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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

if three forces F1.f2 .f3 act at a point on a Cartesian plane in the daigram .....so if the question says write down the x and y components ..... I really don't understand
Syamthanda Reply
hey , can you please explain oxidation reaction & redox ?
Boitumelo Reply
hey , can you please explain oxidation reaction and redox ?
Boitumelo
for grade 12 or grade 11?
Sibulele
the value of V1 and V2
Tumelo Reply
advantages of electrons in a circuit
Rethabile Reply
we're do you find electromagnetism past papers
Ntombifuthi
what a normal force
Tholulwazi Reply
it is the force or component of the force that the surface exert on an object incontact with it and which acts perpendicular to the surface
Sihle
what is physics?
Petrus Reply
what is the half reaction of Potassium and chlorine
Anna Reply
how to calculate coefficient of static friction
Lisa Reply
how to calculate static friction
Lisa
How to calculate a current
Tumelo
how to calculate the magnitude of horizontal component of the applied force
Mogano
How to calculate force
Monambi
a structure of a thermocouple used to measure inner temperature
Anna Reply
a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4
Amahle Reply
How is energy being used in bonding?
Raymond Reply
what is acceleration
Syamthanda Reply
a rate of change in velocity of an object whith respect to time
Khuthadzo
how can we find the moment of torque of a circular object
Kidist
Acceleration is a rate of change in velocity.
Justice
t =r×f
Khuthadzo
how to calculate tension by substitution
Precious Reply
hi
Shongi
hi
Leago
use fnet method. how many obects are being calculated ?
Khuthadzo
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Hulisani
how to calculate acceleration and tension force
Lungile Reply
you use Fnet equals ma , newtoms second law formula
Masego
please help me with vectors in two dimensions
Mulaudzi Reply
how to calculate normal force
Mulaudzi
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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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