From Matt Bellis

Searches for the baryon- and lepton-number violating decays , , and

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.

Contents 1 The paper 2 References for the interested reader 2.1 Physics background 2.1.1 Baryon asymmetry 2.1.2 Particles 2.1.3 The BaBar detector and running conditions 3 Exercises for motivated potential-audience members

The paper

• http://arxiv.org/abs/1101.3830
  • Abstract:

Searches for B mesons decaying to final states containing a baryon and a lepton are performed, where the baryon is either Λ_c 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 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.

Particles

• 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.
  • Υ(4S) (PDG info)
  • mesons (PDG info)
  • mesons (PDG info)
  • Λ_c baryons (PDG info)
  • Λ baryons (PDG info)
  • μ leptons (PDG info)
  • e leptons (PDG info)
• You may also be interested in exploring the particle properties in this visualization I made, using data from the [PDG http://pdg.lbl.gov] and the Google Visualization API.

The BaBar detector and running conditions

• Wikipedia has a nice article about the BaBar experiment
• Our University of Victoria colleagues have put together some very nice animations of the BaBar detector and the PEP-II collider and uploaded them to YouTube.
  • The BaBar detector.
  • The SLAC site, linear accelerator and PEP-II collider.

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.

At this energy, what other fermion-anti-fermion pairs are created by the electron-positron annihilation?

• Some of the particles analyzed in this study decay weakly and can be relatively long-lived. What is cτ for the
  1. B⁰ meson?
  2. Λ baryon?
• In 1980, James Cronin and Val Fitch won the Nobel Prize for observing CP-violation in neutral kaons. In Cronin's acceptance speech he discussed proton decay and how it would proceed if it was mediated by a fractionally charged boson. You can find a diagram of this process on p. 583 of his speech. Using the same mediating bosons (1/3 and 2/3 charge), can you draw tree-level diagrams for all of the following reactions? Some of them?
  1. 
  2. 
  3.