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Search for heavy neutrino in K‾ → µ‾ ν γ decay at ISTRA+ setup

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ISTRA+. Search for heavy neutrino in K‾ → µ‾ ν γ decay at ISTRA+ setup. IHEP U-70 ( Protvino , Russia). Viacheslav Duk , INR RAS ISTRA+ collaboration. Plan. LSND/KARMEN/ MiniBooNE anomaly and heavy sterile neutrino ν h Search for ν h in kaon decays ISTRA+ setup

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  1. ISTRA+ Search for heavy neutrino in K‾→ µ‾ ν γ decay at ISTRA+ setup IHEP U-70 (Protvino, Russia) ViacheslavDuk, INR RAS ISTRA+ collaboration

  2. Plan • LSND/KARMEN/MiniBooNE anomaly and heavy sterile neutrino νh • Search for νh in kaon decays • ISTRA+ setup • Event selection for K‾→ µ‾ ν γ • Signal extraction • Limits for |Uµh|2 • Conclusions V.A.Duk, INR RAS

  3. Kaon decays: motivation experiment theory • Relatively easy to get kaon beams • Possibility to do precise measurements • Low uncertainties in calculations within Standard Model (SM) • New Physics (NP) contributions • Check SM predictions • Search for NP V.A.Duk, INR RAS

  4. Motivation for this work Paper by S.N.Gninenko (INR RAS) Resolution of puzzles of LSND, KARMEN and MiniBooNE experiments Phys.Rev.D83:015015,2011. arXiv: 1009.5536 V.A.Duk, INR RAS

  5. Neutrino oscillations: LSND V.A.Duk, INR RAS

  6. Neutrino oscillations: KARMEN V.A.Duk, INR RAS

  7. Neutrino oscillations: MiniBooNE, neutrino mode V.A.Duk, INR RAS

  8. Neutrino oscillations: MiniBooNE, anineutrino mode Above 475 MeV: Event excess 475-1250 MeV: 20.9±14.0 475-3000 MeV: 24.7±18.0 Below 475 MeV: Event excess 200-475 MeV: 18.5±14.3 V.A.Duk, INR RAS

  9. LSND/KARMEN/MiniBooNE anomalies: summary V.A.Duk, INR RAS

  10. Possible explanation of experimental results(S.Gninenko,INR RAS) Origin of excess V.A.Duk, INR RAS

  11. Possible explanation (S.N.Gninenko) New weakly interacting particle νh: • Produced in NC • Mixing with νμ ( must be in CC, e.g. kaon decays) or separate vertex (may be in NC only) • Decays radiatively via μtr V.A.Duk, INR RAS

  12. Properties of a new particle νh • m > 40 MeV: no event excess inKARMEN (threshold effect) • m < 80 MeV: νh production inLSND suppressed by phase space factor for m > 80MeV • τ(νh) > 10-11 sec: from LEP constraints: BR(Z→ννh) x BR(νh → νγ) < 2.7 x 10-5 • τ(νh)< 10-9 sec: νh‘s decay withinMiniBooNE detector volume • 10-3 < |Uμh|2 < 10-2 : from event excess inMiniBooNE experiment V.A.Duk, INR RAS

  13. New weakly interacting particle νh 40 MeV < m(νh) < 80 MeV 10-3 < |Uμh|2< 10-2 10-11 sec < τ(νh)< 10-9 sec Decays mostly as νh→νγ V.A.Duk, INR RAS

  14. νh : limits from pion and kaon decays Muon energy in 2-body kaon decay V.A.Duk, INR RAS

  15. Search for νh in kaon decays • K→μνh , νh →νγ: • peak in Eμ(cms) • signature the same as for K→ µ ν γ • no background from K→μνμ • sensitive to low masses of νh • secondary decay vertex • K→μνh : • peak in Eμ(cms) • background from K→μνμ • insensitive to low masses of νh because of resolution Muon energy in 2-body kaon decay Suitable for ISTRA+ V.A.Duk, INR RAS

  16. ISTRA+ collaboration • Institute for High Energy Physics, Protvino (IHEP) • Institute for Nuclear Research, Moscow (INR) • Joint Institute for Nuclear Research, Dubna (JINR) ISTRA+ V.A.Duk, INR RAS

  17. ISTRA+ setup T0=S1 . S2 . S3 . S4 . C0 . C1 . C2 .S5 (prescaled by a factor of ~10) T1=T0.(∑SP1 > MIP) C1-C4 – thresh. cherenkov counters; S1-S5 – scintillation counters; PC1-PC3 – proportional chambers; SP2 – veto calorimeter; SP1 – lead-glass calorimeter; DC – drift chambers; DT-drift tubes; MH – matrix scintilation godoscope V.A.Duk, INR RAS

  18. ISTRA+ setup: beam part T0=S1 . S2 . S3 . S4 . C0 . C1 . C2 .S5 (prescaled by a factor of ~10) T1=T0.(∑SP1 > MIP) C1-C4 – thresh. cherenkov counters; S1-S5 – scintillation counters; PC1-PC3 – proportional chambers; SP2 – veto calorimeter; SP1 – lead-glass calorimeter; DC – drift chambers; DT-drift tubes; MH – matrix scintilation godoscope V.A.Duk, INR RAS

  19. ISTRA+ setup: decay volume T0=S1 . S2 . S3 . S4 . C0 . C1 . C2 .S5 (prescaled by a factor of ~10) T1=T0.(∑SP1 > MIP) He vacuum C1-C4 – thresh. cherenkov counters; S1-S5 – scintillation counters; PC1-PC3 – proportional chambers; SP2 – veto calorimeter; SP1 – lead-glass calorimeter; DC – drift chambers; DT-drift tubes; MH – matrix scintilation godoscope V.A.Duk, INR RAS

  20. ISTRA+ setup: magnetic spectrometer T0=S1 . S2 . S3 . S4 . C0 . C1 . C2 .S5 (prescaled by a factor of ~10) T1=T0.(∑SP1 > MIP) C1-C4 – thresh. cherenkov counters; S1-S5 – scintillation counters; PC1-PC3 – proportional chambers; SP2 – veto calorimeter; SP1 – lead-glass calorimeter; DC – drift chambers; DT-drift tubes; MH – matrix scintilation godoscope V.A.Duk, INR RAS

  21. ISTRA+ setup: ECAL, HCAL T0=S1 . S2 . S3 . S4 . C0 . C1 . C2 .S5 (prescaled by a factor of ~10) T1=T0.(∑SP1 > MIP) C1-C4 – thresh. cherenkov counters; S1-S5 – scintillation counters; PC1-PC3 – proportional chambers; SP2 – veto calorimeter; SP1 – lead-glass calorimeter; DC – drift chambers; DT-drift tubes; MH – matrix scintilation godoscope V.A.Duk, INR RAS

  22. K→µνh (νh→νγ) event reconstruction: primary and secondary vertex for signal νμ γ Pγcalculated using A, B K B A μ ν Pγcalculated using A, B: additional energy smearing νh γ K B A μ Eνh ~ 240 MeV , mνh ~ 40–80 MeV smearing not crucial V.A.Duk, INR RAS

  23. K→µνh (νh→νγ): primary and secondary vertices τ=10-9 sec τ=10-10 sec τ=10-11 sec Zνh - ZK dz, cm dz, cm dz, cm τ=10-9 sec τ=10-11 sec τ=10-10 sec (Zνh – ZK)/(ZECAL – ZK) V.A.Duk, INR RAS

  24. K→µνh (νh→νγ): Eγ smearing dE = Etrue - Emeasured τ=10-11 sec τ=10-10 sec τ=10-9 sec dE, GeV dE, GeV dE, GeV V.A.Duk, INR RAS

  25. K→µνh (νh→νγ): kinematics in kaon rest frame assumed isotropic Pγ: kaon rest frame P*γ: νh rest frame θ – (γ-νh) angle general case * * νh ν μ kaon decay vertex γ cos θμγ ~ (-1) Eνh ~ 240 MeV , mνh ~ 40–80 MeV Eγ> 50 MeV peak sharper for smaller mh V.A.Duk, INR RAS

  26. K→µνh (νh→νγ) event selection: K→µνγ signature • Track requirements (one primary track, one secondary track, cuts on track quality) • Veto requirements (no signals above threshold) • Vertex requirements (400 < z < 1600 cm, cut on vertex fit probability) • Particle ID : Photon: isolated shower in ECAL Muon: 1) MIP in ECAL 2) ADC sum in HCAL < 200 3) relative energy deposition in last 3 layers of HCAL > 0.05 V.A.Duk, INR RAS

  27. K→µνγ : decay rate and kinematical variables 3 main terms: IB – dominant SD±, INT± - most interesting (→ Fv , FA) Kinematical variables: x=2*Eγ(cms)/Mky=2*Eµ(cms)/Mk x Dalits-plot IB y V.A.Duk, INR RAS

  28. K→µνh (νh→νγ): background rejection and signal observation • Main background: • K→ µ ν γ (Kµ2γ) • K→ µ ν π0 (Kµ3) with 1 gamma lost (from π0→γγ) • K→ π π0 (Kπ2) with 1 gamma lost (from π0→γγ) and π misidentification • Signal observation: peaks in y and cosθμγwhere θμγ is the angle between pµ and pγ in kaon rest frame. θμγ peaks at (-1) for signal Background rejection procedure: scanning over (y, x) Dalits-plot and looking for a peak in cosθμγ V.A.Duk, INR RAS

  29. K→µνh (νh→νγ): (y, x) Dalits plot signal (MC) Kµ2γ (MC) X X X data X Y Y Kπ2 (MC) Kµ3 (MC) X X Y main background: Kπ2 Y Y V.A.Duk, INR RAS

  30. K→µνh (νh→νγ): signal extraction • (y, x) dalits-plot is divided into stripes with Δx=0.05 width (x-stripes) • cut on y is put in each x-stripe: 1 < y < 1.2 • Simultaneous fit of y and cosθμγis done in x-stripes signal (MC) X 7 x-stripes selected for further analysis in the following region: 1 < y < 1.2 0.2 < x < 0.55 y V.A.Duk, INR RAS

  31. Possible signature for νh in x-stripes; |Uµh|2=0.01, m=60 MeV,τ=10-10 sec Stripe 1: 0.2 < x < 0.25 magenta: signal green: K→µνγ blue: Kμ3 red: Kπ2 cos θµγ Y Stripe 4: 0.35 < x < 0.4 peak sharper for large x cos θµγ Y Stripe 7: 0.5 < x < 0.55 Y cos θµγ V.A.Duk, INR RAS

  32. Possible signature for different masses of νh; |Uµh|2=0.01,τ=10-10 sec m=40 MeV m=80 MeV m=60 MeV cos θµγ cos θµγ cos θµγ peak sharper for small mh V.A.Duk, INR RAS

  33. Possible signature for different lifetimes of νh; |Uµh|2=0.01, m=60 MeV τ=10-11 sec τ=10-9 sec τ=10-10 sec cos θµγ cos θµγ cos θµγ peak sharper for large τh V.A.Duk, INR RAS

  34. Signal efficiency 2 effects mhτ(lab) because of Lorentz boost low efficiency for small mh τ=10-9 sec τ=10-10 sec mνh, MeV mνh, MeV τ=10-11 sec mh E(cms) cut on y (y>1) kills signal mνh, MeV V.A.Duk, INR RAS

  35. K→µνh (νh→νγ): simultaneous fit in x-stripes 0.4 < x < 0.45 fitting cosθμγ and y simultaneously is more reliable Y cos θµγ 0.3 < x < 0.35 Signal and background shapes taken from MC Y cos θµγ magenta – signal, green – Kμ2γ, blue – Kμ3, red – Kπ2 V.A.Duk, INR RAS

  36. |Uµh|2 calculation • BR(νh) measured from BR(νh)/BR(Kμ2γ) • BR(Kμ2) taken from PDG • BR(Kμ2γ) taken from theory • f(mh) contains chirality flip and phase space factors f(mh , mµ) f = 1.1 – 1.5 blue (chirality flip): 1+(mh/mμ)2 red (total): f(mh, mμ) mνh, GeV V.A.Duk, INR RAS

  37. |Uµh|2 calculation • |Uµh|2is calculated for each x-stripe • Nexp(νh)/ Nmc(νh) obtained from simultaneous fit • Values |Uµh|2 for x-stripes are averaged • Upper limit is set for averaged |Uµh|2 V.A.Duk, INR RAS

  38. Averaging |Uµh|2 |Uµh|2 |Uµh|2 X X 1σ interval m=50 MeV, τ=10-10 sec |Uµh|2= (6.6 ± 3.9)*10-6 V.A.Duk, INR RAS

  39. |Uµh|2 for τ=10-9 , 10-10 and 10-11 sec |Uµh|2 |Uµh|2 |Uµh|2 τ=10-9 τ=10-11 τ=10-10 mνh, MeV mνh, MeV mνh, MeV effect does not exceed 2σ V.A.Duk, INR RAS

  40. Main sources of systematics • Fit (shape) systematics • bin size in cos histogram • x-stripe width (bin size in the final fit) • Cut on x (number of x-stripes in the final fit) • Cut on y in x-stripes (study in progress) V.A.Duk, INR RAS

  41. Main sources of systematics • Fit (shape) systematics • bin size in cos histogram • x-stripe width (bin size in the final fit) • Cut on x (number of x-stripes in the final fit) • Cut on y in x-stripes (study in progress) V.A.Duk, INR RAS

  42. Fit (shape) systematics • MC shape is not perfect • Errors of simultaneous fit scaled to χ2=1 • New |Uµh|2 has larger error • Additional error is treated as shape systematics • Dominant source |Uµh|2= (0.9 ± 0.5)*10-5 |Uµh|2= (0.7 ± 0.8)*10-5 |Uµh|2 |Uµh|2 m = 80 MeV τ = 10-10 sec x x V.A.Duk, INR RAS

  43. Main sources of systematics • Fit (shape) systematics • bin size in cos histogram • x-stripe width (bin size in the final fit) • Cut on x (number of x-stripes in the final fit) • Cut on y in x-stripes (study in progress) V.A.Duk, INR RAS

  44. Bin size in simultaneous (cos histogram) and final (x-stripe width) fits • Varying bin size in cos histogram: results are compatible • Varying x-stripe width: results are compatible • No systematics found V.A.Duk, INR RAS

  45. Main sources of systematics • Fit (shape) systematics • bin size in cos histogram • x-stripe width (bin size in the final fit) • Cut on x (number of x-stripes in the final fit) • Cut on y in x-stripes (study in progress) V.A.Duk, INR RAS

  46. Systematics of a cut on x • Varying number of stripes in the final fit • Fitting dependency of |Uµh|2on x • slope multiplied by stripe width gives error estimation • εsyst < 0.2 εstat |Uµh|2 x-stripe number V.A.Duk, INR RAS

  47. Setting UL on |Uµh|2 upper line – total error bottom line – statistical error only UL (95% C.L.) UL (95% C.L.) UL (95% C.L.) τ=10-9 τ=10-11 τ=10-10 mνh, MeV mνh, MeV mνh, MeV V.A.Duk, INR RAS

  48. Comparison with Gninenko’s prediction |Uµh|2 |Uµh|2 |Uµh|2 mνh, MeV mνh, MeV mνh, MeV blue stripe: predictions from LSND, KARMEN. MiniBoonE Black line: ISTRA+ upper limit @ 95% C.L. V.A.Duk, INR RAS

  49. Preliminary results • |Uµh|2 < (4-6) x 10-5 (95% CL) for τ=10-9 sec • |Uµh|2 < (1-2) x 10-5 (95% CL) for τ=10-10 sec • |Uµh|2 < (1.5-2) x 10-5 (95% CL) for τ=10-11 sec • More detailed scan of (m, τ) and study of systematics is in progress V.A.Duk, INR RAS

  50. conclusions • Heavy sterile neutrino νh is proposed for LSND/KARMEN/MiniBoone anomaly explanation: 40 MeV < m(νh) < 80 MeV, 10-11 sec < τ(νh)< 10-9 sec, 10-3 < |Uμh|2< 10-2 • νh can be effectively searched for in kaon decay K→µνh (νh→νγ) • First preliminary limits on |Uµh|2 are obtained from K‾→ µ‾ ν γ decay at ISTRA+ setup: |Uµh|2 < (4-6) x 10-5 (95% CL) for τ=10-9 sec |Uµh|2 < (1-2) x 10-5 (95% CL) for τ=10-10 sec |Uµh|2 < (1.5-2) x 10-5 (95% CL) for τ=10-11 sec • more detailed study is in progress V.A.Duk, INR RAS