Transcript Investigating the Basic Building Blocks of Matter using Electromagnetic Probes at Jefferson Lab Ioana Niculescu JMU Physics Department Research at Jefferson Lab (Newport News, VA)

Investigating the Basic
Building Blocks of Matter
using
Electromagnetic Probes at
Jefferson Lab
Ioana Niculescu
JMU Physics Department
Research at Jefferson Lab
(Newport News, VA)
Elements of Nature
Earth
Water
Fire
Air
10-20-2008
Aristotle and Plato
The Atom
By convention there is color,
By convention sweetness,
By convention bitterness,
But in reality there are atoms and space.
Democritus (c. 400 BCE)
Atom = electrons + nucleus
 Nucleus = protons + neutrons

The Proton and Neutron

Made of quarks
p (uud)
 n (udd)

Proton has positive charge (+1)
 Neutron is neutral (0)

Leptons
Quarks
Quarks and Leptons
?
5
How to Use Quarks?
Proton (uud): Qu+Qu+Qd=+1
 Neutron (udd): Qu+Qd+Qd=0
 Qu= +2/3 and Qd=-1/3

1st
generation
2nd
generation
3rd
generation
+2/3
Up (u)
Charm (c)
Top (t)
-1/3
Down (d)
Strange (s)
Bottom (b)
The Leptons

Electron, muon, tau
Different masses
 Similar properties


Neutrinos
Neutral (different than neutron,
which has charged quarks inside,
but zero charge)
 Small mass (or no mass)

The Scale of
the Atom
The Universe
All matter in Universe is composed of atoms
(neutrons, protons, and electrons)
 Up and down quarks are the most abundant.
 The other quarks are produced in high-energy
laboratories.
 In early Universe they were more common.
 Particle physics – looks into the history of the
Universe.

What Holds It Together?

Force = A push or a pull

Examples:
Gravity
 Friction (due to electromagnetic forces)
 Tension (due to electromagnetic forces)
 Electromagnetic

The Fundamental Forces

Fundamental =
cannot be explained
as arising from the
action of a more basic
force.
Are all these forces the result of just one force?
Classical Picture of Force
Contact or
 Action at a distance:

Interaction Moon – Earth
 Not a contact interaction


Fields
Gravitational field
 Earth and Moon surrounded by gravitational field
 Field exerts a force on anything in it
 Do these fields really exist?

Quantum Picture of Force





Classical physics – does not apply to microscopic
objects.
Quantum physics (1900s)
Einstein – light consists of photons (particles)
Each force is defined by its gauge boson (particle
that mediates the interaction).
The interaction between an electron and proton:
exchange of photons
The Standard Model
11/6/2015
Probing the Subatomic World
11/6/2015
Seeing …
11/6/2015
11/6/2015
Using Electrons to See…
11/6/2015
So what do
we need?
To probe subnuclear structures we need really small
wavelengths:
p


h

h
 
p
The smaller distance one wants to probe, the larger the
energy of the probe
momentum
Particle accelerators…
11/6/2015
p  m*v
100 years of Fixed Target Experiments
Rutherford’s Experiment (1911)
21
Fixed Target Experiments
QCD and the Strong Nuclear Force
• Confinement:
• between quarks at large distances equivalent to 10 tons,
no matter how far apart
• Asymptotic freedom:
• quarks feel almost no strong force when closer together
Inclusive Electron Scattering
scattered
electron
proton
photon
incident
electron
Q2 : Momentum transfer to the quark by electron
x : Fraction of proton momentum carried by
struck quark (Bjorken variable)
11-17-2006
The Structure
Function
F2   e x f i ( x)
2
i
i
Probability that this quark
carries a fraction x of proton
momentum
Quark charge
If we assume
u d , u d
p
n
44 p 11 p
F
F  u u  dd
99
99
pp
22
n
p
44 n 11 n
F
F  ud  du
99
99
n
n
2
The Proton Structure Function
27
The Neutron Structure Function?
No free neutron target!
28
The BONUS Experiment
target
Hall B (The CLAS Detector)
BONUS in CLAS
The JMU Contribution
Delivery at JLab
Installation in the Hall
Data Taking at JLab
(2005-2006)
Data Analysis (JLab and JMU)
Results
(2012)
F
4d  u

F
4u  d
n
2
p
2
The ratio F2n/F2p
F2n 2


p
F2
3
d 1

u 2
n
2
p
2
F
3
d
1



F
7
u
5
n
2
p
2
F
1
d


0
F
4
u
Summary

Jefferson Lab explores the building blocks
of matter and how they make the world
around us.

The BONUS experiment provides essential
data to understand the difference between
proton and neutron.
BoNuS (E03-012) at
Jefferson Lab in CLAS
Beam : 5.268, 4.226, &
2.142 GeV
Beam Current: 35 nA
Target: H2 and D2 (7 atm)
Luminosity: 4.30 x 1033 s1cm-2
Engineering run: Summer ‘05
Production run: Fall-Winter ‘05
Total number of events:
853 M (D2) and 90 M (H2)
11-17-2006