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The image shows the picture of a huge cylindrical shaped proton decay detector with its main door open. It is as high as a double decker bus and as long as a small house. An untold number of cables, wires, and detector modules are arranged in a cylinder around a rectangular crate-like object containing another smaller cylindrical object.
In the Tevatron accelerator at Fermilab, protons and antiprotons collide at high energies, and some of those collisions could result in the production of a Higgs boson in association with a W boson. When the W boson decays to a high-energy lepton and a neutrino, the detector triggers on the lepton, whether it is an electron or a muon. (credit: D. J. Miller)

Summary

  • Attempts to show unification of the four forces are called Grand Unified Theories (GUTs) and have been partially successful, with connections proven between EM and weak forces in electroweak theory.
  • The strong force is carried by eight proposed particles called gluons, which are intimately connected to a quantum number called color—their governing theory is thus called quantum chromodynamics (QCD). Taken together, QCD and the electroweak theory are widely accepted as the Standard Model of particle physics.
  • Unification of the strong force is expected at such high energies that it cannot be directly tested, but it may have observable consequences in the as-yet unobserved decay of the proton and topics to be discussed in the next chapter. Although unification of forces is generally anticipated, much remains to be done to prove its validity.

Conceptual questions

If a GUT is proven, and the four forces are unified, it will still be correct to say that the orbit of the moon is determined by the gravitational force. Explain why.

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If the Higgs boson is discovered and found to have mass, will it be considered the ultimate carrier of the weak force? Explain your response.

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Gluons and the photon are massless. Does this imply that the W + size 12{W rSup { size 8{+{}} } } {} , W size 12{W rSup { size 8{ - {}} } } {} , and Z 0 size 12{Z rSup { size 8{0} } } {} are the ultimate carriers of the weak force?

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Problems&Exercises

Integrated Concepts

The intensity of cosmic ray radiation decreases rapidly with increasing energy, but there are occasionally extremely energetic cosmic rays that create a shower of radiation from all the particles they create by striking a nucleus in the atmosphere as seen in the figure given below. Suppose a cosmic ray particle having an energy of 10 10 GeV converts its energy into particles with masses averaging 200 MeV/ c 2 . (a) How many particles are created? (b) If the particles rain down on a 1 . 00-km 2 area, how many particles are there per square meter?

The figure shows an extremely energetic cosmic ray penetrating into the Earth's atmosphere. High up in the atmosphere, the cosmic ray disintegrates into a shower of particles that start a chain reaction by themselves creating further particles. All these particles shower the surface of the Earth.
An extremely energetic cosmic ray creates a shower of particles on earth. The energy of these rare cosmic rays can approach a joule (about 10 10 GeV size 12{"10" rSup { size 8{"10"} } `"GeV"} {} ) and, after multiple collisions, huge numbers of particles are created from this energy. Cosmic ray showers have been observed to extend over many square kilometers.

(a) 5 × 10 10 size 12{5 times "10" rSup { size 8{"10"} } } {}

(b) 5 × 10 4 particles/m 2

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Integrated Concepts

Assuming conservation of momentum, what is the energy of each γ size 12{γ} {} ray produced in the decay of a neutral at rest pion, in the reaction π 0 γ + γ size 12{π rSup { size 8{0} } rightarrow γ+γ} {} ?

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Integrated Concepts

What is the wavelength of a 50-GeV electron, which is produced at SLAC? This provides an idea of the limit to the detail it can probe.

2.5 × 10 17 m size 12{2 "." 5 times "10" rSup { size 8{ - "17"} } `m} {}

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Integrated Concepts

(a) Calculate the relativistic quantity γ = 1 1 v 2 / c 2 size 12{γ= { {1} over { sqrt {1 - v rSup { size 8{2} } /c rSup { size 8{2} } } } } } {} for 1.00-TeV protons produced at Fermilab. (b) If such a proton created a π + size 12{π rSup { size 8{+{}} } } {} having the same speed, how long would its life be in the laboratory? (c) How far could it travel in this time?

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Integrated Concepts

The primary decay mode for the negative pion is π μ + ν - μ size 12{π rSup { size 8{ - {}} } rightarrow μ rSup { size 8{ - {}} } + { bar {ν}} rSub { size 8{μ} } } {} . (a) What is the energy release in MeV in this decay? (b) Using conservation of momentum, how much energy does each of the decay products receive, given the π size 12{π rSup { size 8{ - {}} } } {} is at rest when it decays? You may assume the muon antineutrino is massless and has momentum p = E / c size 12{p=E/c} {} , just like a photon.

(a) 33.9 MeV

(b) Muon antineutrino 29.8 MeV, muon 4.1 MeV (kinetic energy)

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Integrated Concepts

Plans for an accelerator that produces a secondary beam of K -mesons to scatter from nuclei, for the purpose of studying the strong force, call for them to have a kinetic energy of 500 MeV. (a) What would the relativistic quantity γ = 1 1 v 2 / c 2 size 12{γ= { {1} over { sqrt {1 - v rSup { size 8{2} } /c rSup { size 8{2} } } } } } {} be for these particles? (b) How long would their average lifetime be in the laboratory? (c) How far could they travel in this time?

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Integrated Concepts

Suppose you are designing a proton decay experiment and you can detect 50 percent of the proton decays in a tank of water. (a) How many kilograms of water would you need to see one decay per month, assuming a lifetime of 10 31 y ? (b) How many cubic meters of water is this? (c) If the actual lifetime is 10 33 y , how long would you have to wait on an average to see a single proton decay?

(a) 7 . 2 × 10 5 kg size 12{7 "." 2 times "10" rSup { size 8{5} } `"kg"} {}

(b) 7 . 2 × 10 2 m 3 size 12{7 "." 2 times "10" rSup { size 8{2} } `m rSup { size 8{3} } } {}

(c) 100 months size 12{"100 months"} {}

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Integrated Concepts

In supernovas, neutrinos are produced in huge amounts. They were detected from the 1987A supernova in the Magellanic Cloud, which is about 120,000 light years away from the Earth (relatively close to our Milky Way galaxy). If neutrinos have a mass, they cannot travel at the speed of light, but if their mass is small, they can get close. (a) Suppose a neutrino with a 7 -eV/ c 2 size 12{7"-eV/"c rSup { size 8{2} } } {} mass has a kinetic energy of 700 keV. Find the relativistic quantity γ = 1 1 v 2 / c 2 size 12{γ= { {1} over { sqrt {1 - v rSup { size 8{2} } /c rSup { size 8{2} } } } } } {} for it. (b) If the neutrino leaves the 1987A supernova at the same time as a photon and both travel to Earth, how much sooner does the photon arrive? This is not a large time difference, given that it is impossible to know which neutrino left with which photon and the poor efficiency of the neutrino detectors. Thus, the fact that neutrinos were observed within hours of the brightening of the supernova only places an upper limit on the neutrino's mass. (Hint: You may need to use a series expansion to find v for the neutrino, since its γ size 12{γ} {} is so large.)

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Construct Your Own Problem  

Consider an ultrahigh-energy cosmic ray entering the Earth's atmosphere (some have energies approaching a joule). Construct a problem in which you calculate the energy of the particle based on the number of particles in an observed cosmic ray shower. Among the things to consider are the average mass of the shower particles, the average number per square meter, and the extent (number of square meters covered) of the shower. Express the energy in eV and joules.

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Construct Your Own Problem  

Consider a detector needed to observe the proposed, but extremely rare, decay of an electron. Construct a problem in which you calculate the amount of matter needed in the detector to be able to observe the decay, assuming that it has a signature that is clearly identifiable. Among the things to consider are the estimated half life (long for rare events), and the number of decays per unit time that you wish to observe, as well as the number of electrons in the detector substance.

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Questions & Answers

how can I read physics...am finding it difficult to understand...pls help
rerry Reply
try to read several books on phy don't just rely one. some authors explain better than other.
Ju
And don't forget to check out YouTube videos on the subject. Videos offer a different visual way to learn easier.
Ju
hope that helps
Ju
I have a exam on 12 february
David Reply
what is velocity
Jiti
the speed of something in a given direction.
Ju
what is a magnitude in physics
Jiti Reply
Propose a force standard different from the example of a stretched spring discussed in the text. Your standard must be capable of producing the same force repeatedly.
Giovani Reply
What is meant by dielectric charge?
It's Reply
what happens to the size of charge if the dielectric is changed?
Brhanu Reply
omega= omega not +alpha t derivation
Provakar Reply
u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
Abrar
do to be peaceful with any body
Brhanu Reply
the angle subtended at the center of sphere of radius r in steradian is equal to 4 pi how?
Saeed Reply
if for diatonic gas Cv =5R/2 then gamma is equal to 7/5 how?
Saeed
define variable velocity
Ali Reply
displacement in easy way.
Mubashir Reply
binding energy per nucleon
Poonam Reply
why God created humanity
Manuel Reply
Because HE needs someone to dominate the earth (Gen. 1:26)
Olorunfemi
why god made humenity
Ali
and he to multiply
Owofemi
stuff happens
Ju
God plays dice
Ju
Is the object in a conductor or an insulator? Justify your answer. whats the answer to this question? pls need help figure is given above
Jun Reply
ok we can say body is electrically neutral ...conductor this quality is given to most metalls who have free electron in orbital d ...but human doesn't have ...so we re made from insulator or dielectric material ... furthermore, the menirals in our body like k, Fe , cu , zn
Abrar
when we face electric shock these elements work as a conductor that's why we got this shock
Abrar
how do i calculate the pressure on the base of a deposit if the deposit is moving with a linear aceleration
ximena Reply
Practice Key Terms 7

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Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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