Point 1 activities and perspectives Marzio Nessi ATLAS plenary 2 nd October 2004 Large Hadron Collider (LHC)

From atoms to quarks I

From atoms to quarks II Hadrons are made of quarks, e.g. p = uud  0 = uds  0 b = udb  + = ud  = cc  = bb Baryons Mesons Leptons are fundamental e.g. electron muon neutrinos

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

Tau Muon Electron Tau Neutrino Muon Neutrino Electron Neutrino Bottom Strange Down Top Charm Up 2/3 -1/3 each quark: R, B, G 3 colors Quarks Electric Charge Leptons Electric Charge Quarks and Leptons (Antimatter -Each one has antiparticle)

Quarks, leptons and bosons Higgs boson?

Particle Detectors I Cannot directly “see” the particles just their trajectories Many interesting particles decay very quickly –Lifetimes of particles of interest are too small Even moving at the speed of light, some particles (e.g. Higgs) may only travel a few mm (or less) Must work out what happened by observing long-lived particles resulting from decays –Need to identify the visible long-lived particles Measure their momenta Energy (speed) –Deduce the presence of neutrinos and other invisible particles Conservation laws – measure missing energy

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 gluon W+ W+ W- W- ZoZo 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

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Terrestrial mechanics Universal Gravitation Inertial vs. Gravitational mass (I. Newton, 1687 ) Electricity Magnetism Electromagnetism Electromagnetic waves (photon) (J.C. Maxwell, 1860 ) Electromagnetism Weak force Electroweak Intermediate bosons W, Z ( ) Probing shorter distances reveals deeper regularities UNIFIED DESCRIPTIONS ? Celestial mechanics   n p e - e +  N S Unification of forces

Matter and Forces “The standard model”

The Higgs Major objective of the LHC - What is the origin of Mass? Is it the Higgs Particle? Massless Particle – Travels at the speed of light Low Mass Particle – Travels slower High Mass Particle – Travels slower still

Higgs Boson – Current limit

Identification + Measurement muon proton photon electron neutron TRACKEREM CALO HADRONIC CALORIMETER MUON TRACKER

Searching for Rare Phenomena 9 orders of magnitude The HIGGS All interactions

The Forces Force Range Force Carrier Strength Gravitational long 1 Electromagnetic long photon (massless) Weak short W, Z bosons (heavy) Strong short gluons (massless) 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 Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts

E 2 = p 2 c 2 + m 2 c 4