Studies of the KS and KL lifetimes andBR(K     ) with KLOE±±+­Simona S. Bocchetta*
on behalf of the KLOE Collaboration
KAON09 Tsukuba June 9th 2009
* INFN and University of “Roma Tre”

Outline­ DANE and KLOE experiment­ study of the KS lifetime­ KL lifetime: preliminary update with new data
­ study of the BR(K+ → )2

+ ­The DANE e e collider
W = m (1019.4 MeV)
Lpeak = 1.4×1032 cm­2 s­1­ Collisions at cm energy
around √s ~1019.4 MeV (m )­ Angle between thebeams @ IP: α∼­2*12.5 mrad
­ Residual laboratory momentumof : p ~13 MeV­ Cross section for production @ peak:   ~ 3.1μb
3Summary of KLOE data taking

Integrated luminosity L = 2.5 fb­1about 2.5×109 KSKL; 3.6×109 K+K­

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Kaon Physics at the  resonance

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The KLOE experiment

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KLOE detector performance7

Reconstruction of KS →  EventsKS  decay selection:­ 2 tracks of opposite sign
­ invariant mass consistentwith MK
= 1 MeVMinv() (MeV/c2)

 ~70% (mainly geometrical)
KS angular resolution ~ 1°
KS momentum resolution of 1 MeV
8from track momenta pKS=p+p

KS momentum determination
At a­factory, we have a redundant pKS measurement
For each event we measure:• Data1) pKS from √s and from kinematics­ Montecarloof → KK two­body decay
resolution ~ 1 MeV
dominated by beam energy
spread2) pKS from pion momenta
measurements in the drift
chamber  ~ 1 MeV
Requiring consistency between
momentum measurements guarantees
good track quality

Initial stateradiation tailMeV99 decay point
Average  decay point determinedwith Bhabha events on arun by run basis.
Resolution = beam spot size
(x~1mm, y=O(10 m),z ~ 1.5 cm)
A better determination of
decay point along the beamline (z) is evaluated event by
event by using the point ofclosest approach of KS line offlight to the beam axis line1010

KS lifetime

11Measurement of the KS lifetime
Motivation:­ first measurement with pure KS beam and with an event­by­event
knowledge of KS momentum­ KLOE is well suited to performS measurement as a function of siderealtime which is interesting to test QM, CPT and Lorentz invariance­ Vus from KS with KLOE data
(we measured BR(Kse3) at 1.3%, we can reach 0.5% on the wholedata set)
Method:lifetime obtained from fit to proper time t* distribution ofKS →  decay
LM KL
*t=

c=pc12

Raw Time resolution
LM KL
*t=
=cpcThis first attempt produces
a resolution function notcentered around zero→ not appropriate
for a < 0.1% measurement!
So see next transparency...

t*­ tMC

ns 1313

Improvement of KS decay length resolution1) Further improve reconstruction of IP event­by­event using fullgeometrical fit2) Optimize the selection criteria,
requiring pions to decay at large
angle with respect to the KS lineof flight3) Use only well measured tracks:
cut on the  value from the track fit

20 million events selected in 600 pb­1

Path length resolution
improved by factor of 3t*­ tMC

ns14

Fit to the lifetime
Since resolution depends on K beam direction, fit is done foreach of 270 bins in cosK and K.
This is also necessary to measure S as a function of sidereal coordinates

Fit results by bin S/SPDG+1

cos

entries

Fit ranget*/SPDG­1K
Fit range: from ­2 to 7 tS
Fit function: exponential convoluted with two gaussians(5 parameters: lifetime, 2 normalizations, 2 widths)

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Systematics
SourceValue (/ S x 10­4)
Selection cuts
3.3cos K cut
5.7
Momentum calibration 0.4
Fit range
5.0
We expect a total error competitive with the precise
measurements from KTeV and NA48
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KL lifetime

with KL →   decay channel

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KL lifetime measurement
L = (50.92 ± 0.17 ± 0.25) ns
direct measurement: (d/~0.6%)
PLB 626 (2005) 15
uses 10 M KL →  events from 2001­2002 data
L = (50.72 ± 0.11 ± 0.35) ns
indirect measurement:
PLB 632 (2006) 43
uses constraint ∑BR(KL)=1
The error on L is now the main limiting factor on Vus accuracy
from KL decay rates:
BR/=

L direct measurement can be improved both in statistical and systematic
accuracy using the 2004­05 data sample
Vus f+(0))/(Vus f+(0)) = 0.1%  0.2%  0.1%  0.1% Phases
RadiativeBRL
spacecorrections
integral18

KL →    decay vertex
Reconstruction of KS→ determines KL momentum
within 1 MeV and 1 degree

Vertex reconstruction from theneutral clusters on the calorimeter
Lγ
L θKL
LKKSLK Lt clu =K c cL 2L 2K −2 L L K cos =L2
Can extract LK, L

19Neutral vertex recostruction efficiency
Multiphoton vertex
evaluated from vertices
given by the neutralclusters on the EmC
To reconstruct the KL vertex,
we require at least 3 photons
from the  decay
Reconstruction efficiency
for KL → with N ≥3is high and uniform over abroad interval in LK
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Photon multiplicities

Only retain N≥3for the analysisN21

Neutral vertex calibration
Use of a control sample of KL → δ
decays allows comparison between theLγvertex given by the reconstructed pion tracks Lγ
and the neutral vertex, which is fundamental to:LK
1) calibrate the time scaleKL2) study the neutral vertex resolution

δKS R= Rcha −Rneu
Spatial resolution ~ 2 cm
22Single  reconstruction efficiency
Use of the control sample KL → allow to measure the vertex
reconstruction efficiency from the single photon

N  rec=N  tag

Number of events in which a second photon is detected
where we expect to find from kinematics
Number of events in which at least one photon is detected
EmC barrel+Data+Montecarlo

Rt (cm)EmC barrel+Data+Montecarlo

We correct the MC efficiency with the ratio data/MCE (MeV)2323

Fit result
Fit performed with−t */ f t = sel t  N 0 e**

 f bck B t*

2/dof = 50/54 In the fit region:
Fit range: 8­26 ns data events: 46 millions
background after cuts: 1.81%
1.1pb­1Residuals

KL → KL → KS → regen

Proper time (ns)24Fit result
Fit performed with−t */ f t = sel t  N 0 e**

2/dof = 50/54
Fit range: 8­26 ns

 f bck B t*Fit result:L = (50.56 ± 0.14) ns
Statistical error can beimproved by decreasing thelower limit of the fit region(taking into account of theKL beam losses on theregenerating surfaces)

Proper time (ns)25PreliminarySystematics

 L = (50.56 ± 0.14stat ± 0.21syst) ns26

KL lifetimes
Comparison with previous KLOE measurements:
L = (50.92 ± 0.17stat ± 0.13syst uncorr ± 0.27syst corr) ns

KLOE
PLB 626 (2005)

, taking into account the correlation between syst. errors
L = (50.72 ± 0.11stat ± 0.35syst) ns∑i BRi =1

KLOE
PLB 635 (2006)

Preliminary

 L = (50.56 ± 0.14stat ± 0.21syst) ns

For final result:1) add 2004 data set stat → 0.11 ns2) reduce systematic error on the tagging efficiency

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Absolute K    branching ratio
±±



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Tagging K+K­ beams

25%

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Absolute BR( K    ( ) )+30

Signal selection
tagging K

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The selected sample~ 60000 K+ → 3 events(background subtracted)~ 25000 K+ → 3 events(background subtracted)

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Signal selection efficiency

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Conclusions
KLOE will soon have a competitive result on the measurement of S
taking advantage of pure sample of KS → and precise determinationof event kinematics
KLOE has a new preliminary measurement of L based on 2005 data.
The final measurement will include 2004 data and will have asignificantly reduced systematic error
We are finalizing the measurement of the absolute BR(K+ → );this will allow to constrain the sum of the dominant K+ decay modes

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Spare slides

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Tagging of KSKL beams

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Tagging of K+K- beams (II)to minimize the impact of the trigger efficiency on the signal side we restrict
our normalization sample Ntag to 2-body decays that provide themselves the Emc
trigger of the event self-triggering tags
Emc trigger given by 2 trigger sectors over threshold ∼ 50 MeV

tag µ νtag π π 0
π 0 clusters must satisfy
the Emc trigger

the µ cluster fires 2
trigger sectors

the sample Ntag isreduced by ≅ 75%

the sample Ntag isreduced by ≅ 35%

resolutions: neutral VTX vs DC reconstructed quantitiesσ θ π ≈ 10

dataMCbin pπ = 30 MeV

bin ρ vtx = 5 cm

dataMCσ ρ vtx ≈ 2.2 cm

bin θ π = 30
σ pπ ≈ 14 MeV∆θ πdataMC∆ pπ (MeV)∆ ρ vtx (cm)

BR(K →       )• PDG 04 average:∆ BR/BR = 3.6%average ∆ BR/BR = 1.8% CHIANG ’72:
Σ f BR(K± → f ) = 1 and no info on rad. cut-off

Signal selection• 2-tracks vertex before DC inner wall and along the K path obtained frombackward extrapolation of the tagging kaon track to the I.P.
• Signal peak in the missing mass spectrum (∼ mπ 2)kine MC• Correct MC efficiency with single track efficiency
DATA/MC from K± →π ± π 0π 0 control samplepπ (MeV)39