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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.