Transcript Document

Buxton & District U3A
Science Discussion Group
“Higgs Boson – what is it?”
John Estruch
19 October 2012
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Higgs Boson
Science Discussion
• What is it?
• What difference will finding it make to my life?
• How much did it cost to look for it? Was it
worthwhile?
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What are we going to talk about
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A little bit of history
The standard model
The Large Hadron Collider (LHC)
So what does it mean?
Science Discussion
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When I did my O and A levels
Forces
Particles
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Heard of but didn’t study until university
Gravity
Electrons
Protons
Neutrons
Electricity &
Magnetism
Classical Physics (pre-1900)
Relativity (very fast)
•Speed of light invariant
•Can’t exceed light speed
•Energy/mass equivalence
Quantum Mechanics (very
small)
•Energy “quantised”
•Wave-particle duality
•Uncertainty principle
•Pauli exclusion principle
Beginning of modern Physics
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What was next in Modern Physics?
New Forces
Strong Nuclear Force
•Glues nucleus together
•100 times stronger
than electromagnetism
•Very short range
Weak Nuclear Force
•Explains β radiation
•1010 times weaker than
electromagnetism
•Very short range
Science Discussion
New Particles (created in accelerators)
Leptons
•Includes electron
•Feel
electromagnetic
& weak forces (&
gravity) only
Hadrons
•Includes proton
•Feel electromagnetic,
weak & strong forces (&
gravity)
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An aside
Science Discussion
Where did the Physicists get the particle names from:
from Latin atomus "indivisible particle," from Greek
Atom –
atomos "uncut, unhewn; indivisible,"
Proton – from Greek “protos” meaning “first”
Electron – from “electric” meaning “resembling amber”
Hadron – from Greek “hadros” meaning “thick, bulky”
Lepton – from Greek “leptos” meaning “small, slight”
Quark – from “Three quarks for Muster Mark” in James
Joyce's Finnegans Wake meaning ???????
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What are we going to talk about
•
•
•
•
A little bit of history
The standard model
The Large Hadron Collider (LHC)
So what does it mean?
Science Discussion
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What is the standard model
A “quantum field theory” which:
• Was gradually developed by many people
during the 1960s and 1970s
• Incorporates three of the four forces:
• Electromagnetic
• Weak
• Strong
• Describes the sub-atomic particles
• Quarks (which make up the hadrons)
• Leptons
• “Gauge Bosons” which “mediate” the
forces (they “carry” the force)
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The Higgs mechanism
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• Also known as Englert-Brout-Higgs-Guralnik-Hagen-Kibble
mechanism
• Developed around 1963-1964
• Without it the theory models only “massless” particles
• Implies a new massive boson
“the Higgs leads to all the matter in the universe” – hence “the God
Particle”
Press love it
Physicists hate it
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Is the Standard Model a good theory?
Science Discussion
Yes
• Describes well particles &
behaviour known at the time
• Predicted particles subsequently
found:
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Tau (1975), Tau neutrino (2000)
Bottom quark (1977)
W+,W-, Z0 (1983)
Top quark (1995)
But it’s not the final answer
• Does not incorporate gravity
• Cannot explain large amount of
“dark matter” / “dark energy”
required for current cosmological
theories
• Some claim it is “inelegant”
The big test
• Does the Higgs Boson exist?
• Is the Higgs Field real?
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What are we going to talk about
•
•
•
•
A little bit of history
The standard model
The Large Hadron Collider (LHC)
So what does it mean?
Science Discussion
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Why particle accelerators?
Science Discussion
• Only lightest of each type of particle exists in a “low
energy” environment (i.e. electron, proton, neutron)
• If a heavier particle exists it quickly tends to a lower
energy state (i.e. decays to a lighter particle)
• Heavier particles can exist in high energy environments
(e.g. Shortly after Big Bang)
• If we accelerate particles to high energy & collide them
we can briefly bring heavier particles into existence
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LHC
Science Discussion
• Largest accelerator to date
• 27km circumference tunnel
• 2 beams of protons circulate in opposite
directions at 11,000 revs per second
• Beams cross at 4 points – protons can
collide here
• Energy enough to create particles 7,000 times
heavier than proton
• Operates at -271.3°C (1.9 K) – colder than space
• Vacuum of 10-13 Atm – less gas than the moon
• Consumes 120MW of electric power (6 x Buxton)
• Cost about £2.6bn
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Detectors
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Higgs Boson will decay before it leaves beam pipe – so we can’t see it.
So we look for the shower of particles it produces.
Detector records data about particles.
Complex computer models figure out what came from the collision
Atlas
• 45m long, 25m high, 7,000 tons
• 3,000 physicists, 174 universities,
38 countries
• 3,200 terabytes of data per year
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Another aside
BEBC (Big European Bubble
Chamber)
• The apparatus I used for my PhD
• Now sits in CERN Microcosm
Museum, in the garden
• On this visit in 2003 the guide said
“that was how they did
experiments in the olden days”
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So what have they found?
Science Discussion
July 4 2012 Atlas & CMS teams each announce:
Found a boson with mass between 125GeV/C2
and 126GeV/C2 which is “consistent with” the/a
Higgs Boson
Actually they have also done a lot of other physics but that
isn’t very newsworthy.
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What are we going to talk about
•
•
•
•
A little bit of history
The standard model
The Large Hadron Collider (LHC)
So what does it mean?
Science Discussion
Will the Higgs Boson change my
life?
No!
(not in the short term)
No cure for cancer
No solution to world hunger
No solution to global warming
No new mobile phones
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Science Discussion
Is there any value in pure
science?
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Science Discussion
Standard model is where Quantum Mechanics was 60-90 years ago:
• Esoteric
• Public know very little about it
• No immediate practical use
But Quantum Mechanics led to:
• Most modern Chemistry & Biochemistry
– Materials, medicines etc.
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Understanding of DNA (according to Francis Crick)
MRI Scanners
Transistor, silicon chip, CRT tubes, (imagine no TV, no computers, no electronics!)
etc.
etc.
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More than pure Physics
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Technology developments from CERN/LHC:
• IT developments:
– WWW – 1991
– LHC Computing Grid 2005
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Technology Developments
– Superconducting magnets
– Large scale high vacuum
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Control systems:
– You try keeping many bunches with 1 billion protons each moving in opposite directions in 6.3
cm pipes in 27km circuit at 99.9999991% of the speed of light without touching the sides and
making sure they cross in exactly the right places.
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Lots more…….
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Questions?
Science Discussion