Scientists have found a new ‘Holy Grail’ to hunt: the X Particle.
The hypothetical bit of matter may simultaneously solve two enigma-plagued conundrums: the stuff making up dark matter, and the antimatter puzzle.
The antimatter dilemma
From the day that the existence of antimatter was first postulated, the question that haunted cosmologists became: why didn’t antimatter annihilate all matter? Most scientists studying the creation of the universe believe that equal amounts of both matter and antimatter were created in the first fraction of a second during the Big Bang. The particles and antiparticles should have canceled each other out, yet they didn’t. The very fact that we exists proves matter won out.
This question has bothered theoretical physicist Sean Tulin for some time. “If matter and antimatter were created in equal amounts in the early universe, they would all have annihilated [the other instantaneously].” The net effect would have been the quick unraveling of creation.
Tulin, a member of the Canadian physics institute TRIUMF, adds, “There has to be some asymmetry that was left over.”
That left over stuff from the Big Bang—the antiparticles that make up antimatter—may well be linked to dark matter.
“The protons and neutrons can’t annihilate completely with their antiparticles, because there’s not enough to annihilate with,” Tulin explained. “The same story happens in the hidden sector as well…some dark matter can’t annihilate with anything. So you’re left with some extra dark matter in the universe.”
Wired.com interviewed members of the team that proposed the hypothetical X Particle. During their interviews they spoke with Tulin and others including physicist Kris Sigurdson of the University of British Columbia, who co-authored the paper (November 19 Physical Review Letters “Unified Origin for Baryonic Visible Matter and Antibaryonic Dark Matter”) describing the properties of the X Particle.
“We know you have to have these two ingredients to the universe, both atoms and dark matter,” Sigurdson said. “Since you know you need those ingredients anyway, it seems like a natural thing to try to explain them from the same mechanism.”
To test their hypothesis, Tulin and Sigurdson-along with physicists Hooman Davoudiasl at Brookhaven National Lab and David Morrissey of TRIUMF-have suggested a clever way to solve the riddle of the antimatter that isn’t there: simply store it up as dark matter.
Tulin added, “If our theory is right, it would tell you what dark matter is.”
According to astronomical observations, the mysterious dark matter somehow accounts for about one-quarter of the entire energy density of creation…yet it interacts with normal matter only through gravity.
The WIMP factor
Up until now, the particle theorized to comprise dark matter is called the “weakly interacting massive particle” (WIMP). Because of the restrictive properties of a WIMP, it can only make a connection with the weak nuclear force and gravity. If true, that would explain why dark matter is virtually undetectable at at every wavelength of light.
The math supports a particle about 100 times more massive than a proton. And since it’s thought their are both WIMPs and anti-WIMPs, when they meet they destroy each other.
The X Particle would replace the WIMP as the reason for dark matter.
At the beginning of the universe the Big Bang created both X and anti-X particles. Equal amounts were generated by the blast, and then rapidly decayed becoming lighter particles. According to the hypothesis, each X Particle became either a neutron or two dark matter particles. Tulin and Sigurdson have labeled them as Y and F. Similarly all anti-X Particles became anti-neutrons or anti-dark matter.
The mechanism of decay, however favored X Particles to become ordinary matter while anti-X became dark matter. When most particles that could annihilate each other had, the universe became populated with extra neutrons and extra anti-dark matter.
This accounts for the universe as it exists today.
Ratio of matter to dark matter
Dark matter is about five times more prevalent than matter. Particle physicists have been asking themselves why this should be so for decades. The new X Particle hypothesis elegantly solves that puzzle too and even accounts for the 5 to 1 ratio. For if indeed the universe evolved to a point where the dark matter particles have 2 or 3 times the mass of all protons, then 5 times more dark matter should exist.
It does.
“That’s why the light stuff, the visible matter that we all know and love and are used to, is in exact balance with the excess in the dark matter,” Sigurdson said. “You end up with a little bit more matter and a little bit more antimatter, but they’re in exact compensation with each other.”
So the solution seems evident. The X Particle helped determine the universe we live in today. But, the particle must be proven to exist.
Japan’s SuperKamiokande
If X Particles do exist in reality, they should be able to be detected by a very unique form of ‘telescope.’ One deep underground and filled with water.
The SuperKamiokande in Japan has been designed for the purpose of recording the fleeting signatures of exotic particles. A dark matter particle certainly falls into that category. Although it’s thought that a particle of dark matter would rarely interact with regular matter, it sometimes might smash into an unlucky proton or neutron and destroy it.
According to the scientists the trail—called a signature—would be very similar to that left by a decaying proton.
Tulin and Sigurdson are excited about the prospects that SuperKamiokande might have already found evidence of the X Particle. It may exist in the existing data generated by the Japanese researchers’ hunt for decaying protons. Although the Japanese have found no evidence of decaying protons, by simply sifting through their data again—and searching for a slightly different energy signature—the telltale record of a dark matter event may be discovered.
If they succeed in proving the X Particle exists, it well be another piece of the creation puzzle that will go a long way towards understanding the workings of the place we call home.
