1 Barbara Sciascia – LNF

K semileptonic BR measurement

B. Sciascia4 may 2006 KpmKSL joint meeting

2 Barbara Sciascia – LNF

Analysis scheme

• Tag: Selection. 4 different samples are used.

• Signal: Selection. Counting by means of a Fit procedure.

• Efficiency: From MC. Data/MC corrections for Tracking, Track-to-Cluster, and Photon efficiencies.

• Results: BR(K0e) and BR(K0)

• Systematics: from Tag bias, FilFo, Cosmic veto/T3, Trigger, K nuclear interaction, Fiducial volume, Signal selection, and Efficiencies.

3 Barbara Sciascia – LNF

Signal selection

• 1-prong kaon decay vertex in the fiducial volume (40 VTX 150 cm)

• daughter track extrapol. to EMC• Reject two-body decays: p(m) 195 MeV• 0 search: 2 neutral clusters in EmC,

with ToF matching the K decay vertex (t)<3t)

• Spectrum of charged daughter mass, m2

lept, from TOF measurement:

tdecayK = tlept -Llept /(leptc) = t-L/c

KK

KK

ee

Selection of K± semileptonic decays (Kl3)

• Fit m2lept spectrum with a linear

combination of Ke3 and K3 shapes, and background contribution.

4 Barbara Sciascia – LNF

Signal selection: m2 shapes

K00

K0

K nucl.int.

K3Ke3

• Signals and background have the same signature in m2. • K00 with a 0 undergoing a Dalitz decay• Give a m2

lept under the Ke3 peak.

• K0 with an early give a m2

lept under the K3 peak

5 Barbara Sciascia – LNF

Background rejection-1

• K00 are rejected cutting on Emiss-Pmiss spectrum (<90MeV); the 0 momentum is obtained by mean of a kinematic fit

• K0 events are rejected evaluating the missing momentum at the decay vertex, and cutting on momentum of the secondary track in the Pmiss rest frame (P>80 MeV)

Emiss-Pmiss (MeV)

K00

K0,

K0e

K0

K00

P(MeV)

K0l

6 Barbara Sciascia – LNF

Signal selection: m2 final shapes • The previous cuts reject about 96% of background events• The efficiency on the signal is: about 55% for both Ke3 and K3

K00

K0

K nucl.int.

• The residual background is about 1.5% of the selected Kl3 sample, and has the m

2 signature.

7 Barbara Sciascia – LNF

The ingredients of the measure

BR(Kl3) = N(Kl3) 1 1 (TAG(i) BR(i)) NTAG (1-fNI) FV SELE TAG(Kl3)

Fit resultsTag bias correction,from MC

(KINK)DATA TCA)DATA 0)DATA

4 tag samples

(KINK) MC TCA) MC 0) MC

SELE= SELE_MC

CF

Cosmic veto/T3and FilFo correctionto the Tag bias, from Data and MC

K nuclear interaction correction

Fiducial volumeefficiency 58%

About 9% for each sample

8 Barbara Sciascia – LNF

What’s new

Tracking efficiency correction: Dependency on lepton momentum, studied in 2 samples. - Kl3 enriched vs (K’,K2) enriched Systematics of the correction from difference of control samples.

Signal selection: Good stability wrt selection cuts and tracking variables

fNI: Kaon nuclear interaction measured directly on data Small disagreement MC-Data Correction applied to N(K-) + rescale TB

9 Barbara Sciascia – LNF

BR measurement (almost final)

Tag BR(Ke3)% dBR(1-)% dBR()%

Tag K+2 5.149 0.029 0.124

Tag K+2 5.082 0.051 0.192

Tag K-2 5.290 0.023 0.129

Tag K-2 5.385 0.043 0.228

Tag BR(K3)% dBR()% dBR()%

Tag K+2 3.337 0.025 0.159

Tag K+2 3.275 0.043 0.213

Tag K-2 3.435 0.022 0.099

Tag K-2 3.491 0.040 0.294

BR(Ke3) 5.209 0.077 %

BR(K3) 3.397 0.091 %

• All contributions to the error are included. Some checks “of completeness” are still needed.

• “1-” include syst. from tag and fit counting (0.02-0.04%)

• Final error dominated by uncertainty on the efficiency correction (essentially TRK, poor statistics).

• Syst from tracking calculated and applied “per charge” (not “per tag”): 0.02% absolute

10 Barbara Sciascia – LNF

Conclusions

• Difference wrt the blessing: essentially due to the previous lack of momentum dependency in the tracking efficiency correction.• Important check of negative kaon nuclear interactions, poorly known at pK 100 MeV

• Playing with Vus (thanks to MM) VUSf+(0) value: from 0.21671(48) to .21699(50) “big” fractional errors: Ke3 at 1.5% and K3 at 2.5% level. 2 of KLOE measurements: 7.7/4 (Prob10%); before was 2.3/4. Good agreement with E865 result (…also with rumors from NA48, MA). ? ---- Appreciable difference between charged and neutral estimations ----?

• Blessing of the final result ready in few weeks

11 Barbara Sciascia – LNF

Counting of the events (new)

Tag K+2 K+2 K-2 K-2

NTAG 22 033 840 7 610 348 22 608 408 7 278 319

Tag K+2 K+2 K-2 K-2

NKe3 91 256(391) 31 311(235) 96 914(409) 31 130(235)

NK3 46 800(301) 16 176(180) 49 753 (315) 16 131(179)

• Tag

Number of events selected for each signal divided per tag:

• Correlation matrix from the fit:

Ke3K3 Ke3Bkg K3Bkg

2 % 7 % 30 %

• Signal from the fit

12 Barbara Sciascia – LNF

Counting of the events (old)

Tag K+2 K+2 K-2 K-2

NTAG 21 699 562 8 466 737 22 655 426 8 233 472

Tag K+2 K+2 K-2 K-2

NKe3

62 781 321

24 914 20866 657

33424 225 204

NK337 461

26414 827 170

39 988 277

14 608 168

• Tag

Number of events selected for each signal divided per tag:

• Correlation matrix from the fit:

Ke3K3 Ke3Bkg K3Bkg

4 % 2 % 30 %

• Signal from the fit

13 Barbara Sciascia – LNF

Absolute BR(Ke3()) measurementTag BR(Ke3) BR %

Tag K+2 4.991 0.075

Tag K+2 5.065 0.094

Tag K-2 5.066 0.071

Tag K-2 5.125 0.091

• Uncorrelated errors between the 4 tag samples: Nsig, tag bias, FilFo, CosmicVeto/T3, MC stat. used for efficiency evaluation, photon efficiency.

• Partially correlated error: kink and TCA efficiency corrections of MC efficiency.

• 2/nDof = 3.20/3 for the 4 measurements with uncorrelated errors, P(2>

2) 36%Tag K-2Tag K+2 Tag K-2Tag K+2

14 Barbara Sciascia – LNF

Absolute BR(K3()) measurements

Tag BR(K3) BR %

Tag K+2 3.264 0.067

Tag K+2 3.272 0.079

Tag K-2 3.336 0.064

Tag K-2 3.398 0.079

• 2/nDof = 5.32/3 for the 4 measurements with uncorrelated errors, P(2>

2) 15% •The number of signal events is evaluated in each sample separately, using the SAME FIT PROCEDURE. Systematic errors coming from the fit are common to all samples.

• Also the systematic coming from the selection efficiency is COMMON TO ALL SAMPLES.

Tag K-2Tag K+2 Tag K-2Tag K+2

15 Barbara Sciascia – LNF

Kℓ3 - Results• The error accounts for the data and Monte Carlo statistics used in the fit, the MC statistics for the efficiency estimation, the Data/MC efficiency corrections, and the systematics on the tag selection. • The systematics due to the signal selection efficiency is under evaluation.• 2/nDof for the 4 measurements:

Ke3: 3.20/3, P(2> 2) 36%

K3: 5.32/3, P(2> 2) 15%

• Averages carefully calculated taking correlations into account:

BR(Ke3)5.047 0.046 Sys Sig

%

BR(K3)3.310 0.040 Sys Sig

%

Tag K-2Tag K+2 Tag K-2Tag K+2

Tag K-2Tag K+2 Tag K-2Tag K+2

KLOE preli

min

ary

• The error is dominated by the error on Data/MC efficiency correction.• Fractional accuracy of 0.9% for Ke3, 1.2% for K3.