Thomas Lohse

Humboldt-Universität zu Berlin

Thomas Lohse

Humboldt-Universität zu Berlin

Stuff and GlueParticles and Forces

• Experimental methods

• What is matter?

• Which forces stabilize matter?

• Open questions and the next steps

Greek Philosophy• Empedokles (500-430 B.C.)

– four elements: fire, water, earth, air– two fources: love , hatred mixing, separating

• Platon (427-347 B.C.)– symmetric shapes: beauty of laws of nature

• Demokrit (460-371 B.C.)– atoms: different forms and weights

– emptiness: binding and motion in the void

fire water earth air

How to resolve structures?

eye: ~1 mm resolution

scattering of photons:

lense: ~ 0.1 mm resolution

light microscope: ~ 1 µm

Limited by photon

How to resolve structures?

particle scattering:

Rutherford scattering:

E = O(MeV) α-particles

λ = O(fm) gold atoms with nuclei

ph

modern particle accelerators, e.g.

HERA: e(27 GeV) on p(920 GeV)

resolution 0.001 fm

TV tube

a) linear accelerators

Fermilab injector

the principle

superconducting RF cavity for future linear

collider TESLASLAC linac first linear collider

Particle Accelerators

b) storage rings

Particle Accelerators

Particle Accelerators

c) the big labs in Europe

DESY (Hamburg)

CERN (Geneva )

LEP

SPS

Particle Detection

display of electronic signals

OPAL detector at LEP, CERN

Two Topologies

Colliding beams (e+e–, ep, pp...)

Myon Chambers

Hadron Calorimeter

Tracking ChamberElectromagn. Calo.

e–

cylindrical shell structureof subdetectors

cylindrical shell structureof subdetectors

Two Topologies

Fixed target (μ–A, pA, ...) Forward layerstructure of subdetectors

Forward layerstructure of subdetectors

HERA-B

21 m

Si-vertex detectorSi-vertex detector tracking systemtracking system

magnet

RICH detectorRICH detector EM calorimeterEM calorimeter

hadron absorber& muon system

hadron absorber& muon system

Subdetector Tasks

40 cm

Silicon Microstrip Wafers => vertex tracking

typical impact parameters O(100 μm)

Proportional Drift Chambers => main tracking

typical coordinate resolution O(200 μm)

magnetic field => particle momentum from curvature

Subdetector Tasks

HERA-B RICH

Particle Identification: example Ring Imaging CHerenkov detectors

Ring radius => p/m => π,K,p sep.

charged particle in radiator gas

mirror

light detector (e.g. PM tubes)

Cherenkov cone

point on Cherenkov ring

Subdetector TasksCalorimeters (lead, steel, uranium...)

electromagnetic showers => e,γ energy

hadronic showers => energy of hadrons

penetrating particles => muons

Structure of MatterCrystal

Molecule

Nucleus

Atom

elements of normal matter:

quarks leptons

up

Q = +2/3

neutrino

Q = 0

down

Q = –1/3

electron

Q = –1

• neutrinos: from β-decay / sun burning

• quarks: always bound, ”confinement“

How to see the quarksaccelerators => high energy quarks

quarks => jets of secondary hadrons

jet

jet

e+ e–

quark

antiquark

How to measure quarks in the protonaccelerators => knock quarks out of protons

final state kinematics => initial quark momentum

jet

e

Quantitative: proton structure functions

quark densities in the protonas function of thequark momentum

and theresolution of the scattering

quark densities in the protonas function of thequark momentum

and theresolution of the scattering

Heavier short-lived Generations

very strange mass spectrum...

High energy collisions reveal heavier versions of quarks and leptons!

up ... charm ... top down ... strange ... bottom

electron ... muon ... tau νe ... νμ ... ντ

Strong Similarity to ...groups

peri

ods

The Periodic System ofElementary Particles

u-quark group

d-quark group

neutrino group

electron group

quark/lepton periods

I II II

I

particle physics:periods = families

More Families???

LEP:

ll

qqZeevisible

invisible

ΓZ = Γvis + Γinvis

Γinvis = Nfam · Γν

measurements: Nfam = 3

lineshape of Z resonance from LEPlineshape of Z resonance from LEP

Forces: Exchange of Field Quanta

repulsiverepulsive

attractiveattractive

The Fundamental Forces

force quanta mass range

gravity graviton(?) 0

electromagneticphoton 0

weakW± , Z 80, 90GeV ~.001 fm

stronggluons 0 O(1) fm

N

S

q q pp

nn

nnp

ppp

p

n

nnp

pnpnp

Xvpv

vepn e

(confinement)

Gamma Quantum in Action

ee

γ

Gluon Quantum in Action

jets3 gqqee

W Quanta in Action

jets 4

qqqqWWee

Z Quanta in Action

jets 4

qqbbZZee

The Complete(??) Picture

Supersymmetry: still a hypothesis...

Matter Particles

Spin 1/2

Superpartners of Matter Particles

Spin 0

Supersymmetry: still a hypothesis...

Force ParticlesSuperpartners of Force Particles

Why is the Weak Force Weak?

ep cross section vs. squared momentum transfer

electromagnetic

weak

unification at22WMQ

γ

W

e

νIt isn‘t weak at all!!!

It is just a mass effect!!!

It isn‘t weak at all!!!It is just a mass effect!!!

A Unified Single Force?

We have just seen this:Electroweak unification

E = 100 GeV like 10-10s after big bang

Grand electroweak/strong unificationE = 1014 GeV like 10-35s after big bang Planck Scale: unification with gravity

E = 1019 GeV like 10-43s after big bang

kTE

Big Bang

Ecx

Why such funny asymmetric masses of force particles?

Hypothesis: There is a background field in the

universe... the Higgs field

Vacuum field strength

Symmetric potential energy

Initial state of the universeInitial state of the universe

Inflation: spontaneoussymmetry breaking

Inflation: spontaneoussymmetry breaking

Asymmetric ground state:• masses are created• a Higgs particle appears

Asymmetric ground state:• masses are created• a Higgs particle appears

A conference banquet... The nobel prize winner enters the room...

The physicists next to him turn immediately to talk to him. It becomes hard for him to move (accelerate). He is effectively massive...

physicists = background Higgs fieldnobel prize winner = massive particle

How does Mass Creation Work?

How does Mass Creation Work?

A conference banquet... A rumour is injected... The physicists cluster where the rumour spreads out. It gets hard for the rumour to move (accelerate)...rumour = Higgs particle

The Higgs particle is itself massive!

And Where is the Higgs?

direct search not yet successful:

mH > 114 GeV

Higgs mass enters via quantum corrections

in precision measurements

fit-2

• Why such a strange mass spectrum ?

• Does the Higgs particle exist ?

• Why three families ?

Open Questions

??

• Why symmetric lepton/quark structure ?

• Is there a unified force ?

• Supersymmetric partners of particles and fields ?

• Characteristic pattern of quark family transistions ?

• Transitions in lepton family ?

• Where/how is the antimatter gone ?

• What about gravity ? Extra space-time dimensions? ...

The next big steps: (1) LHC / CERN

ATLAS detector

LHC: 7 TeV protons on 7 TeV protonsStart of operation: 2007-2008

LHC: 7 TeV protons on 7 TeV protonsStart of operation: 2007-2008

LHC goals:• establish the Higgs particle• search for supersymmetry• search for new effects

LHC goals:• establish the Higgs particle• search for supersymmetry• search for new effects

accessible mass scale: ~1 TeV

The next big steps: (2) TESLA / DESY

• 33 km linear e+e–-collider, energy 500-800 GeV• Similar projects proposed by U.S.A. and Japan• start not before 2013

• 33 km linear e+e–-collider, energy 500-800 GeV• Similar projects proposed by U.S.A. and Japan• start not before 2013

TESLA goals:• detailed properties of Higgs particle• highest precision tests of electroweak force• detailed properties of supersymmetric particles• search for extra dimensions ...

TESLA goals:• detailed properties of Higgs particle• highest precision tests of electroweak force• detailed properties of supersymmetric particles• search for extra dimensions ...

It stays interesting...