J-Parc K TO実験における横方向光子検出器の高精度化kunolab/year-end...CsI @inner MB...

J-Parc K0TO実験における横方向光子検出器の高精度化

Dec. 20. 2010 Yamanaka Taku Lab. D1

Rie MURAYAMA

The Upgrade of Barrel (Side) Photon Detector at J-Parc K0TO Exp.

2010年12月20日月曜日

Contents

• Barrel (Side) photon detector at J-Parc K0TO

• Ideas to upgrade “Main Barrel”

• Improvement of “Main Barrel” efficiencyMC simu. about punch-through effect, sampling effect...

• Improvement of “Main Barrel” S/N ratioMC simu., measurement in October run and fiber measurement about “back splash” effect

• Summary


K0TO実験• KL→π0νν の分岐比を検証

標準理論(SM)ではBR=3×10-11と予想E391a実験：2.6×10-8 (90%レベル)上限値

K0TO実験ではSMの感度を目指す分岐比がより大きければ、新しい物理の存在を示す

• 小林益川行列の複素成分ηを数％の小さな理論的不定性で測定可能な

Golden Mode

• 稀崩壊ーη

ーρ

K0L ! π0νν

B ! J/ψ K0

小林・益川理論のユニタリ三角

decay therefore offers information of the ∆S = 1 process. The hadronicmatrix element can be factorized as the well-known branching ratio of theK → πeν decay [8]. The higher-order QCD corrections that couple to thevirtual top quark are calculable but small due to the large mass of the topquark [9]. A long-distance interaction contributes little to the K0

L → π0ννdecay [7, 10, 11], because neutrinos are weakly interacting particles. Conse-quently, an uncertainty in the theoretical calculation is estimated to be onlya few percent, and the K0

L → π0νν decay will offer clean information on animportant basic parameter of current elementary particle physics.

Figure 1: SM diagrams for the K0L → π0νν decay.

In the Standard Model, the decay amplitude of K0L → π0νν is pro-

portional to the imaginary part of a product of CKM matrix elements,Im(V ∗

tsVtd), which corresponds to the height of the unitarity triangle asshown in Fig. 2. The unitarity of the CKM matrix has been considered asone of the most critical checks for new physics beyond the Standard Model.The pure and clean information obtained by the K0

L → π0νν decay is crucialfor checks of the SM as well as those by B decays. By using current esti-mates for SM parameters, the branching ratio for K0

L → π0νν is predictedto be

B(K0L → π0νν) = (2.20 ± 0.07) × 10−10

(λ

0.2248

)8 [Im(V ∗

tsVtd)λ5

X(xt)]2

,

(1)and is expected to lie in the range (2.8 ± 0.4) × 10−11 [12]. Here λ ≡ |Vus|,X(xt) = 1.464±0.041 is the value of Inami-Lim loop function [13] (includingthe QCD correction), and the parameter xt is the square of the ratio of thetop quark and W masses. Because η in Im(V ∗

tsVtd) = −A2λ5η measuresdirectly the height of kaon unitarity triangle, the decay amplitude K0

L →π0νν violates CP directly and offers the best opportunity for measuring theJarlskog invariant:

JCP ≡ −Im(V ∗tsVtdV

∗usVud) = −λ

(

1 − λ2

2

)

Im(V ∗tsVtd) , (2)

7


!"#

横方向光子検出器(Main Barrel(MB))

• E391a実験のMBを再利用、改良して使用する

• 鉛とシンチレータ積層構造のveto検出器

• CsIカロリメータにてπ0からの2γを検出

• CsIカロリメータ以外の全ての検出器にて他事象をvetoする

• 現在予想される主なback groundは、 KL→π0π0　計4γのうち2γをlossした場合が該当


KOTO実験Proposalでの改良• punch-through

photonに対して、E391a型 MBの外側に厚さを加える

E391a型MB

proposal版MB

π0π0 background (7×10^13 KL

,acceptance loss 50%)(from Geant4 MC)

2.9±0.4 events

1.39±0.09 events

E391a MB +　( 5 mm-thick scintillator　+　5 mm-thick lead ) ×5 layers

14X0 +5X0

Proposal版でのInefficiency Function !

ficiency due to punch-through will be greatly improved as shown in Fig. 25.We will use the current vacuum chamber with a little modification.

Figure 25: Comparison of the γ-detection inefficiency of the Main Barrelbetween E391a and Step 1. In Step 1, we will add additional modules made of5 layers of alternating 5-mm-thick lead and 5-mm-thick scintillation plates.Black points are the inefficiency of the E391a Main Barrel, and red ones arefor Step 1.

As shown in Fig. 26, the Front Barrel and the collar counters CC01 andCC02 form an upstream decay chamber in order to suppress KL decays infront of the fiducial region. As shown in Fig. 27, the Front Barrel consistsof 16 trapezoidal-shaped modules that are made of 59 layers of alternatinglead and plastic-scintillator plates (16.5 X0 thickness and 2.75 meters long).The light yield is obtained as 20 (10) photoelectrons per 1-MeV deposit atthe nearest (farthest) point from the PMT.

Table 3 summarizes the parameters of the Barrel Photon Vetos.

4.3.3 Charged Veto

Most KL decays include charged particles such as KL → π+π−π0 (12%),KL → π±µ∓ν (27%), and KL → π±e∓ν (40%), and these decays can becomebackgrounds both in the trigger stage and in the analysis stage. For example,KL → π+π−π0 contains a π0 in the final state and can fake the signalof interest if the two charged pions are missed. Thus, the decay regionmust be surrounded by charged particle veto detectors, as well as photonveto detectors. There are three categories of charged detectors: the main

38

Inef

ficie

ncy

Incident gamma energy10-2　　　　　　　10-1　　　　　　　1

1　　　　　　

　

10-2　　　　　

　　

10-4

10-6

黒＋: E391a型MB

赤＋: proposal版MB

E[GeV]

Thickness (X0 )# scintillator layers# lead layersReadout

E391a MB

14.045 (5 mm-thick)inner:15 (1 mm-thick)+outer:30(2 mm-thick)Both ends by 128 (32 x 4) PMTs


Proposal版でのInefficiencyの要因

• Proposal版MBでのMC simu.

各Energy、各入射角のγを固定位置に入射

・外に抜ける→ punch through

・前方、後方に抜ける→ leak

・PhotoNuclear反応か

・その他→sampling effect

入射

z

MB

MB


10 210 310-710

-610

-510

-410

-310

-210

-110

1

Inefficiency 5 degInefficiency 5 deg

10 210 310-710

-610

-510

-410

-310

-210

-110

1


10 210 310-710

-610

-510

-410

-310

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-110

1

total Inefficiency each degtotal Inefficiency each deg

10 210 310-710

-610

-510

-410

-310

-210

-110

1

total Inefficiency and sampling ratiototal Inefficiency and sampling ratio

10 210 310-710

-610

-510

-410

-310

-210

-110

1



• ~30MeVのLow Energy γではsampling effect、30MeV~のHigh

Energy γではpunch throughが大きな要因。

緑: Sampling effect

青: Punch Through

ピンク: leak

(BackSplash like)

θ＝85° (垂直入射)

E[MeV]

Inefficiency各Incident EnergyのγにおけるInefficiencyの要因

MB

85°

黒: all

赤: Photo Nuclear

• 垂直入射の場合


10 210 310-710

-610

-510

-410

-310

-210

-110

1


10 210 310-710

-610

-510

-410

-310

-210

-110

1


10 210 310-710

-610

-510

-410

-310

-210

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1


10 210 310-710

-610

-510

-410

-310

-210

-110

1


10 210 310-710

-610

-510

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-110

1


θ＝5° (平行入射)

緑: Sampling effect

ピンク: leak

(BackSplash like)青: Punch Through

赤: Photo Nuclear 黒: all

各Incident EnergyのγにおけるInefficiencyの要因• 平行入射の場合

Inefficiency

MB

5°

• ~100MeVのLow Energy γではsampling effect、100MeV~のHigh

Energy γではphoto nuclear interactionが大きな要因。

E[MeV]



MBの課題

4. Back Splash Photon Effect　CsIカロリメータからの電磁シャワーの漏れによりsignal event の一部がveto検出器に反応を生じるシグナルロス

CsI

MB

1. Punch-Through Effect ... ex) 垂直入射の30MeV~　光子吸収長に従ってγが検出器を突き抜け、検出されない

2. Sampling Effect ... ex) 垂直入射の~30MeV、平行入射の~100MeV　鉛シンチの鉛部分でのみ電磁シャワーが生じ、検出されない

3. Photo Nuclear Interaction ... ex) 平行入射の100MeV~　原子核中のNeutronに全エネルギーを落として電磁シャワーを生じない


Punch-Through防止

E391a型MB

proposal版MB

テスト

π0π0 background in 7×10^13 KL

(from Geant4 MC)

2.9±0.4 events

1.39±0.09 events

1.3±0.1 events

14X0

+5X0

+10X0

←垂直入射

E[MeV]

[deg]

• 物質量を更に増やした場合でも、π0π0 background数は変わらない

← proposal版MBにて残るπ0π0 backgroundのEnergyと入射角度分布

入射角が浅いため、Punch-Throughの寄与は十分小さく、

元々の入射粒子が多い。sampling ratio等のInefficiencyにより残る領域


2. CsIを使用　Sampling ratio→0、MCにて検討

1. 鉛シンチレータ　- 1mm厚、2mm厚のうち1mm厚の層を増やす

　- 鉛をさらに薄く　　今までの鉛シンチレータとは異なる制作手法が必要

Sampling Effect を減らす方法

Thickness (X0 )# scintillator layers# lead layersReadout

E391a MB

14.045 (5 mm-thick)inner:15 (1 mm-thick)+outer:30(2 mm-thick)Both ends by 128 (32 x 4) PMTs

previous study

if we add 25layers (Pb 1mm Scinti 5mm) to inner side of MB,2pi0 BG → proposal版と同程度 (simulated in 2008)

+5X0　=proposal版


New Inefficiency

= Ppunch*Pproposal + Pelse

CsI @inner MB

• Proposal版MBに加えた場合のInefficiency

入射

z

CsI

CsI

MB

MB

例えば、最も悪い条件、

CsI厚3cm、垂直入射、Eγ10MeVでもPpunch*Pproposal + Pelse

= 0.5*0.2 + 0　　　→proposalの1/2

10-710

-610

-510

-410

-310

-210

-110

1


10-710

-610

-510

-410

-310

-210

-110

1


10-710

-610

-510

-410

-310

-210

-110

1


10-710

-610

-510

-410

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1


10-710

-610

-510

-410

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1


10-710

-610

-510

-410

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-110

1


E[MeV]

垂直入射

平行入射


MBの課題 (再掲)

4. Back Splash Photon Effect　CsIカロリメータからの電磁シャワーの漏れによりsignal event の一部がveto検出器に反応を生じるシグナルロス

CsI

MB

1. Punch-Through Effect ... ex) 垂直入射の30MeV~　光子吸収長に従ってγが検出器を突き抜け、検出されない

2. Sampling Effect ... ex) 垂直入射の~30MeV、平行入射の~100MeV　鉛シンチの鉛部分でのみ電磁シャワーが生じ、検出されない

3. Photo Nuclear Interaction ... ex) 平行入射の100MeV~　原子核中のNeutronに全エネルギーを落として電磁シャワーを生じない


• BackSplashとBackGround のZ position、Energyの違い

左図: w/ CsICut, w/ MBWeight　右図: w/ CsICut, w/o VetoCut

E[MeV]

• Background(π0π0)のMB hit

Z[mm]

CsI

MB

• Signal(π0νν)でのBack-Splash

Z[mm]

E[MeV]

• 新しいdetectorを用い、 EnergyとZ positionをdetector(またはtiming)によって区切ることで、 BackSplashとBackGroundを区別する

BackSplash の識別


z Energy # BG BkSp (※) (S/N)/(S/N)

- - 1.39 ±0.09 31% 15000~6000 E<20MeV 1.96 ±0.12 13.5% 0.88 +0.13-0.115000~6000

E<10MeV

1.41 ±0.09 14% 1.23 +0.17-0.154500~6000 E<10MeV 1.50 ±0.09 9.6% 1.26 +0.17-0.164000~6000

E<10MeV

1.59 ±0.10 6.9% 1.18 ±0.155000~6148

E<10MeV

- 12.6% -

• BackSplashとみなすEnergy、Z positionのγをvetoしないと仮定し、S/Nの向上を比較

E[MeV]

(※)error......tipical ±0.0% Z[mm]

BG

•Geant4では4500(5000)~6000mmが有力•DetectorのEnergy Resolution

• Detectorを加える領域の検討

(S/N)new / (S/N)ori

BackSplash識別によるS/N向上～Z position とEnergy～

先10月runにてMB位置にCsIを置いてデータ取得、MCと比較予定


1

10

210

310

2000 4000 6000-20-15-10-505

1015202530 cbarPosZvsTime2

Entries 140191Mean x 2.728± 5216 Mean y 0.008814± 4.859 RMS x 1016RMS y 3.281Integral 1.386e+05

1

10

210

310

2000 4000 6000-20-15-10-505


Entries 140191Mean x 5.184± 5496 Mean y 0.01692± 4.093 RMS x 957.8RMS y 3.126Integral 1.601e+04

1

10

210

310

2000 4000 6000-20-15-10-505



1

10

210

2000 4000 6000-20-15-10-505


Entries 86637Mean x 6.232± 5087 Mean y 0.02074± 5.362 RMS x 881.1RMS y 2.933Integral 8485

1

10

210

310

2000 4000 6000-20-15-10-505


Entries 140191Mean x 2.728± 5216 Mean y 0.008814± 4.859 RMS x 1016RMS y 3.281Integral 1.386e+05

1

10

210

310

2000 4000 6000-20-15-10-505



π0π0 、 BackSplash 比較　～Z position とTiming～

※今のMCでは時間分解能（位置分解能も）を0 (σt=0)としている。

• background(π0π0)のhit timingとZposition 　(MC 10^7event)

• backsplash(π0νν)のhit timing とZposition

Z[mm]Z[mm]

hit timing [ns]

decay timeの短いfiberを使うこと等で時間分解能の向上を検討


Timing resolution improvement• Candidate is BCF-92(Bicron) fiber

Decay time [ns]

EmissionPeak [nm]

1/e Length [m]

No. of Photons

BCF-92 Y11-M(Kuraray)

2.7 8.8

492 476

>3.5 >3.5

N/A ?

BCF-92 has short decay time

Y11-M used in current MB

fig1) http://lhcb-calo.web.cern.ch/lhcb-calo/internal/TDR/notes/039/hcfi1.psfig2) http://www.detectors.saint-gobain.com/uploadedFiles/SGdetectors/Documents/Brochures/Scintillating-Optical-Fibers-Brochure.pdfhttp://particulas.cnea.gov.ar/workshops/icfa/wiki/images/a/a7/Kuraray-PSF-Y11.pdf

fig1)

fig2)

光量測定を準備中


http://lhcb-calo.web.cern.ch/lhcb-calo/internal/TDR/notes/039/hcfi1.ps

http://lhcb-calo.web.cern.ch/lhcb-calo/internal/TDR/notes/039/hcfi1.ps

http://www.detectors.saint-gobain.com/uploadedFiles/SGdetectors/Documents/Brochures/Scintillating-Optical-Fibers-Brochure.pdf




http://particulas.cnea.gov.ar/workshops/icfa/wiki/images/a/a7/Kuraray-PSF-Y11.pdf

http://particulas.cnea.gov.ar/workshops/icfa/wiki/images/a/a7/Kuraray-PSF-Y11.pdf

fiber 測定• fiber

• BCF92およびY11

• 長さ7m...真空の外でPMT両読みできる長さ

• Multi anode PMT H7546B

• 吸収波長の合う LEDおよびscinti. (EJ-204, EJ-230) PMT

PMT


Summary• MB inefficiency are analyzed from MC simu.

• Punch-through effect is enough improved by additional 5 radiation length.

• If we use 3cm-thick CsI, background is reduced enough about low energy photon that is not detected by sampling effect.

• By Energy and timing difference, Back-splash photon is separated from background events. About event rate and energy difference, not only MC but also data from October-run will be analyzed for effect of back-splash reaction. About timing difference, fibers of short decay timing are studied.


J-Parc K TO実験における横方向光子検出器の高精度化kunolab/year-end...CsI @inner MB...

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