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Barbara Sciascia – LNF 1 K  semileptonic BR measurement B. Sciascia 4 may 2006 KpmKSL joint meeting.

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Presentation on theme: "Barbara Sciascia – LNF 1 K  semileptonic BR measurement B. Sciascia 4 may 2006 KpmKSL joint meeting."— Presentation transcript:

1 Barbara Sciascia – LNF 1 K  semileptonic BR measurement B. Sciascia 4 may 2006 KpmKSL joint meeting

2 Barbara Sciascia – LNF 2 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(K   0 e  ) and BR(K   0   ) Systematics: from Tag bias, FilFo, Cosmic veto/T3, Trigger, K  nuclear interaction, Fiducial volume, Signal selection, and Efficiencies.

3 Barbara Sciascia – LNF 3 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)<3  t ) Spectrum of charged daughter mass, m 2 lept, from TOF measurement: t decay K = t lept -L lept /(  lept c) =  t  -L  /c  KKKK  KKKK eeee   Selection of K ± semileptonic decays (K l3 ) Fit m 2 lept spectrum with a linear combination of Ke3 and K  3 shapes, and background contribution.

4 Barbara Sciascia – LNF 4 Signal selection: m 2 shapes K  0  0 K  0 K nucl.int. K3K3 Ke3 Signals and background have the same signature in m 2. K     0  0  with a  0 undergoing a Dalitz decay Give a m 2 lept under the Ke3 peak. K     0  with an early      give a m 2 lept under the K  3 peak

5 Barbara Sciascia – LNF 5 Background rejection-1 K     0  0 are rejected cutting on E miss -P miss spectrum (<90MeV); the  0 momentum is obtained by mean of a kinematic fit K     0 events are rejected evaluating the missing momentum at the decay vertex, and cutting on momentum of the secondary track in the P miss rest frame (P>80 MeV) E miss -P miss (MeV) K   0  0 K   0,    K   0 e  K   0   K   0  0 P(MeV) K   0 l 

6 Barbara Sciascia – LNF 6 Signal selection: m 2 final shapes The previous cuts reject about 96% of background events The efficiency on the signal is: about 55% for both Ke3 and K  3 K  0  0 K  0 K nucl.int. The residual background is about 1.5% of the selected K  l3 sample, and has the m  2 signature.

7 Barbara Sciascia – LNF 7 The ingredients of the measure BR(Kl3) = N(Kl3) 1 1  (  TAG (i) BR(i) ) N TAG (1-f NI )  FV  SELE  TAG (Kl3) Fit results Tag 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/T3 and FilFo correction to the Tag bias, from Data and MC K nuclear interaction correction Fiducial volume efficiency  58%   About 9% for each sample

8 Barbara Sciascia – LNF 8 What’s new Tracking efficiency correction: Dependency on lepton momentum, studied in 2 samples. - Kl3 enriched vs (K  ’,K  2) enriched Systematics of the correction from difference of control samples. Signal selection: Good stability wrt selection cuts and tracking variables f NI : Kaon nuclear interaction measured directly on data Small disagreement MC-Data Correction applied to N(K-) + rescale TB

9 Barbara Sciascia – LNF 9 BR measurement (almost final) TagBR(Ke3)% dBR(1-  )%dBR(  )% Tag K +  Tag K +  Tag K -  Tag K -  Tag BR(K  3)%dBR(  )% Tag K +  Tag K +  Tag K -  Tag K -  BR(Ke3)  % BR(K  3)3.397  % All contributions to the error are included. Some checks “of completeness” are still needed. “1-  ” include syst. from tag and fit counting ( %) 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 10 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 p K  100 MeV Playing with Vus (thanks to MM) V US f + (0) value: from (48) to.21699(50) “big” fractional errors: Ke3 at 1.5% and K  3 at 2.5% level.  2 of KLOE measurements: 7.7/4 (Prob  10%); 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 11 Counting of the events (new) Tag K +  2K+2K+2K-2K-2K-2K-2 N TAG Tag K+2K+2K+2K+2K-2K-2K-2K-2 N Ke (391) (235)96 914(409)31 130(235) NK3NK (301)16 176(180) (315)16 131(179) Tag Number of events selected for each signal divided per tag: Correlation matrix from the fit: K e3 K  3 K e3 BkgK  3 Bkg  2 %  7 %  30 % Signal from the fit

12 Barbara Sciascia – LNF 12 Counting of the events (old) Tag K +  2K+2K+2K-2K-2K-2K-2 N TAG Tag K+2K+2K+2K+2K-2K-2K-2K-2 N Ke     204 NK3NK     168 Tag Number of events selected for each signal divided per tag: Correlation matrix from the fit: K e3 K  3 K e3 BkgK  3 Bkg 4 % 2 %30 % Signal from the fit

13 Barbara Sciascia – LNF 13 Absolute BR(Ke3(  )) measurement Tag BR(Ke3)   BR % Tag K +   Tag K +   Tag K -   Tag K -   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 +  2Tag K -  2Tag K +  2

14 Barbara Sciascia – LNF 14 Absolute BR(K  3(  )) measurements Tag BR(K  3)   BR % Tag K +   Tag K +   Tag K -   Tag K -    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 +  2Tag K -  2Tag K +  2

15 Barbara Sciascia – LNF 15 K  ℓ3 - 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% K  3: 5.32/3, P(  2 >   2 )  15% Averages carefully calculated taking correlations into account: BR(Ke3)   Sys Sig% BR(K  3)3.310   Sys Sig % Tag K -  2Tag K +  2Tag K -  2Tag K +  2 Tag K -  2Tag K +  2Tag K -  2Tag K +  2 KLOE preliminary The error is dominated by the error on Data/MC efficiency correction. Fractional accuracy of 0.9% for Ke3, 1.2% for K  3.


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