Reconstruction neutral decay modes (E391)

Doroshenko M.(KEK)

E391 collaboration

Outlines:

• Data summary

• Analysis strategy

• Reconstruction K3p,K2p,Kgg decays

• Example of veto study

• Conclusion

Data summary Beam time: 18 Feb – 1 July 2004 Big amount of data

~110 Gb per one day run ~6 Tb – full statistics (~57 days)

Phys. trigger (N>=2) - 6 Tb (~57 days) Cosmic - all time in off spill Muon beam - ~300 Gb Pi0 calibration - ~500 Gb

Data analysis strategy Separation of the data

One-day Identifying of the main sources

of background One week

Make a clear the sources of background Test our MC Test skimming procedure

1/3 data Background estimation Big statistic of MC

Full data Open signal box

Blind analysis

Strategy for veto study Try to use data sample for study veto-cut instead MC

Correct ADC, TDC information Contain all effects

Pure signal and bgr samples Acc. loss + rejection power The same behavior is expected for K3p,K2p,Kgg

But… Back-splash, shower leakage, shower overlapping…

depends on decay process (next order correction)

Reconstruction of the n-gamma event

21

2

21cos

EE

m

cos2 2122

21

212 RRRRR

%2%2)( E

EEErr

cmxErr 5.1)(

n

ZZ

n

i 1

n

ZErr

ZErr

n

i 1

2)(

)(

n

i

i

ZErr

ZZ

12

22

)(

)(

12R

2R

1R

Z

Solve equations relative Z for each 2-clusters assuming mass of origin particle:

Choose combination with minimum 2

Error estimated on the base of the resolution

Kπ3 reconstruction (Raw spectrum)

Mass K0, GeV

Zdecay point,cm

Pt,Gev/c

P,Gev/c

Kπ3:Combinatorial error

Mass,GeV/c^2

1/1 zErr

Mass,GeV/c^2

1

2Z

Z

2/2 zErr

• Z1 – vertex with best (Err1 – error of vertex)

• Z2 – vertex with second (Err2 – error of vertex)

2

2

0.5

Pure Kπ3 signal sample Cut points

Zdecay – 300-500 cm Pt K0<20 MeV/c < 3 Err1/z1<0.028 Err2/z2>0.029

Mass,GeV/c^2

2

Kπ2 reconstruction (Raw spectrum)

Mass,GeV/c^2

Pt K0,GeV/c Pt pi0,GeV/c

Zdec,cm

Kπ2 reconstruction(2)

Pt pi0,GeV/c

Pt pi0,GeV/cPt pi0,GeV/c

Zdecay,cm

K3p MC

K2p MC

Zdecay,cm

Zdecay,cm

Kπ2 pure signal sample < 1.5 (best) > 10 (second) > 100 (third) Err(Z1)/Z1<0.035 0.1<(E1-E2)/(E1+E2)<0.9 No border hit Zdecay : 300-500 Pt K0 < 15 MeV/c Beam size R<3.5 Background contamination ~4%

mass K0,Gev/c^2

222

Kπ2 pure background sample < 5 (best) > 10 (second) - exist (third) No border hit

Background contamination ~4%

mass K0,Gev/c^2

222

DATA

Kπ2 MC

Kgg reconstruction (Raw spectrum)Pt,Gev/c

Zdec,cm

Pt,Gev/c

Angle,degree

1

2

Kgg pure signal sample No border hit Pt < 50MeV/c Zdecay : 300-500 cm Theta <20 degree Dist g-g >40cm Balance Egam < 0.5 Egam: 0.2-2GeV Diff gamma timing<2ns

DATA Kgg MCK3p MCK2p MC

DATAKgg MCK3p MCK2p MC

Zdecay,cm

Pt,Gev/c

Kgg pure background sample No border hit Pt>100MeV/c Theta >25 deg Diff gamma timing<2ns Balance Egam <0.5 Dist g-g > 40cm

DATAK3p MCK2p MCKgg MC

Kgg MC

Theta,degree

Pt,Gev/c

Zdec,cm

100MeV/c

250

Example veto study: CC03 K3pK2pKgg

Cut point, MeVCut point, MeV

Acceptance loss S/N ratio

MeV1 MeV1

Conclusion We can reconstruct good K3p,K2p,Kgg decay modes

K3p decays The missing the true pairing of the gammas led to bad reconstruction mass

K2p Lower mass tail comes from K3p decays.

Kgg Background near Charge veto from neutrons (see next report)

For comparison of BR the further study is needed

Pure signal and bgr sample of K3p,K2p,Kgg decays can be used for further veto study Purity w/o veto-cut on a level a few%

In future Study the acc. loss and bgr. rejection of the veto system using pure samples