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
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