KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable...

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KOTO CsI calorimeter contents • what is KOTO? • KOTO CsI calorimeter • shower shape on CsI Sato Kazufumi ( Osaka Univ. ) 22 Avril in CHEF2013 1

Transcript of KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable...

Page 1: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

KOTO CsI calorimeter

contents• what is KOTO?• KOTO CsI calorimeter• shower shape on CsI

Sato Kazufumi ( Osaka Univ. )

22 Avril in CHEF2013

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Page 2: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

what’s KOTO?

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Page 3: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

KL→π0νν

Vtd*

d d

KOTO :Br(KL→π0νν) measurement in Japan

Br(KL→π0νν) ∝ | Im(Vtd ) |2

☆ theoretical uncertainty : 1~2% only

 ⇒sensitive to new physics beyond SM

☆ SM expectation : Br(KL→π0νν)=3e-11

upper limit = 2.6e-8 (90% CL) by KEK E391A

⇒ high intensity KL beam @ J-PARC

in SM, CP violation is caused by imaginary part of CKM matrix elements

96 E. Blucher, B. Winstein and T. Yamanaka

Fig. 13. Penguin diagram for K ! !"".

Fig. 14. Unitarity triangle.

New kaon experiments are focusing on K ! !"" decay modes because theyhave small theoretical uncertainties.48) (Re(#!/#) is proportional to $, but hadronicuncertainties are too large to extract a meaningful value of $ in spite of the precisemeasurements.) The K ! !"" decay modes proceed through a penguin diagram asshown in Fig. 13. In the Standard Model, the amplitude is dominated by t quarkin the loop. Since quarks from three generations, d, s and t, are involved, the decayamplitude has an imaginary part of the CKM matrix, Vtd = A%3(1 " & " i$).

The KL ! !0"" decay amplitude is

#!0""|H|KL$ % #!0""|H|Kodd$ (6.1)

& #!0""|H|K0$ " #!0""|H|K0$ (6.2)& Vtd " V "

td & iIm(Vtd) = i%3$. (6.3)

Therefore a measurement of BR(KL ! !0"") determines the height of the unitaritytriangle, $, as shown in Fig. 14. The branching ratio is predicted to be (2.76±0.40)'10#11, based on currently known Standard Model parameters.49) The intrinsictheoretical uncertainty on the $ measurement is 2.8%.

For the K+ ! !+"" decay mode, the branching ratio is proportional to |Vtd|2with a correction for the c quark contribution. Thus, it e!ectively measures one of

s d

ν

ν

Z0t

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Page 4: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

νν

strategy

KL

π0 γγ

CsI

• Only 2 γs from π0 are observable→undoped CsI calorimeter

• KL→π0νν has an unique final state 2γ + Pt

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Page 5: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

νν

KL

π0 γ

γ

CsI

KL→π0νν has an unique final state 2γ + Pt

strategy

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Charged Veto

Photon Veto

Page 6: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

strategy

KL reco. π0

CsI

KL→π0νν has an unique final state 2γ + Pt

we can reconstruct π0 from energies and hit positions of 2γs, assuming Mγγ = Mπ0

Pt

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Page 7: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

KOTO detectorCsI calorimeter

decay region

5m3m

KOTO detector

z=0m 11m7

Page 8: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

gamma energy

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γ energy [MeV]

arb

itra

ry u

nit

Page 9: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

KOTO CsI calorimeter

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Page 10: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

CsI calorimeter• diameter :1.9m• consist of 2716 crystals

• used in KTeV exp. at Fermilab• undoped CsI

•length:50cm(=27X0)→ensure good energy resolution

= good π0 reconstruction

• cross section: 2.5x2.5cm, 5x5cm• smaller than RM (=3.57cm)→shower shape information

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Page 11: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

CsI calorimeter resolution• measured using electrons from KL→πeν decayin 2012, before installing veto detectors

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Page 12: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

CsI calorimeter resolution• tested using electrons from KL→πeν decayin 2012, before installing veto detectors

drift chamber

magnete

π

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Page 13: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

E/p width

• dataー MC

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electron momentum [MeV]E

/p v

ari

an

ce (σ E

2) E resolution

Page 14: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

CsI calorimeter resolutionE

/p w

idth

(σ E

)

electron momentum [MeV]

σE/E = 1.9%/√E[GeV]

black: Datared : MC

E resolution

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subtract the contribution of materials and spectrometer resolution

Page 15: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

pos. resolution

electron momentum [MeV]Δ

x v

ari

an

ce (σ x

2)

electron momentum [MeV]

Δx

[mm

]

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Page 16: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

position resolution

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electron momentum [MeV]

black: Datared : MC

σx [mm]= 1.8 + 2.8/√E[GeV] + 1.73/E[GeV]

subtract the contribution of materials and spectrometer resolution

σ X [

mm

]pos. resolution

Page 17: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

Shower Shape Information

• fusion BG discrimination

• γ angle discrimination

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Page 18: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

shower shape cut

X

X

ex) 2π0_fusion

missinggamma

looks like one gamma = fused cluster

• only 1 extra gammato veto

• similar kinematics as π0νν

shower shape information is useful to reject some types of backgrounds

π0

π0

X

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Page 19: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

fused cluster

Maximum

local maximum

fused clustersingle photon cluster

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Page 20: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

shape χ2

average shower (MC)observed shower (data)

=E_measured[MeV] =E_simulated[MeV]compare

Observed simulation

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Page 21: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

fusion BG suppression

90% BGs are rejected with 85% signal acceptance

shape χ2

shape χ2

ー π0ννー fusion

arb

itra

ry u

nit

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signal acceptanceb

ack

gro

un

d r

eje

ctio

n

Page 22: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

γ angle from shower shapecan derive γ incident angle from shower shape

θ = 10 deg θ = 30 deg

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Page 23: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

Θrec

cos θ = 1− m2

2E1E2

η background

Θtrue

we reconstruct 2γ vertex assuming π0 , but actually η

⇒angle discrimination helps π0 identification

π0

reco. π0 η

ex) beam neutron interacts with material ⇒ η→2γ

Θrec < Θtrue

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material

Page 24: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

strategy for angle discri.

expectation (case of π0)

expectation (case of η)simulation

which ismore likely?

Observed

project to X(Y)

X[mm]

Ed

ep /

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θη

θπ

Page 25: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

likelihood

2D PDF (case of π0)

2D PDF (case of η)simulation

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(i=π,η)

calculate Likelihoodfor each assumption ( Lπ, Lη )

PDFs are prepared for various E, Φ, θ

Page 26: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

likelihood ratioapply cut for likelihood ratio

η BG rejection

94% of η BGs can be rejected with 90% efficiency

likelihood ratio signal acceptance

Lπ0

Lπ0 + Lη

black: π0ννred : η

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Page 27: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

summary

• KOTO = measurement for KL→π0νν• observe 2γ from π0 with the CsI calorimeter

• beam test in 2012

• shower shape information is useful • shape chi2

• 2π0 fusion BG → x 1/10 (85% signal acc.)• angle discrimination

• η BG → x 1/20(90% signal acc.)

σE/E = 1.89%/√E[GeV] σx [mm]= 1.8 + 2.8/√E[GeV] + 1.73/E[GeV]

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Page 28: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

back up

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Page 29: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

ene. and pos. resolution

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Page 30: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

E resolution

electron momentum [MeV]E

/p v

ari

an

ce (σ E

2)

electron momentum [MeV]

E/p

E(by CsI ) / p(by spectro.) E resolution

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Page 31: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

source of energy (MC study)

cluster energy / gamma energy

due to photonuclear effect

photonucl. 1.3%

backsplash 0.25%

shower leak 0.4%

threshold 1.6%

clustering 0.95%

p.e. fluctuation 1.3%

nonuniformity 0.85%

ground noise 0.2%

Page 32: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

FADC ground noise

ground noise

• FADC pedestal fluctuates due to ground noise (σ~2.05cnt) = ~ 0.2MeV

RMS of ground noise

Page 33: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

pi0 reconstruciton

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Page 34: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

how to reconstruct π0

X

X

(E1,r1)

(E2,r2)

CsI calorimeter

• suppose Energies and positions of 2γs are measuredwith CsI

γ

beam-axis

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Page 35: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

(E1,r1)

(E2,r2)

X

θ • 2γs from π0

(q1 + q2)2 = mπ0

⇒ cos θ = 1− m2π

2E1E2

π0 generated onthe circle passing through r1,r2

θ

assuming...

how to reconstruct π0

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Page 36: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

(E1,r1)

(E2,r2)

X

V(0,0,Z)

• 2γs from π0

• π0 on beam-axis

(q1 + q2)2 = mπ0

⇒ cos θ = 1− m2π

2E1E2

assuming...

how to reconstruct π0

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Page 37: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

clustering procedure

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Page 38: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

clustering

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Page 39: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

clustering

7cm

7cm

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Page 40: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

clustering

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Page 41: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

clustering

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Page 42: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

η backgrounds

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Page 43: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

θrec

cos θ = 1− m2

2E1E2

impact of angle discrimination

θtrue

we reconstruct 2γ vertex assuming π0

⇒angle discrimination helps π0 identification

π0

reco. π0 η

⇒ we don’t recognize it is actually π0

ex) beam neutron interacts with material ⇒ η→2γ

θrec < θtrueγ polar angle [deg]

ー assuming ηー assuming π0

reconstructed gamma angle [deg]43

Page 44: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

MC reproduction

Al target run in E391A44

Page 45: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

Probability Density FunctionIncident angle discrimination

•calculate incident angles assuming signal and BG•calculate the likelihood of the observed shower shape for each assumption

1

k

ek/Ej

E-weightedmean

-210 -110 1

-510

-410

-310

-210

-110

-210 -110 1

-510

-410

-310

-210

-110

row energy / total energy

∝ probability density 0° 20° 40°

Li =�

j;γ

x,y

k;row

P (ek|Ej , dk, θij ,φij)

PDF in a certain condition for each incident angle

dk

Incident angle discrimination

•calculate incident angles assuming signal and BG•calculate the likelihood of the observed shower shape for each assumption

1

k

ek/Ej

E-weightedmean

-210 -110 1

-510

-410

-310

-210

-110

-210 -110 1

-510

-410

-310

-210

-110

row energy / total energy

∝ probability density 0° 20° 40°

Li =�

j;γ

x,y

k;row

P (ek|Ej , dk, θij ,φij)

PDF in a certain condition for each incident angle

dk

prepare PDF for each incident angle

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Page 46: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

likelihood ratioIncident angle discrimination

•apply the cut with MC samples with the incident angle of 10° and 30°

0 0.5 1

10

210

310

410

0.6 0.8 1

10

210

Likelihood ratio 10°→←30°

MC, 650MeV10°30°

signal efficiency

S/N MC, 650MeV

S : 10°N : 30°

(a) (b)

Likelihood ratio =Lsignal

Lsignal + LBG

Incident angle discrimination

•apply the cut with MC samples with the incident angle of 10° and 30°

0 0.5 1

10

210

310

410

0.6 0.8 1

10

210

Likelihood ratio 10°→←30°

MC, 650MeV10°30°

signal efficiency

S/N MC, 650MeV

S : 10°N : 30°

(a) (b)

Likelihood ratio =Lsignal

Lsignal + LBG

apply cut for likelihood ratioL10 deg

L10 deg + L30 deg angle separation

95% of 20° difference can be separated with 90% efficiency46

Page 47: KOTO CsI calorimeter · ν ν strategy K L π0 γ γ CsI • Only 2 γs from π0 are observable →undoped CsI calorimeter • K L→π0νν has an unique final state 2γ + Pt 4

shape chi2

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