Matter-Antimatter Asymmetry
The Big Bang should have made matter and antimatter in equal amounts; why did only matter remain?
Open in the interactive tree →Sakharov named three conditions in 1967: baryon-number violation, C and CP violation, and a departure from equilibrium. The Standard Model has CP violation, but by orders of magnitude too little to explain why one matter particle remains for every billion photons. Without the asymmetry there would be no stars, planets or people.
As of October 2026
The LHCb experiment reported the first CP violation in baryons in March 2025 (Nature 643, 1223): in Lambda-b decays to p K- pi+ pi- the asymmetry is 2.45 +/- 0.46 +/- 0.10%, 5.2 sigma. The Standard Model allows this effect, but it cannot account for the surplus of matter in the universe. Further leads are neutrino CP violation (T2K, NOvA) and electron electric-dipole-moment searches; proton decay has never been observed.
What is missing
- A source of sufficiently strong CP violation (new particles or forces)
- Detection of baryon-number violation (proton decay): Hyper-Kamiokande and DUNE are meant to search for it
- Precision measurement of neutrino CP violation (DUNE, Hyper-Kamiokande) to test leptogenesis
- An electron dipole moment above the Standard Model prediction, which is practically zero
Becomes possible once solved
- Understanding why a universe with structure exists at all
- New particles and forces beyond the Standard Model
- A link between neutrino physics and cosmology
Open steps
- Neutrino CP violation, precisely Medium AI leverageMeasure the neutrino CP-violating phase with Hyper-Kamiokande and DUNE to test whether leptogenesis can explain the matter surplus.
- Proton-decay search Low AI leverageDetect proton decay, or exclude it to far longer lifetimes; either would test baryon-number violation.
- Electron dipole moment search Low AI leverageMeasure the electron's electric dipole moment with more sensitivity; any value above the near-zero Standard Model prediction signals new CP violation.
- Searching for new CP-violating physics Medium AI leverageLook for new particles or forces that supply strong CP violation, through LHC anomaly searches and global fits of baryogenesis models.
Where AI could help
Low AI leverage. The missing evidence is new physics seen in huge detectors (Hyper-Kamiokande, DUNE, proton decay); AI sharpens analysis but cannot replace data.
- Reconstruct events in Hyper-Kamiokande and DUNE with deep networks to sharpen neutrino CP-violation measurements
- Run model-independent anomaly triggers at the LHC for unexpected CP- or baryon-number-violating signals
- Speed up simulations and fits of leptogenesis and electroweak baryogenesis models
Shown so far
- Since 2024 the CMS experiment has run an autoencoder-based anomaly-detection trigger (AXOL1TL) at the LHC Level-1 trigger, which records unusual collisions that fixed selections would discard. source
Prerequisites
- Expansion & Big Bang1929
- Antimatter1932The matter-antimatter puzzle only exists because antiparticles do
- Standard Model of Particles1973
- Higgs Boson Discovered2012With a 125 GeV Higgs the Standard Model cannot make the matter surplus