Kiwi Particle Physicist

October 25, 2006

Bottom Baryon Discovery

Congratulations to CDF on the discovery of the Sigma_b plus and the Sigma_b minus, the first baryons to contain a bottom (b)-quark.

In addition to the stable up (u) and down (d) quarks, which make up ordinary matter, there exist heavier unstable quarks named strange (s), charm (c), bottom (b) and top (t), which can be combined to make exotic particles that don’t occur naturally in the world around us. The Sigma_b plus (uub) is an exotic relative of the proton (uud), where the bottom quark has replaced the usual down quark. The Sigma_b minus contains a b-quark and two d-quarks, and is a relative of the less well-known Delta minus.

Tomasso has a good post on the discovery, where he shows the graph below of the mass distribution of the Sigma_b candidates they found, and there is also a good explanation of the discovery on the Physorg page, from where I borrowed the above diagram.

October 16, 2006

KEK Soccer Tournament

We just finished the last game of the KEK soccer tournament today. It was another 0-0 draw. That’s four 0-0 draws out of four matches. Unfortunately we didn’t make it through to the semi finals.

I think we had a pretty good team this year, and we didn’t play too badly. Our defense was very well organized, and the midfield and forwards played alright as well. We just need a bit of practice at putting the ball in the net. It seems that this is a fairly crucial skill to have mastered for soccer.

At least it was a bit of fun. We’ll just have to try again next year I guess.

October 03, 2006

Nobel Prize to COBE

The Swedish Academy of sciences have just announced the winners of the Nobel Prize in Physics for this year are John C. Mather and George F. Smoot "for their discoveries supporting the Big Bang theory." Here's the press release from the Royal Swedish Academy of Sciences.

This year the Physics Prize is awarded for work that looks back into the infancy of the Universe and attempts to gain some understanding of the origin of galaxies and stars. It is based on measurements made with the help of the COBE satellite launched by NASA in 1989.

The COBE results provided increased support for the Big Bang scenario for the origin of the Universe, as this is the only scenario that predicts the kind of cosmic microwave background radiation measured by COBE. These measurements also marked the inception of cosmology as a precise science...

According to the Big Bang scenario, the cosmic microwave background radiation is a relic of the earliest phase of the Universe. Immediately after the big bang itself, the Universe can be compared to a glowing body emitting radiation in which the distribution across different wavelengths depends solely on its temperature. The shape of the spectrum of this kind of radiation has a special form known as blackbody radiation. When it was emitted the temperature of the Universe was almost 3,000 degrees Centigrade. Since then, according to the Big Bang scenario, the radiation has gradually cooled as the Universe has expanded. The background radiation we can measure today corresponds to a temperature that is barely 2.7 degrees above absolute zero. The Laureates were able to calculate this temperature thanks to the blackbody spectrum revealed by the COBE measurements.

COBE also had the task of seeking small variations of temperature in different directions (which is what the term 'anisotropy' refers to). Extremely small differences of this kind in the temperature of the cosmic background radiation – in the range of a hundred-thousandth of a degree – offer an important clue to how the galaxies came into being. The variations in temperature show us how the matter in the Universe began to "aggregate". This was necessary if the galaxies, stars and ultimately life like us were to be able to develop. Without this mechanism matter would have taken a completely different form, spread evenly throughout the Universe.

COBE was launched using its own rocket on 18 November 1989. The first results were received after nine minutes of observations: COBE had registered a perfect blackbody spectrum. When the curve was later shown at an astronomy conference the results received a standing ovation.

The success of COBE was the outcome of prodigious team work involving more than 1,000 researchers, engineers and other participants. John Mather coordinated the entire process and also had primary responsibility for the experiment that revealed the blackbody form of the microwave background radiation measured by COBE. George Smoot had main responsibility for measuring the small variations in the temperature of the radiation.

Congratulations guys. This was an extremely important discovery for physics as a whole, and cosmology in particular. As pointed out in a previous post, a Nobel Prize in Physics for this experiment was widely anticipated. At the moment the Big Bang theory of the universe is the only one left standing, thanks partially to the work of the COBE experiement.

Map of the Cosmic Microwave Background anisotropy of the universe taken by COBE. The different colours represent different temperatures, and show that there were small differences in density in the early universe. The islands of slightly higher than average density became the galaxies we can see today.

Results of the measurement of the blackbody spectrum of the universe (upper graph). The black dots represent the data taken by COBE (FIRAS instrument), and the curve shows the theortical prediction from the Big Bang theory for a universe with a temperature of 2.725 Kelvin (minus 270.425 degrees Celcius). The agreement is so good you can barely see the data points over the curve.

The final word goes to xkcd, which I have shown before.