Study of the Normalization Modes in the Search for the Rare KL 0—>Π0νν

Study of the normalization modes in 0 0 the search for the rare KL —>π νν with the KOTO detector

Brian Beckford University of Michigan On behalf of the KOTO collaboration

2018 ICHEP Intl. Conference July 7, 2018

1 ©2018, B. Beckford: [email protected] KL0—>π0νν K → πνν− and the unitarity triangle • SM predicted Branching Ratio of (KL0—>πνν) predicted to be (3.00+-0.30) x 10-11 Dominant uncertainties for SM BRs are from CKM matrix elements • Clean channel with small theoretical uncertainties (1-2%) Buras et al. • 2nd order FCNC process directly violates CP JHEP 1511

• Sensitive to New Physics (NP) beyond the Standard Model x • Results from this measurement may contribute to tighter constraints on Vtd in SM • Intrinsic theory uncertainties ~ few percent η−

• BR measurements+ overconstrain CKM BR (K+—>π νν) = (9.11 + 0.72) x 10-11 (Buras …et. al 2015) matrix and0 may provide evidence-11 (Buras for …et. NP al 2015) BR (KL—>π νν) = (3.00 + 0.30) x 10

Vts Vtd

d¯ d¯ d¯ d¯

W u,c,t s d s d u,c,t W Z0 n Z0 n

n¯ n¯ KL0—>π0νν (a) Standard Model Diagram (b) Standard Model Diagram

d¯ d¯ • SM predicted Branching Ratio ofd ¯(KL0—>πνν) predicted to bed¯ (3.00+-0.30) x 10-11 u,c,t • Clean channel with small theoretical uncertainties (1-2%) s d s u,c,t d • 2nd order FCNC process directly violates CP H 0 W e, µ,t W Z n • Sensitive to New Physics (NP) beyond the Standard Model n x ¯ n¯ • Results from this measurement may contribute to tighter constraintsn (d) onExtension Vtd in SM to Standard Model Involving (c) Standard Model Diagram Charged Higgs Boson

d¯ d¯

s d

Vts Vtd X New Physics n

n¯ (e) Beyond Standard Model Interaction In-

volving Unknown Particle 3 ©2018, B. Beckford: [email protected] Figure 1.1 Feynman Diagrams for K p0nn¯ decays L ! K—>πνν searches _ + + •Charged decayK → measurement π νν (NA62)& Grossman-Nir provides important information Bound

•SM BR (K●+—>Chargedπνν) predicated decay equally to be (9.11+-0.72)as important x(NA62) 10-11 → SM BR = (9.11 ± 0.72) x 10-11 _ 0 0 ● Set indirect limit on KL→ π νν •Grossman-Nir: indirect limit based on isospin relations between (K+—>πνν) and (KL0—>πνν) Grossman-Nir bound _ _ _ 0 0 0 + + + 0 0 0 -9 -9 •BR (KL —>●πννBR() < K4.4L→ x π BR(Kνν) <—> 4.4πνν x BR() K → π ννBR) →(K LBR(—>KπννL→) π< νν1.5) x< 101.5 x 10

E949 NA62

E949 (2008): BR = (1.7 ± 1.1) x 10-10

NA62 (2018): -11 BRBR <11<= 28 xx -1010 @ @90%CL 68% CL BR < 11 x 10-10 @ 90% CL

CERN-SPSC-2018-010 / SPSC-SR-229

10−1 10−2 Littenberg E731 (e+e-γ) −3 + - 10 E731(e+e-γ) E799 (e e γ) 10−4 E799(e+e-γ) KTeV (γγ)(e+e-γ) E391a (γγ) −5 Branching Ratio 10 KOTO (γγ) KTeV(γγ) 10−6 KTeV(e+e+γ) E391a 10−7 E391a KOTO E391a (2013) 10−8 Grossman Nir limt ~ 1.5 x 10-9 −9 ? 10 E731: FNAL 10−10 new physics? E799: FNAL Standard Model ~ 3.0 x 10-11 −11 KTeV: FNAL/KEK 10 E391a: KEK −12 KOTO: JPARC 10 1985 1990 1995 2000 2005 2010 2015 2020

5 ©2018 B. Beckford: [email protected] IPNS nese and international researchers, by operation and main- Perform both experimental and theoretical studies of atomic tenance of all the KEK accelerators, as well as studies in

nuclei and elementary particles using high energyIPNS electrons, advanced technology.nese and international researchers, by operation and main- positrons, and protons. Perform both experimental and theoreticalARL studies of atomic tenance of all the KEK accelerators, as well as studies in nuclei and elementary particles using high energy electrons, advanced technology. IMSS positrons, and protons. Research and developmentARL in technology relating to radiation Experimental setup IMSS Research and development in technology relating to radiation IPNSIPNS Research on a wide rangenesenese of andand materials internationalinternational ranging researchers,researchers,Research from on those a wide range of byby of materials operationoperationscience, ranging from computerandand those of main-main- science, science, computer science, cryogenic cryogenic science, science, and mechani- and mechani- atomic size to polymers, and biomolecules, using synchrotron cal engineering, as the foundation of overall KEK activities. 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ARL positrons, and protons. • 30ACCL GeV proton beamARL on stationary gold target Lead the accelerator science of the future and develop ad- IMSSIMSS ResearchResearch andand developmentdevelopment inin techtechnologynology relatingrelating toto radiationradiation Provide opportunities for collaborative experimentsHadron to ExperimentalJapa- Facilityvanced technologyMLF for acceleratorsRCS, Rapid andCycle Synchrotron detectors. 1 5 IPNS: nuclear physics Materials and Life Science 3 GeV proton synchrotron ResearchResearch onon aa widewide rangerange ofof materialsmaterials rangingranging fromfrom thosethose ofof science,science, computercomputer science,science, crcryogenicyogenic science,science, 3 andand mechani-mechani-Experimental Facility •Secondary neutral beam extracted forNeutrino KOTO Experimental experiment Facility IMSS: material science & life science MR, Main Ring 2 6 atomicatomic sizesize toto polymers,polymers, andand biomolecules,biomolecules, usingusing synchrotronsynchrotron calcal engineering,engineering, asas thethe foundationfoundationIPNS: neutrino ofof overallphysicsoverall KEKKEK activities.activities. 50 GeV proton synchrotron IPNS nese and international researchers, by operation and main- Injector Linac 4 0 400 MeV proton linac “K at TOkai” Perform both experimental and theoreticalradiation,radiation, studies ofneutrons,neutrons, atomic muons,muons,tenance andand of slowslow all the positrons.positrons. KEK accelerators, as AATwellAAT as studies in ACCLACCL Hadron ExperimentalLeadLead thethe Facility acceleratoraccelerator sciencescience ofof thethe futurefutureMLF andand developdevelop ad-ad-1 RCS, Rapid Cycle Synchrotron nuclei and elementary particles using high energy electrons, advanced technology.1 Hadron Experimental Facility 5 Provide opportunities for collaborative experiments toIPNS: Japa- nuclearvanced physics technology for acceleratorsMaterials and and detectors. Life Science 3 GeV proton synchrotron positrons, and protons. Provide opportunities ARLfor collaborative experimentsIPNS: to nuclearJapa- andvanced particle technology physics for accelerators and detectors. 6 3 Experimental Facility IMSS Research and developmentNeutrino in technology Experimental relating to Facilityradiation IMSS: material3 science & life science MR, Main Ring 2 6 Research on a wide range of materials ranging from those of science, computer science, cryogenicIPNS: neutrinoscience, andphysics mechani- 50 GeV proton synchrotron Injector Linac 500m atomic size to polymers, and biomolecules, using synchrotron cal engineering, as the foundation of overall KEK activities. 4 400 MeV proton linac diameter HadronHadron ExperimentalExperimental FacilityFacility MLF RCS,RCS, RapidRapid CycleCycle SynchrotronSynchrotron radiation, neutrons, muons, and slow positrons.1 AAT MLF 5 1 MaterialsMaterials andand LifeLife ScienceScience 5 ACCL IPNS:IPNS: nuclearnuclearLead physicsphysics the accelerator 33science of the future and develop ad- 33 GeVGeV protonproton synchrotronsynchrotron ExperimentalExperimental FacilityFacility 2 Provide opportunities for collaborative experimentsNeutrinoNeutrino to Japa- ExperimentalExperimentalvanced technology FacilityFacility for acceleratorsIMSS:IMSS: materialmaterial and science sciencedetectors. && lifelife sciencescience MR,MR, MainMain RingRing1 22 66 IPNS:IPNS: neutrinoneutrino physicsphysics 5050 GeVGeV protonproton synchrotronsynchrotron InjectorInjector LinacLinac 44 6 400400 MeVMeV protonproton linaclinac 5 25Hz Hadron Experimental Facility MLF RCS, Rapid Cycle Synchrotron 1 5 3 IPNS: nuclear physics Materials and Life Science 3 GeV proton synchrotron11 300m 3 Experimental Facility 4 Neutrino Experimental Facility IMSS: material science & life science MR, Main Ring 2 6 IPNS: neutrino physics 50 GeV proton synchrotron Sciences6 6at J-PARC, Japan Proton Accelerator Research Complex, in the Tokai campus. Injector Linac (Note) J-PARC is operated jointly by KEK and JAEA, Japan Atomic Energy Agency. 4 400 MeV proton linac Fig. View of the J-PARC facility 33 6 ©2018, B.2 Beckford:Walking in KEK [email protected] Sciences 3

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4 2 Walking in KEK Sciences 3 2 Walking in KEK Sciences 3 Sciences at J-PARC, Japan Proton Accelerator Research Complex, in the Tokai campus. (Note) J-PARC is operated jointly by KEK and JAEA, Japan Atomic Energy Agency.

2 Walking in KEK Sciences 3 CHAPTER 2 The KOTO Experiment

rec. π0 p vs Z T vtx

] 500 c 160 450

[MeV/ 140 T 400 P 0

π 350 120

Rec. 300 100 250 80 200 60 150 40 100 50 20

0 0 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 0 Rec. π Zvtx [mm]

2015-02-28 04:57:41

FigureKOTO beam line 2.2: Z -P distribution for K π0νν decay in MC after applying all veto and kinematic vtx T L → cuts. The black box indicates the signal region. Highly collimated neutral “pencil” beam Collimators

B = 2T Magnetic ProductionExperimental Short-lived Field Setup target 16° particles , n, K ● Located in Tokai, Japan at J-PARCγ L 3m radius ● 30 GeV protons → stationary gold target Primary proton Charged beam(30GeV)● Secondary beam of kaons,particles neutrons, & photonsFig. Depiction of neutral beam line production Target to detector distance = 21.5 m Figure 2.3: Conceptual design of the KL beam.

Primary beam line 8m namely photons, neutrons and K s, survive in the beam. Since photons do not decay and neutron L SUS Vacuum Window decay is negligibly small, hits in detectors outside the beam region are mainly derived from decay K1.1 Ducts particles from KL. Evacuated to ~10-5 Pa to Well-collimated beam suppress background This requirementT1 Target is the most critical for background16° reduction. The beam contains unavoidable “halo” components, which means a portion of beam particles exists outside the beam core. Neutrons Fig. Outer vacuum container houses or K s in suchBe Window region can make background through interaction of detector materials or the K L L → all main KOTO detectors 2γ decay, for example. The edge of the beam hence needs to be sharply collimated so as to minimize such particles. Photon Absorber 1st Collimator 2.1.4 Backgrounds Sweeping Magnet Since the required5 m “positive” signals are onlyBeam two Plug photons in the calorimeter, understanding and reducing background events is crucial. In the KOTO2nd experiment, Collimator backgroundKOTO Detector is expected to come from the following two sources. Fig. Layout inside Hadron Hall 7 Fig. 1: Schematic top view of the KL beam line used by the KOTO experiment. The primary ©2018, B. Beckford: [email protected] 25 proton beam comes in from the left. The KL beam line starts at the T1 target and the beam axis goes o↵ to an angle of 16 with respect to the primary beam line. The front of the KOTO detector is located at the end of the beam line, about 21 m from the T1 target. M. Hutcheson Prelim, 20 April 2018 8 the MR, extracted by using a slow extraction technique [8], and transported through the primary beam line to the facility [9]. The proton beam intensity is monitored by a secondary emission chamber (SEC), located after the extraction point. The primary proton beam, with a cross-section of approximately 1 mm in radius, is injected into the T1 production target. The target consists of a 66-mm-long gold target of 6 6 mm2 cross section. It is equally ⇥ divided into six parts along its length with ﬁve 0.2-mm-thick slits. The KL beam line is o↵-axis by an angle of 16 with respect to the primary proton beam line. The full kinematic reconstruction of the neutral pion in the K ⇡0⌫⌫¯ decay requires L ! a small diameter for the KL beam and was achieved with the collimation scheme shown in Fig. 2. The secondary particles produced at the target pass through a pair of collimators to shape the beam. At the exit of the second collimator, the neutral beam has a square cross-section of 8.5 8.5 cm2 corresponding to a solid angle of 7.8 µsr. Before entering the ⇥ collimation region, the beam passes through a 7-cm-thick (12.5 X0) lead absorber which removes most of the photons. A 2-T dipole magnet, located between the two collimators sweeps out charged particles. Short lived particles decay in the long collimator region leaving only KL mesons, neutrons, and photons at the entry of the detector region. Table 1 lists the composition and location of all the components along the KL beam line. The materials in the beam decrease the KL ﬂux by 60%, as estimated using a Geant4 [10, 11] based MC simulation. The collimation scheme of the KL beam line is described in Ref. [12].

2.2. KOTO Detector Figure 3 shows a cross-sectional side view and the coordinate system of the KOTO detector. The signature of a K ⇡0⌫⌫¯ decay is a pair of photons coming from the ⇡0 decay, without L ! any other detectable particles. The energy and position of the two photons are measured 4 Chapter 1. Introduction 5

between these background events and our signal events, these neutral background events are studied carefully to ensure that they are successfully rejected.

1.3.1 Background

The challenge for the KOTO experiment is that the branching ratio for K0 ⇡0⌫⌫¯ is on the L ! 11 order of 10 , and thus the majority of the decays observed in the experiment will not be the target decay mode (for a list of more probable decays, see Table 1.1). The detectors must be finely tuned to distinguish the background decays (defined as any other decay mode that is not K0 ⇡0⌫⌫¯) to ensure that they are vetoed. Chapter 2 will further explore the instrumentation L ! KOTO detectors methods for detecting the background and distinguishing it from the target decay. Chapter 3 will discuss the data acquisition’s (DAQ) role in utilizing the detector outputs to cut background •Two sub-system design and operation:events. Background is not our friend KOTO detector Decay Mode Branching Ratio •Cesium Iodide Calorimeter (CsI) 0 KL ⇡±e⌥⌫e 0.4055 0.0011 0 ! ± KL ⇡±µ⌥⌫µ 0.2704 0.0007 •Hermetic veto detectors !0 0 ± KL 3⇡ 0.1952 0.0012 0 !+ 0 ± KL ⇡ ⇡⇡ 0.1254 0.0005 •Charged vetoes removes events with0 charged particle !0 0 ± 3 Signature of KL→π νν = 2γ+nothingKL 2⇡ (0.864 0.006) 10 0 ! ± ⇥ 3 0 KL 2 (0.547 0.004) 10 •Photon vetoes to detect other KL decays 0 ! 0 ± ⇥ 11 Calorimeter + Hermetic veto detectorsTable.K Branching⇡ ⌫⌫¯ ratios(2 of. 49various0. 39Kaon decays0.06) (PDG)10 L ! ±Cutaway± view⇥ Table 1.1: Branching ratios of various Kaon decays [pdg]. newBHCV FB Hinemos NCC MB BCV CV LCV CC03 OEV CC04 CC05 CC06 BHCV BHPV BHGCBHTS [m] 2 Three of the main neutral decays are used in simulation studies to compare with experimental data to calibrate the detectors, validate the simulation studies, and improve their identification 1 to successfully distinguishBPCV the target decay. These decays, called normalization modes, are K beam 0 L Decay volume the K0 3⇡0, K0 2⇡0, and the K0 . Features such as the transverse momentum, (Vacuum) L ! L ! L ! Downstream and subsequently the COE, expected number of clusters, andy other kinematic variables set beam pipe Membrane 0 0 0 0 these decays apart from the KL ⇡ ⌫⌫¯ target decay. Thisx thesisz will explore the KL 2⇡ Calorimeter ! Concrete/iron shield ! normalization mode and optimize the veto cuts that are applied during simulation studies, to 0 2 4 6 8 10 12 14 16 improve the background to target signal ratio when studying this decay.[m] Fig. KOTO detector components

While the other kaon decays provide a signiﬁcant background,5 another major source of background comes from a di↵erent parent particle than the kaon. When neutrons react with residual Principle of Experiment Experimental approach

• Detect 2 photon hits from π0 (CsI) + nothing else (Vetoes) Neutral pencil beam Au target • High eﬃciency required to reject events with charged particles or other photons KL ν γ π0 • Require events to have large ν γ transverse momentum /c]

2γ (+Pt≠0) + nothing GeV

Pt [ Signal Box Rec. Pt

• Detect 2 photon hits from π0 (CsI) + nothing else (Vetoes) Neutral pencil beam Au target • CSI—> 2 photon hits • Energy and position

• Constraints 0 • π mass KL ν • Decay position on beam line γ π0 • Reconstruct decay vertex and ν γ calculate transverse momentum /c]

2γ (+Pt≠0) + nothing GeV

Pt [ Signal Box Rec. Pt

0.045 0 0 KL→ π νν KL→π νν̅ decay Detection Principle0 K 3 0.04 L→ π neutral pencil beam E1 K 2 0 Neutral beam line L→ π γ K → 2γ target 0 Arb. Units 0.035 L E2 Monte Carlo CollimatorSignal & Magnet + - 0 π θ KL→ π π π KL 0.03 blinded region CsI γ Target ν proton ● No cuts vs cuts 0.025 γ 0.02 w/o cuts “2γ+Nothing+Pt” ν ν̅ KL 0.015 γ 0 0.01 AssumingAssuming 2γ from 2γ fromπ0, π

ν Rec. Pt 0.005 Calculate z vertex. decay vertex Signal Box Proton 30 GeV 0 2 0 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 M (π )=E2E1E12E(1-cosθ)2(1-cosθ) Rec. Z (mm) Rec. Z(mm) 0 HermeticFig. Monte Carlo Detector of signal and background distributions Calculate π transverse momentum Rec. Z

4 16年9月9日金曜日

500500 500500 K 0 0.07 L→ π νν 450 450450 0 450 KL→ 3π 0 0 K 2 0 400400 KL —>π νν 0.06 400400 L→ π (MeV/c)

T 0 0 KL→ 2γ 350350 → υυ 350350 P KKL L—>π π MCνν 0.05 0 Arb. Units 300π 300 300300 Pt [MeV/c] Pt [MeV/c] Pt [MeV/c] 0.04 Pt [MeV/c] w/o cuts

0 250 0 250 0 250250 0 250 Rec. π π π 200 0.03 π 200200 blinded region blinded region 200 blindedsignal region region 150150 0.02 150150 100 100 Rec. Rec. Rec. 100 Rec. 100 100 11 0.01 5050 5050 0 000 50 100 150 200 250 300 350 400 450 500 0 0 0 Rec. 0 P Momentum [MeV/c] 150015001500 2000 2000 2500 2500 3000 3000 3500 3500 3500 4000 4000 4000 4500 4500 5000 5000 5000 5500 5500 5500 6000 6000 6000 6500 6500 6500 15001500 2000 2000 2500 2500 3000 3000 3500 3500 4000 4000 4500 4500π 5000T 5000 5500 5500 6000 6000 6500 6500 Rec. π0 Pt Μomentum (MeV/c) 0 0 0 Rec.Rec. π 0 πZ Zvtx [mm](mm) Rec. π Z0 [mm] Rec. π Zvtxvtx [mm] Fig. Monte Carlo of signal and background distributionsRec. π vtxZvtx [mm]

500 500500 450 450450 400 400400 M. Hutcheson Prelim, 20 April350 2018 25 350350 300 300300 Pt [MeV/c] Pt [MeV/c] Pt [MeV/c] 250 Pt [MeV/c] 250 0 0

0 250 0 250 π π π 200 π 200200 150 150150 100 100 Rec. Rec.

Rec. 100 Rec. 100 50 50 50 50 0 0 0 0 15001500 2000 2500 3000 3500 3500 4000 4000 4500 4500 5000 5000 5500 5500 6000 6000 6500 6500 15001500 2000 2000 2500 2500 3000 3000 3500 3500 4000 4000 4500 4500 5000 5000 5500 5500 6000 6000 6500 6500 0 0 Rec. π 0 Zvtx [mm] Rec. π Z0 vtx [mm] Rec. π Zvtx [mm] Rec. π Zvtx [mm] KOTO timeline 2013 Run 2015 Run 2016-2017 Run 2018 Run First physics run PRESENT ANALYSIS Analysis in progress Analysis in PTEP 021C01 (2017) Statistics ~20xRun49 preliminary stage 18 80 ×10 80 70 60 60 50 40 40

30 Beam Power (kW) Accumulated P.O.T. 20 20 10 0 0 2012 2013 2014 2016 2016 2017 Dec Dec Dec Jan Dec Dec

2013 results showed the largest background contribution for neutron generated events

•Expected / observed = 0.34/1

•BR (KL0—>πνν) < 5.1 x 10-8 at 90% C.L.

Halo neutrons hitting NCC (π0) Halo neutrons hitting CsI rec. π0 p vs Z T vtx

] 500 Improvements since 2013 run c Observed 0.8 450 Expected 1. 0.7

[MeV/ 87 1 0 •Suppression of neutron background T 400

P 870.17± 0.12 0.03±0.03

0 0.6

π 350

•Improved collimator alignment 0 0.5

Rec. 300 0.56±0.11 250 •Replaced vacuum window 0.4 200 1 0 0.34±0.16 0.03±0.03 0.3 •Special runs to study neutron events 150 0.2 100 9 0 • Photons and charged pions 50 0 7.23±0.52 0.002±0.002 0.1 1.06±0.25 0 0 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 + - 0 0 •Additional downstream vetoes KL—>π π π Rec. π Z vtx [mm] Fig. Reconstructed π0 Pt vs. decay vertex position

2016-07-07 23:55:46 13 ©2018, B. Beckford: [email protected] 0 Fig. 2 Reconstructed π transverse momentum (PT) versus decay vertex position (Zvtx) of the events with all the analysis cuts imposed. The region surrounded with a thick solid line is the signal region. The black dots represent the data, and the contour indicates the distribution of the K π0νν decay from MC. The events in the region surrounded with L → a thin solid line were not examined before the cuts were ﬁnalized. The black italic (red regular) numbers indicate the numbers of observed events (expected background events) for the regions divided by solid and dashed lines.

1 selected. Among all possible combinations of the photons, the combination that had the 0 2 best agreement of the Zvtx values for two (three) π ’s was adopted. Figure 3 shows the four- 0 3 photon invariant mass distribution of the KL 2π events before and after imposing the → 0 4 veto cuts. The events in the low mass region are mostly from the K 3π decays in which L → 5 four out of six photons were detected in the calorimeter. The reduction of these events by

6 detecting the extra two photons in the veto counters is well reproduced by the MC. Figure 4 7 shows the distributions of the reconstructed KL decay vertex position and energy of the 0 8 K 3π events, which indicated the acceptance derived from MC was well understood. L → 9 Slight data/MC discrepancy in the KL energy distribution was taken into account as a source 10 of systematic uncertainty. 0 11 The K 2π decay is the major K background source because there are only two extra L → L 12 photons which can be detected by veto counters. We generated a MC sample with 40-times

13 the statistics of the data. With two MC events that remained in the signal region after

14 imposing all the cuts, the background contribution was estimated to be 0.047 events. For

15 other decay modes, we generated the MC samples with various assumptions of topologies or 0 + 0 16 mechanisms that could cause backgrounds to K π νν. In the case of K π π π , for L → L → − 17 instance, the decay can be a background if charged pions hit the downstream beam pipe,

18 which was made of 5-mm-thick stainless steel, and were undetected. The nine events located 19 in the low-PT region (PT < 120 MeV/c, 2900 150 MeV/c reduced the K π π π background T L → − 21 to a negligible level. The K 2γ decay can be a background if an incident K is scattered L → L 22 at the upstream vacuum window, which was made of 125-µm-thick polyimide ﬁlm, and

6/11 Analysis

● Challenge → background reduction ● Blind analysis method 1. Signal reconstruction 2. Normalization 3.AnalysisBackground Analysis

● Three variables needed to calculate BR

•Blind analysis ○ Number of signal events decays 0 ○ •SignalNumber reconstruction of KLs generated at target ○ Signal acceptance BR~ 19.52% Analysis•Study of neutral normalization modes

because they were fully reconstructed

and clearly identiﬁed. decays decays ● Challenge → background reduction -3 BR~ 0.547x10-3 ●● BlindSingle•Background analysis Event method Sensitivityestimation BR~ 8.64x10 1. Signal reconstruction 2. Normalization 3.•SingleBackground Event Sensitivity Analysis

•KL0 yield ● Three variables needed to calculate BR ○ •SignalNumber acceptance of signal events 0 ○ Number of KLs generated at target ○ Signal acceptance •Branching Ratio M. Hutcheson Prelim, 20 April 2018 11 •Number of observed events 14 ● Single Event Sensitivity ©2018, B. Beckford: [email protected]

M. Hutcheson Prelim, 20 April 2018 11 Normalization modes

•Determine the number of KL0

•KL0 ﬂux ~ number passing through decays the beam exit BR~ 19.52%

•KL0 yield ~ number of remaining

reconstructed events after veto and decays kinematics cuts BR~ 8.64x10-3 •Normalization modes are also used to:

•Evaluate of kinematic and veto cut decays

eﬃciencies BR~ 0.547x10-3

•Evaluate MC reproducibility of data

15 ©2018, B. Beckford: [email protected] RUN65 42kW Kinematical Variables : KL0—>3π0 Event distributions KL→3π0 reconstruction KL0—>3π0 kmass KL mass hrecz Rec. Z ] 2 Data Data 0 0 K →3π 104 K →3π 4 L L 10 K 2 0 K 2 0 •Eﬃciency of kinematic requirements L→ π L→ π K 2 3 K 2 L→ γ 10 L→ γ 103

102 102

i 0 # of events/100.00 [mm] •ε = (Number of reconstructed KL # of events/2.00 [MeV/c 10 eventsRUN65 with 42kW all cuts) / (Number of 10 1 1 4003 450 500 550 600 650 700 10003 2000 3000 4000 5000 6000 7000 400 500 600 7002 2000 4000 6000 2 0 th 2 χ = 434.09 Rec. K z pos. [mm] χ = 54.83 Kinematical VariablesRec. KL mass: [MeV/c ] ndf = 146 L ndf = 43 RUN65reconstructed 42kW KL events w/o i cut ) 2 2 Data/MC 1 χ2/ndf = 2.97 Data/MC 1 χ2/ndf = 1.28 p-value = 0.000 p-value = 0.107 0 0 0 400 450 500 550 600 650 700 1000 2000 3000 4000 5000 6000 7000 0 2 Rec. K mass [MeV/c ] Rec. K z pos. [mm] •DataCut well Eﬃ reproducedciencyKL→ by:3 K πMonteCarloL→ reconstruction3π L L Fig. Reconstructed mass hdvtime hminpos N Rec. KL→3π0 w/ all cuts Delta vertex time Min. fiducial kmass hrecz εi = 1 - 0 KL massth Rec. Z Data Data ] 0 0 N Rec. KL→2 3π w/ all cuts except for i cut 4 Data 4 KDataL→3π 10 KL→3π 1.2 0 10 4 00 0 KL→3π Data 10 KKLL→→23ππ KL→2π 104 0 0 1.1 K →2π KK →→22γπ 3 K →2γ L MC 3 LL 10 L K 2 10 3 K 2 L→ γ 10 L→ γ 1 103

# of events/0.10 [ns] 2 102 10

0.9 # of events/10.00 [mm] 2 Cut Efficiency 10 102 0.8 # of events/100.00 [mm] 10 # of events/2.00 [MeV/c 10 0.7 10 10 1 1 0.6 30 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 30 100 200 300 400 500 600 700 1 10 1 2 3 4 5 0 200 400 600 4003 450 500 550 600 650 700 10003 2000 3000 4000 5000 6000 7000χ2 = 3704.97 χ2 = 100.78 0.5 δ vertex time [ns] ndf = 46 Innermost photon hit position (square) [mm] ndf = 51 400 500 600 7002 2 2000 4000 6000 2 2 2 χ = 434.09 Rec. K z pos. [mm] χ = 54.83 Rec. KL mass [MeV/c ] ndf = 146 L ndf = 43 0.4 2 Data/MC 2 2 Data/MC 2 1 χ /ndf = 80.54 1 χ /ndf = 1.98 p-value = 0.000 p-value = 0.000 Data/MC 1 χ2/ndf = 2.97 Data/MC 1 χ2/ndf = 1.28 0.3 p-value = 0.000 0 p-value = 0.107 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 0 0 Innermost photon hit position (square) [mm] 0.2 dTvtx dKLMassCSITotEKLPt KLChisqdPi0Mass400 dPi0Z450MinGammaE500MinFiducialXYMaxFiducialR550 MinClusDistance600KLZ 650 700 1000 2000 3000 4000 5000 δ vertex6000 time [ns]7000 4 2 Rec. K z pos. [mm] Rec. KL mass [MeV/c ] L Fig. Reconstructed decay vertex position hdvtime hminpos Delta vertex time Min. fiducial Data ©2018, B. Beckford: [email protected] 0 4 0 KL→3π 10 KL→3π 104 0 0 KL→2π KL→2π K →2γ 3 3 K →2γ 3 L 10 L 10

# of events/0.10 [ns] 2 102 10 # of events/10.00 [mm]

10 10

1 1 30 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 30 100 200 300 400 500 600 700 0 1 2 3 4 5 0 200 400 600 χ2 = 3704.97 χ2 = 100.78 Innermost photon hit position (square) [mm] 2 δ vertex time [ns] ndf = 46 2 ndf = 51

Data/MC 1 χ2/ndf = 80.54 Data/MC 1 χ2/ndf = 1.98 p-value = 0.000 p-value = 0.000 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 δ vertex time [ns] Innermost photon hit position (square) [mm] 4 RUN65 42kW Kinematical Variables : KL0—>2π0 Event distributions KL→2π0 reconstruction KL0—>2π0 kmass KL mass hrecz Rec. Z ] 2 Data Data 3 0 0 10 KL→3π KL→3π 0 0 •Eﬃciency of kinematic requirements KL→2π KL→2π 2 KL→2γ 10 KL→2γ 102

i 0 10 10 # of events/100.00 [mm] •ε = (Number of reconstructed KL # of events/4.00 [MeV/c RUN65 42kW events with all cuts) / (Number of 1 1 2503 300 350 400 450 500 550 600 650 10003 2000 3000 4000 5000 6000 7000 300 400 500 600 2 2000 4000 6000 2 Kinematical0 th Variables : 2 χ = 3642.29 χ = 41.58 Rec. K mass [MeV/c ] Rec. K z pos. [mm] RUN65reconstructed 42kW KL events w/o i cut ) 2 L ndf = 95 2 L ndf = 44 Data/MC 1 χ2/ndf = 38.34 Data/MC 1 χ2/ndf = 0.94 p-value = 0.000 p-value = 0.576 0 0 0 0 250 300 350 400 450 500 550 600 650 1000 2000 3000 4000 5000 6000 7000 Cut Eﬃciency : KL→2π Rec. K mass [MeV/c2] Rec. K z pos. [mm] •Data well reproducedKL→ 2byπ MonteCarlo reconstructionL L Fig. Reconstructed mass 0 N Rec. KL→2π w/ all cuts hdvtime Delta vertex time hminpos Min. fiducial kmass hrecz εi = 1 - 0 KL massth Rec. Z N Rec. KL→] 2π w/ all cuts except for i cut Data Data 1.2 2 Data 103 Data 0 0 3 0 KL→3π0 KL→3π 10 KL→3π Data KL→3π 0 0 1.1 0 KL→2π0 KL→2π KL→2π KL→2π 2 MC 2 K →2γ K →2γ K 2 10 K L 2 10 L 1 L→ γ 102 L→ γ 102

0.9 # of events/0.10 [ns] Cut Efficiency 0.8 1010 # of events/10.00 [mm] 10 10 # of events/100.00 [mm] # of events/4.00 [MeV/c 0.7 1 0.6 1 1 1 30 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 30 100 200 300 400 500 600 700 0.5 2503 300 350 400 450 500 550 600 650 100030 20001 3000 2 4000 3 5000 46000 70005 0 200 400 600 300 400 500 600 2000 4000 6000 χ2 = 914.27 χ2 = 61.13 χ2 = 3642.29 χ2 = 41.58 Rec. K mass [MeV/c2] Rec.δ vertexK z pos. time [mm] [ns] ndf = 33 Innermost photon hit position (square) [mm] ndf = 59 0.4 2 L ndf = 95 22 L ndf = 44 2

Data/MC 2 Data/MC 2

Data/MC Data/MC χ /ndf = 27.71 χ /ndf = 1.04 χ2/ndf = 38.34 1 χ2/ndf = 0.94 1 0.3 1 1 p-value = 0.000 p-value = 0.399 p-value = 0.000 p-value = 0.576 0.2 dTvtx dKLMassCSITotEKLPt KLChisq0dPi0MassdPi0Z MinGammaE MinFiducialXYMaxFiducialRMinClusDistanceKLZ KLBeamExitXY 00 0 250 300 350 400 450 500 550 600 650 10000 0.5 20001 1.53000 2 40002.5 3 50003.5 46000 4.5 70005 0 100 200 300 400 500 600 700 2 Rec.δ vertexK z pos. time [mm] [ns] Innermost photon hit position (square) [mm] 6 Rec. KL mass [MeV/c ] L Fig. Reconstructed decay vertex position hdvtime Delta vertex time 17 hminpos Min. fiducial Data ©2018, B. Beckford: [email protected] 103 0 0 KL→3π KL→3π 0 0 KL→2π 5 KL→2π 2 KL→2γ 10 KL→2γ 102 # of events/0.10 [ns]

10 # of events/10.00 [mm] 10

1 1 30 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 30 100 200 300 400 500 600 700 0 1 2 3 4 5 0 200 400 600 χ2 = 914.27 χ2 = 61.13 Innermost photon hit position (square) [mm] 2 δ vertex time [ns] ndf = 33 2 ndf = 59

Data/MC 1 χ2/ndf = 27.71 Data/MC 1 χ2/ndf = 1.04 p-value = 0.000 p-value = 0.399 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 δ vertex time [ns] Innermost photon hit position (square) [mm] 6 RUN65 42kW Kinematical Variables : KL0—>2γ Event distributions KL→2γ reconstruction KL0—>2γ hpt KL Pt hrecz Rec. Z

3 Data Data 10 3 0 10 0 KL→3π KL→3π K 2 0 K 2 0 •Eﬃciency of kinematic requirements L→ π L→ π 2 KL→2γ KL→2γ 10 102

10 # of events/100.00 [mm] i 0 # of events/2.00 [MeV/c] •ε = (Number of reconstructed KL 10 RUN65 42kW events with all cuts) / (Number of 1 1 30 20 40 60 80 100 120 140 10003 2000 3000 4000 5000 6000 7000 0 50 100 1502 2000 4000 6000 2 Kinematical0 th Variables K: P [MeV/c] χ = 192.35 Rec. K z pos. [mm] χ = 72.03 L t ndf = 74 L ndf = 47 RUN65reconstructed 42kW KL events w/o i cut ) 2 2 Data/MC 1 χ2/ndf = 2.60 Data/MC 1 χ2/ndf = 1.53 p-value = 0.000 p-value = 0.011 0 0 0 20 40 60 80 100 120 140 1000 2000 3000 4000 5000 6000 7000 K P [MeV/c] Rec. K z pos. [mm] •DataCut well E ﬃreproducedciencyKL→ by:2 KMonteCarloγL →reconstruction2γ L t L Fig. Reconstructed traverse momentum N Rec. KL→2γ w/ all cuts hdvtime Delta vertex time hminpos Min. fiducial hpt KL Pt hrecz Rec. Z 3 i = 1 - 4 10 ε N Rec. KL→2γ w/ all cuts except for ith cut 10 Data Data 3 Data Data 0 0 1.2 10 0 3 KL→3π 0 KL→3π 10 0 0 KL→3π Data KKL→→23ππ K →2π 0 3 L 0 L 1.1 KL→2π 10 KL→2π 2 MC KL→2γ 10 KL→2γ K →2γ K →2γ 1 2 L L 10 102 2 0.9 # of events/0.10 [ns] 10 Cut Efficiency # of events/10.00 [mm] 10 0.8 10 # of events/100.00 [mm] # of events/2.00 [MeV/c] 10 10 0.7 1 0.6 1 11 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 800 900 1000 0.5 0 20 40 60 80 100 120 140 31000 2000 3000 4000 5000 6000 7000 3 3 03 1 2 3 4 5 2 0 200 400 600 800 10002 0 50 100 150 2000 4000 6000 χ = 1516.85 χ = 81.92 2 δ vertex time [ns] 2 Innermost photon hit position (square) [mm] K P [MeV/c] χ = 192.35 2 Rec. K z pos. [mm]ndfχ = = 72.03 14 2 ndf = 69 0.4 2 L t ndf = 74 2 L ndf = 47 Data/MC χ2/ndf = 108.35 Data/MC χ2/ndf = 1.19

Data/MC Data/MC 1 1 0.3 1 χ2/ndf = 2.60 1 p-valueχ2/ndf = = 1.53 0.000 p-value = 0.137 p-value = 0.000 p-value = 0.011 0 0 0.2 dTvtx CSITotEKLPt 0 MinGammaE MinFiducialXYMaxFiducialRMinClusDistanceKLZ 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 800 900 1000 0 20 40 60 80 100 120 140 1000 2000 3000 4000 5000 δ vertex6000 time [ns]7000 Innermost photon hit position (square) [mm] 8 KL Pt [MeV/c] Rec. KL z pos. [mm] Fig. Reconstructed decay vertex position hdvtime Delta vertex time 18 hminpos Min. fiducial 3 ©2018, B. Beckford: [email protected] 104 Data 10 Data 0 0 KL→3π KL→3π 0 0 K →2π K →2π 3 L 7 L 10 2 KL→2γ 10 KL→2γ

# of events/0.10 [ns] 10

# of events/10.00 [mm] 10

1 1 30 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 30 100 200 300 400 500 600 700 800 900 1000 0 1 2 3 4 5 0 200 400 600 800 1000 χ2 = 1516.85 χ2 = 81.92 Innermost photon hit position (square) [mm] 2 δ vertex time [ns] ndf = 14 2 ndf = 69

Data/MC 1 χ2/ndf = 108.35 Data/MC 1 χ2/ndf = 1.19 p-value = 0.000 p-value = 0.137 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 800 900 1000 δ vertex time [ns] Innermost photon hit position (square) [mm] 8 KL0 yield • Yield obtained from three normalization modes are within systematics

• KL0 yield (KL0—> 2π0) =KL 4.58 yieldx 1012 from : 3-mode 2.2 x 1019 POT comparison

KL Yield in the 2015 run 5 4.9 Mode Yield at Beam Exit 4.8

@BeamExit] 4.7 L 0 12 KL—>2π (4.58+-0.04) x 10 K 4.6 12 4.5 10 × 4.4 KL—>2γ (4.38+-0.02) x 1012 4.3 Yield [ L

K 4.2 KL—>3π0 (4.62+-0.02) x 1012 4.1 4 0 0 K →2γ KL→3π KL→2π L

Fig. Calculated KL0 yield at beam exit 5

• Summary of KOTO ﬁrst results

0 -8 •2013 ﬁrst run set a BR(KL—>π νν) upper limit of < 5.8 x 10 (90% C.L.) (PTEP 021C01) • Present status •In 2015, collected 20 times larger data set than the 2013 run

•KL0 yield (KL0—> 2π0) = 4.58 x 1012 (at beam exit)

•Sensitivity of 2015 run will be determined based on this result

•Data collected in 2016-2018 is being analyzed

•2015 run results will be presented in the next talk

•DON’T MISS IT!

Dec ’17 collaboration meeting

Study of the Normalization Modes in the Search for the Rare KL 0—&gt;Π0νν

Study of the Normalization Modes in the Search for the Rare KL 0—>Π0νν