Cosmic Rays, Neutrinos, Star Trek and the Universe

1
Cosmic Rays, Neutrinos, Star Trek and the Universe

• Kevin McFarland
• University of Rochester

2
The Mysterious Link Between Particles and the
Universe

• In science, you
• ask questions
• figure out how to answer them
• spend a long time answering them, probably with
  many little false steps along the way
• learn enough to ask the next question
• Sure, it seems repetitive, but sometimes it leads
  to really interesting questions from very odd or
  obscure ones

3
A Brief History of the Universe

• In the beginning, the Universe wasvery small and
  very hot
• Why small? Well, if we look at other galaxies,
  we see they are ALL moving away from us?
• It is somethingwe did? No.
• How do we know? Doppler.

4
A Brief History of the Universe

• In the beginning, very small and very hot
• Why hot?
• When you let a gas expand, it cools
• Remember that heat is energy
• When the Universe was about 400000 years old, it
  was so hot that atoms kept being torn apart and
  recombining
• a lot like in our vapor lamp!
• Then as the universe cools, that stops. But what
  happens to all this energy from the glowing
  Universe?

5
Cosmic Microwave Background

• Ive got to be joking right?
• Actually, its a very interesting subject with
  perhaps the worst name ever
• This is EXACTLY where the energy went. As the
  Universe cooled, so did the light
• now it is very low energy light so low it is in
  the microwave frequency

6
Discovering the Cosmic Microwave Background

• would you believe it was an accident?
• Penzias and Wilson(shown below) weretrying to
  developmicrowavecommunications forBell Labs
• was too noisy!
• kept trying to scrub bird droppings off the
  receiver
• but not even Mr. Clean can remove stains from the
  Big Bang!

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What does it look like?

• Its pretty bland important fact!

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What does it look like?

• Doppler effect of earth (parts per thousand)

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What does it look like?

• Residual fluctuations (parts per
  million).Picture of Universe 400000 years after
  Big Bang

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Where Did Particles Come From in the Big Bang?

• They came from decays of particles produced from
  energy in the Big Bang.
• How do particles (matter) become energy or energy
  become matter?

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What Particles are found in the Early Universe?

• lets look atthe particle periodic table
• it has up and downquarks which makeprotons and
  neutrons
• which bind with electronsto make atoms
• so whats all the stuff to the right?

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Yeah! What is that Stuff?

• there just appear to be threecopies of all the
  matter thatreally matters
• all that distinguishes thegenerations is their
  mass

13
Particles in the Universe

• In the beginning, very small and very hot
• Now remember mass is also energy (Emc2)
• Very early in the Universe, it was so hot that
  the masses of the different generations didnt
  matter
• Then as the universe cools, suddenly generational
  mass differences were a big deal, and themassive
  generations needed to shedtheir extra mass
  (energy)
• Physicists call this sort of thingsymmetry
  breaking
• But how do particles shed thatextra mass?

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Detecting Cosmic Rays and Neutrinos
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So what are cosmic rays?

• Cosmic rays are believed to initiate with very
  high energy (relativistic) protons
• Acceleration mechanism is unknown

• Except for small component from solar flares,
  cosmic rays originate outside solar system
• Probably galactic (rates, energy)

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What on earth happens?

• Primary cosmic rays interact in atmosphere
• Kinetic energy of cosmic ray creates a shower of
  matter and anti-matter particles

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Cosmic Ray Showers

• Shower of matter anti-matter particles
• Lots of heavy particles are produced.
• They decay to things that can reach the ground
• muons, electrons, neutrinos
• Muon horizontal flux is 1/cm2/min
• Hmmm sounds like early Universe particles

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How do we see this?

• Scintillator and photomultipliers works well for
  finding muons from cosmic rays!

• Thats what you used for your work!

19
How do we see this (contd)

• Meet the Mother of all paddles
• Built in summer 2004 by a group of HS students
  andteachers at U of R
• Lives above myoffice in attic
• Data available onthe web

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What could we use these for?

• Study the effect of the atmosphere

21
More dramatic ask if our solar system has an
effect!

• Forbush decreases, GLEs

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How to Find Subatomic Particles

• How do we see any fundamental particle?
• Electromagneticinteractions kickelectrons
  awayfrom atoms
• This is why radiation is ahealth hazard

23
An Aside on Radiation and Biology

• Ive learned everything I need to know on this
  subject from comic books
• the reality is less dramatic, more awful,but
  quantifiable. often not worthy of panic.

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How to Find Subatomic Particles

• How do we see any fundamental particle?
• Electromagneticinteractions kickelectrons
  awayfrom atoms
• This is why radiation is ahealth hazard
• But remember that neutrinos dont have electric
  charge. They only interact weakly.

25
How Weak is Weak?

• Weak is, in fact, way weak.
• A 3 MeV neutrino producedin fusion from the sun
  will travelthrough water, on average, before
  interacting.
• The 3 MeV positron (anti-matter electron)
  produced in the same fusion process will travel 3
  cm, on average.
• Apparently to hold up that VISOR, Jordy LaForge
  has a neck that would put an NFL offensive guard
  to shame
• To find neutrinos, you need a lot of neutrinos
  and a lot of detector!

53 light-years
26
Getting lost along the way

• Muons have a tough road to get down to the
  surface where we can see them!
• Atmosphere slows electrons and muons
• Muons decay (half-life of 1.5 microseconds)
• Neutrinos unaffected by both problems!

27
So How Should we Detect Neutrinos?

• Leave it to Star Trek to point the way!
• Apparently, according to severalepisodes, Lt.
  Jordy LaForges VISORcan actually detect
  neutrino fieldemissions
• and what do we do in science exceptemulate Star
  Trek?
• Sadly, however, there is a catch

28
Modern Neutrino Hunting

• Super-Kamiokande(Masatoshi Koshiba,UR PhD 1955,
  Nobel 2002)

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What does a neutrino from the atmosphere look
like?

• Muons or electronsproduced in inverseb-decay
  are goingnear c
• This exceeds speedof light in water, soget
  Cerenkov light
• Cones of light (thinka boat wake in
  3-D)intersect wall ofdetector and give rings

30
Modern Neutrino Hunting

• The Sun, imaged in neutrinos, bySuper-Kamiokande

The Sun, optical image
Existence of the sun confirmed by neutrinos!
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Where are Neutrinos Found?

• In the sun
• If the sun shinesby fusion, energy reaching
  earth in light and in neutrinos is similar
• 100 billion neutrinos per cm2 per second rain on
  us
• Supernova 1987A (150000 light years away)
  exploded, releasing 100 times the neutrinos the
  sun will emit in its whole lifetime
• we observed 11 neutrinos in detectors on earth!

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Where are Neutrinos Found?

• Bananas?
• We each contain about 20mg of 40K which is
  unstable and undergoes ß decay
• So each of us emits 7500 neutrinos/sec
• For the same reason, the radioactivityof the
  earth results in 10 millionneutrinos per cm2 per
  second here

33
Where are Neutrinos Found?

• The early Universe
• Decays of heavy generationsleft a waste trail
  (decays) of100/cm3 of each neutrino species
• They are (now) very cold andslow and hard to
  detect
• But if they have even a very small mass,
  theymake up much of the weight of the Universe

34
Anti-matter?

• Every fundamental particle has an anti-matter
  partner
• When the meet, they annihilate into pure energy.
  Alternatively, energy can become matter plus
  anti-matter

35
So you might ask

• The early Universe had a lot of energy. Where is
  the anti-matter in the Universe?
• Good question how do we know it isnt around
  today?
• look for annihilations.
• As far away as we can tell, today there arent
  big matter and anti-matter collisions

36
My Research Goal(with more than a little help
from my friends)

• Prove or disprove the hypothesis
• neutrinos cause the matter anti-matter asymmetry
  in the Universe!
• We are using accelerators to make neutrinos to
  study whether or not neutrino anti-neutrino
  differences seeded this as the Universe cooled

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What does it take?

• Megawatts of acceleratedprotons to produce
  neutrinos
• e.g., T2K beam 0.8-4.0 MW
• 100-1000kTon detectors,hundreds of km from
  source
• 1MTon is a cube of water,100 meters on a side
• Experiments with 107 neutrinosseen to precisely
  measure howthey interact
• MINERvA at FNAL, led by Rochester

2010
UNO neutrino detector concept
2020
2008
38
Conclusions

• Neutrinos! They are everywhere, so wed better
  learn to live with them!
• long-term goal is to demonstrate matter
  andanti-matter differences in neutrinos
• can this seed the same asymmetry in the Universe?
• The mystery continues

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Backup
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ß-Decay?

• You learned about this in chemistry?
• ß-decay turns neutrons into protons, increasing
  the atomic number of an atom
• that sounds awfully anticlimactic who cares?
• actually,you do. A lot.
• Fusion in the sun requires that a protonturn
  into a neutron. Inverse of ß-decay!
• Without ß-decay, we are stuck where the sun dont
  shine

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ß-Decay and the Universe

• Extra generations must have shed mass by decaying
  to light generations
• Why? Well, we dontsee the heavy onestoday in
  the Universe!
• And the only way for that to happen is
• ß-Decay!!
• Just as neutrons could decay to protons by
  ß-decay, so heavy generations decay to light.

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Neutrinos-or-What I do for a Living
43
The Birth of the Neutrino

• Wolfgang Pauli

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Translation, Please?
4th December 1930 Dear Radioactive Ladies and
Gentlemen, As the bearer of these lines, to whom
I graciously ask you to listen, will explain to
you in more detail, how because of the wrong
statistics of the N and 6Li nuclei and the
continuous beta spectrum, I have hit upon a
desperate remedy to save the exchange theorem
of statistics and the law of conservation of
energy. Namely, the possibility that there could
exist in the nuclei electrically neutral
particles, that I wish to call neutrons, which
have spin and obey the exclusion principle and
which further differ from light quanta in that
they do not travel with the velocity of light.
The mass of the neutrons should be of the same
order of magnitude as the electron mass (and in
any event not larger than 0.01 proton masses).
The continuous beta spectrum would then become
understandable by the assumption that in beta
decay a neutron is emitted in addition to the
electron such that the sum of the energies of the
neutron and the electron is constant... From now
on, every solution to the issue must be
discussed. Thus, dear radioactive people, look
and judge. Unfortunately I will not be able to
appear in Tübingen personally, because I am
indispensable here due to a ball which will take
place in Zürich during the night from December 6
to 7. Your humble servant, W. Pauli
4th December 1930 Dear Radioactive Ladies and
Gentlemen, As the bearer of these lines, to whom
I graciously ask you to listen, will explain to
you in more detail, how because of the wrong
statistics of the N and 6Li nuclei and the
continuous beta spectrum, I have hit upon a
desperate remedy to save the exchange theorem
of statistics and the law of conservation of
energy. Namely, the possibility that there could
exist in the nuclei electrically neutral
particles, that I wish to call neutrons, which
have spin and obey the exclusion principle and
which further differ from light quanta in that
they do not travel with the velocity of light.
The mass of the neutrons should be of the same
order of magnitude as the electron mass (and in
any event not larger than 0.01 proton masses).
The continuous beta spectrum would then become
understandable by the assumption that in beta
decay a neutron is emitted in addition to the
electron such that the sum of the energies of the
neutron and the electron is constant... From now
on, every solution to the issue must be
discussed. Thus, dear radioactive people, look
and judge. Your humble servant, W. Pauli
4th December 1930 Dear Radioactive Ladies and
Gentlemen, As the bearer of these lines, to whom
I graciously ask you to listen, will explain to
you in more detail, how because of the wrong
statistics of the N and 6Li nuclei and the
continuous beta spectrum, I have hit upon a
desperate remedy to save the exchange theorem
of statistics and the law of conservation of
energy. Namely, the possibility that there could
exist in the nuclei electrically neutral
particles, that I wish to call neutrons, which
have spin and obey the exclusion principle and
which further differ from light quanta in that
they do not travel with the velocity of light.
The mass of the neutrons should be of the same
order of magnitude as the electron mass (and in
any event not larger than 0.01 proton masses).
The continuous beta spectrum would then become
understandable by the assumption that in beta
decay a neutron is emitted in addition to the
electron such that the sum of the energies of the
neutron and the electron is constant... From now
on, every solution to the issue must be
discussed. Thus, dear radioactive people, look
and judge. Your humble servant, W. Pauli
45
Translation, Please?

• To save the law of conservation of energy?
• If the above picture is complete, conservation of
  energy says ß has one energy
• but we observe this instead
• Pauli suggests neutron takes away energy!

ß-decay
The Energy of the ß
46
The Story so Far

• Neutrinos are essential for ß-Decay to occur
  (Paulis idea)
• ß-Decay
• makes the sun shine
• allows the cold Universe to be made of what we
  see today
• So although we are not made of neutrinos,
• we wouldnt be here without them!
• Wow maybe someone should study neutrinos

47
ns what are they good for?

• Neutrinos only feel the weak force
• a great way to study the weak force!
• or applications of weak forces (i.e., the sun)
• Is there just one weak interaction?
• one weak interaction (b decay, n?pe-?)connects
  electrons and neutrinos
• but wait theres more. Another weak force
  discovered with ns!

Gargamelle, event from neutral weak force
48
What about this other weak force?

• It turns out that this weak force was the
  prediction of a theory that unified the
  electromagnetic and weak forces
• (Glashow, Salam, Weinberg, Nobel 1979)
• We still dont know how to add the strong force
  and gravity to this picture
• unification still drives muchof particle
  physics

49
A confusing aside (made in Rochester)

• The basics of this neutral force are as expected
• however
• concluded the neutral weak force isa tiny bit
  too weak

NuTeV Experiment (Profs. Bodek McFarland
at Rochester) Studied 1.7M neutrino and 0.35M
anti-neutrino interactions
50
Discovery of the Neutrino

• Reines and Cowan (1955)
• Nobel Prize 1995
• 1 ton detector
• Neutrinos from a nuclearreactor

51
Modern Neutrino Hunting

• Radiochemical Detector Ray Davis (Nobel prize,
  2002)
• ?n?pe- (stimulated ß-decay)
• Use this to produce an unstable isotope,
  ?37Cl?37Are- , which has 35 day half-life
• Put 615 tons ofPerchloroethylenein a mine
• expect one 37Ar atomevery 17 hours.

52
Modern Neutrino Hunting

• Ran from 1969-1998
• Confirmed that sun shines from fusion
• But found 1/3 of ? !

53
Neutrino Flavor

• Remember that neutrinos were discovered by
• the appearance of the positron is noaccident!
• it turns there are threeneutrinos,
  eachassociated with aparticular flavor
• OK so heres a question

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Would the real neutrino please stand up?

• Are these neutrinos of definite flavorthe
  real neutrinos
• i.e., is a neutrino flavor eigenstate inan
  eigenstate of the neutrino mass matrix
• Or are we looking at neutrino puree?
• And of course, why does anyone care?

55
Neutrino FlavorMixing

• What if neutrinosmixed?
• normal modesnot a or bbut a mix
• We havelearned thisphenomenology!

This is called neutrino flavor
oscillationa?b?a
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The Role of Neutrino Mass

• There is an important condition for
  oscillation the masses of the different
  mass eigenstates must be distinct!

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Summary of Neutrino Oscillations

• If neutrinos mass states mixto form flavors
• and the masses are different
• This would explain the disappearing solar ns!
• since only electron flavor neutrinos make the
  detection reaction, ?n?pe-, occur

58
Schoedinger-ology

• So each neutrino wavefunctionhas a time-varying
  phase in its rest frame
• Now, imagine you produce a neutrino of definite
  momentum but is a mixture of two masses, m1, m2
• so pick up a phase difference in lab frame

59
Schoedinger-ology (contd)

• Phase difference
• Phase difference leads to interference effect,
  just like with sound waves
• Analog of volume disappearing in beats is
  original neutrino flavor disappearing

60
More Neutrino Flavor Changes

• Pions decay to make amuon flavored neutrino
• Muons decay to makeone muon and one
  electronflavored each

• A very robust prediction

61
Atmospheric Neutrino Oscillations

• Muon like neutrinos going through earth
  disappear
• probably change to tau neutrinos

62
Future Neutrino Hunting

• New Ideas afoot
• Produce neutrinos at accelerators, send them long
  distances to massive detectors
• Goal study differencesbetween neutrinos
  andanti-neutrinos

63
Why Neutrinos and Anti-Neutrinos?

• Every fundamental particle has an anti-matter
  partner
• When the meet, they annihilate into pure energy.
  Alternatively, energy can become matter plus
  anti-matter

64
So you might ask

• The early Universe had a lot of energy. Where is
  the anti-matter in the Universe?
• Good question how do we know it isnt around
  today?
• look for annihilations.
• As far away as we can tell, today there arent
  big matter and anti-matter collisions

65
Our New Goal

• Prove or disprove the hypothesis
• neutrinos cause the matter anti-matter asymmetry
  in the Universe!
• We are using accelerators to make neutrinos to
  study whether or not neutrino anti-neutrino
  differences seeded this as the Universe cooled