Beyond the God Particle (54 page)

23
. See “Tevatron,”
http://en.wikipedia.org/wiki/Tevatron
(site last visited 6/21/13).

24
. The antiprotons are created in a system called the “Antiproton Source.” The Main Injector–accelerated 120 GeV protons collide with a nickel target, producing a spray of different subatomic particles, which includes antiprotons. These are collected and “cooled,” meaning that compact stable bunches are formed. They are then stored in the accumulator ring, and then passed back to the Main Injector, then ultimately into the Tevatron.

25
. See “Large Electron–Positron Collider,”
http://en.wikipedia.org/wiki/Large_Electron%E2%80%93Positron_Collider
(site last visited 3/26/2013).

26
. See “Large Hadron Collider,”
http://en.wikipedia.org/wiki/Large_Hadron_Collider
(site last visited 3/26/2013).

27
. See “Georges Charpak,”
http://en.wikipedia.org/wiki/Charpak
(site last visited 3/26/2013).

28
. See “International Linear Collider,”
http://en.wikipedia.org/wiki/International_Linear_Collider
and
http://www.linearcollider.org/
(sites last visited 3/26/2013).

CHAPTER 9. RARE PROCESSES

1
. “Wilhelm Conrad Röntgen,”
http://www.nobelprize.org/nobel_prizes/physics/laureates/1901/rontgen-bio.html
; see “Wilhelm Röntgen,”
http://en.wikipedia.org/wiki/Wilhelm_Röntgen
; “The Discovery of X-Rays,”
http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/discoveryxrays.htm
(sites last visited 3/23/2013). Gottfried Landwehr,
Röntgen Centennial: X-Rays in Natural and Life Sciences
, ed. A. Hasse (Singapore: World Scientific Publishing Co., 1997), pp. 7–8.

2
. See “Henri Becquerel,”
http://en.wikipedia.org/wiki/Henri_Becquerel
. Quoting from the article:

As often happens in science, radioactivity came close to being discovered nearly four decades earlier when, in 1857, Abel Niepce de Saint-Victor, who was investigating photography under Michel Eugène Chevreul, observed that uranium salts emitted radiation able to darken photographic emulsions. By 1861, Niepce de Saint-Victor realized that uranium salts produce a radiation that is invisible to our eyes. (Note that Niepce de Saint-Victor knew Edmond Becquerel, Henri Becquerel's father). See “Beta decay,”
http://en.wikipedia.org/wiki/Beta_decay#History
, “Marie Curie,”
http://en.wikipedia.org/wiki/Marie_Curie
, and “Pierre Curie,”
http://en.wikipedia.org/wiki/Pierre_Curie
(sites last visited 3/23/2013).

3
. “What Is Radioactivity?”
http://www.oasisllc.com/abgx/radioactivity.htm
. For a good historical summary on radioactivity, see
http://www.chemteam.info/Radioactivity/Disc-of-Alpha&Beta.html
and
http://www.chemteam.info/Radioactivity/Disc-Alpha&Beta-Particles.html
(sites last visited 3/23/2013).

4
. See “Ernest Rutherford,”
http://en.wikipedia.org/wiki/Ernest_Rutherford
(site last visited 3/23/2013).

Half-life: In a certain time interval, called the “half life,” there will be exactly half as much of a radioactive material as one began with; in another half-life interval the amount will be reduced to half as much again, or a quarter of the initial amount, and so on; materials with short half-lives are very radioactive, e.g., technecium-99 used in most medical imaging has a 2-hour half-life and therefore requires a small dose;
²³⁵
U, the weapons-grade isotope of uranium has a half-life of 700,000 years;
²³⁸
U about 4 billion years.

5
. See “Positron emission tomography,”
http://en.wikipedia.org/wiki/Positron_emission_tomography
and
http://www.webmd.com/a-to-z-guides/positron-emission-tomography
(sites last visited 3/23/2013).

6
. See “Paul Dirac,”
http://en.wikipedia.org/wiki/Paul_Dirac
(site last visited 3/23/2013). Dirac was one of quantum theory's towering figures. For one thing, Dirac wrote
the
book on quantum physics, called
The Principle of Quantum Mechanics
, which became the standard reference. Dirac's original contributions to quantum physics are among the greatest of the twentieth century, anticipating modern topology with his “magnetic monopole” and Feynman's “path integral” formulation of quantum theory. Perhaps one of the most profound discoveries of foundational physics in the twentieth century, however, happened when Dirac combined the theory of the electron with Einstein's theory of special relativity and discovered antimatter some four years before it was discovered in experiments. See also Graham Farmelo,
The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom
(Basic Books; First Trade Paper Edition, 2011).

7
. The Pauli exclusion principle is discussed further in our book:
Quantum Physics for Poets
(Amherst, NY: Prometheus Books, 2011). The quantum orbital state of motion in an atom can actually have two electrons, but one must have spin up and the other spin down.

8
. We call this view of the vacuum the “Dirac sea.” The Dirac sea is not empty but rather is a completely filled “ocean” that metaphorically represents the infinity of filled negative energy levels.

Now, usually when a high-energy gamma ray collides with a negative-energy electron in the vacuum, nothing happens. A single gamma ray hitting a negative-energy electron cannot raise it out of the vacuum because such a process wouldn't conserve all of the necessary quantities that physics demands be conserved, i.e., momentum, energy, angular momentum. However, if there are other particles also participating in the collision (like a nearby heavy atomic nucleus to recoil slightly and conserve the overall momentum, energy, and angular momentum of the participants in the collision; we call this a 3-body collision), then the electron could be ejected out of the Dirac sea into a state of positive energy. The gamma ray could then successfully eject an electron out of its negative energy state and into one of positive energy, and that could register in the physicist's instruments.

9
. See “Carl David Anderson,”
http://en.wikipedia.org/wiki/Carl_David_Anderson
and “Positron,”
http://en.wikipedia.org/wiki/Positron
(sites last visited 3/23/2013).

10
. The momenta of the outgoing electron and proton didn't add up to that of the neutron either, since neutrons at rest in the lab decayed into protons and electrons that were not seen to be emitted back-to-back; the reaction can also be “crossed” into
p
⁺
+
e
^–
→
n
+ (missing energy).

11
. See “Wolfgang Pauli,”
http://en.wikipedia.org/wiki/Wolfgang_Pauli
. The full letter is in the CERN Pauli Archive, which may be visited online at
www.library.cern.ch/archives/pauli/pauliletter.html
and is reproduced in our book
Symmetry and the Beautiful Universe
(Amherst, NY: Prometheus Books, 2007). We thank the CERN Pauli Archive Committee for permission to reproduce it.

12
. It also allows the angular momentum to be conserved if the neutrino has spin 1/2; Enrico Fermi gave the name “neutrino” to the invisible particle in the decay process. Pauli had used the name “neutron” for his new particle, the name we now use for the heavy neutral constituent of the nucleus. You will note that this is a slight variation of the process
p
⁺
+
e
^–
→
n
⁰
+
v
_e
, which causes a supernova. The squeezing together of a proton and electron can happen only at the extreme densities inside a massive star collapse. A neutron in free space decays into proton, electron, and neutrino a half-life of about 11 minutes by the related process of “beta decay,”
.

13
. Fermi's theory involves an “interaction strength” that is G
_F
. If we use the units in which
=
c
= 1, then we find 175
.

14
. See “Frederick Reines,”
http://en.wikipedia.org/wiki/Frederick_Reines
and “Clyde Cowan,”
http://en.wikipedia.org/wiki/Clyde_Cowan
(sites last visited 3/26/2013).

15
. For the Lederman, Schwartz, Steinberger experiment, see chap. 6, note 1. When a third heavy lepton was discovered, the
τ
, or “tau,” it was quickly realized that there was also a
τ
-neutrino. Today we know that there are three distinct kinds of neutrinos, electron neutrinos (
v
_e
), muon neutrinos (
v
_µ
), and tau neutrinos (
v
_τ
), each matching their charged lepton counterparts. This zoology of particles is further elaborated in the Appendix. The
τ
-neutrino was discovered at Fermilab in 2000, in the “DONUT experiment”; see “Tau neutrino,”
http://en.wikipedia.org/wiki/Tau_neutrino
.