tag:theconversation.com,2011:/ca/topics/particle-articles-155/articlesParticle articles – The Conversation2011-09-26T01:52:31Ztag:theconversation.com,2011:article/35132011-09-26T01:52:31Z2011-09-26T01:52:31ZNeutrinos and the speed of light? Not so fast …<figure><img src="https://images.theconversation.com/files/3825/original/aapone-20110924000346156010-file_switzerland_cern_opera-original.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Another week, another rush to proclaim Einstein was wrong.</span> <span class="attribution"><span class="source">Martial Trezzini/AFP</span></span></figcaption></figure><p><em>The bartender says, “We don’t serve your kind in here”</em></p>
<p><em>A faster-than-light neutrino walks into a bar …</em></p>
<p>The media is champing at the bit to proclaim a discovery of <a href="http://www.bbc.co.uk/news/science-environment-15017484">faster-than-light travel by a subatomic particle</a>, with some going as far as claiming <a href="http://www.news.com.au/technology/sci-tech/particles-seen-to-travel-faster-than-light/story-fn5fsgyc-1226144226826">“Einstein was wrong: relativity theory busted”</a>. </p>
<p>The scientists responsible for the experiment and analysis <a href="http://www.nature.com/news/2011/110922/full/news.2011.554.html">let slip they have some preliminary data</a> that suggests the particles travelled faster than light, but they seem to be the only ones not jumping to conclusions just yet.</p>
<p>The team at the <a href="http://operaweb.lngs.infn.it/">Oscillation Project with Emulsion-tRacking Apparatus (OPERA)</a> in Italy regularly measures the detection of <a href="http://theconversation.com/explainer-the-elusive-neutrino-431">neutrinos</a> emitted from another experiment at the <a href="http://public.web.cern.ch/public/en/LHC/LHC-en.html">Large Hadron Collider</a> (LHC) in Switzerland, 730 kilometres away.</p>
<p>Neutrinos (electrically neutral subatomic particles) are rather indifferent to the presence of trivial things such as Earth, and zip through without so much as a passing interest (their cross-section, the probability for <a href="http://www.britannica.com/EBchecked/topic/222177/fundamental-interaction">interaction</a>, is extremely small). Owing to their small mass, they should do so at approximately the speed of light, <em>c</em> (see video below) – the speed light travels in a vacuum, known quite well to be 299,792,458 metres per second.</p>
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<p>Using <a href="http://www.radio-assa.org.au/GPS_Timing">GPS timing</a> and position data, the OPERA team claim to know the distance between the point at which neutrinos are emitted from the LHC and the point at which they are detected in Italy to a precision that allows them to predict the time the neutrinos should arrive to within ten nano-seconds (a nanosecond being a billionth of a second).</p>
<p>What they claim to have found, though, is neutrinos arriving 60 nano-seconds (0.00000006 seconds) early. If accurate, this would be a six <a href="http://www.robertniles.com/stats/stdev.shtml">standard-deviation</a> result – enough to convince physicists that something is genuinely awry.</p>
<p>The scientists concerned have <a href="http://arxiv.org/abs/1109.4897">released the findings</a> to the scientific community in the hope that, if something has been overlooked, it will be picked up by their peers. The peer-review process is usually quite efficient at eliminating likely sources of error, and in this case there are plenty of possibilities. But on the face of it, it seems the OPERA team has been very careful.</p>
<p>There’s the issue of knowing the exact positions of the source and detector to within the quoted uncertainty – keeping in mind that in the extra 60 nano-seconds the neutrinos are supposedly travelling they will cover a total of 18 metres. This means knowing those two positions – and the <a href="http://en.wikipedia.org/wiki/Geodesic">geodesic</a> distance between them – to within three metres out of 730,000 metres.</p>
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<img alt="" src="https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=902&fit=crop&dpr=1 600w, https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=902&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=902&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1134&fit=crop&dpr=1 754w, https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1134&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/3827/original/aapone-20110923000346086023-italy-science-physics-neutrino-cern-original_1_.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1134&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p>Traditional civilian grade GPS has an accuracy of about 15 metres. More sophisticated methods are used for proper surveying, such as differential GPS (10-centimetres accuracy). At the very top range is “<a href="http://en.wikipedia.org/wiki/Global_Positioning_System#Carrier_phase_tracking_.28surveying.29">carrier phase tracking”</a>, which can beat one-centimetre accuracy. </p>
<p>This does require the GPS antenna to be above ground, though, so one also needs to take into account the timing for signals to travel along wires to the underground experiments.</p>
<p>The OPERA scientists made use of the more precise GPS system and a <a href="http://science.howstuffworks.com/atomic-clock3.htm">cesium atomic clock</a> to ensure their timing and positions were as accurate as possible.</p>
<p>Presuming for now all the possible sources of error are accounted for, what would this result mean? <a href="http://theconversation.com/is-the-large-hadron-collider-a-time-machine-447">Time-travel</a> seems to be the go-to topic when faster-than-light particles are mentioned, but don’t hold out hope for a <a href="http://www.bbc.co.uk/doctorwho/classic/tardiscam/intro.shtml">TARDIS</a> just yet. </p>
<p>If a particle is able to travel faster than <em>c</em>, a few odd things happen. Critically, it breaks <a href="http://www2.slac.stanford.edu/vvc/theory/relativity.html">(special) relativity</a>, which states there’s an absolute speed-limit – the speed at which massless particles travel – that doesn’t depend on <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/relmot.html">relative motion</a>.</p>
<p>One practical aspect of relativity is that the concept of <a href="http://www.fourmilab.ch/documents/RelativityOfSimultaneity/">simultaneity</a> is frame-dependent. If two events occur at different locations (say, flashing a torch) then, depending on how you are travelling relative to each of those events, you may see them occurring at different times (for instance, if you are accelerating relative to one then you will see it occur later, as if time is slowed). The order in which you observe them to occur depends on the relative motion.</p>
<p>Now, if one of those events was flashing a torch (photons) and the other was flashing super-luminous particles (travelling faster than light) your interpretation would not just be that they occurred at different times, but that one must have travelled back in time.</p>
<p>So, the particles can appear to travel back in time, but there’s still no method of accelerating a <a href="http://www.imdb.com/title/tt0088247/">cyborg killing-machine</a> to super-luminal speeds.</p>
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<img alt="" src="https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=391&fit=crop&dpr=1 600w, https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=391&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=391&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=491&fit=crop&dpr=1 754w, https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=491&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/3826/original/aapone-20110923000346086007-italy-science-physics-neutrino-cern-original.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=491&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p>The peer-review process is an important step to deciding whether or not to believe a particular result, but is the latest potential finding an isolated incident? Apparently not. In 2007 <a href="http://arxiv.org/abs/0706.0437">the MINOS experiment observed the same thing</a>, albeit with a smaller significance (1.8 standard deviations – not enough to get excited about). </p>
<p>Measurements of arrival times of photons and neutrinos from <a href="http://heritage.stsci.edu/1999/04/sn1987anino.html">supernova SN1987a</a> in 1987 provided a much better agreement with the speed of light, but those neutrinos were of a much lower energy. The possibility remains that velocity depends on energy.</p>
<p>Somewhat less rigid explanations include neutrinos taking “shortcuts” through <a href="http://theconversation.com/explainer-string-theory-2983">extra dimensions</a>. Undoubtedly, many more possible explanations will arise if all conventional sources of error are excluded. </p>
<p>The much more likely scenario is that the analysis has overlooked some seemingly insignificant but critical aspect, and that re-analysis will led to a very good agreement with the speed of light.</p>
<p>Should that be the case, the follow-up press-release will no doubt refer to the “Phantom of the OPERA”.</p><img src="https://counter.theconversation.com/content/3513/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Carroll receives funding from the ARC in the form of a Research Associate position for an ARC Laureate Fellow. He is affiliated with The University of Adelaide.</span></em></p>The bartender says, “We don’t serve your kind in here” A faster-than-light neutrino walks into a bar … The media is champing at the bit to proclaim a discovery of faster-than-light travel by a subatomic…Jonathan Carroll, Post Doctoral Research Associate, Centre for the Subatomic Structure of Matter, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/27852011-08-10T20:34:08Z2011-08-10T20:34:08ZOur new antimatter belt … all the rage in 2011<figure><img src="https://images.theconversation.com/files/2798/original/NASA.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Get to grips with the latest development in cosmic couture.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>In the past week, many media outlets have <a href="http://www.wired.com/wiredscience/2011/08/earth-antimatter-belt/">reported the discovery</a> of an antimatter “belt” circling the earth.</p>
<p>A range of potential uses for this belt have already been floated – perhaps the most exciting of which is the possibility of it <a href="http://news.sciencemag.org/sciencenow/2011/08/antimatter-belt-found-circling-e.html?ref=hp">being employed to fuel future space missions</a>.</p>
<p>But before we can understand how antimatter might be used as fuel, we need to understand what antimatter actually is and where this particular belt was found.</p>
<h2>What happened?</h2>
<p>The antimatter belt is confined to the inner regions of <a href="http://en.wikipedia.org/wiki/Magnetosphere">Earth’s magnetosphere</a> – the area of space around Earth that extends oval-like for many thousands of kilometres, created during the interaction of the <a href="http://solarscience.msfc.nasa.gov/SolarWind.shtml">solar wind</a> and the earth’s magnetic field.</p>
<p>This rather startling finding, <a href="http://arxiv.org/abs/1107.4882">published in online journal arXiv</a> in late July, confirms earlier theoretical predictions of the presence of antiprotons trapped in “orbit” above Earth by the planet’s magnetic field. </p>
<p>So what are antiprotons?</p>
<p>Well, almost all particles in our matter world also have antiparticles – particle doppelgangers that, according to our best physical theories, <a href="http://www2.slac.stanford.edu/vvc/theory/antiquarks.html">have the same mass but opposite charge</a> to their matter counterparts. </p>
<p>The most common examples of these are the <a href="http://www.positron.edu.au/faq.html#faq3">positron</a> – the positive antiparticle to the ubiquitous (negative) <a href="http://www.guardian.co.uk/science/life-and-physics/2011/mar/17/1?INTCMP=SRCH">electron</a> – and the aforementioned antiproton – the negative antiparticle to the positively charged <a href="http://www.guardian.co.uk/science/life-and-physics/2011/mar/26/1">proton</a>.</p>
<p>The antiprotons in the antimatter belt are thought to be produced by interactions between the <a href="http://en.wikipedia.org/wiki/Cosmic_ray">cosmic ray flux</a> – streams of energetic particles, mostly electrons and protons – with matter in the upper atmosphere.</p>
<p>The resultant negatively-charged antiprotons then effectively become trapped in motion along the magnetic field lines of the earth (see image below), assuming their kinetic energy and relative angle to the field lines are such that they cannot “escape” across those field lines. </p>
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<img alt="" src="https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/2799/original/NASA1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The magnetic field lines around the Earth.</span>
<span class="attribution"><span class="source">NASA</span></span>
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<p>The discovery of these trapped antiprotons was made using a satellite-borne instrument known as <a href="http://pamela.roma2.infn.it/index.php">PAMELA (Payload for Antimatter/Matter Exploration and Light-nuclei Astrophysics)</a>. </p>
<p>PAMELA – which is monitored by a <a href="http://pamela.roma2.infn.it/index.php?option=com_content&task=view&id=19&Itemid=276">multinational research collaboration</a> – was designed to measure the flux of particles and their antiparticles in the region between 350 kilometres and 610 kilometres above Earth’s surface. </p>
<p>One of the key findings made by physicists working with PAMELA was that the trapped antiprotons spiral around the earth’s magnetic field lines and likely bounce between <a href="http://en.wikipedia.org/wiki/Magnetic_mirror_point">mirror points</a> – points where the shape of the field causes the particles to reverse their motion.</p>
<p>Surprisingly, it only took the discovery of 28 trapped antiprotons with kinetic energies less than 1 million <a href="http://www.universetoday.com/56463/electron-volt/">electron volts</a> over more than 800 days in satellite orbit for the researchers to declare the existence of a “belt”.</p>
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<p>While the density of antiprotons discovered is incredibly low, it is still several <a href="http://www2.pvc.maricopa.edu/tutor/chem/chem151/metric/magnitude.html">orders of magnitude</a> in excess of what might be “normally” expected in the interstellar medium – the “stuff” between solar systems in a galaxy – in the absence of Earth’s strong magnetic field.</p>
<h2>Space vs Lab</h2>
<p>The finding provides an interesting contrast to the terrestrial, man-made antiproton “traps” found in laboratories such as <a href="http://alpha-new.web.cern.ch/">CERN</a> in Switzerland – the European Organisation for Nuclear Research.</p>
<p>In such experiments, antiprotons are used for the production and study of antihydrogen atoms – a combination of an antiproton and a positron – as opposed to the proton and electron combination in a “conventional” hydrogen atom. </p>
<p>Among other things, these laboratory studies hope to reveal if there are any subtle differences between the properties of matter and antimatter, aside from the obvious difference in charge.</p>
<p>One such recent experiment by the <a href="http://alpha-new.web.cern.ch/">ALPHA collaboration at CERN</a> <a href="http://www.nature.com/nphys/journal/v7/n7/full/nphys2025.html">successfully trapped hundreds of antihydrogen atoms</a> for up to 15 minutes. </p>
<p>The density of antiprotons in these man-made traps is many orders of magnitude higher than was observed in the magnetospheric “trap” – so in this case, nature still has a long way to go to catch up to the big (and expensive) science being done in labs around the world.</p>
<h2>Rocket fuel</h2>
<p>So how could this antimatter belt be used to power future space craft?</p>
<p>Well, <a href="http://thefutureofthings.com/articles/33/new-antimatter-engine-design.html">the theory</a> is that antiprotons from the belt around Earth could be harvested, fed into a specially-built reactor on board a space craft where they would then mix with protons.</p>
<p>The resulting interaction would result in the annihilation of both protons and antiprotons, creating highly energetic photons which would then be used to propel the craft.</p>
<p>Is this possible? Well yes, but probably not in the near future. We are a long, long way from the sort of numbers of antiprotons that would be required for such a space fuel source. </p>
<p>But the newly discovered belt, far from constraining future endeavours, will help scientists, and their science, to expand considerably.</p><img src="https://counter.theconversation.com/content/2785/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Buckman receives funding from the Australian Research Council and the Australian National University. He is a Professor of Physics at the ANU and the Research Director of the ARC's Centre of Excellence for Antimatter-Matter Studies. </span></em></p>In the past week, many media outlets have reported the discovery of an antimatter “belt” circling the earth. A range of potential uses for this belt have already been floated – perhaps the most exciting…Stephen Buckman, Professor; Research Director ARC Centre for Antimatter-Matter Studies, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2802011-04-14T04:05:48Z2011-04-14T04:05:48ZExplainer: the Higgs boson particle<figure><img src="https://images.theconversation.com/files/369/original/DE0063M.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">As yet we can only guess what the Higgs boson might look like.</span> <span class="attribution"><span class="source">DESY Zeuthen</span></span></figcaption></figure><p>Theoretical physics is full of mysteries and unknowns. In the case of some particles, we can predict their existence even if we can’t find them.</p>
<p>Such is the status of the Higgs boson. And yet detecting this particle would revolutionise physics as we know it.</p>
<h2>But let’s start with mass</h2>
<p>When you place your suitcase on the scales at the airport check-in counter, you are hoping it weighs less than the limit so you won’t have to pay any excess baggage fees. </p>
<p>The force of Earth’s gravity acting on the suitcase’s mass determines its weight. A suitcase that weighs 20kg on Earth would weigh 3kg on the moon, while its mass remains the same. What determines the suitcase’s mass? And even more fundamentally, what is mass?</p>
<p>This is one of the most important questions in particle physics today. The leading explanation for the origin of mass is the Higgs mechanism developed in 1964, which involves the Higgs field and the Higgs boson. </p>
<p>My favourite description of the Higgs mechanism comes from <a href="http://www.hep.ucl.ac.uk/%7Edjm/">David J. Miller</a>, the winner of a competition among physicists to find the best way of explaining the physics to the UK Science Minister in 1993 to acquire funding. The analogy goes a something like this …</p>
<p>Imagine that a room full of physicists chattering quietly is like space filled with the Higgs field. A well-known scientist walks in, creating a disturbance as he moves across the room and attracting a group of admirers with every step. </p>
<p>This increases his resistance to movement. In other words, he acquires mass, just like a particle moving through the Higgs field. Now imagine if, instead of a well-known scientist entering, somebody started a rumour. </p>
<p>As the rumour spreads throughout the room, it creates the same kind of grouping, but this time it’s the scientists grouping together. </p>
<p>In this analogy, these groups are the Higgs bosons. If we find these groups, we can prove the Higgs field exists and thus explain the origin of mass.</p>
<p>To try finding the Higgs boson, scientists collide other particles together at very high energies and search the debris for traces of this elusive particle. </p>
<p>Scientists at the previous <a href="http://hepwww.rl.ac.uk/public/phil/ppintro/lep.html">LEP particle accelerator</a> at CERN near Geneva felt they came close before the machine shut down in 2000. </p>
<p>Scientists using the <a href="http://www-bdnew.fnal.gov/tevatron/">Tevatron accelerator</a> at Fermilab near Chicago are hoping to publish a discovery before the machine shuts down later this year.</p>
<p>The most promising prospect for finally discovering the Higgs boson is the most powerful particle collider ever built: The <a href="http://lhc.web.cern.ch/lhc/">Large Hadron Collider</a> (LHC) at CERN, a 27km accelerator located 100m under the French-Swiss border that took 25 years to plan and $6 billion to build. </p>
<p>There haven’t been any hints of the particle yet, but it’s early days for the accelerator, which is expected to run for at least 10 years.</p>
<h2>What’s at stake? </h2>
<p>Both the discovery and exclusion of the Higgs boson at the LHC have vast and important consequences. It is the final missing piece of the <a href="http://physics.info/standard/">Standard Model</a>, the theory physicists use to describe the electromagnetic, strong and weak forces. </p>
<p>All the other particles in the Standard Model have been proven to exist through experiment. </p>
<p>An example of such a prediction and subsequent discovery are the W and Z bosons, which mediate the <a href="http://www-project.slac.stanford.edu/e158/weakforce.html">weak force</a>. </p>
<p>These particles were predicted in 1968 and discovered in 1983, an achievement so significant that <a href="http://nobelprize.org/nobel_prizes/physics/laureates/1984/press.html">Carlo Rubbia and Simon van der Meer</a> were awarded a Nobel Prize in 1984. The same reward may be waiting if we find the Higgs boson.</p>
<p>Finding the Higgs boson will provide insight into why particles have certain masses, and will help to develop subsequent physics. </p>
<h2>What’s the hold-up?</h2>
<p>The technical problem is that we do not know the mass of the Higgs boson itself, which makes it more difficult to identify. </p>
<p>Physicists have to look for it by systematically searching a range of mass within which it is predicted to exist. </p>
<p>The yet unexplored range is accessible using the LHC, which will determine the existence or otherwise of the Higgs boson. </p>
<p>If it turns out that we cannot find it, this will leave the field wide open for physicists to develop a completely new theory to explain the origin of particle mass. </p>
<p>It is a very exciting time to be in particle physics.</p>
<p><strong>Related stories:</strong></p>
<p><a href="https://theconversation.com/is-the-large-hadron-collider-a-time-machine-447">Is the Large Hadron Collider a time machine?</a></p>
<p><a href="https://theconversation.com/explainer-the-z-hypothetical-particle-665">Today’s (hypothetical) particle: the Z’</a></p>
<p><a href="https://theconversation.com/explainer-the-elusive-neutrino-431">Today’s particle: the elusive neutrino</a></p><img src="https://counter.theconversation.com/content/280/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anna Phan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Theoretical physics is full of mysteries and unknowns. In the case of some particles, we can predict their existence even if we can’t find them. Such is the status of the Higgs boson. And yet detecting…Anna Phan, Postgraduate Student, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/6652011-04-06T04:27:23Z2011-04-06T04:27:23ZExplainer: the Z’ (hypothetical) particle<figure><img src="https://images.theconversation.com/files/377/original/File_First_Gold_Beam-Beam_Collision_Events_at_RHIC_at_100_100_GeV_c_per_beam_recorded_by_STAR.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Is the "Z-prime" lurking within a "jungle" of particles at the LHC?</span> <span class="attribution"><span class="source">Argonne National Laboratory</span></span></figcaption></figure><p>There’s nothing like an unexpected result to get physicists excited. </p>
<p>So in 2008, when some strange behaviour was detected from a rarely-produced particle known as the “top quark”, there was much interest and speculation.</p>
<p>Now, with the publication of an <a href="http://www.sciencenews.org/view/generic/id/72095/title/Remodeling_the_standard_model">intriguing new study by University of Michigan researchers</a> we may be closer to explaining the top quark’s behaviour.</p>
<p>The <a href="http://physics.info/standard/">Standard Model of Particle Physics</a> describes the fundamental particles (and their interactions) that combine to form everything we see in the universe. </p>
<p>But this model is not complete.</p>
<p>There are already hints from high-energy experiments that suggest the existence of so-called missing elements – particles that have yet to be seen. The properties of these particles might be able to solve some important riddles.</p>
<p>Let’s take stock for a moment. Everyday matter (including you and I) is made up of just a few ingredients: relatively light “up” and “down” <a href="http://www.youtube.com/watch?v=SMgi2j9Ks9k&feature=related">quarks</a> stuck together with <a href="http://www.youtube.com/watch?v=ZYPem05vpS4&feature=related">“gluons”</a> (think “glue”) to form “protons” and “neutrons”. </p>
<p>Along with “electrons”, these last two particles make up the atoms from which all matter is constructed.</p>
<p>In studying the results from high-energy systems such as those produced by Europe’s <a href="https://theconversation.com/is-the-large-hadron-collider-a-time-machine-447">Large Hadron Collider</a> (LHC), we’ve found there are a handful of other interesting particles out there. </p>
<p>And importantly, there are four more types of quarks, the heaviest of which is named “top”.</p>
<p>So why the current excitement? Strap yourself in, reader; this is where things get complicated. </p>
<p>The 2008 discovery, made by physicists at the <a href="http://www-bdnew.fnal.gov/tevatron/">Tevatron</a> (a particle collider near Illinois), uncovered a strange asymmetry in the direction that top quarks exit a collision between protons and anti-protons.</p>
<p>What does this mean? In short, the top quarks preferred to move in a particular direction rather than being uniformly distributed.</p>
<p>This result, on this scale, was not predicted by the Standard Model, and as a result has caused a bit of a stir amongst physicists (who nit-pick such predictions with a fine-toothed comb).</p>
<p>As is customarily the case in particle physics, theories abound for a “new” particle that can explain the discrepancy. This “new” particle could be any number of different things.</p>
<p>Well, it could be a particle that comes from a pool of mysterious “supersymmetric” or dark matter particles whose existence we are yet to confirm. It could also originate from an as-yet unseen force.</p>
<p>Unfortunately, such theories tend to raise more questions than they answer. Luckily, some very elegant options remain, including the solutions described by the University of Michigan researchers.</p>
<p>According to their study, the Tevatron results could point towards the existence of the <a href="http://www.interactions.org/quantumuniverse/qu2006/scenarios/scenario_08.html">hypothetical Z’</a> (pronounced “Z-prime”) particle.</p>
<p>Beautiful as this theory might be, it is mere speculation unless the Z’ particle can be found.</p>
<p>One way to tell if the Z’ actually exists is to look for it in the jungle of particles created in collisions at the LHC, which operates at a much higher energy level than the Tevatron.</p>
<p>With any luck, the LHC will be able to create the Z’ within a couple of months, assuming the particle has a mass lower than a particular limit.</p>
<p>So what happens if we <em>do</em> detect the Z’? </p>
<p>Well, at the moment, the existence of Z’ is simply one theory competing with several other theories, so finding it would be an unexpected result for a great number of physicists.</p>
<p>And physicists love unexpected results.</p>
<p><strong>More stories on this topic</strong></p>
<p><a href="https://theconversation.com/is-the-large-hadron-collider-a-time-machine-447">Is the Large Hadron Collider a time machine?</a></p>
<p><a href="https://theconversation.com/explainer-the-elusive-neutrino-431">Today’s particle: the elusive neutrino</a></p><img src="https://counter.theconversation.com/content/665/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Carroll receives funding from the ARC in the form of a Research Associate position for an ARC Laureate Fellow. He is affiliated with The University of Adelaide.</span></em></p>There’s nothing like an unexpected result to get physicists excited. So in 2008, when some strange behaviour was detected from a rarely-produced particle known as the “top quark”, there was much interest…Jonathan Carroll, Post Doctoral Research Associate, Centre for the Subatomic Structure of Matter, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/4312011-03-31T03:46:24Z2011-03-31T03:46:24ZExplainer: the elusive neutrino<figure><img src="https://images.theconversation.com/files/253/original/neutrino_detector.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Could neutrinos be responsible for the shape of the universe?</span> <span class="attribution"><span class="source">The Super-Kamiokande Neutrino Detector, Japan</span></span></figcaption></figure><p>Of all the known particles in our universe, neutrinos are perhaps the most elusive; their origins are mysterious, their purpose unknown and they are notoriously difficult to detect. </p>
<p>You’ll already know that ordinary, everyday matter is made up of combinations of “elementary” particles called protons, neutrons and electrons. Put these together in different arrangements and you can make any of the substances we see around us, from air to plastics to steel.</p>
<p>But there are many other weird and wonderful particles we don’t encounter in everyday life. Some of these are unstable and exist only briefly before disappearing in a flash of energy. Others pass, ghostlike and unseen, through the everyday world.</p>
<p>The first hint that neutrinos – perhaps the most ghostly of these – existed came in 1930 when a physicist, <a href="http://www.library.ethz.ch/exhibit/pauli/neutrino_e.html">Wolfgang Pauli</a>, noticed that in certain nuclear processes, particles would jump off in random directions as if they’d been pushed. </p>
<p>He guessed that this was because there was another unseen particle involved (the neutrino) that was giving them a kick in the opposite direction.</p>
<p>The problem? While the particle he proposed turned out to be very convenient for his theory, it also turned out to be very hard to detect. </p>
<p>As physicists, we normally see things by measuring reflected particles of light known as photons. Unfortunately, neutrinos don’t reflect photons and, even if they did, move too quickly to be spotted in this manner. </p>
<p>Another way physicists detect particles is by placing something solid, such as a brick, in their path, then looking for the resulting flash of energy when the particle hits it. </p>
<p>But this too presents issues: as a technique, it’s a bit like trying to figure out what a tennis ball is, without ever having seen one, by listening to a Wimbledon match: it’s possible, but not particularly easy. </p>
<p>The problem is that neutrinos pass through familiar forms of matter almost as if it wasn’t there. </p>
<p>Our sun emits vast numbers of neutrinos, and billions pass through you every second, but only one in a trillion stops or slows down as it passes through your body.</p>
<p>In the 1950s, <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/particles/cowan.html">Fred Reines and Clyde Cowan built detectors</a> out of tanks of water and surrounded them with very sensitive cameras so that when that one-in-a-trillion neutrino happened to interact with the water, they could catch the tiny flash of light it produced. </p>
<p>Eventually they had success. In 1956, the Cowan-Reines experiment detected several neutrinos, confirming Pauli’s speculation from more than two decades earlier.</p>
<p>But the fact neutrinos are so elusive also has some advantages.</p>
<p>Astronomers normally use telescopes to look at light, but this light can be blocked by dust clouds or dense radiation fields in the space between stars. </p>
<p>Neutrinos pass straight through all of this cosmic interference, giving us valuable information about what might be happening on the other side. </p>
<p>Suppose the nuclear furnace at the centre of the sun went out: it would be tens of thousands of years before the outside of the sun cooled down; and, because of interference, we wouldn’t notice it getting dimmer. </p>
<p>But the neutrinos coming from the centre of the sun would stop immediately, and we’d notice this within minutes.</p>
<p>Thankfully, we don’t seriously expect the sun to go out any time soon, but some other stars (not like our sun) <em>do</em> turn themselves off in massive explosions called supernovae. Looking at the neutrinos from inside those explosions can tell us much about what is really going on.</p>
<p>Stars are not the only astronomical objects to produce neutrinos. There are massive black holes at the cores of distant galaxies. </p>
<p>Neutrinos from those galaxies (if we’ve got the theory right) should be travelling very close to the speed of light, much faster than those from the sun or supernovae. </p>
<p>We expect them to be very rare, so we either need to wait a lot longer before we see one, or to build huge detectors to catch more of them. Fortunately, we can cheat a bit. </p>
<p>Since these neutrinos are travelling at an incredible speed, they make powerful flashes when they hit something. So, rather than building our own detector, we just watch something big (such as Antarctica, or the moon) for a little burst of light. </p>
<p>Also, there’s a chance neutrinos are responsible for the shape of the universe. When we look at other galaxies, we can see they have been pulled around by the gravity of some invisible clumps in space, which we call dark matter. Could these be clumps of neutrinos? </p>
<p>We don’t know yet, but we’ll do our best to find out.</p><img src="https://counter.theconversation.com/content/431/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Justin Bray receives funding from the Australian Research Council to conduct research into high-energy neutrinos. He is affiliated with the University of Adelaide and CSIRO Astronomy & Space Science.</span></em></p><p class="fine-print"><em><span>Roger W. Clay does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Of all the known particles in our universe, neutrinos are perhaps the most elusive; their origins are mysterious, their purpose unknown and they are notoriously difficult to detect. You’ll already know…Roger W. Clay, Professor of Astrophysics, University of AdelaideJustin Bray, Postgraduate Research Student in High Energy Astrophysics, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.