Physics at the TeV Scale

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

Phil AllportUniversity of Liverpool

• 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

Einstein’s dream of deeper unification (Gravity?)

Introduction

+

Forces in Physics

Classically, forces are described by

+

Field

charges and fields

++

Forces in Physics

Continuous field exchange of quanta

Low energies and large distances classical mechanics

+ +

For Electromagnetism

The quanta are photons,

Other forces are mediated by other particles ...

High energies and small distances quantum mechanics

Forces in Particle Physics

The Forces of Nature

Gravity

Nucleus

Atom

Gluon, g

W

Z0

Photon,

Not directly accessible at accelerators

-decay,sunshine

Mass

0

0

80 GeV

91 GeV

1

1

1

1

Electro-magnetic:

Strong:

Weak:

MediatorSpin

They are all bosons (integer spin)

Positron

Mediation of the Forces

Electron

Feynman Diagram

The strength of the force

The Matter Particles

e

Neutrino

Electron

Protonmass mp = 1.7 10-27 kg

size ~ 10-15 mcharge +1

mass ~ 10-11 mp ?size = 0 ?charge 0

Mass ~ 5. 10 - 4 mp size =0 ? charge -1

u

ud

(Neutron) (charge 0)

Leptons charge = 0

charge = - 1

The First Generation

e

uu

dd

u

d

e

Quarks with 3 “colours”charge = + 2/3

charge = - 1/3

velocity

All these matter particles are spin-1/2

Left Handed Right Handed

all are fermions

2 helicity states

The Dirac Equation

Special Relativity + Quantum Mechanics

An equation that describes spin-1/2 particlesCorrect magnetic momentsPredicted the existence of antimatter

A further doubling of the spectrum ...

centenary

The First Generation

uu

dd

u

d

e

e

ucuc

dcdc

uc

dcec

-tctc t btc t b

t bc

bc

bc

bc

-ucuc u duc u d

u dec

dc

dc

dc

ee

Multiplicity of states

Completion of a pattern?

-ucuc u duc u d

u dec

dc

dc

dc

ee

-cccc c scc c s

c sc

sc

sc

sc

Cosmic rays

Accelerators

s

Number of generations = ?...

Precision e+e- Measurements

Ngen= 2.98410.0083

LEP : e+e-, Ecms~ 210 GeVLHC : pp, Ecms~ 14 TeV

CERN

ud

The Known-Particle Spectrum

10-11 GeV1

0

2

3

?

Escale

5 10 - 4 GeVe

10 - 1 GeV

e

2 GeV

u d

s

c

200 GeV

s cb

t

Spin ½ Spin 1

, g

Z0

W

Spin 0

?

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.

The ATLAS experiment is 26m long, stands 20m high, weighs 7000 tons and has 200 million read-out channels.

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 central tracker is made of thousands of modules which each require several thousand connectionsThis double-sided module has 6144 connections and has 1536 read-out channels.The required connections are at pitch down to 240 per cm

New matter particlecharge = ?mass = ?

New force carrier particlemass = ?

Energy (E = m c2)

Positron spin=½

spin = ?

Spin structure ?

spin = ?

Initial spin

Energy precision

Initial spin precision

Luminosity (particle flux)

Mediation of the ForcesElectron spin ½

Energy (E = m c2)

Initial spin

Energy precision

Initial spin precision

Luminosity (particle flux)

The Linear e+e- Collider

3.4 - 5.8 1034 cm-2 s-1

500 - 800 GeV

10-4

~ 0.5% Pel ~ 80 % , Ppos ~ 60 %

Precision at e+e- Colliders

E, p E, - p

e+ e-Etot=2Eptot=0

Broad Reach at Proton Colliders

p pE, p E, - p

du

Etot=?Ptot=?

Polarization

No polarization

Event Energy Precise

Broad Range of Event Energies

Energy

Complementarity

LHC Linear Collider

Energy

Need for a High Precision Detector

Excellence

TrackingCalorimetry

VertexingGranularityHermeticity

Precision studies of the top-quark

Physics Opportunities at the TeV Scale

Precision studies of the origin of mass

Supersymmetry

Grand Unification

New spatial dimensions

Strong Electroweak Symmetry Breaking

Compositeness

Leptoquarks

Anomalous couplings

GigaZ...

Precision Measurement of the Top Mass

Precision measurement of fundamental particle properties

The top quark is the heaviest: most sensitive to new physics

Etot(GeV)

Cross section (pb)

Statistical Precision ~0.05 GeV0.02%

Mtop=175 GeV100 fb-1 per

point

00

00

Origin of Mass ?

1. Start with a mass-less particle

2. Introduce a new field H that interacts with the particle

3. Let H be non-zero in the vacuum

m=0, v = speed of light

m=0, v = speed of light

H

H

H

H

V < c, m > 0

Should be< ~200 GeV

Hint of a signal at mass=115 GeV

?

Discover a Higgs Particle

Measure its mass

The vacuum has no preferred direction

the Higgs must be spin 0

Measure its spin

Every field has quanta

The decay amplitude m

Measure its lifetime

Measure branching ratios

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

hH

m

H

m

Clear Predictions from Higgs Theory

h

The vacuum potential

The Higgs Mechanism

Energy

shape

h

h h

Discover a Higgs Particle.

Measure its mass.

Measure its spin.

Measure its lifetime.

Measure its branching ratios.

Measure the shape of potential

Measure the shape of potential.

Yes (Even if decays invisibly)

Yes to high precision (0.05%)

Yes (few %)

Yes

Yes (few %)

Yes (~20 %)

Higgs discovered before the

LHC ?

Yes No

Yes

No

Explorequantum level

(GigaZ)

No

Explore!

YesYes

Light higgs:Super-

symmetry?

Precisionmeasurements

InvisibleHiggs ?

New physics ?

No-Lose for TeV Colliders

Unification of the Forces

The strength of the force

Three Forces 1 , 2 , 3

1/1 ~ 60

1/2 ~ 301/3 ~ 10

Could there be one unified force?

Need to extrapolate to ultra-high energies...

(Energy)

The Vacuum

Higgs field

The Vacuum is exceedingly complex

Particle propertiesdepend on energy scale

The entire particle spectrum contributes

Virtual particles(quantum effects)

What remains after allthe atoms have gone ?

• The masses and couplings are fundamental physical quantities

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

30

60

50

40

20

10

0

i-1

Log 10 [Energy Scale (GeV)]3 5 7 9 11 13 15 17

3-1

2-1

1-1

SimpleGrand Unification ?

Before precision e+e-After precision e+e-

1-1

2-1

3-1

Either: No Grand Unificationor: more particles...

The Need for Precision

TeV scale supersymmetry?

Pr e

cisi

on

Mea

sure

met

s

A further doubling of the particle spectrum

eL ee

A Candidate: Supersymmetry

A symmetry relating fermions with bosons

-ucuc u duc u d

u dec

ddc

dc

ee

eR

-ucuc u duc u d

u dec

ddc

dc

ee

Spin ½

?0

Spin 0 200 GeV ~ 1 TeVEscale

t

t

Necessary Tasks

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

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

• Combine e+e- and pp measurements Complementarity

Simplicity at Ultra-High Energy Scales

0

0000000

10-11 s 10-35 s

103 GeV 1015 GeV

Complexity Simplicity

New fine structures ?

Age of Universe

Energy Scale

The Need for PrecisionLHC OnlyLHC + LC

Su

per

sym

met

ric

Mas

s T

erm

s (G

eV)

0

Log 10 [Energy Scale (GeV)]

TeV scale measurements

500

400

300

200

100

3 5 7 9 11 13 15

U1

L1

E1

Does gravity mediatewith the

superworld ?

Summary

Particle physics explores:

• the fundamental forces

An e+e- linear collider, building on the results from theLHC, 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?

• the fundamental building blocks of matter

The richness and diversity of this programmemake the combined potential of both a pp andan e+e- TeV collider vital for particle physics.