Physics at the TeV Scale

1
Physics at the TeV Scale
Phil Allport University of Liverpool

• Particles and forces
• The known particle spectrum
• The need for TeV energies
• The origin of mass
• The path to Grand Unification
• Supersymmetry
• Conclusions

2
Introduction

• Particle physics studies the fundamental
  building blocks of nature and their
  interactions.
• The 20th Century yielded
• an explosion of particles and interactions
• a beautiful explanation in terms of
  symmetries
• hints of deeper unity in nature.
• We are on the verge of a revolution in
  understanding
• new forces and symmetries
  (super-symmetries ?)
• complexity turned to simplicity
• the origin of mass, unification of the
  forces
• Einsteins dream of deeper unification
  (Gravity?)

3
Forces in Physics
Classically, forces are described by
charges
and fields



Field
4
Forces in Particle Physics
Forces in Physics
Low energies and large distances ? classical
mechanics
High energies and small distances ? quantum
mechanics
Continuous field ? exchange of quanta
For Electromagnetism


The quanta are photons, ?
Other forces are mediated by other particles ...
5
The Forces of Nature
Spin
Mass
Electro- magnetic
Photon, ?
Atom
0
1
Nucleus
Gluon, g
0
1
Strong
W?
?-decay, sunshine
80 GeV
1
Weak
Z0
91 GeV
1
They are all bosons (integer spin)
Gravity
Not directly accessible at accelerators
6
Mediation of the Forces
Electron
The strength of the force
??
?
??
Positron
Feynman Diagram
7
The Matter Particles
u
mass mp 1.7 10-27 kg size 10-15 m charge 1
Proton
u
d
(Neutron)
(charge 0)
mass 10-11 mp ? size 0 ? charge 0
Neutrino
?
Mass 5. 10 - 4 mp size 0 ? charge -1
Electron
e
8
The First Generation
Quarks with 3 colours charge 2/3 charge
- 1/3
u
u
u
?
d
e
d
d
All these matter particles are spin-1/2
? all are fermions
velocity
? 2 helicity states
Leptons charge 0 charge - 1
?
Left Handed
Right Handed
e
9
The Dirac Equation
centenary
Special Relativity Quantum Mechanics
An equation that describes spin-1/2 particles
Correct magnetic moments
Predicted the existence of antimatter
? A further doubling of the spectrum ...
10
The First Generation
s
Cosmic rays
u
u
u
?e
uc
uc
uc
d
e
d
d
dc
ec
dc
dc
Accelerators
-uc
uc
u
d
dc
Multiplicity of states
uc
u
d
dc
d
dc
? Completion of a pattern?
u
ec
e
?e
Number of generations ?...
11
Precision ee- Measurements
Ngen 2.9841?0.0083
LEP ee-, Ecms 210 GeV
LHC pp, Ecms 14 TeV
CERN
12
The Known-Particle Spectrum
Spin ½
Spin 1
Spin 0
10 - 1 GeV
2 GeV
200 GeV
10-11 GeV
5 10 - 4 GeV
?1
?
e
Escale
?
t
?
?
c
?2
?3
Z0
W?
s
d
?
u
b
0
?, g
?
u
?
s
c
?
e
d
13
In high energy physics, the existence of at least
one fundamental spin-0 Higgs particle is
required to consistently explain how particles
have mass.
But what about Spin-0?
The Large Hadron Collider (LHC)
accelerates counter-rotating bunches of protons
in two 27km rings to 7 TeV and collides them at
4 interaction regions instrumented with 4 giant
detector systems.
Two General Purpose Experiments are
designed to find such Higgs particles over the
full range of masses (0.1 to 1TeV) allowed by
current theoretical and experimental results.
14
One of these is ATLAS. It is being built by a
collaboration of 2000 physicists from nearly 200
different institutes in 33 different countries
including 13 UK universities.
The ATLAS experiment is 26m long, stands 20m
high, weighs 7000 tons and has 200 million
read-out channels.
15
The ATLAS central tracker is made of thousands of
modules which each require several thousand
connections This double-sided module has 6144
connections and has 1536 read-out channels. The
required connections are at pitch down to 240 per
cm
16
Mediation of the Forces
Electron spin ½
??
Spin structure ?
Luminosity (particle flux)
New force carrier particle mass ?
Energy (E m c2)
Energy precision
spin ?
Initial spin
New matter particle charge ? mass ?
Initial spin precision
??
spin ?
Positron spin½
17
The Linear ee- Collider
Luminosity (particle flux)
3.4 - 5.8 ?1034 cm-2 s-1
Energy (E m c2)
500 - 800 GeV
Energy precision
? 10-4
Initial spin
Pel 80 , Ppos 60
Initial spin precision
0.5
18
Precision at ee- Colliders
Etot2E ptot0
E, p
E, - p
e
e-
Polarization
Event Energy Precise
Broad Reach at Proton Colliders
E, - p
E, p
Etot? Ptot?
p
p
u
d
No polarization
Broad Range of Event Energies
19
Complementarity
Energy
LHC
Linear Collider
20
Need for a High Precision Detector
Excellence
Calorimetry
Tracking
Vertexing
Granularity
Hermeticity
21
Physics Opportunities at the TeV Scale
Precision studies of the top-quark
Precision studies of the origin of mass
Supersymmetry
Grand Unification
New spatial dimensions
Strong Electroweak Symmetry Breaking
Compositeness
Leptoquarks
Anomalous couplings
GigaZ
...
22
Precision Measurement of the Top Mass
Precision measurement of fundamental particle
properties
The top quark is the heaviest most sensitive to
new physics
Cross section (pb)
Mtop175 GeV 100 fb-1 per point
Statistical Precision 0.05 GeV ?0.02
Etot(GeV)
23
Origin of Mass ?
1. Start with a mass-less particle
m0, v speed of light
2. Introduce a new field H that interacts with
the particle
3. Let H be non-zero in the vacuum
0
0
H
H
V lt c, m gt 0
m0, v speed of light
0
0
H
H
24
Clear Predictions from Higgs Theory
Discover a Higgs Particle
Every field has quanta
Measure its mass
Measure its spin
H
Measure its lifetime
H
h
h
Hint of a signal at mass115 GeV
Measure branching ratios
?
m
m
The decay amplitude ? m
The vacuum has no preferred direction
Should be lt 200 GeV
? the Higgs must be spin 0
25
The Higgs Mechanism
The vacuum potential
Discover a Higgs Particle.
Yes (Even if decays invisibly)
h
Measure its mass.
Yes to high precision (0.05)
Energy
Measure its spin.
Yes
shape
Measure its lifetime.
Yes (few )
Measure its branching ratios.
Yes (few )
h
h
Measure the shape of potential.
Yes (20 )
Measure the shape of potential
26
No-Lose for TeV Colliders
Higgs discovered before the LHC ?
No
Yes
Invisible Higgs ?
Precision measurements
Yes
No
New physics ?
Explore quantum level (GigaZ)
Light higgs Super- symmetry?
No
Yes
Yes
Explore!
27
Unification of the Forces
??
The strength of the force
1/?1 60
Three Forces ? ?1 , ?2 , ?3
1/?2 30
1/?3 10
??
Could there be one unified force?
? Need to extrapolate to ultra-high energies...
28
The Vacuum
??(Energy)
What remains after all the atoms have gone ?
Virtual particles (quantum effects)
??
The entire particle spectrum contributes
??
Particle properties depend on energy scale
Higgs field
The Vacuum is exceedingly complex
29
The Need for Precision

• The masses and couplings are fundamental
• physical quantities

60
?1-1
?1-1
Before precision ee-
After precision ee-
50
40
?2-1
?2-1
Precision Measuremets
?i-1

• They enter the procedure for extrapolation to
• ultra-high energy scales

30
?3-1
?3-1
20
Simple Grand Unification ?
Either No Grand Unification or more
particles...
10
TeV scale supersymmetry?
0
3
5
7
9
11
13
15
17
Log 10 Energy Scale (GeV)
30
A Candidate Supersymmetry
A symmetry relating fermions with bosons
Spin ½
Spin 0
Necessary Tasks
200 GeV
1 TeV
Escale

• Produce the particles ( E mc2 )
• ?High Energy, high luminosity

-uc
uc
u
d
d
-uc
uc
u
d
d
?
uc
u
d
dc
uc
u
d
dc
t
d
dc
d
dc
u
u

• Measure to high precision their mass,
• spin, couplings, decay channels
• ? High precision, polarization

ec
e
ec
e
eL
e
e
eR
?e
?e
A further doubling of the particle spectrum

• Combine ee- and pp measurements
• ? Complementarity

t
0
31
Simplicity at Ultra-High Energy Scales
Age of Universe
Energy Scale
Complexity ? Simplicity
New fine structures ?
32
Does gravity mediate with the superworld ?
The Need for Precision
LHC Only
LHC LC
500
U1
400
300
TeV scale measurements
L1
Supersymmetric Mass Terms (GeV)
200
E1
100
0
3
5
7
9
11
13
15
Log 10 Energy Scale (GeV)
33
Summary
Particle physics explores
The richness and diversity of this programme make
the combined potential of both a pp and an ee-
TeV collider vital for particle physics.

• the fundamental building blocks of matter

• the fundamental forces

An ee- linear collider, building on the results
from the LHC, will be uniquely placed for

• Searches for new particles and forces

• Detailed tests of the origin of mass

• Precision measurements

? explore the physics of ultra-high energy scales
? the interface between gravity and particle
physics?