TOP 100 SCIENCE SITES
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| Conservation boost for rare goanna A new conservation park on Kangaroo Island in South Australia will aim to better protect a rare goanna. abc.net.au |
From liquid argon to M theory? | Jon Butterworth Claiming to understand the universe from first principles is all very well, but the foundations have to be built on experiment and observation. And it is slow, hard work. Even in PisaYou may have noticed that my contribution to the recent hoohah about Stephen Hawking's book was not exactly a ringing endorsement of M theory.This is at least partly because I'm an experimentalist. I care much more about the ability of a theory to stand up to experimental test than I do about its mathematical beauty. M theory, and string theory, have a long way to go in this regard. Even supersymmetry struggles a bit.It's true that my experiment, Atlas, at the Large Hadron Collider (LHC), may discover supersymmetry, and/or find evidence for extra dimensions. This is really exciting, and either discovery would certainly add credibility to M theory, as well as revolutionising our understanding of fundamental physics.But finding such evidence is the main thing, and the search tends to keep your feet on the ground even if the goals are lofty. Not only do we need the accelerator, we need our detectors to record what happens when protons collide. We also need to know how to interpret what our detectors are telling us.This week many of us are in Pisa, sharing ideas and results from the Atlas calorimeter.Most high energy particle physics detectors surround the "collision point" of the beams with onion layers of different technologies, each designed to tell us something different about the collision. One of the most important layers is the calorimeter.It measures energy – calories. Burgers carry energy, and particles carry energy when they are produced in a proton-proton collision at the LHC. We want to know how much.The basic idea is to stop the particles with some very dense material. They hit the material, slow down, and as they do so they give off electromagnetic radiation (light, basically). The amount of light given off has a one-to-one correspondence with the energy the particle had in the first place. So the trick is to measure the light, work out the correspondence, and so measure the energy.Working out the correspondence is called calibration. It's difficult, and it is why we're in Pisa.The main calorimeter technology in the Atlas detector uses liquid argon (to produce and detect the light) interleaved with lead or copper to stop the particles.Liquid argon may sound exotic, but we use it because it gives out light in a very nice way proportional to the energy going in. Plus it's very stable – the proportionality doesn't change with time – and it is resistant to radiation.Even so, it gives a different amount of light when it is hit by an electron compared to when it is hit by, for example, a pion (which is a common hadron made up of a quark and an anti-quark). There are many such subtleties you have to calibrate for before you really believe what you see. The whole calibration process is equivalent to checking your experimental setup in science experiment on a bench. It consists of many, many "control" studies – measuring stuff you already know, in order to understand your detectors. Without such procedures, we couldn't believe any particle measurement we make, whether it's a couple of particles produced in a hospital scanner, or a spray of particles indicating extra dimensions at the LHC. If and when the experiments start seeing well understood signals, over and over again, for supersymmetric particles or extra dimensions, that's when those theories win. And that's when, maybe, I'll start taking M theory more seriously.If for any reason you want the definitive published technical descriptions of Atlas calorimetry, the rest of Atlas, the LHC detectors and the LHC itself, you can find it all here. * maybeJon Butterworthguardian.co.uk © Guardian News & Media Limited 2010 | Use of this content is subject to our Terms & Conditions | More Feeds guardian.co.uk |
A Guided Tour of Modern Medicine’s Underbelly In Dr. Carl Elliott’s survey of all that is shifty in modern medicine, humdrum events are exactly what make up medicine’s dark side. feeds.nytimes.com |
Observatory: Salt Infusion Could Be a Remedy for Damaged Cells An infusion of sodium helped tadpoles regenerate amputated tails. feeds.nytimes.com |
Krill fishery closed An area of krill fishery in the Southern Ocean has been closed for the first time following a massive increase in the amount taken by the commercial industry. abc.net.au |