status report on rare k decays - experiment -

July 2-8, 2006 T. Nomura (Kyoto U.), BEACH 2006 - Lancaster, England

1

Status Report on Rare K Decays

- Experiment -

Tadashi Nomura(Kyoto University)


2

Rare K Decays

Considering the program,I will concentrate onK experiments


3

K in the Standard Model

FeatureZ penguin and Box diagramTop in the loop, Sensitive to Vtd

Small theoretical uncertainty W Ws

id

Vis V*id

e,,

i=u,c,t

W

Z

VisV*

id ds i

11

20

2410

10)1.10.8(

)(100.1)(

AKB

11

2

5

*100

10)4.08.2(

)()Im(

102.2)(

t

tdtsL xX

VVKB


4

K beyond the SM

Minimal Flavor Violation• Flavor symmetry breaking occurs at very high energ

y and mediated via Yukawa coupling

• Small deviation from SM

Beyond MFV• New source of

Flavor symmetry breaking at TeV scale

Z

dLsL

uL(d)~uL(s)

~uR

~


5

Status of K++ experiments

•Current (Run finished)•E787/E949 at BNL

•Future•P326 at CERN


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- Current K++ experiment -

BNL E787/E949Event signature of K++

= K+ comes in, only + comes outBasic concepts

Stopped K+ experimentMeasure full kinematics of +

Energy (E) / Momentum (P) / Range (R)

PID by recording --e decay chainHermetic photon veto detectors

Momentum in K+ rest frame(= in Lab frame)


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E949 Detector

Active target (scintillation fibers) to stop K+

Chamber and the magnetic field to measure + momentum19 layers of scintillators (“Range Stack”) to measure E and RWaveform digitizer to record --e decay chain in RS counterPhoton vetoes surrounding 4 (BV / BVL / Endcap /…)

K

Side view (cutaway) End view (top half)


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E949 Evaluation of Backgrounds

P for and

K++, but short range P and NN function

K++, … rm and NN function

rm=(Rmeas–Rexpect)/R

Neural Net function for and

--e decay chain in the stopping RS

K++0

P(E,R) and Photon veto

BG level evaluated as functions of cut positions

PV rejection ~10-6 when 80% acceptance


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E787/E949 ResultRange vs Energyafter all the cuts

3 candidates observedE949 E787Simulation

Combined E787/E949

• E949 alone

solid : E949 boxdashed : E787 box

1030.189.0 1047.1)(

KBr

1009.447.0 1096.0)(

KBr

-1-2-3-4-5-6-7-8-9

-10-11-12

A factor of 2 larger than SM prediction ? Need more statistics !!


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E949 StatusPNN1 analysis finished PRL93(2004)031801

PNN2 (140<P<199) on analysis

Simultaneously taken with PNN1Goal: S/N ~ 1• 1/10 in E787 PRD70(2004)037102

• Dominant backgrounds from K2,+ scattered in the target

• PV upgrade (BVL, Beam PV) in E949 helps the BG rejection

Will be completed in < 1 year

PNN1PNN2


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- Future K++ experiment -

P326 at CERNBased on NA48 detectorDecay in flightFor BG rejection …

K+ tracking in 1GHzPID(/) by RICHHigh E 0, low ineff.Missing mass cut

80 SM events in 2 years

Details in Talk in “Future Directions” session

K+ +


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Status of KL0 experiments

•Current (Run finished)•E391a at KEK

•Future•JPARC-K (P-14)


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- Current KL0 experiment -

KEK E391a


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KEK E391a DatasetRun I Feb 04 - Jul 04

Membrane problem (described later)

Run II Mar 05 - Apr 05Fix membrane problem

Run III Nov 05 - Dec 05New BA (in-beam PV: PWO+Quartz sandwich)


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E391a AnalysisEvent Reconstruction

Find 2 clustersReconstruct Z vertex

assuming M(2)=M(0)Calculate PT


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E391a Background in Run I

This problem was fixed after Run I


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E391a Result (Run I 1week)

BG EstimationCore n multi 0

Bifurcation(PV cut/EH cut)

Halo n CC02Z tail from

“0 run”(put Al in beam)


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E391a Result (Run I 1week)

S.E.S=[9.11 0.20(stat.) 0.64(syst.)] x 10-8

Dominant systematic error• Data/MC mismatch in EMainBarrel (4.2%)• Data/MC mismatch in shower shape in CsI (4%)

BR < 2.1 x 10-7 (90% C.L.) A little bit updated from Kaon2005 by analysis refinement

2.8 times improvement of current limit

-1-2-3-4-5-6-7-8-9

-10-11-12


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E391a StatusRun I

Finish 1 week data sample will submit to PRLProcess under going for Run I full period

Run II / III (Blind analysis)Glance at 1 week sample, improvement confirmed1/3 of Run II sample now being studiedWill open the box by the end of 2006 ? (Hopefully) Finish full analysis by the end of 2007 ? (Hopefully)


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- Future KL0 experiment -

J-PARC K experimentJ-PARC = Japan Proton Accelerator Research ComplexNow under construction at Tokai-siteHigh intensity PS

30 / 50 GeV3x1014 ppp3.4 sec cycle

First beam in 2008


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J-PARC K experiment : Step1

•16 degree production angle•Pencil beam with 9 str

Proton


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J-PARC K : Detector upgrade

Calorimeter : use KTeV CsI (KEK and FNAL under negotiation)

More radiation length, reduce shower leakage Better segmentation (7cm 2.5cm), reduce fused photons


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J-PARC K : Detector upgrade

In-beam photon veto detectorKOPIO-type Lead-Aerogel “sparse” sandwich

Less sensitive to beam neutron• Efficiency <10-3 for En=1GeV

(cf) neutron rate: ~0.5GHz, En>0.1GeV


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J-PARC K : Goal and Time-line

In Step1, observe ~5 SM events, with S/N=1.43 years run, 2010-2012Acceptance loss, estimated from E391a experience

In Step2, collect >100 SM eventswith new detector, and dedicated beam line

Proposal Submitted in April, 2006 (J-PARC P-14)First J-PARC PAC in last weekend


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Summary (I)

K among Rare K experiments• Unitarity triangle via K decays• Explore physics beyond the SM

K++3 candidate events observed by BNL E787/E949 • BR = 1.47 +1.30 -0.89 x 10-10

New experiment at CERN : P326• Aims to observe ~100 events


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Summary (II)

KL0First dedicated experiment KEK E391a

successfully finished• On analysis• Sensitivity < 10-8 expected

Proposal to JPARC : P-14• Step1 for discovery, with E391a detector : ~

5 SM events • Step2 for precise measurement :

>100 SM events

status report on rare k decays - experiment -

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