“The Story of the neutrino” Does the missing matter matter? or.

“The Story of the neutrino”

Does the missing matter matter?

or

21st/22nd March 2002 Particle Physics MasterclassOxford University

2

An Introduction

Sudbury Neutrino Observatory (SNO)

2km underground

To observe the To observe the Sun !Sun !


3

Discovery of RadioactivityHenri Becquerel, 1896

Accidentally left photographic plates in a dark drawer with some uranium salts...

The plates became “fogged”

The Uranium was emitting something which was interacting with the film...


4

Radioactivity and momentum conservation

Unstable nucleus

Recoiling (more) stable nucleus

• A* is at rest (PTOTAL = 0)

•A and B must have equal and opposite momenta:

p + (-p) = 0

• But, E2 = p2 + m2 and the total energy loss is fixed...

• So, there can be only one value of the energy of the escaping particle...

A*

A

B

p

-p

MA

mB

Conservation of momentum

Einstein: Relativity


5

The Beta-decay puzzle

A*

A

e-

Beta-particle energy

N

A nucleus decays giving out an electron...

Something must be wrongwith the picture...?

The electron has arange of energies

Energy and momentum aren’t conserved!?


6

The “neutrino” hypothesisWhat Pauli “saw”:

“What if the missing energy is carried off by an otherwise “invisible” particle...?”

Wolfgang Pauli, 1930

A*

A

e-

C


7

The birth of the neutrino

Pauli: “I have done a terrible thing. I have invented a particle which cannot be detected...”

• It must be very lightvery light, possibly massless:(sometimes, the electron takes all the energy in the decay)

• It must be electrically neutralelectrically neutral:(charge conservation in beta decay)

• It is produced along with an electron:(they can’t be made on their own...)

• It must interact very rarelyinteract very rarely:(it always escapes the detector without being seen)


8

25 years later: Hard but not impossible

Beta decay in a nuclear reactor

n p

e-

e

“Inverse” Beta decay

p n

e+e

It would take 1019 m (300 light years) of water to absorb a single neutrino.

Therefore we need many neutrinos...

…and a very large detector

...and it’s the sametype of reaction in“reverse”


9

Neutrinos from the Sun

p

p

pn

e

e+

The biggest nuclear reactorThe biggest nuclear reactorof them all...of them all...

Two protons fuse togive a “deuteron”, a positron and an electron neutrino

10 billion neutrinos from 10 billion neutrinos from the sun pass through the sun pass through your finger tip every your finger tip every

second!second!


10

380,000 bottles of cleaning fluid

Neutrinos can change chlorine atoms to argon atoms by Inverse Beta Decay

Cl + Cl + ee Ar + e Ar + e--

Measure the amount of argon produced in one month......find 10 atoms in 1030!

n + ee p + e p + e--


11

Some of our neutrinos are missing...

• We “understand” how each nuclear reaction works...

• We can measure how much energy the sun gives out...

• We can accurately predict the number of neutrinos we expect!

p + p p + n + e + e + (Energy)

SunTotal energy

“Light detector”

Nneutrinos = Total energy Reaction energy

Something must be wrong with the neutrinos...


12

Neutrinos as waves... Oscillations!

• What if neutrinos were made up of two quantum waves with different wavelengths...?

• These waves would interfere

• Electron neutrinos disappear depending on the distance and mass difference of the neutrinos

Quantum waves interfering over 100

million miles!


13

SNO - two measurements at once

1000 tonnes of heavy water (D20)

10,000 light detectors

100 million km to the sun

2039m to surface


14

Sudbury Neutrino Observatory


15

SNO - two measurements at once

•Reaction like beta decay to detect electron neutrinos

e + d p + p + ee

•All neutrinos can break up deuterons (electron, muon or tau)

any + d p + any + nn

•See ee or nn from flash of light

•If oscillation occurs:Number of e

Number of any <1


16

Cosmic encounters...

proton• High energy protons from space in all directions

• Hit the atmosphere and produce a “shower” of particles

• This shower includes muons

• These particles decay like beta decay to give...

...neutrinos!

100 particles m-2s-1

This is why all This is why all neutrino neutrino

detectors are detectors are undergroundunderground


17

Atmospheric neutrinos

“Showerparticle”

muonmuon

neutrino

e

electronneutrino

muonneutrino

• Muons and electrons can’t just be made or decay on their own...

•Particle “type” must be conserved

• A shower particle produces a muon and a muon neutrino.

• The muon decays to a muon neutrino... ...and an electron along with an electron neutrino

2 2 : : 1 1 ee


18

Detecting neutrino oscillations...

Knowing what ratio of neutrino types to expect...

...count neutrinos after different distances

See how many neutrinosof each type havedisappeared (oscillated)

Atmospheric neutrinos

Compare “up” and “down”

Soudan 2


19

Soudan 2: Disappearing neutrinos...

e

1000 tonnes of iron!

What do electron and muon neutrino interactions look like?

Interacting electron neutrinos produce electrons

Electrons create e+e- pairs“Electromagnetic Showers”

Interacting muon neutrinos produce muons

Muons are heavier than electrons Straight track until it runs out of energy

muon

e


20

What we (don’t) know...

• There are three types of neutrino, each associated with a “lepton”

• They appear to change (oscillate) between neutrino types

• Real quantum waves in action over millions of miles!

e

nu-e

mu

nu-mu

tau

nu-tau

“The Story of the neutrino” Does the missing matter matter? or.

Documents

Transcript of “The Story of the neutrino” Does the missing matter matter? or.