A new cylindrical photon-veto detector for the KOTO experiment

Osaka University Manabu Togawa for the KOTO collaboration

- We installed a new photon-veto detector (Inner Barrel) in April 2016.

- Suppress KL->2π0 background to be 1/3 - First physics run with the Inner Barrel at May-June.Background from KL0-> 2π0

4

• CsI calorimeter (π0 -> 2γ) + Hermetic detectors (veto)

• Pencil beam -> can reconstruct decay vertex assuming π0 mass

FB NCC MB CVCsI calorimeter

CC03OEV

CC04 CC05 CC06 BHCV BHPV

LCVBCVHINEMOS

Saturday, April 20, 2013

KL γγ

30 GeV proton

Ni, Pt, Au target

Collimator

16 degree

20 m

10 m

γ γ

New detector : Inner Barrel detector

• 内層に同様の鉛-シンチサンドイッチカロリメータをインストール

• 13.5 X0（メインバレル）+ 5 X0（インナーバレル）

• EM反応に対して十分な厚み：BGを1/3に低減5

FB NCC MB CVCsI calorimeter

CC03OEV

CC04 CC05 CC06 BHCV BHPV

LCVBCVHINEMOS

Saturday, April 20, 2013

KLγ

30 GeV proton

Ni, Pt, Au target

Collimator

16 degree

20 m

γ

γ

γ

Trapezoidal shape x 32

Inner BarrelGluing WLS fibers

30

Finished gluing 12000 WLS fibers (50 km) for 30.5 modules9

2013年終わり

紫外線硬化樹脂 NOA61

~2013

2014

2015

2016

- Sandwich Calorimeter 5 mm-thick scinti. (MS resin) x 25 1 mm-thick lead plate x 24 Read out by WLS fiber (BCF92) τ~2.7 ns

Fixed specification.

Fiber attachment with company

Due to uncured glue. Re-cure, re-production…

IB construction (4)

33

lifted at both ends by a crane, rotated and mounted on the ring

Detector upgrade: IB

Module construction

Installed !!

MB

IB

Looks KL->π0νν event… :( Remove by increasing efficiency :)

2016 physics run (May - June)

OK Tν

νs

d

Timing resolution evaluated by cosmic-ray

200 250 300 350 400 450 500 550 600 6501

10

210

310

410

200 250 300 350 400 450 500 550 600 6501

10

210

310

KL -> 2π0 reconstruction by 4 γevent w/ MB&IB veto cut

Module&dependence&

ModID&

Timing&resolu+on&[ns]&

MB_Outer#:#0.308#±#0.006(stat)#MB_inner#:#0.416#±#0.004(stat)#IB#:#0.219#±#0.008(stat)#

Timing resolution (ns) MKL (MeV)

Black : Real data Blue : KL->3π0 (MC)

13.5 X0 13.5 + 5 X0IBBackground from

KL->2π0

~3 m

~2 m

Crack appears !!

Alignment of support rings

Installation of modules