Buxton & District U3A Science Discussion Group

“Higgs Boson – what is it?”

John Estruch19 October 2012

Buxton & District

Science DiscussionHiggs Boson

• What is it?

• What difference will finding it make to my life?

• How much did it cost to look for it? Was it worthwhile?

Buxton & District

Science DiscussionWhat are we going to talk about

• A little bit of history• The standard model• The Large Hadron Collider (LHC)• So what does it mean?

Buxton & District

Science DiscussionWhen I did my O and A levels

Forces

Gravity

Electricity & Magnetism

Particles

ElectronsProtonsNeutrons

Heard of but didn’t study until university

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

Classical Physics (pre-1900) Beginning of modern Physics

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Science DiscussionWhat 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

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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Science DiscussionAn aside

Where did the Physicists get the particle names from:Atom –

Proton –Electron –Hadron –Lepton –Quark –

from Latin atomus "indivisible particle," from Greek atomos "uncut, unhewn; indivisible,"from Greek “protos” meaning “first”from “electric” meaning “resembling amber”from Greek “hadros” meaning “thick, bulky”from Greek “leptos” meaning “small, slight”from “Three quarks for Muster Mark” in James Joyce's Finnegans Wake meaning ???????

Buxton & District

Science DiscussionWhat are we going to talk about

• A little bit of history• The standard model• The Large Hadron Collider (LHC)• So what does it mean?

Buxton & District

Science DiscussionWhat 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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Science DiscussionThe Higgs mechanism

• 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 itPhysicists hate it

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Science DiscussionIs the Standard Model a good theory?

Yes• Describes well particles & behaviour

known at the time• Predicted particles subsequently

found:– 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?

Buxton & District

Science DiscussionWhat are we going to talk about

• A little bit of history• The standard model• The Large Hadron Collider (LHC)• So what does it mean?

Buxton & District

Science DiscussionWhy particle accelerators?

• 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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Science DiscussionLHC

• 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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Science DiscussionDetectors

• 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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Science DiscussionAnother 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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Science DiscussionSo what have they found?

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.

Buxton & District

Science DiscussionWhat are we going to talk about

• A little bit of history• The standard model• The Large Hadron Collider (LHC)• So what does it mean?

Buxton & District

Science DiscussionWill the Higgs Boson change my life?

No! (not in the short term)

No cure for cancerNo solution to world hungerNo solution to global warmingNo new mobile phones

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Science DiscussionIs there any value in pure science?

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.• 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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Science DiscussionMore than pure Physics

Technology developments from CERN/LHC:• IT developments:

– WWW – 1991– LHC Computing Grid 2005

• Technology Developments– Superconducting magnets– Large scale high vacuum

• 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.

• Lots more…….

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Science DiscussionQuestions?