1 Barbara Sciascia October, 26th - LNF Barbara Sciascia
KK semileptonic decays: semileptonic decays: status report status report
Charged Kaon Meeting October, 26st - LNF
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Outline
• Tag bias• Cosmic veto/T3 correction• Efficiency determination: (0)
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Tag selection
KK
KK
ee
Tag events with a K:• track from IP • momentum cut: 70 MeV pK 130 MeV• decay vertex in fiducial volume: 40cm VTX 150 cm• 2-body decay identified in kaon rest frame: p(m): 3 cut• track pointing into the calorimeter• Associated cluster on the Barrel with E>90 MeV (99%)• Emc Trigger satisfied by muon cluster (30%)
Absolute BR measurement via a Tag technique.
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Signal selectionKl3 selection: 1-prong kaon decay vertex in the
fiducial volume 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, from TOF measurement:
tdecayK = tlept -Llept /(leptc) = t-L/c
KK
KK
ee
2 further kinematical cuts to reject
background from K and K2 decays.
Absolute BR measurement via a Tag technique.
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Selection efficiency
BR(Kl3) =N(Kl3) (TAG(i) BR(i)) 1 NTAG TAG(Kl3) SELE
Fit results Tag bias correction
[(KAON+VTX+TRK) TCA) 0)]DATA
3 samples
[(KAON+VTX+TRK) TCA) 0) ]MC
SELE= SELE_MC
C
Cosmic veto/T3correction
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Measuring BR(Kl3)
• 12 Tag samples: K2 + -trigger K2 + 0-trigger K2 + Global_Emc-trigger
• Counting Kl3 from fit.• KPM04 MC production.
• Tag bias: trigger and kinematics stability checked• Cosmic veto correction• Selection efficiencies:
Tracking: global, from Paolo Massarotti; syst. at 0.3% level.
Track-to-Cluster: from neutral kaons (Paolo Branchini).0: from single photon efficiency
(work is in progress, Simone dell’Agnello).
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Tag bias: stability wrt tag kine selection
• Stability of tag-bias value wrt the cut around the “p* 2-body peak” • Select events with a n- cut around the peak: 236 MeV for K2, -trig 205 MeV for K2, 0-trig• TB stable within the errors (now: 3 cut for both Ke3 and K3).
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Trigger: EMC/DC-1
DC/EMC
EMC/DC
• Measure EmC-trigger efficiency wrt the DC trigger: (EMC/DC) (errors are statistical only)
Data MC
K 94.982 0.003 95.130 0.006
K 95.129 0.003 95.188 0.006
• (EMC/DC) is stable within the errors wrt the threshold requirement at the 2nd level DC trigger.
(EMC/DC) Data
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Trigger: EMC/DC-2
CTRGData MC Truth
K 92.752 0.003 92.896 0.007
K 92.949 0.003 93.007 0.007
• From MC, evaluate the correlation factor, CTRG, between DC and EmC Trigger• Correct (EMC/DC) from data, using CTRG • Compare with MC truth (errors are statistical only):
• Difference at the 0.1 % level (0.14% for K and 0.06% for K)• First check of the reliability of Tag-bias measurement for what concern Emc-global-trigger.
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Trigger: “Two-emisphere method”-1 • “Two-emisphere method” (KLOE memo 223) successfully used in studying trigger efficiency in neutral kaon analyses
KK
KK
ee
•Define: EMC=1 P(Tag=1)P(DarkSide=0) where:
- P(Tag=1): probability for the selected “Tag Emisphere” of firing only one trigger sector (here the -cluster)
- P(DarkSide=0): probability for “the rest of the event” (included machine bkg clusters) of not firing any sectors
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Trigger: “Two-emisphere method”-2•The “division of the event” has a degree of arbitrarity which can be kept under control defining a MAX and a min probability for the selected list of clusters: P P; with P = PMAX PMin
• Good agreement within the errors between MC and Data• Reliability of the method: 0.8% of difference wrt the MC truth• Correcting data with factor C = EMC(MC)/EMC(MCtruth) we get EMC(Data) values in very good agreement with Mctruth.
• Good check of trigger effectson tag-bias evaluation.
EMC(Data) EMC(MC)
K 91.96 0.23 92.21 0.25
K 92.09 0.25 92.27 0.25
EMC (MCtruth)
92.896 0.007
93.007 0.007
CEMC(Data)
K 92.64 0.23
K 92.83 0.25
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Cosmic ray veto – T3 correction
• The correction factor C can be evaluated directly on data, using T3 and Cosmic veto flags.
m2(MeV2)
Ke3 K3
•
• CT is evaluated in each Tag sample separately.• To evaluated CS a raw cut is applied in the m2 distribution to separate Ke3 and K3 events.• C is of the order of 0.1% for all samples.• The contribution to the final error is negligible (104)
(1+CS/S)
(1+CT/T)
C =
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0-from-vertex efficiency - Old
Pmiss (MeV)DATA/MC
• P0 reconstruction efficiency is estimated as a function of p0 momentum, from Kpp0 decays.• DATA/MC ratio is flat: 97.70 0.09 %
K kinematic selection
MC
DATA
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Single photon efficiency-1
• Select events with K2 or K2 tag.• Unbias for the trigger: require Emc-trigger to - or 0-clusters, following the tag.• Ask for a K2 selection (p* cut) in the signal side. • Get 0 from the missing momentum at vertex.• Look for a 0-photon from the vertex, excluding clusters already used by the tag or connected to a track.
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Single photon efficiency-2
• Starting with K2+ selection, estimate the energy and the position of the “other photon”. • Look for a cluster close to the other photon.• “Close to” criteria: 1- distance between cluster and estimated position. 2- opening angle between estimated and cluster direction from the vertex.
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Single photon efficiency-3
• Measurement o the single photon efficiency as a function of estimated energy ot the photon, separately for different tags (K2 or K2) and charges.• The efficiency behaviour at high energy (similar to the KL0 measurement) indicate a not correct acceptance definition.
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Single photon efficiency-4
• 40 pb-1 of 2002 Data and 2002 MC all_phys have been used.
• Data and MC have different resolutions in p* and in cluster selection variables.
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Conclusions
• The tag bias is stable wrt the kinematical cut applied for the selection of the different tag samples.• A first study of the trigger efficiency for K events has been presented, using two different metod. The agreement between MC and Data is very good within the errors• The evaluation of the correction due to the cosmic veto has been presented.• Work is in progress for the 0 efficiency: single-photon efficiency correction applied on MC.•The NEW KPM04 MC reduces the MC statistics contribution to the BR measurements by a factor 3.• The study of the systematics related to efficiency determination has to be completed, taking correlations into account.
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Spare slides
Spare slides
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On the way towards 0 efficiencyE
min(MeV)Emin(MeV)
p 0ki
ne(M
eV)
Kl3 (MC)
K0 (MC)
• The low component of the 0 momentum spectrum for Kl3 events span a region of E
min which is fully contained in the Emin
range of K decays.• Plenty of statistics to minimize contribution to efficiency error.
• Single-photon efficiency measured with K2 events.
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Single photon efficiency. Data/MC-Old
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Single photon efficiency. Data/MC-New
• 20 pb-1 of Data and MC (KPM04)
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• The errors on Kl3 BR measurements are at 2% level.• They are dominated by the Kpm MC statistics • As an example: BR(K+e3) = (4.8xx 0.110)% with: 0.110 % (0.033 0.102 0.025)%
A note on Kpm MC statistics
• A Kpm-MC campaign with 1/1 MC statistics wrt to Data will lower the MC sample contribution to the error from 2% to 0.5%
[(KAON+VTX+TRK) TCA) 0)]DATA
[(KAON+VTX+TRK) TCA) 0) ]MC
SELE= SELE_MC
From the fit
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KPW04 - Conclusions• A selection has been presented aiming at measuring absolute Kl3 BR, on a sample of K2 tagged decays.• The signal events has selected using a ToF technique (m2
lept spectrum is obtained).• Further kinematic cuts are applied to reduce residual background contamination.• Result of the fit on the m2
lept spectrum gives a yield of 200k Ke3
decays on the whole 2001-2002 data sample.• Selection efficiency is taken from MC, with DATA/MC correction for what concern K+Vtx+Trk, TCA and 0 efficiencies.• The contributions to the fractional error on BR(Ke3) are 0.6% from the fit and 1% from the efficiency• A first attempt has been performed in order to extract the slope of the form factor + from a fit of the Dalitz plot of Ke3 decay.• The study of the systematics related to efficiency determination has to be completed, taking correlations into account.
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