A separation method for Gamma ray and Neutron in J-parc E-14 Koto Experiment

using a Pulse Shape Discrimination (PSD) with CsI Crystal Scintillator.

Jong-Kwan Woo (Dept. of Physics, Jeju Nat’l Univ.)

2011-10-24Jeju N. Univ. Unipark (SeoGuiPo)

Abstract

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A brief introduction of J-Parc E14 experiment will be presented in this talk. A branching ratio of KL->π0νν decay, a flavor changing neutral current (FCNC) violating the CP conservation, provides the lowest error among the many physical quantities predicted by a Standard Model. People concentrate on this decay mode, because the theory is very simple. And it gives a clue to understand the relation between quarks' generation because this decay mode involves the three quarks interaction simultaneously. It is also ideal to decide the Cabibbo-Kobayashi- Maskawa(CKM) parameter η indicating the mixing amplitude in the frame of the Standard Model. We expect to find a new physics beyond the Standard Model with studying of KL->π0νν decay mode. A calculation of the amplitude of KL->π0νν is simple with the minimum error while it is not easy to measure the decay. The E391a, an experiment using a proton synchrotron in KEK, showed in 2004 the first possibility proving whether the branching ratio predicted in the Standard Model is true. We will measure the amplitude of KL->π0νν decay mode more precisely using J-parc E14 detector that is the extended and the advanced version of the E391a in KEK. We hope to accumulate the first data of J-Parc E14 in December 2011.

A major detection mechanism of KL->π0νν decay is to measure the gamma ray from π0->γγ decay. So, the separation of gamma ray from neutron, background induced in beam line plays the key role for J-parc E-14 experiment.

We will introduce a pulse shape discrimination (PSD) method for separation gamma ray (Minimum Ionization Particle (MIP)) from neutron (Heavy Ionization Particle (HIP)) using a CsI crystal scintillator.

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Motivation and Goal

In Experimental nuclear and particle physics, Identifying particles, especially γ-ray, neutron, and charged particles,

Is fundamental. Ex) Dark Matter (WIMP), a Neutral kaon experiment at J-Parc

E-14, Neutrino experiment…

Pulse shape discrimination (PSD; 파형모양판별법 ): An elastic collision between incident particle and scintillator signal detection with PhotoMultiplier Tube (PMT) identification incident particle.

PSD with Liquid Scintillator: higher efficiency, difficult to handle

PSD with Crystal Scintillator: lower efficiency, easy handling.

Goal for our study: to improve PSD method with Crystal scintillator

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Dark Matter (WIMP)

Galaxies 에 있는 물질을 직접 관측함으로써 dark Matter 의 존재를 알 수 있다 .

Vobj2 = GM/R

M >> Mvisible

90~99% of Universe Mass is Not observed (hidden mass), yet.

We call it Dark Matter . currently ¼.

Assume: Most of Dark matter stays in galactic halo.

1A Particle Physics Experiment using Pulse Shape Discrimination (PSD)

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Dark Matter Candidates9*10-72M⊙(10-5eV, Axion) < MDM < 104M⊙ (Black hole)

* Baryonic Dark Matter

• MACHO: (10-7 M⊙<MBD<10 M⊙)

-brown dwarfs:( MBD<0.08 M⊙)

-Jupiters : (~0.001 M⊙)

• Neutral Hydrogen and molecular clouds

* Non-Baryonic Dark Matter

• Hot type: (V ≥ c/100) -light neutrino

• Cold Type:(V ≤ c/100) -WIMP: (10GeV ~ few TeV)

-axion (10-5eV)

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Neutralino (candidate for WIMP)

• MSSM predicts the neutralino that is consisted of supersymmetric partners of photons, Z bosons and Higgs.

• Neutralios (WIMP) are localized in the galactic scale.

.

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Anti-matter

matter

Matter - Anti matter Annihilation

The meeting of Matter and Anti-matter annihilates each other with radiating photon.

Evidently, however, matter won against antimatter. Just a tiny deviation from perfect symmetry seems to have been enough –

(particles of matter: particles of antimatter = 1010+1 : 1010)

This excess of matter was the seed of our whole universe, which filled with galaxies, stars and planets – and eventually life.

But what lies behind this symmetry violation in the cosmos is still a major mystery and an active field of research.

2A Particle Physics Experiment applying Pulse Shape Discrimination

(PSD)

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Through the looking glass

Natural laws should be perfectly symmetrical and absolute. But not always.

Three Symmetries in Elementary Particle Physics

1) P (Parity) x -x

2) C (Charge) Cmatter=-Canti-matter

3) T (Time) t -t : motion should be independent whether forwards or backwards in time.

Symmetries in Physics should be conserved.

Ex) Energy conservation before and after event

Energy is symmetrical in time.

Ex) Charge conservation

symmetry in electromagnetic theory 총 33 장 가운데 8

Maybe, Sakharov’s conditions (incorporated) SM of physics.

Then the surplus of matter created at the birth of the universe. Fitch and Cronin found doubly broken symmetry.

Solving the mystery of the broken symmetry

Why a considerably smaller broken symmetry exist in kaons decay.

(SM couldn’t explained).

1972, Makoto Kobayashi and Toshihide Maskawa (University of Kyoto), who were well acquainted with quantum physics calculations, found the solution in a 3 x 3 matrix.

SU (3)quarkSU (3) color

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노벨상 위원회의 2008 년 노벨 물리학상 공식 발표

symmetry broken

( 대칭 깨짐 ) 이 수상 동기

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= K0 at Tokai KK00TOTO

60 members/16 institutes/6 countries

KOTO Experiment, KEK, J-PARC E-

14 KL 0 experiment

Korean Participants

우종관 , 김용주 , 고재우 , 임계엽 1, 김은주 2,

박인규 3, 정명신 3, 강서곤 3, 김유상 3, 안정근 4, 이효상 4, 백광윤 4

( 제주국립대학교 1KEK   2 전북대학교 3 서울시립대학교 4 부산대학교 )

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Neutral Kaon DecayKL 0 BR (=2.8±0.4ⅹ10-11 by SM) 측정

determination Cabibbo-Kobayashi-Maskawa (CKM) parameter η ( 측정오차가 가장 큼 )

CKM: Matter-Anti Matter symmetry breaking comes from mixing with quarks in 3 generations.

Reason and Amplitude=? Experiment will give the Answer.

• KL 0 BR 계산 ( 이론 ) 매우 간결하나 측정 ( 실험 ) 매우 까다로움

KL 0 measurement by using measurement 0e+e- Problem: BR<1% 0 (BR=99%): Kinematical Constraint

• 실험 제안 1989• 2004 KEK-PS e391a 실험의 가능성을 보여줌• 2008 J-Parc E-14 실험 제안 proved ( 건설 및 빔 테스트 완료

2010)• 2011 년 4 월 실험 예정

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Flavor Changing neutral Current (FCNC)

KL 0 ( sd FCNC process)Interaction with Lepton-current of

(intermediated by t).

붕괴 진폭은 약상호작용 만의 미지의 파라미터에 의해서 결정됨 (K→eπʋ 과 비교해서 알 수 있음 ).

J. Ellis

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KOTO at hadron hallin KEK J-Parc

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KL 0 measurement at KEK e391a

• Measurement KL 0 using 0

• New method: 1) reduce missing with photon detector

covering 4. 2) Get rid of transverse momentum of KL

Pt=0 for .

need the smallest KL beam cross section.

(optimized by GEANT4 simulation)• Major back ground (Neutron making 0

easily : n+An+A+0 ) Currently unique Sol.; High Vacuum (10−5

Pa) reduce collision n & A.총 33 장 가운데 15

e391a

Signal region

KL

0

BG by CO2

BG by material

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Direct Detection Mechanism using PSD method with a Liquid

Scintillator

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Nucl.Inst. & Meth. 196 101 (1982)

Nucl.Inst. & Meth. 3 207 (1982)

P.R. B20 3486 (1979)

P.R. B21 2632 (1979)

J.Luminescence 18/19 487 (1979)

J. Chem Phys. 50 3143 (1969)

J. Chem Phys. 42 4250 (1965)

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Singlet and Triplet states of Excimer X2*

Meta-stable target molecule X2* same as 2-body

analysis

Two nuclei can have 4 spin states. |X1,X2> =|↑,↑>

|X1,X2> =|↑,↓> + |↓,↑>

|X1,X2> =|↑,↓> - |↓,↑>

|X1,X2> =|↓,↓>

Total spin s = 1ℏ or 0 target nucleus’ spin 1/2ℏ .

s=1: sz = mℏ, m = 1, 0, -1 (triplet state)

s=0: sz = mℏ, m = 0 (singlet state)

Τtriple = (27 ns) << Tsingle (2.2 s) 입사입자에 따라서 핵자의 단일항 (singlet) 상태와 삼중항 (triplet)

상태에서 방출하는 광자의 세기와 방출시간의 비율이 다름 .총 33 장 가운데 19

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Direct Detection Mechanism using PSD method with a Liquid

Scintillator

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Amplification Processes

JKPS 50-2 (2007) p524, JKPS 49-1 (2006) p266총 33 장 가운데 21

An Excitation process in Crystal Scintillator

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(NS/NT)MIIP > (NS/NT)HIP Previous Studies

NT: Amplitude of Fast signal from Triplet state.

NS: Amplitude of Slow signal from Singlet state. Heavy Ionization Particle (HIP), Minimum Ionization Particle (MIP) Neutron, Proton, Muon HIP, Gamma Ray MIP

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Experimental Setup

MC-50 proton cyclotron at KIRAMS( 원자력의학원 ) produces p (50 MeV). p collides Be Target. produce. n or .

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Beam Specification and

Beam Current: 40 μA Average proton Energy: 35 MeV

Neutron Production rate: 2.75*1011/hr/cm2 Spreading 120 cm below collimator

N-Beam scanning Area: 54X54 cm Square region.

Place CsI crystal (7.5*7.5*20 cm) Scintillator at 10, 27, and 50 cm from center of N-beam.

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Typical Signals

X : time [s] Y: amp [v] left) signals form neutron beam, right) signals form cosmic ray.

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Pulse Shape Analyzing

integrating Pulse Finding Break point after 3-dim fitting (right) Calculating the ratio of areas the tail to Body

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Slow signal VS Fast signal

X: amp of slow signal (tail) Y: amp of fast signal (head) 중성자가 많은 (rich) 실험일수록 fast signal (Y) 의 비율이 커짐 Cosmic 그림에서 두 개의 묶음에서 위쪽 ( 좌측 ) 의 묶음이 중성자 Slope 약 18 인 (y=18x+5) 선을 기준으로 나뉨

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Histogram of Slow signal VS Fast signal

x: ratio of (amp of Fast/amp of slow)/5 Deeps Slope 18 (at previous page)

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Comparison Liquid and Crystal Scintillator after applying my PSD method

CsI Crystal Scintillator

Xe Liquid scintillator

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Comparison signals between CsI crystal with myPSD and Liquid Scintillator with

classical PSD

CsI crystal Scintillator (cosmic ray)

BC501A Liquid Scintillator (artificial source)

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Comparison signals between CsI crystal with my PSD and Liquid Scintillator with

classical PSD(Exposured by Cosmic Ray)

CsI crystal Scintillator

Xe Liquid Scintillator [APH 28 132 (2007)]

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Detail analysis will be published soon.32

Summary We established a Pulse shape discrimination (PSD)

method with CsI crystal Scintillator.

We found the possibility of PSD method using CsI crystal scintillator to separate the neutron signal from gamma ray signal.

Recommend this PSD method for the rare event experiment.

Next Step We need the additional and more detail

experiments. And, more precise analysis tool.

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