1. the charged kaon lifetime
KLOE measurements of
the charged kaon lifetime
and BR(K+p+p0)
Paolo Massarotti *
on behalf of the KLOE collaboration
*Università degli studi di Napoli “Federico II” – INFN Napoli

2. The charged kaon
lifetime

3. K± lifetime: experimental picture
12.385(25) ns
S = 2.1
Poor consistency
Needs confirmation
PDG
average
Discrepancy between
in-flight and at-rest
measurements
Discrepancy among
different stoppers in
at-rest measurements
Confirmation is needed
tPDG = (12.385± 0.024) ns

4. K± lifetime @ KLOE: two methods
Method #1: fit proper time (T*) distribution from decay length
Using all the charged kaon decays, measure the K decay
length taking into account the energy loss: T* = Si DLi / bi gi c
Method #2: fit proper distribution time from decay time
Use all the charged K decays with a p0 in the final state
to measure the kaon decay time from p0gg clusters time
Two methods allow us to cross check systematics

5. K± lifetime: method #1 Signal K track extrapolated backwards to the IP
K ® mn tag
K decay vertex in the Drift Chamber fiducial volume
Signal K track extrapolated backwards to the IP
dE/dx taken into account Þ 2mm step
Efficiency evaluated directly on data

6. DC vertex reconstruction efficiency0
E,t,x ±
E,x,t
K tag t pK t0 lK xK
FV º 40 cm ≤ r ≤ 150 cm

7. Method #1: proper time fit
KLOE preliminary
16-30 ns
~ 1
T*(ns)
The proper time distribution,
corrected with the efficiency,
is fitted with a convolution of
an exponential function and a
resolution function.
Fit between 16 and 30 ns
Preliminary
t = ( ±0.044)ns

8. Preliminary systematic estimate
Source of systematic uncertainties
Systematic uncertainties (ps)
Range stability
± 60*
Bin stability
± 20
Efficiency correction
± 10
Beam Pipe wall thickness
DC wall thickness
± 15
Systematic uncertainties of the order of 65 ps
* We already know that this contribution will improve considerably

9. K± lifetime: method #2
K ® mn tag
K ®p0 X decay(looking for neutral clusters in the EMC)
K neutral decay vertex (p0  gg) in the fiducial volume
Efficiency evaluated directly on data

10. EMC vertex reconstruction efficiency
Kmn tag m K
vtx Li
K±  m± n
Control sample given by
kaon decay vertex in the fiducial volume using only DC informations

11. Method #2: proper time fit
The proper time distribution,
corrected with the efficiency,
is fitted with a convolution of
an exponential function and
a resolution function.
Fit between 13 and 42 ns
>2l
Preliminary
t = ( ±0.049)ns

12. Preliminary Systematic estimate
Systematic uncertainties ps
Range stability
± 15
Bin stability
± 10
Efficiency correction
Systematic uncertainties of the order of 25 ps

13. Method #2: Directly measure decay time
Preliminary results
Method #1: fit t* distribution from decay length
Preliminary
t = ( ±0.044stat±0.065syst)ns
Method #2: Directly measure decay time
Preliminary
t = ( ±0.049stat±0.025syst)ns
Correlation
r = 0.338

14. . Weighted mean tPDG 06 = (12.385±0.024)ns t = (12.384 ±0.048)ns
KLOE 07
t = (12.384±0.048) ns .
tPDG 06 = (12.385±0.024)ns
Preliminary
t = ( ±0.048)ns

15. Measurement of BR(K+p+p0)

16. Measurement of BR(K+p+p0)
PDG fit ‘ BR(K±p±p0) = (20,92 ± 0.12)% DBR/BR = 5,7x10-3
CHIANG ’72 BR(K±p±p0) = (21,18 ± 0.28)% DBR/BR = 1,3x10-2
This decay enters in the normalization of BR(Kl3) by NA48, ISTRA+, E865
Method:
Normalization sample is given by K-m-n tag
Number of K±p±p0 decays from the fit of the distribution of the
momentum of the charged decay particle in the kaon rest frame
assuming the pion mass (p*)
Selection efficiency related to Drift Chamber information only and
measured directly on DATA using the K±X±p0 decay vertex
control sample as done for the lifetime measurement

17. K+p+p0 signal selection
BR(K+p+p0): signal selection
tag on one side with K
preselection
-zPCA  20cm
- rPCA  10cm
- pK (70,130) MeV
selection
- rVTX  (40,150) cm
- dp  (-320,-120) MeV
- p(mp)  (180,270) MeV
2) look for signal on the other side
vertex in fiducial volume rVTX  (40,150) cm
kaon track can be extrapolated to the I.P. (time info)
K+p+p0 signal selection

18. statistical fractional accuracy < 0.5%
BR(K+p+p0): a preview
mn peak p*(p mass) distribution from DATA control sample
selected using calorimetric information only
pp0 peak p*(p mass) distribution from DATA control sample
3-body decays p*(p mass) distribution from MC
Using 260 pb-1 we can reach a
statistical fractional accuracy < 0.5%

19. Conclusions KLOE is the unique experiment able to
measure all the parameters needed for the
determination of the element of the
CKM matrix VUS
The charged kaon lifetime is one of these parameters:
It has been measured using two different techniques
both with a fractional accuracy of the order of 0.6%
obtaining a total fractional accuracy of 0.4%
The complete data set will allow us to reach a statistical
fractional accuracy of the order of the PDG 06 one (0.2%)
We are also measuring the absolute BR(K+→p+p0),
entering in the normalization of all present BR(Kl3)
measurements but the KLOE one.
Using 260 pb-1 we can reach a
statistical fractional accuracy < 0.5%
A preliminary result will be presented soon