J. Goodman – May 2003 Ghosts in the Universe Jordan A. Goodman University of Maryland Fall 2003 The world we don’t see around us

J. Goodman – May 2003

Ghosts in the Universe

Jordan A. Goodman

University of Maryland

Fall 2003

Jordan A. Goodman

University of Maryland

Fall 2003

The world we don’t see around us

The world we don’t see around us


Outline

• How we see particles• How we know about things we can’t see (like

neutrinos)• What is the structure of matter• What makes up most of the Universe• Neutrino mass• “” and the Dark side of the force


The early periodic table


The structure of matter

1869 - Mendeleyev – grouped elements by atomic weights1869 - Mendeleyev – grouped elements by atomic weights


How do we know about Atoms

• Brownian Motion - Einstein


Seeing Atoms


Seeing Atoms


How do we see into atoms

• Atomic Spectra– We see spectral lines– The colors and the spacing of these lines tell us about

the structure of the atoms

EE


Hydrogen Spectra


What are fundamental particles?

• We keep finding smaller and smaller things


How do we see particles?

• Most particles have electric charge– Charged particles knock electrons out of atoms– As other electrons fall in the

atoms emit light

The light from your TV is The light from your TV is from electrons hitting the from electrons hitting the screenscreen

In a sense we are In a sense we are “seeing” electrons“seeing” electrons

The light from your TV is The light from your TV is from electrons hitting the from electrons hitting the screenscreen

In a sense we are In a sense we are “seeing” electrons“seeing” electrons


The search for fundamental particles

• Proton and electron– These were known to make up the atom

• The neutron was discovered• Free neutrons were found to decay

– They decayed into protons and electrons– But it looked like something was missing

• In 1930 Pauli postulated a unseen neutral particle

• In 1933 Fermi named it the “neutrino” (little neutron)


Why do we care about neutrinos?

• Neutrinos – They only interact

weakly– If they have mass at all

– it is very small • They may be small, but there sure are a

lot of them!– 300 million per cubic meter left over from the

Big Bang– with even a small mass they could be most

of the mass in the Universe!


Facts about Neutrinos

• Neutrinos are only weakly interacting

• 40 billion neutrinos continuously hit every cm2 on earth from the Sun (24hrs/day)

• Interaction length is ~1 light-year of steel

• 1 out of 100 billion interact going through the Earth


Seeing Big Picture


Why do we think there is dark matter?

• Isn’t obvious that most of the matter in the Universe is in Stars?

Spiral GalaxySpiral Galaxy



• In a gravitationally bound system out past most of the mass V ~ 1/r1/2

• We can look at the rotation curves of other galaxies– They should drop off

But they don’t!



• There must be a large amount of unseen matter in the halo of galaxies– Maybe 20 times more than in the stars!– Our galaxy looks 30 kpc across but recent data

shows that it looks like it’s 200 kpc across


Measuring the energy in the Universe

• We can measure the mass of clusters of galaxies with gravitational lensing

• These measurements give mass ~0.3

• We also know (from the primordial deuterium abundance) that only a small fraction is nucleons

nucleons < ~0.04 Gravitational

lensingGravitational

lensing


What is this ghostly matter?

• Could it be neutrinos?• How much neutrino mass would it take?

– Proton mass is 938 MeV– Electron mass is 511 KeV– Neutrino mass of 2eV would solve the galaxy

rotation problem – 20eV would close the Universe

• Theories say it can’t be all neutrinos– They have difficulty forming the kinds of structure

observed. The structures they create are too large and form too late in the history of the universe


Does the neutrino have mass?


Detecting Neutrino Mass

• If neutrinos of one type transform to another type they must have mass:

• The rate at which they oscillate will tell us the mass difference between the neutrinos and their mixing

GeV

kmeVxe E

LmLP

222 27.1

ins2sin;


Neutrino Oscillations

1212

=Electron =Electron

Electron

Electron

1212

=Muon =Muon

Muon Muon


Solar Neutrinos


Solar Neutrino Spectrum


Solar Neutrino Experiment History

• Homestake - Radiochemical– Huge tank of Cleaning Fluid (perchloroethylene)

e + 37Cl e- + 37Ar

– Mostly 8B neutrinos + some 7Be– 35 years at <0.5 ev/day– ~1/3 SSM– (Davis - 2002 Nobel Prize)

• Sage/Gallex - Radiochemical– “All” neutrinos

– e + 71Ga e- + 71Ge

– 4 years at ~0.75 ev /day– ~2/3 SSM

• Kamiokande-II and -III – 8B neutrinos only

– e Elastic Scattering

– 10 years at 0.44 ev /day– ~1/2 SSM– (Koshiba 2002 Nobel Prize)


The Solar Neutrino Problem






Neutrino OscillationsF o r t w o n e u t r i n o s p e c i e s

e a n d w e h a v e :

cossin

sincos

21

21

e

w h e r e 1 a n d

2 a r e t h e m a s s e i g e n s t a t e s .

I n a w e a k d e c a y o n e p r o d u c e s a d e f i n i t e w e a k e i g e n s t a t e

t e 0 .

.

A t a l a t e r t i m e t h e p r o b a b i l i t y o f t h e f i n a l s t a t e w i l l b e :

sincos 2121

tiEtiE eet

T h e s u r v i v a l p r o b a b i l i t y i s :

GeV

kmeVee E

LmLP

222 27.1

ins2sin1; .


Neutrino Oscillations

• Could Neutrino Oscillations solve the solar neutrino problem?– Simple oscillations would require a cosmic conspiracy– The earth/sun distance would have to be just right to get rid of

Be neutrinos

• Another solution was proposed –

Resonant Matter Oscillations in the sun (MSW- Mikheev, Smirnov, Wolfenstein)

• Because electron neutrinos “feel” the effect of electrons in matter they acquire a larger effective mass– This is like an index of refraction


MSW Oscillations

Sin 2Spring =

e

Length = Mass

When length (i.e. effective mass) are equal the couplingis enhanced.

Mechanical Analogy for Neutrino Oscillations

In theSun

In theVacuum

Resonance

(Mikheev, Smirnov, Wolfenstein)


Oscillation Parameter Space

LMA

LOW

VAC

SMA


Solar Neutrinos in Super-K

• The ratio of NC/CC cross section is ~1/6.5


Super-Kamiokande


Super-Kamiokande


Super-K

• Huge tank of water shielded by a mountain in western Japan– 50,000 tons of ultra clean water – 11,200 20in diameter PMTs– Under 1.5km of rock to reduce downward cosmic rays

• (rate of muons drops from ~100k/sec to ~2/sec)

• 100 scientists from US and Japan• Data taking began in 1996


Super-K site

MozumiMozumi


Cherenkov Radiation

Boat moves throughwater faster than wavespeed.

Bow wave (wake)


Cherenkov Radiation

Faster than wave speedSlower than wave speed


Cherenkov Radiation

Aircraft moves throughair faster than speed ofsound.

Sonic boom


Cherenkov Radiation

When a charged particle moves throughtransparent media fasterthan speed of light in thatmedia.

Cherenkov radiation

Cone oflight


Cherenkov Radiation


Detecting neutrinos

Electron or

muon track

Electron or

muon track

Cherenkov ring on the

wall

Cherenkov ring on the

wall

The pattern tells us the energy and type of particle

We can easily tell muons from electrons

The pattern tells us the energy and type of particle

We can easily tell muons from electrons


A muon going through the detector












Stopping Muon


Stopping Muon – Decay Electron


Solar Neutrinos in Super-K

• 1496 day sample (22.5 kiloton fiducial volume)• Super-K measures:

– The flux of 8B solar neutrinos– Energy spectrum and direction of recoil electron

• Energy spectrum is flat from 0 to Tmax

– The zenith angle distribution– Day / Night rates– Seasonal variations


Solar Neutrinos

)s cm 10 x (syst)0.03(stat) (2.32

ssm) (syst) %0.5%(stat) (45.1%

1-2-608.00.07

1.61.4 -

e


Energy Spectrum


Seasonal/Sunspot Variation


Combined Results e to

SK+Gallium+Cholrine - flux only allowed 95% C.L.

95% excluded by SK flux-independent zenith angle energy spectrum

95% C.L allowed. - SK flux constrained w/ zenith angle energy spectrum

(Like SK)


SNO CC Results

e= (35 ± 3 )% ssm


Combining SK and SNO

• SNO measures e= (35 ± 3 )% ssm

• SK Measures es= (47 ± .5 ± 1.6)% ssm

• If Oscillation to active neutrinos:– SNO Measures just e

• This implies that ssm (~2/3 have oscillated)

– SK measures es =(e + ( /6.5)

• Assuming osc. SNO predicts that SK will see es ~ (35%+ 65%/6.5) ssm = 45% ± 3% ssm


SNO Results (NC/CC)

• SNO Results


SNO Results


Combined SK and SNO Results


Kamland – Terrestrial Neutrinos


Reactors Contributing to Kamland


Kamland Results (Dec. 2002)


Kamland


Kamland


All Experiments Combined with Kamland


• It looks like the Solar Neutrino problem has been solved!– All Data (except LSND) is now consistent

with the large angle MSW solution – e->

– We have ruled out SMA and Low solutions– Disfavor Sterile Neutrino solutions

• Neutrinos have mass!– This confirms the atmospheric neutrino results

– The Solar mass difference ~0.003eV

• Future Experiments – – MiniBoone – LSND effect

Solar Neutrino Conclusions


Atmospheric Neutrino Production

Ratio predicted to ~ 5%

Absolute Flux Predicted to ~20% :

2

ee


Atmospheric Oscillations

about 13,000 km

about 15

km

Neutrinos produced in

the atmosphere

Neutrinos produced in

the atmosphere

We look for transformations

by looking at s with different distances from production

SK


Telling particles apart

MuonElectronMuonElectron


Moderate Energy Sample


Multi-GeV Sample


Summary of Atmospheric Results

Best Fit for to

Sin22 =1.0,

M2=2.4 x 10-3eV2

2min=132.4/137 d.o.f.

No Oscillations

2min=316/135 d.o.f.

99% C.L.

90% C.L.

68% C.L.

Best Fit

Compelling evidence for to atmospheric neutrino oscillations

Now the most cited exp. HEP paper

Skip Tau studies


Neutrinos have mass

• Oscillations imply neutrinos have mass!

• We can estimate that neutrino mass is probably <0.2 eV – (we measure M2)

• Neutrinos can’t make up much of the dark matter –

• But they can be as massive as all the visible matter in the Universe!

• ~ ½% of the closure density


Supernova Cosmology Project

• Set out to directly measure the deceleration of the Universe

• Measure distance vs brightness of a standard candle (type Ia Supernova)

•The Universe seems to be accelerating!•Doesn’t fit Hubble Law (at 99% c.l.)


Energy Density in the Universe

may be made up of 2

parts a mass term and a “dark energy” term

(Cosmological Constant)

massenergy

• Einstein invented to keep the Universe static

• He later rejected it when he found out about Hubble expansion

• He called it his “biggest blunder”

m


The Cosmological Constant


What is the “Shape” of Space?

• Open Universe <1

– Circumference (C) of a circle of radius R is

C > 2R

• Flat Universe =1

– C = 2R– Euclidean space

• Closed Universe >1

– C < 2R


Results of SN Cosmology Project

• The Universe is accelerating

• The data require a positive value of “Cosmological Constant”

• If =1 then they find

~ 0.7 ± 0.1


Accelerating Universe


Accelerating Universe


Measuring the energy in the Universe

• Studying the Cosmic Microwave radiation looks back at the radiation from 400,000 years after the “Big Bang”.

• This gives a measure of 0


Recent Results - 2002

0=1 nucleon


WMAP -2003


WMAP - 2003


What does all the data say?

• Three pieces of data come together in one region

~ 0.73 m~ 0.27 (uncertainty ~0.04)

• Universe is expanding & won’t collapse

• Only ~1/6 of the dark matter is ordinary matter (atoms)

• A previously unknown and unseen “dark energy” pervades all of space and is causing it to expand and accelerate


What do we know about “Dark Energy”

• It emits no light• It acts like a large negative pressure

Px ~ - x

• It is approximately homogenous– At least it doesn’t cluster like matter

• Calculations of this pressure from first principles fail miserably – assuming it’s vacuum energy you predict a value of ~ 10120

• Bottom line – we know very little!


Conclusion

• total = 1.02 ± 0.02

– The Universe is flat!

• The Universe is : ~1/2% Stars

~1/2% Neutrinos

~27% Dark Matter (only 4% is ordinary matter)

~73% Dark Energy

• We can see ~1/2%• We can measure ~1/2%• We can see the effect of

~27% (but don’t know what most of it is)

• And we are pretty much clueless about the other 3/4 of the Universe

There is still a lot of Physics to learn!

Documents

J. Goodman – May 2003 Ghosts in the Universe Jordan A. Goodman University of Maryland Fall 2003 The world we don’t see around us