Why in news?

Recently, European scientists observed, for the first time, that matter and antimatter versions of a subatomic particle called a baryon decay at different rates.

This difference in behavior could help explain why the universe is predominantly made of matter, offering a crucial clue to the long-standing antimatter mystery.

What’s in Today’s Article?

• Matter and Antimatter
• Why the Universe Has More Matter Than Antimatter
• First Observation of CP Violation in Baryons
• How Scientists Observed CP Violation in Baryon Decay
• Conclusion

Matter and Antimatter

• Matter is what makes up everything we see around us—people, planets, stars—composed of particles like protons, neutrons, and electrons.
• Antimatter is like matter’s mirror image: for every matter particle, there’s a corresponding antiparticle with the same mass but opposite charge.
• For example:
  • The antiparticle of an electron (negative charge) is a positron (positive charge).
  • The antiparticle of a proton is an antiproton, with negative charge.
• When a particle and its antiparticle meet, they annihilate, releasing energy.

Why the Universe Has More Matter Than Antimatter?

• The Big Bang should have produced equal amounts of matter and antimatter, but today, the universe is overwhelmingly made of matter.
• This imbalance remains one of science's greatest mysteries. A key to understanding it lies in a phenomenon called CP violation—where the universe treats matter and antimatter differently.
  • CP stands for charge conjugation (swapping particles with their opposites) and parity (mirror flipping left and right).
    • Charge conjugation involves replacing every particle in a system with its antiparticle. 
    • For example, an electron would be replaced with a positron, a proton with an antiproton, and so on. 
  • CP symmetry implies that physical laws should remain the same when a particle is replaced by its antiparticle and its spatial coordinates are inverted.
• If both symmetries held perfectly, matter and antimatter would behave identically.
• However, experiments have shown that CP symmetry can be broken.
• This violation is essential to explaining how the early universe ended up with more matter than antimatter.

First Observation of CP Violation in Baryons

• Until now, CP violation had only been observed in mesons—particles made of a quark and an antiquark.
• For the first time, scientists have detected CP violation in baryons, which are three-quark particles like protons and neutrons that make up most visible matter.
• The breakthrough came from studying the decay of the Λb⁰ baryon.
  • The Λb⁰ baryon is a subatomic particle known as a "bottom lambda baryon." 
  • It's a type of baryon, meaning it's composed of three quarks, and it contains one up quark, one down quark, and one bottom quark. 
  • The "0" in Λb⁰ indicates that it is electrically neutral. 
  • This particle is also sometimes referred to as an "open-beauty baryon". 
• Researchers found that these two decayed differently into a proton, a kaon, and two pions, providing the first evidence of CP violation in baryon decays and offering new insight into the matter-antimatter imbalance in the universe.

How Scientists Observed CP Violation in Baryon Decay?

• The discovery was made at Europe’s Large Hadron Collider (LHC) using the LHCb detector, which recorded data from billions of proton-proton collisions over several years.
• These collisions occasionally produced Λb⁰ baryons and their antiparticles (Λb⁰-bar).
• Scientists then compared how often each version decayed into those particles. A difference in decay rates, after correcting for experimental biases, indicated CP violation.
• To ensure accuracy, the team used a control channel—where no CP violation is expected—to filter out false signals and isolate the real effect.

Conclusion

While the observed CP violation is not enough to fully explain the matter-antimatter imbalance, it opens new avenues for further study.

Scientists will now explore other baryon decays and refine measurements to uncover deeper sources of CP violation—potentially revealing unknown forces or particles.

This discovery takes us closer to answering one of the universe’s most profound questions: why does anything exist at all?