june 9, 20041 tetsuro sekiguchi, kek bnl-e949 collaboration the e949 experiment the analysis the...

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)


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


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


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.


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


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 background functions Likelihood Analysis


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


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


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)


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


Event Display


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


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?


Back-up slides


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


TD pulse shape


samples and with candidate of properties TD

Events with early decay are selected signal: blue background: red arrow: candidate event


samples and for timepulse second Typical

decay from pulse second :sample

pulse fluctuatedor accidental pulse second :sample


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


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


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


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(


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


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

june 9, 20041 tetsuro sekiguchi, kek bnl-e949 collaboration the e949 experiment the analysis the...

Documents

e949 data

background functions

data background measurement

analysis signal region

total background level

measure e949

e949 results

weeks e949