| Famed Tasmanian devil euthanized after tumor found By KRISTEN GELINEAU 2010-09-01T07:44:54ZSYDNEY (AP) -- A Tasmanian devil named Cedric, once thought to be immune to a contagious facial cancer threatening the iconic creatures with extinction, has been euthanized after succumbing to the disease, researchers said Wednesday.... hosted.ap.org |
Europe plans large lunar lander Led by Germany, Europe is pressing ahead with plans to send a sophisticated, unmanned spacecraft to the surface of the Moon. bbc.co.uk |
Quarks, gluons and jets | Jon Butterworth The LHC paper I've been working on for the past few months is finally out. It shows quarks and gluons doing what they should do, and I love itIn July we (ATLAS) released a preliminary version of our first jet cross section measurement, and showed it at the International Conference on High Energy Physics (ICHEP) in Paris. Today we submitted the final version of this measurement to the European Physical Journal and to the archive."Cross section" in this context is basically a probability. If you fire two footballs at each other, they have a bigger cross-sectional area than two snooker balls, so they are more likely to hit each other. A "jet cross section" is a measure of how likely we are to see jets when we fire two protons at each other.Jets are what quarks and gluons do when they try to escape. The proton is made up of quarks stuck together by gluons. Most of the fundamental forces get weaker with distance - the Earth's gravitational pull gets weaker the further out into space you go, for example. But the strong nuclear force is the other way round.The force between two quarks actually gets stronger as you pull them apart, more like an elastic band. When two quarks in LHC protons bounce off each other they head away really quickly, feeling almost no force at first (physics buzzwords: asymptotic freedom. See this Nobel Prize citation). But at some point that has to end, because as they get further and further from the protons they were knocked out of, the force pulling them back gets stronger and stronger.You can think of the quarks as being the ends of the elastic band. They fly away from each other until at some point the band snaps and two new ends (new quarks) are produced. Eventually, we see a spray of hadrons (particles, like the proton, which contain quarks and generate amusing typos). Because the initial quarks get kicked so hard, this spray is collimated into a jet, and despite all the splitting and production of new quarks, the direction of the jet reflects pretty well the initial direction of the quark.ResultSo, what you see in the plot below reflects the distribution of quarks and gluons scattered in collisions at the LHC.When we collide protons, we really care most about the collisions between the proton's constituents - quarks or gluons. Unfortunately the quarks and gluons only carry a fraction of the energy of the proton, and we have no way of choosing how much. If the fraction was a half, for example, then we would have jets with 1750 gigaelectronvolts (GeV) of energy (half of 3.5 TeV). But most of the quarks and gluons carry much smaller fractions.To have a real measurement of this, and show that the theory prediction (quantum chromodynamics, labelled QCD on the plot) agrees with the data, is a real achievement. It directly involved dozens of people, and less directly hundreds. One key component is the energy calibration which I described here.This result, like the minimum bias results, is part of finding our feet in the new energy regime of the LHC - but these collisions are much closer to where we want to be. And we already have about 300 times more data to play with than is shown here, with more flooding in. We are already using these data to look for new forces and particles (see here and here).PSWhen we put the preliminary results out, I wrote an earlier version of this article. Unlike the data, it changed quite a bit in between! In a good way.Jon Butterworthguardian.co.uk © Guardian News & Media Limited 2010 | Use of this content is subject to our Terms & Conditions | More Feeds guardian.co.uk |
Video | Learn to speak chimpanzee Ape actor Peter Elliott shares his knowledge of chimpanzee and gorilla vocabulary and facial expressions guardian.co.uk |
Gulf corals in oil spill zone appear healthy By BRIAN SKOLOFF 2010-10-22T15:32:40ZON THE FLOOR OF THE GULF OF MEXICO (AP) -- Just 20 miles north of where BP's blown-out well spewed millions of gallons of oil into the sea, life appears bountiful despite initial fears that crude could have wiped out many of these delicate deepwater habitats.... hosted.ap.org |