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 was very small and very hot
Why small? Well, if we look at other galaxies, we see they are ALL moving away from us?
It is something we did? No.
How do we know? Doppler.
bread model tells us this is nothing special about the sun…

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 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?
bread model tells us this is nothing special about the sun…

5. Cosmic Microwave Background
I’ve got to be joking right?
Actually, it’s 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) were trying to develop microwave communications for Bell 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!

7. What does it look like?
It’s pretty bland… important fact!

8. What does it look like?
Doppler effect of earth (parts per thousand)

9. What does it look like?
Residual fluctuations (parts per million). Picture of Universe years after Big Bang

10. 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?

11. What Particles are found in the Early Universe?
let’s look at the particle “periodic table”
it has up and down quarks which make protons and neutrons
which bind with electrons to make atoms
so what’s all the stuff to the right?
My attitude has totally changed!

12. Yeah! What is that Stuff?
there just appear to be three copies of all the matter that really matters…
all that distinguishes the “generations” is their mass
My attitude has totally changed!
-- I.I. Rabi

13. Particles in the Universe
In the beginning, very small and very hot
Now remember mass is also energy (E=mc2)
Very early in the Universe, it was so hot that the masses of the different generations didn’t matter
Then as the universe cools, suddenly generational mass differences were a big deal, and the massive generations needed to shed their extra mass (energy)
Physicists call this sort of thing symmetry breaking
But how do particles shed that extra mass?
bread model tells us this is nothing special about the sun…

14. Detecting Cosmic Rays and Neutrinos

15. 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)

16. What on earth happens? “Primary” cosmic rays interact in atmosphere
Kinetic energy of cosmic ray creates a shower of matter and anti-matter particles

17. 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…

18. How do we see this?
Scintillator and photomultipliers works well for finding muons from cosmic rays!
That’s what you used for your work!

19. How do we see this (cont’d)
Meet the “Mother of all paddles”
Built in summer 2004 by a group of HS students and teachers at U of R
Lives above my office in attic
Data available on the web…

20. 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

22. How to Find Subatomic Particles
How do we see any fundamental particle?
Electromagnetic interactions kick electrons away from atoms
This is why radiation is a health hazard…

23. An Aside on Radiation and Biology
I’ve 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.

24. How to Find Subatomic Particles
How do we see any fundamental particle?
Electromagnetic interactions kick electrons away from atoms
This is why radiation is a health hazard…
But remember that neutrinos don’t have electric charge. They only interact weakly.

25. How Weak is Weak? 53 light-years Weak is, in fact, way weak.
A 3 MeV neutrino produced in fusion from the sun will travel through 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 several episodes, Lt. Jordy LaForge’s VISOR can actually detect “neutrino field emissions”
and what do we do in science except emulate Star Trek?
Sadly, however, there is a catch

28. Modern Neutrino Hunting
Super-Kamiokande (Masatoshi Koshiba, UR PhD 1955, Nobel 2002)

29. What does a neutrino from the atmosphere look like?
Muons or electrons produced in inverse b-decay are going near c
This exceeds speed of light in water, so get Cerenkov light
Cones of light (think a boat wake in 3-D) intersect wall of detector and give rings

30. Modern Neutrino Hunting
The Sun, imaged in neutrinos, by Super-Kamiokande
Existence of the sun confirmed by neutrinos!
The Sun, optical image

31. Where are Neutrinos Found?
In the sun
If the sun shines by fusion, energy reaching earth in light and in neutrinos is similar
100 billion neutrinos per cm2 per second rain on us
Supernova 1987A ( 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!

32. Where are Neutrinos Found?
Bananas?
We each contain about 20mg of 40K which is unstable and undergoes β decay
So each of us emits 7500 neutrinos/sec
For the same reason, the radioactivity of the earth results in 10 million neutrinos per cm2 per second here

33. Where are Neutrinos Found?
The early Universe
Decays of heavy generations left a waste trail (decays) of 100/cm3 of each neutrino species
They are (now) very cold and slow and hard to detect
But if they have even a very small mass, they make 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 isn’t around today?
look for annihilations.
As far away as we can tell, today there aren’t 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…

37. What does it take?
Megawatts of accelerated protons to produce neutrinos
e.g., T2K beam: MW
kTon detectors, hundreds of km from source
1MTon is a cube of water, 100 meters on a side
Experiments with 107 neutrinos seen to precisely measure how they interact
MINERvA at FNAL, led by Rochester
~2010
UNO neutrino detector concept
~2020
~2008

38. Conclusions
Neutrinos! They are everywhere, so we’d better learn to live with them!
long-term goal is to demonstrate matter and anti-matter differences in neutrinos
can this seed the same asymmetry in the Universe?
The mystery continues…

39. Backup

40. β-Decay? You learned about this in chemistry?
β-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 proton turn into a neutron. Inverse of β-decay!
Without β-decay, we are stuck where the sun don’t shine…

41. β-Decay and the Universe
Extra generations must have shed mass by decaying to light generations
Why? Well, we don’t see the heavy ones today in the Universe!
And the only way for that to happen is…
β-Decay!!
Just as neutrons could decay to protons by β-decay, so heavy generations decay to light.
bread model tells us this is nothing special about the sun…

42. Neutrinos -or- What I do for a Living…

43. The Birth of the Neutrino
Wolfgang Pauli

44. 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.
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. 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

45. Translation, Please? To save the law of conservation of energy?
If the above picture is complete, conservation of energy says β has one energy
but we observe this instead
Pauli suggests “neutron” takes away energy!
β-decay
The Energy of the “β”

46. The Story so Far
Neutrinos are essential for β-Decay to occur (Pauli’s idea)
β-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 wouldn’t 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p+e-+ν) connects electrons and neutrinos
but wait… there’s more. Another weak force discovered with ns! n
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 don’t know how to add the strong force and gravity to this picture
“unification” still drives much of particle physics

49. A confusing aside… (made in Rochester)
The basics of this neutral force are as expected
however…
… concluded the neutral weak force is a 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 nuclear reactor

51. Modern Neutrino Hunting
Radiochemical Detector Ray Davis (Nobel prize, 2002)
ν+np+e- (stimulated β-decay)
Use this to produce an unstable isotope, ν+37Cl37Ar+e- , which has 35 day half-life
Put 615 tons of Perchloroethylene in a mine
expect one 37Ar atom every 17 hours.

52. Modern Neutrino Hunting
Ran from
Confirmed that sun shines from fusion
But found 1/3 of ν !

53. Neutrino Flavor Remember that neutrinos were discovered by
the appearance of the positron is no accident!
it turns there are three neutrinos, each associated with a particular flavor
OK… so here’s a question…

54. Would the real neutrino please stand up?
Are these neutrinos “of definite flavor” the “real neutrinos”
i.e., is a neutrino flavor eigenstate in an eigenstate of the neutrino mass matrix
Or are we looking at neutrino puree?
And of course, “why does anyone care?”

55. Neutrino Flavor Mixing
What if neutrinos mixed?
“normal modes” not a or b but a mix
We have learned this phenomenology!
This is called “neutrino flavor oscillation” a→b→a

56. The Role of Neutrino Mass
There is an important condition for oscillation… … the masses of the different mass eigenstates must be distinct!

57. Summary of Neutrino Oscillations
If neutrinos mass states mix to form flavors
and the masses are different…
This would explain the disappearing solar ns!
since only electron flavor neutrinos make the detection reaction, ν+n→p+e-, occur

58. Schoedinger-ology…
So each neutrino wavefunction has 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 (cont’d)
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 a muon flavored neutrino
Muons decay to make one muon and one electron flavored 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 differences between neutrinos and anti-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 isn’t around today?
look for annihilations.
As far away as we can tell, today there aren’t big matter and anti-matter collisions

65. neutrinos cause the matter anti-matter asymmetry in the Universe!
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…