Latest news with #nuclearPhysics
Yahoo
18-05-2025
- Science
- Yahoo
When quarks misbehave, symmetry breaks down and changes the rules of physics
For decades, physicists have relied on the principle of symmetry to simplify and understand the complex behaviors of subatomic particles. Symmetry in physics basically means that some rules of nature stay the same even if you change things around. This idea has served as one of the foundations of nuclear physics, helping scientists build models of how matter behaves at the smallest scales. However, a team of researchers led by Mississippi State University (MSU) professor Dipangkar Dutta has found cracks in this foundation. Results from the new study suggest that symmetry, once thought to be a constant, can break down under certain conditions. This finding can reshape our understanding of the strong nuclear force, a force that governs everything from the behavior of particles inside atomic nuclei to the formation of matter across the universe. To test whether certain symmetries in physics really hold up, the researchers conducted an interesting experiment at the Thomas Jefferson National Accelerator Facility in Virginia. They used a high-energy beam of electrons and fired it at protons and deuterons (a hydrogen isotope). This allowed them to observe how quarks, the tiny building blocks inside protons and neutrons (inside the deuteron), behave when struck. The technique the scientists used is called semi-inclusive deep-inelastic scattering (or SIDIS). In simple terms, it's a way to knock loose a quark and then study what kind of particle it turns into afterward. The researchers focused on how often quarks turned into positively or negatively charged pions (a type of subatomic particle), depending on whether they came from protons or deuterons. This process, called fragmentation, gives physicists clues about how quarks behave when they're released from the tight grip of the strong nuclear force. Now here's where the symmetry jumps in. According to a principle called charge symmetry, an up quark in a proton should behave the same way as a down quark in a neutron, once you flip the charge. That's been a helpful assumption for decades because it simplifies calculations. However, until now, this idea hadn't been tested carefully in the context of fragmentation. When the researchers compared the behavior of these quarks, they found small but clear deviations, especially at lower energy levels. These deviations caused the symmetry between the behaviors of up and down quarks to break down, suggesting that charge symmetry doesn't always hold, at least not during fragmentation. The possibility of symmetry failing under certain conditions can lead to many changes in nuclear physics. For instance, by understanding where and why symmetries break down, scientists can reevaluate theoretical models and more accurately explain particle behavior and interactions. "The assumptions we make based on symmetries greatly simplify our analyses. But they haven't been tested quantitatively with precision until now. Our new results show when the symmetries are valid and when they need certain corrections," said Dutta, in a statement released by MSU. Hopefully, future studies will also shed light on other scenarios where symmetries break and lead to an improved understanding of nuclear physics. The study is published in the journal Physics Letters B.
The Independent
13-05-2025
- Science
- The Independent
Scientists accidentally achieve alchemy by turning lead into gold
Medieval alchemists dreamed of transmuting lead into gold. Today, we know that lead and gold are different elements, and no amount of chemistry can turn one into the other. But our modern knowledge tells us the basic difference between an atom of lead and an atom of gold: the lead atom contains exactly three more protons. So can we create a gold atom by simply pulling three protons out of a lead atom? As it turns out, we can. But it's not easy. While smashing lead atoms into each other at extremely high speeds in an effort to mimic the state of the universe just after the Big Bang, physicists working on the ALICE experiment at the Large Hadron Collider in Switzerland incidentally produced small amounts of gold. Extremely small amounts, in fact: a total of some 29 trillionths of a gram. How to steal a proton Protons are found in the nucleus of an atom. How can they be pulled out? Well, protons have an electric charge, which means an electric field can pull or push them around. Placing an atomic nucleus in an electric field could do it. However, nuclei are held together by a very strong force with a very short range, imaginatively known as the strong nuclear force. This means an extremely powerful electric field is required to pull out protons – about a million times stronger than the electric fields that create lightning bolts in the atmosphere. The way the scientists created this field was to fire beams of lead nuclei at each other at incredibly high speeds – almost the speed of light. The magic of a near-miss When the lead nuclei have a head-on collision, the strong nuclear force comes into play and they end up getting completely destroyed. But more commonly the nuclei have a near miss, and only affect each other via the electromagnetic force. The strength of an electric field drops off very quickly as you move away from an object with an electric charge (such as a proton). But at very short distances, even a tiny charge can create a very strong field. So when one lead nucleus just grazes past another, the electric field between them is huge. The rapidly changing field between the nuclei makes them vibrate and occasionally spit out some protons. If one of them spits out exactly three protons, the lead nucleus has turned into gold. Counting protons So if you have turned a lead atom into gold, how do you know? In the ALICE experiment, they use special detectors called zero-degree calorimeters to count the protons stripped out of the lead nuclei. They can't observe the gold nuclei themselves, so they only know about them indirectly. The ALICE scientists calculate that, while they are colliding beams of lead nuclei, they produce about 89,000 gold nuclei per second. They also observed the production of other elements: thallium, which is what you get when you take one proton from lead, as well as mercury (two protons). An alchemical nuisance Once a lead nucleus has transformed by losing protons, it is no longer on the perfect orbit that keeps it circulating inside the vacuum beam pipe of the Large Hadron Collider. In a matter of microseconds it will collide with the walls. This effect makes the beam less intense over time. So for scientists, the production of gold at the collider is in fact more of a nuisance than a blessing. However, understanding this accidental alchemy is essential for making sense of experiments – and for designing the even bigger experiments of the future. Ulrik Egede is a Professor of Physics at Monash University
