Tag Archives: antiproton

The proton and antiproton are incredibly similar — indicating that perhaps, our universe shouldn’t exist

Matter and antimatter violently annihilate each other. If they’re absolutely symmetrical, then maybe — just maybe — the universe shouldn’t exist.

We see matter around us every day. Unlike matter, antimatter is much more elusive. Researchers are now playing the world’s most complex ‘spot the difference’ game with matter and antimatter. (Depicted here, two nitrogen gasses Image credits: Greenhorn1)

Just like there is matter in the universe (pretty much everything that exists), there is also antimatter. Basically, all particles have a corresponding anti-particle — with the same mass, but opposite electric charge, and other differences in quantum parameters. The proton, for instance, has a positive charge, while the antiproton has a negative charge. When a proton and an antiproton collide, they annihilate each other in a violent outburst.

Researchers at CERN in Switzerland have made the most precise measurement ever of the magnetic moment of an antiproton. The magnetic moment determines how a particle reacts to an external magnetic force. They found that the two moments are absolutely identical but with an opposite sign. This is really problematic.

“All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” says Christian Smorra, a physicist at CERN’s Baryon–Antibaryon Symmetry Experiment (BASE) collaboration. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.”

“It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator,” added Smorra, who is first-author of the study.

Since matter and antimatter annihilate themselves and the universe exists and hasn’t annihilated itself (yet), there’s good reason to believe that there is much more matter than antimatter in the universe. But why? There must be some discrepancy in the parameters of these particles that allows matter to dominate, but researchers haven’t found it yet. It’s like playing spot the difference at a particle level.

The work of Smorra and his colleagues is an elegant design, a two-particle measurement method developed in Stefan Ulmer’s RIKEN laboratory. Researchers simultaneously capture and measure two separate antiprotons one at a high temperature (350 degrees Kelvin / 76 C / 170 F) and the other at a very cold temperature (0.15 K / -273 C / -459 F), very close to absolute zero. The first particle is used for calibration, while the colder one is used to measure a parameter called the Larmor frequency, which governs how a particle precesses (rotates and spins) under a magnetic influence. Even doing this for protons was a breakthrough (published in Nature in 2014), but doing it for antiprotons is a whole new ball game.

The BASE experiment at the CERN antiproton decelerator in Geneva. Image credits: Stefan Sellner, Fundamental Symmetries Laboratory, RIKEN, Japan.

With this method, they managed to keep an antiproton captured for inside a special chamber about as big as a tall pint. Measurements were incredibly accurate, indicating a value for the antiproton magnetic moment of −2.7928473441 μNN is a constant called the nuclear magneton). Precise to nine significant digits, this measurement is 350 times more accurate than the previous measurement. It’s the equivalent of measuring the Earth’s circumference to a few centimeters.

Their results are identical to those obtained for the proton, aside from the minus sign.

“It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator, ” added first-author of the study Christian Smorra.

However, for all these elegant improvements, they still couldn’t answer the fundamental question of why our universe exists — why matter and antimatter are so unevenly distributed through the universe, allowing us to exist. Still, Smorra says that they can still improve significantly.

“By upgrading the experiment with several new technical innovations, we feel that some further improvement can still be made, and in the future, following the CERN upgrade expected to finish in 2021, we will be able to achieve an at least ten-fold improvement.”

In the meantime, nature continues to consist of matter and we still don’t know why there’s not much antimatter around. Researchers continue to try and solve this mystery which could unlock one of the keys to understanding the universe.

A new measurement by RHIC's STAR collaboration reveals that the force between antiprotons (p with bar above it) is attractive and strong--just like the force that holds ordinary protons together within the nuclei of atoms. Credit: Brookhaven National Laboratory

Matter and antimatter have the same properties, experiment suggests

All models of particle physics are based on the mundane assumption that matter and anti-matter behave indistinguishably, but we can’t be sure. Luckily, an experiment at Brookhaven National Lab seems to confirm this basic caveat of particle physics after it found the attractive forces between antiprotons are the same as those seen in regular matter.

The quest for antimatter

A new measurement by RHIC's STAR collaboration reveals that the force between antiprotons (p with bar above it) is attractive and strong--just like the force that holds ordinary protons together within the nuclei of atoms. Credit: Brookhaven National Laboratory

A new measurement by RHIC’s STAR collaboration reveals that the force between antiprotons (p with bar above it) is attractive and strong–just like the force that holds ordinary protons together within the nuclei of atoms. Credit: Brookhaven National Laboratory

For every type of matter particle we’ve found, there also exists a corresponding antimatter particle, or antiparticle. These should look and behave just like their corresponding matter particles, except with opposite charge. A proton is naturally positively charged, as thought in any basic chemistry or physics class. The antiproton, however, is negatively charged. When matter and anti-matter these annihilate each other, releasing energy in the process.

During the Big Bang, matter and antimatter were created in equal amounts, but that’s clearly not what we’re seeing today. In fact, it’s difficult if not impossible to detect antimatter outside of a laboratory setting. For that matter, we wouldn’t have existed in the first place if antimatter and matter were still in equal proportion, given their tendency to annihilate each other. There has to be an explanation, but at this point opinions are mixed.

Some physicists think that after the Big Bang, fractions of a second in, all matter and antimatter canceled each other out but in the process created radiation. Out of this radiation new matter-antimatter pairs were formed, which again annihilated each other creating new radiation and so on. When the universe expanded and cooled to below the temperature where particle-antiparticle pair production could happen, all the antimatter and matter that were in equal proportions annihilated with each other, leaving only radiation. Here’s the kick though. It may be that matter and antimatter weren’t created equal. There is a tiny, *tiny* chance that you only get matter when you try to create matter and antimatter or one particle of matter for every billion annihilation event.  As the universe evolved after the Big Bang, these very small symmetry violations may have resulted in the abundance of matter and the dearth of antimatter we see today.

Zhengqiao Zhang, a graduate student from the Shanghai Institute of Applied Physics, with STAR physicist Aihong Tang at the STAR detector of the Relativistic Heavy Ion Collider (RHIC). Credit: Brookhaven National Laboratory antimatter.

Zhengqiao Zhang, a graduate student from the Shanghai Institute of Applied Physics, with STAR physicist Aihong Tang at the STAR detector of the Relativistic Heavy Ion Collider (RHIC). Credit: Brookhaven National Laboratory antimatter.

We can’t don’t this for certain yet. “Although this puzzle has been known for decades and little clues have emerged, it remains one of the big challenges of science. Anything we learn about the nature of antimatter can potentially contribute to solving this puzzle,” says  Aihong Tang, a Brookhaven physicist.

Tang was involved with  Relativistic Heavy Ion Collider where he and colleagues smashed accelerated gold ions together at high energy and relativistic speeds. When the gold ions smashed instead of forming new gold particles, the collision created mostly forms of hydrogen and helium, but also exotic particles like  heavy quarks or their antimatter counterparts.

“We see lots of protons, the basic building blocks of conventional atoms, coming out, and we see almost equal numbers of antiprotons,” said Zhengqiao Zhang, a graduate student in Professor Yu-Gang Ma’s group from the Shanghai Institute of Applied Physics of the Chinese Academy of Sciences, who works under the guidance of Tang when at Brookhaven. “The antiprotons look just like familiar protons, but because they are antimatter, they have a negative charge instead of positive, so they curve the opposite way in the magnetic field of the detector.”

“By looking at those that strike near one another on the detector, we can measure correlations in certain properties that give us insight into the force between pairs of antiprotons, including its strength and the range over which it acts,” he added.

Ultimately, the researchers were able to investigate the effective and scattering range of two antiprotons. The effective range between two particles is a measure of how close they have to be to influence each other with their electric charge, while the scattering range is a measure of how much these particles deviate as they travel from source to destination. During this experiment the  the scattering length was around 7.41 femtometers and the effective range was 2.14 femtometer, which is roughly the same as the those of a proton pair. Whether matter or antimatter, it seems these types of interactions are virtually indistinguishable.

“This discovery isn’t a surprise,” said Kefeng Xin, a graduate student at Rice. “We’ve been studying the interaction between nucleons (particles that make up an atom’s nucleus) for decades, and we’ve always thought the forces between antimatter particles are the same as for matter. But this is the first time we’ve been able to quantify it.”

“There are many ways to test for matter/antimatter asymmetry, and there are more precise tests, but in addition to precision, it’s important to test it in qualitatively different ways. This experiment was a qualitatively new test,” said Richard Lednický, a STAR scientist from the Joint Institute for Nuclear Research, Dubna, and the Institute of Physics, Czech Academy of Sciences, Prague.

“The successful implementation of the technique used in this analysis opens an exciting possibility for exploring details of the strong interaction between other abundantly produced particle species,” he said, noting that RHIC and the Large Hadron Collider (LHC) are ideally suited for these measurements, which are difficult to assess by other means.

We’ve yet to solve the puzzle. Namely, we still don’t know why there’s so little antimatter left in the universe, but at least we now know that it’s not due to some difference in how the two types of matter interact.

New exotic particle behaviour found at CERN

The Large Hadron Collider at CERN has started doing some serious business. This time, an extremely rare particle containing equal parts of matter and antimatter popped up during experiments at the world’s largest and hottest particle accelerator.

CREDIT: CERN/Maximilien Brice, Rachel Barbier

 

The particle, named a B meson is made out of one quark (the building blocks of protons and neutrons) and one antiquark (the building blocks of antiprotons and antineutrons). What are antiprotons and antineutrons ? Well, they are just like their positive brothers… only they are negative. They have the exact same properties, only opposite in signs. For example, an antiproton has the exact same charge a proton has, but it is negative instead of positive.

All normal particles are thought to have antimatter analogues, and when matter and antimatter meets, they destroy each other. Scientists believe that at first, matter and antimatter were created equally, but if this is the case, then where is all the antimatter ? The most plausible solution would be that a huge quantity of matter and antimatter annihilated each other, and the remaining matter is what we see in our universe today.

The particle in case, the B meson, is thought to have been common right after the Big Bang, but it is believed that at the moment, it doesn’t occure naturally in nature. They aren’t stable, and after created, quickly start decaying; this process, a B meson decay has long been theoretized, but never seen before.

“Our experiment is set up to measure the decays of B mesons,” sayd Sheldon Stone, physicist at Syracuse University. “We discovered some new and interesting decay modes of B mesons, which hadn’t ever been seen before.”

Studying this type of behaviour can provide the answer to the ultimate question of antimatter – why do we see all this matter around us today, and no antimatter. Meanwhile, the search for the elusive Higgs boson is continued.

“When the universe was created in the Big Bang about 14 billion years ago, the number of particles and antiparticles was the same,” Stone said. “One of the major questions that we really don’t know the answer to is why are there particles around now and not antiparticles. By studying the differences we can learn maybe what the physics is behind that difference.”

LHC produces first results

Since the Large Hadron Collider went back in business, all sort of rumors have been circling the scientific circles (and not only). However, until these rumors are proven wrong or right, the first official paper on proton collisions from the Large Hadron Collider has been published in this week’s edition of Springer’s European Physical Journal C. .

lhc

Designed to reach the highest energy ever explored in particle accelerators, it features a circular tunnel with the circumference of 27 km. Since it’s been recommissioned, a total of 284 collisions have been recorded, all of which have been analyzed and interpreted. The researchers have been able to determine what is called ‘pseudorapidity density’ (the average number of charged particles that are emitted perpendicular to the beam direction. The goal of this was to compare the results with those obtained in the case of proton-antiproton collisions that took place in the same conditions.

The paper was published by ALICE (a Large Ion Collider Experiment that brings together authors from 113 institutions). As well as the actual results, the paper also explains how their detecting and analyzing system works. The results are not only consistent with earlier measurements, but they also fit the theoretical model produced by researchers.

Dr. Jürgen Schukraft from CERN and ALICE spokesperson said: “This important benchmark test illustrates the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase. LHC and its experiments have finally entered the phase of physics exploitation.”