how particles acquire mass...
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The discovery of the Higgs boson How particles acquire mass
3 S
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, UvA
Ivo van Vulpen, Institute of Physics (IoP)
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FNWI
Maurice ‘Sherlock’ Aalbers
Forensic Science
Christa ‘Darwin’ Testerink
Biology
10-15 m
Particle Physics
Elementary building blocks of nature
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Particles
Quarks
Leptons
Forces
1) Electromagnetism
2) Weak nuclear force
3) Strong nuclear force
Anti-Quarks
Anti-Leptons
Anti-particles neutrino
electron
Building blocks of protons/neutrons
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Comes at a price: extra scalar par:cle
The Higgs boson
€
SU(2)L ⊗U(1)Y ⊗ SU(3)C
The Standard Model:
Theory Reality
Massless (force-)particles Massive (force-)particles
≠ Describes all phenomena and measurement to high precision
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-‐ September 1964 -‐
Higgs field in the vacuum
“If I’m right there has to be a new scalar particle: the Higgs boson”
“It’s properties depend on it’s mass, … a mass that I cannot predict. Go find it!”
Theory Reality
Comes at a price: extra scalar par:cle
The Higgs boson
€
SU(2)L ⊗U(1)Y ⊗ SU(3)C
The Standard Model: =
The Higgs mechanism
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The Higgs boson Paris Hilton
(In)famous Higgs boson
Being famous is not the same as being important
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Energy and mass are equivalent you can create new particles
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The Large Hadron Collider (LHC) CERN, Geneva, Switzerland
2012: center-of mass energy = 8 TeV
8000 times the proton mass energy of a flying mosquito
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40 million collisions per second
beam 1
beam 2
Colliding beams of protons ATLAS detector
Paleis op de dam
Was an (unstable) Higgs boson produced ?
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Nikhef technicians at work
De Atlas pixel detector
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The SCT end-cap: constructed at Nikhef (across the street)
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µ+
µ-
2 muons produced in a proton-proton collision
Muon is the brother of the electron from the 2nd family
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Higgs ZZ 4µ candidate
4 muons produced in a proton-proton collision
Higgs boson ? Look for specific excess in collisions that contain: - 2 photons - 4 muons - …
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4 leptons
Probability to observe such an excess given the Standard Model without the Higgs boson ~ 10-9 We discovered something new!
Result of the ATLAS experiment (juli 2012)
Expected background
Expected Higgs signal (mh = 125 GeV)
Background fit Background + signal fit
4 lepton invariant mass [GeV]
Num
ber o
f ev
ents
Num
ber o
f ev
ents
Excess (peak) in the collisions where 2-photons or 4-leptons were produced
2 photon invariant mass [GeV]
E
xces
s
2 photons
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- The Large Hadron Collider works
- Discovered the Higgs* boson, so we think we understand how particles acquire mass
Discovery of a new particle
Standard Model of elementary particles
Few ‘tiny’ unresolved issues - why the large spread in masses ?
- Nature of dark matter ?
- Where did all the anti-matter go ?
- …
Hope to discover new phenomena
Supersymmetry ?
*well ok, a Higgs-boson like particle