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

The charged kaon lifetime

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

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

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

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

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 = (12.367 ±0.044)ns

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

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

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

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 = (12.391 ±0.049)ns

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

Method #2: Directly measure decay time Preliminary results Method #1: fit t* distribution from decay length Preliminary t = (12.367 ±0.044stat±0.065syst)ns Method #2: Directly measure decay time Preliminary t = (12.391 ±0.049stat±0.025syst)ns Correlation r = 0.338

. 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 = (12.384 ±0.048)ns

Measurement of BR(K+p+p0)

Measurement of BR(K+p+p0) PDG fit ‘06 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

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

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%

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