Neutrinos and the Case
of the Missing Antimatter
Steve Boyd, University of Warwick
A little bit of history
What are neutrinos?
Where do they come from?
Why study them?
A recent surprise
CRISIS
Energy(Ra) Energy(Ac)+Energy(e)
Neils Bohr
“At the present stage of atomic
theory we have no arguments
for upholding the concept of
energy balance in the case of
b-ray disintegrations.”
Wolfgang Pauli
“Desperate remedy.....”
“I do not dare publish this idea....”
“I admit my way out may look
improbable....”
“Weigh it and pass sentence....”
“You tell them. I'm off to a party”
Energy(Ra) = Energy(Ac)+Energy(e)
+ Energy(Neutrin
What are neutrinos?
Electron, e
Tiny mass ( 1 )
Electron, e
Electron Neutrino, ne
Tiny mass ( 1 )
0
Very tiny mass
(<0.0000001)
mass of a neutrino =
mass of an electron =
mass of a nice cup of tea =
Electron, e
Electron Neutrino, ne
-
0
Tiny mass ( 1 )
Very tiny mass
(<0.0000001)
e
e
ne
ne
In experiments neutrinos are NEVER seen.
We can only detect them through the
byproducts of their interactions with matter.
Type of the charged particle detected used
to infer the type of incoming neutrino.
e
e
Electron, e
mass ( 1 )
Muon, m
mass ( 200 )
Tau, t
mass ( 3500 )
-
Electron
Neutrino, ne
-
Muon
Neutrino, nm
-
Tau
Neutrino, nt
3 Lepton Types, or Flavours
m
t
ne
ne
m
t
ne
ne
Positron, e+
mass ( 1 )
Muon, m+
mass ( 200 )
Tau, t+
mass ( 3500 )
+
Electron
Antineutrino, ne
+
Muon
Antineutrino, nm
+
Tau
Antineutrino, nm
3 Antileptons
Antimatter is not....
From Angels and Demons, Dan Brown, 2009
Matter
Anti-Matter
anti-quark
quark
Negative
electric charge
Predicted by Dirac in 1928
Discovered by Anderson in 1932
Positive
electric charge
Where do they come
from?
Everywhere....
Sun
Supernovae
Atmosphere
Reactors
Accelerators
Geoneutrinos
Here be dragons
Earth's heat source is probably
radioactive decay....which
generates neutrinos
From the Big Bang
One cubic foot of space contains
about 10,000,000 neutrinos left
over from the Big Bang (maybe).
They are present in vast numbers
≈ 5 billion per cm2 per second at the Earth
5,000,000,000,000,000 solar n just
went through you
So why don't we notice?
n are almost ghosts. They interact extremely
weakly with matter.
To a neutrino a planet is mostly empty space.
Probability 5 x 10-13
= 0.00000000000005
"The chances of a neutrino actually hitting something
as it travels through all this howling emptiness are
roughly comparable to that of dropping a ball bearing
at random from a cruising 747 and hitting, say, an
egg sandwich."
Douglas Adams
Probability 2 x 10-13
e
n
p

e
n
p
n
e
n
p
n
e
n
p
n
Why do we study them?
Probes of
environments that
we otherwise cannot
study
Cosmological and
astrophysical probes
IceCube Experiment
The Universe
The Universe
but where is all the antimatter?
light
matter
light
antimatter
Equal amounts created - but no antimatter
now - so matter and antimatter must behave
differently after creation
Understanding this is a Big
Physics QuestionTM
How are we studying this?
The Sun is Broken!!!
Ray Davis in his solar neutrino
detector – Early 1970s
Less than expected
Number n observed
The sun produces and Davis detected only e
Expected
Measured
Neutrino Oscillations
THE discovery in neutrinos of the last 20 years
e
e
ne
ne
A typical neutrino experiment
Neutrino Oscillations
THE discovery in neutrinos of the last 20 years
m
e
ne
nm
Neutrinos were changing flavour between
sun and detector!
m
e
ne
nm
Fraction of e
1
Fraction
of m
Fraction
of e
0
Distance Travelled
Oh Come on, pull the other one!
Q. How can a ne spontaneously turn into a nm?
Oh Come on, pull the other one!
Q. How can a ne spontaneously turn into a nm?
A. It's complicated...and can only be correctly
described using the full mathematical
machinery of quantum mechanics.
Oh Come on, pull the other one!
Q. How can a ne spontaneously turn into a nm?
A. It's complicated...and can only be correctly
described using the full mathematical
machinery of quantum mechanics.
| ν α >= ∑ i= 1 U α i | ν i >
3
where Uai is a unitary matrix
| ν k (t , x )>= e i( E t − p x) | ν k (0,0)> → P(ν α (0,0)→νβ (t , x ))= | < ν β( t , x)| ν α (0,0)> |2
k
k
| <ν β(t , x)| ν α (0,0)>|2= ∑ k ∑ j U α k U *α j U β k U β* j e i((E − E )t− ( p − p ) x)
j
U=
cosθ sin θ
− sin θ cosθ
(
)
k
j
k
2
Δ
m
2
2
12 L
P(ν α (0,0)→ν β(t , x ))= sin (2 θ)sin (
)
4E
In English this time?
Q. How can a ne spontaneously turn into a nm?
In English this time?
Q. How can a ne spontaneously turn into a nm?
A. The ne isn't a particle. It's three!
e
ne
ne ≡ “that thing which was
always produced/detected
with an electron but is
never observed itself”
Quantum Stuff
Posit three other particles with definite mass : n1, n2 and n3
e
n1
or
e
ne
e
=
or
e
50%
n2
30%
n3
20%
m
e
Long journey
ne
Original
n1,n2,n3
mixture
nm
n1,n2,n3
travels
at different
speeds
Fraction
of m
Fraction
of e
Different
n1,n2,n3
mixture
Why?
If the flavour change probability of
neutrinos is different from that of
anti-neutrinos, thenwe have a handle
to study the matter/antimatter asymmetry
on earth and hence find out how
the universe worked at very early times
Prob(νμ →ν e )≠ Prob(ν μ →νe )
The T2K Experiment
University of Warwick
University of Sheffield
Imperial College, University of London
Oxford University
University of Liverpool
University of Lancaster
Queen Mary College, University of London
Rutherford-Appleton Laboratories
295 km
Summary
The non-existence of antimatter in the
universe is one of the outstanding
problems in cosmology
Understanding this problem brings us
closer to a full Grand Unified Theory
Neutrinos, the smallest and wierdest of
the fundamental particles, could hold
the key
Open Questions
How much do n1,n2 and n3 weigh?
Why are they so much lighter than all the other
massive particles?
Are neutrinos the same as antineutrinos?
Are neutrinos the reason we are here at all?
“If we are to understand “why we
are here” and the basic properties
of the universe we live in, we must
understand the neutrino.”
American Physical Society Report - 2004
Thank you
Quantum Stuff
1
2
3
e
50%
30%
20%
m
25%
30%
40%
t
25%
30%
40%
P(e  1 m) = (50%)(25%) = 12%
Why do blue sky research?
Curiosity about the world around us.
5-10% of jobs in UK are in physics-based sectors
Gross added value from physics sectors was estimated to
be 70 billion pounds in 2005
Synergy between PP projects and industry – industry
acquires added skills base for other applications
Training - 50% of PP PhDs go into other sectors
Radioisotope production
Sensors for medical applications
High level computing for biological modelling
Spin off tools for other science (e.g. DIAMOND)
Nuclear fusion research
Muon tomography in border security
Security scanners
Rock Imaging
Cancer treatment using next gen cyclotrons
Funding
UK Science Funding : 1.8% GDP (15th in world)
18 billion to 2015
(BIS Press Release)
Particle Physics Share : 1 billion to 2015
Total LHC Cost : 2.1 bn for accelerator
0.6 bn for experiments
UK contribution : 500 million in development
95 million / year
(STFC Pres
Cost of the Shard : 1.2 bn
Cost of one Vanguard submarine : 1.5 bn
Universal Structure
m0 eV
m1 eV
m eV
m4 eV
Only
An atom a day
37
e
Cl e-
37
Ar
1 Ar atom every
two days
From Cosmic
Rays.
JPARC Facility
JPARC Facility
TARGET
nm
295 km
nm
Super-Kamiokande
ne
Water Cerenkov
Electron-like : has a
fuzzy ring
Muon-like : has a
sharp edged ring and
particle stopped in
detector.
From the Big Bang
One cubic foot of space contains
about 10,000,000 neutrinos left
over from the Big Bang.
Artist's conception
From Astrophysical Objects
Supernovae created the heavy elements (us)
and neutrinos appear to be important to the
explosion dynamics.