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33.4 Particles, patterns, and conservation laws  (Page 2/21)

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Hadrons and leptons

Particles can also be revealingly grouped according to what forces they feel between them. All particles (even those that are massless) are affected by gravity, since gravity affects the space and time in which particles exist. All charged particles are affected by the electromagnetic force, as are neutral particles that have an internal distribution of charge (such as the neutron with its magnetic moment). Special names are given to particles that feel the strong and weak nuclear forces. Hadrons are particles that feel the strong nuclear force, whereas leptons    are particles that do not. The proton, neutron, and the pions are examples of hadrons. The electron, positron, muons, and neutrinos are examples of leptons, the name meaning low mass. Leptons feel the weak nuclear force. In fact, all particles feel the weak nuclear force. This means that hadrons are distinguished by being able to feel both the strong and weak nuclear forces.

[link] lists the characteristics of some of the most important subatomic particles, including the directly observed carrier particles for the electromagnetic and weak nuclear forces, all leptons, and some hadrons. Several hints related to an underlying substructure emerge from an examination of these particle characteristics. Note that the carrier particles are called gauge bosons . First mentioned in Patterns in Spectra Reveal More Quantization , a boson    is a particle with zero or an integer value of intrinsic spin (such as s = 0, 1, 2, ... size 12{s=0,`1,`2,` "." "." "." } {} ), whereas a fermion    is a particle with a half-integer value of intrinsic spin ( s = 1 / 2, 3 / 2, . . . size 12{s=1/2,`3/2,` "." "." "." } {} ). Fermions obey the Pauli exclusion principle whereas bosons do not. All the known and conjectured carrier particles are bosons.

The upper image shows an electron and positron colliding head-on. The lower image shows a starburst image from which two photons are emerging in opposite directions.
When a particle encounters its antiparticle, they annihilate, often producing pure energy in the form of photons. In this case, an electron and a positron convert all their mass into two identical energy rays, which move away in opposite directions to keep total momentum zero as it was before. Similar annihilations occur for other combinations of a particle with its antiparticle, sometimes producing more particles while obeying all conservation laws.
Selected particle characteristics The lower of the ∓ size 12{ -+ {}} {} or ± size 12{ +- {}} {} symbols are the values for antiparticles.
Category Particle name Symbol Antiparticle Rest mass ( MeV / c 2 ) B L e L μ L τ size 12{L rSub { size 8{τ} } } {} S size 12{S} {} Lifetime Lifetimes are traditionally given as t 1 / 2 / 0 . 693 (which is 1 / λ size 12{ {1} slash {λ} } {} , the inverse of the decay constant). (s)
Gauge Photon γ size 12{γ} {} Self 0 0 0 0 0 0 Stable
Bosons W size 12{W} {} W + size 12{W rSup { size 8{+{}} } } {} W − size 12{W rSup { size 8{ - {}} } } {} 80 . 39 × 10 3 size 12{"80" "." "22" times "10" rSup { size 8{3} } } {} 0 0 0 0 0 1.6 × 10 − 25 size 12{3 times "10" rSup { size 8{ - "25"} } } {}
Z size 12{Z} {} Z 0 size 12{Z rSup { size 8{0} } } {} Self 91 . 19 × 10 3 size 12{"91" "." "19" times "10" rSup { size 8{3} } } {} 0 0 0 0 0 1.32 × 10 − 25 size 12{3 times "10" rSup { size 8{ - "25"} } } {}
Leptons Electron e − size 12{e rSup { size 8{ - {}} } } {} e + size 12{e rSup { size 8{ - {}} } } {} 0.511 0 ± 1 size 12{ +- 1} {} 0 0 0 Stable
Neutrino (e) ν e size 12{e rSup { size 8{ - {}} } } {} v ¯ e size 12{ { bar {v}} rSub { size 8{e} } } {} 0 7 . 0 eV size 12{0` left (<7 "." 0`"eV" right )} {} Neutrino masses may be zero. Experimental upper limits are given in parentheses. 0 ± 1 size 12{ +- 1} {} 0 0 0 Stable
Muon μ − size 12{μ rSup { size 8{ - {}} } } {} μ + size 12{μ rSup { size 8{+{}} } } {} 105.7 0 0 ± 1 size 12{ +- 1} {} 0 0 2 . 20 × 10 − 6 size 12{2 "." "20" times "10" rSup { size 8{ - 6} } } {}
Neutrino ( μ size 12{μ} {} ) v μ size 12{v rSub { size 8{μ} } } {} v - μ size 12{v rSub { size 8{μ} } } {} 0 ( < 0.27 ) 0 0 ± 1 size 12{ +- 1} {} 0 0 Stable
Tau τ − size 12{τ rSup { size 8{ - {}} } } {} τ + size 12{τ rSup { size 8{+{}} } } {} 1777 0 0 0 ± 1 size 12{ +- 1} {} 0 2 . 91 × 10 − 13 size 12{2 "." "29" times "10" rSup { size 8{ - "13"} } } {}
Neutrino ( τ size 12{τ} {} ) v τ size 12{v rSub { size 8{τ} } } {} v - τ size 12{ { bar {v}} rSub { size 8{τ} } } {} 0 ( < 31 ) 0 0 0 ± 1 size 12{ +- 1} {} 0 Stable
Hadrons (selected)
  Mesons Pion π + size 12{π rSup { size 8{+{}} } } {} π − size 12{π rSup { size 8{ - {}} } } {} 139.6 0 0 0 0 0 2.60 × 10 −8
π 0 size 12{π rSup { size 8{0} } } {} Self 135.0 0 0 0 0 0 8.4 × 10 −17
Kaon K + size 12{K rSup { size 8{+{}} } } {} K − size 12{K rSup { size 8{ - {}} } } {} 493.7 0 0 0 0 ± 1 size 12{ +- 1} {} 1.24 × 10 −8
K 0 size 12{K rSup { size 8{0} } } {} K - 0 size 12{ { bar {K}} rSup { size 8{0} } } {} 497.6 0 0 0 0 ± 1 size 12{ +- 1} {} 0.90 × 10 −10
Eta η 0 size 12{η rSup { size 8{0} } } {} Self 547.9 0 0 0 0 0 2.53 × 10 −19
(many other mesons known)
  Baryons Proton p size 12{p} {} p - size 12{ { bar {p}}} {} 938.3 ± 1 0 0 0 0 Stable Experimental lower limit is >5 × 10 32 size 12{>5 times "10" rSup { size 8{"32"} } } {} for proposed mode of decay.
Neutron n size 12{n} {} n - size 12{ { bar {n}}} {} 939.6 ± 1 0 0 0 0 882
Lambda Λ 0 size 12{Λ rSup { size 8{0} } } {} Λ - 0 size 12{ { bar {Λ}} rSup { size 8{0} } } {} 1115.7 ± 1 0 0 0 ∓ 1 size 12{ -+ 1} {} 2.63 × 10 −10
Sigma Σ + size 12{Σ rSup { size 8{+{}} } } {} Σ - − size 12{ { bar {Σ}} rSup { size 8{ - {}} } } {} 1189.4 ± 1 0 0 0 ∓ 1 size 12{ -+ 1} {} 0.80 × 10 −10
Σ 0 size 12{Σ rSup { size 8{0} } } {} Σ - 0 size 12{ { bar {Σ}} rSup { size 8{0} } } {} 1192.6 ± 1 0 0 0 ∓ 1 size 12{ -+ 1} {} 7.4 × 10 −20
Σ − size 12{Σ rSup { size 8{ - {}} } } {} Σ - + size 12{ { bar {Σ}} rSup { size 8{+{}} } } {} 1197.4 ± 1 0 0 0 ∓ 1 size 12{ -+ 1} {} 1.48 × 10 −10
Xi Ξ 0 size 12{Ξ rSup { size 8{0} } } {} Ξ - 0 size 12{ { bar {Ξ}} rSup { size 8{0} } } {} 1314.9 ± 1 0 0 0 ∓ 2 size 12{ -+ 2} {} 2.90 × 10 −10
Ξ − size 12{Ξ rSup { size 8{ - {}} } } {} Ξ + size 12{Ξ rSup { size 8{+{}} } } {} 1321.7 ± 1 0 0 0 ∓ 2 size 12{ -+ 2} {} 1.64 × 10 −10
Omega Ω − size 12{ %OMEGA rSup { size 8{ - {}} } } {} Ω + size 12{ %OMEGA rSup { size 8{+{}} } } {} 1672.5 ± 1 0 0 0 ∓ 3 size 12{ -+ 3} {} 0.82 × 10 −10
(many other baryons known)

Questions & Answers

how does the planets on our solar system orbit
cheten Reply
how many Messier objects are there in space
satish Reply
did you g8ve certificate
Richard Reply
what are astronomy
Issan Reply
Astronomy (from Ancient Greek ἀστρονομία (astronomía) 'science that studies the laws of the stars') is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution.
Rafael
vjuvu
Elgoog
what is big bang theory?
Rosemary
what type of activity astronomer do?
Rosemary
No
Richard
the big bang theory is a theory which states that all matter was compressed together in one place the matter got so unstable it exploded releasing All its contents in the form of hydrogen
Roaul
I want to be an astronomer. That's my dream
Astrit
Who named the the whole galaxy?
Shola Reply
solar Univers
GPOWER
what is space
Richard
what is the dark matter
Richard
what are the factors upon which the atmosphere is stratified
Nicholas Reply
is the big bang the sun
Folakemi Reply
no
Sokak
bigbang is the beginning of the universe
Sokak
but thats just a theory
Sokak
nothing will happen, don't worry brother.
Vansh
what does comet means
GANGAIN Reply
these are Rocky substances between mars and jupiter
GANGAIN
Comets are cosmic snowballs of frozen gases , rock and dust that orbit the sun. They are mostly found between the orbits of Venus and Mercury.
Aarya
hllo
John
hi
John
qt rrt
John
r u there
John
hey can anyone guide me abt international astronomy olympiad
sahil
how can we learn right and true ?
Govinda Reply
why the moon is always appear in an elliptical shape
Gatjuol Reply
Because when astroid hit the Earth then a piece of elliptical shape of the earth was separated which is now called moon.
Hemen
what's see level?
lidiya Reply
Did you mean eye sight or sea level
Minal
oh sorry it's sea level
lidiya
according to the theory of astronomers why the moon is always appear in an elliptical orbit?
Gatjuol
hi !!! I am new in astronomy.... I have so many questions in mind .... all of scientists of the word they just give opinion only. but they never think true or false ... i respect all of them... I believes whole universe depending on true ...থিউরি
Govinda
hello
Jackson
hi
Elyana
we're all stars and galaxies a part of sun. how can science prove thx with respect old ancient times picture or books..or anything with respect to present time .but we r a part of that universe
Reply
w astronomy and cosmology!
Michele
another theory of universe except big ban
Albash Reply
how was universe born
Asmit Reply
there many theory to born universe but what is the reality of big bang theory to born universe
Asmit
what is the exact value of π?
Nagalakshmi
by big bang
universal
there are many theories regarding this it's on you believe any theory that you think is true ex. eternal inflation theory, oscillation model theory, multiple universe theory the big bang theory etc.
Aarya
I think after Big Bang!
Michele
from where on earth could u observe all the stars during the during the course of an year
Karuna Reply
I think it couldn't possible on earth
Nagalakshmi
in this time i don't Know
Michele
is that so. the question was in the end of this chapter
Karuna
in theory, you could see them all from the equator (though over the course of a year, not at pne time). stars are measured in "declination", which is how far N or S of the equator (90* to -90*). Polaris is the North star, and is ALMOST 90* (+89*). So it would just barely creep over the horizon.
Christopher
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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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