Book contents
- Frontmatter
- Contents
- Foreword: an apology
- 1 The beginning of the journey to the small: cutting paper
- 2 To molecules and atoms
- 3 The magical mystery of the quanta
- 4 Dazzling velocities
- 5 The elementary particle zoo before 1970
- 6 Life and death
- 7 The crazy kaons
- 8 The invisible quarks
- 9 Fields or bootstraps?
- 10 The Yang-Mills bonanza
- 11 Superconducting empty space: the Higgs-Kibble machine
- 12 Models
- 13 Coloring in the strong forces
- 14 The magnetic monopole
- 15 Gypsy
- 16 The brilliance of the Standard Model
- 17 Anomalies
- 18 Deceptive perfection
- 19 Weighing neutrinos
- 20 The Great Desert
- 21 Technicolor
- 22 Grand unification
- 23 Supergravity
- 24 Eleven-dimensional space-time
- 25 Attaching the superstring
- 26 Into the black hole
- 27 Theories that do not yet exist…
- 28 Dominance of the rule of the smallest
- Glossary
- Index
6 - Life and death
Published online by Cambridge University Press: 05 April 2013
- Frontmatter
- Contents
- Foreword: an apology
- 1 The beginning of the journey to the small: cutting paper
- 2 To molecules and atoms
- 3 The magical mystery of the quanta
- 4 Dazzling velocities
- 5 The elementary particle zoo before 1970
- 6 Life and death
- 7 The crazy kaons
- 8 The invisible quarks
- 9 Fields or bootstraps?
- 10 The Yang-Mills bonanza
- 11 Superconducting empty space: the Higgs-Kibble machine
- 12 Models
- 13 Coloring in the strong forces
- 14 The magnetic monopole
- 15 Gypsy
- 16 The brilliance of the Standard Model
- 17 Anomalies
- 18 Deceptive perfection
- 19 Weighing neutrinos
- 20 The Great Desert
- 21 Technicolor
- 22 Grand unification
- 23 Supergravity
- 24 Eleven-dimensional space-time
- 25 Attaching the superstring
- 26 Into the black hole
- 27 Theories that do not yet exist…
- 28 Dominance of the rule of the smallest
- Glossary
- Index
Summary
When we talk about a particle's lifetime we always mean its average lifetime. A particle that is not absolutely stable has, at every moment of its life, the same chance of decaying. Some particles live longer than others, but the average lifetime is a characteristic of any particle species.
One can also use the concept of ‘half-life’. If we have a large number of identical particles, the half-life is the time it takes for one-half of all the particles to decay. The half-life is 0.693 times the average lifetime.
One glance at Table 1 shows that some particles have a much longer average lifetime than others. The lifetimes differ enormously. A neutron, for example, lives 1013 times longer than a sigma-plus, and the sigma-plus has more than 109 times as long a lifetime as the sigma-zero. But if you observe that the ‘natural’ time scale for an elementary particle (which is the time it takes for their quantum mechanical state, or wave function, to evolve or oscillate) is somewhere around 10−24 seconds, you can safely state that all these particles are pretty stable. In our professional jargon, they are all called ‘stable particles’.
How is a particle's lifetime determined? Particles with long lifetimes, such as the neutron and the muon, have to be captured, preferably in great numbers, after which one registers the decays electronically. Particles with lifetimes around 10−10 to 10−8 seconds used to be registered in a bubble chamber; nowadays this happens more often in a spark chamber.
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- In Search of the Ultimate Building Blocks , pp. 33 - 36Publisher: Cambridge University PressPrint publication year: 1996