PHENIX Measurement of Charged Kaon Interferometry in Au+Au Collisions at s NN = 200 GeV
Charged kaon lifetime
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Transcript of Charged kaon lifetime
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: 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