P. Massarotti
Charged kaon lifetime
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Outlook
Length measurement:
Resolution effects evaluation
Fit error
Angular checks
Efficiency checks
Time measurement:
efficiency evaluation
MC fit
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Analysis status: length
t = (12.367±0.044stat ±0.065syst) ns
Weighted mean between
t+ and t0.024
preliminary
KLOE
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Point of Closest Approach
The resolution functions given by the P.C.A. method
are an underestimate of the correct resolution functions but
these ones reproduct the corrept asimmetry.
So we use as resolution functions
The Gaussian given by the MonteCarlo true
with the centres given by the P.C.A. method.
With these resolution functions we can reproduce
the different MonteCarlo lifetimes and we also
obtain a smaller systematic given by the
fit stability as a function of the range used: ± 32 ps
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Resolution checks: MC t+ measurements
We weight MC proper time distribution to obtain different lifetimes
t +11 = (10.998 ± 0.058) ns
c2 =1.17
Pc2 =28.9%
t +12 = (12.019 ± 0.075) ns
c2 =1.35
Pc2 =18.1%
t + = (12.390 ± 0.059) ns
c2 =1.06 Pc2 =39%
t +13 = (12.994 ± 0.076) ns
c2 =1.50
Pc2 =10.7%
t +14 = (14.004 ± 0.084) ns
c2 =1.64
Pc2 =6.7%
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
To do: fit error
We make the fit in the region between 15 and 35 ns.
To fit the proper time distribution we construct an histogram,
expected histo, between 12 and 45 ns. This is a region larger than
the actual fit region in order to take into account border effects.
The number of entries in each bin is given by the integral of the
exponential decay function, which depends on one parameter only,
the lifetime, convoluted with the efficiency curve.
A smearing matrix accounts for the effects of the resolution.
We also take into account a tiny correction to be applied to the
efficiency given by the ratio of the MonteCarlo datalike and
MonteCarlo kine efficiencies.
nbins
Nexpj = S Csmearij × ei × eicorr × Nitheo
i=1
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
What about the bin error ?
We have calculated the error is given by:
N
(S
 (S
ex p
j
Cij   e i  e
nbin
i 1
corr
i
Cij  e i   e co rr )  N
nbin
i 1
i
)
exp
j
Is this over- or under-estimated?
MC Toy to evaluate the correct error on
the bin entries is needed
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Angular checks:
We have to evaluate the lifetime for two different angular windows:
Vertex between 75o and 105o
Vertex smaller than 75o or greater than 105o
Efficiency checks:
We have to evaluate the systematics given by the efficiency cuts
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Time Strategy
Self triggering muon tag
Considering only kaon decays with a p0
K X p0 X gg
we look for the neutral vertex asking
 clusters on time:
(t - r/c)g1 = (t – r/c)g2
 p0 invariant mass
 agreement between kaon flight
time and clusters time
Ep,xp,tp
pK
tm
Kmn tag
xK
p±
lK
t0 pK
p0
Eg,tg,x
Eg,tg,xg
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Time: Efficency comparison
MonteCarlo kine vs MonteCarlo reco  fit window definition
Fit window
10 : 40 ns
MC reco
MC kine
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
Time: Data and MonteCarlo
reco MC
Data
Paolo Massarotti
reco MC
Data
Charged Kaon Meeting
4 may 2006
Time: MC measure
between 18 and 37 ns
t +MC = (12.319 ± 0.072) ns
c2 =1.08 Pc2 = 36%
T(ns)
We have to evaluate data
Paolo Massarotti
Charged Kaon Meeting
4 may 2006
KLOE soccer tournament 2006
Charged kaons
Neutral kaons
Branchini
Bossi
Massarotti
Gatti
Meola
Moulson
Patera
Passeri
Versaci
Spadaro
Radiatives: Bini, De Santis, Nguyen, Venanzoni, Mr X
Paolo Massarotti
Charged Kaon Meeting
4 may 2006