Neutrino PhysicsMEMBER

ERIKO KUSUNOKIKENJI SHUTAKESHI SAITOMESANORI IWAMOTOMITSUTAKA NAKAO

NISHIMURA GROUP

CONTENTS

• Theory of Neutrino Physics• Super Kamiokande (Super K)• Measuring Cosmic Rays• T2K Experiment• Analyzing T2K data

ν- Source

ν- Oscillation

ν- Detector

Theory of Neutrino Physics

What is neutrino?

・ Three Flavors・ Neutral (no charge)・ Only Weak Interaction・ Very Tiny Mass

very difficult for detecting…

The interesting point is…

Neutrino Oscillation

Neutrino Oscillation(Two mixing case)

・ The mass basis is different from the interaction basis.

flavour massΘ:mixing angle

The probability to change νμ into ντ is… L : Length [km]E : energy[GeV]Δm2 : mass square difference[eV2]but nature is more complex…

✔✔✔

Neutrino Oscillation(Three mixing case)

Atmospheric Neutrinos

νμ→ντ

Solar Neutrinos

νe→νxAccelerator

νμ→νe

What we want to know is …

Mixing Parameter

✔ ✔❓~45° ~34°

T2K

CP violation~What is δCP in PMNS matrix?~

This parameter leads to CP violation.

CP term

Leading Term

How can we detect neutrinos?

The answer is…

Super K

Super-Kamiokande1km

Kamioka

39.3m

41.4m

50,000 t

Inner tank

outer tank

11,129 PMTs (50cm)detect neutrinos.

1,885 PMTs (20cm)distinguish neutrinos from muons coming from outside.

water

We can block muons that originate from cosmic ray.

1km Underground

Red : strong light

Blue : weak lightVertex

1. Timing of detection2. Vertex position 3. Finding Cherenkov ring4. Neutrino traveling

direction and energy

Event display

OH

p n

𝝂𝒆

𝑒+¿ ¿𝑊+¿¿

Cherenkov light

inverse beta decay

Neutrino detection @Super-Kamiokande

Neutrinos interact with particle in water.

→ SK detect Cherenkov light that is created when a charged particle travels faster than the speed of light in water.

neutrino

Next: Hyper-Kamiokande

HK might uses HPDs instead of PMT.

ｅｅ

~8kV

Avalanche diode

Super-Kamiokande

ｅMetal dynode

~2kV

Photon

To measure the light energy, we use PMTs.

Neutrino detectors

HPD accomplish superior performance in low cost !!

Improving performance(Volume of tank) ×25

PMT (PhotoMultiplier-tube) HPD (Hybrid-Photo Detector)‐

photoelectric effect

Let’s use HPD !!!!

These PMT are used in super-Kto measure the cosmic rays. HPDs may be used in Hyper-K . We tested an HPD and a PMT to measure the angular Distribution of cosmic ray muons . 　　

HPD

PMT

Testing PMTs and HPDs

The Angular Distribution of Cosmic ray Muons

The flux is given by J(x,θ) = J(x,0) (n = 　 Where λ is mean free pathThe purpose of thisexperiment was finding the value of n.

Set up We used two sets of two detectors to measure the angular distribution. 　

Scintillator(20cm×20cm)

PMT

HPD

PMT

Scintillator(50cm×50cm)

First detector Second detector

μ

We made a coincident circuit to count muons which activated all detectors.

Resultsangle[degree] measuring

time[second]

count flux[Hz/counter]

0 15502.80 1276 0.0823

30 23489.36 1015 0.0397

50 42961.68 1345 0.0241

70 50647.65 817 0.00901

We corrected flux by a solid angle

We fitted a× and determined n = 2.470.53 .

fitting

T2K Experiment

What is T2K?

• Tokai(J-PARC) to Kamioka(SK)

• Pure • SK can distinguish

and 　• Observe

appearing and 　 disappearing

http://t2k-experiment.org/ja/

𝑣𝜇

?

Devices to discovery

• Distance • Off axis

2.5。𝜋+¿¿

E ～ 0.6 GeV

L = 295 km

𝜈𝜇 (on axis)

SK

appearensae in E = 0.6 GeV

disappearing in L =295 km

Enrichment signals

• Reduce BG cuts using Monte Carlo calculations

193

60

cut BG

377 events is first selected by timing

Number of rings e -like evernts

cut NC,μ

cut collapse π,μ 　 cut in beam 57 44 39 28

• Selection one ring -like events

events

• Proton created in J-PARC :• expected BG : 4.92• So we calculate expectation and estimate

6.57

28 -like single ring events were found𝜈𝑒

Was happened? 　　　 ?

Analyzing T2K data

What we have• T2K result

number :

Proton number :

Very new : Physical Review Letters, 2014 Feb

• Theory

Maximum Likelihood Method to find • Likelihood function : ← maximize L• ← minimize

Compare numbers obs. vs exp.

Poisson distribution

Restrict systematic parameters

f : systematic errors ← parametersExpectation of numbers observed

: signal of oscillation depends on ←par : background appeared as by M.C. simulation (depends on , , , function was given)

Get

sin22 𝜃13=0.137

• Best fitChange minimizing That = experimental result!!!

Get errors• Error(1 sigma)

→

get at

+0 .0370 .137−0 .032

Get confidence level for

→

get at

Significance : 6.9s

actually exists and non-zero!!!

√ 46.9=6.9𝜎

Comparison with actual T2K

ACTUAL T2K

• C.L. :

OUR VERIFICATION

• C.L. :

Same value, same error

T2K was correct!!!

(C.L. is better by using energy likelihood function)

In actual T2K experiment…• Likelihood function

: oscillation parameter : systematic error parameterf are more than 49!

Future experiment

• T2K is just in beginning• Continue to get 10 times more data• Check the sensitivity ()

(We did)→ twice more precise

• Anti-Neutrino experiment by Hyper-K can measure

Summary

Theory

Experiment Analyzing