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Paolo Massarotti Charged Kaon Meeting 4 may 2006 Charged kaon lifetime P. Massarotti

Charged kaon lifetime

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P. Massarotti. Charged kaon lifetime. Outlook. Length measurement: Resolution effects evaluation Fit error Angular checks Efficiency checks Time measurement: efficiency evaluation MC fit. 0.024. KLOE. Analysis status : length. t = (12.367 ±0.044 stat ± 0.065 syst ) ns. - PowerPoint PPT Presentation

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Paolo Massarotti Charged Kaon Meeting 4 may 2006

Charged kaon lifetime

P. Massarotti

Paolo Massarotti Charged Kaon Meeting 4 may 2006

Outlook

Length measurement:Resolution effects evaluationFit errorAngular checksEfficiency checks

Time measurement:efficiency evaluationMC fit

Paolo Massarotti Charged Kaon Meeting 4 may 2006

= (12.367±0.044stat ±0.065syst) ns

KLOE

0.024 preliminary

Analysis status: length

Weighted mean between and

Paolo Massarotti Charged Kaon Meeting 4 may 2006

Point of Closest Approach

The resolution functions given by the P.C.A. methodare 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 reproducethe 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

+14 = (14.004 ± 0.084) ns 2 =1.64 P2 =6.7%

+12 = (12.019 ± 0.075) ns 2 =1.35 P2 =18.1%

+11 = (10.998 ± 0.058) ns 2 =1.17 P2 =28.9%

+13 = (12.994 ± 0.076) ns 2 =1.50 P2 =10.7%

Resolution checks: MC measurements

+ = (12.390 ± 0.059) ns 2 =1.06 P2 =39%

We weight MC proper time distribution to obtain different lifetimes

Paolo Massarotti Charged Kaon Meeting 4 may 2006

To do: fit errorWe 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.

Nexpj = Csmear

ij × i × icorr × Ni

theo i = 1

nbins

Paolo Massarotti Charged Kaon Meeting 4 may 2006

What about the bin error ?

We have calculated the error is given by:

MC Toy to evaluate the correct error on the bin entries is needed

exp1

1

)(

)(exp

jiijnbini

corriij

nbiniN

NC

C

corri

ij

Is this over- or under-estimated?

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

Self triggering muon tagConsidering only kaon decays with a

X X we look for the neutral vertex asking clusters on time: (t - r/c) = (t – r/c)

invariant mass agreement between kaon flight time and clusters time

0

E,t,x

±

E,x,t

K tagt

pK

pKt0

lK

xK

E,t,x

Time Strategy

Paolo Massarotti Charged Kaon Meeting 4 may 2006

Time: Efficency comparisonMonteCarlo kine vs MonteCarlo reco fit window definition

MC recoMC kine

Fit window 10 : 40 ns

Paolo Massarotti Charged Kaon Meeting 4 may 2006

Time: Data and MonteCarlo

reco MCData

reco MCData

Paolo Massarotti Charged Kaon Meeting 4 may 2006

Time: MC measure

between 18 and 37 ns

T(ns)

+MC = (12.319 ± 0.072) ns

2 =1.08 P2 = 36%

We have to evaluate data

Paolo Massarotti Charged Kaon Meeting 4 may 2006

KLOE soccer tournament 2006

Charged kaons

Branchini

Massarotti

Meola

Patera

Versaci

Neutral kaons

Bossi

Gatti

Moulson

Passeri

Spadaro

Radiatives: Bini, De Santis, Nguyen, Venanzoni, Mr X