it. While the blockbuster delivered its share of action and intrigue, it fell short on facts. Two of the film's biggest mistakes revolved around antimatter's potential use as both an energy source and a weapon. Yes, when an antimatter particle comes in contact with normal matter, the two particles destroy each other and release energy. But CERN is quick to point out that the energy payoff simply isn't there. In fact, the transaction is so inefficient that scientists only get a tenth of a billionth of their invested energy back when an antimatter particle meets its matter counterpart. As for developing an antimatter bomb, the same principles apply. CERN points out that, at current production rates, it would take billions of years for the organization to produce enough antimatter to generate an explosion equal to an atomic blast.
4. Fun-sized Black Holes
Some concepts don't become tamer when you tack a "micro-" or a "mini-" prefix in front of them. For example, a mini-stroke is still an excellent reason to visit the hospital, and you'd certainly be ill advised to question the power of a minigun. So when CERN scientists mention that they might create microscopic black holes in the midst of their particle smashing, it's easy to understand some of the ensuing panic. Based on Einstein's theory of relativity, a few speculative theories lend a sheen of possibility to micro-black hole creation. The good news is that these theories also predict the micro-black holes would disintegrate immediately. If these black hole welterweights did hang around a little longer, it would take billions of years to consume the mass of a tiny grain of sand. That means no reducing the European countryside to a singularity and certainly no destroying the planet "Star Trek" style.
3. Attack of the Strangelets
Read enough space publications and your perception of the universe changes pretty fast. Once you get beyond the absurd vastness of the cosmos, you encounter such mind-rending notions as black holes, antimatter and dark matter. After you've swallowed the notion of a gigantic star collapsing into something smaller than a pinhead, it's easy to get bowled over by the idea of universe-destroying strangelets. Strange matter is presumed to be 10 million times denser than lead and was birthed during the Big Bang from the hearts of dense stars. The fear, which originated with the start-up of the Relativistic Heavy Ion Collider (RHIC) in 2000, is that the LHC will inadvertently produce strangelets -- tiny particles of strange matter -- and that these particles will swiftly convert surrounding normal matter into even more strange matter. It only takes a thousand-millionth of a second for the chain reaction to convert the entire planet. Strangelets, however, are purely speculative, and haven't surfaced in over eight years of RHIC operation. CERN says that the RHIC was far more likely to produce the theoretical matter than the LHC, so there's really no chance of it consuming the planet.
2. Time Travelers Hate It
In "Bill & Ted's Excellent Adventure," the titular slacker duo wields time travel with the logic of a 12-year-old. When Bill and Ted need a cell key to bust a few historical figures out of a modern California jail, they simply make a mental note for their future selves to travel back in time and plant the key where they can find it. While the 1989 buddy comedy is pretty much the antithesis of hard science fiction, its view of time-travel logic is shockingly similar to a 2009 theory regarding the LHC. Danish string theory pioneer Holger Bech Nielsen and Japanese physicist Masao Ninomiya, in a series of posted physics articles, laid out their theory that the Higgs boson particle is so abhorrent to nature that its future creation will send a ripple back through time to keep it from being made. Naturally, this theory summons images of T-800s, Jean-Claude Van Damme and Hermione Granger all galloping back through time to prevent future disasters, but not everyone is busy cracking jokes and reminiscing about time-travel movies. The two scientists aren't even talking about shadowy strangers from the future, but merely "something" looping back through the fourth dimension. Imagine a poorly designed bomb that, upon creation, destroys half the bomb factory. Now expand that example out from the confines of linear time.
1. Gateway to Hell
Black holes, antimatter explosions and even strangelets all originate from scientific fact and theory (albeit with a bit of imagination thrown in). Forget all that for the moment and consider the "Satan's Stargate" theory, proposed by Chris Constantine, better known on the Internet as YouTube user gorilla199. Constantine charges that the LHC exists "to disrupt a hole in the Van Allen belt that surrounds the Earth" and "to allow the return of the Annunaki from the planet Nibiru in order that they can come here, corrupt the rest of the Earth and do battle with God at Armageddon." There's also some stuff in there about freemasonry, cosmic rays and the Old Testament offspring of humans and fallen angels. According to BBC News, Constantine received a suspended sentence for DVD pirating after his defense attorney charged that Constantine suffered from a serious psychiatric condition. The Antichrist could not be reached for comment.