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Matter-Antimatter Asymmetry

Matter-Antimatter Asymmetry. Sridhara Dasu University of Wisconsin. Some portions adapted from H. Maruyama, UC-Berkeley. Outline. What is anti-matter? What led us to it? But, why is it so rare? The Standard Model Flavor Mixing Fundamental asymmetry between matter-antimatter

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Matter-Antimatter Asymmetry

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  1. Matter-Antimatter Asymmetry Sridhara Dasu University of Wisconsin Some portions adapted from H. Maruyama, UC-Berkeley

  2. Outline • What is anti-matter? • What led us to it? • But, why is it so rare? • The Standard Model • Flavor • Mixing • Fundamental asymmetry between matter-antimatter • Experimental Program • Meson decay asymmetries • Quark mixing parameters

  3. The smallness of the electron • At the end of 19th century • Physicists pondered about the electron • Electron is point-like • At least smaller than 10-17 cm • Like charges repel • Hard to keep electric charge in a small pack • Need a lot of energy to keep it small!

  4. Need LOTS of energy to pack electric charge tightly inside the electron But the observed energy of the electron is only 0.5 MeV Breakdown of theory of electromagnetism E=hn, E=mc2

  5. Energy-Time Uncertainty Principle: You can violate energy conservation but only for a short time Uncertainty Principle Werner Heisenberg

  6. Relativistic Quantum world • Dirac formulated Relativistic Quantum Mechanics • Schrodinger equation • Not relativistic (space2 but time1) • Predicted antimatter • Anderson discovered positron • Vacuum is full of quantum bubbles! Paul Adrian Maurice Dirac

  7. Electron creates a force to repel itself Vacuum bubble of matter anti-matter creation/annihilation Electron annihilates the positron in the bubble  Size of the electron is no longer a relevant parameter - the closer you probe, the more you see the structure of vacuum … matter and antimatter pairs Anti-Matter Helps

  8. Anti-Matter Helps • “Anti-matter attraction” cancels “Like-charge repulsion” • It does not cost too much energy to tightly pack the electric charge inside the electron • Needed anti-matter: double #particles • Theory of electromagnetism (QED) now works at very short distances (12 digits accuracy!)

  9. Matter-Antimatter • All elementary particles come in matter- antimatter pairs • Opposite electric charge • Identical in almost all other respects • Electron-Positron • Proton-Antiproton • Neutron-Antineutron • Up quark - Anti up quark • Energy conservation can be violated for short periods of time to generate any of these or other particle-antiparticle pairs in vacuum • Relativistic Quantum Mechanics

  10. e- b c g,Z t b e- e+ W+ W- n Elementary particles Heavier elementary particles decay - only the first generation (e,u,d), photons (g) and neutrinos (n) are stable.

  11. c b e- W- n Flavor Changing Interactions • Charged W± particles (like photons but massive - 80 GeV) change flavor of quarks • For short period energy conservation can be violated to create virtual heavy W± particles • Heavier quarks, leptons decay to lighter generations (u, d, electron, neutrinos) • Cross generational coupling exists • b quark decays to c quark + X • The down-type quarks mix together • Quantum mechanical superposition of states

  12. Quark Mixing Matrix Matter reactions are transposed to antimatter reactions using CP transformation - i.e., CP asymmetry is allowed.

  13. Mesons and Baryons Free quarks cannot exist - they always occur in meson or baryon clusters.

  14. Mesons • Many types • Decays • Detection • Interactions with matter • Calculating combined masses using detected particles

  15. Matter-Antimatter AsymmetryEarly Universe 10,000,000,001 10,000,000,000 They basically have all annihilated away except a tiny difference between them

  16. Baryon AsymmetryCurrent Universe us 1 They basically have all annihilated away except a tiny difference between them

  17. Sakharov’s Conditions • Necessary requirements for genesis of our universe: • CP violation • Baryon, Lepton number violation • #protons ≠ #anti-protons • #electrons ≠ #positrons • Consequences • CP violation • Proton decay, etc. CP violation is experimentally observed in meson systems. However, all particle reactions observed in nature so far conserve total Baryon and Lepton numbers!

  18. CP Violation: Strange Mesons • Discovered in kaon system (Cronin and Fitch) • Theoretically difficult (confinement effect for light quarks in mesons is difficult to compute - relativistic quantum mechanics calculations) Pursuing studies in more theoretically accessible heavy B meson system

  19. Detector Particle physicists can reconstruct the events that occur when high energy matter-antimatter are annihilated. Allows one to probe what happened in the early universe when these particles were abundant!

  20. Upsilon Meson: BaBar Events

  21. CP Violation: B meson system

  22. Summary • Matter Antimatter Asymmetry • Is necessary for the very existence of our universe • Requires CP violation and Baryon/Lepton number violation • CP Violation • Observed in K meson system 1964, 1998 • Observed in B meson system • Detailed measurements in progress • Baryon/Lepton number violation • Proton decay not observed yet • Many theoretical models • Avenues for exploration abound • Both laboratory and astrophysical searches underway/planned

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