Investigations of Semileptonic Kaon Decays at the NA48 Е xperiment

1. Investigations of Semileptonic Kaon Decays at the NA48 Еxperiment Milena Dyulendarova (University of Sofia “St. Kliment Ohridski”) for NA48 Collaboration

2. Outline of the Talk • Theoretical Description • NA48Experiment • Analyses ofKL →π e νe(K0e3)decay modes • NA48/2Experiment • Analysis ofK±e3decay • Conclusion

3. Theoretical Description • Dalitz plot density: where mK-massof particle i, E*i –energy of iinCoM (center of mass); fS, fV (f+and f-), f T- scalar, vector and tensor form factors. - four momentum transferred to the lepton pair; • The vector form factors can be approximated by Taylor expansion with

4. NA48 Experiment • Designed for measurement of direct CP-violation in the K0 system • Simultaneous near collinear beams of KL and KS with average energy ~110 GeV

5. NA48 Experiment - Detector System • Magnet Spectrometer (two drift chambers DCH before and two DCH after the magnet spectrometer) • Hodoscope CHOD • (time resolution – 200 ps per track) • Homogenous electromagnetic calorimeter LKr • Hadron calorimeter HAC • Muon veto system MUV

6. KL →π e νe(K0e3)Analysis Experimental data • Special run with KL beam - September (1999) • ~2 TBdata recorded • 5.6 millionK0e3events were selected and analyzed. MC simulation • The detector performance is simulated by GEANT package. • The radiative correctionsin (virtual and real) were generated by PHOTOS routine. Basic Selection Criteria • Two tracks with different charges coming from a common vertex • Vertex located in the decay region • Tracks in detector aperture • Time difference of the tracks

7. K0e3 Analysis (continued) • Minimal momentum of each track pmin = 10 GeV • Minimal distance between tracks • Identification of the particles in the final state 0.93 < E/p < 1.1 for one of the tracks (e±) &E/p < 0.9 for the other one (π±) • No MUV signal around the event time (± 6 ns) Background

8. Assuming only V-A couplings: the linear dependence of the K0e3 vector form factor on q2 is: in addition a quadratic term is admitted: Admitting scalar and tensor couplings in addition to V-A currents linear slope of the f+(q2): and the following form factor values: polar parametrization: K*(892) Experimental Results for K0e3

9. Worldresults NA48: fS/f+(0) < 0.028 fT/f+(0) < 0.09 PDG: fS/f+(0) < 0.04 fT/f+(0) < 0.23

10. NA48/2 Experiment – Charged Beam Formation • Simultaneous K+ and K- beams with average energy ~60 GeV • Two achromat systems – two dipole magnets with opposite polarities • Kaon Beam Spectrometer (KABES)

11. Analysis of K±e3 Decay DATA • 56 hours special run taken in 2002. • About 4 million K±e3events were selected. MC • The NA48/2 detector response is simulated by MC program based on GEANT. • The radiative corrections in K±e3 were generatedby using GinsbergandPHOTOS routine. Basic Selection Criteria • 1 charged track forming a vertex with the z-axis • Vertex in decay region • Detector geometry acceptance • Minimum momentum of the Ptr > 5 GeV • e± and 0 identification • Event in Dalitzplot region

12. Analysis of K±e3 Decay Dalitz plot distribution from Ginsberg+PHOTOS simulation Background Reducing main K  0background - region excluded: • 55 GeV < EK < 65 GeV • 234 MeV < E* < 264 MeV • MK 12 MeV around the PDG value Comments • Summing all sources the systematic error is less 1% (maximal possible value) • The systematic uncertainty is < 0.5%

13. Conclusion • TheK0e3results are in agreement with the linear approximations tested in former experiments. • The slope in the vector form factor is measured witha high precision • The scalar and tensor form factors are consistent with zero, the measurement is the most precise up to now • The results areconsistent with a lack of quadraticterm in the vector form factor, and at the same time consistent with a Taylor expansion of a pole-dominance form factor with a pole mass of MV=859±18 MeV • . K±e3decay mode is under detailed investigation.