1. Proton Decay The Next Big Thing?
Chiaki Yanagisawa
Science Department, BMCC/CUNY
Physics/Engineer/Astronomy Seminar
November 29, 2017

2. The Standard Model of Particle Physics

3. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model + Gauge theory 
The Standard Model
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
11/29/17

4. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model + Gauge theory 
The Standard Model
The members of one generation:
- two quarks, one +2/3e another -1/3e
(actually quarks come with 3 colors)
- two leptons, charged and neutrino
(electron) (electron
neutrino)
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
11/29/17

5. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model + Gauge theory 
The Standard Model
The members of one generation:
- two quarks, one +2/3e another -1/3e
(actually quarks come with 3 colors)
- two leptons, charged and neutrino
(muon) (muon
neutrino)
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
11/29/17

6. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model + Gauge theory 
The Standard Model
The members of one generation:
- two quarks, one +2/3e another -1/3e
(actually quarks come with 3 colors)
- two leptons, charged and neutrino
(tau) (tau
neutrino)
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
11/29/17

7. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model + Gauge theory 
The Standard Model
The members of one generation:
- two quarks, one +2/3e another -1/3e
(actually quarks come with 3 colors)
- two leptons, charged and neutrino
Force carriers, a.k.a, gauge bosons
- g mediates electromagnetic force
- g (gluons) mediates strong force
- Z0/W± bosons mediate weak force
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
11/29/17

8. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model + Gauge theory 
The Standard Model
The members of one generation:
- two quarks, one +2/3e another -1/3e
(actually quarks come with 3 colors)
- two leptons, charged and neutrino
Force carriers, a.k.a, gauge bosons
- g mediates electromagnetic force
- g (gluons) mediates strong force
- Z0/W± bosons mediate weak force
Higgs, a.k.a, God particle
- Responsible for masses
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
11/29/17

9. H - What Is Matter Made of?
Building blocks of matter (the Standard Model)
Quarks, hadrons and mesons
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
Proton p : uud
Neutron n : udd
Pion p+/p-/p0 : ud/ud/uu+dd -
baryons
hadrons
mesons
Particles made of quarks are called
hadrons: mp ~ 1GeV, mp ~ 0.1 GeV
Note: quarks and gluons have
“colors”- red, blue and green
1 eV = energy of an electron accelerated by
1 V of electric potential difference: Note E = mc2
11/29/17

10. H - What Is Matter Made of?
Building blocks of matter (the Standard Model)
Quarks, hadrons and mesons
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
Proton p : uud
Neutron n : udd
Pion p+/p-/p0 : ud/ud/uu+dd -
baryons
hadrons
mesons
Particles made of quarks are called
hadrons: mp ~ 1GeV, mp ~ 0.1 GeV
Particles that are not made of quarks
and are not force carriers are called
leptons: me~0.5 MeV, mm ~0.1 GeV
mn=0 eV (assumed but wrong)
1 eV = energy of an electron accelerated by
1 V of electric potential difference: Note E = mc2
11/29/17

11. H - What Is Matter Made of?
Building blocks of matter (the Standard Model)
Quarks, hadrons and mesons
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
Proton p : uud
Neutron n : udd
Pion p+/p-/p0 : ud/ud/uu+dd -
baryons
hadrons
mesons
Particles made of quarks are called
hadrons: mp ~ 1GeV, mp ~ 0.1 GeV
Particles that are not made of quarks
and are not force carriers are called
leptons: me~0.5 MeV, mm ~0.1 GeV
mn=0 eV (assumed but wrong)
Force carriers mediate interactions/
forces: mW,Z~100 GeV, mg,g = 0 eV
1 eV = energy of an electron accelerated by
1 V of electric potential difference: Note E = mc2
11/29/17

12. H - What Is Matter Made of?
Building blocks of matter (the Standard Model)
Quarks, hadrons and mesons
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
Proton p : uud
Neutron n : udd
Pion p+/p-/p0 : ud/ud/uu+dd -
baryons
hadrons
mesons
Particles made of quarks are called
hadrons: mp ~ 1GeV, mp ~ 0.1 GeV
Particles that are not made of quarks
and are not force carriers are called
leptons: me~0.5 MeV, mm ~0.1 GeV
mn=0 eV (assumed but wrong)
Force carriers mediate interactions/
forces: mW,Z~100 GeV, mg,g = 0 eV
Source of masses: Higgs particle
mHiggs ~ 125 GeV
11/29/17

13. Fundamental Forces Fundamental interactions/forces
There are four known fundamental forces:
Gravitational, weak, electromagnetic, and strong forces
W/Z BOSONS
GLUONS
11/29/17

14. The Standard Model Fundamental interactions/forces electromagnetic
weak
strong
strong
weak
weak
electromagnetic
11/29/17

15. Fundamental Forces Fundamental interactions/forces Feynman Diagrams
11/29/17

16. Grand Unified Theories (GUTs)

17. Idea of Unification of Forces
Fundamental interactions/forces
Strength of fundamental forces
unification point
- At the unification point
three forces become
one force.
- At the beginning of the
Universe, Big Bang,
this must have happened
as, at Big Bang, tremendous
energy was confined in a
extremely small space.
Strong force
Electromagnetic force
Weak force
11/29/17

18. Idea of Unification of Forces
History of unification
Maxwell
Weinberg-Glashow- Salam
20th Century ~1959,1967
Wilczek-Gross-Politzer
1973
Many
20th- 21st Century
Grand
Unification
Theory of
Everything
The Standard Model is not a grand unified model.
But it describes weak, electromagnetic and strong forces with a common language called gauge theory with a help from group theory and Higgs mechanism.
Fermi et al.
1933
Newton
1687
Einstein
1915
11/29/17

19. The Simplest GUT Model Based on SU(5) Group
A model of grand unified model (Georgi and Glashow 1981)
Quarks and leptons and their anti-particles
are in two groups.
Note:
There is no anti-neutrino.
New “gauge” bosons X and Y mediate new force.
11/29/17

20. The Simplest GUT Model Based on SU(5) Group
Proton decay p  e+ + p0 p0 p
11/29/17

21. The Simplest GUT Model Based on SU(5) Group
What the Georgi and Glashow model brings?
Quarks, anti-quarks, leptons, anti-leptons in two groups
Charge quantization
- the minimum charge unit is 1/3 e.
It describes the electroweak and strong forces in a unified way.
- with a language of gauge theory based on SU(5) group theory.
Predict nucleon decays such as pe+ + p0 etc.
- quarks and leptons can convert to each others.
- Most of grand unified theories predict this decay.
11/29/17

22. Super-Kamiokande Detector

23. Cherenkov Radiation Principle of Cherenkov radiation bullet
Shock wave
bullet
When a charged particle moves faster than the speed of light in a medium such as water (v > c/n), electrons in atoms
of the medium oscillate and radiate electromagnetic waves
(=light) like shock waves produced by super-sonic jet or bullet.
11/29/17

24. How To Detect Charged Particles
Water Cherenkov detector (Note: Cerenkov is wrong spelling)
Water Cherenkov Detector: IMB, Kamiokande, Super-Kamiokande, SNO
Cherenkov radiation discovered by Pavel Cherenkov (Nobel Prize 1958)
When the speed of a charged
particle exceeds that of light
IN WATER, electric shock
waves in form of light are
generated similar to sonic boom
sound by super-sonic jet plane .
These light waves form a cone
and are detected as a ring by
a plane equipped by photo-
sensors.
11/29/17

25. How to Distinguish e±/g from others
Electromagnetic shower
Electron/positron in matter
Photon/g in matter
An electron radiates a photon when it travels a distance of X0
While it travels in matter it loses energy due to ionization loss
and elastic scattering as well
A photon creates an electron-positron pair when it travels a
distance of (9/7)X0
While it travels in matter it loses energy due to Compton
scattering as well
Electromagnetic shower g e+ e-
5/12/07
C. Yanagisawa, PHY431

26. How To Detect Neutrinos (One Method)
How do we find flavor of neutrinos
Non-showering muon-like ring (simulated) ne
+ n  p + e- nm
+ n  p + m-
Showering electron or g -like ring (simulated)
Most of time invisible
11/29/17

27. The Super-Kamiokande (SK) Detector
An atmospheric neutrino detected by Super-Kamiokande
Seeing atmospheric neutrino underground
The Super-Kamiokande detector
50 kton Water Cherenkov
~40 m (diameter) x ~40 m (height)
1000 m under Mt. Ikeno, Japan
An atmospheric muon neutrino
captured by Super-Kamiokande
11/29/17

28. How To Detect Neutrinos
Super-Kamiokande
Super-Kamiokande
11/29/17

29. Nucleon Decays

30. Nucleon Decays What does proton decay pe+p0 event look like?
Signal events:
3 showering rings with 2 rings
making a p0 mass and with 3 rings
making a proton mass
Proton decay : p  e+ + p0 gg g e+ g
But there is a problem!
11/29/17

31. Major Background Atmospheric neutrino Earth’s atmosphere is constantly
bombarded by cosmic rays.
Energetic cosmic rays (mostly
protons from supernova explosions)
interact with atoms in the air.
These interactions produce many
particles-air showers.
Neutrinos are produced in decays
of charged pions and muons.
p+m+ + nm , m+e+ + nm + ne
11/29/17

32. Signal and Background
Atmospheric neutrino events mimicking proton decay pe+p0
Proton decay : p  e+ + p0 gg
Atmospheric (anti-)neutrinos: p+m+ + nm , m+e+ + nm + ne
Atmospheric neutrino interaction in water: ne + p  e- + n + p0 gg
Invisible as a ring
but it is sometime
captured by proton
followed by gamma
ray emission
11/29/17

33. Signal and Background
Atmospheric neutrino events mimicking proton decay pe+p0
Proton decay : p  e+ + p0 gg
Atmospheric (anti-)neutrinos: p+m+ + nm , m+e+ + nm + ne
Atmospheric neutrino interaction in water: ne + p  e- + n + p0 gg
Invisible as a ring
but it is sometime
captured by proton
followed by gamma
ray emission
Total mass Mtot ~ Mproton
Total momentum Ptot ~ 0
11/29/17

34. Signal and Background Total momentum Ptot vs. Total mass Mtot
500 yr MC
0.306 Mt·yr
exposure
Apr 1996 –
Mar 2015
Ptot (MeV/c)
500
1000
500
1000
500
1000
Mtot (MeV/c2)
No candidate
in the signal
region!
11/29/17

35. Signal and Background Total momentum Ptot vs. Total mass Mtot
No candidate is found with Mt·yr exposure
Proton lifetime > 1.6 × 1034 yr at 90% C.L.
- The age of the Universe is 14 x 109 yr.
- The simple SU(5) model predicts the lifetime 1029 – 1032 yr,
so this model is disfavored by Super-Kamiokande.
- A more complex model is required such as supersymmetric
SU(5) model or SO(10), but supersymmetry is nowhere to be found.
11/29/17

36. Conclusion
Discovery of proton decay would be a game changer – Grand Unification
But no proton decay p  e+ p0 candidate has been found.
This put the lower limit on the proton lifetime at 1.6 x 1034 year.
This limit rejects the simplest grand unified theory of SU(5) group.
We are still waiting for proton to decay.
NOW
Credit: Symmetry Magazine
11/29/17

37. Conclusion
Discovery of proton decay would be a game changer – Grand Unification
But no proton decay p  e+ p0 candidate has been found.
This put the lower limit on the proton lifetime at 1.6 x 1034 year.
This limit rejects the simplest grand unified theory.
We are still waiting for proton to decay.
Hyper-Kamiokande (10 x Super-Kamiokande) may find it someday.
My dream: Some day in the future….
Credit: Symmetry Magazine
11/29/17

38. Future Prospective
Hyper-Kamiokande (10 x Super-Kamiokande volume), if approved, may discover proton decay some day.
A big improvement in detection efficiency or in background rejection
may help to increase a chance to find proton decay.
- I have been trying in the past one year to improve these using
an algorithm of machine learning called Supper Vector Machine.
standard
SK cut
Possible
improved
cut
100 MeV/c
11/29/17

39. Backup Slides

40. Examples of Interactions (Feynman Diagrams)
Weak interaction: neutrino production
Free neutron decay: np+e-+ne neutrino source from nuclear reactor e- ne d u p n W-
Muon decay: m-W- + nm e- + ne + nm neutrino source from accel./atm. e- W- m- nm ne
11/29/17

41. Examples of Interactions
Neutrino production and interactions
Charged pion decay p+m++nm neutrino source from accel./atm. u d W+ m+ nm p+
Charged current (CC)
neutrino interaction
nm + n m- + p
Neutral current (NC)
neutrino interaction
nm + p(n) nm + p(n) Z nm u d n W nm m- u d n p
11/29/17

42. Nucleon Decays Proton Decay p  e+ + p0
Almost all GUTs theories predicts p  e+ + p0
11/29/17

43. How to Detect Neutrinos (One Method)
Supersonic wave
dir. of
sound
Wave front
In phase
The sound source moves
slower than sound wave
The sound source moves
as fast as sound wave
The sound source moves
faster than sound wave
When the jet fighter breaks
the sound barrier, it creates
shockwave.
11/29/17

44. What Is Matter Made of?
Building blocks of matter (the Standard Model)
Discoveries of too many “elementary”
particles lead to more fundamental
model: the Standard Model.
The members of one generation:
- two quarks, one +2/3e another -1/3e
(actually quarks come with 3 colors)
- two leptons, charged and neutrino
Force carriers, a.k.a, gauge bosons
- g mediates electromagnetic force
- g (gluons) mediates strong force
- Z0/W± bosons mediate weak force
Higgs, a.k.a, God particle
- Responsible for masses
+2/3 e
-1/3 e
0 e
-1 e Q
±1 e H
1 eV = energy of an electron accelerated by
1 V of electric potential difference: Note E = mc2
11/29/17

45. Idea of Unification of Forces
History of unification
11/29/17

46. The Simplest Model
A model of grand unified model (Georgi and Glashow 1981)
11/29/17

47. Support Vector Machine
1-min review (see more details in the backup slides)
Maximize the margin
separating the signal
events (S) from back-
ground events (B).
Wikipedia
margin S B
6/2/2017

48. Support Vector Machine
1-min review (see more details in the backup slides)
Maximize the margin
separating the signal
events (S) from back-
ground events (B).
Wikipedia
margin S B
If the complete separation
fails, introduce penalty
Cx (C parameter,
x ~ distance from ---) x
6/2/2017

49. Support Vector Machine
1-min review (see more details in the backup slides)
Maximize the margin
separating the signal
events (S) from back-
ground events (B).
If the complete separation
fails, introduce penalty
Cx (C parameter,
x ~ distance from ---)
If non-linear separation
is needed, transform
points into another
feature space using
a function f in form of
the kernel.
Wikipedia
margin S B x
f-1
Kernel : K(x, x’) = fT(x)f(x’) = (xT·x’ + 1)d polynomial
= exp(-g|x-x’|2) Gaussian
x, x’ : feature vector such as (Ptot, Mtot)
6/2/2017

50. Support Vector Machine
1-min review (see more details in the backup slides)
Maximize the margin
separating the signal
events (S) from back-
ground events (B).
If the complete separation
fails, introduce penalty
Cx (C parameter,
x ~ distance from ---)
If non-linear separation
is needed, transform
points into another
feature space using
a function f.
Wikipedia
margin S B x
f-1
For the analysis Gaussian based transforming function is used.
There are four parameters: Gaussian width g-1, strength of the penalty
function C, weights for sig/bkg (wsig/wbkg)
Software used is a python package called scikit-learn a.k.a. sk-learn!
6/2/2017

51. Support Vector Machine
Effect of g value
For the analysis Gaussian based transforming function is used.
There are four parameters: Gaussian width g-1, strength of the penalty
function C, weights for sig/bkg (wsig/wbkg)
Software used is a python package called scikit-learn a.k.a. sk-learn! x
= 0.10
wider width
g = 10.0
= 100.0
narrower width
The bigger g, the more individual events become powerful to
determine the boundary.
6/2/2017

52. Support Vector Machine
Effect of C and wsig value
For the analysis Gaussian based transforming function is used.
There are four parameters: Gaussian width g-1, strength of the penalty
function C, weights for sig/bkg (wsig/wbkg)
Software used is a python package called scikit-learn a.k.a. sk-learn! x
C = 10.0
C =
C =
The larger C, the more aggressively intruders are removed.
The smaller wsig compared with wbkg, the more aggressively
background evens are removed.
6/2/2017