Large Hadron Collider: Unveiling CP Violation in Baryons

The Large Hadron Collider (LHC) is the world’s largest and most powerful particle accelerator, located in a 27-km underground ring where particles, mainly protons, are accelerated to nearly the speed of light. These particles collide at four locations where massive detectors collect data on the collisions.

Matter vs. Antimatter Mystery

• The universe predominantly consists of matter over antimatter, although post-Big Bang, both were believed to exist in equal amounts.
• The dominance of matter is linked to a phenomenon called CP violation, a difference in the behavior of matter and antimatter.
• CP violation has previously been observed in mesons but not in baryons, which are the particles like protons and neutrons.

Recent Discoveries in Baryons

• The LHCb collaboration in Europe reported the first-ever observation of CP violation in baryon decays, specifically in the Λb⁰ baryon.
• The decay involves the Λb⁰ baryon transforming into a proton, a negatively charged kaon, a positively charged pion, and a negatively charged pion.
• The experiment utilized data collected between 2011 and 2018 from the LHCb detector, using machine learning and particle identification tools to validate decays.

CP Symmetry and Violation

• CP Violation implies that the laws of physics are not identical for matter and antimatter.
• The observed CP asymmetry was about 2.45%, significantly deviating from the expected zero if no violation occurred.
• The findings align with the Standard Model, though the amount of CP violation observed is insufficient to explain the universe’s matter-antimatter imbalance.

Future Research Directions

• Physicists are exploring ‘new physics’ beyond the Standard Model to account for the matter-antimatter asymmetry.
• The complex phase of CP violation in baryons, crucial for understanding this phenomenon, remains difficult to extract from current data.
• In 2022, new methodologies were proposed for measuring the complex phase in baryons.

Significance of CP Violation in Baryons

Observing CP violation in baryons is crucial as baryons constitute the visible matter of the universe. The discovery marks a significant step towards resolving the matter-antimatter asymmetry mystery, though further experimental and theoretical advancements are essential for a comprehensive understanding.

Sakharov’s Conditions

• The three conditions necessary for a matter-dominated universe:
  • Baryon number violation. 
  • CP violation in baryons. 
  • Departure from thermal equilibrium to prevent rebalancing of baryon and antibaryon production.

The recent observation of CP violation in baryon decays contributes to understanding these conditions, yet the discovery opens new avenues to investigate potential new physics that could better explain the universe's composition.