- 3039 - ANTIMATTER - the opposite of normal matter? "Antimatter." is just like normal matter, with all the same properties and all the same abilities to make up atoms and molecules, except for one crucial difference: It has an opposite charge
--------------- 3039 - ANTIMATTER - the opposite of normal matter?
- "Antimatter." Take the humble electron, for example. Mass of 9.11 x 10^-31 kg. Quantum spin of 1/2. Charge of -1.6 x 10^-9 coulombs.
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- It has an antimatter evil twin, the “positron“. The positron has a mass of 9.11 x 10^-31 kg. Quantum spin of 1/2. Charge of … 1.6 x 10^-9 coulombs.
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- There is an twin for the top quark, the neutrino, the muon and on and on and on. All the fundamental particles that make up our daily lives have an equivalent antiparticle.
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- Not only are matter and antimatter paired up like this, they're symmetric. Every particle of normal matter produced in a reaction comes paired with its antimatter equivalent.
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- Our universe ought to be swimming with antimatter, existing in equal parts with normal matter. Whole planets, stars and galaxies made of antimatter! Or at the very least, loads of antimatter particles just floating around in space.
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- Just as the pairs are produced in perfect symmetry in fundamental interactions, they are destroyed in symmetry as well. When a particle finally gets to meet and with its antiparticle, they annihilate each other.
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- All their combined matter is converted into energy, usually in the form of high-energy gamma-ray radiation.
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- We don't see signs of abundant free-floating carefree antimatter, because we don't see the aftermath of its inevitable destruction upon meeting regular matter. The universe is filled with constantly-interacting stuff. High-energy particles zipping across light-years.
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- Fountains of material escaping from galaxies and new junk drifting in. Stars colliding. In our universe, stuff mixes with stuff all the time. If some decent proportion of that was antimatter, the universe ought to be a lot more energetic than it is.
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- Where did the antimatter go? One possibility is that our universe was simply born this way, with an abundance of matter and a severe lack of antimatter.
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- Perhaps something in the early universe caused an imbalance between matter and antimatter.
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- And then an imbalance. A strange process that produced more matter than antimatter. Most of the pairs would be annihilated, but a few normal particles would remain. It wouldn't have to be much: Just one particle in a billion would be enough to lay the foundations for all the stars and galaxies that we see today.
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- It would indeed have to be a very peculiar set of conditions to cause such an imbalance. Our universe is governed by rules of how particles and forces should interact and behave. -
- But sometimes rules need to be broken, as in the case of the early universe. After all, it's those same rules that say that the divergence between matter and antimatter ought not to be in the first place.
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- Whatever interaction, whatever process, led to matter's ultimate victory had to be strange indeed. It had to start with producing not just an excess quantity of regular matter, but also an excess quantity of charge to counterbalance it. Otherwise, because total charges must stay the same throughout a process, that matter-loving route would've been perfectly balanced by a twin antimatter-loving road.
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- This process had to happen during a sharp boundary, when the infant universe was transforming rapidly from one state to another. It's only there that the physics would permit such a rule-breaking violation to take place; otherwise a universe in equilibrium would just end up balancing all interactions out anyway.
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- Is there anything in all of known physics that could make the antimatter go away? There are some hints and suggestions buried in rare particle interactions involving the weak nuclear force.
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- The origins of the asymmetry between matter and antimatter is an outstanding problem in physics. A problem that pushes the boundaries of current knowledge and pushes our understanding of the universe into some of its earliest moments.
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- An innovative laser experiment at the CERN lab in Switzerland has brought physicists one step closer to understanding mysterious antimatter. Antimatter particles have the opposite charge of normal matter particles. When particles of matter and antimatter meet, they destroy each other. However, antimatter behaves similarly to ordinary matter.
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- An antihydrogen atom, consisting of an antiproton and a positron (the antimatter counterpart of an electron), is the antimatter version of a hydrogen atom. Researchers combined antiprotons with positrons to form antihydrogen atoms.
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- Then, the researchers trapped hundreds of antihydrogen atoms in a vacuum and used laser pulses to excite the atoms, prompting them to jump into a higher energy state. Prompting or measuring this change, known as the “Lyman-alpha transition“, is a method used frequently in astronomy to study dark energy, that unseen, abundant force that makes up about 68 percent of the total energy of the universe.
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- When the antihydrogen atoms drop back down to a lower energy state, they release photons. The researchers measured these photons, which revealed that the antihydrogen emissions were the same as those one would expect from a normal hydrogen atom.
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- One of the biggest mysteries in physics is why there's matter in the universe at all. Physicists at the world's largest atom smasher, the “Large Hadron Collider‘, might be closer to an answer: They found that particles in the same family as the protons and neutrons that make up familiar objects behave in a slightly different way from their antimatter counterparts.
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- While matter and antimatter have all of the same properties, antimatter particles carry charges that are the opposite of those in matter. In a block of iron the protons are positively charged and the electrons are negatively charged.
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- A block of antimatter iron would have negatively charged antiprotons and positively charged antielectrons (known as positrons). If matter and antimatter come in contact, they annihilate each other and turn into photons (or occasionally, a few lightweight particles such as neutrinos).
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- Other than that, a piece of matter and antimatter should behave in the same way, and even look the same, a phenomenon called charge-parity (CP) symmetry.
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- Besides the identical behavior, CP symmetry also implies that the amount of matter and antimatter that was formed at the Big Bang, some 13.7 billion years ago, should have been equal. Clearly it was not, because if that were the case, then all the matter and antimatter in the universe would have been annihilated at the start, and even humans wouldn't be here.
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- But if there were a violation to this symmetry, meaning some bit of antimatter were to behave in a way that was different from its matter counterpart, perhaps that difference could explain why matter exists today.
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- To look for this violation, physicists at the Large Hadron Collider, a 17-mille-long (27 kilometers) ring beneath Switzerland and France, observed a particle called a lambda-b baryon.
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- Baryons include the class of particles that make up ordinary matter; protons and neutrons are baryons. Baryons are made of quarks, and antimatter baryons are made of antiquarks. Both quarks and antiquarks come in six "flavors": up, down, top, bottom (or beauty), strange and charm, as scientists call the different varieties.
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- A lambda-b is made of one up, one down and one bottom quark. A proton is made of two up and one down, while a neutron consists of two down and one up quark.
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- If the lambda and its antimatter sibling show CP symmetry, then they would be expected to decay in the same way. Instead, the team found that the lambda-b and antilambda-b particles decayed differently.
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- Lambdas decay in two ways: into a proton and two charged particles called pi mesons (or pions), or into a proton and two K mesons (or kaons). When particles decay, they throw off their daughter particles at a certain set of angles. The matter and antimatter lambdas did that, but the angles were different.
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- This is not the first time matter and antimatter have behaved differently. In the 1960s, scientists studied kaons themselves, which also decayed in a way that was different from their antimatter counterparts. B mesons, which consist of a bottom quark and an up, down, strange or charm quark, have also shown similar "violating" behavior.
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- Mesons, though, are not quite like baryons. Mesons are pairs of quarks and antiquarks. Baryons are made of ordinary quarks only, and antibaryons are made of antiquarks only. Discrepancies between baryon and antibaryon decays had never been observed before.
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- While tantalizing, the results were not quite solid enough to count as a discovery. For physicists, the measure of statistical significance, which is a way of checking whether one's data could happen by chance, is 5 sigma.
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- Sigma refers to standard deviations, and a 5 means that there is only a 1 in 3.5 million chance that the results would occur by chance. This experiment got to 3.3 sigma, good, but not quite there yet. That is, 3.3 sigma means that there's about a 1 in 4,200 chance that the observation would have occurred randomly, or about a 99-percent confidence level.
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- Antimatter is about to go on its first road trip. Physicists are getting ready to pack up a cloud of billions of antiprotons for the journey of a "few hundred meters" between the physics lab CERN's antimatter factory and the site of an experiment designed to figure out the shapes of bulky, radioactive atoms.
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- Antiprotons are rare but hugely important particles. Every matter particle has an antimatter twin with exactly reversed physical properties. And antiprotons are the oppsite versions of protons, the positively charged particles at the center of atoms. When they collide with protons, they annihilate each other.
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- In nature, antimatter particles are pretty rare. Positrons do occur in lightning bolts and occasionally show up in outer space, but they tend to annihilate one another long before they have a chance to accumulate.
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- So physicists at the CERN (European Organization for Nuclear Research) physics laboratory near Geneva generate them, Nature reported, by "slamming a proton beam into a metal target, then dramatically slowing the emerging antiparticles so they can be used in experiments.
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- Researchers don't know exactly what the nuclei of big, radioactive atoms look like. A heavy isotope might contain dozens of protons and neutrons, and physicists have long known exactly how many of each there are. But they generally don't know how those particles are arranged. Are the protons clustered in the center, surrounded by a shell of neutrons? Do the neutrons orbit in a surrounding halo?
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- For a project called the antiProton Unstable Matter Annihilation (or PUMA), Nature reported, researchers plan to fire antiprotons at atomic nuclei and, by studying the annihilations, figure out how often those antiprotons collide with neutrons and how often they collide with protons.
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- That will tell them a great deal about where each kind of particle lives in the nucleus. The process happens so fast that they expect to be able to study even the most short-lived nuclei, extremely heavy elements that exist only in laboratories for brief moments before decaying.
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- But to pull off the experiment, the researchers need to bring the antiprotons to the nuclei. To that end, they intend to magnetically trap large clouds of them, enough to last for weeks on end, in vacuum chambers, load those traps onto vans and drive them the short distance to the experiment site.
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- It's a short journey, but a first for the exotic particles
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February 10, 2021 3039
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