GOD PARTICLE OR GOD-DAMN PARTICLE? WORK AT THE LARGE HADRON COLLIDER - DR VICTORIA MARTIN UNIVERSITY OF EDINBURGH IESIS WES MCMILLAN LECTURE
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God particle or god-damn particle?
Work at the Large Hadron Collider
Dr Victoria Martin
University of Edinburgh
IESIS WES McMillan Lecture
1
Why care about the Higgs boson?
2
Contents
•The world of particle physics and the need for the Higgs
boson
•A recipe: how to find a Higgs boson.
•The Large Hadron Collider: an engineering marvel.
•And, the results are in
•Higgsteria!
3
The World of Particle Physics
• Particle physics aims to understand the universe on the smallest
accessible length scales.
➡ We investigate the smallest components of matter − the
fundamental particles − that make up you and me.
➡ We investigate the interactions between these particles.
4
The World of Particle Physics
z
5
Interactions
• The interactions of the quarks and leptons are governed by four forces
• The strong nuclear force
Strongest to weakest
• The electromagnetic force
• The weak nuclear force
• Gravity
• The strong and weak forces are only felt over very, very short
distances e.g. (0.00000000000000001m = 10 −17 m)
• The electromagnetic and gravitational forces can be felt over large
distances.
6
Interactions
• The interactions of the quarks and leptons are governed by four forces
Force carrying particle
• The strong nuclear force
Strongest to weakest
gluons, g
• The electromagnetic force photons, γ
• The weak nuclear force “W and Z bosons”, W, Z
• Gravity
gravitons
• The strong and weak forces are only felt over very, very short
distances e.g. (0.00000000000000001m = 10 −17 m)
• The electromagnetic and gravitational forces can be felt over large
distances.
6
The “Standard Model” of Particle Physics
• The Standard Model of Particle Physics describes the quarks, leptons
and the strong, weak and electromagnetic interactions between using:
• Einstein’s theory of special relativity
(physics of the very fast)
• Quantum physics (physics of the very
small)
• Symmetries (observed in many areas of
physics)
• Possibly the best tested and validated theory
in physics!
7
The W-boson
• The effects of the W-boson were know since Enrico Fermi in the 1930s
• The W-boson was discovered by the UA1 and UA2 experiments at
CERN, 30 years ago.
8
The Z-boson
• The effects of the Z-boson were discovered in 1973 at the
Gargamelle experiment at CERN.
• The UA1 and UA2 experiments at CERN also discovered the Z-boson.
9W-boson in the Sun
• The W-boson can change the nature of
particles:
➡ it can turns protons into neutrons,
and vice-versa
• proton → neutron + anti-electron + neutrino
H + H → 2H + e+ + νe
• W-bosons facilitate the first step of
Hydrogen gas burning in the sun!
10The Higgs Mechanism
• Proposed The Higgs Mechanism was
proposed in 1964 separately by Higgs;
Brout & Englert; Guralnik, Hagen &
Kibble.
• The Higgs mechanism an proposes an extra potential:
V (φ) = −µ2 φ2 + λφ4
V(ϕ)
• The depth of the potential is
proportional to the W boson mass.
• Also related to the Z-boson mass.
11The Higgs Mechanism
• Proposed The Higgs Mechanism was
proposed in 1964 separately by Higgs;
Brout & Englert; Guralnik, Hagen &
Kibble.
• The Higgs mechanism an proposes an extra potential:
V (φ) = −µ2 φ2 + λφ4
V(ϕ)
• The depth of the potential is
proportional to the W boson mass.
• Also related to the Z-boson mass.
11The Higgs Boson
12The Higgs Boson
In 1964 Peter Higgs was the only one of the six to observe this
potential would also create a new boson: the Higgs boson!
12The Higgs Mechanism
1. IESIS members before the James
Watt Dinner; all free to move around
the room.
13The Higgs Mechanism
1. IESIS members before the James
Watt Dinner; all free to move around
the room.
13The Higgs Mechanism
1. IESIS members before the James 2. In comes Muffy Calder; everyone
Watt Dinner; all free to move around wants to speak to her.
the room. Everyone crowds around her. Muffy
is not free to move around; she has
gained inertia by interacting with
the crowd.
13The Higgs Mechanism
1. IESIS members before the James 2. In comes Muffy Calder; everyone
Watt Dinner; all free to move around wants to speak to her.
the room. Everyone crowds around her. Muffy
is not free to move around; she has
gained inertia by interacting with
the crowd.
This is analogous to how the particles acquire mass: by interacting with
the Higgs field. Science advisors of different popularity gain different
masses.
13The Higgs Boson
3. Later in the evening; IESIS
members enjoying a digestive.
A rumour enters the room: Muffy
has convinced Alex Salmond to
appoint a minster for Engineering &
Science !
14The Higgs Boson
3. Later in the evening; IESIS
members enjoying a digestive.
A rumour enters the room: Muffy
has convinced Alex Salmond to
appoint a minster for Engineering &
Science !
14The Higgs Boson
3. Later in the evening; IESIS
members enjoying a digestive.
A rumour enters the room: Muffy
has convinced Alex Salmond to
appoint a minster for Engineering &
Science !
4. Everyone gather together to
spread the rumour. The group of
engineers acquire inertia.
14The Higgs Boson
3. Later in the evening; IESIS
members enjoying a digestive.
A rumour enters the room: Muffy
has convinced Alex Salmond to
appoint a minster for Engineering &
Science !
4. Everyone gather together to
spread the rumour. The group of
engineers acquire inertia.
The clustering of the field of engineers is as if a new massive particle has
formed. This is the Higgs boson.
14Q: Why care about the Higgs boson?
A: The Higgs boson makes the W-boson
heavy.
The heaviness of the W-boson makes
the burning of Hydrogen in the sun
relatively slow.
The slow burning means the sun will
support life on earth for the next one
billion years!
15How to find a Higgs
16A note on units
Particle physicists don’t use SI units. We typically use:
• GeV or TeV for energy.
• 1 GeV is 1.6 × 10−10 Joules.
• 1 TeV is 1.6 × 10−7 Joules, or about the energy of a flying
mosquito
• GeV/c 2 for mass. 1 GeV/c2 is:
• 3.1 × 10−23 grams
• 0.93 atomic mass units
• roughly the mass of a proton
17A simple recipe
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
2. Smash together.
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
2. Smash together.
3. One in 100 billion collisions will form a
Higgs boson.
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
2. Smash together.
3. One in 100 billion collisions will form a
Higgs boson.
4. Once formed, the Higgs boson will decay
after 10−22 seconds.
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
2. Smash together.
3. One in 100 billion collisions will form a
Higgs boson.
4. Once formed, the Higgs boson will decay
after 10−22 seconds.
5. Assemble a highly sophisticated, state-of-
the-art detector around the collision
point.
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
2. Smash together.
3. One in 100 billion collisions will form a
Higgs boson.
4. Once formed, the Higgs boson will decay
after 10−22 seconds.
5. Assemble a highly sophisticated, state-of-
the-art detector around the collision
point.
6. Observe the particles produced from the
Higgs boson decay.
18A simple recipe
1. Take two very high energy protons (fresh
from CERN).
2. Smash together.
3. One in 100 billion collisions will form a
Higgs boson.
4. Once formed, the Higgs boson will decay
after 10−22 seconds.
5. Assemble a highly sophisticated, state-of-
the-art detector around the collision
point.
6. Observe the particles produced from the
Higgs boson decay.
7. Repeat 25 million times a second for 1½
years.
18CERN
• CERN is the European
Organization for Nuclear
Research (Organisation
européenne pour la recherche
nucléaire).
• Located at the Franco-Swiss border
near Geneva, Switzerland.
• A collaboration of 20 European
countries, including the UK.
• 3,900 employees
• 10,000 visiting scientists and
engineers from 608 Universities and
Research facilities (including
Edinburgh and Glasgow!)
• CERN provides particle
accelerators, used by 17
experiments.
19CERN’s Large Hadron Collider
• The Large Hadron Collider (LHC) is current CERN’s main activity.
• Six experiments use the LHC.
• A chain of accelerators, developed over decades, accelerates protons to 4 TeV,
the highest ever energy for an accelerator.
• From 2015, the LHC will run at 8 TeV.
• Linear accelerator: up to 50 MeV
• Proton Synchroton Booster: 50 MeV → 1.4 GeV
• Proton Synchroton: 1.4 GeV → 26 GeV
• Super Proton Synchroton: 26 GeV → 450 GeV
• Large Hadron Collider: 450 GeV → 4 TeV
20CERN’s Large Hadron Collider
• The Large Hadron Collider (LHC) is current CERN’s main activity.
• Six experiments use the LHC.
• A chain of accelerators, developed over decades, accelerates protons to 4 TeV,
the highest ever energy for an accelerator.
• From 2015, the LHC will run at 8 TeV.
• Linear accelerator: up to 50 MeV
• Proton Synchroton Booster: 50 MeV → 1.4 GeV
• Proton Synchroton: 1.4 GeV → 26 GeV
• Super Proton Synchroton: 26 GeV → 450 GeV
• Large Hadron Collider: 450 GeV → 4 TeV
20LHC: Facts and Figures
21LHC: Facts and Figures
21LHC: Facts and Figures
21LHC: Facts and Figures
21LHC: Facts and Figures
• 27km circumference
• 50 to 175 m underground
• 9300 magnets used to
keep the beam in orbit
• 1232 are dipole magnets:
• 14.3 m long,
• operate at 1.9 K,
• provides 8.3 Tesla,
• cost 500,000 CHF each
21LHC: Facts and Figures
22LHC: Facts and Figures
•The ultimate atom
smasher:
•smashing 1011
protons into 1011
protons,
•25 million times a
second,
•at 4 points around
the circle.
•The energy circulating
around the LHC is
equivalent to a aircraft
carrier travelling at 10
knots
22Finding the Higgs
• One in every 10 10 collisions in the LHC will form a Higgs boson.
• Once formed, the Higgs boson decays into other particles in 10−22 seconds.
• We have a pretty good idea of what the Higgs bosons will decay into…
➡ pairs of Z-bosons: H→ZZ
➡ pairs of W-bosons: H→WW
➡ pairs of photons: H→γγ
➡ pairs of b-quarks: H→bb̅
➡ pairs of τ-leptons: H→τ+τ−
• A waiting game. We sift through all of the data from all the collisions and
look for pairs of these particles.
23Under the Genevois Soil
24The ATLAS Experiment
25The ATLAS Experiment
25The ATLAS Experiment
25ATLAS In Real Life
• https://www.youtube.com/watch?v=QA3bUz9nodU
26ATLAS In Real Life
ATLAS is essentially the largest and most
sophisticated digital camera ever built
45 meters long
25 meters high
7,000 tonnes
• https://www.youtube.com/watch?v=QA3bUz9nodU
26ATLAS Collaboration
• 3,000 physicists at 175 institutions in 37 countries
• 25 from the University of Edinburgh
27ATLAS is not alone in this endeavour. Our friendly
rivals CMS (Compact Muon Solenoid) built this:
28ATLAS is not alone in this endeavour. Our friendly
rivals CMS (Compact Muon Solenoid) built this:
28Higgs
Boson
Decay
to
Two
Photons
29Higgs
Boson
Decay
to
Two
Photons
29H→ γγ
Decay
The Higgs boson can
decay into two
“photons”: H→ γγ
Photons are particles
of lights
Right: two very high
energy photons
detected in ATLAS
30Advanced Higgs
Boson Physics
31Advanced Higgs
Boson Physics
• The Higgs boson also can decay into
Z-bosons: H→ZZ
• Z-bosons themselves also decay
very quickly.
• Search for Z-bosons decay products:
e.g. H→ZZ→e+e−e+e− 4 electrons
31Advanced Higgs
Boson Physics
• The Higgs boson also can decay into
Z-bosons: H→ZZ
• Z-bosons themselves also decay
very quickly.
• Search for Z-bosons decay products:
e.g. H→ZZ→e+e−e+e− 4 electrons
31Advanced Higgs
Boson Physics
• The Higgs boson also can decay into
Z-bosons: H→ZZ
• Z-bosons themselves also decay
very quickly.
• Search for Z-bosons decay products:
e.g. H→ZZ→e+e−e+e− 4 electrons
• Right: Picture of four electrons in
ATLAS from a collision.
• The other 99,999,999 in
10,000,000,000 collisions
(where no Higgs boson is produced)
can produce a similar picture.
• The challenge is to work out if each
individual picture is from a Higgs
boson, or from something else!
31+ − +
H→ZZ→µ µ µ µ −
32ATLAS Higgs Search Result
• Mass of photon pairs
from LHC collisions,
detected by ATLAS.
• Small excess of events
at mass mγγ ~ 125 GeV/c2
• We believe this is due to
Higgs bosons with a mass
of mH ~ 125 GeV
3334
H→ZZ results
Compatible with a peak at m4ℓ ~ 125 GeV/c2 in
addition to background processes.
35Higgsteria!
364 th of July 2012 at CERN
374 th of July 2012 at CERN
3738
Me on the telly!
39Some letters…
40Some emails...
Dear Sirs,
We are a craft beer micro company (Ca
l'Arenys- GUINEU BEER), and we would like
to make a Brewing Special Edition (10hl)
as an Homage to Mr. Higgs
First of all we would like to know if
there is any concern about it.
The idea is absolutely NON lucrative
-We would like to know, if possible, if
Mr. Higgs likes beer and what styles does
he prefer in order to adapt our receipt.
Best Regards
Xavier Serra
info@calarenys.com
Ca l'Arenys brewing Manager
Valls de Torruella ( Barcelona )
Spain
41Some emails... Dear Sirs,
Some emails... Dear Sirs,
September 2012: Published!
Observation of a New Particle in the
Search for the Standard Model Higgs
Boson with the ATLAS Detector at the
LHC Phys. Lett. B 716 (2012) 1-29
15 pages plus 14 page author list!
“Clear evidence for the production of
a neutral boson with a measured mass
of 126.0 ± 0.4(stat) ± 0.4(sys) GeV is
presented.”
Observation of a new boson at a mass of
125 GeV with the CMS experiment at the
LHC Phys. Lett. B 716 (2012) 30–61
15 pages plus 16 page author list!
“An excess of events is observed […]
signalling the production of a new
particle. [… with] a mass of 125.3 ± 0.4
(stat.) ± 0.5 (syst.) GeV.”
42Peter Higgs visits ATLAS
43Outlook: the LHC
• This year and next year the LHC is
being upgraded:
• All connections (welds) between
the magnets are being upgraded
• ATLAS and CMS experiments also
being upgraded: new detecting
equipment added.
• The LHC will start again early 2015
at twice the energy: 13 or 14 TeV.
• We’ll run until 2019.
• If funding is forthcoming future
plan is to further upgrade the LHC
and the detectors and run into the
late 2020’s!
• For the 2020s, plans are currently being developed to keep
44
running with higher intensity beams.Outlook: the Higgs boson
• ATLAS and CMS physicists still analysing the
data taken in the last few months of 2012.
• So far, all indications say new particle with
mass is exactly as expected: it’s “a Higgs
boson”.
• The new LHC run will allow us to make
further, more precise, measurements of
our Higgs boson.
• Only then we can find if our boson behaves
precisely as the Standard Model of particle
physics predicts…
• or hopefully we’ll discover our Higgs
boson is subtly different.
45Outlook: the Higgs boson
• ATLAS and CMS physicists still analysing the
data taken in the last few months of 2012.
• So far, all indications say new particle with
mass is exactly as expected: it’s “a Higgs
boson”.
• The new LHC run will allow us to make
further, more precise, measurements of
our Higgs boson.
• Only then we can find if our boson behaves
precisely as the Standard Model of particle
physics predicts…
• or hopefully we’ll discover our Higgs
boson is subtly different.
45Outlook: the Higgs boson
• ATLAS and CMS physicists still analysing the
data taken in the last few months of 2012.
• So far, all indications say new particle with
mass is exactly as expected: it’s “a Higgs
boson”.
• The new LHC run will allow us to make
further, more precise, measurements of
our Higgs boson.
• Only then we can find if our boson behaves
precisely as the Standard Model of particle
physics predicts…
• or hopefully we’ll discover our Higgs
boson is subtly different.
• Of course, other new particles could yet be discovered by the LHC.
45Thanks to: the ATLAS Edinburgh Team
4647
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