EXPERIMENT INR/IHEP Protvino-Moscow, Russia Viacheslav Duk INR RAS QUARKS 2006 Rare Kaon Decays

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

Kaon Physics Rare kaon decays Strong interactionsTesting SMNew Physics CKM matrix elements V ij Checking CKM matrix unitarity Testing ChPT New interactions (Tensor, Scalar, Pseudoscalar) Direct CP violation Lepton flavor violation

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

Recent ISTRA+ Results K – → µ - ν π 0 γ : First observation (~550 events) BR=(8.82±1.27)x10 -5 (Theory: BR=6.86x10 -5 ) Region 1: 5 < E γ < 30 MeV BR=(1.46±0.39)x10 -5 (Theory: BR=1.53x10 -5 ) Region 2: 30 < E γ < 60 MeV T-odd asymmetry A ξ =-0.03±0.013 First observation (~550 events) BR=(8.82±1.27)x10 -5 (Theory: BR=6.86x10 -5 ) Region 1: 5 < E γ < 30 MeV BR=(1.46±0.39)x10 -5 (Theory: BR=1.53x10 -5 ) Region 2: 30 < E γ < 60 MeV T-odd asymmetry A ξ =-0.03±0.013 K – → e - ν π 0 γ : BR=(3.05±0.02)x10 -4 (Theory: BR=3.0x10 -4 ) Region: E γ > 30 MeV, θ eγ > 20 o ( ~3850 events) T-odd asymmetry A ξ =-0.015±0.021 See talk by A.Yu.Polarush BR=(3.05±0.02)x10 -4 (Theory: BR=3.0x10 -4 ) Region: E γ > 30 MeV, θ eγ > 20 o ( ~3850 events) T-odd asymmetry A ξ =-0.015±0.021 See talk by A.Yu.Polarush K – → µ - ν γ : BR=(1.25±0.05)x10 -3 (Theory: BR=1.28x10 -3 ) Region: 30 < E γ < 130 MeV, 150 < E μ < 230 MeV (~22500 events) See this talk BR=(1.25±0.05)x10 -3 (Theory: BR=1.28x10 -3 ) Region: 30 < E γ < 130 MeV, 150 < E μ < 230 MeV (~22500 events) See this talk K – → e – ν π 0 ( γ) : BR=[5.17  0.011(stat)  0.034(norm)  0.045(syst)]×10 -2 (PDG: BR=(4.87±0.06)x10 -2 ) |V us |=0.2286± BR=[5.17  0.011(stat)  0.034(norm)  0.045(syst)]×10 -2 (PDG: BR=(4.87±0.06)x10 -2 ) |V us |=0.2286±0.0026

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

K → µ ν γ : Theory Differential decay rate : 3 main terms: IB – dominant SD±, INT± - most interesting (→ F v, F A ) Kinematical variables: x=2*E γ (cm)/M k y=2*E µ (cm)/M k

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 < Z vertex < 1650cm Additional cuts: Missing energy > 1GeV SP2 veto missing momentum points to ECAL aperture

K → µ ν γ : main background K→ µ ν π 0 (Kµ3) with 1 gamma lost (from π 0 →γγ) K→ π π 0 (Kπ2) with 1 gamma lost (from π 0 →γγ) and π misidentification

K → µ ν γ: signal observation MMS=(P k -P µ -P γ ) 2 MMS peaks at 0 for signal M(µνγ)= √(P µ +P ν +P γ ) 2 where p ν =p k -p µ -p γ ; E ν =|p ν | M(µνγ) peaks at kaon mass (0.494 GeV) for signal More preferable OR M(µ ν γ) Signal peak in (x,y) bin First observation of K→µνγ in decays-in-flight !!!

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 Large background changing with energy Background after fit looks like signal (2) - more preferable OR

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

K → µ ν γ: selected kinematical region EµEµ EγEγ

K → µ ν γ: M(µνγ) for selected bins Kµ3Kµ3 signal Kµ3+Kπ2 signal Kµ3Kµ3 Kµ3Kµ3 M(µνγ), GeV

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

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)

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

K → µ ν γ : normalization on Kµ3 M(µνπ 0 ) for Kµ3 before and after kinematical fit M(µνπ 0 ), GeV

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< E γ <130MeV 150<E µ <230MeV Theory: BR(K→ µ ν γ)~1.28x10 -3

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

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

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

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< E γ <130MeV 150<E µ <230MeV Theory: BR(K→ µ ν γ)~1.28x10 -3 INT effect in BR too small, additional study is under way

ISTRA+ work is supported by: - RFBR grants N (IHEP) and N (INR) - Russian Science Support Foundation (INR) Acknowledgments