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EXPERIMENT

Rare Kaon Decays. @. ISTRA+. EXPERIMENT. Viacheslav Duk INR RAS QUARKS 2006. INR/IHEP Protvino-Moscow, Russia. Talk outline. 1. Kaon physics 2. ISTRA+ experimental setup 3. Recent results on kaon decays @ ISTRA+ 4. Study of K ­ → µ - ν γ @ ISTRA+ 5. Conclusions.

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EXPERIMENT

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  1. Rare Kaon Decays @ ISTRA+ EXPERIMENT Viacheslav Duk INR RAS QUARKS 2006 INR/IHEP Protvino-Moscow, Russia

  2. Talk outline 1. Kaon physics 2. ISTRA+ experimental setup 3. Recent results on kaon decays @ ISTRA+ 4. Study of K­→ µ-ν γ @ ISTRA+ 5. Conclusions

  3. Kaon Physics Rare kaon decays Testing SM New Physics Strong interactions • CKM matrix elements Vij • Checking CKM matrix unitarity • New interactions (Tensor, Scalar, Pseudoscalar) • Direct CP violation • Lepton flavor violation • Testing ChPT

  4. ISTRA+ experimental setup (U-70, Protvino)for studying rare kaon decays 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

  5. Recent ISTRA+ Results • BR=(1.25±0.05)x10-3 (Theory: BR=1.28x10-3) • Region: 30 < Eγ < 130 MeV, 150 < Eμ < 230 MeV (~22500 events) • See this talk K–→ µ-ν γ : • First observation (~550 events) • BR=(8.82±1.27)x10-5 (Theory: BR=6.86x10-5) • Region 1: 5 < Eγ < 30 MeV • BR=(1.46±0.39)x10-5 (Theory: BR=1.53x10-5) • Region 2: 30 < Eγ < 60 MeV • T-odd asymmetry Aξ=-0.03±0.013 K–→ µ- ν π0γ : • BR=(3.05±0.02)x10-4 (Theory: BR=3.0x10-4) • Region: Eγ > 30 MeV, θeγ > 20o ( ~3850 events) • T-odd asymmetry Aξ=-0.015±0.021 • See talk by A.Yu.Polarush K–→ e-ν π0 γ : K–→ e– νπ0 (γ): • BR=[5.170.011(stat)0.034(norm) 0.045(syst)]×10-2(PDG: BR=(4.87±0.06)x10-2) • |Vus|=0.2286±0.0026

  6. The Study of Decay at ISTRA+ Setup K→ µ ν γ

  7. K→ µ ν γ : Theory • Differential decay rate : • 3 main terms: IB – dominant SD±, INT± - most interesting (→ Fv, FA) • Kinematical variables: x=2*Eγ(cm)/Mk y=2*Eµ(cm)/Mk

  8. K→ µ ν γ at ISTRA+ setup • Event Selection: • 1 charged track • Muon flag in HCAL • 1 shower in ECAL (not associated with charged track) • 300cm < Zvertex < 1650cm • Additional cuts: • Missing energy > 1GeV • SP2 veto • missing momentum points to ECAL aperture

  9. K→ µ ν γ : main background • 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

  10. K→ µ ν γ: signal observation • MMS=(Pk-Pµ-Pγ)2 MMS peaks at 0 for signal • M(µνγ)= √(Pµ+Pν+Pγ)2 where pν=pk-pµ-pγ ; Eν=|pν| M(µνγ) peaks at kaon mass (0.494 GeV) for signal Signal peak in (x,y) bin First observation of K→µνγ in decays-in-flight !!! OR M(µ ν γ) More preferable

  11. K→ µ ν γ: background suppression • (1) general constraint fit +kinematical cuts • (2) dividing Dalits-plot (x,y) into little bins and fitting M(µνγ) in each bin OR Large background changing with energy (2) - more preferable Background after fit looks like signal

  12. K→ µ ν γ: Dalits-plot for signal, Kµ3 and Kπ2 x x x Kµ3 (MC) Kπ2 (MC) Signal (MC) y y y x Experimental Dalits-plot after event selection and preliminary cuts Real data Signal peak in (x,y) bin Selected bins (signal peak in M (µ ν γ) ) M(µ ν γ) y

  13. K→ µ ν γ: selected kinematical region Eµ Eγ

  14. K→ µ ν γ: M(µνγ) for selected bins Kµ3 signal signal Kµ3 M(µνγ), GeV M(µνγ), GeV signal Kµ3+Kπ2 Kµ3 signal M(µνγ), GeV M(µνγ), GeV

  15. K→ µ ν γ: background subtraction Fitting background Experimental data and background Signal after background subtraction M(µνγ), GeV M(µνγ), GeV M(µνγ), GeV

  16. K→ µ ν γ: observed statistics Total number of K→ µ ν γ events 22472±465 To measure BR(K→ µ ν γ) we normalize on BR(Kµ3)

  17. K→ µ ν γ: normalization on Kµ3 Kµ3 selection: • 1 charged track • 2 gammas • Additional cuts (the same as for K→ µ ν γ) • cosθπµ > (-0.95) for Kπ2 rejection • Fit probability > 0.005

  18. K→ µ ν γ: normalization on Kµ3 • M(µνπ0) for Kµ3 before and after kinematical fit M(µνπ0), GeV

  19. K→ µ ν γ: BR measured • Supposing BR(Kµ3)=(3.27±0.06)x10-2 (PDG) • BR(K→µ ν γ)=[1.25±0.04(stat)±0.02(norm)]x10-3 • Region: 30< Eγ <130MeV 150<Eµ<230MeV • Theory: BR(K→ µ ν γ)~1.28x10-3

  20. K→ µ ν γ: searching for INT and SD terms Dalits-plot for different terms x x INT- INT+ x IB y y x x SD+ SD- y y y

  21. K→ µ ν γ: searching for INT and SD terms • Our region: • Possible INT- contribution • BR(K→ µ ν γ,IB)=1.29x10-3 • BR(K→ µ ν γ,all terms)=1.28x10-3 • Too small INT effect in BR

  22. K→ µ ν γ: comparison with other experiments Main experiments: KEK: Akiba et al, 1985 BNL: E787, 2000 ISTRA+: 2006 x E787(BNL) KEK ISTRA+ y

  23. Conclusions • First observation of K→ µ ν γ in decays in flight and in a new kinematical region • 22472±465 events of K→ µ ν γ observed • BR(K→ µ ν γ) = [1.25±0.04(stat)±0.02(norm)]x10-3 Region: 30< Eγ <130MeV 150<Eµ<230MeV Theory: BR(K→ µ ν γ)~1.28x10-3 • INT effect in BR too small, additional study is under way

  24. Acknowledgments • ISTRA+ work is supported by: • RFBR grantsN03-02-16330(IHEP) and N03-02-16135(INR) • Russian Science Support Foundation(INR)

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