# 33.6 Guts: the unification of forces  (Page 5/12)

 Page 5 / 12

## 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.

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.

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

## 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 ${\text{10}}^{\text{10}}\phantom{\rule{0.25em}{0ex}}\text{GeV}$ converts its energy into particles with masses averaging $\text{200}\phantom{\rule{0.25em}{0ex}}\text{MeV/}{c}^{2}$ . (a) How many particles are created? (b) If the particles rain down on a $1\text{.}{\text{00-km}}^{2}$ area, how many particles are there per square meter?

(a) $5×{\text{10}}^{\text{10}}$

(b) $5×{\text{10}}^{4}\phantom{\rule{0.25em}{0ex}}{\text{particles/m}}^{2}$

Integrated Concepts

Assuming conservation of momentum, what is the energy of each $\gamma$ ray produced in the decay of a neutral at rest pion, in the reaction ${\pi }^{0}\to \gamma +\gamma$ ?

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.

$2.5×{\text{10}}^{-\text{17}}\phantom{\rule{0.25em}{0ex}}\text{m}$

Integrated Concepts

(a) Calculate the relativistic quantity $\gamma =\frac{1}{\sqrt{1-{v}^{2}/{c}^{2}}}$ for 1.00-TeV protons produced at Fermilab. (b) If such a proton created a ${\pi }^{+}$ having the same speed, how long would its life be in the laboratory? (c) How far could it travel in this time?

Integrated Concepts

The primary decay mode for the negative pion is ${\pi }^{-}\to {\mu }^{-}+{\stackrel{-}{\nu }}_{\mu }$ . (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 ${\pi }^{-}$ is at rest when it decays? You may assume the muon antineutrino is massless and has momentum $p=E/c$ , just like a photon.

(a) 33.9 MeV

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

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 $\gamma =\frac{1}{\sqrt{1-{v}^{2}/{c}^{2}}}$ be for these particles? (b) How long would their average lifetime be in the laboratory? (c) How far could they travel in this time?

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 ${\text{10}}^{\text{31}}\phantom{\rule{0.25em}{0ex}}\text{y}$ ? (b) How many cubic meters of water is this? (c) If the actual lifetime is ${\text{10}}^{\text{33}}\phantom{\rule{0.25em}{0ex}}\text{y}$ , how long would you have to wait on an average to see a single proton decay?

(a) $7\text{.}2×{\text{10}}^{5}\phantom{\rule{0.25em}{0ex}}\text{kg}$

(b) $7\text{.}2×{\text{10}}^{2}\phantom{\rule{0.25em}{0ex}}{\text{m}}^{3}$

(c) $\text{100 months}$

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 $7\text{-eV/}{c}^{2}$ mass has a kinetic energy of 700 keV. Find the relativistic quantity $\gamma =\frac{1}{\sqrt{1-{v}^{2}/{c}^{2}}}$ 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 $\gamma$ is so large.)

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.

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.

how can I read physics...am finding it difficult to understand...pls help
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
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Jiti
the speed of something in a given direction.
Ju
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u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
Abrar
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Saeed
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Because HE needs someone to dominate the earth (Gen. 1:26)
Olorunfemi
Ali
and he to multiply
Owofemi
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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
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Abrar
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