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02 History .pdf



Original filename: 02-History.pdf
Title: Remove this slide
Author: Steve Lloyd

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EPP

A Brief History of Particle Physics

1930s
The known 'Elementary Particles' were :
electron
proton
neutron (inside the nucleus)
'neutrino' (now anti-neutrino) in beta decay
photon ()– the quantum of the electromagnetic field

Nothing exists except atoms and empty space
Δημόκριτος (Democritus)

PHY-306 EPP

A Brief History of Particle Physics

Slide 1

EPP

A Brief History of Particle Physics

1930s
The known 'Elementary Particles' were :
electron
proton
neutron (inside the nucleus)
'neutrino' (now anti-neutrino) in beta decay
photon ()– the quantum of the electromagnetic field
1932
The positive electron (positron) discovered by Carl Anderson

Carl Anderson
C.D. Anderson, Physical Review 43, 491 (1933).

PHY-306 EPP

A Brief History of Particle Physics

Slide 2

The Neutron

EPP
1932
Neutron discovered by James Chadwick

James Chadwick

1933
Fermi theory of beta decay
(weak interactions)
n → p + e– +e
Enrico Fermi
PHY-306 EPP

A Brief History of Particle Physics

Slide 3

Pions and Muons

EPP

1935
Yukawa's meson hypothesis – nuclear force due to
exchange of particles with mass (mesons)
1937
 lepton (muon) discovered by Carl Anderson and
Seth Nedermeyer. Initially assumed to be Yukawa's
meson but it was too penetrating

Hideki Yukawa

1946
Charged  meson (pion)
discovered by Cecil
Powell. The previous 
produced from  decays
via + → + + 
1950
Neutral pion (0) discovered via 0 →  + 
PHY-306 EPP

A Brief History of Particle Physics

Cecil Powell

Slide 4

EPP

A Theory of Electromagnetism

By 1950
Quantum Theory of Electromagnetism – Quantum Electrodynamics
(QED) – charged particles interact via exchange of photons ().
Richard Feynman, Julian Schwinger and Sin-itiro Tomonaga

Richard
Feynman

PHY-306 EPP

Julian
Schwinger

Sin-itiro
Tomonaga

A Brief History of Particle Physics

Slide 5

Strange Particles

EPP

1947
Discovery of the kaon (K meson). 'Strange' long lived particles
discovered in cosmic ray events by Clifford Butler and George
Rochester. Gave rise to a new quantum number 'strangeness'.
Further 'V' events discovered at Brookhaven, New York in 1952/53
Charged
K± decay

Neutral
K0 decay

Robin Marshall, University of Manchester

PHY-306 EPP

A Brief History of Particle Physics

Slide 6

Anti-matter

EPP

1955
Discovery of the anti-proton (p) by Owen Chamberlain
and Emilio Segrè

Owen
Chamberlain

PHY-306 EPP

A Brief History of Particle Physics

Emilio Segrè

Slide 7

EPP

Half-life by Frank Close

1930-1960
Story in latest Frank Close's book:
Half life. The divided life of Bruno Pontecorvo, Physicist or spy.

Professor Frank 
Close will come to 
give a colloquium 
in QMUL on 
Friday March 4th
at 16:30

PHY-306 EPP

A Brief History of Particle Physics

Slide 8

EPP

The Particle Zoo

1960s/70s
Hundreds of 'elementary particles' discovered – , , K*, …, , , …
a real mess!

All these particles explained by combinations of more
fundamental 'quarks', u, d, s and their anti-quarks
PHY-306 EPP

A Brief History of Particle Physics

Slide 9


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