Status Report of Neutral Kaon Study byNeutral Kaon Spectrometer 2Masashi Kanetafor the NKS2 Collaboration

Department of Physics, Tohoku University

The experimentInvestigation of strangeness production mechanismThreshold region of productionNo resonance decayGood for comparison with modelsSmall cross-section, i.e. high statistics is requiredNeutral channel in strangeness photo-productionPast experiments studied by K+ productionNot enough data for g+n K0+L(S0)Neutral Kaon Spectrometer (NKS) experiment at LNS-TohokuSuccessfully done in 2004 using NKSUsed TAGX spectrometer of INSSome weak points was found in TAGXNo coverage on forward regionNo Stereo wire in Chambers

Now we are on the second stage (NKS2)New Spectrometer was designed and constructed in 2004-2006Runs in Mar., Jun. 2006 by Carbon target

The NKS2 CollaborationDepartment of Physics, Tohoku UniversityN. Chiga, T. Fujibayashi, Y. Fujii, K. Futatsukawa, O. Hashimoto,K. Hirose, K. Hosomi, A. Iguchi, H. Kanda, M. Kaneta, T. Kawasaki,D. Kawama, Y. Ma, K. Maeda, N. Maruyama, A. Matsumura,M. Matsuzawa, M. Mimori, K. Miwa, Y. Miyagi, H. Miyase,S.N. Nakamura, K. Nonaka, Y. Okayasu, M. Sumihama, H. Tamura,N. Terada, K. TsukadaLaboratory of Nuclear Science, Tohoku UniversityT. Ishikawa, T. Nakabayashi, H. Shimizu, K. Suzuki, T. Tamae,H. YamazakiDepartment of Electrical and Electric Engineering, Akita UniversityA. SasakiDepartment of Electrical Engineering, Ichinoseki National College of TechnologyO. Konno

Tagged Photon Beam at LNS-Tohoku200 MeV electron beamfrom LINAC1.2 GeV Stretcher-Booster RingPhoton taggingsystemNeutral KaonSpectrometer 2Sweep magnet

Tagged Photon Beam at LNS-TohokuPhoton beamElectron beam on carbon wireTagged by electron which has energy lossE=0.8-1.1 GeVfrom 1.2GeV electron beam6 MeV coverage per tagging counter TaggerFingerTaggerBackupRadiator

Neutral Kaon Spectrometer 2

Detector Setup beam680 magnetDipole magnet with 0.42 T800mm radius of the poleTargetNatural CarbonLiquid deuteronInner HodoscopeOuter HodoscopeTrigger counterTime of flight measurementStraw Drift ChamberCylindrical Drift ChamberTracking (momentum)Decay vertex findingElectron veto counter (EV)e+e- background suppressiong + n K0S + X p+ p-To measure1700 mm3720 mm

680MagnetCylindricalDriftChamberElectron Vetog beamInner HodoscopeStraw Drift ChamberOuterHodoscope

Run SummaryTwo weeks for the run 2006-JuneNatural Carbon targetFinished with no physical injury 2/3 of time is used for setupto make counters readyto make efforts of noise reductionto fix some troubles of DAQ and chamber readoutto re-wiring to fix wires loosedTrigger study and data taking4 days for trigger study~11 hours for data takingUseful data~2.7 x 106 eventsNumber of K0S estimated = ~10

Particle IdentificationPID by 2D cut on TOF vs. momentum plotTOF between Inner Hodoscope and Outer HodoscopeMomentum is reconstructed by hits on CDC and SDC1/bcharge sign momentum [GeV/c]

TrackingTrack is reconstructed from hits on CDC and SDC

V0 Vertex DistributionMain background is e+e- pair produced by airOpening angle cut works to remove background in off-line analysisHuge number of background in data...Vacuum pipe was shortNow (Sep. 2006), the window stays at ~20 cm from the target for incoming run

SummaryWe have finished the construction of Neutral Kaon Spectrometer 2 (NKS2)The commissioning run was carried outUsed carbon targetThere were many troubles.., howeverFinally we could move to data taking stage Analysisthe code is ready to usesame with NKSneed to have more work for calibrationReady to long run for data taking

OutlookConstruction2004~2005Commissioning2006, Mar. and Jun.Carbon targetDetector start-upTrigger StudySome modification of detectors after run2006 SepTrigger Study with longer vacuum pipePhysics data taking with Carbon target

Deuteron target run2 weeks/month over 5 months

Backup

p distribution from K0S

K0 momentum [GeV/c]coslabBlack contour:AcceptanceRed contour: D2 targetK0 productioncross-sectionfrom Kaon-MAIDmodelComparison acceptance -NKSNKS2Eg = 0.9-1.0 GeVEg =1.0-1.1 GeVEg = 0.8-0.9 GeVNote:CLAS coverage| cosq | < 0.80.0 1.01.0

0.50.0 1.0

Gain of Acceptance with NKS2MC (GEANT4) studyChecked by two distributions for inputKaon-MAIDSLA (rkk=-1.9)

Note: In NKS, K0 and Lambda yield (recorded and reconstructed) are almost same

Time to Position dl [cm] dl [cm]Time [nsec]Time [nsec]Not so goodc2

Liquid Deuteron TargetTemperature : 19 0.1 KPressure (residual gas) : 50 2 kPa g density r ~ 0.17 0.01g/cm3beamThe windows on the beam line : 75mm mylar filmLiq. D230 cm