Monday, 28 March 2011

special B mesons found at LHCb


Interesting news from the LHCb detector today. are carrying a story about group of scientists led by Syracuse University physicist, Sheldon Stone, who have apparently become the first to observe the decays of a rare particle - a special type of B meson - thought to be present right after the Big Bang. write:
"B mesons are a rare and special subgroup of mesons composed of a quark and anti-quark. While B mesons were common after the Big Bang, they are not believed to occur in nature today and can only be created and observed under experimental conditions in the LHC or other high-energy colliders.

Sheldon Stone comments: "We know when the universe formed from the Big Bang, it had just as much matter as antimatter. But we live in a world predominantly made of matter, therefore, there had to be differences in the decaying of both matter and antimatter in order to end up with a surplus of matter."

Because these particles don't play by the same rules of physics as most other matter, scientists believe B mesons may have played an important role in the rise of matter over antimatter. The particles may also provide clues about the nature of the forces that led to this lack of symmetry in the universe.

Sheldon Stone, notes on Physorg, "we want to figure out the nature of the forces that influence the decay of these particles. These forces exist, but we just don't know what they are. It could help explain why antimatter decays differently than matter."


Nature Network


Particle Decelerator has joined the Nature blogosphere.

As well as being a portal to the blogs written by Nature editors and journalists, Nature Blogs aggregates posts from science blogs. We're in the P section.


Tuesday, 8 March 2011

Is the Universe really cloaked in invisible cloth?


This week the science blogs have been alive with conflicting views about dark matter.

Dark matter is the invisible stuff that is supposed to make up around 20% of the Universe. But not everyone is willing to buy the idea that the Universe is cloaked in "invisible cloth." Proponents of an alternative, older theory, modified Newtonian dynamics (MOND), insist theories of dark matter, may simply have no clothes.

The latest MOND vs Dark Matter discussions have been promoted by the publication of a highly controversial paper by University of Maryland astronomer, Stacy McGaugh in the Physical Review Letters, which suggests that for galaxies, MOND fits the facts more reliably than theories of dark matter.

The Weizmann Wave - the blog of the Weizmann Institute, who came up with MOND in 1983 - immediately picked up on this: They wrote:

"Dark matter [...] was thought up to explain a puzzling observation. The amount of mass we can see through our telescopes is not enough to keep galaxies from spinning apart. The existence of great quantities of hidden mass would provide the gravitational pull needed to form those galaxies and enable them to rotate in the way that they do.
[But] an alternate theory, first put forward by Weizmann Institute astrophysicist Prof. Moti Milgrom in 1983, doesn't require dark matter to explain the phenomenon. Instead, it posits that gravity works differently on the intergalactic scale. With a good tweak to Newton's formula, the observed Universe falls into place. This is not the violation of a basic law of physics that it might appear: Milgrom points out that gravity works fine in our every-day world, but the formula breaks down at extremes - at the speed of light or in the sub-atomic world of quantum mechanics, for example. So super-galactic scales could be another case in which the rules of gravity simply don't apply quite as Newton wrote them.
While most are still waiting for the hunt for the mysterious dark matter to yield results, a growing minority of physicists are starting to admit that MOND (modified Newtonian dynamics) could provide a better explanation."

This view is deeply controversial. Many senior researchers were quick to criticise the media feeding frenzy which surrounded the publication of McGaugh's paper:

In an article on Cosmic Variance blog, Sean Carroll noted:

"McGaugh's new paper doesn't give any evidence at all against dark matter. What it does is to claim that an alternative theory - MOND, which replaces dark matter with a modification of Newtonian dynamics - provides a good fit to a certain class of gas-rich galaxies. That's an interesting result! Just not the result the headlines would have you believe"

In an illuminating post on Starts With a Bang, Ethan Siegel went one step further, concluding emphatically:

"MOND was designed to work for rotating galaxies. The problem is it doesn't do anything else. And its adherents never point to anything other than rotating galaxies to support it. [...] If you want to be taken seriously as a theory, you need to do more than just the one thing you were designed to do. [...] this isn't to say that MOND isn't an interesting idea, or that the people working on it are frauds. But what's being reported is grossly misleading at best, and blatantly dishonest at worst. General Relativity could still need fixing, and there could be something else going on with gravity beyond dark matter. But we still need dark matter -- or something heretofore indistinguishable from it -- to explain all our large-scale observations."

Phil Plait's analysis on the topic on his well known Bad Astronomy blog is pretty much summed up in the title - "Dark matter is alive and well, thankyouverymuch"

But this isn't a debate which is likely to go away any time soon, so keep an eye on Science blogs for the latest ripostes in the battle of theories.