Interactions

Kihyeon Cho

September 6, 2004

People have long asked,• What is world made of? and

• What holds it together?

• In Ancient time

What is world made of?

water

fire

earth

air

What is World Made of?

Standard Model• t, b, c are heavier

than other quarks - heavy flavor quarks

• W, Z, top are stand out from the rest.

Matter• Hadron (Quark) - size

– Baryon (qqq): proton, neutron– Meson (q qbar): pion, kaon

• Lepton – no size– Point particle

How to know any of this?(Testing Theory)

• Example

– Light bulb (Source)– Tennis ball (target)– Eye (detector)

• Accelerators solve two problems:

– High energy gives small wavelength to detect small particles. (Lambda = h /p )

– The high energy create the massive particles that the physicist want to study.(E=mc^2)

How to detect?

Accelerator design• Shapes

– Linacs (SLAC)– Synchrotrons (Fermilab)

• Collision types– Fixed target (E687, FOCUS)– Colliding beams (CDF, Belle, BTeV) => CM = 1TeV+1TeV => 2TeV

High Energy Experiment

Fixed target vs Colliding beams

(total energy)2-(total momentum)2 = invariant in all frames of referenceAssume that 800GeV(Ebeam) proton collides in a fixed target(proton).

Center of mom. frame Laboraroty frame Total energy: ECM Ebeam+mp

Total momentum: 0 Pbeam Invariant: ECM

2 (Ebeam+mp )2-Pbeam

2

E = [ 2(mp2+Ebeammp) ]1/2 = 38.8GeV

We are enough to 19.4GeV+19.4GeV proton beams in collider !!!Question: What’s the advantage of a fixed target experiment?

The Fermi National Accelerator Laboratory

Where is Fermilab?• 20 mile west of

Chicago• U.S.A

Fermilab

Fermi National Accelerator LaboratoryHighest Energy Accelerator in the

WorldEnergy Frontier: CDF, D0 Search for New Physics (Higgs, SUSY, quark composites,…

Precision Frontier: charm, kaon, neutrino physics(FOCUS, KTeV, NUMI/MINOS,BOONE,…etc.

Connection to Cosmology: Sloan Digital sky survey, Pierre Auger,…

Largest HEP Laboratory in USA

2200 employees2300 users (researchers from univ.)Budget is >$300 million

Overview of Fermilab

Main Injectorand Recycler

p source

Booster

CDF

D0

Fixed Target

Experiment

Tevatron Run 1 (1992-1996)

Protons

H source (18 KeV) → Cockcroft Walton accelerator (750 KeV) → Linac (400 MeV) → Booster (8 GeV) → Main Ring (150 GeV) → Tevatron (900 GeV)

Antiprotons Main Ring (120 GeV) → Antiproton Source (Ni) → Debuncher (8 GeV) Accumulator (8 GeV) → Main Ring (150 GeV) → Tevatron (900 GeV)

Tevatron Run II (2001 – 2007)

• Main Injector (150 GeV proton storage ring) replaces Main Ring

• Pbar improved – Cooling system – a new permanent

magnet recycler

• Increased number of p and pbar bunches (6 36 100 )

What holds it together?(The four interactions)

Masses of Fundamental Particles

• t, b, c are heavier than other quarks - heavy flavor quarks

• W, Z, top are stand out from the rest.

Electromagnetic interactions w/ atoms

Weak Electromagnetic

Strong

Range 1/Mw Infinitive 1F=1/m Typical

Lifetime(sec)

10^-12 or longer

10^-20~10^-16

10^-23

Typical Cross section(m

b)

10^-11 10^-3 10

TypicalCoupling

10^-6 10^-2 1

Summary of interactions

pp 0 pppp

References• B.G Cheon’s Summer School (2002)• S.H Yang’s Colloquium (2001)• PDG home page (http://pdg.lbl.gov)