New Status of KL π νν analysis at J-PARC KOTO · 2018. 3. 11. · td V ts V tb 1 A 0 @ d s b 1 A ... Japan Proton Accelerator Research Complex = J-PARC KL beam 30GeV Proton Beam

Kota Nakagiri ( Kyoto Univ. )for the KOTO collaboration

1

Status of KL→π0νν analysisat J-PARC KOTO

OK Tν

νs

d

KL→π0νν Decay

2

⌫⌫̄

s dd̄

W�

t

d̄

Z0V ⇤tdVts

＜崩壊ダイアグラムの１つ＞

V ⇤ts Vtd

• direct CPV• highly suppressed in the SM : Br = 3×10-11• theoretically clean : ~2%➡ good probe for new physics that violates CP symmetry 0

@d0

s0

b0

1

A =

0

@Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb

1

A

0

@dsb

1

A

λ ~ 0.2λ2λ3

K system ~λ5 << Bd system ~λ3

1

⚫ SM⚫ SM + NP

M.Tanimoto, K.Yamamoto arXiv: 1603.07960

a model w/ O(10TeV) SUSY

indi

rect

limit

1σ from exp.

direct limit : 2.6×10-8 (90% C.L.)indirect limit (Grossman-Nir limit) Br(KL) < 4.4 × Br(K+) = 1.5×10-9 (90% C.L.)

10-8

10-9

10-10

10-11

NP ?

s→d FCNC

a model w/ heavy Z’ (50 TeV)

A.J.Buras, et al. arXiv: 1408.0728

KOTO Experiment @ J-PARC

3

Japan Proton Accelerator Research Complex = J-PARC

KL beam

30GeV Proton Beam

16°

KOTO

Collaboration photo @J-PARC2017 Dec. 16th

K0 at TOkai

Tokai village

Au target

Experimental Method

4

CsI Calorimeter

KL

γ

ν ν

R~1m

(π0) γ

KL ! ⇡0 ⌫⌫̄π0→2γ on CSI calorimeter

5

KL ! ⇡0 ⌫⌫̄missing : hermetic veto

KL

Veto counters

ν ν

(π0)γ

γ

Experimental Methodπ0→2γ on CSI calorimeter

CsI Calorimeter

R~1m

6

KL

Veto counters

(2π0)

γ

γγ

γ

KL ! ⇡0 ⌫⌫̄


missing : hermetic veto

CsI CalorimeterKL→2π0 BG

R~1m

7

Decay Z

π0 P

t Signal boxν ν

KL 2γ

( π0 )

KLZ

θ

γ (E1)

γ (E2)

cos ✓ = 1�M2

⇡0

2E1E2

ν ν

Experimental Methodπ0 reconstruction from 2γs

νν carry away momentum = rec. π0 has large Pt➡ signal box on Pt v.s. Z plane

History of the KOTO data taking

8

Jul2013

Dec2013

Jul2014

Dec2014

Jul2015

Jan2016

Jul2016

Dec2016

Jul2017

Dec2017

Acc

umul

ated

P.O

.T.

0

10

20

30

40

50

601810×

Bea

m P

ower

(kW

)

0

20

40

602015 run2013 run

operation of Hadron facility was stopped

first physics run

First physics run in 2013

9

One event was observed. consistent with BG expectation→ Br(KL→π0νν) < 5.1 ×10-8 (90%C.L.)

Single Event Sensitivity = 1.29 ×10-8

Signal box: 3000 < Zvtx [mm] < 4700 150 < PT [MeV/c] < 250

Lessons from the 2013 run

10π± disappear @vacuum pipe

1st Hit

2nd Hit

neutron

①

②

③

KL ② KL→π+π-π0

π±

2γ

neutron③ π0@NCC 2γ

π± →missing

① hadron cluster BG

dominant BG in the 2013 run

Lessons from the 2013 run

11

π±

new scintillation counterBeam pipe : SUS → Al

Suppress KL→π+π-π0 BG

For ② For ① & ③

thinner vacuum window : 125μm→12.5μm

Beam profile monitor for better beam alignment

Reduce halo neutrons～ 1/20 ～ 1/2

calorimeter

2015 run analysis :

12

Hadron cluster BG

1st Hit

2nd Hit

neutron n

Al plate as a scattering source

Special run to take control sample

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

5

10

15

20

25

30

5798(4496)

60

2250 576

1932

0277

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

20

40

60

80

100

0(0)

1707

7856 2170

8315

01233

control samplePhysics data

5798 (4496)

13

Pulse shape discrimination

1/10 BG reduction & 90% signal acceptance

Cluster shape discrimination

neutron pulse hasa longer tail

• cluster shape neural net cut (NEW)


1/300 BG reduction &80% signal acceptance

（NEW）

Hadron cluster BG2015 run analysis :new cuts to discriminate γ-cluster from n-cluster w/ calorimeter

• cluster shape χ2 cut :cluster shape is consistent with that of γ MC → pass

timing information is used

14

Rejection Power

Cluster Shape Cut ( 2.2 ± 1.0 ) ×10-4

Pulse Shape Cut ( 9.1 ± 0.4 ) ×10-2

0.26±0.08

0.11±0.05 0.03±0.01

0.10±0.05

0.02±0.01

Hadron cluster BG2015 run analysis :

※ with ×10 statistics of that of 2013 run

Preliminary

CV-η BG : Mechanism

15Z=6148

Z=6093Z=5842

CV

neutron

η→2γ

rec. π0 Z

Ω

cos⌦ = 1�m2

⇡0

2E1E2Ω is calculated to be smaller because mη > mπ (mη ~ 4mπ).➡ rec. Z goes upstream.

CSI

CV-Eta BG : Estimation

3 Decay Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

0.002

0.004

0.006

0.008

0.01

0.53(0.46)

0.00

0.15 0.02

0.00

0.000.11

CV-Eta BG MC

0.46 events is estimated with Tight cut condition → Need to develop a new cut !

New Cut for the CV-Eta BG

16

MaxEtaThetaChisq cut : • if the cluster shapes are consistent with the assumption that

they are derived from η→2γ decay at CV, the event is rejected• good consistency = small MaxEtaThetaChisq value

BestMaxEtaThetaChisq Distribution

8

BestMaxEtaThetaChisq0 5 10 15 20 25 30 35 40 45 50

a.u.

0

0.05

0.1

0.15

0.2

0.25

0.3

Signal MC CV-Eta MC

※ Tight cut is applied as a pre-cut

MaxEtaThetaChisq

7

0

5

10

15

20

25

MaxEtaThetaChisq

500− 400− 300− 200− 100− 0 100 200 300 400 500500−

400−

300−

200−

100−

0

100

200

300

400500MaxEtaThetaChisq Z = ZFCV

X [mm]

Y [m

m]

True Vertex

BestMaxEtaThetaChisq = min( MaxEtaThetaChisq[i] )

CV-η MC

BestMaxEtaThetaChisq distribution

Preliminary

New Cut for the CV-Eta BG

17

MaxEtaThetaChisq cut : • if the cluster shapes are consistent with the assumption that

they are derived from η→2γ decay at CV, the event is rejected• good consistency = small MaxEtaThetaChisq value

MaxEtaThetaChisq

7

0

5

10

15

20

25

MaxEtaThetaChisq

500− 400− 300− 200− 100− 0 100 200 300 400 500500−

400−

300−

200−

100−

0

100

200

300

400500MaxEtaThetaChisq Z = ZFCV

X [mm]

Y [m

m]

True Vertex

BestMaxEtaThetaChisq = min( MaxEtaThetaChisq[i] )

CV-η MC

BestMaxEtaThetaChisq threshold0 2 4 6 8 10 12 14 16 18 20

Acc

epta

nce

0

0.1

0.2

0.3

0.40.5

0.6

0.7

0.8

0.9

1

N C

V-Et

a B

G

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Signal : 89% CV-Eta : 1/10

Cut acceptance

1/10 BG reduction was obtained

Preliminary

2015 run status : Sensitivity

18

momentum [MeV/c]LRec. K0 2000 4000 6000 8000

# of

eve

nts/1

00.0

0 [M

eV/c

]

1

10

210hmome

Data0π3→LK 0π2→LKγ2→LK

hmome

momentum [MeV/c]LRec. K0 1000 2000 3000 4000 5000 6000 7000 8000

0 1000 2000 3000 4000 5000 6000 7000 8000

Dat

a/M

C

0

1

2

3

ndf = 52 = 34.642χ

p-value = 0.969/ndf = 0.672χ

KL flux from KL→2π0 analysis

KL yield : 4.62×1012

Single Event Sensitivity = 1(KL yield) × (Signal acceptance)

= 1.2 ×10-9

×10 higher sensitivity than that of 2013

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

10

20

30

40

50

Signal Acceptance from MCKL→π0νν MC

Acceptance : 1.8×10-4

※ including decay probability (3.8%)

Rec. KL momentum—Data —MC

2015 run status

19

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0(0)

284 0 0

1

01

2015 whole data S.E.S. : 1.2×10-9

0.18±0.04

02.29±0.19

0.70±0.19

0.02±0.02

Observed Estimated

Preliminary

0.88±0.18

mode # of BG KL→2π0 0.07 ± 0.07 KL→π+π-π0 0.18 ± 0.05 KL→3π0 0.17 ± 0.12 KL→2γ 0.02 ± 0.02

Hadron Cluster 0.26 ± 0.08NCC-π0 0.13 ± 0.07

CV-η 0.05 ± 0.02Total 0.88 ± 0.18

2015 run status

20

mode # of BG KL→2π0 0.07 ± 0.07 KL→π+π-π0 0.18 ± 0.05 KL→3π0 0.17 ± 0.12 KL→2γ 0.02 ± 0.02

Hadron Cluster 0.26 ± 0.08NCC-π0 0.13 ± 0.07

CV-η 0.05 ± 0.02Total 0.88 ± 0.18

Possible further reduction :

Higher Pt thresholdOptimize veto cuts

Smaller Z region

10

π0 Rec. Z [mm]

π0 R

ec. P

t [M

eV/c

]

250

130

2000 5000π0 Rec. Z [mm]

π0 R

ec. P

t [M

eV/c

]

250

130

2000 5000

10

π0 Rec. Z [mm]

π0 R

ec. P

t [M

eV/c

]

250

130

2000 5000π0 Rec. Z [mm]

π0 R

ec. P

t [M

eV/c

]

250

130

2000 5000

※ For further reduction in future runs, we plan to upgrade detectors in summer-autumn 2018.

(if necessary)

under discussion

Summary & Prospects

21

• KOTO 2015 run analysis is ongoing• KL→π0νν search with S.E.S. = 1.2 ×10-9• expected to improve the current upper limit by a factor of 10

• Remaining work• finalize sensitivity / BG estimation • final MC production is now ongoing

• evaluate systematic uncertainty

• We will release the result this summer !

22

23

24

KL

Veto counters

(3π0)

γγ γ

γ γγ

KL ! ⇡0 ⌫⌫̄



CsI CalorimeterKL→3π0 BG

R~1m

25

KL

Veto counters

(π0)

π+

γγ π-

KL ! ⇡0 ⌫⌫̄



CsI CalorimeterKL→π+π-π0 BG

R~1m

Other detector upgrades

26

new in-beam charged veto was installedfor acceptance recovery

Beam

in-beam charged veto

• wire chamber• insensitive to neutron

additional photon counters are installed for reducing KL→2π0 BG

in-beam photon veto

※ original one was 3-mm-thick plastic scintillator

4 modules of aerogel Cherenkov counterswere added

Acrylic Cherenkov conterwas newly added

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.77(0.50)

0.14 0.00 0.00

0.05

0.001.09

KL→2π0 BG

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.09(0.05)

0.00 0.00 0.00

0.00

0.000.23

Loose veto (2013 cut set) 2015 cut set

27

tighter veto

Property of the remaining events in the Signal Box

28

FBAR ineff. (Low-E γ) / CBAR punch-throughID : 43

Rec. Z [mm]0π1000 2000 3000 4000 5000 6000

Pt [

MeV

/c]

0π

0

100

200

300

400

500 veto informationCBARVetoEne : 0.0 MeVBCVVetoEne : 0.2 MeVOEVVetoEne : 0.0 MeVFBARVetoEne : 0.0 MeVNCCVetoEne : 0.0 MeVNCCScintiVetoEne : 0.0 MeVCBARMod39VetoEne : 0.0 MeVBHGCVetoEne : 0.0 MeV

other additional cuts MaxThetaChisq : 0.6 BestMaxEtaThetaChisq : 9999.0

ID : 43

0 2000 4000 6000 8000 10000

1000−

500−

0

500

1000

ID : 43ID : 43

1000− 500− 0 500 1000

1000−

500−

0

500

1000

ID : 43ID : 43

800− 600− 400− 200− 0 200 400 600 800

800−

600−

400−

200−

0

200

400

600

800

50

100

150

200

250

300

800−600−400−200−0200400600800

Gamma 0 Energy : 547.8 MeV (X,Y) = (320.6, 327.3)

: 3.02χ Shape CSD : 1.01

: 0.62χ Theta

Gamma 1 Energy : 139.3 MeV (X,Y) = (485.1, -531.4)

: 4.42χ Shape CSD : 0.911

: 0.12χ Theta

ID : 43FileID : 28936DstEntryID : 16222

RecZ : 4471.4 mm0π Pt : 151.6 MeV/c0π

: -0.2 nsvtxTΔClusDist : 874.3 mmTrueGammaEnerg, EndPos 0 : 143.9 MeV : 495.1 -529.4 6220.4 mm 1 : 538.2 MeV : 326.4 339.4 6192.3 mm 2 : 28.9 MeV : -619.3 -228.3 2743.6 mm 3 : 216.5 MeV : -1262.4 -493.9 5973.2 mm

( KL→2π0 MC )

KL→π+π-π0 BG

※ w/ small data set and loose veto are used1/10 BG reduction for KL→π+π-π0

29

π±

new scintillation counter

Beam pipe : SUS → Al

Observed KL→π+π-π0 MC

➡ 1/2 BG reduction

KL→3π0 BG : masking backgroundBG updates: masking KL→πeν, 3π0

Accidental hits may shift a hit timing to be out of veto timing window. Evaluated by overlaying accidental data (taken with physics data simultaneously) on simulation.

13

Evaluation for 2015 data has been done

Example of an overlaid pulse

Found some contribution (0.17) from KL→3π0 due to a loss in Front Barrel (FB).

複数パルスの重複による背景事象• Accidental Hitの影響で、Veto検出器のHit時間が正しく求められないとイベントのタイミングから外れてVeto出来なくなり、背景事象となる。

• KL崩壊由来背景事象のMCでの見積もりの際にこの影響を考慮する必要がある。

5

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000

CV ModID : 78, AccidentalEntryNo : 111215

sum (0.872MeV, 34.1clock)

MC (0.23MeV, 33.6clock)

acc (0.642MeV, 38.5clock)


FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

500

1000

1500

2000

MCMC

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

AccAcc

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000

CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000






FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

500

1000

1500

2000

MCMC

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

AccAcc

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000

CV ModID : 78, AccidentalEntryNo : 111215CV ModID : 78, AccidentalEntryNo : 111215FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000






FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

500

1000

1500

2000

MCMC

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

AccAcc

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000


FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000






FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

500

1000

1500

2000

MCMC

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

AccAcc

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000


FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]0

1000

2000

3000

4000

5000

6000

7000






FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

500

1000

1500

2000

MCMC

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

AccAcc

FADC sample0 10 20 30 40 50 60

puls

e he

ight

[AD

C c

ount

]

0

1000

2000

3000

4000

5000

6000

7000


CsI

CsI

X

XKL→2π0 　→4γ

Vetoしたいγのタイミング

Peak Findingで見つかるPeakのタイミング

30ns Shift

AccidentalHit

"Pulse to be Vetoed■Accidental Pulse▲Merged

Pulse

γ γ

γγ

True pulse timing

2015 data analisys

KOTO detector (2012-2015)

Signature of KL→π0νν = 2γ+nothing Calorimeter + Hermetic veto detectors

4

Cutaway view

0�

1�

2�[m]�

0� 2� 4� 6� 8� 10� 12� 14� 16�[m]�

Calorimeter� Concrete/iron shield�

FB� NCC�Hinemos� MB� BCV� CV� OEV�LCV�CC03� CC04� CC05� CC06� BHCV� BHPV�

Decay volume (Vacuum)�

BHTS�

z

y

x

Downstream beam pipe�

Membrane�

KL beam�

introduction

FB is a 2.75-m-long detector with a single-end readout,covering upstream region with less granularity, and could be especially affected.

30

Sensitivity : 2013 run v.s. 2015 run

31

2013 run 2015 run

P.O.T. 1.19×1018 2.21×1019

NKL 2.40×1011 4.62×1012

ASignal 3.25×10−4 1.8×10−4

S.E.S. (= 1/ (A * N)) 1.28×10−8 1.2×10−9

Signal box extension : ×1.35unused neural net cut : ×1.3Tight veto : ×0.7Hadron cluster / CV-η cut : ×0.7Accidental signal loss : ×0.6

×20

×10

×1/2

~ 1/2

Z0 v.s. Physics

32

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

20

40

60

80

100

0(0)

1707

7856 2170

8315

01233

Z [mm]0πRec. 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Pt [

MeV

/c]

0 πR

ec.

0

50

100

150

200

250

300

350

400

450

500

0

5

10

15

20

25

30

5798(4496)

60

2250 576

1932

0277

Z0Al Physics

Kinematic VariablesEntries 4769Mean 732.981RMS 269.195Integral 1

Max Gamma Energy [MeV]500 1000 1500 2000

# of

eve

nts/2

0.0

[MeV

]

4−10

3−10

2−10Entries 4769Mean 732.981RMS 269.195Integral 1Entries 18365Mean 734.965RMS 279.595Integral 1

Entries 18365Mean 734.965RMS 279.595Integral 1

h_MaxE2

Z0Phys

Max Gamma Energy [MeV]200 400 600 800 1000 1200 1400 1600 1800 2000 2200

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Z0/P

hys

0.51

1.52


Min Gamma Energy [MeV]200 400 600 800 1000

# of

eve

nts/1

0.0

[MeV

]

4−10

3−10

2−10

1−10

Entries 4769Mean 316.797RMS 105.8Integral 1Entries 18365Mean 310.118RMS 106.847Integral 1


h_MinE2

Z0Phys

Min Gamma Energy [MeV]100 200 300 400 500 600 700 800 900 1000 1100

100 200 300 400 500 600 700 800 900 1000 1100

Z0/P

hys

0.51

1.52

MaxGammaE


CsI fiducial R [mm]200 400 600 800 1000

# of

eve

nts/1

0.0

[mm

]

4−10

3−10



h_MaxFiducialR2

Z0Phys

CsI fiducial R [mm]100 200 300 400 500 600 700 800 900 1000 1100

100 200 300 400 500 600 700 800 900 1000 1100

Z0/P

hys

0.51

1.52


CsI fiducial XY [mm]100 200 300 400 500 600

# of

eve

nts/5

.0 [m

m]

4−10

3−10

2−10 Entries 4769Mean 248.796RMS 66.5324Integral 1Entries 18365Mean 236.154RMS 60.8156Integral 1


h_MinFiducialXY2

Z0Phys

CsI fiducial XY [mm]100 150 200 250 300 350 400 450 500 550 600

100 150 200 250 300 350 400 450 500 550 600

Z0/P

hys

0.51

1.52

33

BlindBox

Pt

Z

MinGammaE

MaxFiducialR MinFiducialXY

Kinematic VariablesEntries 4769Mean 268.453RMS 59.0096Integral 1

Pt [MeV/c]0πRec. 0 100 200 300 400 500

# of

eve

nts/5

.0 [M

eV/c

]

4−10

3−10

2−10

1−10



h_Pt2

Z0Phys

Pt [MeV/c]0πRec. 0 50 100 150 200 250 300 350 400 450 500

0 50 100 150 200 250 300 350 400 450 500

Z0/P

hys

0.51

1.52


z pos. [mm]0πRec. 3000 4000 5000 6000

# of

eve

nts/3

5.0

[mm

]

4−10

3−10

2−10

1−10



h_RecZ2

Z0Phys

z pos. [mm]0πRec. 2500 3000 3500 4000 4500 5000 5500 6000

2500 3000 3500 4000 4500 5000 5500 6000

Z0/P

hys

0.51

1.52

Pi0Pt


Cluster Distance [mm]300 400 500 600 700

# of

eve

nts/5

.0 [m

m]

4−10

3−10

2−10

1−10



h_ClusterDistance2

Z0Phys

Cluster Distance [mm]250 300 350 400 450 500 550 600 650 700 750

250 300 350 400 450 500 550 600 650 700 750

Z0/P

hys

0.51

1.52

Entries 4769Mean 7.52489RMS 2.93675Integral 0.998323

ClusSize []0 5 10 15 20 25

# of

eve

nts/1

.0 []

4−10

3−10

2−10

1−10Entries 4769Mean 7.52489RMS 2.93675Integral 0.998323Entries 18365Mean 7.48664RMS 2.97174Integral 0.99853


h_ClusSize2

Z0Phys

ClusSize []0 5 10 15 20 25

0 5 10 15 20 25

Z0/P

hys

0.51

1.52

34

BlindBox

Pt

Z

Pi0RecZ

ClusterDistance ClusterSize

Neutron Cut Variables

35


MaxShapeChisq []0 100 200 300 400 500

# of

eve

nts/5

.0 []

4−10

3−10



h_MaxShapeChisq2

Z0Phys

MaxShapeChisq []0 50 100 150 200 250 300 350 400 450 500

0 50 100 150 200 250 300 350 400 450 500

Z0/P

hys

0.51

1.52

Entries 4769

Mean 05−4.02587e−

RMS 0.0394733Integral 0.998952

MinCSDVal []0 0.5 1

# of

eve

nts/0

.0 []

4−10

3−10

2−10

1−10

1

Entries 4769

Mean 05−4.02587e−

RMS 0.0394733Integral 0.998952

Entries 18365Mean 0.00049079

RMS 0.0388277Integral 0.998911

Entries 18365Mean 0.00049079

RMS 0.0388277Integral 0.998911

h_MinCSDVal2

Z0Phys

MinCSDVal []0 0.2 0.4 0.6 0.8 1

0 0.2 0.4 0.6 0.8 1

Z0/P

hys

0.51

1.52

MaxShapeChisq CSD


PSLH []0 0.5 1

# of

eve

nts/0

.0 []

4−10

3−10

2−10

1−10

1

Entries 4769Mean 0.0576473RMS 0.178028Integral 1Entries 18365Mean 0.0616346RMS 0.183301Integral 0.999946


h_PSLH2

Z0Phys

PSLH []0 0.2 0.4 0.6 0.8 1

0 0.2 0.4 0.6 0.8 1

Z0/P

hys

0.51

1.52

PSLH

Shape χ2

36

size of CsI crystals : 25mm x 25mm (for inner, 50mm x 50mm for outer) < Molier radius (35.7mm) ➡ give us the information of 2D shower shape

compare the observed Edep. in each crystals in a cluster with its expected energy derived from MC

Einc : measured photon energy ei : measured deposit energy in ith crystal in a cluster μ : expected mean e/E σ : expected RMS of e/E

➡ 1/300 BG reduction & 80% signal acceptance (w/ threshold = 4.6)

Cluster Shape Discrimination

37

Neural net cut using cluster shape information compare data with MC input variables: • crystal energy χ2 • crystal energy probability • crystal timing χ2 • cluster energy difference • cluster timing probability • cluster probability • cluster COE, RMS, energy & RMS balance

timing information is used

Neutron samples KL->3π0 & KL->2γ samples

0 10.2 0.4 0.6 0.8 NN output

1

2

0

a.u.

Energy Distribution

0 200 400-200X

Y

0

200

400

-200

Timing Distribution

0 200 400-200

0

200

400

-200

Y

X

0

0.8

-0.8

Δt

[mm][mm]

[mm

]

[mm

]


Pulse Shape Likelihood

38

use waveform information to distinguish photons from neutrons ➡ extract the information by fitting the waveform

difference of dE/dx of EM and hadronic shower may make difference of scintillating mechanism ➡ hadronic cluster has larger tail component ➡ larger “a”

calculate Likelihood ratio and determine which is more likely (nn, γγ)


39

KOTO detector since 2016

Inner Barrel detector (IB) installed Additional 5 X0 thickness in barrel region fine sampling (sandwich of 1mm lead and 5mm scintillator)

18

0�

1�

2�[m]�

0� 2� 4� 6� 8� 10� 12� 14� 16�[m]�

Calorimeter� Concrete/iron shield�

FB� NCC�Hinemos� MB� BCV� CV� OEV�LCV�CC03� CC04� CC05� CC06� BHCV� BHPV�

Decay volume (Vacuum)�

BHTS�

z

y

x

Downstream beam pipe�

Membrane�

KL beam�

IB

2016-17 data analisys

IB

40

Calorimeter both-end readout

29

neutron

Signal Background

MPPC PMTundoped CsI : 50cm

Timing difference (TMPPC-TPMT) gamma < neutron background

KL ! ⇡0⌫⌫

2�

2nd cluster by neutron case

photon case

ΔT (γ) < ΔT (neutron) expectedTiming Difference ΔT = T(MPPC)-T(PMT)

Calorimeter upgrade

41

Remaining KL→π+π-π0 in MC

44

Major Background

π0

n π+γ

n γK

π-

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 65000

50

100

150

200

250

300

350

400

450

500

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 65000

50

100

150

200

250

300

350

400

450

500

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 65000

50

100

150

200

250

300

350

400

450

500

Rec. π0 Zvtx (mm)

Rec

. π0 P t

(MeV

/c)

Pion produced at detector upstream.

Neutron direct hit on CsI Particles missing in the downstream gap

Interaction occurs at • membrane between

low and high vacuum • G10 support for membrane • vacuum flanges

motivation• #$ → !&!'!" decay(has(large(contribution(to(BG.-#(of(BG(is(0.04�0.01 at(the(10%(statistics(in(2015(data.

• End(point(of(#$ → !&!'!" MC-Some(events((~30%)(disappeared(around(the(beam(pipe(region.- If(we(can(remove(the(beam(pipe,(we(may(reduce(those(BGs.

2017/1/6 3collaboration(meeting(@Tokai

flange

windowpipe

kamijiUsan(slide@2016(Aug(collaboration(meeting

CC04 CC05 CC06BPCV

vacuum tankbeam pipe

membrane

motivation• #$ → !&!'!" decay(has(large(contribution(to(BG.-#(of(BG(is(0.04�0.01 at(the(10%(statistics(in(2015(data.

• End(point(of(#$ → !&!'!" MC-Some(events((~30%)(disappeared(around(the(beam(pipe(region.- If(we(can(remove(the(beam(pipe,(we(may(reduce(those(BGs.

2017/1/6 3collaboration(meeting(@Tokai

flange

windowpipe

kamijiUsan(slide@2016(Aug(collaboration(meeting

vacuum tankbeam pipe

Liner charged veto inside these structures is effective to reduce this background

➔ New downstream CV (2018 upgrade)

42

Documents

New Status of KL π νν analysis at J-PARC KOTO · 2018. 3. 11. · td V ts V tb 1 A 0 @ d s b 1 A ... Japan Proton Accelerator Research Complex = J-PARC KL beam 30GeV Proton Beam