Investigations of Semileptonic Kaon Decays at the NA48 Еxperiment

Milena Dyulendarova(University of Sofia “St. Kliment Ohridski”)

for NA48 Collaboration

Outline of the Talk

• Theoretical Description

• NA48 Experiment

• Analyses of KL →π e νe (K0

e3) decay modes

• NA48/2 Experiment

• Analysis of K±e3 decay

• Conclusion

Theoretical Description

Dalitz plot density:

where mK - mass of particle i, E*i – energy of i in CoM (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

2

222222222 1

,

qfEE

mqfDqCfqfqBfqfA

dEdE

NdEE Tl

KS

ll

22PPq K

...)'1)(0(

1

)0()( 4

4

''

2

2

2

2

2

mq

mq

f

Mqf

qf

V

Mm22'

2''

NA48 Experiment

Simultaneous near collinear beams of KL and KS with

average energy ~110 GeV

Designed for measurement of direct CP-violation in the K0 system

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

%009.048.0 pp

p

%42.00.92.3

EEE

E

KL →π e νe (K0e3) Analysis

Experimental data

• Special run with KL beam - September (1999)• ~ 2 TB data recorded • 5.6 million K0

e3 events were selected and analyzed.

MC simulation

• The detector performance is simulated by GEANT package.• The radiative corrections in (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

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

Bg Kµ3 K3π Ke4 Ke3

(misidentification)

<1 x 10-4 3 x 10-5 2 x 10-5 2 x 10-5

Experimental Results for K0e3

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)

3' 101.15.08.28 syststat

3' 105.19.10.28 syststat 3'' 102.04.02.0

syststat

3' 103.17.04.28 syststat

03.005.0)0(

)( 03.004.0

2

f

qfT

0012.00015.0)0(

)( 007.0001.0

2

f

qfS

MeVmV 18859

World results

NA48:

fS/f+(0) < 0.028

fT/f+(0) < 0.09

PDG:

fS/f+(0) < 0.04

fT/f+(0) < 0.23

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)

Analysis of K±e3 Decay

DATA

• 56 hours special run taken in 2002.• About 4 million K±

e3 events were selected.

MC

• The NA48/2 detector response is simulated by MC program based on GEANT.• The radiative corrections in K±

e3 were generated by using Ginsberg and PHOTOS 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 Dalitz plot region

Analysis of K±e3 Decay

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%

Dalitz plot distribution from Ginsberg+PHOTOS simulation

Conclusion

• The K0e3 results are in agreement with the linear approximations tested in

former experiments. • The slope in the vector form factor is measured with a high precision • The scalar and tensor form factors are consistent with zero, the

measurement is the most precise up to now

• The results are consistent with a lack of quadratic term 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±

e3 decay mode is under detailed investigation.