K → 崩壊の探索と京都グループの活動

K→崩壊の探索と京都グループの活動

KOPIO (BNL) : 笹尾　野村　 (+ 新スタッフ )　　　　　　　　　　隅田 (D2) 森井 (D1) 横山 (D1) 　　　　　　　　　　白井 (M2) 谷口 (M2) 中島 (M1)

KL→0

K+→+

E391a (KEK) : 笹尾野村隅田 (D2) 森井 (D1)

E787 (BNL) 　 : 藤原 (D3)

E949 (BNL) : 笹尾野村　藤原 (D3) 溝内 (D3)

KOPIO Apparatus – CG with High-lights–

Shashlyk calorimeter

2X0 PreradiatorDecay region

Beam veto

Eye-pipe charged veto　　（ビームパイプ内壁部分）

日本 ( 京都 ) グループ担当箇所• Beam Catcher 　（全面的に担当）

– 最下流の中性ビーム中の光子 Veto• 横 3.6 ～ 6 ｍ（ビームの拡がりに

応じて増す）、高さ３０ｃｍ• 中性子の数が多い

– ３００個 /microbunch (>830 MeV)

– 検出すべき光子• 比較的高いエネルギー（ >300Me

V ）に集中　 ( 運動学的カットのおかげ）

– 性能要求• >99% for 300 MeV photon• <3x10-3 for 830 MeV neutron• 時間分解能 1 nsec• 2 信号分離能力　 3 nsec

• Eye-pipe Charged Veto（デザイン、パート試験を担当）– 真空槽内で荷電粒子を検出

• <10-5

• <10-4

– プリラディエータ、カロリメータのビーム側内層をカバー（ビームパイプに沿う形）

– シンチ＋波長変換ファイバー＋高量子効率 PMT

エアロジェル性能評価システム– チェレンコフ発光量 –

• ビームより簡易に、宇宙線より迅速に！テーブルトップ・単色ベータビームを開発

1.5MeV,E=10%

2.5MeV,E=6%

106Ru そのまま

2段ソレノイド・スペクトロメータ

光量測定結果

黒：データ、赤： MC光量のエネルギー依存を

迅速に測定可能

• 測定 : (⇒ ) + nothing

• KL 生成 : KEK 12GeV PS– “Pencil beam”

• 検出器– 高精度の CsI カロリーメータ– 崩壊領域を完全に覆う veto 検出

器• バレル部光子 veto• ビーム周りの “ Collar” 検出器

– 崩壊領域 : ~10-5 Pa の高真空

• Sensitivity 　 O(10-10) – SM Prediction ～ 3x10-11

E391a: KL→0 測定実験

10 m

100mm

KL

Z 軸

E391a Data Taking• Run-I

– 2004: 2/16 ～ 6/30 300 ⇒ シフト• 187 シフト : 物理データ取得• 24 シフト : 0 生成ターゲットを用いた較正• 89 シフト : ビームチューニング等

– KL 生成 • 1 次陽子ビーム取り出し : 2 秒 (4 秒 spill)• 2.2×1012 proton / spill

⇒ 5x105 KL /spill• ~110 GB/ 日 ⇒ full data: 6TB

• Run-II– 2005: 2/3 ～ 3/17( 予定 ) 100 ⇒ シフト– 改良点 ( 後述 )

• 新 collar counter • Multi-hit TDC ⇒ レート耐性の強化• ビーム中に Be absorber を挿入

2004.1.22検出器完成

Run-I: 解析の現状• 1 week data analysis

– KL → 3,KL → 2による KL ビームの理解

3 の質量

±20%

崩壊点運動量分布

– バックグラウンドの見積り

• single 分布の比較 – Final plot (1 week data) and

Sensitivity

Zvtx (cm) Pt (GeV/c)Recon Mass (GeV/c2)

Nex

t sl

ide

…

Run-I: 解析の現状 (2)バックグラウンドの予測各崩壊モード分布　(MC)

中性子が真空膜に衝突

2trigger data MC vs Data (1week data)

Zvtx (cm)

Run-I: 解析の現状 (3)Final Plot (1Week data)

No significant signal/background observed.

Sensitivity ~ 10-8

PT (GeV/c) Vertex Zvtx(cm)

Run-II での改良点

CC

02

CC

03

CC

04

CC

05

CC

06

CC

07 FB

MB

CV

CsI

BH

CV

BA

BA

CV

RUN-IRUN-II

RUN-II with Be

Accidental veto の確率

RUN-IRUN-II

RUN-II with Be

– Core beam が真空膜に当たっている（改）ビームに対して正確に固定– Halo neutron 起源のバックグラウン

ド　　（改）新 Collar counter

– K/n 比と False Veto

( 改 ) Be absorber

京都グループの貢献

• 隅田 (D2)– Run-I

• DAQ システム構築• 検出器組み立て• シミュレーション

– Run-II• 物理解析

• 森井 (D1)– Run-II

• 各検出器のエネルギー較正

• KL → 3 CsI の較正

E391a : まとめと今後の展望• Run-I

– 2004/Feb/16 ~ Jun/30 300 シフト　 (187 シフト物理ラン )– 1week data の解析

• 10-8 の sensitivity• 問題点の理解• バックグラウンドレベルの見積りが進行中

• Run-II– 2005/Feb/3 ~ Mar/17 100 シフト– Run-I における問題点への対策

• core neutron ⇒ 真空膜の張り直し ⇒ 効果を確認 (x1/5)• halo neutron ⇒ 新 collar counter の導入• n/K 比 , acceptance Be absorber⇒ の導入⇒ acc 向上を確認

– 目的• 解析方法の確立• バックグラウンドが十分少いことの確認

⇒ 秋の PS 運転でさらに 100 シフトを申請中 10-10 オーダの感度を目指す

K+→+崩壊の探索

• Introduction• Experimental Method• Analysis• Results

(Flavor Changing Neutral Current: FCNC)

l

WW

Vtds t d

Second order: Top quark dominant Vtd vertex Theoretical uncertainty

Good decay to measure |Vtd|

7% ~ )(in KBr

1010)12.078.0( 1075.182.0 10)57.1(

SM prediction Current measurement

ννπKfor ratio Branching

it with consistentbut ,prediction SM 2

Motivation

Detection Strategy

Charged Particle Momentum from K+

K+→+(nothing)

K+→+

K+→+0

K+→+

K+ generation

• BNL AGS 24GeV/c (down to 21.5 GeV/c)

• 2sec beam-on in 5sec repetition

• 6.0×1013 proton/spill on Target

• K+/+ electrostatic separator (K/ ratio = 4/1)

• 3.5×106 K+/spill at P of 700MeV/c

Pt target 19.6 m in length

Platinum target

Before E949 data taking After E949 data taking

K+ generation







Electrostatic Mass Separator

K+ generation







Possible Background List

Process Rate

K+→+ 0.77×10-10

K+→+0 0.21

K+→+ 0.63

K+→+ 0.55×10-2

K+→+ 0.33×10-1

CEX 0.46×10-5

Scat + beam 0.25×10-2

E949 detectorside view (upper half)

E949 Detector

Blue : Updated system for E949

1T magnetic field

E949 detectorend view (upper half)

phi

(1) K+/+ ID in Cerenkov counter(2) Stop K+ in scintillator fiber target(3) Wait at least 2ns for K+ decay(4) Measure P in drift chamber(5) Measure range R and energy E in target and range stack 　 (RS)(6) Stop + in range stack(7) Observe + →+ →e+ in RS(8) Veto extra activities.

K+/+ Identification in Cerenkov


E949 Detector

Blue : Updated detectors for E949


phi


1T magnetic field

Stop K+ in Scinti. Fiber Target

0ns 20ns

Tout – Tin (ns)

Kaon decay

Pion scattering

15cm


E949 Detector


1T magnetic field


phi


Barrel Part - End View -


E949 Detector


1T magnetic field


phi


Trace decay sequence

Time (ns)0 ns 100 ns

+ stop counter

life time : 26 nsenergy4MeV+ life time : 2.2 s


E949 Detector


1T magnetic field


phi


CsI for photon veto

DAQ Summary

Physics run in 2002 (12 weeks) beam intensity x2 Detector worked very well Smooth data taking Beam condition was not optimized

1210daccumulate

ratio

%factorduty

Tpintensity beam

KN

K 9.5

4

52

4025

8.1

3

41

60

E787 E949

2 events observed

(60 weeks approved)

1

2

1N

atur

e F

eb/7

/200

2

2

Nat

ure

Feb

/14/

2002

Analysis Strategy

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

Analysis

Backgrounds can be characterized using background functions

Example : muon backgrounds

R

measrm

RR

exp

counter stopping

in the e

Neural net function for and

Background distribution

Range deviation

Decay chain trace

n

i

n

i

X1

1

) ( ) (

)

1(exp

! ) (exp

! ) (exp

) ( ib iSiS ib

ib

ib ibiSiS

id id

id idid

BR

Likelihood estimator

Likelihood AnalysisDivide signal region into cells.

For the cell , # of expected signal

iki AKBNS )( )acceptance : ( iA

ib# of expected background … from background functions

T. Junk [NIM A434, 435 (1999)]

iSi

# of actually observed event id

In the likelihood analysis,the ratio for each cell is a key. The total background level isn’t a mater in signal region.

Sensitivity

Background

Note:10% larger acceptance results 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

003.0024.0

005.0044.0

023.0216.0

background Total

E787 E949

05.014.0 024.0298.0

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)

diff

Sensitivity and Background

Opening the BOX

Range (cm) and Energy (MeV) plot after all other cuts applied.

signal boxSingle candidate found.

.K 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

Branching ratio & Confidence level

)(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)

CL) (68% 1096.0)( 1009.447.0

KBr

1030.189.0 1047.1)(

KBr

(68% CL)

E949 result alone:

Combine E787 and E949 results increase statistics

Effect on unitarity triangleEffect on unitarity triangleThanks to Gino Isidori

Limits from measurements of:

BR(K+ - π+νν) : ------- central value

68% interval

90% interval

Without constraints that depend on Bd mixing

Conclusions

t.measuremen )K(Brfor analysis Likelihood

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?

collected. werekaons 108.1N 12K

Appendix

counter stopping

in the e

Neural net function for and

Event Display

Motivation is clear and simple

(sin2sinJ/

Ks

Use K+ and K0 to measure the CPV related elements

To construct the K unitarity triangle and confirm the “golden” relation which is valid in the SM and MFV.

A.J. Buras et.al hep-ph/0405132

BNL-E949 detector -- Rejecting beam backgrounds

e+

Beam backgrounds include pion scattering, kaon decay-in-flight, and charge-exchange reactions.

Beam backgrounds include pion scattering, kaon decay-in-flight, and charge-exchange reactions.

cerenkov

K cerenkov

B4

K

Top half of side view

Charge exchange

Beam 1

Beam 2

K cluster

cluster

K decay

Target fibres

BNL-E949 detector -- Powerful and redundant particle

ID

Resolutions:P/P ~ 1.1%; R/R~ 3.0%; Rejectionsfor ~for photon with 4 sr coverage.

Top half of end view

-ID from its decay chain.

dE/dxR/P

Photon veto

E787

E949

This is a team effort!

16 institutes and universities in 4 countries.

…more than 60 physicists from 6 countries.

BNL/FNAL/SBU/UNM, U.S.AIHEP/INR, Russia Fukui/KEK/Kyoto/NDA/Osaka, Japan TRIUMF/UA/UBC, Canada

Unique Strategy for data analysis

Full data set

1/3 data 2/3 data

Beam bkg

Background study

Background estimate

Step 1

Step 2

Step 3

Step 4

Open the box Step 5E787/E949: we bought a one-way ticket,-no way back after opening the box!

E787/E949: we bought a one-way ticket,-no way back after opening the box!

Cuts tuningE787: <0.1 eventE949: <0.5 event

Background suppression

Cut

Bkg

Kinematics cuts(p/R/E)

Particle ID

Photon veto

Timing cuts

K

K

Beams

Knp, Kl-

How to achieve a reliable background estimate?

Blind analysis in tuning the cuts.Bifurcated analysis in estimating backgrounds.

1. Form two independent cuts.2. Estimate the background.3. Check the correlation.

Pathology background

K+

K+

B4

Target

Pions scattered back into the target overlaying a non-decaying kaon can make a fake signal.

x

y

zr

Reason: track reconstruction only down to the kaon decay vertex.Remedy: check the hits in the opposite direction of the track.

Readout fibre

Backgrounds outside the boxMotivations:1) To check the correlations;2) To estimate systematic errors.

Bkg. C Prob. 0.85 0.17

1.15 0.67

1.06 0.40

Fit Nobs. = c Npred.

Npred.

Nobs.

Deviations of c from unity give the systematic errors.

Deviations of c from unity give the systematic errors.

Acceptance

Br(P.D.G value is 0.211±0.001

Phase space and nuclear interaction effects from Monte Carlo.Acceptance loss due to PID, photon veto, timing and other kinematics cuts directly measured from data.

E949 acceptance: 0.0022 ± 0.002E787 acceptance: 0.0020 ± 0.002

Verification from B(measurements.

Impact on CKM matrix

More data needed for reducing the uncertainty.

New neutral kaon experiments (for example KOPIO) expected for further justification.

More data needed for reducing the uncertainty.

New neutral kaon experiments (for example KOPIO) expected for further justification.

Many thanks to A. Höcker & J. Ocariz et alThe CKM fitter group, hep-ph/0406184

First E949 resultsIlektra A. Christidi

A better determination of Vtd from K+ π+νν will provide a sensitive test of the SM by comparing the results from the K and B sector and probe new physics

|Vub|, |Vcb| : tree-level semileptonic B decays

|Vtd| : ΔMBs/ ΔMBd & K+ π+νν

sin2β (& 2α) : CP assymetry in hadronic B decays A(Bd J/ψ Κs

o) & BR(K+π+νν)/BR(Kο πονν)

εκ comes from CP violation in the K sector

Measurements of unitarity triangleMeasurements of unitarity triangle


Likelihood ratio methodLikelihood ratio methodTo calculate confidence levels:

• Poisson probability for sg+bg and for bg only:

• Sum over all configurations that give X Xobserved (less “signal-like”):

• Modified Frequentist confidence level:

Pe s b

d

Pe b

d

s b

s bi i

d

ii

n

b

bi

d

ii

n

i i i

i i

( ) ( )

!

!

1

1

C L P X X P

C L P X X P

s b s b o b s s bX d X d

b b o b s bX d X d

i i o b s

i i o b s

( )

( )

({ } ) ({ } )

({ } ) ({ } )

,

,

C LC L

C Lss b

b


Some more details…Some more details…

The probability that known bg sources give a configuration of 3 events as signal-like as the 2 E787 + 1 E949 events or more, is 0.001

(compare to 0.077 for E949 alone)

Central value, although smaller, is still ~ 2 SM , but consistent within errors…

0.0055 < |Vtd| < 0.0271


Effect on unitarity triangleEffect on unitarity triangleThanks to Gino Isidori

Limits from measurements of:

BR(K+ - π+νν) : ------- central value

68% interval

90% intervalεΚ

|Vub|/|Vcb|

sin2β

ΔΜd , ΔΜs /ΔΜd

Combined all but K+ - π+νν (68%, 90%, 95%)

Depend on Bd mixing

Without constraints that depend on Bd mixing

Documents

K → 崩壊の探索と 京都グループの活動

K → 崩壊の探索と京都グループの活動