Beyond the God Particle (53 page)

9
. See “Technetium-99,”
http://en.wikipedia.org/wiki/Technetium-99
(site last visited 3/26/2013).

10
. “Magnetic Field Basics,”
http://www.physics4kids.com/files/elec_magneticfield.html
(site last visited 3/26/2013). Digested from the article:

Magnets and magnetism were known to ancients. The magnetic field on the surface of a spherical magnet was mapped using iron needles in 1269 by Petrus Peregrinus de Maricourt. He coined the term “poles” in analogy to Earth's poles where the field lines converged at two points on the sphere. In 1600 in a publication,
De Magnete
, William Gilbert of Colchester demonstrated explicitly that Earth is a magnet, helped to establish magnetism as a science. In 1819, Hans Christian Oersted discovered that an electric current generates a magnetic field encircling it. André-Marie Ampère in 1820 showed that parallel wires having currents in the same direction attract one another. Jean-Baptiste Biot and Félix Savart discovered the force law in 1820 which correctly predicts the magnetic field around any current-carrying wire.
     Extending these experiments, Ampère published his own successful model of magnetism in 1825…. Further, Ampère derived both Ampère's force law describing the force between two currents and Ampère's law which, like the Biot–Savart law, correctly described the magnetic field generated by a steady current. Also in this work, Ampère introduced the term “electrodynamics” to describe the relationship between electricity and magnetism.
     In 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field. He described this phenomenon in what is known as Faraday's law of induction. Later, Franz Ernst Neumann proved that, for a moving conductor in a magnetic field, induction is a consequence of Ampère's force law. In the process he introduced the magnetic vector potential which was later shown to be equivalent to the underlying mechanism proposed by Faraday.…
     Between 1861 and 1865, James Clerk Maxwell developed and published Maxwell's equations which explained and united all of classical electricity and magnetism. The first set of these equations was published in a paper entitled
On Physical Lines of Force
in 1861. These equations were valid although incomplete. He completed Maxwell's set of equations in his later 1865 paper,
A Dynamical Theory of the Electromagnetic Field
, and demonstrated the fact that light is an electromagnetic wave. Heinrich Hertz experimentally confirmed this fact in 1887.
     Although implicit in Ampère's force law the force due to a magnetic field on a moving electric charge was not correctly and explicitly stated until 1892 by Hendrik Lorentz who theoretically derived it from Maxwell's equations. With this last piece of the puzzle, the classical theory of electrodynamics was essentially complete.
     Mapping the magnetic field of an object is simple in principle. First, measure the strength and direction of the magnetic field at a large number of locations. Then, mark each location with an arrow (called a vector) pointing in the direction of the local magnetic field with a length proportional to the strength of the magnetic field.
     A simpler method to map the magnetic field is to “connect” the arrows to form magnetic field lines. On a magnetic field line diagram, the direction of the magnetic field at any point is represented by the direction of nearby field lines. Further, if drawn carefully, a higher density of nearby field lines indicates a stronger magnetic field.
     Magnetic field lines are like the contour lines (constant altitude) on a topographic map in that a different mapping scale would show more or fewer lines. An advantage of using magnetic field lines, though, is that many laws of magnetism (and electromagnetism) can be stated completely and concisely using simple concepts such as the “number” of field lines through a surface. These concepts can be quickly “translated” to their mathematical form. For example, the number of field lines through a given surface is the surface integral of the magnetic field.
     Various phenomena have the effect of “displaying” magnetic field lines as though the field lines are physical phenomena. For example, iron filings placed in a magnetic field line up to form lines that correspond to “field lines.” Magnetic fields’ “lines” are also visually displayed in polar auroras, in which plasma particle dipole interactions create visible streaks of light that line up with the local direction of Earth's magnetic field.
     Field lines can be used as a qualitative tool to visualize magnetic forces. In ferromagnetic substances like iron and in plasmas, magnetic forces can be understood by imagining that the field lines exert a tension (like a rubber band) along their length, and a pressure perpendicular to their length on neighboring field lines. “Unlike” poles of magnets attract because they are linked by many field lines; “like” poles repel because their field lines do not meet, but run parallel, pushing on each other.
     The twentieth century extended electrodynamics to include relativity and quantum mechanics. Albert Einstein, in his paper of 1905 that established relativity, showed that both the electric and magnetic fields are part of the same phenomena viewed from different reference frames.

11
. Note that acceleration is the time rate of change of a velocity. Velocity is a vector, meaning it has both magnitude (speed) and direction. If the speed is constant but the direction varies in time, as is the case for uniform circular motion, then the particle is being accelerated.

12
. See “André-Marie Ampère,”
http://en.wikipedia.org/wiki/Andr%C3%A9-Marie_Amp%C3%A8re
(site last visited 3/26/2013).

13
. This is called “direct current,” or DC, not the “alternating current,” or AC, which oscillates in the wires in your home; the oscillating current also produces magnetic fields, but the forces will oscillate and average to zero, so you won't see the wires deflecting one another

14
. The magnetic property of iron is a consequence of the intrinsic spin of electrons in the iron atoms and is a rather complex quantum phenomenon. See “Ferromagnetism,”
http://en.wikipedia.org/wiki/Ferromagnetism
(site last visited 1/26/2013).

15
. Magnetic monopoles would in principle exist if certain conditions in particle physics were realized. Such objects would be extremely heavy (at least many TeV in mass, probably higher); there is to date no evidence, other than various theories, of their existence See “Magnetic monopole,”
http://en.wikipedia.org/wiki/Magnetic_monopole
(site last visited 1/26/2013).

16
. See iron filings revealing the magnetic field lines at
http://en.wikipedia.org/wiki/Magnetism#History
; see also
http://www.wired.com/wiredscience/2011/09/magnetic-invisibility-cloak/
(sites last visited 3/26/2013), or search online for keywords “iron filings magnetic.”

17
. See “Cyclotron,”
http://en.wikipedia.org/wiki/Cyclotron
and illustrations therein, (site last visited 1/26/2013).

18
. See “Strong focusing,”
http://en.wikipedia.org/wiki/Strong_focusing
and “Synchrotron,”
http://en.wikipedia.org/wiki/Synchrotron
(sites last visited 1/26/2013).

19
. “Synchrotron radiation,”
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/synchrotron.html
;
http://www.hep.ucl.ac.uk/~jpc/all/ulthesis/node15.html
;
http://physik.uibk.ac.at/~emo/physics/synchrotron.html
(sites last visited 1/26/2013).

20
. See “Quadrupole magnet,”
http://en.wikipedia.org/wiki/Quadrupole_magnet
(site last visited 1/26/2013).

21
. The “FODO” lattice is discussed in D. Edwards and M. Syphers,
An Introduction to the Physics of High Energy Accelerators (Wiley Series in Beam Physics and Accelerator Technology)
(Wiley, 1992). For information on the Brookhaven AGS, see
http://en.wikipedia.org/wiki/Alternating_Gradient_Synchrotron
(site last visited 1/26/2013).

22
. Lillian Hoddeson, Adrienne Kolb, and Catherine Westfall,
Fermilab: Physics, the Frontier, and Megascience
(University of Chicago Press, 2011); see also “Tevatron,”
http://en.wikipedia.org/wiki/Tevatron
(sites last visited 3/26/2013). From the source:

December 1, 1968 saw the breaking of ground for the linear accelerator (linac). The construction of the Main Accelerator Enclosure began on October 3, 1969 when the first shovel of earth was turned by Robert R. Wilson, NAL's director. This would become the 6.4 km circumference of Fermilab's Main Ring.
     The linac's first 200 MeV beam started on December 1, 1970. The booster's first 8 GeV beam was produced on May 20, 1971. On June 30, 1971, a proton beam was guided for the first time through the entire National Accelerator Laboratory accelerator system including the Main Ring. The beam was accelerated to only 7 GeV…
     A series of milestones saw acceleration rise to 20 GeV on January 22, 1972 to 53 GeV on February 4 and to 100 GeV on February 11. On March 1, 1972, the then NAL accelerator system accelerated for the first time a beam of protons to its design energy of 200 GeV. By the end of 1973, NAL's accelerator system operated routinely at 300 GeV.
     On 14 May, 1976 Fermilab took its protons all the way to 500 GeV. This achievement provided the opportunity to introduce a new energy scale, the Tera electron volt (TeV), equal to 1000 GeV. On 17 June of that year, the European Super Proton Synchrotron accelerator (SPS) had achieved an initial circulating proton beam (with no accelerating radio-frequency power) of only 400 GeV.
     The old copper magnet accelerator was shut down on August 15, 1977 for superconducting magnets to be mounted “piggy-back” on the main ring magnets. The “Energy Doubler,” as it was known then, produced its first accelerated beam—512 GeV—on July 3, 1983. Its initial energy of 800 GeV was achieved on February 16, 1984. On October 21, 1986 acceleration at the Tevatron was pushed to 900 GeV, providing a first proton–antiproton collision at 1.8 TeV on November 30, 1986.
     The Main Injector, which replaced the Main Ring, was the most substantial addition, built over six years from 1993 at a cost of $290 million. Tevatron collider Run II began on March 1, 2001 after successful completion of that facility upgrade. From then, the beam had been capable of delivering an energy of 980 GeV.
     On July 16, 2004 the Tevatron achieved a new peak luminosity, breaking the record previously held by the old European Intersecting Storage Rings (ISR) at CERN. That very Fermilab record was doubled on September 9, 2006, then a bit more than tripled on March 17, 2008, and ultimately multiplied by a factor of 4 over the previous 2004 record on April 16, 2010 (up to 4 × 10
³²
cm
⁻²
s
⁻¹
).
     By the end of 2011, the Large Hadron Collider (LHC) at CERN had achieved a luminosity almost ten times higher than Tevatron's (at 3.65 × 10
³³
cm
⁻²
s
⁻¹
) and a beam energy of 3.5 TeV each (doing so since March 18, 2010), already ~3.6 times the capabilities of the Tevatron (at 0.98 TeV).
     The initial design luminosity of the Tevatron was 10
³⁰
cm
⁻²
s
⁻¹
, however the accelerator has following upgrades been able to deliver luminosities up to 4 ×10
³²
cm
⁻²
s
⁻¹
.
     The Booster is a small circular synchrotron, around which the protons pass up to 20,000 times to attain an energy of around 8 GeV. From the Booster the particles pass into the Main Injector, which was completed in 1999 to perform a number of tasks. It can accelerate protons up to 150 GeV; it can produce 120 GeV protons for antiproton creation; it can increase antiproton energy to 120 GeV, and it can inject protons or antiprotons into the Tevatron. The antiprotons are created by the Antiproton Source. 120 GeV protons are collided with a nickel target producing a range of particles including antiprotons which can be collected and stored in the accumulator ring. The ring can then pass the antiprotons to the Main Injector.
     The Tevatron could accelerate the particles from the Main Injector up to 980 GeV. The protons and antiprotons are accelerated in opposite directions, crossing paths in the CDF and DØ detectors to collide at 1.96 TeV. To hold the particles on track the Tevatron uses 774 niobium-titanium superconducting dipole magnets cooled in liquid helium producing 4.2 teslas. The field ramps over about 20 seconds as the particles are accelerated. Another 240 NbTi quadrupole magnets are used to focus the beam.
     The Tevatron confirmed the existence of several subatomic particles that were predicted by theoretical particle physics, or gave suggestions to their existence. In 1995, the CDF experiment and DØ experiment collaborations announced the discovery of the top quark, and by 2007 they measured its mass to a precision of nearly 1%. In 2006, the CDF collaboration reported the first measurement of B
_s
oscillations, and observation of two types of sigma baryons.