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
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