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QUARKS, GLUONS, HIGGS BOSONS
AND OTHER EXOTIC CREATURES
Lorenzo Magnea
Università di Torino - INFN Torino
Scuola di Fisica, Torino, 29/01/13
Outline
• The Size of
Things
• The Machine
• The Standard Model of Elementary Particles
• Feynman Diagrams
• Collision: the Movie
• A Higgs Boson Factory
THE SIZE OF THINGS
A good map correctly reproduces relative sizes
Bad maps distort relative sizes
The solar system?
An atom?
Planet Earth
The world in scale 1:1000000000
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
• Diameter of the Sun: 1,4 meters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
• Diameter of the Sun: 1,4 meters
• Average radius of Jupiter’s orbit: 780 meters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
• Diameter of the Sun: 1,4 meters
• Average radius of Jupiter’s orbit: 780 meters
• Jupiter’s diameter: 14 centimeters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
• Diameter of the Sun: 1,4 meters
• Average radius of Jupiter’s orbit: 780 meters
• Jupiter’s diameter: 14 centimeters
• Average radius of Pluto’s orbit: 5,9 kilometers
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
• Diameter of the Sun: 1,4 meters
• Average radius of Jupiter’s orbit: 780 meters
• Jupiter’s diameter: 14 centimeters
• Average radius of Pluto’s orbit: 5,9 kilometers
• Pluto’s diameter: 2,3 millimeters
The world in scale 1:1000000000
• Diameter of the Earth: 1,2 centimeters
• Average distance Moon-Earth: 38 centimeters
• Diameter of the Moon: 3,4 millimeters
• Distance Earth-Sun: 150 meters
• Diameter of the Sun: 1,4 meters
• Average radius of Jupiter’s orbit: 780 meters
• Jupiter’s diameter: 14 centimeters
• Average radius of Pluto’s orbit: 5,9 kilometers
• Pluto’s diameter: 2,3 millimeters
• Distance to Alpha Centauri: 41300 kilometers
The world in scale 1:1000000000
The speed of light
(provided we don’t change the time scale!)
The world in scale 1:1000000000
The speed of light
(provided we don’t change the time scale!)
30 centimeters per second
(approximately 8 minutes to travel 150 meters ...)
The world in scale 10000000000000:1
The world in scale 10000000000000:1
• Proton radius: 8 millimeters
The world in scale 10000000000000:1
• Proton radius: 8 millimeters
• Hydrogen atom radius: 500 meters
The world in scale 10000000000000:1
• Proton radius: 8 millimeters
• Hydrogen atom radius: 500 meters
• Typical size of a virus:
10 kilometers
The world in scale 10000000000000:1
• Proton radius: 8 millimeters
• Hydrogen atom radius: 500 meters
• Typical size of a virus:
10 kilometers
• Diameter of a human red blood cell:
700 kilometers
The world in scale 10000000000000:1
• Proton radius: 8 millimeters
• Hydrogen atom radius: 500 meters
• Typical size of a virus:
10 kilometers
• Diameter of a human red blood cell:
700 kilometers
• A meter:
10 billion kilometers
The world in scale 10000000000000:1
• Proton radius: 8 millimeters
• Hydrogen atom radius: 500 meters
• Typical size of a virus:
10 kilometers
• Diameter of a human red blood cell:
700 kilometers
• A meter: 10 billion chilometers
• A kilometer: 1 light-year
The known Universe
26
10
meters
Hubble Deep Field
-19
10
meters
An LHC event
THE MACHINE
The Large Hadron Collider: a geographical perspective
The Large Hadron Collider: a biker’s perspective
The Large Hadron Collider: some data
• The ring: 27 km, depth between 50 and 180 m.
• Proton energy: target 7 TeV (now 4). 1 Tev ∼ 1.6 10-7 J.
• Cost: ∼ 8 billion €, including detectors and computing.
• Superconducting magnets: ∼104, 1232 dipoles, 8T field.
• Dipole temperature: 1.9 oK ∼ − 271.3 oC .
• Proton bunches: target 2800 bunches, 1011 protons each.
• Beam energy: target 350 MJ ∼ 1 TGV at 150 Km/h.
• Number of collisions: (40M x 20 x 4)/sec.
• Data flow: 1GB/sec ∼ 15 PB/year
• Four major detectors: ATLAS, CMS, ALICE, LHCb.
One of 1232 15m. dipole magnets being lowered into the LHC tunnel
A cross-section of an LHC dipole magnet
World-wide nodes of the LHC Computing Grid
Anatomy of the CMS Detector
The CMS Detector in real life: endcap with technician
Anatomy of the ATLAS Detector
The ATLAS Detector in the building stage
ATLAS event display: production of a Z boson decaying into muons
ATLAS event display: production of a Z boson decaying into electrons
CMS event display: production of a Higgs boson decaying into two photons
THE STANDARD MODEL
OF ELEMENTARY PARTICLES
All elementary particles according to the Standard Model
Ordinary matter is built up of a small subset of the SM particles
Other gauge bosons, mediating weak
(W, Z), and strong interactions (the
gluons g), only act at very short
distances, less than the proton radius,
albeit for very different reasons
(confinement and symmetry breaking)
Nature provides two extra copies (second and third
generation) of the particles comprising ordinary matter
(first generation). The copies have the same charges and
interactions, but a larger mass
Other gauge bosons, mediating weak
(W, Z), and strong interactions (the
gluons g), only act at very short
distances, less than the proton radius,
albeit for very different reasons
(confinement and symmetry breaking)
Who ordered
that?
Nature provides two extra copies (second and third
generation) of the particles comprising ordinary matter
(first generation). The copies have the same charges and
interactions, but a larger mass
Isaac Rabi
Other gauge bosons, mediating weak
(W, Z), and strong interactions (the
gluons g), only act at very short
distances, less than the proton radius,
albeit for very different reasons
(confinement and symmetry breaking)
It’s about
time to take
away that
question mark!
Peter Higgs
Nature provides two extra copies (second and third
generation) of the particles comprising ordinary matter
(first generation). The copies have the same charges and
interactions, but a larger mass
Isaac Rabi
Who ordered
that?
Theoretical calculations for LHC
• New physics emerges as a deviation from SM predictions
• Theoreticians compute scattering cross sections, σ:
✴Probabilities
for a chosen final state expressed as effective target areas
✴Intricacies
of the initial state are dealt with by a factorization theorem
⇤⌅ 1
⇥
h1 h2
2
ab
2
⇥H (S, Q ) =
dx1 dx2 fa/h1 (x1 , µf ) fb/h2 (x2 , µf ) ⇥
⇧P x1 x2 S, Q , µf
a,b
0
2
b s, Q , µf
1
=
2s
LHC as a quark and gluon Collider
Z
2
dLIPS(ki ) A s, Q , ki , µf
2
• Factorization proofs are highly non-trivial.
• Gluons may rearrange partons before collision.
• Correlations are suppressed by powers of Λ/Q.
• Parton distributions are universal and
determined by experiment
• Parton cross sections are process-specific and
computable in perturbation theory.
Cross Sections and Luminosity
• (luminosity) x (cross section) = event rate.
• Interesting events are extremely rare.
• Ten billion collisions for one Higgs boson.
• We need many for a significant result.
• High luminosity is crucial
• High theoretical precision is needed.
• Sophisticated statistical techniques as well.
• Completely new phenomena might appear.
• It has not happened thus far
• Black holes are ruled out ....
Cross sections for various LHC processes
FEYNMAN’S DIAGRAMS
Richard Feynman
• A great teacher, a decent percussionist, a safecracker in his free time, ....
• Nobel prize for Physics in 1965.
• Participated in the Manhattan Project.
• Was one of the developers of Quantum
Electrodynamics (QED) , the first Quantum
Field Theory and a cornerstone of the
Standard Model.
• Feynman developed an elegant and intuitive
method to represent graphically the
calculations of quantum field theory.
• The method is applicable whenever the
Richard Feynman (1918-1988)
interactions between particles are not too
strong: it guides the construction of the
perturbative expansion.
A Feynman diagram for the process
(electron + positron)
(muon + antimuon)
Space
Time
A Feynman diagram for the process
(electron + positron)
(muon + antimuon)
Electron
Every kind of line corresponds to
the propagation of a species of particle.
Space
Antimuon
Photon
Muon
Positron
Time
A Feynman diagram for the process
(electron + positron)
(muon + antimuon)
Electron
Every kind of line corresponds to
the propagation of a species of particle.
Space
Antimuon
Photon
Arrows distinguish particles from
antiparticles (arrows `towards the past’)
Muon
Positron
Time
A Feynman diagram for the process
(electron + positron)
(muon + antimuon)
Every graphical element is associated to a precise mathematical expression
u(p1)
v(p2)
Every external particle carries
a factor of its wave function, giving
its spin, energy and momentum.
v(p3)
u(p4)
Every graphical element is associated to a precise mathematical expression
u(p1)
v(p3)
Every external particle carries
a factor of its wave function, giving
its spin, energy and momentum.
Every vertex carries a coupling
constant: the charge appropriate
for the relevant interaction.
e
v(p2)
e
u(p4)
Every graphical element is associated to a precise mathematical expression
u(p1)
v(p3)
Every external particle carries
a factor of its wave function, giving
its spin, energy and momentum.
Every vertex carries a coupling
constant: the charge appropriate
for the relevant interaction.
e
e
1/(E2 - p2 - m2)
v(p2)
Every internal line is corresponds
to a `virtual’ particle, which has short
lifetime. The propagator gives
the probability amplitude for its survival
u(p4)
Every graphical element is associated to a precise mathematical expression
The process is algorithmic and can be implemented on a computer
Is it really that easy?
Is it really that easy?
No.
A complicated, but realistic and important process
A complicated, but realistic and important process
(proton + antiproton)
up + antiup
top + antitop
...
A complicated, but realistic and important process
b
u
e
t
g
t
W+
W
u
(proton + antiproton)
νe
c
s
b
up + antiup
top + antitop
...
COLLISION: THE MOVIE
A HIGGS BOSON FACTORY
The Higgs Field
Particles acquire a mass because the vacuum ... is not empty.
The Higgs Boson
• The Higgs boson is a local perturbation in the Higgs
field fluctuating around its constant vacuum value.
• The Higgs boson has spin 0, the first elementary particle
ever discovered with this property.
• The Higgs boson mass is now accurately determined to
be between 125 and 126 GeV.
A Higgs-like potential
• The Higgs boson interacts with other particles with an
intensity proportional to their mass.
m
• Thus the Higgs boson is very difficult to observe: it
interacts very weakly with light particles, which are the
most common and easy to produce.
• It is necessary to produce very heavy particles, in great
abundance, and to detect their decay products in the
midst of the strong interaction background.
Interaction strength
proportional to the mass
The Higgs Field
One of many popularizations found on the internet ...
The Higgs boson
One of the main mechanisms of production and detection of the Higgs boson at LHC
The Higgs boson
g
γ
t
t
h
One of the main mechanisms of production and detection of the Higgs boson at LHC
The Higgs boson
A candidate event with a Higgs boson decaying to two photons
The Higgs boson
A candidate event with a Higgs boson decaying to four muons
The Higgs boson
The distribution of Higgs bosons decaying into two photons in CMS (2012)
Summarizing
• Our knowledge of the universe spans 45 orders of magnitude.
• We are edging into the 46th, exploring the TeV energy scale.
• The Standard Model of elementary particles is 50 years old.
• It is alive and kicking.
• The last missing piece of the SM been found.
• The SM is not a complete theory!
• We hope to get hints of what lies beyond in the next LHC run.
Thank you!