Status of the KEK E391a Status of the KEK E391a ExperimentExperiment Status of the KEK E391a Status of the KEK E391a ExperimentExperiment

G. Y. LimIPNS, KEK

質量起源と超対称性物理の研究

2005年 3月 7日

IntroductionIntroductionIntroductionIntroduction E391a searching for KL decay

Very clean FCNC process Golden mode for a test of the SM and sear

ch for a new physics The first dedicated experiment to the KL decay

Contents Detection principle Data taking The 1st version of analysis

(M. Doroshenko – Ph.D. theses) Run-II Summary

JPARC, 　KOPIO

A dream of theorist and a nightmare of experimentalist

Detection PrincipleDetection PrincipleDetection PrincipleDetection Principle

KL

Nothing

pure CsI calorimeter 4 veto system

Clear single 0 with high PT

High High -detection efficiency-detection efficiencyHigh High -detection efficiency-detection efficiency

Expected main background is KL

4veto system without any dead space

Low energy threshold for -detection Noise reduction Accidental hits

Making a correct inefficiency table for -detection

Pencil beam and vacuum systemPencil beam and vacuum system Pencil beam and vacuum systemPencil beam and vacuum system

E391a detector setupE391a detector setupE391a detector setupE391a detector setup

KL beam

E391a detector setupE391a detector setupE391a detector setupE391a detector setup

Data TakingData TakingData TakingData Taking Data taking during 18, Feb ~ 1, July 2004

Detector/ DAQ tuning (44 shifts ) - with low intensity (30 shifts) Beam break due to water leakage of beam line magnets (21 shifts) Additional fine tuning of DAQ, beam line (8 shifts) Start stable data taking from 15th, March

~ 28, April (116 shifts) 19th, May ~ 21th June (71 shifts)

Calibration Run Data with air / production (24 shifts)

6 TB of data Tape library on KEK computer center

Data analysis 1 Day 1 Week (1/10 of the full data) We are trying to understand characteristics of the backgrounds correctly estimate the sensitivity

Fine monitoring channelsFine monitoring channelsFine monitoring channelsFine monitoring channels

MC

data

03K

02K

MC

data

MC

data

MC

data

03K

02KK

Invariant Mass of 6(GeV/c2)

Invariant Mass of 4(GeV/c2)

Reconstructed decay vertex of KL (cm)

6- event sample 4- event sample 2- event sample

Pure data sample for Photo Veto counters

M.C. reproduce data reasonably

KL KL KL

Normalization for the number of KL

Pure signal and background sample for veto counter study

Study of photon veto counters (example)Study of photon veto counters (example)Study of photon veto counters (example)Study of photon veto counters (example)

Two gamma eventsTwo gamma eventsTwo gamma eventsTwo gamma events

Data without tight veto

Reconstructed vertex (cm)

CsI S

urfa

ce

PT(G

eV/c

)

KL KL

KL KL

KL e KL

Hard to explain using KL decay only

M.C. for KL decays ( Without Normalization)

KL Decay

Unexpected Unexpected oo production by Neutrons production by NeutronsUnexpected Unexpected oo production by Neutrons production by Neutrons

Various contributions to the 2-gamma sampleVarious contributions to the 2-gamma sampleVarious contributions to the 2-gamma sampleVarious contributions to the 2-gamma sample

Reconstructed vertex (cm)

Cou

nts

K2

K

Halo n

Core n

Neutron related events are dominant

n/separation

Halo neutron generate 2- in the CsI calorimeter (M.C.)

Example of n/Example of n/separationseparationExample of n/Example of n/separationseparation Shower shape at the calorimeter Distance between gammas

There are varieties in real application in detail.

Current acceptance reduce to 0.14~0.5 due to these additional cuts.

After finishing Photon Veto / Kinematical cutsAfter finishing Photon Veto / Kinematical cutsAfter finishing Photon Veto / Kinematical cutsAfter finishing Photon Veto / Kinematical cuts

B.G. events can be controlled

Acceptance loss

- Shower leakage

- Neutron related events

o production at the detector

To study fiducial region events

More statistics (in progress)

Clearer beam condition(Run-II)

BR(K) < )%90(1091.1 6 CL

@ 1-day statistics

Run-IIRun-IIRun-IIRun-II

Improve sensitivity Increasing statistics by removing the membrane by installation of CC00

Understand B.G. Characterize neutron B.G. by

comparing Run-I and Run-II Clearer condition to understand

backgrounds related to the KL decays

Data taking for 100 shifts from 2nd, Feb. 2005

Run-III in this autumn

Semi-online plots for 2-cluster events

PT (GeV/c) Decay Vertex (cm)

RUN-I RUN-II

RUN-I

RUN-II

SummarySummarySummarySummary The data taking has taken successfully

300 shifts in Run-I (187 shifts for physics data) The first version of analysis (1-day)

Good indication for data quality Identify the nature of background Make a direction for further study (expecting improvements)

Run-II After fixing a hardware trouble Clearer condition to study about the background

Diligent progress in step-by-step to the JPARC New physics search across the Grossman-Nir limit

BR(K) < )%90(1091.1 6 CL