Neutrinos and the Case of the Missing Antimatter

Steve Boyd, University of Warwick

A little bit of historyWhat are neutrinos?Where do they come from?Why study them?A recent surprise

CRISIS

Energy(Ra) ≠ Energy(Ac)+Energy(e)

“At the present stage of atomictheory we have no argumentsfor upholding the concept ofenergy balance in the case ofb-ray disintegrations.”

Neils Bohr

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(Neutrino)

What are neutrinos?

Electron, e

Tiny mass ( 1 )

-

Electron Neutrino, ne

0Very tiny mass(<0.0000001)

Electron, e

Tiny mass ( 1 )

-

mass of a neutrino =

mass of an electron =

mass of a nice cup of tea =

Very tiny mass(<0.0000001)

e

ne

e

ne

Electron Neutrino, ne

0Very tiny mass(<0.0000001)

Electron, e

Tiny mass ( 1 )

-

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 Neutrino, ne

Electron, emass ( 1 ) -

Muon Neutrino, nm

Muon, mmass ( 200 ) -

TauNeutrino, nt

Tau, tmass ( 3500 ) -

3 Lepton Types, or Flavours

m

ne

t

ne

m

ne

t

ne

Electron Antineutrino, ne

Positron, e+

mass ( 1 ) +

3 Antileptons

Muon Antineutrino, nm

Muon, m+

mass ( 200 ) +Tau Antineutrino, nm

Tau, t+

mass ( 3500 ) +

Antimatter is not....

From Angels and Demons, Dan Brown, 2009

Negativeelectric charge

Positiveelectric charge

quarkanti-quark

Matter Anti-Matter

Predicted by Dirac in 1928 Discovered by Anderson in 1932

Where do they come from?

Everywhere....Sun Supernovae

Atmosphere

Reactors

Accelerators

Geoneutrinos

Here be dragons

Earth's heat source is probablyradioactive decay....whichgenerates neutrinos

From the Big Bang

One cubic foot of space contains about 10,000,000 neutrinos leftover 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

ne

"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

enp

enpn

enpn

enpn

enpn

enpn

enpn

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

light

matter

antimatter

Equal amounts created - but no antimatter now - so matter and antimatter must behavedifferently after creation

Understanding this is a Big Physics QuestionTM

How are we studying this?

The Sun is Broken!!!

Ray Davis in his solar neutrinodetector – Early 1970s

Less than expected

Expected

Measured

Num

ber n

obs

erve

d

The sun produces and Davis detected only e

Neutrino OscillationsTHE discovery in neutrinos of the last 20 years

e

ne

e

ne

A typical neutrino experiment

Neutrino OscillationsTHE discovery in neutrinos of the last 20 years

e

ne

m

nm

Neutrinos were changing flavour betweensun and detector!

Distance Travelled

Frac

tion

of e

0

1

e

ne

m

nm

Fraction of e

Fraction of

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.

|α >=∑ i=1

3U α i | i > where Uαi is a unitary matrix

|k (t , x )>=ei( Ek t− pk x) |k (0,0)> → P(α(0,0)→ β (t , x ))=| <β( t , x) |α (0,0)> |2

U=( cosθ sin θ−sin θ cosθ) P(α (0,0)→ β(t , x ))=sin 2(2θ)sin2(

Δ m122 L

4 E)

| < β( t , x ) | α (0,0 )> |2=∑ k∑ jU α k U α j

* U β kU β j* e i( (E j− E k ) t−( p j− p k) x )

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!

ne ≡ “that thing which was always produced/detected with an electron but is never observed itself”

e

ne

Quantum Stuff

ene

en1

en2

en3

=or

or

50%

30%

20%

Posit three other particles with definite mass : n1, n2 and n3

e

ne

m

nmOriginal n1,n2,n3mixture

Different n1,n2,n3mixture

n1,n2,n3travelsat differentspeeds

Long journey

Fraction of e

Fraction of

Why?

Prob ( → e )≠Prob ( → e )

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 howthe universe worked at very early times

The T2K Experiment

University of WarwickUniversity of SheffieldImperial College, University of LondonOxford UniversityUniversity of LiverpoolUniversity of LancasterQueen Mary College, University of LondonRutherford-Appleton Laboratories

295 km

SummaryThe non-existence of antimatter in theuniverse 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 ofthe fundamental particles, could holdthe 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 weare here” and the basic propertiesof the universe we live in, we mustunderstand the neutrino.”

American Physical Society Report - 2004

Thank you

Quantum Stuff

e

P(e) = (50%)(25%) = 12%

Why do blue sky research?Curiosity about the world around us.5-10% of jobs in UK are in physics-based sectorsGross added value from physics sectors was

estimated to be 70 billion pounds in 2005Synergy between PP projects and industry – industry

acquires added skills base for other applicationsTraining - 50% of PP PhDs go into other sectors

Radioisotope productionSensors for medical applicationsHigh level computing for biological modellingSpin off tools for other science (e.g. DIAMOND)Nuclear fusion researchMuon tomography in border securitySecurity scannersRock ImagingCancer treatment using next gen cyclotrons

FundingUK 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 experimentsUK contribution : 500 million in development 95 million / year

(STFC Press Release)

Cost of the Shard : 1.2 bnCost of one Vanguard submarine : 1.5 bn

Universal Structure

m eV m eV

m eV m eV

An atom a day e Cl37 e- Ar37

1 Ar atom every two days

Only

From Cosmic Rays.

JPARC Facility

JPARC Facility

TARGET nm

295 km

Super-Kamiokande

nm

ne

Water Cerenkov

Electron-like : has a fuzzy ring

Muon-like : has a sharp edged ring andparticle stopped in detector.

From the Big Bang

Artist's conception

One cubic foot of space contains about 10,000,000 neutrinos leftover from the Big Bang.

From Astrophysical Objects

Supernovae created the heavy elements (us) and neutrinos appear to be important to the explosion dynamics.