The must fundamental constituents of matter Physics 100 Chapt 26.
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Transcript of The must fundamental constituents of matter Physics 100 Chapt 26.
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The must fundamental constituents of matter
Physics 100
Chapt 26
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Anaximenes
Anaximenes ~600BC
All types of matter areformed from different combinations of:
•Earth•Air•Fire•Water
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Closer to home
Earth
Wind
Fire
Water
Elements
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Anaximenes idea
• Good point: Economical– All of matter reduced to 4 easy-to-remember
components
• Bad point: Wrong– Alchemists (including Isaac Newton) tried for
centuries to changing one chemical element into another with no success
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Enter Mendeleev
All matter is comprised of different combinations of(now 92) different chemical elements
Good point Correct; successfully predicted the existence of
Scandium, Gallium & Germanium
Bad point Uneconomical; 92 basic constituens
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Rutherford
All elements are constructedfrom 3 basic particles:
•electrons
•neutrons•protons
Feel the strong force
& are heavy hadrons
Doesn’t feel the strong
force & is light lepton
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The “elementary particles” circa 1935
Category particle symbol charge mc2 strong electric weak
Leptons electron e- -1 0.511 MeV
no yes yes
neutrino 0 ~0 no no yes
Hadrons proton p +1 938.3MeV
yes yes yes
neutron n 0 939.6MeV
yes yes yes
Light photon 0 0 no yes no
Economy is restored
Forces felt
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These “good” times
didn’t last long
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Paul Adrien Maurice Dirac
1902 - 1984
Combined relativity
&QuantumMechanics
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p = mV
xpx = mVx
E = 1/2 mv2
py = mVy
y
Pre relativity
px can be + or -
E is always +
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p = mV
xpx = mVx
E = mc22 2( )
E = mc2±
py = mVy
y
px can be + or -
E also can be + or -
Post relativity:
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QM waves: =h/p f=E/h
Pre relativity:
p = m0 v (v =p/m0)
E =1/2 m0v2 =p2/2m0
= h/p can be + or f=p2/2m0h always +
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QM waves: =h/p f=E/h
after relativity:
p = m0 v (v =p/m0)
E2 = (mc2 )2 E= ± mc2
= h/p can be + or
f= can be + or mc2
h
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Negative wavelength : wave in backward direction.
Negative frequency : wave backward in time????
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What does it mean to move backwards in time?
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backward time motion
t
B
when viewed forward in time:
L R
: C
: P
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When antimatter comes in contact
with matter,
what happens?
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- +- +- +
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Anti-hydrogen
p
+
Anti-hydrogen atoms are made routinely at the CERN laboratory in Switzerland.
It is found to have the same size and allowed energy levels as ordinary hydrogen
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Anti-Carbon
+
+
++
+
+
•antielectrons
•antineutrons•antiprotons
Although it would be impossibly difficult to make anti-atoms more complex than anti-hydrogen, it is in principle possible
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CP Violation:
Asymmetry matteranti-
matter
Big Bang
matter-antimattersymmetric
all matterno
antimatter
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Our research
Where did all theanti-people go???
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Include anti-particles in our list
Category particle symbol charge mc2 symbol charge
Leptons electron e- -1 0.511 MeV
positron e+ +1
neutrino 0 ~0 anti-neutrino
0
Hadrons proton p +1 938.3MeV
anti-proton
p -1
neutron n 0 939.6MeV
anti-neutron
n 0
Light photon 0 0 photon 0
anti-particleparticle
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Quantum Electro-Dynamics (QED)
Combined Relativity, Quantum Mechanics and Photons into one single theory
Richard Feynman Julian SchwingerShinichiro Tomonaga
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QED explains action-at-a-distance
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QED is a fabulously accurate theory
QEDtheory
measure
Strength of electrons magnetic field:
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Ideas of QEDstrong nuclear force
Hideki Yukawa
Short range (10-15m) of the strong nuclear force:predicts existence of a “” particle Mc2 140 MeV
1935
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Look for in cosmic rays
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“Spark chamber” tracks
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+ and – particle discovered in cosmic rays
m+c2 = m-c2 = 106 MeV
Near expectations
for Yukawa’s
Experiments show that the + & - do not feel the Strong Nuclear Force and,
therefore, cannot be Yukawa’s
the + & - are additional leptons(i.e. like the e+ & e- but with larger mass)
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Yukawa’sfinally discovered in 1947
In fact there are 3 of them:
+ M+c2 = 139.6 MeV
0 M0c2 = 135.0 MeV
- M-c2 = 139.6 MeV
Anti-particles
Photographicemulsion
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“Atom smashers”
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Inside the accelerator tunnel
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e+e- collider
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Belle Detector
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Electronic detectors
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Fermilab (near Chicago)
2 km
detector
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Inside a Fermilab Tunnel
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Biggest of all is in Europe
~5 miles
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Detectors
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Neutrino interacts in a Bubble Chamber
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Leptons (circa 2005)anti-particleparticle
name symbol charge mc2 name symbol charge
electron e -1 0.511 MeV
positron e +1
electron neutrino
e 0 ~0 anti-elec neutrino
e 0
muon +1 105.7MeV
anti-muon
+1
muon- neutrino
0 ~0 anti-mu neutrino
0
tau -1 1876 MeV
anti-
tau +1
tau- neutrino
0 ~0 anti-tau neutrino
0
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1950’s & 1960’s, Many other particles are discovered
p-
M=1116MeV
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K0 “meson”
K0 -
M=498 MeV
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Two classes of hadrons
Baryons (p, n, , …..)
ultimate decay products include a proton
Mesons (, K, …)
ultimate decay products e’s, ’s & ’s
Both baryons & mesons feel the Strong Nuclear Force
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Lots of baryons have been discovered
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& even more mesons
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The elementary particle chart revisited
Economy is lost!!
6 leptons: e e; ;
(+ 6 anti-leptons)
Category particle symbol
Leptons electron e-
neutrino Hadrons proton p
neutron n
1935 NOW
hundreds of hadrons + anti-hadrons
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Elementary Particle Zoo
Lepton House
Electrons,
Muons,Taus,
& lots of neutrinos
Hadron Savannah
100’s of Baryons,
Latest new Mesons
+anti particles galore
& lots of photons
Special today:
live pions being exhanged
proton
neutron