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June 9, 2004 1Italy Frascati, di Nazionali Laboratori 2004, NEDA
πKon Result Recent
Tetsuro Sekiguchi, KEK
BNL-E949 Collaboration
The E949 experiment
The analysis
The results
Conclusions
BNL, FNAL, UNM, Stony Brook Univ. (USA)Alberta, TRIUMF (Canada)IHEP, INR (Russia)Fukui, KEK, Kyoto, NDA, Osaka, Osaka RCNP (Japan)
June 9, 2004 2Italy Frascati, di Nazionali Laboratori 2004, NEDA
BNL-E949 = Successor of E787
side view end view
Signal = Stopped + nothingK
Low energy beam and stop in the target (intensity = E787) Kinematics measurement momentum, energy and range in the stopping counter Photon veto hermetic detectors
K
e
2
K
June 9, 2004 3Italy Frascati, di Nazionali Laboratori 2004, NEDA
Improved kinematics measurement
Kinamatics measurement is sensitive to signal selection
Range andEnergy Momentum, K π2
cm 0.9 :
MeV 3.0 :
MeV/c 2.3 :
R
E
P
ratedetector 2with
resolutionbetter even or sameAlmost
(histo) E949 vs)( E787
RS Layer 1-5 replacement more light output RS gain monitor system better energy calibration
June 9, 2004 4Italy Frascati, di Nazionali Laboratori 2004, NEDA
Improved photon veto
detectors γline beam New
2.3 add
region barrelin r calorimete New
0
X
rejection π0
E949
E787 2
Rejection to background as a function of acceptance for E787 and E949. better rejection at 80% of nominal acceptance.
2~
2K
γNew detectors in blue.
June 9, 2004 5Italy Frascati, di Nazionali Laboratori 2004, NEDA
Data Taking
Physics run in 2002 (12 weeks) Beam condition was not optimized Detector worked very well Smooth data taking
intensity 2
12108.1 KN
1210daccumulate
ratio
%factorduty
Tpintensity beam
KN
K 9.5
4
52
4025
8.1
3
41
70
E787 E949
June 9, 2004 6Italy Frascati, di Nazionali Laboratori 2004, NEDA
Analysis
Signal region “the BOX”
Background sources
Analysis Strategy
(PNN1)region ππK Above 0
background Beam
))((K backgroundMuon
ππK 0
Blind Analysis Measure Background level with real data To avoid bias, 1/3 of data cut tuning 2/3 of data background measurement Characterize backgrounds using back- ground functions Likelihood Analysis
June 9, 2004 7Italy Frascati, di Nazionali Laboratori 2004, NEDA
Background characterization
Background can be characterized using background functionsFor muon backgrounds
R
measrm
RR
exp
and for )Momentum(P
counter stopping
in the e
Neural net function for and
:(band)K
:(tail)K 2
m
2K
)etc ,(Kdecay Kmultibody
but range is small due to interactions in RS.
Changing cut position
Acceptance & background level at each point of parameter
Functions
June 9, 2004 8Italy Frascati, di Nazionali Laboratori 2004, NEDA
Likelihood Analysis
Branching ratio and Confidence level
id
Both and are small Poisson statistic The ratio of two Poisson probabilities # of observed candidate events in the cell
iS ib
i
The signal region is divided into cells. Cell construction by binning the parameter space of each function.
The signal and the background in the cell
The cell is characterized by the signal to background ratio
Likelihood ratio technique (T. Junk [NIM A434, 435 (1999)])
i iS ib
(BR) ( : Acceptance)iSiAiK AN )( KB
iiS ib
n
i
n
i
X1
1
) ( ) (
)
1(exp
! ) (exp
! ) (exp
) ( ib iSiS ib
ib
ib ibiSiS
id id
id idid
BR
Likelihood estimator
iS
ib of cells containing candidate events
June 9, 2004 9Italy Frascati, di Nazionali Laboratori 2004, NEDA
For the likelihood analysis,important isthe ratio in each cellNOT the total background levelin signal region.
Sensitivity and background
Sensitivity
BackgroundNote:10% larger acceptance by enlarging the signal region, resulting in more backgrounds
ii bS
All cuts are fixed and ready to open the BOX !
background Beam
(band)K
(tail)K
K
K
2
2
2
m
050.0
064.0
032.0
003.0014.0
010.0024.0
005.0044.0
023.0216.0
background Total
E787 E949
05.014.0 026.0298.0
Source
83.0
02.020.0
9.5
336.06.2
1.102.022.0
305.08.1
E787 E949
Total acceptance (%)
Sensitivity (10-10)
NK (1012)
June 9, 2004 10Italy Frascati, di Nazionali Laboratori 2004, NEDA
Opening the BOX
Range (cm) and Energy (MeV) for E949data after all other cuts applied.
Solid line shows signal region.
Single candidate found.
.K
unvetoed is MeV 110near Cluster 0
Beam
(ns) decay time
(ns) decay time
(ns) decay time K
Photon
(MeV)Energy
(cm) Range
(MeV/c) Momentum
e
3.227
3.4
1370
2.6
9.1282.39
June 9, 2004 11Italy Frascati, di Nazionali Laboratori 2004, NEDA
Event Display
June 9, 2004 12Italy Frascati, di Nazionali Laboratori 2004, NEDA
Branching ratio & Confidence level
CL) (68% 1096.0)( 1009.447.0
KBr
1030.189.0 1047.1)(
KBr
(68% CL)
)(K on tocontributi signal :)( BrbSSW iiii
E949(02) = combined E787&E949.E949 projection with full running period.
E787 E949
i
ii
K
W
bS
N
Candidate
)(10 12
88.00.98
750
E787CE787A
0.48
0.9
E949A
9.5 8.1
(~60 weeks)
E949 result alone:
Combine E787 and E949 results increase statistics
June 9, 2004 13Italy Frascati, di Nazionali Laboratori 2004, NEDA
Conclusions
)K( Br
Upgrades of E787 to E949 were successful.
Likelihood analysis was performed to measure
K1030.1
89.0 1047.1)K(
Br
E949 has observed an additional
candidate.
(68% CL, PNN1 region)
from the combined E787 and E949 result.
We need more data.
0 K- Analysis of “below (PNN2) region”
- Further E949 running?
June 9, 2004 14Italy Frascati, di Nazionali Laboratori 2004, NEDA
Back-up slides
June 9, 2004 15Italy Frascati, di Nazionali Laboratori 2004, NEDA
Trianglety on Unitari )(K ofImpact B
By courtesy of G. Isidori
Central value [dashed], 68% interval [dot-dashed], 90% interval [solid](including theoretical uncertainties)
3352 1008110240:)1(
0271000550
.λ.iλAVV λ
.V.
t-
td*
ts
td
June 9, 2004 16Italy Frascati, di Nazionali Laboratori 2004, NEDA
TD pulse shape
June 9, 2004 17Italy Frascati, di Nazionali Laboratori 2004, NEDA
samples and with candidate of properties TD
Events with early decay are selected signal: blue background: red arrow: candidate event
June 9, 2004 18Italy Frascati, di Nazionali Laboratori 2004, NEDA
samples and for timepulse second Typical
decay from pulse second :sample
pulse fluctuatedor accidental pulse second :sample
June 9, 2004 19Italy Frascati, di Nazionali Laboratori 2004, NEDA
Signal rate and background level for the candidate cell
Signal Si Background bi
5103.5)( BRSi101047.1)(with KB
5107.5 ib
9.0107.5103.5 55 ii bS
June 9, 2004 20Italy Frascati, di Nazionali Laboratori 2004, NEDA
Acceptance calculation
)(PDG value 001.0212.0 005.0219.0)( 0 KBr
ns 2after decay
efficiency stop
K
K
flight-in-decay &n interactio nucl.
acceptance angle Solid
space phase
K
sconstraint kinematicOther
efficiencytion Reconstruc
acceptancedecay e
loss Accidental
analysis target and Beam
C. M.
C. M.
C. M.
Real
Real
Real
Real
Real
Real
Real
851.0
702.0
527.0
409.0
136.0
554.0
969.0
392.0
751.0
706.0
%196.0acceptance Total
factor Acceptance Data E787-'98 E949-'02
846.0
774.0
495.0
411.0
164.0
501.0
996.0
391.0
820.0
648.0
%222.0
tmeasuremen ratio branching 2K
Cross check
June 9, 2004 21Italy Frascati, di Nazionali Laboratori 2004, NEDA
2.810.42.25.21.03.20.41.30.090.31Predicted
1.521.81.014.50.69.10.11.40.030.35Predicted
5.662.43.131.11.312.40.64.90.181.1Predicted
115411Observed
25161210Observed
5322943Observed
mK
K
K
40802080205020201010KINTD
501205080505020201010KINTD
100505050502020201010KINPV
2
2
Verify background prediction by loosening cuts
Cut R = PV or TD: loosen by Cut K = KIN: loosen by
MN
more background event should be observed in loosened BOX. ( )
NM NM
obsN expN
June 9, 2004 22Italy Frascati, di Nazionali Laboratori 2004, NEDA
Branching ratio and confidence limits
2002 candidate event alone Branching ratio:
Combined measurement (1995-2002) Combined BR:
1009.447.0 10)96.0(
1030.189.0 10)47.1(
June 9, 2004 23Italy Frascati, di Nazionali Laboratori 2004, NEDA
Likelihood Analysis with T. Junk method
The Poisson probability to observe di with Si + bi or bi expected
Si (BR) BR : signal BR: NK: # of Kaon decay Ai: Acceptance
bi: backgrounddi: # of observed events
)( KB iK AN
n
i
n
i
PP1 1
) (
!
) (exp) ; ( iS ib
id
iS ib
ididS b S b
iS ib
n
i
n
i
PP1 1
) (
!
) (exp) ; ( ibib
id
id
ibidb b
n
i
n
i
X1
1
) ( ) (
)
1(exp
! ) (exp
! ) (exp
) ( ib iSiS ib
ib
ib ibiSiS
id id
id idid
BR
June 9, 2004 24Italy Frascati, di Nazionali Laboratori 2004, NEDA
Likelihood Analysis with T. Junk method
Summing all the set di to satisfy
Then obtain the confidence level
CLCLCL S S bb
}) ({}) ({ 1
) (
}) ({}) ({ 1
) (
!
) (exp)(
!
) (exp)(
XX
n
i
obs
XX
n
i
obs
XXPCL
XXPCL
iS ib
id
S b S
b
b
b
ib
id
id
id '
id '
id
iS ib
ib
id
id