_

0
Search for the KL→π νν at

E391a Experiment
KAON 09 @ Epochal Tsukuba(2009 Jun 12)

Hideki MORII (Kyoto Univ.)

2009 Kaon International Conference @ Epochal Tsukuba

2009/Jun/12

1

Contents

Contents• Introduction• physics motivation• principle of E391a experiment• Data analysis of Run3
• study on halo neutron background• KL ﬂux estimation• sensitivity & results2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

2

Introduction

Introduction

iδ KleinknechtmanK.
andc eiδb ! (Carnegie-Mellon
s1 s2 c1 sUniversity),
c
+c
s
e
c
s
s
−c
b
2
3
2
3
1
2
3
2
3
bbo
mixingwithθ
identified
(up
to
a
sign)
with
the
Cabibboangle [21Introduction
niversität
Mainz).
! " !
"! "

_
0
0
eθcaseKK""#
and V0 are
realdecay
and V complex, illustrating a different
V L!!
and →πs = sin θ ννfor i = 1,Decay2, 3. In the limit θ =(11.4)
θ = 0, this reduced!
c1−s1 c3−s1 s3dubtdcb(2)×U(1)as the gauge group of electroweak interactions,ss ! = s1 c2 c1 c2 c3 −s2 s3 eiδ c1 c2 s3 +s2 c3 eiδ
,

L
2
3
i!
i standard
assigned
toi beinleft-handed
doubletsand right-handed
phase
than
the
parametrization.
iδiδb
s1 s2 c1 s2 c3 +c2 s3 e
c1 s2 s3 −c2 c3 e
b
bbo
with
(up to aandsign) with the Cabibbo
angle [2ates mixing
are notthesameθ1as identified
the weakeigenstates,dct”
CPviolation
processtion
totheforstandard
parametrization
proposedby Wolfenstein [4]wasdefinedsix
quarksandgiven
an modeexplicit
Features
of
this
decay
0
•
and
V
are
real
and
V
complex,illustratinga different
case
V
!0
θi and si ub= sin θi for td
i = 1, 2, 3. In the limit cb
θ2 = θ3 = 0,K this reduces ±d Maskawain[1]thein 1973.
This
generalizes
thesfour-quarkW
erarchysizeof theangles,#sCabibbo# ssangle. Setting
λ ≡ ds12 , th
12
23
13
bbo
mixingwithθ
identified
(up
to
a
sign)
with
the
[2].
phase
than
in
the
standard
parametrization.
1“direct”
CPd by a•single
parameter,
the violating
Cabibbo angleprocess
[2].
td λ:
bo
angle,
oneVtdexpresses
theVcbotherelements
in termsof powersVof
are real andcomplex,illustratinga differents caseVub andoften
interms of parametrization.
a parametrization
3 × 3 unitary matrix Vproposed byu,c,tWolfenstein
tion
to
the
standard[4]phaseexpressedthanin thestandard
measuresηin
CKM
matrixZ0
urementoftheparameter
$
in
CKM
•
!
ark
mass eigenstates (d, s, and _b):erarchy
in
the
size
of
s123 (ρ#sWolfenstein# s13 . [4]Setting λ ≡ s12 , th
 the angles,parametrization
 to the2 /2tion
standard
proposed
by−
23
0
2
1
−
λ
λ
Aλ
iη)
d νν) ηVubL→πVud VBr(Kus size
ierarchy
in
the
of
the
angles,s122other# s23 elements# s13 . Setting
λ≡ s12 , ofthe4powers of λ: !
boangle,
one
expresses
the
in
terms
2






s
.
(11.1)VV
V=
1 − elements
λ /2 in terms=bo angle,
Aλof powers of+λ:O(λ ) .
(11.
cs−λcb
cd oneexpresses
the
other
d
small
uncertainty•b
Vtd
Vts Vtb theoretical
3
2
Aλ
(1
−
ρ
−
iη)
−Aλ
1

K0
u,c,t
!0


2
3
1~−
λfew
/2principle
λ 3determined
Aλmode(ρ − iη) s
ix elements
inall be
from
1−
λcan
Aλ
(ρ − iη)a2 /2%: λ“gold-plated”
d
±
±
W
W
4
2
2
4
2
2
 or, in−λ+
somecases,1 −from
deepinelastic
neutrino
triangleof CKM matrix + O(λλ /2Aλ(11.5)O(λ ) . unitarity−λ1−
λ==rks,
/2
Aλ
)
.
(11.
-11
eal
numbersthat
wereintended
to
be
of
order
unity.
This
approxima
3
2
rare
decay
:
2.5x10@SM!
vel constraints
discussed
below together
•
Aλ
(1
−ρ−
iη)
−Aλ
1 with unitarity,
3
2
0
Z
(1 −
ρ−
iη)limits−Aλons, Aλthe90%confidence
on the magnitudeof1theed,especiallyforB-physics,
but
care
must
be
taken,
especially for
Comparison
to
the
!
•
are
real
numbersthat
wereintended
to
be
of
order
unity.
This
approximate
ts in K-physics, since the phaseenters Vcd and Vcs through terms tha
litudesed,
especiallyforthatB-physics,
but
care mustbetaken,
especiallyfor This0.221
to 0.227
0.0029toin
0.0045dmeasurement
B-systemealnumbers
wereintended
to
be
of
order
unity.
approxima
5
ncts
λ.
These
higher
order
terms
up
to
order
(λ
)
are
given
in
[5]. !0
0
0
0
0
0
0
0

K
0.9730to
0.9744
0.039
to
0.044
.
(11.2)
inK-physics,
since
the
phase
entersV
andV
through
terms
that
K
!!
""#
)
A(K
!!
""#
)
A(
K
#
!!
""#
)
cs
cd
L especially for B-physics, buted,mustin betaken, especially
for
5care
precise
check
of
SM
s
d
0.037
to
0.043
0.9990to
0.9992nλ.
Thesehigher
order
terms
up
to
order
(λ
)
are
given
[5].
•
±
etrization has been advocated [6] that arises naturally where
one
build
u,c,t
W
ts in K-physics,
since
phase
Vcdwhere
andoneVcs
through terms th
Vtd
*V
-the
V
*V
ts
tsthattd
dividualmatrixelements.
The
constraints
ofenters
unitarity
metrization
has
been
advocated[6]
arisesnaturallybuildsprobe
toNP
massesinwhichinitiallymurestricts= mdthe=range
0. Withno phases in the third
!
•
5
osing
a
specific
value
for
one
element
nmassesλ. Thesehigherto noorder(λin )the
arethird
given in [5].lin which
initiallyordermu = terms
md = 0.up
Withphasesmn,
theconnection
connection
measurementsof effects
CP2009/Jun/12-violating
effects for= 2 between
x Vbetween
Im(V
$CP
ts x
td) of@mn, 2009
themeasurements-violating
for B
Kaon International
Conference(KAON09)
Epochal
Tsukuba4± H.MORIIW!

Introduction

E391a Experiment_• Measures KL → π0νν @ KEK 12GeV PS• ﬁrst dedicated experiment• pilot experiment for KOTO (J-PARC E14)

• Three Physics Runs

KEK 12GeV PS East Counter Hall

• Run1 (2004 Feb-Jul)• Run2 (2005 Feb-Apr)• Run3 (2005 Nov-Dec)2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

A-lineC-line2009/Jun/12

E391a

H.MORII

5

Experimental Principles

Introduction• To identify
ー stateKL→π0νν→cannot detect→2γ• “2γ + nothing”• 2γ → CsI calorimeter (energy, position)• nothing → hermetic veto detector

θ• Reconstruct decay vertex with M(π0)M(π0)2 = 2E1E2(1-cosθ)← “pencil” beam to improve pT resol.

• select signal using decay vertex andtransverse momentum
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

6

Introduction

E391a Detector

KL

ν

γ

ν

γ

7

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

Introduction

E391a Detector
pure CsI crystal
7x7x30cm (5x5x50cm)
576 channels
CsI Calorimeter

KL

ν

γ

ν

γ

7

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

Introduction

E391a Detector
pure CsI crystal
7x7x30cm (5x5x50cm)
576 channels
CsI Calorimeter

KL

ν

γ

ν

γ

Photon Veto Detector

Back-Anti : veto γ
escaping into beamhole

72009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

Introduction

E391a Detector
Charged Particle
Veto Detector

pure CsI crystal
7x7x30cm (5x5x50cm)
576 channels
CsI Calorimeter

KL

ν

γ

ν

γ

Photon Veto Detector

Back-Anti : veto γ
escaping into beamhole

72009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

Introduction

E391a Detector
Charged Particle
Veto Detector

pure CsI crystal
7x7x30cm (5x5x50cm)
576 channels
CsI Calorimeter

KL

ν

γ

ν

γ

Photon Veto Detector

Back-Anti : veto γ
escaping into beamhole

72009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

Motivation of Run3 Analysis

Motivation of Run3 Analysis

Motivation of Run3 Analysis

Review of Run2 Analysis• E391a Run2 Result• blind analysis• No event observed in
the signal box• Upper limit 6.7 x 10-8(90% C.L.)(Phys. Rev. Lett. 100 201802, 2008)• Background sources• halo neutron BG• Collar Counter (CC02) π0• CV π0• CV η
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

9

Motivation of Run3 Analysis• Halo neutron• neutron ﬂux surrounding

rec. pT

Halo Neutron BackgroundCC02-π0CV-π0ﬁducialregionbeam coreCV-η• Halo neutron BG

rec. z vertex

halo-n hits detector
around beam core
→ creates π0,η→2γ

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

10

Motivation of Run3 Analysis• Collar Counter (CC02) π0 BG
miss-measures Eγ lower(shower leakage

rec. pT

Mechanism of Neutron BackgroundCC02-π0CV-π0ﬁducialregion& photo-nuclear eﬀect)••→ reconstruct θ larger
CV π0 BG
miss-measures Eγ higherCV-η(due to fusion cluster)γ→ reconstruct θ smallerCV η BG
diﬀerence in M(π0) and M(η)→ reconstruct θ smallerrec. z vertex

E1

θ

γ

E2

M(π0)2 = 2E1E2(1-cosθ)2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

11

Motivation of Run3 Analysis

Motivation for the Run3 Analysis• halo neutron BG• CC02 π0 BG (→ extrapolation of the Al-target data)• CV π0 BG (→ bifurcation)(→ geant4 + geant3 MC)• CV η BG→ in Run2, these are estimated in diﬀerent mannerdiﬃcult to...
- systematic study on BG- eﬀective optimization

In Run3 Analysis,
BG estimation for these 3 BG sources in one method→ simple & effective optimization / BG understandings
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

12

Study on halo-n BG

Study on Halo Neutron BG

Study on halo-n BG

Halo Neutron BG Study in Run3
• Two step MC for halo neutron BG
1st stage : ﬂuka MC- to estimate hadronic interaction
2nd stage : geant3 MC- to estimate electro-magnetic shower in CsI• Run3 halo neutron background study• check the hadronic interaction model by special run••(Al-taget run)
optimize the event selection
background estimation2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

14

The
Aluminumplaterun
Al Target Run
4.4. Calibration Runs

• Setting 5 mm thick Al plate
Motivation
at 6.5 cm from the CC02’s surface• Statistics
estimate π0, η- 5.57x1016 POT (data: 1.40x1018)

production rate
• BG
using the Al
plate run→estimation
confirm hadronicinteraction- CC02 events
model
of
fluka
simulation$ contamination to downstream by•- shower leakage
Altargetrun- photonuclear effectconfirmation of fluka model
MB

•

•

Study on halo-n BG

FB! 0, "!##

CV

neutronCC02
5mm AlCsI

Figure 4.1: Illustration of the Al plate run set-up. The Al plate was located at 6.5 cm dow
the edge of CC02.
2105

4.4 Calibration Runs
104

invariant mass(GeV/c ):assuming Z = Z_plate

In addition to the physics run and the special runs for the physics analysis, we took data for thcalibration.
3

Insert 5mm thick Al target into beamline•10% production
4.4.1 Cosmic Run→
canreconstructmass with10 fixed z-vertex
When the beam from the accelerator was stopped, the data with the cosmic trigger were tak$ evaluate the cross section
the pre-scaling. The gains of the CsI calorimeters were monitored with data taken in the cos
2• Statisitics- 5.57 x 1016 POT

4.4.2 Muon Run

10

Muons came from the upstreamof the neutral beam line through the collimators and the1
0 detector
0.1 uniformly
0.2
0.3and almost
0.4
0.5
0.6
0.7 When theshield. The muons entered theperpendicularly.
2
mass(
GeV/cand) only the h
the collimatorsystemwas closed, neutral particles in theinvariant
beam were
blocked0031
l. 1, 2008
“Search for the Decay
Kcould”T. SumidaL!!
muons@
be""#enhanced;this condition
was called “Muon” run.
CC00,
CC02, CC04–07,
2009 Kaon International Conference (KAON09)
Epochal
Tsukuba
2009/Jun/12
H.MORII
15
BHCV, and BA were calibrated by the data with the muon trigger. The Muon run was carrie

Study on halo-n BG

confirmation of fluka model0
π , η Production Rate

• Ratio π0 / η → OK
# of events

Reconstructed mass of 2γ

measured by CsI

M(2γ)2 = 2E1E2(1-cosθ)

calculated fromfixed vtx-position

dot : Al target run data
blue : MC (fluka)

η peak↓↑π0 peakrec. z-vtx. (cm)reconstructed mass (GeV/c2)

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

16

Cut Optimization

Study on halo-n BG

cut optimization• Principle• maximize the acceptance keeping S/N as
similar level as Run2 case• during optimization, we masked the signal
box for both Run2 and Run3 data to avoid
biasing• What is done?
• New cut as “cluster-shape NN”• Replacement of several cuts
• Automatic parameter tuning
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

17

Study on halo-n BG

Cluster Shape NN Cut (for CV-η BG)• cluster-shape NN for eta BG
eta BG tends to have wider cluster(γ tends to have shallow incident angle to CsI)

• input parameters : energy, r, phi-position (eachNeural Network value
black : signal MC
red : CV-η MC

NN value for γ2

crystal)correlation colored : signal
dots : etaBG

veto
Neural-Net value

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

H.MORIINN value forγ1

2009/Jun/12

18

Study on halo-n BG

γ-fusion NN Cut (for CV π0 BG)•

CV π0 BG

normalfusion likemade by “fusion” cluster in CsI• Optimized ascluster size cut → fusion NN cut~40% accept. loss → ~20% accept. loss
rejection power is similar (~70% reduction)veto2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

19

Study on halo-n BG

Acceptance / Rejection Power• exclusive acceptance / rejection for each cut
black : signal MC
blue : CC02 π0 BG
green : CV π0 BG
red : CV η BG

↑fusion NN2009 Kaon International Conference (KAON09) @ Epochal Tsukuba←cluster shape NN
2009/Jun/12

H.MORII

20

Study on halo-n BG

Result of Optimization

cond.
Run2
New

Signalcut optimization

S/N (arb.)

30328
5054
45945(+51%)5105
S/N : almost same as Run2 cut
acceptance : +50% from Run2 cut

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

21

Background Estimation

Background Estimation
Halo neutron backgroundKL backgroundBackground Estimation

Background Estimation• Halo neutron background• CC02 π0 : from upstream• CV π0 : from downstream• CV η• KL originated background• neutral mode : KL→2π0• charged mode : KL→π+π-π0
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

23

Background Estimation

halo-n BG
0CC02 π Background (upstream)• CC02 π0 BG (BG from upstream)• 0.150.05 event (w/ photo-nuclear eﬀect)
CC02 π0 background
CC02 BG

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

24

Background Estimation

halo-n BG
0
CV π Background (downstream)• CV π0 BG (BG from downstream)• estimated as 0.0 (< 0.15) event
CV π0 backgroundwith fusion NN cut

pT (GeV/c)

w/o fusion NN cut

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

25

Background Estimation

halo-n BG

CV-η Background• CV-η BG
estimated as 0.14

0.07 event

CV η background
w/o shape NN cut

with shape NN cut

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

26

Background Estimation

KL Originated Background

KL BG

KL→2π0 background• Estimation for KL BG• same as Run2
0
K
→2π
L
•
estimated BG: 0.140.05

KL→π-e+ν background• KL→π-e+νmost dangerous in charged modes(π- charge exchange/ e+ annihilation): 4.7 ( 0.7) x 10-3
→ small2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

27

Background Estimation

Summary of Background Estimation• Summing up all background sources→ estimated # of background : 0.44

sourceKL→2π0KL
KL→π-e+νCC02 π0
halo-n
CV π0
CV η
total

0.10

estimated BG
0.14 ± 0.05
4.7(±0.7) x 10-30.15±0.05
0.0 (<0.15)
0.14 ± 0.07
0.44 ± 0.10

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

28

Background Estimation

Summary of BG Estimation• Comparison to Run3 data
→ matches well !

Run3 data

Background MC±(stat.) ±(syst.)
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII29

KL Flux Estimation

KL Flux Estimation
KL→3π0KL→2π0KL→γγ

f = L(P )KL Flux Estimation

" 1
1−β
1
f dx
U=
= !1
2
0 f dx PU
" PL
1−β
1
L=
= !1
f dx
2
0 f dx 0

KL Flux Estimation(

0 reconstructionK
ﬂux
measurement
L
K
•
L

E1

0
N
• KL→3π• ! (K (→6γ)) reconstruction
w/ 2 photons
F =A × Br(K) × Br(π → γγ)0• KL→2π (→4γ)• KL→2γ E = 0.95 × #e × E × E
0

L

0

Mπ20
$ cosθ = 1 −2E1 E22
r12= d21 + d22 − 2d1 d2 cosθ!
r12 + (dz)2
d1 =!
r22 + (dz)2d2 Data=dz≡ Zcsi − Zvtx #EM C = 1.0 ×

nπ 0

r1
θ

(0,0,Zvtx)
down

up

r12

d1

e × Eup × Edown2
χ = i=1 (ziσ−z̄)2i$zi /σiz̄ = $i 1/σii• to check MC quality

!0
z1

&

z2

(0,0,Zcsi)%2

2

Scale = 1.11

! /dof = 60.0 / 41

Data
!0!0!0 MC

10 3
10 2

10

1

• Flux estimation• CutsPhoton Vetoes: typically O(1) MeV
calculateacceptance for KL•
Kinematic cuts
z3

0

CsI

-

- Photon quality cuts

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

3.5

4

4.5

5

Chi-Squared

Data / MC$3beam axis

8.1. KL0 Flux

• Comparison between data & MC
2

r2

dz

• K0L reconstruction w/ K0L!2!0, 3!0- Take the best %2 for the vertex distribution in paring
$

(1
E2

d2

Counts per 0.1 units

0

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

39.82

/ 38
0.94780.4441E-01

A0
A1

0

0.5

1

1.5

0.1712E-01
0.1386E-01

2

2.5

3

Chi-Squared

Jul. 1, 2008

“Search for the Decay K0L!!0""#”2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

16
T. Sumida
Figure 8.3: Lowest χ2Z value (left)
and the secon0000KL → π π π .

2009/Jun/12

H.MORII

31

KL Flux Estimation

6γ, 4γ, 2γ : Comparison between Data & MC

Rec. mass of 6γ sample

Rec. mass of 4γ sample

Rec. z-vtx. of 2γ sample# of events# of events# of events• Comparison between data & MC
• check reproductivity of MC
dots : Run3 data
blue: KL→3π0 MC

0.5

0.3

0.6

0.4

0.5

0.6

ratio (data / MC)ratio (data / MC)
0.4

0.5

0.6

reconstructed mass (GeV/c2)

300

400

500

600

reconstructed z position (cm)Ratio between data and MC

Ratio between data and MC

Ratio between data and MC

200

reconstructed mass (GeV/c2)

reconstructed mass (GeV/c2)

dots : Run3 data
pink : KL→2γ MC

ratio (data / MC)

0.4

dots : Run3 data
red : KL→2π0 MC

0.3

0.4

0.5

0.6

reconstructed mass (GeV/c2)

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

200

300

400

500

600

H.MORII

32

reconstructed z position (cm)2009/Jun/12

KL Flux Estimation

6γ, 4γ, 2γ : Comparison between Data & MC

Rec. mass of 6γ sample

Rec. mass of 4γ sample

Rec. z-vtx. of 2γ sample# of events# of events# of events• Comparison between data & MC
• check reproductivity of MC
dots : Run3 data
blue: KL→3π0 MC

0.5

0.3

0.6

0.4

0.5

0.6

ratio (data / MC)ratio (data / MC)

300

400

500

600

reconstructed z position (cm)Ratio between data and MC

Ratio between data and MC

Ratio between data and MC

200

reconstructed mass (GeV/c2)

reconstructed mass (GeV/c2)

dots : Run3 data
pink : KL→2γ MC

ratio (data / MC)

0.4

dots : Run3 data
red : KL→2π0 MC

MC well reproduces the distributions of data!
0.4

0.5

0.6

reconstructed mass (GeV/c2)

0.3

0.4

0.5

0.6

reconstructed mass (GeV/c2)

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

200

300

400

500

600

H.MORII

32

reconstructed z position (cm)2009/Jun/12

KL Flux Estimation

KL Flux Estimation• # of KL is estimated via 3 decay modes: KL→3π0, 2π0, 2γ
mode
3π0
2π0
γγ

# of eventsin data# of eventsin MC(addbg)

48229

7986
(stat. 5.0e9)

acceptanceflux

7.46 x 10-5

3.30 x 109(-5.1%)

1072

11367
(stat. 1.5e9)

3.54 x 10-4

3.48 x 109
(---)

14278

30452
(stat. 2.0e8)

7.12 x 10-3

3.66 x 109(+5.2%)cf.) Run2 3π0 : 5.02 x 109 (-2.1%)
2π0 : 5.13 x 109 (---)
γγ : 5.45 x 109 (+6.2%)

Run3 Flux : 3.48 (± 0.11 ± 0.22) x 109
Run3 statistics : ~70% of Run2

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

33

Sensitivity & Results

Sensitivity & Results
Sensitivity
Results

Sensitivity

Sensitivity & Results• Signal acceptance(# accept MC)
x (accloss by TDI, Tdiff)(# generation) x (decay prob.)= 0.975 0.005 0.067 %(cf. Run2 with Run2 cut : 0.670%)• Flux : 3.48 x 109 (Run3)• SES = 1/(Acc. x #KL)= 2.95 x 10-8 (Run3)

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

35

Sensitivity & Results

Opening the Box : Run3
• Opening the box for Run3 data

Y
R
INA

M
I
L
E
PR

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

36

Sensitivity & Results

Opening the Box : Run3
• Opening the box for Run3 data

Y
R
INA

M
I
L
E
PR

2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

36

Sensitivity & Results

Result• Acceptance = 0.975

0.005 0.067 %(cf. Run2 previous : 0.670%)• SES = 1/(Acc. x #KL)
Run3 : 2.95 x 10-8

(cf. Run2 previous : 2.91 x 10-8)• Upper limit
no event observed → x 2.3 with Poisson stat.
Run3 : BR(KL→π0νν) < 6.8 x 10-8 (90% C.L.)(cf. Run2 previous : 6.7 x 10-8 @ 90% C.L.)

Y
R
A
N
I
M
I

L
E
R
P
2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

37

Summary

Summary (1)• E391a experiment @ KEK 12GeV PS_• ﬁrst dedicated experiment for KL→π0νν• Run3 data analysis• halo-n BG study : simple method- check for the hadronic model- optimization- BG estimation• KL ﬂux estimation2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

38

Summary

Summary (2)• Acceptance : 0.975 %• Sensitivity
SES : 2.95 x 10-8 (Run3)• Opening the box for Run3
→ No event observed!

• Upper Limit
BR < 6.8 x 108 (Run3)

Y
R
A
N
I
M
I
L

PRE

(cf. Run2 previous : 6.7 x 10-8 @ 90% C.L.)2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

39

Summary

Prospects• Combined result of Run2 & Run3 is coming
soon- trying re-analysis for Run2 with optimized
event selection
Note that we didnʼt see inside the box
during the optimization stage.
(both Run2 and Run3 samples)2009 Kaon International Conference (KAON09) @ Epochal Tsukuba

2009/Jun/12

H.MORII

40

Thank You!