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OLLI lectures Fall 2016Horst D Wahl

(hwahl@fsu.edu)

lecture 4, 1 Nov 2016

Hot Topics in Physics

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Outline of 2nd class Recap Present paradigm, cont’d

Cosmos Neutrinos (maybe??)

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A theoretical model of interactions of elementary particles, based on quantum field theory

Symmetry: SU(3) x SU(2) x U(1)

Matter particles: fermions Quarks: up, down, charm,

strange, top, bottom Leptons: electron, muon, tau,

+ their neutrinos Force particles

Gauge Bosonso γ (electromagnetic force)o W±, Z (weak, electromagnetic)o g gluons (strong force)

Higgs boson spontaneous symmetry

breaking of SU(2) mass

“Standard Model” of Particle Physics

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Beginning of Time: Big Bang Big Bang theory with inflationMost widely accepted cosmological theoryStarts with “Big Bang”, i.e. abrupt appearance of

expanding space time (13.798±0.037) Gy ago inflationary epoch: t ≈ 10-36 to 10-32, space expands by

huge factor 1027 to size of a grapefruitAfter cosmic inflation, expansion continues at

decreasing rate Expansion ⇒cooling ⇒ formation of particles, nuclei “recombination”: at t ≈ 380ky formation of atoms (H)

⇒ Cosmic background radiation (CMB)Accelerated expansion: from t ≈ 7 Gy to now

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Timeline of the metric expansion of space; space (including hypothetical non-observable portions of the universe) is represented at each time by the circular sections. On the left the dramatic expansion occurs in the inflationary epoch, and at the center the expansion accelerates (artist's concept; not to scale). (https://www.wikiwand.com/en/Big_Bang )

https://www.wikiwand.com/en/Big_Bang

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Other cosmological theories

Cyclic theory (Big Bang – Big Crunch):Every Ty (1012 years), expansion changes to

contraction ⇒universe shrinks, becomes infinitesimally small, then a new Big BangCycles of Big Bang and Big Crunch continue

forever Eternal inflation: Spacetime infinite in space and in past and

future timeOur Big Bang and universe is just one of many

(“multiverse”)…..

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Chronology of the Universe Very early universe (1st ps):

Planck epoch (before tP = 10-43 s)o None of present theories apply, all forces unified

Grand unification epoch (From Planck epoch until inflation):o 3 forces unified – electronuclear forceo We hardly know anything about this

Early Universe (first 380000 years): From quark epoch to photon epoch:

o Emergence of familiar forces and particleso Ends with formation of atoms ⇒ CMB

“Dark Ages” (0.38 to 150 My) Universe transparent, but no stars, no galaxies

Large structure formation (150My to now until 100Ty?) Stars, galaxies, galaxy clusters,..

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Cosmic History

Cosmic Microwave Background (CMB) = oldest light in the universe (380,00 y) patterns imprinted on this light encode the events that happened only a tiny fraction of a second after the Big Bang. In turn, the patterns are the seeds of the development of the structures of galaxies we now see billions of years after the Big Bang.

Credit: NASA / WMAP Science Team http://map.gsfc.nasa.gov/media/020622/index.html

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Hubble deep field view

http://hubblesite.org/newscenter/archive/releases/2014/27/image/a/format/xlarge_web/https://www.nasa.gov/mission_pages/hubble/main/index.html

Hubble Space Telescope: project of international cooperation between NASA and ESA (European Space Agency).

From Hubble Deep Field View, estimated about 225 billion galaxies in the visible universe

Latest analyses, combining HST data and date from other telescopes ⇒ estimate at least 10 times more

About 1012 stars in our galaxy

http://www.skyandtelescope.com/astronomy-resources/how-many-galaxies/http://www.nasa.gov/feature/goddard/2016/hubble-reveals-observable-universe-contains-10-times-more-galaxies-than-previously-thoughthttp://phys.org/news/2016-10-universe-ten-galaxies-previously-thought.htmlhttp://www.esa.int/Our_Activities/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe

http://hubblesite.org/newscenter/archive/releases/2014/27/image/a/format/xlarge_web/https://www.nasa.gov/mission_pages/hubble/main/index.htmlhttp://www.nasa.gov/feature/goddard/2016/hubble-reveals-observable-universe-contains-10-times-more-galaxies-than-previously-thoughthttp://www.nasa.gov/feature/goddard/2016/hubble-reveals-observable-universe-contains-10-times-more-galaxies-than-previously-thoughthttp://phys.org/news/2016-10-universe-ten-galaxies-previously-thought.htmlhttp://www.esa.int/Our_Activities/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe

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Cosmic background radiation CMB = leftover radiation from the Big Bang, fills the entire Universe Until 380,00 years after the Big Bang, Universe filled with hot plasma of

particles (mostly protons, neutrons, and electrons) and photons (light). photons constantly interacting with free electrons ⇒ could not travel long

distances ⇒ early Universe was opaque at 380,000y (“recombination”), temperature low enough (3000K) for protons

and electrons to combine to form hydrogen Absence of free electrons ⇒ Photons could move freely⇒ Universe

transparent expansion of the universe ⇒ photon wavelengths increased ("red shift");

now about 1 mm, corresponding to a temperature of about 2.7 K CMB is the oldest light from the universe, ⇒ can get information about

universe at 380,000 years CMB nearly isotropic (i.e. same in all directions), but small deviations from

uniformity (few in 104) due to slight temperature and density variations before the time of emission

Anisotropy gives us information about state of the universe at that time

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Origin of CMB

http://map.gsfc.nasa.gov/media/990053/990053sb.jpg

http://map.gsfc.nasa.gov/media/990053/990053sb.jpg

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Discovery of CMB Predicted by Ralph Alpher and Robert Herman in 1948 Discovered serendipitously by Arno Penzias and Robert

Wilson in 1965Measured by COBE (Cosmic Background Explorer) (1989 -1993)

(https://science.nasa.gov/missions/cobe, http://lambda.gsfc.nasa.gov/product/cobe/ )

(Nobel Prize 2006 for John Mather + George Smoot)WMAP (Wilkinson Microwave Anisotropy Probe)

(http://map.gsfc.nasa.gov/ ) (2001 to 2011) Planck (2009 – 2013)

(http://www.esa.int/Our_Activities/Space_Science/Planck )

https://science.nasa.gov/missions/cobehttp://lambda.gsfc.nasa.gov/product/cobe/http://map.gsfc.nasa.gov/http://www.esa.int/Our_Activities/Space_Science/Planck

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CMB spectrum

CMB spectrum looks like spectrum emitted by a Black Body of temperature T = 2.725 K

http://map.gsfc.nasa.gov/universe/bb_tests_cmb.html

http://map.gsfc.nasa.gov/universe/bb_tests_cmb.html

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Planck’s radiation formula (1900)

From assuming that oscillator energies are integer multiples of hν, Planck derived a formula for the blackbody spectrum that agreed with observations

spectral radiance of blackbodies = the power emitted from the emitting surface, per unit projected area of emitting surface, per unit solid angle, per spectral unit (frequency or wavelength)

2

3 /

2

5 /( )

2( , )1

2 1( , )1

h kT

hc kT

hTc ehcT

e

ν ν

λ λ

ν νρ ν

ρ λλ

=−

=−

ν = frequency, λ= wavelength, T = temperature, c = speed of light, h = (Planck’s) constanth = 6.626 10-34 Js = 4.13 10-15 eV·s k = Boltzmann constant

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Black-body radiation spectrumMeasurements of Lummer

and Pringsheim (1900)calculation

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Wien’s displacement law

Intensity ρ(λ,T) = power radiated per unit area per unit wavelength at a given temperature

Maximum of the distribution shifts to smaller wavelengths as the temperature increases

Wavelengths for visible light: 400 to 700 nm, UV < 400 nm, IR> 700nm

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CMB -- COBE

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CMB -- WMAP

The anisotropies of the Cosmic microwave background (CMB) as observed by WMAP. The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380 000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. (blue – hot – less dense, red – cold – denser)

https://map.gsfc.nasa.gov/media/121238/ilc_9yr_moll2048.png

https://map.gsfc.nasa.gov/media/121238/ilc_9yr_moll2048.png

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CMB -- Planck

The anisotropies of the Cosmic microwave background (CMB) as observed by Planck. The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380 000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. (blue – hot – less dense, red – cold – denser)

http://www.esa.int/spaceinimages/Images/2013/03/Planck_CMB

http://www.esa.int/spaceinimages/Images/2013/03/Planck_CMB

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The "angular power spectrum" of the fluctuations in the Planck full-sky map. This shows the relative brightness of the "spots" in the map vs. the size of the spots. Green line = fit with “standard model”, red dots = Planck measurements

http://sci.esa.int/science-e-media/img/63/Planck_power_spectrum_orig.jpg

http://sci.esa.int/science-e-media/img/63/Planck_power_spectrum_orig.jpg

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Content of the Universe contents of the universe:

4.6% atoms: the building blocks of stars and planets.

23% Dark matter: DM is different from atoms, interacts only weakly, does not emit or absorb light. detected only indirectly by its gravity.

72% "dark energyo acts as a sort of an anti-gravity. o distinct from dark matter, o responsible for the present-day

acceleration of the universal expansion.

http://map.gsfc.nasa.gov/media/080998/index.html

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Contents of the universe

Planck's high-precision cosmic microwave background map has allowed scientists to extract the most refined values yet of the Universe's ingredients. Normal matter that makes up stars and galaxies contributes just 4.9% of the Universe's mass/energy inventory. Dark matter, which is detected indirectly by its gravitational influence on nearby matter, occupies 26.8%, while dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe, accounts for 68.3%. (http://sci.esa.int/planck/51557-planck-new-cosmic-recipe/ )The 'before Planck' figure is based on the WMAP 9-year data release presented by Hinshaw et al., (2012).

http://sci.esa.int/planck/51557-planck-new-cosmic-recipe/

26http://particleadventure.org/images/history-universe-2013.jpg

http://particleadventure.org/images/history-universe-2013.jpg

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http://particleadventure.org/images/history-of-the-universe-2015.jpg

http://particleadventure.org/images/history-of-the-universe-2015.jpg

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http://hubblesite.org/ http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/

http://hubblesite.org/http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/

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http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/http://vixra.org/pdf/1305.0034v1.pdf

http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/http://vixra.org/pdf/1305.0034v1.pdf

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Summary

Cosmology now a mature quantitative scienceAll observations explained by ΛCDM theory of Big

Bang detailed studies of the CMB power spectrum and

better distance calibration using SNe as standard candles leads to quantitative information about age of the universe and its composition

Big Bang 13.798 Gy agoOnly 4.6% of Universe is “standard matter”, rest is

“Dark Matter (26.9%) and “Dark Energy” (68.3%)

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And Now: Neutrinos!!!

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Neutrinos – why are they interesting?Neutrinos are everywhere: at the Big Bang from the Sun from Cosmic Rays from Supernovas from Nuclear Reactors from Particle Accelerators all around you

For physicists:Neutrinos provide clues for

o Understanding weak interactiono understanding starso understanding supernovaeo Understanding the early universeo ……

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Where do Neutrinos Appear in Nature?

AstrophysicalAccelerators Soon ?

Cosmic Big Bang (Today 330 ν/cm3)

Indirect Evidence

Nuclear Reactors

Earth Atmosphere(Cosmic Rays)

Sun

Supernovae(Stellar Collapse)

SN 1987A

Earth Crust (Natural Radioactivity)

Particle Accelerators

34http://particleadventure.org/images/history-universe-2013.jpg

http://particleadventure.org/images/history-universe-2013.jpg

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http://particleadventure.org/images/history-of-the-universe-2015.jpg

http://particleadventure.org/images/history-of-the-universe-2015.jpg

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Beta decay puzzle

James Chadwick’s (U. Manchester) studies of β decay (1914)

(A, Z) → (A, Z + 1) + e-

Observation: energy spectrum of electrons continuous —violate energy conservation???

Speculation: some unobserved radiation emitted in addition

Ellis and Wooster (1927): study decay

measure the total energy deposited in a thick target

Find: average deposited energy = 0.337 MeV per decay

but nuclear mass difference = 1.05 MeV ⇒ missing energy!!!

210 210Bi Po e−→ +

Three-types of radioactivity: α, β, γ Both α, γ discrete spectrum because

Eα, γ = Ei – Ef

http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.htmlhttp://web.calstatela.edu/faculty/kaniol/f2000_lect_nuclphys/lect1/betadecay_queens_hist.htm

http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.htmlhttp://web.calstatela.edu/faculty/kaniol/f2000_lect_nuclphys/lect1/betadecay_queens_hist.htm

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β decay crisis

(Z,A)

(Z+1,A)

electron

Spin 1/2

Spin 1/2

Spin 1/2

Spin ½ ≠ spin ½ + spin ½ ERa ≠ EBi + Ee

Two problems:apparent violation of energy conservation

+ apparent violation of angular momentum conservation

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Niels Bohr: “At the present stage of atomictheory we have no argumentsfor upholding the concept ofenergy balance in the case ofβ-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”

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Pauli’s solution to the puzzle

Pauli: letter to a Physical Society meeting in Tübingen:“Dear Radioactive Ladies and Gentlemen...”postulated the invisible neutrino

Suppose that beta decay were a 3 body process, with an additional invisible particlenew particle would have to be:* Neutral* Very light or massless* have only rare interactions

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Pauli’s neutrino letter Dear Radioactive Ladies and Gentlemen! I have hit upon a desperate remedy to

save…the law of conservation of energy. …there could exist electrically neutral

particles, which I will call neutrons, in the nuclei…

The continuous beta spectrum would then make sense with the assumption that in beta decay, in addition to the electron, a neutron is emitted such that the sum of the energies of neutron and electron is constant.

But so far I do not dare to publish anything about this idea, and trustfully turn first to you, dear radioactive ones, with the question of how likely it is to find experimental evidence for such a neutron…

I admit that my remedy may seem almost improbable because one probably would have seen those neutrons, if they exist, for a long time. But nothing ventured, nothing gained…

Thus, dear radioactive ones, scrutinize and judge.

http://www.symmetrymagazine.org/cms/?pid=1000450

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Desperate Idea of Pauli

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Pauli’s “desperate” attempt to save appearances Hypothesis of Pauli (1930): Tried to explain puzzle of decay 14Ca → 14N + e-

o Missing energy and wrong spin of 14N

an unobserved neutral, spin-1/2 “neutron” accounts for the apparent anomaly -- a new particle with mass < 1%that of the proton (later called neutrino by Fermi)

Initial thought:o neutrino Is a stable constituent of the nucleuso Suggested by the spin puzzle presented by 14N,

with Z=7 A system of seven protons should have half-integer spin,

addition of a spin-half neutrino constituent would resolve this problem

“I have done a terrible thing: I have postulated a particle that cannot be detected”

Chadwick’s discovery of neutron (1932) Fermi proposes “neutrino” as name for the particle,

made in decay, not part of nucleus before

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Weak interaction

1932:Chadwick’s discovery of the “neutron”1933 Solvay conference: Pauli finally presented his theory of the “neutrino.” Fermi suggested the name “neutrino” to distinguish it

from Chadwick’s heavy neutral nucleon 1934: Fermi “effective theory” of β decay incorporates both the neutron and the neutrino

Proposed that the neutrino was produced in the decay,accompanying the outgoing electron

bound bound en p e ν−→ + +

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Detection of the Neutrino

1950 – Reines and Cowan set out to detect ν

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1951

I. Explode bombII.At same time let detector fall in vacuum tankIII. Detect neutrinosIV. Collect Nobel prize

OK – but repeatability is a bit of a problem

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Discovery, Reines & Cowan 1956 Conducted a series of experiments Stage 1: Hanford site, Washington

Too much background from cosmic rays

Stage 2: Savannah River, South Carolina Better shielding 11 m from reactor 12 m underground

200 liters of water with 40 kg CdCl2 Sandwiched between scintillator layers

Results: ~3 neutrino events per hour detected Used on-off switch on reactor Neutrinos disappeared when reactor

was off

Cowan died in 1974, but Reines awarded Nobel Prize in 1995

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Project Poltergeist Use reactor as neutrino source, First Hanford, later Savannah

river Use water tank with liquid

scintillator and CdCl2 Reaction “inverse beta

decay” (proton of hydrogen in water becomes neutron when hit by a neutrino, positron emitted)

Positron annihilates with an electron ⇒ 2γ

Neutron absorbed by Cadmium-108 → excited state of Cadmium-109 ⇒emits photon (γ)

γ detected by scintillation counter

Clyde Cowan Fred Reines

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Detecting the neutrinoInverse beta decay, followed by e+ e-annihilation:

Experimental needs: Strong neutrino source → reactor Proton target → H in water Positron and neutron detector

Liquid scintillator to detect gammas CdCl2 target to capture neutrons Delayed (5µs) coincidence of γ from

Cd with γ from annihilation2

e p e ne e γν +

+ −

+ → +

+ →

108 109

109

mn Cd CdCd γ

+ →

→ +

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More than one neutrino!

Lederman, Schwartz, Steinberger:Experiment at BNL

(Brookhaven Nat. Lab.)Use neutrinos from pion

decay Show that they are

different from the neutrinos emitted in beta decay

Shielding: 2000 tons of steel from scrapped warships (armor)

Nobel Prize 1988

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OLLI lectures Fall 2016�Horst D Wahl�(hwahl@fsu.edu)�lecture 4, 1 Nov 2016Outline of 2nd classSlide Number 3Beginning of Time: Big Bang Slide Number 5Other cosmological theoriesSlide Number 7Slide Number 8Chronology of the UniverseCosmic �HistoryHubble deep field viewCosmic background radiationOrigin of CMBDiscovery of CMBCMB spectrumPlanck’s radiation formula (1900)Black-body radiation spectrumWien’s displacement lawSlide Number 19CMB -- COBECMB -- WMAPCMB -- PlanckSlide Number 23Content of the UniverseContents of the universe Slide Number 26Slide Number 27Slide Number 28Slide Number 29SummaryAnd Now: Neutrinos!!!Neutrinos – why are they interesting?Where do Neutrinos Appear in Nature?Slide Number 34Slide Number 35Beta decay puzzleSlide Number 37Slide Number 38Pauli’s solution to the puzzlePauli’s neutrino letterDesperate Idea of PauliPauli’s “desperate” attempt to save appearances Weak interactionSlide Number 44Slide Number 45Discovery, Reines & Cowan 1956Project PoltergeistDetecting the neutrinoMore than one neutrino! Slide Number 50