Nuclear Physics/Quantum Chromodynamics (QCD)
 Big questions
 why are quarks confined inside protons ?
artist’s view :)
 what does the vacuum look like ?
 can we use understanding of 2-body physics to
describe complex behavior of n-body physics
11/03/2009
cogilvie@iastate.edu
1
Quantum Chromodynamics (QCD)
quark
t
quark
z
quark
quark
Strong interaction/scattering by exchange of gluons
Force between two quarks does not weaken as you separate them
Completely counter-intuitive
Gravity, electric, magnetic forces
all are weaker at larger distances
11/03/2009
cogilvie@iastate.edu
2
Confinement: A Partial Answer
 Attractive interaction
 try to separate quarks, force pulls them back
 More complicated ……
try to separate quarks
narrow “string” or
color field / gluons
11/03/2009
cogilvie@iastate.edu
3
Confinement: The rest of the story
q
q
q
“vacuum” is not empty!!,
short-lived creation/destruction of particle pairs
q
vacuum expels QCD field (gluons),
Restricts gluons to be between quarks in “string”
Confinement
1) Attractive force as you try to separate quarks
2) vacuum expels color field
 quarks must stay “outside the vacuum” i.e. inside hadrons!
11/03/2009
cogilvie@iastate.edu
4
Attack QCD on Multiple Fronts: ISU Program
 Experiments that push our understanding of strong QCD
 Form + study a bulk system of very hot quarks and gluons
Quark-gluon plasma
Melts the vacuum
 Detailed study of the quarks, gluons inside a proton
 Spin of a proton
 Low-momentum region <= high density of gluons
11/03/2009
cogilvie@iastate.edu
5
The Quark-Gluon Plasma
 In all protons, neutrons, the quarks are
confined to radius ~ 1x10-15m
 Inside a nucleus, average separation
between nucleons is ~ 2x10-15m
 Increase density by compression or
heating
 nucleons significantly overlap
 quarks, gluons no longer confined,
 QGP : new form of hot, dense matter
11/03/2009
cogilvie@iastate.edu
6
RHIC
BRAHM
S
PHOBO
S
 Two independent
accelerator rings
 3.83 km in
PHENIX
circumference
STAR
 Accelerates
everything,
from p to Au
s
p-p
500 GeV
Au-Au 200 GeV
11/03/2009
cogilvie@iastate.edu
7
Au on Au Event at CM Energy 130 GeV*A
STAR
11/03/2009
cogilvie@iastate.edu
8
PHENIX at RHIC
 2 central
spectrometers
West
 2 forward
spectrometers
South
East
North
11/03/2009
cogilvie@iastate.edu
9
Silicon Detector Upgrade to PHENIX
Two layers of silicon pixel detectors
Two layers of silicon strip detectors
Tracks extropolate back to collision vertex
Displaced vertices => charm (D), beauty (B)
Requires ~ 50 mm precision
e
X
De+X
Au
e
p0 e+e X
11/03/2009
cogilvie@iastate.edu
Au
B e+X
e
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Nuclear Physics @ ISU
 Many-body QCD
 Experiment and theory
Densest, hottest matter: QGP, RHIC and LHC
Detailed study of the quarks, gluons inside a proton
Strongest gluon field possible in protons+nuclei
 Large, active, enthusiastic group
 Well-funded
 Hardware experience
 Exciting physics
 Open invitation to join our group
11/03/2009
cogilvie@iastate.edu
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