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Ian Sample - LHC http://www.iansample.com:/site/?q=taxonomy/term/16/0 en Another one bites the dust http://www.iansample.com:/site/?q=content/another-one-bites-dust <p>And so to the media scramble at Easter that scientists at the Large Hadron Collider had finally glimpsed the Higgs boson, or at least its fleeting footprint: a flicker of light in the giant Atlas detector.</p> <p>You&#39;ll recall what happened. <a href="http://www.math.columbia.edu/~woit/wordpress/?p=3643">A leaked note from the Atlas collaboration</a> pointed to an excess in one of the ways a Higgs particle might decay - that is, into two high energy photons. An excess means extra particles coming from somewhere beyond the Standard Model, and in this case, potentially from the Higgs (which is highly unstable) decaying into particles of light.</p> <p>The internal note was just that, a very preliminary finding, and it was posted to a blog before it had been scrutinised in any serious detail.</p> <p>This was not the first time researchers (if only a handful) had got their hopes up that a discovery was at last in the offing. Nor was it the first time there were serious doubts that the Higgs had suddenly popped up and been measured. <a href="http://www.guardian.co.uk/science/2011/apr/28/higgs-boson-rumour-cern-lhc">See here for some of the previous incidents and a few early doubts raised over the latest Higgs signal</a>.</p> <p>Internal notes like these are not exceptional and there is a well-worked process for assessing them. The ones that point to evidence of the Higgs boson (and it&#39;s arguable that this one did) go to a bunch of specialists called the Higgs working group, who look at the claims in detail. If they are happy the analysis is sound, the abstract goes out to the whole Atlas collaboration for further scrutiny. That is some serious intellectual clout being brought to bear.</p> <p>Since the fuss at Easter, researchers at Cern have been studying the latest claim. And what have they found? The answer, as you might have guessed, is nowt. In the latest analysis of Atlas data, there was no sign of a Higgs particle decaying into high energy photons at a mass of 115GeV (the mass indicated in the original note), or any other mass for that matter. The conclusion of the latest note, published earlier today, is this:</p> <p><strong>&quot;No excess is observed, neither with the analysis criteria described in this note nor with other selections studied.&quot;</strong></p> <p><a href="https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2011-071/ATLAS-CONF-2011-071.pdf">Read the full conference note here</a>.</p> <p>The knockdown doesn&#39;t come as a surprise and in these days of thousands-strong collaborations, scientists&#39; blogs and a genuinely enthused media, nor does the mass coverage of the non-sighting. There will be more, and we can certainly expect some fun in the run up to the summer conferences. <a href="http://www.economist.com/node/18618015">Or as the Economist put it, &quot;expect plenty more herrings, red or otherwise.&quot;</a></p> http://www.iansample.com:/site/?q=content/another-one-bites-dust#comments CERN God particle Higgs boson Large Hadron Collider LHC Sun, 08 May 2011 11:56:10 +0000 Ian Sample 31 at http://www.iansample.com:/site Waiting for the Godot particle http://www.iansample.com:/site/?q=content/waiting-godot-particle <p>To get to <a href="http://www.fnal.gov/">Fermilab</a> from downtown Chicago, you find <a href="http://www.chicagotraveler.com/maps/chicago-beaches-map.htm">Lake Michigan</a> and drive in the opposite direction. After about an hour on the freeway, the city shrinks to nothing in the rear-view mirror and you pick up an access road that turns into the 7,000 acre campus where the laboratory is based.</p> <p>The road cuts through a landscape of forests and lakes before arriving at one of my favourite sculptures. At first glance, it could be <a href="http://www.cretewest.com/PIX/talos.jpg">Talos straddling the road in case the Argonauts pay a visit</a>, but this 21-ton metal monster was designed and built by Robert Wilson, a former cowboy and first director of the laboratory. From almost any angle, the sculpture looks ungainly and off-kilter <a href="http://www.fnal.gov/pub/presspass/vismedia/gallery/buildings.html">(scroll down here)</a>, but lie on the road beneath it and look up. The sculpture&rsquo;s strained lines are hidden and a perfectly symmetrical form appears. It was meant to be that way. Wilson called the sculpture &ldquo;Broken Symmetry&rdquo;.</p> <p>The concept of symmetry breaking is fundamental in physics and central to the Higgs mechanism. The Higgs field breaks the symmetry between the electromagnetic force and the so-called weak force, the latter of which goes to work in certain radioactive processes and plays a vital role in keeping the sun shining. The field does this by giving mass to the weak force carrier particles, the W and Z bosons, while leaving the photon, which carries the electromagnetic force, massless and free to hurtle about at the speed of light. But that&rsquo;s another story.</p> <p>Fermilab is home to the Tevatron particle collider, an impressive old workhorse that lists among its successes the discovery of the top quark in 1995. The top quark is the heaviest known fundamental particle and weighs as much as a tungsten atom. If that doesn&rsquo;t sound much, bear in mind that a tungsten atom contains 74 protons, 110 neutrons and 74 electrons. It&rsquo;s the heaviest element used by living organisms.</p> <p>The Tevatron has been in the news again in recent weeks. <a href="http://www.science20.com/quantum_diaries_survivor/rumors_about_light_higgs">A vague rumour</a> emerged on a physicist&rsquo;s blog that the Tevatron had found the Higgs boson. Some media outlets got a bit tangled up over the story, reporting one day that <a href="http://www.telegraph.co.uk/science/large-hadron-collider/7885997/Large-Hadron-Collider-rival-Tevatron-has-found-Higgs-boson-say-rumours.html">the particle has been found</a>, and the next <a href="http://www.telegraph.co.uk/science/large-hadron-collider/7888012/Higgs-boson-discovery-rumours-false-say-Tevatron-scientists.html">that it hadn&#39;t</a>. At the time, <a href="http://twitter.com/iansample/status/18368225595">I bet Martin Rees&rsquo;s dog</a> that the Tevatron has not discovered the Higgs boson. That might seem an odd (not to say unethical) thing to bet, but <a href="http://iopscience.iop.org/0264-9381/25/22/229001">it&rsquo;s not the first time</a> the poor creature&rsquo;s life has been wagered.</p> <p>There are two detector teams at the Tevatron, CDF and Dzero, and the teams are due to announce the combined results from their Higgs searches at 4pm Central European Time on Monday&nbsp; 26th July from the <a href="http://www.ichep2010.fr/">ICHEP conference in Paris</a>. I&rsquo;ll post the results here at the same time, but for now, some background to explain why I don&rsquo;t think the Higgs has been found and why Lord Rees&#39;s dog is safe.</p> <p>In January, the Tevatron teams <a href="http://arxiv.org/abs/1001.4162">published their last combined search for the Higgs particle</a>. The paper is pretty technical, but essentially it looks to see whether there is evidence for so-called Standard Model Higgs particles decaying into W bosons, however they are made in the first place in the machine. The searches rule out any Higgs boson (with 95% confidence) between a mass of 162 GeV and 166 GeV. A previous accelerator at Cern, the Large Electron Positron (LEP) collider, ruled out the possibility of the Higgs particle weighing less than 114.4 GeV. &nbsp;</p> <p>With six months or so more collisions under their belts, we might expect the Tevatron teams to have ruled out the existence of a Higgs particle over an even greater range of masses. That would be good news. It would narrow down the region where the Higgs must be hiding. We can&#39;t really expect them to have found the elusive beast. As I joked (very lamely) a week or so ago, physicists have waited so long to see the Higgs boson, or &quot;God particle&quot;, in their experiments, they might want to rename it <a href="http://twitter.com/iansample/status/18983671870">the Godot particle</a>.</p> <p>&nbsp;<br /> What is clear is that the Tevatron and its detector teams are working well and making solid progress in the hunt for the Higgs particle. Officially, the machine is due to close at the end of 2011, but a proposal to run for a few years longer is under consideration. With the <a href="http://lhc.web.cern.ch/lhc/">Large Hadron Collider at Cern</a> having little chance of finding the Higgs boson before it begins high energy runs at the end of 2012, there is surely a strong argument to keep the Tevatron in the race.<br /> &nbsp;</p> http://www.iansample.com:/site/?q=content/waiting-godot-particle#comments CERN God particle Higgs boson Large Hadron Collider LHC Tevatron Sun, 25 Jul 2010 22:43:50 +0000 Ian Sample 21 at http://www.iansample.com:/site