Point 1 activities and perspectives Marzio Nessi ATLAS plenary 2 nd October 2004 Large Hadron...

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Point 1 activities and perspectives

Marzio Nessi

ATLAS plenary 2nd October 2004

Large Hadron Collider (LHC)

• Leptons– Electron , muon and tau – all negatively charged– Radioactive decay produces a different particle –

neutrino () . There are three types of neutrino!

• Quarks– have fractional electric charges and are never seen

alone!(qqq or q+antiquark make up hadrons like proton,pion …)

– Each quark also is found with three different colour charges

– Proton mass ~ 1 GeV, top quark mass ~175 GeV

• Both– Three ‘generations’ of quarks and leptons– All quarks and leptons have antiparticles– Quarks and Leptons are all spin ½ particles

Basic constituents

Electron

TauNeutrino

MuonNeutrino

ElectronNeutrino

Bottom

Strange

each quark: R, B, G 3 colors

QuarksElectric Charge

LeptonsElectric Charge

Quarks and LeptonsQuarks and Leptons

(Antimatter -Each one has antiparticle)

Basic Forces

• Gravitational – by far the weakest force

• Electromagnetic – vital for atomic structure

• Strong – holds quarks inside the proton

• Weak – responsible for radioactive decay and nuclear reactions in sun and stars

Force Carriers

• Gravitational – • Electromagnetic –

• Strong –

• Weak –

photon

W+ W- Zo

All quarks and leptons are fermions (spin ½)

All force carriers are bosons (spin 1)

The discovery of the W and Z dramatically confirmed the electroweak theory. Its unification of the seemingly unrelated phenomena of nuclear beta decay and electromagnetism is one of the major achievements of twentieth century physics.

Robert N. Cahn and Gerson Goldhaber

“The Experimental Foundations of Particle Physics”

Cambridge University Press

Matter and Forces

“The standard model”

Higgs Boson – Current limit

The Forces

Force Range Force Carrier Strength Gravitational long 1Electromagnetic long photon (massless) 1035

Weak short W, Z bosons (heavy) 1033

Strong short gluons (massless) 1038

Gravity – solar system, galaxies …Electromagnetic – atoms, electricity …..

Weak force

Strong – binds quarks inside proton

Weak – beta decay, how stars generate energy

Some of the big questions

Where do the particles get their mass from?

Where has all the anti-matter gone?

What is dark matter made of?

What else is out there?

What is Mass?

In the mid 1960s, British physicist Peter Higgs came up with a theory on why some particles have mass.

He proposed a new heavy particle, now called the Higgs boson, which generates a Higgs field.

Particles who ‘feel’ this field gain mass. Light particles don’t feel this field strongly, heavy particles do.

What is Dark Matter?

Normal: Made from atoms Includes stars, planets, people…

Dark matter: Unknown substance (not atoms) May be a “fat cousin” of light (SUSY) Hope to make & study it at the LHC

Dark energy: Even weirder!

A basic “Tracker”

Multiple thin layers of, for example, silicon sensors

Basics

The past

Challenges

Where to start?

Detector Design Tracker Calorimetry Particle ID

LHC detectors

“Events”

Final thoughts

A basic calorimeter

Total # of particles is proportional to energy of incoming particle

Active detector slices produce a signal proportional to the number of charged particles traversing