Particle Physics: Status and PerspectivesPart 1: Particles
Manfred Jeitler
2
Overview (1)
what are elementary particles? the first particles to be discovered
historical overview a few formulas
relativistic kinematics quantum mechanics and the Dirac equation common units in elementary particle physics
the Standard Model detectors accelerators
3
Overview (2)
completing the Standard Model the second generation (charm and J/ψ) the third generation (beauty (bottom) and Υ
(“upsilon”), top) gauge bosons of electroweak interactions: the W and Z
bosons testing at the Precision Frontier: the magnetic moment
of the leptons the Higgs boson fundamental symmetries and their violation
parity violation CP-violation T-violation
4
Overview (3)
neutrinos and neutrino oscillations particle physics and cosmology, open questions
the Energy Frontier and the Precision Frontier Supersymmetry dark matter gravitational waves
slides and formulas athttp://wwwhephy.oeaw.ac.at/u3w/j/jeitler/www/LECTURES/ParticlePhysics/
5
Literature A few useful books are:
Donald Perkins, Introduction to High Energy Physics Otto Nachtmann, Elementary Particle Physics
You will find many other good books in your library
On recent experiments, much useful information can be found on the internet (Wikipedia, home pages of the various experiments etc.)
6
What are (elementary)
particles?
7
8
1897
the electrone-
ThomsonThomson
9
J.J. Thomson’s “plum-pudding model” of the atom
... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...
10
1897
the proton
e-
1900-1924
1914
RutherfordRutherford
p
11
12
13
1897
the photon
1900-1924
PlanckPlanck EinsteinEinstein
ComptonCompton
e-
p
14
1897
the neutron
e-
1900-1924
1914
np
1932
ChadwickChadwick
15
1897
the positron (anti-matter)
e-
1900-1924
1914
e+
p
1932
n
1937
1947
Anderson Anderson
Dirac Dirac
16
17
18
1897
the muon
e-
1900-1924
1914
µp
1932
n
1937
• Hess• Anderson, Neddermeyer
e+
Who ordered this ?
muon lifetime
muon lifetime ~ 2.2 μs
speed of muons: almost speed of light
speed of light = ?
path travelled by muons = ?
19
20
21
relativistic kinematics
elementary particles travel mostly at speeds close to speed of light because their masses are small compared to
typical energies
(almost) always use relativistic kinematics
in particle physics, “special relativity” is sufficient most of the time
remember a few basic formulae !
a bit of maths
Special Relativity Quantum Mechanics Dirac Equation
22
23
relativistic kinematics
1
v 1/γ
24
+
-e-
1V
the electron-volt (eV)
10-4 eV: 3 K cosmic background radiation (~ 0.25 meV)
10-2 eV: room temperature (~ 30 meV) eV: ionisation energy for light atoms
(13.6 eV in hydrogen) 103 eV (keV): X-rays in heavy atoms 106 eV (MeV): mass of electron
me = 511 keV/c2
109 eV (GeV): mass of proton (~1GeV/c2) ~ 100 GeV/c2: mass of W, Z ~ 200 GeV/c2: mass of top
1012 eV (TeV): range of present-day man-made accelerators
1020 eV: highest energies seen for cosmic particles
1028 eV (1019 GeV/c2): ~ Planck mass
units: energy and mass
25
units: speed and distance
velocity: speed of light ~ 3 * 108 m/s ~ 30 cm/ns approximately, all speeds are equal to the speed
of light in high-energy particle physics ! all particles are “relativistic”
distance: fm (femtometer) 1 fm = 10-15 m sometimes also called “Fermi”
26
27
relations and constants
28
“natural” units
29
gravitation is weak!
30
1897
the pion
e-
1900-1924
1914
p
1932
n
1937
µ
1947
Powell Powell Yukawa Yukawa
e+
EXPI, Aug. 201231
Force carriers
Interaction between particles due to exchange of other (“virtual”) particles
L.J. C
urt
is
gauge bosons
32
1897
the neutrino
e-
1900-1924
1914
p
1932
n
1937
µ
1947
e+
Pauli Pauli Reines Reines
33
34
1897
„strange“ particles
e-
1900-1924
1914
KKp
1932
n
1937
µ
1947
e+
Rochester,Butler,...
1947-...
Too many particles!
36
life time (s)
n
c
KL
D
Kc
KS
0
B
J1s 2s
3s
4s
D*
c
0
mass (GeV/c2)
the particle zoo
1s
1 ms
1 µs
10-15s
10-20s
10-25s
100000
n
KL
D
Kc
KS
0
B
J1s 2s
3s
4s
D*
c
0
E=1eV
e-
W±, Zo
p
1 ns
37
1897
„I have heard it said that the finderof a new elementary particle usedto be rewarded by a Nobel Prize,but that now such a discovery ought to be punished by a $10,000 fine.“
e-
1900-1924
1914
K
p
1932
n
1937
µ
1947
e+
1947-...
In his Nobel prize speech in 1955, Willis Lamb expressed nicely the general attitude at the time:
LambLamb
The “particle zoo” of the subatomic world
Is there something analogous to the Periodic Table of the elements?
?? ?
?
?
?
?
Is there something missing?
The periodic table today
41
Teilchen Wechselwirkungenstark
schwach
e
Ladung
0
-1
+2/3
-1/3
gravitation?
weakW, Z
electromagnetic
strongge
d
u
s
c
b
t
+1/3 +1 0
d
u
d
uu
du
d
Proton Neutron
q
q
q
„Leptonen“ „Quarks“
42
Anti-Teilchen Wechselwirkungenstark
schwach
e
Ladung
0
+1
-2/3
+1/3
gravitation?
weakW, Z
electromagnetic
strongge
d
u
s
c
b
t
+1 Pion ()
d
u
43
++
u
uu
d
dd
us
u
us
c
d
D
s
u
b
b
44
fermions (spin ½)
charge
0
-1
+2/3
-1/3
d
uu
du
d
leptons quarks
the Standard Model
+1 0 proton neutron
baryons
interactions
strong
weak
gravitation?
weakW, Z
electromagnetic
strongg
force carriers = bosons (spin 1)
e
e
u c t
d s b
45
d
u
s
c
b
t
e
e
anti-particles
interactionsstrong
weak
e
charge
0
+1
-2/3
+1/3
gravitation?
weakW, Z
electromagnetic
strongge
d
u
s
c
b
t
leptons quarks
force carriers = bosons (spin 1)
46
d
u
s
c
b
t
e
e
anti-particles
interactionsstrong
weak
e
charge
0
+1
-2/3
+1/3
gravitation?
weakW, Z
electromagnetic
strongge
d
u
s
c
b
t
leptons quarks
force carriers = bosons (spin 1)
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the 4 fundamental interactions
Gravitation
Strong Interaction
Electromagnetism Weak Interaction
48
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lifetime and width
50
cross section
defined via scattering probability W = n . σ
n ... number of scatterers in beam σ ... cross section of individual scatterer
naive picture: each scatterer has a certain “area” and is completely opaque absorption cross section
can also be used for elastic scattering ... into certain solid angle dΩ: dσ/dΩ
... or particle transformation differential cross section for a certain reaction
unit: “barn”: (10 fm)2 = 100 fm2 = 10-28 m2 = 10-24 cm2
51
fundamental interactions
interaction Strong electro-magnetic
Weak gravity
gauge boson
gluon photon W, Z graviton
mass 0 0 ~ 100 GeV 0
range 1 fm 10-3 fm
source “color charge”
electric charge
“weak charge”
mass
coupling ~ 1 α ~ 1/137 10-5 10-38
typical σ fm2 10-3 fm2 10-14 fm2 -
typical lifetime (s)
10-23 10-20 10-8 -
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Feynman diagrams
53
electron scattering(Bhabha scattering)
54
Feynman diagrams for electromagnetic interactions
55
Feynman diagramsfor Weak interactions
56
57
58
experimental setup for measuring deep-inelastic electron-proton scattering
(from Robert Hofstadter’s Nobel prize lecture, 1961)
59
60
61
color charge
color anticolor
RED CYAN
BLUE YELLOW
GREEN MAGENTA
Apart from their electric charge, quarks also have “color charge”. The particles which convey this interaction and keep the quarks together are called gluons.
62
Free quarks have never been observed, they always appear in bound states (quark confinement).
2 types of bound states are observed:
• 3 quarks of three different colors: baryons
• 2 quarks of a color and its anticolor: mesons
baryons
q
qq q
q
d
u
mesons
q
q
63
Feynman diagramsfor Strong interactions
64
3-jet event(Aleph experiment, LEP Collider, CERN, Geneva, Switzerland)
65
++
u
uu
u
d
d
us
c
d
D
s
u
b
b
d
uu
du
d
proton neutron
mesons
baryons
...
...
nucleus
He nucleus(-particle)
atom
matter
66
Robert Hofstadter (Nobel prize lecture, 1961)
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eeµµ
decay
ee
26 ns 2200 ns
scatteringe-
e+e+
KKp
p
e-
e+e+
What do we observe?
decays & scattering
KK
68
fermions (spin ½)
charge
0
-1
+2/3
-1/3
leptons quarks
the Standard Model
interactions
strong
weak
gravitation?
weakW, Z
electromagnetic
strongg
e
e
u c t
d s b
Astro
Accelerator
