Status of E391a

G.Y.Lim

IPNS, KEK

KL decay

Experimental difficulties Tiny branching fraction

Great number of KL decays Weak Kinematical constaints

Background suppression From KL decays

KL

Other modes Beam related events

production Accidentals

What would be a main obstacle ? How to estimate backgroud level?

KTeV, Phys. Lett. B447(1999)

Hyperon decays – lower momentum ?Multi- events – tighter vetoing ?Neutron events – removing sources ?

KEK-PS E391a The first dedicate experiment

To confirm the methodology Large acceptance

Single ( ) detection Background rejection

Tight vetoing High PT selection

E391a concepts Pencil beam Hermetic veto system Double decay chamber Highly evacuated decay region

Step-by-step approach

J-PARC

E391a collaborationJoint Institute for Nuclear Research (Dubna), Russia

High Energy Accelerator Research Organization, KEK, Japan

Department of Physics, Kyoto University, Japan

National Defense Academy of Japan, Japan

Department of Physics, National Taiwan University, Taiwan

Department of Physics, Osaka University, Japan

Department of Physics, Pusan National University, Korea

Research Center for Nuclear Physics, Osaka University, Japan

Faculty of Science and Engineering, Saga University, Japan

Department of Physics, University of Chicago, USA

Department of Physics, Yamagata University, Japan

More than 50 collaborators from 11 institutes from 5 countries

Milestones of the E391a

Dec.1996: conditionally approved Mar.1999: constructed the beam line July 2001: approved Oct. 2002: engineering run Jan. 2004: finish detector assembling Feb. –June 2004: 　 Data taking Feb. –Mar. 2005 : 　 Run-II Fall 2005 : Run-III (conditionally approved)

Detection Principle

KL

Nothing

pure CsI calorimeter 4 veto

system

Clear single 0 with high PT

Related to the KL decays

KL

Main possible background source Br(KL0)/Br(KL00)~10-8

High detection efficiency Hermetic veto system Double decay chamber Low detection threshold

High PT selection with pencil beam Reject dominant multi- events

High energy -missing Rejection of odd pairing

Making a correct inefficiency table for -detection

Related to the Beam

Hyperondecays n

Short lifetime/low momentum Length of beam line

o production n + A o + n + A With detector components

Clean beam With Residual gas

Evacuated decay region 0.1 S.M. event @ 10-5 pa

Source Event#/E391a-Sensitivity

Λ at target 0.0044

Λ at C6 < 0.11

Λ by n with detector <0.002

π by n with residual gas

0.0005 ～ 0.0062

　 π 　 by n with detector

0.014 ～ 0.114 at CC-04

total <0.3

Pencil Beam

5 stages of collimators made of heavy metal (tungsten)

2 stages of sweeping magnets

Thermal neutron absorber

Lead/Be plug for controls gamma/neutron flux

Fine alignment using telescope

GEANT M.C. agree well to the measurements

E391a detector setup

KL beam

Recycled 576 Un-doped CsI

(70X70X300 mm3 (from E162)

50X50X500 mm3 (from KTeV))

CC03 (Tungsten + Scin.)

Covered by plastic scintillators

(Charged Veto (CV))

Assembled three parts

Detector Integration was finished on Jan 22, 2004

Detector inside vacuumTo reject o production by neutron interaction with residual gas

Differential pumping technique

80 μm LDPE

15 μm EVAL (aluminized)

15 μm nylon

80 μm LDPE

Data taking Run time (physics run)

Run-I : Feb. 16th – Jul. 1st 2004: (~60days) KEK 12 GeV PS : Incident protons

2.2 X 1012/spill at target 2-sec spill length & 4-sec repetition

KL flux in front of detector 5x105 /spill Peak momentum : ~2 GeV/c

Trigger : No. of cluster >=2 Energy threshold for a cluster : 60 MeV. DAQ live-time ratio : 75 % Vacuum : ~10-5 Pa

Online event display

Calibration Energy & timing

Cosmic-ray muon. CsI, barrels Punch-through muon. Collar counters 0 production at Al target.

Precise calibration of CsI

Muon Data

(KEK-preprint-2004-85, accepted for publication in NIM.)

0 production at target

Normalization channels (without tight vetoing)

Invariant Mass of 4(GeV/c2)

MC

data

Reconstructed vertex of KL (cm)Invariant Mass of 6(GeV/c2)

03K02KKKL KL KL

6 events 4 events 2 events

Vertex-finding cut Vertex-finding cut + fusion-cutPT+decay-position cut

Monte-Carlo simulation well reproduces data.Pure kaon sample. Veto counter study

2 analysisData without tight veto

Reconstructed vertex (cm)

PT(G

eV/c

)

M.C. for KL decays ( Without Normalization)

KL

KL

KL

KL

o produced at CC02

o produced at CV (?)

MC ~material in front of CV?~

CH2, ~1g/cm3

10 g/cm3

& 2 mm-thick

PT(G

eV/c

)

Reconstructed vertex (cm) Well reproduces data distributions.

Remove neutron events

B C

A

D

Kinematical constraints for two gammas

1) Distance between two gammas

2) Energy balance of two gammas

Unexpected acceptance loss

Veto Optimization ~Main-barrel timing (low E sample)~

KL pure sample

B.G.sampleupstream

downstream

Backsplash should NOT veto! ① Real photon hit should veto.② Backsplash should NOT veto.

① ②early late

Results of 1-Day analysis

Intensive study using part of data

obtained during 1-day (2 %)

B.G. events can be controlled

Acceptance loss

- Neutron related events

- Tight photon vetoing

More statistics – 1 week analysis

-o production at the detector

- To study fiducial region event

Clearer beam condition(Run-II)S.E.S ~ 7103.8 @ 1-day statistics

1-Week Analysis Lager size of data sample

Factor of 5 Deeper understanding about

the background events Another sources ? Access to the KL decays

Detailed M.C. study for veto counters Pure M.C. + accidental overlay Reproduce the low energy

distribution Finer veto counter tuning

Preliminary results will be reported at the KAON 2005

Energy distribution of veto counters

Run-II To fix the dropped membrane Install additional collimator in front of detector Minor up-dates of detector systems Apply the Be absorber (better KL/n ratio) Finer tuned DAQ / beam condition Data taking during 40 days from Feb. 2005

Beam-line endpoint

Detector upstream section

CC0030cm-long x 40φ(20mm-W / 5mm-Scinti.)

Membrane Correction

Better quality of data (online plots)

Reconstructed vertex (cm)

PT(G

eV/c

)

Run-I Run-II

Run-II analysis Run-III on this fall( Conditionally approved )

Run-I

Run-II

PT Vertex

E E

(GeV/c)

(GeV) (GeV)

(cm)

Better quality of data

Summary KEK-PS E391a – The first dedicated experiment

To get a guideline for the precise measurement Lots of list to study (hoping to various suggestions)

Successful data taking To realize a trial of one method We are on right track

Too early to declare To find problem To fix it

1-day analysis Close to the KTeV limit Feed-back to the Run-II

1-Week analysis Preliminary results at the KAON2005

Better data quality at Run-II Run-III in coming fall

Acceptance for KL Acceptance loss due to kinematical M.C. Acceptance loss due to veto Pure Kaon samples

Decay probability is included

Cuts Acceptance

Decay + geometry + skimming 5.49x10-3

E > 200MeV 3.55x10-3

Distance between 2-‘s >50 cm 2.77x10-3

0.92 < E1+E2+E3/Ecluster <0.98 1.71x10-3

0.6< Emax/Ecluster < 0.92 9.46x10-4

Energy balance betw. 2-‘s< 0.5 7.56x10-4

300 < Z < 500 cm 0.12< PT < 0.25 GeV/c 3.20x10-4

Vetos 1.21x10-4

Prospect ~Run-II~ Membrane was fixed.

Additional collar counter was installed. to reduce halo-neutron effects.

Be absorber was installed in the beam line. better n/ ratio, less halo-neutron.

CC00

Membrane at Endcap

W/Scintillator Sandwich(2.5I)in front of detector.

We are working hard on (and enjoying) this challenging experiment.

Kaon Reconstruction (KL30 ,20 ,)

No. of reconstructed -cluster : equal to 2,4,6

(E >= 50MeV) No other cluster ( E < 20 MeV) in CsI 0 reconstruction (assuming 0-mass vertex Z) Best chi2 Kinematical cuts

- Chi2 < 2

- 2nd Chi2 >20

- Pt < 10(MeV/c)

- Beam size< 4cm

1

2

3

4

z1

z2

beam direction

Pt

Example : KL20