Interactions Kihyeon Cho September 6, 2004
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)