Pentaquarks: LHC Has Discovered an Exotic Particle

Now that the Large Hadron Collider (LHC) is smashing protons together at record energies, physicists are hoping to discover new and exotic particles emerge from the collisions. But there are a few unsolved mysteries surrounding different configurations of known subatomic particles that still have to be wrapped up.

And today, CERN announced the discovery of the "pentaquark" - a collection of five quarks bound together to form an exotic state of matter, a particle that has been theorized for some time but other experiments have had a hard time nailing down a true detection.

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"The pentaquark is not just any new particle," said Guy Wilkinson, spokesperson for the LHCb experiment at the LHC, in a CERN press release. "It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we're all made, is constituted."

Quarks are the subatomic constituents of regular particles, called hadrons. Hadrons come in two varieties, baryons (which contain 3 quarks) and mesons (which contain 2 quarks). Protons and neutrons are baryons where, for example, a proton is composed of 2 "up" quarks and 1 "down" quark; a neutron has 2 "down" quarks and 1 "up" quark.

But in the 1960′s, theorists realized that the Standard Model also allows the formation of 5 quarks in the same particle, known as a pentaquark. But experimental searches for this elusive 5-quark particle kept drawing blanks and any vaguely positive detection was quickly shot down by follow-up experiments.

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Now, a strong signal in the LHCb detector has led to the pentaquark's discovery.

LHCb physicists examined the decay of a baryon known as Lambda b (Λb) into 3 other particles, the J-psi (J/ψ-), a proton and a charged kaon. By using the highly sensitive detector to characterize the masses of these decay products, the physicists were able to see that intermediate states were sometimes involved in their production. They named these intermediate states Pc(4450)+ and Pc(4380)+ and indicate that pentaquarks are at play.

In a nutshell, the physicists noticed a signal emerge from the post-collision noise of particles. This signal, or "excess," indicated the creation of J/ψ-, protons and kaon in quantities predicted by theories surrounding subatomic decay processes that involve pentaquarks. The decay particles acted as a "fingerprint" of sorts.

"Benefiting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states," said Tomasz Skwarnicki, a LHCb physicist from Syracuse University, New York. "More precisely the states must be formed of two ‘up' quarks, one ‘down' quark, one ‘charm' quark and one ‘anti-charm' quark."

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Although their decay signatures have been found, there's still some ambiguity as to their configuration. Are the quarks all bound together as a 5-quark particle? Or is there a 3-quark particle (baryon) and a 2-quark particle (meson) interacting together to form a 5-quark "molecule"?

"The quarks could be tightly bound," said Liming Zhang, LHCb physicist from Tsinghua University, "or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei."

For now, the pentaquark's configuration isn't exactly known, but what is known is that it exists, and the newly-upgraded LHC will continue to examine its signal, revealing more detail behind the nature of this elusive particle.

Source: LHC/CERN

This is a computer model of the pentaquark in a possible tightly-bound 5-quark state.

Introduction

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.