Transcript Professor Liss

Tony Liss
Saturday Physics for Everyone
November 9, 2013
(With debts to Chris Quigg, Leonard Susskind, Hitoshi Murayama)
Mass is stuff
Mass is the stuff that gravity acts on
FG ravity  G
M blue M red
r
r
2
Mass is stuff that resists you when you
push it
F  Ma
Mass is rest energy
E0  M c
2
Ordinary Matter
A proton is made of u u d
Add an electron to make a
hydrogen atom
A neutron is made of d d u
Now you have all the building blocks
of the periodic table.
~173000 Mev/c2
~4.8 Mev/c2
~2.3 Mev/c2
.511 MeV/c2
According to theory, the Higgs boson gives these particles their mass.
Helium:
Iron:
Hydrogen:
26 Two
protons,
protons,
One 30
proton,
neutrons,
two one
neutrons,
electron
26 electrons
two electrons
2 = 938.890124
MFeM
c2He=M
c252,019
=3,728.398128
MeV
MeV
MeV
Hc
MFe/(26M
MHeP+30M
/M(2M
+2M
)=0.9909
= 0.999999986
H/(M
NP+26M
P+MeN)e+2M
e) = 0.9927
~173000
Mev/c2
No!
Proton: Two up quarks and a down quark
(2Mu+Md)c2< 10 MeV
MPc2 = 938 MeV !
Neutron: Two down quarks and an up quark
(2Md+Mu)c2 ~12 MeV
MNc2 = 940 MeV !
~4.8 Mev/c2
~2.3 Mev/c2
The mass of neutrons and
protons
is2 due (mostly) to
.511
MeV/c
the strong force (QCD) that holds them together:
M  E c
2
• The mass of atoms is the sum of the mass of their parts (with very small
corrections) – protons+neutrons+electrons
• The mass of protons and neutrons is not the sum of the mass of their
parts (quarks)
• It is mostly from the energy in the strong force (QCD) binding the
quarks together.
• Therefore, the mass of periodic table and the visible universe comes not
from the masses of the fundamental particles, but from QCD!
Consider the proton & neutron masses
The proton is electrically charged & therefore surrounded by
its own electric field. The neutron is electrically neutral.
E ( field )   M c
2
You would guess that the proton is
heavier than the neutron. But
M
N
M
P
 1.29 M eV c
2
Mdown > Mup
Mneutron > Mproton


e e
The heavier neutron “beta decays” in about 15 minutes into a
proton plus an electron and a neutrino
If the quarks had no mass, then MP > MN
The proton would beta decay into a neutron
No hydrogen atom
If the electron had no mass…
No atoms at all
No me
No you
The Higgs ‘potential’
Electroweak force
Force carriers
Interactions
Atoms
Beta decay
d
u
d
d
u
u
–
W

e–
e

e e
http://www.philica.com/display_article.php?article_id=126
In the 1960s, the electromagnetic & weak interactions were unified
into a single framework based on electroweak symmetry.
The symmetry principle requires the carriers of the electromagnetic and
weak forces to have zero mass. Quarks and leptons also have no mass.
But this isn’t true. Only the photon has no mass.
Weak interactions are very short-ranged, implying that the carriers,
W & Z bosons, are very massive.
Electroweak symmetry must be hidden.
I first saw this demo in a talk by Chris Quigg
?
Energy of field
All other fields
0
Strength of field
The Higgs field
The minimum energy has a non-zero
Higgs field!
http://commons.wikimedia.org/wiki/File:Mexican_hat_potential_polar_with_details.svg
+
p
Water molecules: Electrically neutral,
but with a ‘dipole moment’
-
H
H
O
O
H
H
H
+
-
O
O
E
H
H
H
(Thanks to Leonard Susskind)
It is certainly A Higgs boson
Therefore we know
It is responsible for at least some of the W and Z mass
(strong evidence).
It is probably responsible for at least some of the fermion
masses (evidence getting stronger).
We don’t yet know:
If it is the ONLY Higgs boson.
Why it is so light.
The energy in the electric field
adds to the electron mass
2
mec ~
Electric field lines
around an electron
1
re
We know the mass of the electron:
2
m e c  0.511 M eV
This observed mass is an unobservable bare mass plus
a correction due to the field energy

0.511 M eV  m e c
We know re
 10
17
cm
2

bare
 mec
2
, then mec2 ~ 10 GeV and
0.511 MeV = (-9999.489 + 10000.000) MeV
This is fine tuning
Hitoshi Murayama
http://arxiv.org/abs/hep-ph/0002232
+
+
+
+
+
-
+
+
+
Electron-positron pairs ‘pop’ out of the
vacuum and shield the bare charge of the

electron
e
e


2
Mh

obs
h

2
 Mh
0

bare
t
h

2
 M h

0
t
The problem is,  M h2 is very very large (~1038 GeV) if there is nothing
else going on.
This requires   M h
and give
2

to be equally large in magnitude to cancel it
bare
 M h  obs
 125 G eV c
2
SUSY includes a partner to the top quark, the ‘stop quark’ or ‘top
squark’ that nearly cancels the top quark loop
h
t
0
h
0
t

2
M h

top

2
 M h

stop

2
2
~ m top  m stop

But we haven’t found the stop quark yet. The more we
don’t find it, the heavier it must be – if it exists at all…
Nature could be fine tuned. There is no law that
forbids
125 G eV =
100000000000000000000000000000000000000
- 99999999999999999999999999999999999987 5
It’s just not very pleasing.
Since we are here, the fundamental constants must
have values in the narrow range compatible with
conscious life.
 Is there more than one Higgs boson?
• Supersymmetry, and many other ideas, include a family.
 Does the Higgs boson give dark matter it’s mass?
 Does the Higgs boson have anything to do with neutrino mass?
 Is the anthropic principle correct?
 What in the Universe is dark energy?