《粒子物理学 英文》（美）理查德·A.邓拉普（Richard A. Dunlap）著|(epub+azw3+mobi+pdf)电子书下载

图书名称：《粒子物理学 英文》

【作　者】（美）理查德·A.邓拉普（Richard A. Dunlap）著

【丛书名】国外优秀物理著作原版系列

【页 数】 135

【出版社】 哈尔滨：哈尔滨工业大学出版社 , 2021.09

【ISBN号】978-7-5603-9639-2

【价 格】68.00

【分 类】粒子物理学-英文

【参考文献】 （美）理查德·A.邓拉普（Richard A. Dunlap）著. 粒子物理学 英文. 哈尔滨：哈尔滨工业大学出版社, 2021.09.

图书封面：

《粒子物理学 英文》内容提要：

本书在标准模型的基础上对粒子结构进行了描述，给出了中微子性质的最新发现，阐述了亚原子粒子的性质，提供了粒子物理的标准模型的概述，不仅包括希格斯玻色子的发现和性质的概述，还总结了中微子物理学的重要研究，并提供了这些研究的解释概述。

《粒子物理学 英文》内容试读

IOP Concise Physics

Particle Physics

Richard A Dunlap

Chapter 1

Historical overview of particle physics

1.1 Introduction

In the present chapter,we review the discovery and theoretical understanding of particlesthat were observed prior to the mid-part of the twentieth century.Until around 1930.thestudy of particle physics closely followed that of atomic physics and our understanding ofparticles stemmed from our need to explain the properties of atoms and radioactive decayprocesses.In the two or three decades that followed,the field of particle physics dealtmore with the interaction between particles and the understanding of particles on the basisof fundamental quantum mechanics.By the 1950s it became clear that the knownparticles were not just a random assortment of unrelated particles,but that there werewell-defined relationships between the particles based on their properties.Here weoverview the basic categories of particles that were known in the 1950s.

1.2 Photons

The earliest theories concerning the nature of light typically viewed light as beingcomprised of discrete particles.Around the 17th century with increasing exper-imental evidence on the nature of light from diffraction and refraction studies.theconcept that light was made up of waves became prevalent.Wave theories of lightwere promoted by Rene Descartes (~1637).Robert Hooke (-1665)and Christiaan

Huygens (~1678).Isaac Newton,on the other hand,continued to support the ideathat light consisted of particles and it was for this reason that the particle theory oflight continued to some extent throughout the 18th century.

Around 1803 Thomas Young performed the two-slit experiment(now known asthe Young two-slit experiment)and obtained results as illustrated in figure 1.1.Theinterference patterns as seen in this experiment clearly indicated that light could bedescribed by fundamental theories of the properties of waves.

In 1865 James Clerk Maxwell provided a description of electromagnetic radia-tion,which included visible light,as oscillating electric and magnetic fields.Later inthat century Heinrich Hertz detected radio waves and in 1895 Wilhelm Conrad

doi:10.1088/2053-2571/aae6d3chl

1-1

Morgan Claypool Publishers 2018

Particle Physics

Figure 1.1.Young's two-slit experiment.which clearly suggested the wave nature of light.

Rontgen produced and detected x-rays.These discoveries seemed to unify Maxwell'sconcept of electromagnetic radiation and to definitively demonstrate the wave-likenature of visible light.

However.all experimental evidence was not readily described by Maxwell'stheory.which predicted that the energy carried by a light wave was a function of itsintensity and not its frequency.However,some experimental evidence seemed tosuggest that frequency was an important factor in determining the energy of light.

These experimental observations included the study of certain chemical reactionswhich could be induced by light at a high frequency and low intensity but not bylight at a lower frequency.even if it was very intense.In addition,results of extensiveinvestigations of blackbody radiation carried out in the latter half of the 19thcentury were not consistent with Maxwell's theory.

The concept that the energy associated with light was quantized was presented in1900 by Max Planck when he hypothesized that light could only be absorbed oremitted by matter in discrete quanta with an energy that was proportional to thefrequency according to the relation

E=hv ho)

(1.1)

Here is the Planck constant and v is the frequency.h is defined as h/(2m)and theangular frequency is 2m.In 1905 Einstein explained the photoelectric effect.whereby metal surfaces emitted electrons in response to the absorption of light,interms of the quantization of energy in electromagnetic radiation.Although Einsteinenvisioned light as being comprised of particles.there was still a widespread beliefamong physicists that light should still be viewed as waves and that the quantizationwas a feature of the absorption and emission process and not the light itself.Einsteinshowed that if light itself existed as quantized particles,then these particles carriedquantized momenta.

p=

(1.2)

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Particle Physics

Arthur Holly Compton showed that light quanta carry momentum according to

Einstein's prediction and are therefore,particles.His experiments demonstrated thatlight that was incident on electrons could only be re-emitted as light at a lowerfrequency and that the energy lost by the light was given up as kinetic energy of theelectron.This phenomenon,now known as the Compton effect,can only beexplained if the quanta of light carry momentum and are particles.These particlesare now known as photons.

The wave-particle duality of photons was clarified in 1924 by Louis de Brogliewho proposed that particles exhibited wave-like properties according to Einstein'srelation above,where the wavelength could be expressed in terms of the particle'smomentum as

(1.3)

The concept of photons as mediators of the electromagnetic interaction wasdeveloped as a part of quantum field theory in the 1930s and will be discussed inmore detail in the next chapter.

1.3 Electrons

Although our knowledge of electricity dates back to ancient times,the concept of theelectron as a particle is much more recent.Perhaps the first experimental evidencefor the existence of the electron as a charged particle comes from experiments in the1880s by Thomas Alva Edison.Edison developed a device which exhibits what isnow known as the 'Edison Effect'.Electrons produced by a hot filament in anevacuated tube were used to carry current to complete an electric circuit.

Further experimentation by Joseph John ('J.J.)Thomson,led to his 1897conclusion that the current in Edison's device was carried by particles with anegative charge.These are now known as electrons.In 1899 Ernest Rutherfordinvestigated the types of radiation that were emitted by radioactive atoms andcategorized these as alpha particles(which were later shown to be the nuclei of *Heatoms),beta particles (which were shown to be the same as Thomson's electrons)and gamma rays (which were later shown to be a form of electromagnetic radiation).

1.4 Protons

Rutherford had shown that the alpha particles that are emitted by some radioactiveatoms were heavy particles (compared to the electron)and that they carried apositive charge with a magnitude of twice the electron charge.At this time the actualnature of the atom was not clear.It was known that the atom was neutral and that itcontained negatively charged electrons as well as some positively charged particles.

There were basically three models at the time which described how these chargedparticles combined to produce a neutral atom.These were:

1.The negatively charged electrons were each paired with a positively chargedparticle that formed a bound pair.

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Particle Physics

2.A positively charged core was orbited by a number of electrons thatelectrically canceled the charge of the core.

3.The negatively charged electrons and the positively charged particles wereuniformly mixed together to form the neutral atom.

In 1904 J J Thomson put forth the 'plum pudding'model of the atom whichfollowed the third hypothesis above.This model was favored by a significantnumber of scientists over the next few years,until,in 1911.Rutherford conducted hisnow well known experiment involving the scattering of alpha particles from goldatoms.This experiment showed conclusively that the angular distribution ofscattered alpha particles indicated that the atom consisted of a very small centralpositively charged core that was surrounded by the spatially distributed negativelycharged electrons(model #2 above).This type of scattering experiment was useful indetermining the charge distribution in the atom and several decades later,the samebasic approach was used to determine the charge distribution within the nucleus andeven more recently has been utilized to understand the internal structure of theproton (as discussed in chapter 4).The details of Rutherford scattering (or moregenerally Coulombic scattering)which has been instrumental in our understandingof the structure of the atom.the structure of the nucleus and the structure ofhadrons.is described in some detail in chapter 3.

In 1919,in a series of experiments involving the collision between alpha particlesand nuclei.Rutherford showed that the collision of an alpha particle with a nitrogennucleus (for example)resulted in the alpha particle being absorbed by the nucleusand a particle with a single positive charge being emitted.In 1920 he hypothesizedthat these positively charged particles were a fundamental component of all nucleiand referred to them as protons (from the Greek word meaning 'first').

1.5 Neutrons

With Rutherford's discovery of the proton,the structure of the atom became clear

However.one major inconsistency existed.It was obvious that the mass of theneutral atom was,in general,much larger than the mass of the protons in the nucleusand the mass of the electrons orbiting the nucleus.Rutherford's investigation of betaradiation from certain unstable nuclei.whereby an electron was emitted from thenucleus.suggested that the nucleus contained not only protons but electrons as well.

He hypothesized that the extra mass of the atom was made up by bound protonelectron pairs that existed within the nucleus and that during the beta decay process,the proton and electron became unbound and the electron was emitted.

However,an analysis of this model using the de Broglie hypothesis shows that theconfinement of electrons in the nucleus is not possible.The argument considers acalculation of the energy scale for this confinement by two different approaches.Firstly,the energy scale may be estimated from the de Broglie hypothesis in equation (1.2)as

E=D

h2

(1.4)

21122

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Particle Physics

where m is the electron mass.Secondly,the energy scale is characterized by the

Coulombic potential as

E=Ze2

(1.5

4πeo

In equation (1.4)is the de Broglie wavelength.or the spatial distribution of theparticle wavefunction.and in equation (1.5)r is the physical distance between thetwo charges and Z is the number of positive charges in the nucleus.If we set A=rand apply this approach to atomic electrons.where r is the atomic radius for a lightatom (i.e.a fraction of a nm),and Z is a few,then both calculations give an energyscale of a few tens of eV.This value is consistent with the ionization potential of lightatoms.On the other hand,using r equal to a few fm (as appropriate for the size ofthe nucleus),we find that the two energy scales are not consistent.While the

Coulombic potential is of the order of an MeV,consistent with observed beta decayenergies (as discussed below).the energy scale from equation (1.4)is several ordersof magnitude larger.

When performing calculations such as those in equations (1.4)and(1.5)that arecommon in nuclear and particle physics,it is convenient to take some liberties withthe strict SI system of units.It is appropriate to use energies which are multiples ofthe electron volt (i.e.eVs for atomic physics,MeV for nuclear physics and MeV or

GeV for particle physics)and to use distances in nm for atomic physics and fm fornuclear physics.It is also useful to multiply the right-hand side of equation (1.4)byc2/c2 and to use the value of the constant

hc 1240 MeV.fm 1240 eV.nm

(1.6

and the rest mass energy of the electron

mc2 0.511 MeV

(1.7)

In equation (1.5).the Coulomb constant may be written as

e2-=1.44 MeV fm =1.44 eV.nm

(1.8)

4πE0

From the analysis as presented above,it became clear that the extra nuclear masscould not be viewed as a neutral bound electron-proton pair inside the nucleus.

Another observation which conflicted with this hypothesis was the rotational energylevels of the N2 molecule.Experimental results showed that theN nucleus shouldhave integer spin.If theN nucleus consisted of 7 protons (to give the nuclearcharge)plus 7 electrons bound to 7 more protons (to give the proper mass).then thenet spin of these 21 fermions would be a half integer spin.On the other hand,if the14N nucleus consisted of 7 protons and 7 neutrons(as we now know that it does)then the spin would be the result of 14 fermions or an integer spin.

The first evidence that a new neutral particle might account for this mass camefrom the discovery,in 1931,by Walther Bothe and Herbert Becker that alphaparticles incident on light elements such as lithium.beryllium and boron caused

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Particle Physics

them to emit uncharged particles.It was assumed that this radiation was gammarays,as had been identified by Rutherford from the decay of certain radioactivenuclides.However,about a year later Irene Joliot-Curie and Frederic Joliotobserved that this radiation,when incident on hydrogen-containing compounds,caused the emission of protons.Ettore Majorana concluded that this behaviorindicated that the radiation had to be an unknown type of neutral particle.

Following along the lines of previous experiments and making more accuratemeasurements of the energy of the protons emitted in hydrogen-compound experi-ments,James Chadwick was able to determine the mass of the new neutral particle.

These results from 1932 were the first definitive proof of the existence of the neutron.

1.6 Neutrinos

The first experimental evidence for the existence of the neutrino was provided in1911 by Lise Meitner and Otto Hahn who measured the spectrum of beta particles(i.e.electrons)from a beta decay process.They found that the electrons had acontinuous energy spectrum,as shown in figure 1.2,rather than a single discreteenergy as had been observed for alpha particles that were produced in radioactivedecay processes.Since the energy associated with the beta decay process isquantized.it was assumed that the energy spectrum of the emitted electrons shouldshow a peak at a single energy.As the electrons exhibited a broad distribution up tothe so-called end point energy,which was the expected energy of the decay process,it was believed that the electrons that were produced in the decay were losing energybefore they were being detected.

In 1930 Wolfgang Pauli suggested that nuclei contained a very light neutralparticle,which he called the 'neutron'and that these particles were emitted,alongwith the electrons,during beta decay and that the decay energy was shared between

0

0.2

0.40.60.81.01.2

Kinetic energy,MeV

Figure 1.2.Energy spectrum of electrons from the beta decay of2Bi(http://hyperphysics.phy-astr.gsu.edulhbase/nuclear/beta2.html).

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