Baryon number violation talk background material

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Searches for the baryon- and lepton-number violating decays B^0\rightarrow\Lambda_c^+\ell^-, B^-\rightarrow\Lambda\ell^-, and B^-\rightarrow\barĪ›\ell^-

This page contains background material for my talk on this analysis. It contains good fodder for a motivated undergraduate or graduate student reading group

None of this material is required to follow the talk. I will pitch the talk to the level of the audience, assuming that people have not read this webpage.


The paper

Searches for B mesons decaying to final states containing a baryon and a lepton are performed, where the baryon is either Λc or Λ and the lepton is a muon or an electron. These decays violate both baryon and lepton number and would be a signature of physics beyond the standard model. No significant signal is observed in any of the decay modes, and upper limits in the range (3.2-520)\times 10^{-8} are set on the branching fractions at the 90% confidence level.

References for the interested reader

Physics background

Baryon asymmetry

  • From the paper:

Observations show that the universe contains much more matter than antimatter (Coppi, Steigman:1976ev). This suggests that there are processes that violate CP-symmetry and baryon-number conservation (Sakharov). However, experimentally observed CP violation, combined with the baryon-number violating processes that are allowed by the standard model (Kuzmin), cannot explain the observed matter-antimatter asymmetry.

  • Andre Sakharov's paper, Violation of CP Invariance, C Asymmetry and Baryon Asymmetry of the Universe.
    • JETP Letters
    • This is generally considered the canonical paper that established the three ``Sakarov conditions", necessary to explain the baryon asymmetry of the universe.
    • This paper is pitched at a higher level and may not be terribly enlightening to non-graduate-level experts and up. Having said that, it is referenced so often that it is worth reading through at least once.


  • While this is not a comprehensive list, this analysis primarily made use of the following particles. I have provided links to the relevant PDG pages that detail the properties of these particles.
  • It is not necessary to know everything about these states, but familiarizing yourself with the masses and quark content (where applicable) will give you more intuition for these processes.
  • You may also be interested in exploring the particle properties in this visualization I made, using data from the [PDG] and the Google Visualization API.

The BaBar detector and running conditions

Exercises for motivated potential-audience members

  • The PEP-II collider, used by the BaBar experiment, collided electrons and positrons at sufficient energy to produce bottom and anti-bottom quarks.

e^+ e^- \rightarrow b \bar{b} At this energy, what other fermion-anti-fermion pairs are created by the electron-positron annihilation?

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