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Scientific American
6 days ago
- Science
- Scientific American
Mysterious Antimatter Physics Discovered at the Large Hadron Collider
Matter and antimatter are like mirror opposites: they are the same in every respect except for their electric charge. Well, almost the same—very occasionally, matter and antimatter behave differently from each other, and when they do, physicists get very excited. Now scientists at the world's largest particle collider have observed a new class of antimatter particles breaking down at a different rate than their matter counterparts. The discovery is a significant step in physicists' quest to solve one of the biggest mysteries in the universe: why there is something rather than nothing. The world around us is made of matter—the stars, planets, people and things that populate our cosmos are composed of atoms that contain only matter, and no antimatter. But it didn't have to be this way. Our best theories suggest that when the universe was born it had equal amounts of matter and antimatter, and when the two made contact, they annihilated one another. For some reason, a small excess of matter survived and went on to create the physical world. Why? No one knows. So physicists have been on the hunt for any sign of difference between matter and antimatter, known in the field as a violation of 'charge conjugation–parity symmetry,' or CP violation, that could explain why some matter escaped destruction in the early universe. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Today physicists at the Large Hadron Collider (LHC)'s LHCb experiment published a paper in the journal Nature announcing that they've measured CP violation for the first time in baryons —the class of particles that includes the protons and neutrons inside atoms. Baryons are all built from triplets of even smaller particles called quarks. Previous experiments dating back to 1964 had seen CP violation in meson particles, which unlike baryons are made of a quark-antiquark pair. In the new experiment, scientists observed that baryons made of an up quark, a down quark and one of their more exotic cousins called a beauty quark decay more often than baryons made of the antimatter versions of those same three quarks. 'This is a milestone in the search for CP violation,' says Xueting Yang of Peking University, a member of the LHCb team that analyzed the data behind the measurement. 'Since baryons are the building blocks of the everyday things around us, the first observation of CP violation in baryons opens a new window for us to search for hints of new physics.' The LHCb experiment is the only machine in the world that can summon sufficient energies to make baryons containing beauty quarks. It does this by accelerating protons to nearly the speed of light, then smashing them together in about 200 million collisions every second. As the protons dissolve, the energy of the crash springs new particles into being. 'It is an amazing measurement,' says theoretical physicist Edward Witten of the Institute for Advanced Study, who was not involved in the experiment. "Baryons containing b [beauty] quarks are relatively hard to produce, and CP violation is very delicate and hard to study.' The 69-foot-long, 6,000-ton LHCb experiment can track all the particles created during the collisions and the many different ways they can break down into smaller particles. 'The detector is like a gigantic four-dimensional camera that is able to record the passage of all the particles through it,' says LHCb spokesperson and study co-author Vincenzo Vagnoni of the Italian National Institute of Nuclear Physics (INFN). 'With all this information, we can reconstruct precisely what happened in the initial collision and everything that came out and then decayed.' The matter-antimatter difference scientists observed in this case is relatively small, and it fits within predictions of the Standard Model of particle physics—the reigning theory of the subatomic realm. This puny amount of CP violation, however, cannot account for the profound asymmetry between matter and antimatter we see throughout space. 'The measurement itself is a great achievement, but the result, to me, is not surprising,' says Jessica Turner, a theoretical physicist at Durham University in England, who was not involved in the research. 'The observed CP violation seems to be in line with what has been measured before in the quark sector, and we know that is not enough to produce the observed baryon asymmetry.' To understand how matter got the upper hand in the early universe, physicists must find new ways that matter and antimatter diverge, most likely via particles that have yet to be seen. 'There should be a new class of particles that were present in the early universe, which exhibit a much larger amount of this behavior,' Vagnoni says. 'We are trying to find little discrepancies between what we observe and what is predicted by the Standard Model. If we find a discrepancy, then we can pinpoint what is wrong.' The researchers hope to discover more cracks in the Standard Model as the experiment keeps running. Eventually LHCb should collect about 30 times more data than was used for this analysis, which will allow physicists to search for CP violation in particle decays that are even rarer than the one observed here. So stay tuned for an answer to why anything exists at all.
Yahoo
6 days ago
- Science
- Yahoo
Breaking: Major Antimatter Discovery May Help Solve Mystery of Existence
We're now a step closer to understanding how the Universe avoided an antimatter apocalypse. CERN scientists have discovered tantalizing clues of a fundamental difference in the way physics handles matter and antimatter. Experiments at the Large Hadron Collider (LHC) have verified an asymmetry between matter and antimatter forms of a particle called a baryon. Known as a charge-parity (CP) violation, the effect has only previously been detected in another class of particles, called mesons. But experimental evidence in baryons, which make up the bulk of the Universe's matter, is something physicists have been long hunting for. "It shows that the subtle differences between matter and antimatter exist in a wider range of particles, indicating that the fundamental laws of physics treat baryons and antibaryons differently," Xueting Yang, CERN physicist and first author of the study, told ScienceAlert. Related: "The matter-antimatter asymmetry in the Universe requires CP violation in baryons, such that the discovery is a key step forward in testing how complete our current theory is, and in exploring whether new physics might be hiding in places we haven't looked closely enough before." To make the discovery, the team analyzed around 80,000 particle decay events in data gathered at the LHC between 2011 and 2018. Focussing on particles called lambda-beauty (Λb) baryons and their antimatter counterparts, the researchers searched for any hint of a difference in the way they decayed. If CP was symmetrical, both the matter and antimatter forms of the particle should decay into the same – if mirrored – products. However, the team found a 2.5 percent relative difference between the matter and antimatter baryon decays. "This may sound small, but the results are statistically significant enough," says Yang. "It shows that Λb and anti-Λb do not decay in exactly the same way, providing an observation of CP violation in baryons." Importantly, the find reached a statistical significance of 5.2 sigma. That means the chance that the observed effect comes from random fluctuations is just 1 in 10 million. The discovery has major implications for physics – including questions as fundamental as "why are we here?" Despite its eerie name, antimatter should be mundane. Its main difference from regular matter is having the opposite charge. But that seemingly minor detail means that if ever the two shall meet, they will annihilate each other in a burst of energy. In theory, the Big Bang shouldn't have favored one over the other, creating both matter and antimatter in equal amounts. And if that was the case, the entire contents of the Universe should have blasted itself into oblivion in the first few moments of existence, leaving the cosmos a profoundly empty place. Since that obviously didn't happen, it seems some unknown factor intervened so that slightly more matter was created than antimatter. Everything that exists today – from galaxies to grains of sand – are made of that tiny fraction that survived early annihilation. In a simple Universe, inverting both the charge and spatial coordinates of a particle – basically, whether it's matter or antimatter – shouldn't change how it behaves under the laws of physics. This concept is known as CP symmetry, and while it was once considered as immutable as the conservation of energy, some level of CP violation has been predicted by the Standard Model of physics since the mid-20th century. "CP violation is one of the essential ingredients needed to explain the matter-antimatter asymmetry. However, physicists estimate that the amount of CP violation in nature must be much larger than what's predicted by the Standard Model of particle physics," said Yang. "This strongly suggests that new physics beyond the Standard Model must exist, providing additional sources of CP violation. Studying CP violation in different systems, including baryons, provides an important test of the Standard Model and could offer hints of new physics beyond it." For instance, there was a chance that antimatter could be repelled by gravity rather than attracted – meaning it would fall upwards. To test the idea, CERN physicists previously conducted 'drop' tests and found that antimatter does fall down, like regular matter. In that respect, there was no CP violation. But the new detection reveals that something does cause matter and antimatter to decay in different ways. This long-awaited confirmation is exciting – but it's still not enough. "The CP violation observed in baryon decays – like in the new LHCb result – is consistent with Standard Model predictions, so it does not provide enough CP violation to solve the matter-antimatter puzzle on its own," says Yang. "But it opens a new window into how CP violation behaves in the baryon sector, which was largely unexplored." "Physicists are looking for new sources of CP violation, beyond what the Standard Model of particle physics predicts. Discovering such sources could lead to new physics." The research was published in the journal Nature. Related News The World's First Nuclear Explosion Created a Rare Form of Matter Sound of Earth's Flipping Magnetic Field Haunts Again From 780,000 Years Ago Extreme Conditions of Early Universe Recreated in Collider Experiment Solve the daily Crossword
Gizmodo
6 days ago
- Science
- Gizmodo
CERN Physicists Find Key Piece of the Matter-Antimatter Puzzle
All matter in our universe has an evil twin: antimatter. Cosmological models suggest that the Big Bang should have created equal amounts of matter and antimatter that cancel each other out. But for reasons physicists still aren't completely sure about, that didn't happen. As a result, our universe today hosts slightly more matter than antimatter—our very existence being clear, physical proof. Now, we might be one step closer to explaining why there's an imbalance between matter and antimatter, an unsolved mystery in physics formally known as the charge-parity (CP) violation, or CP asymmetry. In a paper published today in Nature, researchers at the Large Hadron Collider beauty (LHCb) Collaboration at CERN, Switzerland, report the first experimental verification of the CP violation in the decay of baryons—fundamental particles that make up most matter in the observable universe. The results were announced earlier this year at the Rencontres de Moriond conference. 'Until recently, CP violation had only been clearly observed in mesons [or] particles made of a quark and an antiquark,' explained Xueting Yang, LHC physicist and study lead author, in an email to Gizmodo. 'This result shows that baryons—which are made of three quarks like protons and neutrons—can also violate CP symmetry.' While a significant first step, the new finding still falls short of observing baryon asymmetry, which refers to that paradox of there being more matter than antimatter in the universe today. What Yang's team observed specifically was an instance of CP violation in baryon decay, or the slight difference in behavior between a baryon and its antimatter counterpart as the particle breaks down into smaller particles. 'Well, it's a small part of a much bigger puzzle—but you know, every part matters,' Sean Carroll, a theoretical physicist at Johns Hopkins University who wasn't involved in the new work, told Gizmodo in a video call. 'It's intrinsically interesting when you find a phenomenon that has never been observed before, but…maybe it will teach us something about why there are more baryons than anti-baryons in the universe.' For the study, Yang's team took around nine years of data from observing the decay of almost one trillion beauty-lambda (Λb) baryons, the heavyweight cousin-particle of protons and neutrons. In about a mere trillionth of a second, beauty-lambda baryons and their antimatter counterparts break down into smaller parts, requiring the technical prowess of something as big as the LHC to capture. From the data, the researchers sifted through the different interactions to pick out the ones of interest to them, namely the decay behavior of beauty-lambda baryons and their antimatter counterparts. 'If CP symmetry were true, you'd have exactly the same rate for these interactions,' Carroll explained. 'But it is violated, so you get slightly different rates.' That rate was about 2.5%, a small but statistically significant difference—at least, enough for the team to start brainstorming ideas for how they'd like to build on this result. 'Studying how baryons are formed, how they interact, and how they decay is essential to understanding the fundamental forces of nature,' Yang said. 'This observation marks just the beginning. To answer why [the universe contains] more matter than antimatter, we need more sources of CP violation than the current [Standard Model of particle physics].' The Standard Model—the theory that describes particle behavior with chilling accuracy—is both the magnum opus and the punching bag of particle physics. It explains everything so ludicrously well, while missing some huge chunks of known physical phenomena, such as gravity or dark matter, to name a few. And so, when the LHC came along, physicists expected it to achieve great things—which it did, and continues to do. But as with all great physics discoveries, it's a holy grail that'll take some more time to realize. 'We were, to be honest, a little bit disappointed that the Large Hadron Collider hasn't found any physics beyond the Standard Model,' Carroll said. 'But I think it's super important to keep looking. The LHC is a beautiful machine that has done amazing work—and yet, it hasn't quite taken us to the promised land. So it's another reminder that there are really big questions out there, and one way or the other we, as the human race, should be doing our best to answer them.'
The Hindu
6 days ago
- Science
- The Hindu
CERN collider reveals major clue to universe's bias against antimatter
The universe is made mostly of matter, not antimatter, but scientists believe that after the Big Bang, both must have existed in equal amounts. One of the big mysteries in physics is understanding why matter dominates the universe today and what happened to all the antimatter. A key clue comes from something called CP violation — a difference in the behaviour of matter and antimatter. While CP violation has been observed in certain types of particles called mesons, it has never been reported in baryons, which are the particles (like protons and neutrons) that make up most of the matter around us. Based on new data, the LHCb collaboration in Europe has now reported the first-ever observation of CP violation in baryon decays, specifically in a particle called the Λb⁰ baryon (pronounced 'lambda bee-zero baryon'). Their findings were published in Nature on July 16. 'For the first time, we have clear evidence of CP violation in baryons,' Xueting Yang, the corresponding author of the study, a member of the LHCb team, and a PhD student at Peking University in Beijing, told The Hindu. 'The matter-antimatter asymmetry in the universe requires CP violation in baryons, such that the discovery is a key step forward.' Looking for the signal In CP, 'C' stands for charge conjugation, which means the action of swapping a particle with its antiparticle. 'P' stands for parity, which is the action of flipping the spatial coordinates, like looking in a mirror. CP symmetry stipulates that if you swap particles for antiparticles and look in a mirror, the laws of physics should be the same. CP violation thus means this symmetry is broken and that the laws of physics are slightly different for matter and antimatter. This is important because CP violation is a necessary ingredient to explain why the universe is made mostly of matter. The Λb⁰ baryon is made up of three smaller particles: an up quark, a down quark, and a bottom quark. The antiparticle of the Λb⁰ baryon is called the Λb⁰-bar. The newly reported result focuses on a specific decay of the Λb⁰ baryon: into a proton, a negatively charged kaon, a positively charged pion, and a negatively charged pion. This is denoted: Λb⁰ → p K⁻ π⁺ π⁻. The collaboration also studied the same decay for the antiparticle, Λb⁰-bar, but with all charges reversed. The experiment used data from the Large Hadron Collider at CERN, specifically from the LHCb detector on the machine. The LHCb team collected data between 2011 and 2018, corresponding to a very large number of collisions between beams of protons accelerated to nearly the speed of light. In these collisions, Λb⁰ and Λb⁰-bar baryons are produced and then rapidly decay. The LHCb researchers looked for events where the decay products matched p K⁻ π⁺ π⁻. To reduce background noise — in the form of random combinations of particles that mimic the signal — they used machine learning to distinguish real decays from fake ones. They also used particle identification tools on computers that could tell protons, kaons, and pions apart. The main quantity they measured was the CP asymmetry. It compares the number of Λb⁰ decays to the number of Λb⁰-bar decays: if there is no CP violation, the value of CP asymmetry should be zero. In practice, they measured the yield asymmetry, which is the difference in the number of decays observed for Λb⁰ and Λb⁰-bar. There are some effects that can mimic CP violation. For example, the proton-proton collisions may produce more Λb⁰ than Λb⁰-bar to begin with. For another, the LHCb detector on the Large Hadron Collider might have been slightly better at detecting one charge over another. To correct for these possible biases, the researchers used a control channel — a similar decay where no CP violation is expected. Here, an Λb⁰ baryon decays to a positively charged Λc baryon, and a negatively charged pion: Λb⁰ → Λc⁺ π⁻. Any asymmetry seen in this control channel was considered a nuisance and subtracted from the main measurement. Mesons, then baryons The researchers used statistical methods to determine how many real Λb⁰ baryon and Λb⁰-bar antiparticle decays the detector recorded. Then they checked their results for consistency across different data-taking periods, detector settings, and analysis methods. Thus, the team found a significant difference in the decay rates: about 2.45%. According to the paper, this result is 5.2 standard deviations away from zero, which is well above the statistical threshold required for physicists to claim a discovery in particle physics. 'It was expected that the LHCb group had enough data. They are reporting it now,' theoretical physicist, University of Hawai'i affiliate graduate faculty, and Chennai's Institute of Mathematical Sciences retired professor Rahul Sinha told The Hindu. This is the first time CP violation has been observed in baryon decays. Previously, physicists had reported CP violation only in mesons, particles which are made of a quark and an antiquark, and not baryons, which are made of three quarks. The result matches the predictions of the Standard Model, the main theory of particle physics, which says CP violation comes from the way quarks mix and decay. However, the amount of CP violation in the Standard Model is not enough to explain the matter-antimatter imbalance in the universe. 'The observation of CP violation in baryons still doesn't settle the mystery of the universe's missing antimatter,' Prof. Sinha said. 'The Standard Model predicts a rate of disappearance of antimatter that doesn't match what we're seeing in the universe.' The new announcement opens new ways to search for 'new physics', the name for hitherto unknown effects or particles beyond what the Model predicts, and which physicists believe will reveal the 'complete' theory of subatomic particles. Mind the phase According to Prof. Sinha, the new paper reports observing CP violation in baryons but doesn't say whether the amount of violation is higher or lower than that predicted by the Standard Model. Ascertaining that requires researchers to determine the complex phase. In the context of CP violation, the complex phase is a combination of variables present in the Cabibbo-Kobayashi-Maskawa (CKM) matrix, a mathematical tool physicists use to understand how the quarks in a baryon interact with each other. If the complex phase has a non-zero value, it means the laws of physics are not identical for matter and antimatter, leading to observable differences in their behaviour. The Standard Model predicts specific values for the amount of CP violation, which are determined by the magnitude and phase of the variables in the CKM matrix. By measuring the phase associated with CP violation in baryon decays, physicists can compare the observed amount of violation to the Standard Model's predictions. In their paper, the LHCb researchers have reported that the complex phase information proved too difficult to extract from the data collected by the detector. 'Until we measure the phase, we can't say if the rate of antimatter's disappearance is too high or too low compared to the Model's prediction,' Prof. Sinha said. The same technique to measure the phase for mesons can't be used for baryons. To this end, Prof. Sinha added that in 2022, he and his peers Shibasis Roy and N.G. Deshpande described a new way to measure the complex phase for baryons. It was published in Physical Review Letters. Observing CP violation in baryons is important because the visible matter around us today is made of baryons. Some baryons like protons and neutrons are very stable and don't decay for a long time. Others, like Λb⁰, decay in around 1.5 picoseconds. The point is what is true for one baryon should be true for all baryons. 'To definitively resolve the asymmetry problem, both experimental and theoretical progress are needed,' Dr. Yang said. 'Experimentally, more precise and comprehensive measurements across different particle systems are required to build a coherent and consistent picture of CP violation. Theoretically, improved calculations and refined models are essential to connect these experimental observations with the fundamental physics driving the matter-antimatter asymmetry.' The Sakharov conditions How did matter gain an overwhelming upper hand over antimatter in the universe? CP violation in baryons is an important piece of this puzzle — but also only one piece. In 1967, the Soviet physicist and later political dissident Andrei Sakharov said three conditions will have to be met for the universe to be made predominantly of only matter. They are: (i) Baryon number violation: physical processes must exist that create an imbalance between the number of baryons and the number of antibaryons. (ii) CP violation in baryons (iii) Departure from thermal equilibrium: to prevent processes from balancing baryon and antibaryon production, interactions must occur out of equilibrium. The observation of CP violation in baryon decays provides a 'source' that adds to CP violation among mesons. The complex phase of the mesons' violation has been measured whereas that of the baryons is pending. Once the latter is known physicists will be able to compare it to that predicted by the Standard Model. If they match, it will mean the Standard Model is right — but at the same time leave a gap between the predicted matter-antimatter asymmetry and that observed in the universe. If the values don't match, it could be a sign of 'new physics', which physicists will have to explain using new theories and experiments. Overall, the newly reported observation is a milestone showing that the laws of physics treat matter and antimatter differently not just in mesons but also in baryons — the building blocks of the visible universe.
New York Times
6 days ago
- Science
- New York Times
New Clue to How Matter Outlasted Antimatter at the Big Bang Is Found
Understanding why matter and antimatter behave differently is key to understanding why there is a universe at all. Now physicists have discovered the latest example of a subtle difference between the stuff that makes up galaxies, stars, planets and us, and its evil-twin opposite. Particles of antimatter, like anti-electrons and anti-protons, possess the same mass but opposite electric charge as the usual electrons and protons. In a discovery published on Wednesday in the journal Nature, an international collaboration of scientists working at the CERN particle physics laboratory outside Geneva described an imbalance among particles that are cousins to the protons and neutrons that make up everyday objects. That makes the new observations 'very important for us to further understand bigger questions like the matter-antimatter asymmetries in the universe,' said Xueting Yang, a graduate student at Peking University who led the analysis. The Big Bang that created the universe should have produced equal amounts of matter and antimatter. When a particle of matter bumps into its antimatter counterpart, the two particles annihilate. Thus, all of the matter should have annihilated all of the antimatter in a cataclysmic burst of radiation, leaving an empty universe for eternity. And yet, 13.8 billion years later, you — made of matter, not antimatter — are reading this news on a device (or in a newspaper), which is also made of matter. Somehow, in the instant after the Big Bang, for each billion or so pairs of matter and antimatter, an extra particle of matter persisted. This slight tipping of the laws of physics toward matter is known as charge-parity, or CP, violation. Want all of The Times? Subscribe.
