Search for K L →π 0 νν Takao Shinkawa National Defense Academy Particle Physics [email protected]

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Search for KL→π 0 νν Takao Shinkawa National Defense Academy Particle Physics [email protected] August 7, 2008

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Transcript of Search for K L →π 0 νν Takao Shinkawa National Defense Academy Particle Physics [email protected]

  • Search for KL0Takao ShinkawaNational Defense AcademyParticle Physics [email protected] 7, 2008

  • OverviewPhysics of KL0decayKEK E391a at 12-GeV PS Data taking was done in 2004-2005. Run data analysis has been recently completed.PRL 100, 201802(2008.5)E14 at J-PARC Stage 2 recommendation by PAC in July 2007

  • Physics Motivation KL0FCNC loop diagrams s dDirect CP violation CP - + Standard Model PredictionBR= (2.490.39) x 10-11Theoretical uncertainty 1-2% Imaginary part of Vtd () Different between K and B signifies new physics beyond SM. sdtWZ0K0L0K++1Vtdunitarity triangle

  • Beyond the Standard ModelGrossman-Nir limit model independent limitF. Mescia, CKM 2006KL0 is one of most promising process in a search for new physicsGrossman-Nir limit model independent limitBr(KL0
  • KL0search before E391aBr( KL0 )SM = (2.490.39)x10-11L.S.Littenberg extracted a limit from KL00 decay experiment. Br(KL0)< 7.6x10-3(90%C.L.) (1989)KTeV at Fermilab searched for KL0+nothing by two ways. 0e+e- (Br=1.2%) Br( KL0) < 5.9x10-7(90%C.L.) (2000) 0 one day data Br(KL0 ) < 1.6x10-6 (90%C.L.) (1999)

  • E391a collaborationStarted by Takao Inagaki in 1995 with 7 other members.

    Now 12 institutes, ~50 membersDept. of Physics, Pusan National Univ. Dept. of Physics, Saga Univ.Joint Institute for Nuclear ResearchDept. of Physics, National Taiwan Univ.Dept. of Physics and Astronomy, Arizona State Univ.KEK & SOKENDAIDept. of Physics, Osaka Univ.Dept. of Physics, Yamagata Univ.Enrico Fermi Institute, Univ. of ChicagoNational Defense AcademyDept. of Physics, Kyoto Univ.Research Center for Nuclear Physics, Osaka Univ.

    5 countries: Japan, the US, Taiwan, South Korea, and Russia

  • Experimental MethodKL0 decay two photons w/o any other observable charged or neutral particles. Constraint of two photon effective mass, m= m0 gives distance to the decay point.

    K0Lphoton detectorhermetic photon veto 12distance two photon energies and positions

  • Narrow (pencil) beamWith pencil beam, decay vertex Zvtx is defined from beam direction and vertex distance.Transverse component of kinematical component PT can be estimated.Edecay point ZvtxKLbeam pencil beamPTdistance PT0 = PT1 + PT2Most important constraints for KL0

  • Experimental Setup

  • Neutral beam lineProtons 12-GeV PS 2 x 1012 POT/4s (duty 50%)Neutral Beam production angle 4 degrees core neutron/KL 4060 solid angle 12.6 str (=2 m radian) pencil beam 6cm at the middle of the detectorPKL peak at 2 GeV/c (mean 2.6 GeV/c)Halo/core 10-4 NIM A 545, pp.542-553(2005)

  • The E391a Detector10mL x 3.5 m

  • Features of E391a apparatusDecay regionHigh vacuum: 10-5 Pato suppress the background from interactions w/ residual gas

    Detector componentsSet in the vacuum: 0.1 Paseparating the decay region from the detector region with membrane: 0.2mmt filmCsI calorimeterCharged Veto (CV)Main Barrel (MB)Front Barrel (FB)

  • Electromagnetic CalorimeterUndoped CsI crystal 7x7x30 cm3(16X0) 496 blocks specially shaped 80 blocks sandwich type 24 blocks Charged veto(CV) 6mmt plastic scintillation counters in front of CsI and beam side

    190cm beam hole 12cmx12cm

  • Photon VetoSampling counterAround the decay region Main Barrel (MB) 13.5 X0 5.5 m Front Barrel (FB) 17.5 X0 2.75 mAround the beam Collar counter CC00,CC02-07Beam region BA, (alternating layers of lead, quartz, and scintillator)

  • Electronics and DAQNumber of channelsCsI calorimeter: ~600chVeto counters: ~400chAmpDiscri ModuleDiscrimination for TDCSet near the detectorlow noise; min. threshold: ~0.5 mV (ex. ~0.7MeV for CsI)8ch sum for the triggerTriggerLogicCsI hardware clustering (N>1) (thres. 80MeV) + Veto (20-100MeV)~300 events / 2 sec spill = 150HzDAQ live time~90%

  • Run SummaryRunning conditions K0 beamline in the East Counter Hall of KEK 12 GeV PSIntensity:2 x 1012 protons on target (POT) per 2sec spill, 4sec cycleproduction angle: 4, KL peak momentum 2GeV/c, n/KL ratio: 60~40

    Physics and calibration runsRun I: February to July of 2004 w/o Be ~3 x1018 POT problematic Run II: February to April of 2005 w/ Be~2 x1018 POT good conditionRun III: October - December of 2005 mostly w/ Be~1.4 x 1018 POT good condition

  • Result from Run-I Using 10% of Run-I data (Run-I one week)

    set new limitBr < 2.1x10-7(@90%C.L.) (PRD 74:051105, 2006) a factor of 3 improvement to KTeV result. CVCC02

  • A serious problem in Run-IBeam core hits the membrane, which are accidentally drooped into the beam-line -core neutron background-This problem was fixed before Run-

  • Analysis

  • Run analysis overviewKL reconstruction KL flux calculation6: KL000 (Br=19.56%)4: KL00 (Br=8.69x10-4) 2: KL (Br=5.48x10-4)Normalization by MCSystematicsKL0 searchBackgroundsResults

  • KL reconstruction0(KL) reconstruction w/ 2 photons

    KL reconstruction w/ KL20, 30Take the best 2 for the vertex distribution in paring

    CutsPhoton Vetoes: typically O(1) MeVKinematic cutsPhoton quality cuts

  • Channels used for normalization (KL flux estimation) and tuning of MC simulation KL30Signal regionCVPhoton Veto data MC

  • PV onlyInvariant mass of 20PV + kinematics 4 invariant mass distribution in particular the tail due to KL30 (2 out of 6 photons were undetected) was well understood by MC.M4(GeV/c2)

  • Summary of KL flux

    ModeSignal Events(Full Data Set)Acceptance(with Accidental Loss)Flux (w/ systematic errors)Discrepancy(X - 00) /00K L 20,685 (0.697 0.004Stat)%(5.41 0.37) x 109 5.0%KL 001494.9 (1500 - 5.1)(000 contribution) (3.35 0.03Stat) x 10-4(5.13 0.40) x 109 0%KL 00070,054 (7.13 0.06Stat) x 10-5(5.02 0.35) x 109-1.9%

  • Systematic Errors on the flux

    CsI Veto6.1%Decay Vertex (Z) Spectrum2.3%Decay Vertex (Radial) Spectrum1.8%Charged Veto1.3%Fusion Neural-Network1.3%Photon Hit Position (CsI Position)1.2%23 Others (Total)2.9%TOTAL (In Quadrature)7.7%

  • Search for KL0

  • KL0 searchBlind analysis was taken to remove bias.Hide signal region (+ Control region)The blind Box: on PT - Z plotAll backgrounds are estimated w/o looking into the BoxAfter completion of BG estimation, the Box was opened

  • Kaon backgroundsBG from Kaon decaysKL00missing 2 photonsMain background in Kaon decaysKLby PT mis-measurement

    PTZKL20KL2signal region

  • Backgrounds from KL00 decays Estimated by MC simulations, relying on the good reproduction of the 00 distribution at low mass by KL000 MC. The missing 2-photon feature is similar. MC data = 11xdata BG=0.11 events.

  • Backgrounds from the other KL-decays ZKL2Energy mis-measurement or response tail can make higher PT events, but the a-coplanar angle cut is quite effective to reduce them.KL charged (Ke3, K3 and charged-K3)Backgrounds from all these decays are negligibly smallPTKL MC No cuts

  • Halo neutron backgroundsTails of 2produced by halo neutrons at the detectorsCC02Tail of energy measurement due to leakage or mis-measurementCV Multi-0 + odd combination (548MeV) : shift of vertex due to the assumption of M2 = M0

  • CC02 backgroundS/NUpstream edge of the signal regionEstimated from the special run data, which were normalized to the CC02 events. Upstream edge of the signal region was determined by S/N.Al plate runCC02Signal regionm0CC02 BG 0.160.05 ev

  • CV-0 background Estimated from the data using a bifurcation method. We also checked the reproduction of CV events by a halo neutron 17 events, MC: 18.26.1 eventsCut setsset-up cutsupstream veto detectors, CsI, and 0 kinematicsset Adownstream veto detectorsset Bgamma selectionSignal regionCV-0 BG 0.080.04 evCV regionNAB=NABxR_B

  • CV- background Estimated from MC with 200 times statistics, after carefully checked the cross section, momentum and PT distributions using the target run data.

    Al plate run16events CV-BG 0.060.02 eventsregionm

  • Background summary(1) 300-340cm : 1.90.2CC02: 1.90.2observed: 3 events (2) 340-400cm: 0.150.05CC02: 0.110.04CV-: 0.040.02

    (3) 400-500cm: 0.260.11CC02: 0.050.03CV-: 0.020.01CV-0: 0.080.04KL00: 0.110.09 0.41+0.11 for signal region

    (4) 300-500cm, Pt

  • Open the signal regionNo event observed!!

  • Result of Run IIAcceptance: A = 0.67%Flux: NKL = 5.1 x 109S.E.S = 1 / (ANKL) = (2.9 0.3) x 10-8

    Upper Limit0 event observed 2.3 events w/ Poisson stat.Br(KL0) < 6.7 x 10-8 (@90% C.L.) PRL 100, 201802(2008.5)Runhas similar quality. 70%of Rundata.Analysis is going on.

  • J-PARCHigh intensity proton accelerator at Tokai 56 km from KEK beam intensity x100 12-GeV PSAccelerator construction will be completed in this year.

  • Step by Step approachTo event observationKEK E391aThe first experiment dedicated to KL0 To establish the experimental method

    J-PARC E14Step1Prompt startThe E391a DetectorCommon beamlineThe first event observationgoal: ~3 eventsStep2Longer decay volume and larger detectorHigher intensity beamlinegoal: ~100 events

  • CsI 7x7x30cm3 2.5x2.5x50cm3 , 5x5x50cm3 (from KTeV)Reduce leakageBetter positioningReadout ElectronicsWave-form digitizationNew DetectorsBeam Hole Photon VetoFull active CC02MB linerNew CVE14 at J-PARC

  • E14 tentative schedule2009 Beam line construction Beam survey KL flux measurement with KL+-0 decay.Flux might be three times more.2010 CsI stacking Engineering Run2011 First run 1 event/year

  • SummaryKEK E391a the first dedicated experiment for KL0 decay. Br(KL0)< 6.7x10-8 (90%C.L.) Rundata analysis is going on.J-PARC produces 100 times more intense proton beam than KEK 12 GeV PS. E14 is taking step by step approach to precise measurement of the branching ratio of KL0decay.

  • Backup Slides

  • KL beam Beam profiles at the beam exit by MC.KL momentum distribution at the beam exit by MC.

  • Vetoes

    counterthreshold (MeV)commentsFB1.0take sum of inner and outer channelsCC021.0MBinner: 1.0outer: 1.0E = sqrt( Eup * Edn), x0.95 for dataCVouter : 0.3 inner : 0.7convert gamma position to crystal number,then check corresponding CV planeCsI d < 17 cm : 10.017< d < 25 cm : 5.02.0 d > 25 cm : 2.0require the local flagd: distance from the gamma position to the crystalintermediate region (17-25cm): threshold = 5.0 - (3.0/8.0) * ( d-17)Sandwich2.0CC032.0CC04calorimeter : 2.0scintillator : 0.7CC05calorimeter : 3.0scintillator : 0.7BAscintillator sum : 20.0quarts : 0.5 MIPstake AND of both conditionsBCV0.75E = sqrt( Eup * Edn)CC0610.0CC0710.0BHCV0.1CC002.0

  • gamma, 0 cuts

    minimummaximumcommentssignal box z-vertex340 cm500 cmsignal box Pt0.12 GeV/c0.24 GeV/cgamma time difference-3.40002.8922gamma energy low0.25 GeVgamma energy high0.15 GeVgamma size 5MeV3gamma size 1MeV5gamma energy ratio0.88gamma TDI2.0gamma RMS4.0gamma energy balance0.75(Ehigh - Elow) / (Ehigh + Elow)gamma distance15 cmgamma hit position18 cmsquare regiongamma hit radii88 cmcircleacoplanarity angle45 degrees0 energy2.0 GeV21.02 = ( (r1- rec)2 / r12 )projection R(0 kinematics cut)in the (z, Pt/Pz) plane, take the inside of(300, 0.1), (400, 0.1), (500, 0.15), (500, 0.34), (300, 0.2)reconstructed KL momentum2.0 GeVassuming the invariant mass of nu-nubar system is 0: two body decay

    Au: trilinear scalar couplings in the soft SUSY breaking termsdetector region is also evacuatedwe appreciate the accelerator peoples effort for the operation of the PS