barbara sciascia – lnf 1 k semileptonic br measurement b. sciascia 4 may 2006 kpmksl joint...
TRANSCRIPT
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.
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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.
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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
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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.
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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
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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
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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
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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
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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.