We live in a matrix of neutrinos, the most abundant and perhaps the most elusive of all the known massive particles. The neutrino’s interactions dictate how the Sun shines, how the Sun will evolve, and the dynamics of dying stars. The neutrino, a tangible misfit, also tells us that our theory of the fundamental building blocks of Nature called the “Standard Model” is incomplete. There have been four neutrino-related Nobel prizes in physics awarded since 1995, but to date, the neutrino is still among the most mysterious of all known particles. A recent publication of the T2K experiment, one of the ten most remarkable discoveries of science in 2020, suggests that neutrinos do not respect the charge-conjugation parity-reversal (CP) symmetry, which in turn could explain how our matter-dominated Universe has emerged. The talk will highlight what we have known and what we expect to know in the following decades about this elusive particle. Also, we will discuss how to weigh the extraordinarily tiny mass of the neutrino and detect the CP violation via a quantum mechanical phenomenon called neutrino oscillation.

1. 2021-May-21, VLLT Joint Seminar Series on Physics and Astronomy
The Neutrino: Elusive Misfit and
revolutionary Discoveries
Son Cao,
IFIRSE/ KEK research fellow

2. …from “crisis” in explaining beta decay
2
https:/
/en.wikipedia.org/wiki/Beta_decay
Physicists had trouble to explain the continuity
of the beta energy spectrum
Before 1930, beta decay: XA
Z → XA
Z+1 + e−
Neutron: 939.57 MeV
/c2
Proton: 938.27 MeV
/c2
Bohr, for example, thought that the energy conservation could be the reason
Total energy released
Expected a de
fi
nite energy released (via electron only)
from the decay
Q = (m(XA
Z ) − m(XA
Z+1) − me) c2
🆘

3. …Neutrino was born as a “desperate" way out
3
https:/
/en.wikipedia.org/wiki/Beta_decay
W.Pauli proposed the existence of Neutrino in 1930
XA
Z → XA
Z+1 + e−
+ νe
Before 1930: XA
Z → XA
Z+1 + e−
Continuity of the
Beta spectrum is explainable
But why neutrino didn’t show up in the experiments?
💡
✅
🤔
Q = (m(XA
Z ) − m(XA
Z+1) − me) c2
Q = (m(XA
Z ) − m(XA
Z+1) − me − mνe) c2
carried by electron only
carried by both electron and neutrino
🙅
Undetected

4. Neutrino properties pictured before detection
4
No charge
Very small mass, probably zero, at
least small compared to electron mass
Spin 1/2
Fermi statistic
Magnetic moment < 1/7000 Bohr
magnetons, if any
No detectable effects in free state
http:/
/neutrinohistory2018.in2p3.fr/proceedings/jarlskog.pdf
“I have done a terrible thing. I have postulated a
particle that cannot be detected” —W. Pauli—
👻
The Elusive
Catch me if you can!

5. Neutrino: Here, there, every where, but practically invisible
5
~ 1013 neutrinos from the Sun passing
through your hand every second

6. Birth certificate of the Neutrino
6
Telegram from Rein & Cowan to Pauli
Pauli replies
“We are happy to inform you that we have de
fi
nitely detected neutrinos ... ”
“Thanks for message. Everything comes to him who knows how to wait”.
http:/
/hyperphysics.phy-astr.gsu.edu/hbase/Particles/cowan.html
Rein & Cowan, Science 124, 103 (1956).
Nature 178, 446 (1956)

7. Neutrino story just began…
7
In 1957, one year after neutrino discovery,
Parity violation was found in the beta decay (weak
interaction) [Lee, Yang Wu]
Neutrinos are 100% left-handed
[Goldhaber, Grodzins, Sunyar]
https:/
/en.wikipedia.org/wiki/Parity_(physics)
Parity transformation
Gravity, electromagnetism, strong interaction
are invariant under parity transformation

8. Neutrino is massless in Standard Model
8
In SM, neutrino is quite …boring. Its existence seems to only preserve
conservations of energy, momentum, spin, lepton numbers,
fl
avor numbers
No right-handed neutrino found yet mean ➔ ZERO Dirac mass
term for neutrino
ℒY ⊂ −Lϕ̃yννR + h . c .
→ −L⟨ϕ̃⟩yννR + h . c .
→ −νLmDνR + h . c .
http:/
/hitoshi.berkeley.edu/neutrino/neutrino4.html
Higgs mechanism:
Particles get mass via interaction
with the Higgs
fi
eld, transforming
left-handed state to right-handed
state and vice versa

9. …But neutrino is not boring at all…
9

10. 10
More detail: https:/
/neutrino-history.in2p3.fr/neutrinos-milestones-and-historical-events/

11. 11
More detail: https:/
/neutrino-history.in2p3.fr/neutrinos-milestones-and-historical-events/

12. Neutrino oscillations: A game-changer
“…for the discovery of neutrino oscillations, which shows
that neutrinos have mass"
12

13. Massive neutrinos are the misfit to the
Standard Model and so far the only
tangible evidence of New Physics
beyond the description of this model.
13

14. Tiny particle, but grand role in the Cosmos
14
Neutrino mass is extraordinary tiny, ~ 10-9 of
proton, but being the second most abundant
particles w/ average density of 330 neutrinos/
cm3, ~1087 in the Universe, neutrinos in total
weigh as much as all starts combined
http:/
/hitoshi.berkeley.edu/neutrino/neutrino4.html

15. How the neutrino gets mass?
Two types of theoretical models
Theoretical Model #1:
Right-handed neutrino exits but has extremely weak
interaction with matter, thus couldn’t detect.
Neutrino gets mass via Higgs mechanism
Neutrino and antineutrino are distinguishable
Theoretical Model #2:
Right-handed neutrino exits but very heavy and exist in very
short time before changing back to left-handed neutrino
Neutrino gets mass via so-called Seesaw mechanism
Neutrino and antineutrino are the same particles (no quantum
number to distinguish them)
If this is true, it would be a revolutionary discovery
since the mass mechanism is completely different
from what we have known.
15

16. Can neutrino a key to solve the biggest mysteries of our Universe?
Theoretical Model #2:
Right-handed neutrino exits but very heavy and exist in very short
time before changing back to left-handed neutrino
Neutrino gets mass via so-called Seesaw mechanism
Neutrino and antineutrino are the same particles (no quantum
number to distinguish them)
16
The indistinguishable btw neutrino and antineutrino means that
they can naturally convert into each other. If the two processes
( and ) are not symmetric, it could cause the
imbalance between matter and anti-matter in the Universe
ν → ν̄ ν̄ → ν
Very exciting scenario!

17. Leptogenesis to explain matter-antimatter asymmetry
1,000,000,001
Proton
1,000,000,001
Anti-Proton
Begin of Universe
1,000,000,00
+2
Proton
1,000,000,00
0+0
Anti-Proton
Shortly After
?
17
Heavy neutrino

18. Neutrino: our primordial Mother?
Neutrino can be “our primordial Mother”, can be a reason for the
Universe existence by making imbalance between matter-antimatter
NEUTRINOS
1,000,000,001
Proton
1,000,000,001
Anti-Proton
Begin of Universe
1,000,000,00
+2
Proton
1,000,000,00
0+0
Anti-Proton
Shortly After
?
Leptogenesis
18

19. How we can get there (understand of neutrino
nature & if leptogenesis is really the answer for
the birth of our matter-dominated Universe)?
19
Short answer:
Still long journey but extremely exciting
and worthy to pursue.

20. Two most promising pillars (along w/ other unknown
assets) for the adventure and only experimental
data can shed light on the answers
20
Neutrino-less double beta decay, if
discover, will con
fi
rm that Neutrino is
indeed Majorana particle
How we can get there?
CP violation in neutrino oscillation,
and leptogenesis imply each other
https:/
/physics.aps.org/articles/v11/30
https:/
/cerncourier.com/a/the-search-for-leptonic-cp-violation/
≠?
Both, if found, will be revolutionary discoveries

21. Neutrino oscillation

22. What is neutrinos oscillation?
𝜈
e
e
W
𝜈𝝁
W
Detector Detector
Neutrino can change its
fl
avor when give it time to propagate
Some distance
22

23. Neutrino oscillation: How is it possible?
𝜈
e
e
W
𝜈𝝁
W
Detector Detector
𝜈
1
𝜈
2
𝜈
3
|να⟩ =
∑
i
U*
αi
|νi⟩
Some distance
• Neutrino oscillations requires an existence of
neutrino mass spectrum, i.e mass eigenstate
𝜈
i
with de
fi
nite mass mi (where i is 1, 2, 3* at least)
• It requires
fl
avor eigenstate with de
fi
nite
fl
avor,
𝜈
(where
𝛼
is e,
𝜇
,
𝜏
) must be superpositions of
the mass eigenstates PMNS** leptonic
mixing matrix
**PMNS is shorted for Pontecorvo-Maki-Nakagawa- Sakata
mass eigenstate
fl
avor eigenstate
*It’s still possible that there are more than 3 mass eigenstates
23

24. Neutrino oscillation: Neutrino is massive
𝜈
e
e
W
𝜈𝝁
W
Detector Detector
P(να → νβ) = δαβ−4
∑
i>j
Re(U*
αi
UβiUαjU*
βj
)sin2
(
Δm2
ij
L
4E)
+2
∑
i>j
Im(U*
αi
UβiUαjU*
βj
)sin
(
Δm2
ij
L
2E)
𝜈
1
𝜈
2
𝜈
3
|να⟩ =
∑
i
U*
αi
|νi⟩
Some distance
Δm2
ij = m2
i − m2
j
where
Well-established neutrino oscillation phenomena imply that
neutrino is massive
for anti-neutrino,
this changes to (-)
neutrino energy
24

25. PMNS leptonic mixing matrix: Standard 3-flavor
• UPMNS is 3x3 unitary matrix and parameterized with
3 mixing angles (
𝜽
12,
𝜽
13,
𝜽
23) and one irreducible
Dirac CP-violation phase (
𝛿
CP)
• If neutrino is Majorana particle, there are two
additional CP-violation phase, which play no role in
neutrino oscillations
• Neutrino oscillation measurements provide only the
mass2 spectrum but not the absolute values of mass
P(να → νβ) = δαβ−4
∑
i>j
Re(U*
αi
UβiUαjU*
βj
)sin2
(
Δm2
ij
L
4E)
+2
∑
i>j
Im(U*
αi
UβiUαjU*
βj
)sin
(
Δm2
ij
L
2E)
Main goal is to measure these oscillation parameters
and verify if UPMNS is 3x3 unitary or not
arxiv:1301.1340
PMNS matrix
25

26. CP-violation phase (
𝛿
CP) ≠ CP violation amplitude
• Amplitude of leptonic CP violation can be
presented model-independently by
Jarlskog invariant
JLepton
CP
= Im[UαiU*
αj
U*
βi
Uβj]
=
1
8
sin 2θ12 sin 2θ23 sin 2θ13 cos θ13 sin δCP
Unitary of the matrix can write down in six
relations (scalar product of any row/column vector )
• Jarlskog invariant is 2 times of area of
unitary triangle
|να⟩ =
∑
i
U*
αi
|νi⟩
U*
e1
Uμ1 + U*
e2
Uμ2 + U*
e3
Uμ3 = 0
eg.
• If
𝛿
CP ≠ 0, Jarlskog invariant is also
non-zero and vice versa
26

27. Three neutrino flavors, three mass eigenstates. Why Three?
‘Đàn Bầu’
1 string
‘Đàn Nhị’
2 string
‘Đàn Tam’
3 string
𝝂
e
𝝂
e
𝝂𝝂
e
𝝂𝝂
https:/
/en.wikipedia.org/wiki/Traditional_Vietnamese_musical_instruments
27

28. …or it can be more
Đàn tranh
𝝂
e
𝝂𝝂𝝂
s?
Does sterile
neutrino (s)
exist?
https:/
/en.wikipedia.org/wiki/Đàn_tranh
16 strings in the standard version
There are some hints for this scenario but
not detailed in this talk
28

29. Neutrino Experiment is not simple …but you can imagine like this
29
https:/
/higgstan.com/

30. Experimental method in general
(GeV)
ν
E
0.5 1 1.5 2 2.5 3
Osc.
Prob
0
0.02
0.04
0.06
0.08
0.1
flux
µ
ν
Off-axis
°
2.5
ν
, NH,
°
=0
cp
δ
ν
, NH,
°
=270
cp
δ
ν
, NH,
°
=0
cp
δ
ν
, NH,
°
=270
cp
δ
e
ν
→
µ
ν
,
e
ν
→
µ
ν
Hypothesis
(parameters)
observed data
data-based
statement
Experiment
setup
T2K has made the
fi
rst observation of electron neutrino
appearance in a muon neutrino beam…with
a signi
fi
cance of 7.3
𝜎
over the the hypothesis of sin2
2θ13 = 0
(GeV)
ν
E
0.5 1 1.5 2 2.5 3
Osc.
Prob
0
0.02
0.04
0.06
0.08
0.1
flux
µ
ν
Off-axis
°
2.5
ν
, NH,
°
=0
cp
δ
ν
, NH,
°
=270
cp
δ
ν
, NH,
°
=0
cp
δ
ν
, NH,
°
=270
cp
δ
e
ν
→
µ
ν
,
e
ν
→
µ
ν
(GeV)
ν
E
0.5 1 1.5 2 2.5 3
Osc.
Prob
0
0.02
0.04
0.06
0.08
0.1
flux
µ
ν
Off-axis
°
2.5
ν
, NH,
°
=0
cp
δ
ν
, NH,
°
=270
cp
δ
ν
, NH,
°
=0
cp
δ
ν
, NH,
°
=270
cp
δ
e
ν
→
µ
ν
,
e
ν
→
µ
ν
30

31. 31
Neutrino detection
Bird’s-eye view only.

32. Neutrino detection principle
Neutrinos basically can’t see/directly but we know it via their trace when
interacting with nucleon/nuclei w/ help of photon detectors/sensors
This is just a single illustration. Many detection technique out there.
Photon detectors
Event reconstruction
Neutrino interactions
W
a
n
n
a
k
n
o
w
t
h
is
g
u
y
s
nucleon/nuclei
Charged particles
(
𝜇
, e,
𝝅
, p,…)
Neutral particles
(n,
𝜋
0,
𝛾
,…)
“eyes”
“lot of eyes”
“Pattern of light induced by
neutrino interaction”
W
h
a
t
o
b
s
e
r
v
e
d
32

33. Neutrino detection is complicate
PN physics
Material science
Mechanics
Electronic
Data mining
Neutrino detection is a complicate, interdisciplinary
fi
eld
33

34. Involved Particle and Nuclear physics
PN physics
Material science
Mechanics
Electronic
Data mining
F. Sanchez, neutrino 2018
• Neutrino-nucleon/nuclei interaction is complicated
• For oscillation analysis, you need, essentially
(1) Particle identity
(2) Neutrino energy
Charged particles
neutral particles
Based on induced charged particle
in
fi
nal state interaction
34

35. Material science in neutrino experiments
PN physics
Mechanics
Electronic
Data mining
T2K far detector use water; NOvA use liquid scintillator; MINOS
used magnetized steel, OPERA used Emulsion, etc…?
• T2K, NOvA needs to identify both
𝜈
and
𝜈
e
• MINOS focus on
𝜈
and its antineutrino
• OPERA need to see
𝜈
Material selection depends on particle you want to detect and
its properties. Also detector size & our understanding of
neutrino interaction on selected material are important factors.
Water
Liquid scintillator
magnetized iron
Emulsion
PN physics
Material science
Mechanics
Electronic
Data mining
35

36. Mechanics in neutrino detection
• In Nov 2001, Super-K suffered a serious blow, ~700 PMT tubes
exploded (cost $3000 per each) (5000 PMT remain undamaged)
• Cause: one tubes (contain a vacuum) exploded, released energy,
caused shock wave —> chain reaction of explosion
• To mitigate this possibility: Acrylic shield is developed and used
Bare PMT
PMT w/ acrylic shield
Similar structure in aquarium
One example
PN physics
Material science
Mechanics
Electronic
Data mining
36

37. Electronics in neutrino experiments
• Number of photon sensor/ “eyes” per each detector is often
very large: 13,000 channels in Super-K, 334,000 channels
in NOvA far detector, ~60,000 in Super-FGD (T2K)
• With many “eyes”, you need a “nervous” system to
manipulate and collect data ef
fi
ciently
• “Eyes” don’t not always open, no need and not good for
lifetime of electronics
• “Eyes” actually operate when receiving “trigger” signal,
and often within a prede
fi
ned time window
Depend on how often your detector get data; how many
events interact in your detector in a time window, etc…
Ex: NOvA electronics at Near Detector
PN physics
Material science
Mechanics
Electronic
Data mining
For long time, Physicists called
it Data Acquisition, but later
coined “Internet of Things”
become popular
37

38. Data mining in neutrino experiments
•How do you know this is likely due to
𝜈
e interaction?
•Basically, you need guidance from simulation
•The method is something like this:
1. Build detector simulation to simulate what you can observe when particles
enter your detector (so called Geant 3,4 and your detector geometry)
2. Simulate neutrinos (you know true info. such as neutrino type, energy,
direction, interaction point in detector)
3. Obtain pattern for simulated neutrino events and store as an event library
4. Compare your data pattern with library and see how likely data match
with what simulated events
PN physics
Material science
Mechanics
Electronic
Data mining
38

39. Neutrino detection is complicate
PN physics
Material science
Mechanics
Electronic
Data mining
Neutrino detection is a complicate, interdisciplinary
fi
eld.
You don’t need to know all of these. Expert in one
fi
eld is probably enough.
39

40. Present Landscape of
Neutrino Oscillation

41. MINOS, T2K, NOvA; Daya Bay, RENO, Double Chooz, KamLAND;
SNO, Borexino; IceCube, Super-K
What we have learned up-to-date?
𝜈
e
𝜈𝜈
Δm2
atm.
Δm2
21
Inverted hierarchy
𝜈
3
𝜈
1
𝜈
2
m2
lightest = ?
Δm2
atm.
Δm2
21
𝜈
1
𝜈
2
𝜈
3
Normal hierarchy
m2
= 0
|Δm2
31 | = 2.514+0.028
−0.027 × 10−3
eV2
Δm2
21 = 7.42+0.21
−0.20 × 10−5
eV2
We know there are at least two mass square
level, mean there exists at least three mass
eigenstates
We don’t know if neutrino mass spectrum is
in normal or inverted hierarchy
41
JHEP 09 (2020) 178
Global neutrino exp.
fi
t We don’t know the absolute mass either
(some constraint fr. cosmology or beta decay )

42. θ23 = 49.0+1.1
−1.4 θ13 = 8.57+0.13
−0.12 (δCP = 195+51
−25) θ12 = 33.44+0.78
−0.75
JHEP 09 (2020) 178
Global neutrino exp.
fi
t
MINOS, T2K, NOvA; Daya Bay, RENO, Double Chooz, KamLAND;
SNO, Borexino; IceCube, Super-K
What we have learned up-to-date?
PMNS matrix
42
What’
s behind the difference
in the mixing patterns of
quark and lepton is unknown.
It’
s can be essential for a
unification theory
*Dot area is proportional
to the matrix element
amplitude

43. Methodology of the CP violation measurement in neutrino oscillation
43
(1)Measure probability of neutrino oscillations
(2)Measure probability of anti-neutrino oscillations
(3)Compare neutrino vs. anti-neutrino oscillation prob.
Matter effect

44. T2K’
s latest result on the CP violation measurement
44
https:/
/t2k-experiment.org/2020/04/t2k-results-restrict-possible-values-of-neutrino-cp-phase/
Update to 2020 data
Nature volume 580, pages 339–344 (2020)
Statistical limited
Data favors CP violation
Integrate whole spectra
Find the best para. to
describe the data

45. Compare two leading neutrino experiments: T2K vs. NOvA
45
T2K favors maximal CP violation & normal MH
NOvA data shows no indication of CP violation
& normal MH
Some tension btw them, but
still agree each other within the statistic error

46. Leptonic CP violation
Jquarks
CP
= (3.18 ± 0.15) × 10−5
(pdg2018)
JLepton
CP
= − 0.031 at T2K best
fi
tted para.
Amplitude of the leptonic CP violation
can be much larger than its of quarks
Compare to quarks
(Real)
ρ
0.4
− 0.2
− 0 0.2 0.4 0.6 0.8 1 1.2
(Imagine)
η
0.4
−
0.3
−
0.2
−
0.1
−
0
0.1
0.2
0.3
0.4
A(0,0) B(0,1)
2
µ
U
*
e2
U
1
µ
U
*
e1
U
2
µ
U
*
e2
U
3
µ
U
*
e3
U
= -0.031
2
|
2
µ
U
*
e2
)x 2 x Area x |U
CP
δ
= sign(
CP
J
C(0.17,0.31)
°
=20.61
γ
°
=61.41
β
(Real)
ρ
0.4
− 0.2
− 0 0.2 0.4 0.6 0.8 1 1.2
(Imagine)
η
0.4
−
0.3
−
0.2
−
0.1
−
0
0.1
0.2
0.3
0.4
A(0,0) B(0,1)
2
µ
U
*
e2
U
1
µ
U
*
e1
U
2
µ
U
*
e2
U
3
µ
U
*
e3
U
= -0.009
2
|
2
µ
U
*
e2
)x 2 x Area x |U
CP
δ
= sign(
CP
J
C(0.33,0.08)
°
=6.64
γ
°
=13.48
β
JLepton
CP
= − 0.009 at Global data best
fi
tted para.
W/ global data @2020
W/ T2K data @2020
Search for the leptonic CP violation is limited by statistics.
More data is really needed.
46

47. Future prospects

48. Open questions
On neutrino mass
• Is neutrino Dirac or Majorana particle?
• What’s the mass mechanism
• What’s the absolute mass of neutrino
• What is the neutrino mass hierarchy?
On leptonic CP violation and mixing
• Neutrino oscillation violate CP symmetry?
• it this related to matter-antimatter
asymmetry of the Universe
• Mixing angles: theta 23 is maximal?
underlying a new symmetry
More fundamental questions
• Are there more than 3 mass eigenstates, or are there
“sterile” neutrinos?(not coupling to the weak bosons)
• Do neutrinos have non-standard model interactions?
• Do neutrinos break fundamental rules (Lorentz, CPT)?
Good thing in neutrino physics is unknown known, which clearly
pave the way for the future research
*The list is incomplete & biasedly selected
Neutrino oscillations
couldn’t answer these
Roadmap for the international, accelerator-based
neutrino programme, arXiv:1704.08181
48

49. Future means now
T2K(-II), Japan now running, plans to run up to 2026 in order to achieve 3
𝝈
sensitivity to CP
violation in case δCP is close to -π/2 and high precision on the atmospheric neutrino parameters
)
°
(
CP
δ
True
200
− 100
− 0 100 200
=0
CP
δ
to
exclude
sin
2
χ
∆
0
5
10
15
20
=0.43
23
θ
2
True sin
=0.50
23
θ
2
True sin
=0.60
23
θ
2
True sin
90% C.L.
99% C.L.
C.L.
σ
3
POT w/ eff. stat. & sys. improvements
21
20x10
POT w/ 2016 sys. errs.
21
7.8x10
23
θ
2
sin
0.4 0.5 0.6
32
2
m
∆
2.2
2.4
2.6
2.8
3
3
−
10
×
POT by 2014 , 90% C.L
POT, 90% C.L
21
7.8x10
POT w/improvement, 90% C.L
21
20x10
Stat. only
Systematics
NOvA, US now running, plans to run until 2025 to have more than 3
𝝈
sensitivity to neutrino
mass hierarchy and 2
𝝈
sensitivity to CP violation
Vietnam (IFIRSE/IOP, VAST) joined
since 10/2018 as 12th country. HUST
joined recently
*all exp. have rich program, have no time to discuss
49

50. Future means coming soon
JUNO, China ~20kton liquid scintillator detector, plan to take data from 2020, 3
𝝈
sensitivity
to mass hierarchy determination with reactor neutrino source
*all exp. have rich program, have no time to discuss
50

51. Some our recent work in collaboration w/ Indian colleagues
51
https:/
/arxiv.org/abs/2009.08585
We may have some
signi
fi
cant answers to
neutrino mass hierarchy
and CP violation ~ 2027
Accepted to publish on PRD

52. Future means coming soon
Hyper-Kamiokande, Japan: Gigantic water Cherenkov detector (260kton), plan for operation
start from 2026, 5
𝝈
sensitivity to CP violation, proton decays sensitivity up to 1035 year
DUNE, US: ~40kton liquid Argon, more than 5
𝝈
sensitivity to mass hierarchy and ~4
𝝈
sensitivity to CP violation
*all exp. have rich program, have no time to discuss
52
Started reconstruction. We aim to join
as long as we have enough human power

53. Neutrino science:
From the “undetectable” to
world-wide science program

54. Neutrino frontiers:
From the “undetectable” to world-wide science program
@Intensity
Accelerator
𝜈
Reactor
𝜈
@Energy
Astrophysical
𝜈
Multi-messenger
Collider
@Sensitivity
CP violation
Mass mechanism
Sterile neutrino
Leptogenesis
Solar
𝜈
Atmospheric
𝜈
Detector tech.
𝜈
-nucleus int.
54
https:/
/conferences.fnal.gov/nu2020/
The Neutrino 2020 conference included
4,350 registrants from 67 countries on all 7 continents.

55. https:/
/arxiv.org/abs/1910.11878
CNB = Cosmic Neutrino Background
BBN = Big-Bang Nucleonsynthesis
DSNB = Diffuse Supernova
Neutrino Background
Neutrino: Here, there, Every where
55
~10
13
/s
solar
nu
through
your
hand
Span ~ 24 order of energy magnitude

56. Neutrino: Here, there, Every where
56
What we have explored
W
hat we barely touch
Someone is trying This decade?
https:/
/arxiv.org/abs/1910.11878
CNB = Cosmic Neutrino Background
BBN = Big-Bang Nucleonsynthesis
DSNB = Diffused Supernova
Neutrino Background

57. The fate of the Sun (and other stars)
57

58. Supernova: neutrino-powered
58
Modern theory:
99% of the star’s binding energy
released via neutrinos
SN1987A observed
Opened era of
neutrino astrophysics
Caveat: You build detector and wait! (Supernova must happen near the Earth to be observable)
(Super-K waited > 25 years). Will be a BIG party if happen now!!!

59. Why supernova neutrino study is important?
59
https:/
/en.wikipedia.org/wiki/Nucleosynthesis
Heavy elements on the
earth originate from the
supernova
https:/
/en.wikipedia.org/wiki/Composition_of_the_human_body
Parts of you are
remnant of the stars.

60. Diffuse Supernova Neutrino Background (DSNB)
60
Thousands of SN explosions
per hour in the Universe
https:/
/arxiv.org/abs/1910.11878
CNB = Cosmic Neutrino Background
BBN = Big-Bang Nucleonsynthesis
DSNB = Diffuse Supernova
Neutrino Background
Build up
Detectable w/ the new Era of Super-Kamiokande exp.

61. Can neutrino be practical thing?
“I don’t say that the neutrino is going to be a practical thing, but it has been a time-
honored pattern that science leads, and then technology comes along, and then, put
together, these things make an enormous difference in how we live”
——Fredrick Reines, Nobel prize winner, co-discover of the neutrino, NYT 1997

62. With neutrino detector, the sun never set
Neutrinos carry ~
1.3% of the Sun’
s
energy output
62
http:/
/www-sk.icrr.u-tokyo.ac.jp/sk/sk/solar-e.html
Without neutrino, the sun won’t shine
Neutrinos take ~ 3s to escape the Sun’
s surface
and 8min. to reach the Earth; but generated
photons take ~ 100,000 years to escape the Sun’
s
surface

63. Monitoring Reactor: Neutrino for PEACE
Essentially, Nothing can stop neutrinos!
If somehow a neutrino source is
produced, eg. Fr. Nuclear reactor
activity, neutrino and thus information
can’t be concealed
A lot of neutrinos are produced but …
they interact weakly with matter…
… A massive detector is needed if want
to detector
Number of groups in US/JP .. are trying
to realize/establish this technique
63
https:/
/www.aps.org/publications/apsnews/201404/neutrinos.cfm

64. Geo-neutrino: A novel way to better the Earth
Geoneutrino is new interdisciplinary field
Measure contribution of radiogenic heat to
the total surface earth flux
Understand composition of radioactive isotopes
Understand the Earth’
s geological model
64
H. Watanabe @ Neutrino 2020
Geoneutrino & radiogenic heat are generated
via decays of radioactive isotopes
Geoneutrino have been observed!
238
U →206
Pb + 8α + 8e−
+6 anti-neutrinos + 51.7MeV
232
Th →208
Pb + 6α + 4e−
+4 anti-neutrinos + 42.8MeV
40
K →40
ca + e−
+1 anti-neutrinos + 1.323MeV
https:/
/www.sciencenewsforstudents.org/article/explainer-earth-layer-layer

65. Summary
Exciting time to work in neutrino science. If you are interested, join us
and
Join T2K experiment for CP violation search and other unknown and
Super-K experiment for diffuse supernova neutrino background and
proton decay
Build lab in ICISE focusing on low-light detection technique (photosensor
and scintillation materials)
(Long-term) to build small detector in Vietnam to explore the sensitive
frontier (eg. Reactor neutrino, Geoneutrino, other unknown particles..)
65
Learn more about Neutrino, apply VSON-2021, Aug. 29 - Sept. 9, 2021
https:/
/i
fi
rse.icise.vn/nugroup/vson/2021/overview.html
Or apply ICISE internship
https:/
/i
fi
rse.icise.vn/nugroup/internship/index.html

66. Man inside of Son Doong cave SC inside of Super-K, 2018
• Inside of some void under some mountain
• Be isolated, need more light & at high risk of falling
• Search for something super
fl
uous (presumedly beauty of Nature)
rather than for necessities
We are different in many dimensions but what do we share?
(SC is T2K, Super-K and Hyper-K (Japan)
collaborator, was in MINOS (USA) for Ph.D)
66

67. “Neutrino mistakes: wrong tracks and hints, hopes and failures”
—- By Maury Goodman at History of the Neutrino, 2018
I was in MINOS
exp. & work for
both wrong tracks
Mistake is always out there
67

68. “Neutrino mistakes: wrong tracks and hints, hopes and failures”
—- By Maury Goodman at History of the Neutrino, 2018
Mistake is always out there
Soudan mine, Feb. 2012
716m from surface
Surface of Soudan mine
Feb. 2012
Auxiliary Detector
I was in MINOS
exp. & work for
both wrong tracks
68

69. Cave exploration with cosmic ray source and
scintillator hodoscopes?
Can we do a practical thing?
Hodoscope concept at IFIRSE, Quy Nhon
69

70. What actually are we doing?
Work as an international collaboration
• Join T2K (Oc. 2017~) an international accelerator-based long-
baseline neutrino experiment in Japan (~500 collaborators from 65
institutes of 12 countries)
• Neutrino Event Generator, Neutrino Oscillation Analysis
• Join WAGASCI (now part of T2K) (Feb. 2018~) a neutrino-nuclei
interaction-focused experiment in Japan,
• Detector construction (our students are working directly with
Japanese and other colleague)
J-PARC,
April 2019
Build the lab at ICISE:
• Focus on Multi-pixel Photon Counting (MPPC)
and properties of plastic scintillators
• Practice with cosmic ray measurements
• Organize annually Vietnam School on Neutrinos (2021 is the 5th in the series) to train and encourage students
and young researchers working on neutrino physics
• Host the International Symposium on Neutrino Frontiers (2018)
70

71. The path forward
Lab development
• Photon sensor
• Multi-pixel Photon Counter
• microPMT
• Scintillator materials
• (Water-based) Liquid scintillator
• Lab test bench, detector prototype
single-element MPPC array
Portraits of MPPCs (taken from Hamamatsu)
International collaboration work
• Keep working with T2K experiment
• in 2018, T2K
fi
rstly presented that oscillation data exclude the CP
conserving cases at 2 sigma
• Contribute for other supporting program: neutrino
fl
ux, neutrino-
nucleon/nucleus interactions
• We are also interested in non-standard neutrino physics (CPT violation,
sterile neutrino)
• T2K is proposed to extend the run up to 2026 to achieve 3 sigma
sensitivity on CP violation
• Will join Hyper-Kamiokande experiment
• Effectively 8 times larger than Super-Kamiokande
• This is the 3rd generation of neutrino experiments, tentative plan is to
start operation from 2027
• Along with data analysis, we may want to work on PMT or microPMT
The most important is to build local human source & attract young, ambitious
physicists working now outside of Vietam 71

72. Beam-Induced Fluorescence (BIF): general principle
72
noble
Proton beam
Fluorescence photons
Uses
fl
uorescence induced by proton interactions with gas
injected into beamline. Transverse pro
fi
le of
fl
uorescence will
match its of proton beam
BIF is under development with some required speci
fi
cations:
Gas needs to be injected in the beamline: since gas normally at ~ 10-6 Pa, is
not enough to see BIF signal. Also need to be localized only near measurement
point
Method to deal with space charge effect: can use fast readout to capture the
early
fl
uorescence photons
High radiation environment near the beamline: non-rad-hard components, if
use, must be in the sub-tunnel
What we observe w/ CID camera
Proton beam

73. BIF working prototype
73
A complete prototype was installed in Summer 2019
1st beam test was carried out in early 2020
2nd beam test w/ upgraded prototype this T2K run (Mar-Apr. 2021)
More eg. IBIC 2020, http:/
/accelconf.web.cern.ch/ibic2020/papers/wepp34.pdf

74. Fiber installation & additional electronics
10 new 29m-length
fi
bers
have been fabricated
and installed
f=20cm lens
74
Optical
fi
ber end aligned to
MPPC PCB to
To supply bias
Voltage and for
Fibers
Optical
Optical
MPPC
On PCB
Fiber
• 3 MPPC arrays (4x4)
• 32 ADC channel of
250Mhz sampling

75. O-BLM R&D
Charge particles generate Cherenkov light when passing through
the optical
fi
ber, which also plays a role as a light guider to the
fast photosensor. Number of observed photons are essentially
proportional to the
fl
ux of charge particles, i.e beam loss
Key features:
Fast-response, portable, economical
•Proton speed: 3.3ns/m
•Light propagation in
fi
ber: 5ns/m
•Signal separation (maximal): 8.3ns/m
•Bunch width ~ 13ns; signal readout resolution 5ns
➔ well-separated if two signal-induced position
separated by ~7m (assumed background<<signal )
Timing bins [33.3ns/bin]
0 50 100 150 200 250 300 350 400
ADC
counts
100
−
50
−
0
50
100
150
200
250
300
350
30Mhz sampling
Gas-based BLM
Optical fiber-based BLM
Gas-based BLM vs. O-BLM: spill
75
http:/
/accelconf.web.cern.ch/ibic2020/papers/wepp06.pdf