EXPERIMENTEXPERIMENT

INR/IHEP

Protvino-Moscow, Russia

Viacheslav Duk INR RAS

QUARKS 2006

Rare Kaon Decays

ISTRA+@

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

Kaon PhysicsRare kaon Rare kaon

decaysdecays

Strong interactionsTesting SM New Physics

CKM matrix elements Vij

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 π0 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

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– → e- ν π0 γ :

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

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– → µ- ν γ : 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

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– → e– ν π0 (γ) : BR=[5.170.011(stat)0.034(norm) 0.045(syst)]×10-2 (PDG: BR=(4.87±0.06)x10-2)

|Vus|=0.2286±0.0026

BR=[5.170.011(stat)0.034(norm) 0.045(syst)]×10-2 (PDG: BR=(4.87±0.06)x10-2)

|Vus|=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 (→ Fv, FA)

Kinematical variables:

x=2*Eγ(cm)/Mk y=2*Eµ(cm)/Mk

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

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

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

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 backgroundchanging with energy

Background after fitlooks 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) )

xxx

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

140-150 150-160 160-170 170-180 180-190 190-200 200-210 210-220 220-230 230-240

130-140

120-130

110-120

100-110

90-100

80-90

70-80

60-70

50-60

40-50

30-40

20-30

10-20

EµEγ

K→ µ ν γ: M(µνγ) for selected bins

Kµ3signal

Kµ3+Kπ2signal

Kµ3

Kµ3

signal

signal

M(µνγ), GeV

M(µνγ), GeVM(µνγ), GeV

M(µνγ), GeV

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

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)

• cosθπµ > (-0.95) for Kπ2 rejection

• Fit probability > 0.005

K→ µ ν γ : normalization on Kµ3

• M(µνπ0) for Kµ3 before and after kinematical fit

M(µνπ0), 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< Eγ <130MeV 150<Eµ<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

y y

y y

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< 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

ISTRA+ work is supported by:- RFBR grants N03-02-16330(IHEP) and N03-02-16135(INR)- Russian Science Support Foundation (INR)

Acknowledgments