STUDY OF K + + 0 DECAY QUYNH HUONG VUONG YAMANAKA GROUP - - PowerPoint PPT Presentation

STUDY OF K+→𝝆+𝝆0 DECAY

QUYNH HUONG VUONG YAMANAKA GROUP

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YEAR-END PRESENTATIONS 2019

THE KOTO EXPERIMENT

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• Purpose: Search for New Physics that violates CP symmetry
• Probe: KL→𝝆0𝜉𝜉
• Signature: 2 photons with 𝝆0 invariant mass and finite pT

KL

𝛿 𝛿 𝝆0

MOTIVATION

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• Want to know if there is K+ contamination in KL beam
• Major decay mode: K+→𝝆+𝝆0 (3 clusters: 2 photons from pi0 and 1

pseudo-photon pi+)

• Main background: KL→𝝆+𝝆-𝝆0 (1 charged pion escapes detection)
• Develop a new algorithm to reconstruct K+ from 3 clusters
• Kaon mass, chi2, PT, energy, etc are reconstructed and used to

evaluate the performance of new algorithm using MC data

• Different cut criteria are also studied

𝝆0 RECONSTRUCTION

(x1, y1) (x2, y2)

• Position and energy info of the two

photon clusters

• Assumption: pi0 decays on the z axis

𝜌0 z

p2

π0 = (p1 + p2)2

→ m2

π0 = 2E1E2(1 − cosθ)

𝜄

− → a1

− → a2

− → a1.− → a2 = |− → a1||− → a2|cosθ

− → a1 = (x1, y1, z) − → a2 = (x2, y2, z)

− → p1 = − → a1 a1 E1 − → p2 = − → a2 a2 E2

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ALGORITHM

(x1, y1) (x2, y2) 𝜌0 z 𝜄

− → a1

− → a2

(x, y) 𝜌+

p+

x = −(p1x + p2x)

p+

y = −(p1y + p2y)

E = q p+2 − m2

π+

• Assumption: K+ decays on z axis

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=> From pi0 and pi+ 4-momenta, kaon invariant mass can be reconstructed.

𝝆+ RECONSTRUCTION

ALGORITHM

p+ = p+T sin(atan( p x2 + y2/z))

z

THETA ANGLE

pT axis 𝜄p 𝜄l

• Theta angle: Angle pi+ cluster made with

pT axis (reconstructed from 2 pi0 clusters):

(x1,y1,E1) (x2,y2,E2) (x0,y0)

θ = θp − θl = θ(x1, y1, E1, x2, y2, E2, x0, y0)

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θl = atan E1x1

r1

+ E2x2

r2 E1y1 r1

+ E2y2

r2

!

θp = atan ⇣x0 y0 ⌘

where

(

ALGORITHM

(MeV)

K

M 200 300 400 500 600 700 800 1000 2000 3000 4000 5000 6000 7000 8000

(KL3pi) Kaon mass histogram (loose veto)

h

Entries 151256 Mean 380.3 RMS 90.67

(KL3pi) Kaon mass histogram (loose veto)

(MeV)

K

M 200 300 400 500 600 700 800 2000 4000 6000 8000 10000

(Kppipi0) Kaon mass histogram (loose veto)

h

Entries 258731 Mean 484.7 RMS 88.64

(Kppipi0) Kaon mass histogram (loose veto)

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KAON MASS

RECONSTRUCTION

signal background

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𝝆+ ENERGY DEPOSIT

RECONSTRUCTION

(MeV)

Pi

E 200 400 600 800 1000 1200 1400 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000

(Kppipi0) Energy of charged pion (loose veto)

hE

Entries 252328 Mean 384.3 RMS 231

(Kppipi0) Energy of charged pion (loose veto)

signal background

(MeV)

Pi

E 200 400 600 800 1000 1200 1400 1000 2000 3000 4000 5000 6000 7000

(KL3pi) Energy of charged pion (loose veto)

hE

Entries 151256 Mean 380 RMS 253.5

(KL3pi) Energy of charged pion (loose veto)

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THETA ANGLE

RECONSTRUCTION

theta (rad) 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 2000 4000 6000 8000 10000

(Kppipi0) Theta angle (loose veto)

ht

Entries 252328 Mean 0.0004011 − RMS 0.6065

(Kppipi0) Theta angle (loose veto)

signal background

theta (rad) 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 500 1000 1500 2000 2500 3000 3500 4000

(KL3pi) Theta angle (loose veto)

ht

Entries 151256 Mean 0.004931 RMS 0.737

(KL3pi) Theta angle (loose veto)

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𝝆0 PT

RECONSTRUCTION

(MeV)

T

Pi0 P 50 100 150 200 250 300 350 400 450 500 2000 4000 6000 8000 10000

(Kppipi0) Transverse momentum of Pi0 (loose veto)

hPt

Entries 252328 Mean 173 RMS 65.94

(Kppipi0) Transverse momentum of Pi0 (loose veto)

(MeV)

T

Pi0 P 50 100 150 200 250 300 350 400 450 500 1000 2000 3000 4000 5000 6000

(KL3pi) Transverse momentum of Pi0 (loose veto)

hPt

Entries 148294 Mean 102.7 RMS 68.03

(KL3pi) Transverse momentum of Pi0 (loose veto)

signal background

DATA

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• MC events: + K+→𝝆+𝝆0 : 2E+7

+ KL→𝝆+𝝆-𝝆0 : 1E+8

• Branching Ratio: + K+→𝝆+𝝆0 : ~20%

+ KL→𝝆+𝝆-𝝆0 : ~10%

• Flux Ratio (Simulation): K+/KL~1E-5

Assumption: Same amount of K+ and KL in the beam => Scaling factor: 10

theta (rad) 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 500 1000 1500 2000 2500 3000 3500 4000

(KL3pi) Theta angle (loose veto)

ht

Entries 151256 Mean 0.004931 RMS 0.737

(KL3pi) Theta angle (loose veto)

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KAON MASS W CUTS

RECONSTRUCTION

K+→𝝆+𝝆0 KL→𝝆+𝝆-𝝆0

theta (rad) 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 2000 4000 6000 8000 10000

(Kppipi0) Theta angle (loose veto)

ht

(Kppipi0) Theta angle (loose veto)

h

Entries 167132 Mean 496.4 RMS 74.36 (MeV)

K

M 200 300 400 500 600 700 800 10000 20000 30000 40000 50000 60000 70000 80000

(Kppipi0) Kaon mass histogram (loose veto + theta)

h

Entries 167132 Mean 496.4 RMS 74.36

h

Entries 77527 Mean 393.9 RMS 99.88

(Kppipi0) Kaon mass histogram (loose veto + theta)

h Entries 258731 Mean 484.7 RMS 88.64 (MeV)

M 200 300 400 500 600 700 800 20 40 60 80 100

10 ×

(Kppipi0) Kaon mass histogram (loose veto)

h Entries 258731 Mean 484.7 RMS 88.64 h Entries 151256 Mean 380.3 RMS 90.67

(Kppipi0) Kaon mass histogram (loose veto)

Peak Height Ratio (PHR) ~10 PHR ~20

h

Entries 76220 Mean 501.2 RMS 70.12 (MeV)

K

M 200 300 400 500 600 700 800 5000 10000 15000 20000 25000 30000 35000

(Kppipi0) Kaon mass histogram (loose veto + MIP)

h

Entries 76220 Mean 501.2 RMS 70.12

h

Entries 26725 Mean 361.1 RMS 71.95

(Kppipi0) Kaon mass histogram (loose veto + MIP)

(MeV)

E 200 400 600 800 1000 1200 1400 1000 2000 3000 4000 5000 6000 7000

(KL3pi) Energy of charged pion (loose veto)

hE Entries 151256 Mean 380 RMS 253.5

(KL3pi) Energy of charged pion (loose veto)

(MeV)

E 200 400 600 800 1000 1200 1400 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000

(Kppipi0) Energy of charged pion (loose veto)

hE Entries 252328 Mean 384.3 RMS 231

(Kppipi0) Energy of charged pion (loose veto)

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KAON MASS W CUTS

RECONSTRUCTION

h Entries 258731 Mean 484.7 RMS 88.64 (MeV)

M 200 300 400 500 600 700 800 20 40 60 80 100

10 ×

(Kppipi0) Kaon mass histogram (loose veto)

h Entries 258731 Mean 484.7 RMS 88.64 h Entries 151256 Mean 380.3 RMS 90.67

(Kppipi0) Kaon mass histogram (loose veto)

PHR ~10 PHR ~18

K+→𝝆+𝝆0 KL→𝝆+𝝆-𝝆0

h

Entries 202417 Mean 485.8 RMS 87.39 (MeV)

K

M 200 300 400 500 600 700 800 10000 20000 30000 40000 50000 60000 70000 80000

(Kppipi0) Kaon mass histogram (loose veto + DCV)

h

Entries 202417 Mean 485.8 RMS 87.39

h

Entries 89462 Mean 386.9 RMS 95.84

(Kppipi0) Kaon mass histogram (loose veto + DCV)

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KAON MASS W CUTS

RECONSTRUCTION

DCV CSI

Beam hole Require no hit on DCV: DCVVetoEne<2MeV

h Entries 258731 Mean 484.7 RMS 88.64 (MeV)

M 200 300 400 500 600 700 800 20 40 60 80 100

10 ×

(Kppipi0) Kaon mass histogram (loose veto)

h Entries 258731 Mean 484.7 RMS 88.64 h Entries 151256 Mean 380.3 RMS 90.67

(Kppipi0) Kaon mass histogram (loose veto)

PHR ~20 PHR ~10

K+→𝝆+𝝆0 KL→𝝆+𝝆-𝝆0

h Entries 258731 Mean 484.7 RMS 88.64 (MeV)

M 200 300 400 500 600 700 800 20 40 60 80 100

10 ×

(Kppipi0) Kaon mass histogram (loose veto)

h Entries 258731 Mean 484.7 RMS 88.64 h Entries 151256 Mean 380.3 RMS 90.67

(Kppipi0) Kaon mass histogram (loose veto)

h

Entries 45813 Mean 502.7 RMS 60.33 (MeV)

M 200 300 400 500 600 700 800 5000 10000 15000 20000 25000

(Kppipi0) Kaon mass histogram (loose veto + all3)

h

Entries 45813 Mean 502.7 RMS 60.33

h Entries 7030 Mean 374.5 RMS 85.74

(Kppipi0) Kaon mass histogram (loose veto + all3)

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KAON MASS W CUTS

RECONSTRUCTION

• 0.5<theta<0.5

300<E pi+<360 All 3 cuts No cut DCVVetoEne<2

h Entries 76220 Mean 501.2 RMS 70.12 (MeV)

M 200 300 400 500 600 700 800 5000 10000 15000 20000 25000 30000 35000

(Kppipi0) Kaon mass histogram (loose veto + MIP)

h Entries 76220 Mean 501.2 RMS 70.12 h Entries 26725 Mean 361.1 RMS 71.95

(Kppipi0) Kaon mass histogram (loose veto + MIP)

h Entries 202417 Mean 485.8 RMS 87.39 (MeV)

M 200 300 400 500 600 700 800 10000 20000 30000 40000 50000 60000 70000 80000

(Kppipi0) Kaon mass histogram (loose veto + DCV)

h Entries 202417 Mean 485.8 RMS 87.39 h Entries 89462 Mean 386.9 RMS 95.84

(Kppipi0) Kaon mass histogram (loose veto + DCV)

h Entries 167132 Mean 496.4 RMS 74.36 (MeV)

M 200 300 400 500 600 700 800 10000 20000 30000 40000 50000 60000 70000 80000

(Kppipi0) Kaon mass histogram (loose veto + theta)

h Entries 167132 Mean 496.4 RMS 74.36 h Entries 77527 Mean 393.9 RMS 99.88

(Kppipi0) Kaon mass histogram (loose veto + theta)

PHR ~10 PHR ~50

K+→𝝆+𝝆0 KL→𝝆+𝝆-𝝆0

SUMMARY

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• The new algorithm can be used to discriminate between K+ and

KL. However K+ contamination is low even after cuts, more selection criteria are needed to be implemented to improve SN ratio.

• The new algorithm’s results show agreement with theory.
• Next steps:

+ Apply more different cuts to improve SN ratio + Study a new tagging algorithm for better 𝝆+ event selection

BACKUP

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MAXIMUM PT OF PI0

E1 = M 2 + m2

1 − m2 2

2M

CM frame E, M E1, m1 E2, m2 z

• K+→𝝆+𝝆0 : maximum 𝝆0PT can reach ~250MeV

=> large PT distribution

• KL→𝝆+𝝆-𝝆0 : maximum 𝝆0PT can’t reach 250MeV

=> smaller PT distribution !? The large PT tail may come from hadronic interaction

P T

1 ≤ E1

4 SOLUTIONS!?

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RECONSTRUCTION

Quadratic equation of z2 => there are 4 solutions + z3, z4: behind the calorimeter + z1, z2: possible solutions

VETO CONDITIONS

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VETO CONDITIONS

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• Tight Veto Condition 2017:

if(CBARVetoEne<=1 && IBVetoEne<=1 && IBWideVetoEne<=2 && IBCH55VetoEne<=1 && (MyVetoCondition&0x100)==0 && FBARVetoEne<=1 && NCCVetoEne<=1 && NCCScintiVetoEne<=1 && OEVVetoEne<=1 && CVVetoEne>0.3 && IBCVVetoEne<=0.5 && MBCVVetoEne<=0.5 && !(newBHCVModHitCount>1 && newBHCVVetoEne>884.e-6/4.) && BHGCVetoEne<=2.5)

• Loose Veto Conditions 2017:

if(CBARVetoEne<=2 && IBVetoEne<=2 && IBCH55VetoEne<=1 && (MyVetoCondition&0x100)==0 && FBARVetoEne<=2 && NCCVetoEne<2 && CVVetoEne>0.3 && IBCVVetoEne<=1 && MBCVVetoEne<=1 && !(newBHCVModHitCount>1 && newBHCVVetoEne>884.e-6/4.) && BHGCVetoEne<=2.5)

EVENT SELECTION

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σ2

θ =

⇣ ∂θ ∂x1 ⌘2 σ2

x1 +

⇣ ∂θ ∂y1 ⌘2 σ2

y1 +

⇣ ∂θ ∂E1 ⌘2 σ2

E1 + ...

@✓ @x1 = ✓(x1 + ✏) − ✓(x1) ✏

χ2 = θ2 σ2

θ

θ = θp − θl = θ(x1, y1, E1, x2, y2, E2, x0, y0)

Note: The dependence on x0, y0 is not taken into account because position resolution is dependent on energy of pi+ which is not known.

CHI2 CALCULATION