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Status of the ee analysis Mauro Raggi, LNF INFN 29 th August 2013 NA48/2 rare decay session NA62 Collaboration meeting Liverpool

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Outline Introduction to ee decay Status of the MC generators The CMC DE generator vs theory Review of the analysis strategy List of cuts Data and MC sample BG evaluation technique Likelihood method Meeg cut and side band evaluation Data MC comparison (ppee IB) Resolutions and energy scales (charged neutral and global) Mee resolution vs mee Measurement of the Kaon Flux BG evaluation in K2pDg Trigger efficiency BR values and systematic checks 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Introduction to ee decay 28 August 2013 The interference thanks to the possibility of measuring the plane of polarization of the e+e- pair is splitted into 3 terms: IB/E, IB/M and E/B. IB/M cancels when integrated over as in , while E/B is only non- zero if CP violation is allowed. Short and long distance parity violation contributions Theoretical paper on ppee are currently: H. Pichl, ``K --> pi pi0 e+ e- decays and chiral low-energy constants,'’ Eur. Phys. J. C 20, 371 (2001) [arXiv:hep-ph/0010284]. L. Cappiello, O. Cata, G. D'Ambrosio and D. Gao Eur. Phys. J. C (2012) 72:1872 Never observed so far Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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BR IB isospin breaking correction 28 August 2013 Cut IB Pub. IB isospinCut IB stand IB isospin The isospin breaking correction only changes the absolute value of the BR (- 2%) not the shape of the Q distribution. Values are not published (G. D’Ambrosio private communication) Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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DE matrix element 28 August 2013 New set of form factors including unknown parameters Combination are the same as K ± -> Need to implement the T3 components From NA48/2 K ± -> While Thanks to P. Massarotti Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Table of comparison MC theory 28 August 2013 Q>MeVIB thIB MCDE thDE MC 2*m e 11.00000011 2 MeV0.736 0.8570.865 4 MeV0.4660.4670.6890.693 8 MeV0.2620.2630.5170.519 15 MeV0.1340.1350.3660.363 35 MeV0.03710.03730.1640.167 55 MeV0.01340.01360.0800.082 85 MeV0.003280.003320.026 100 MeV0.001600.001540.0140.013 120 MeV0.000570.000510.005 140 MeV0.0000960.000150.00070.0016 Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy Both IB and DE generators have been implemented in a private version of CMC007 For both components all 2003 MC sample has been generated with a statistics which exceeds 10 time the data one.

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Analysis strategy Use only the full 2003 data sample (SS0-1-2-3) Use + 0 D ( ) IB as normalization channel Use: (1Vtx or 2Vtx or 1TrkP) as trigger sample Perform the BR IB and possibly charge asymmetry measurements Leave the enlargement of the sample and P violation for final result 28 August 2013 Correction nameDataMC Non linearity (1) X Projectivity XX Alpha and Beta XX Blue Field XX Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Analysis definitions cuts (presel) Good Vertex -1000 < Z VTX < 8000 NVTXtrk = 3 Good Track TrackQual >0.75 new 2 GeV

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Common preselection Preselection cuts (common to PPD and signal analysis) NgoodVertex=1 3 < NgoodCluster < 8 3 < NgoodTracks < 8 Ellipse 3pc cut 116ns < Track time <154ns new! 3 good track are the same used in vertex fitting 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Signal selection ngoodCl ≥4 N electrons =2 E/P>0.85 new N pions =1 E/P<0.85 N gammas =2 cluster with no associated track &E cl >3 GeV COG < 2 cm abs(E TOT -p k )< 6 GeV abs(Mpi0-M PI0 PDG)<10 MeV Mee > 0.001022 GeV Distance of electrons @ DCH1 > 0.25 against conversions Total charge of electrons = 0 abs(Mee -M PI0 PDG)>0.005) cut on Dalitz decay mass abs(M K -M K PDG) < 10 MeV 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Data MC comparison ppee 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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M K for data and MC (no BG sub) Data MC comparison is non good due to 10% BG in the data sample MK(MC) media = 493.30 MeV Sigma = 5.6 MeV MK(data) media = 492.69 MeV Sigma = 5.85 MeV 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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M K for data and MC (BG sub) Data MC comparison is good after BG subtraction in the data sample MK(MC) media = 493.30 MeV Sigma = 5.6 MeV MK(data) media = 493.29 MeV Sigma = 5.37 MeV 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Z V data MC for signal 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Data MC M ee no BG sub 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy Region above 100 MeV dominated by D BG Bad agreement between data and MC

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Data MC M ee BG sub 28 August 2013 Good agreement in between D’Ambrosio and data Data peak at 120MeV due to 3PD BG almost disappeared Is the remaining discrepancy due to DE events? Or only insufficient MC statistics in 3pD? Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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BG estimate signal 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Final set of cuts except M K 28 August 2013 Integrating in the mass plot BG(3PD)= 190.5±11 BG(2PD)= 100±5 Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Flux normalization 28 August 2013 Use the flux measurement and BRs to estimate BG value Scale the MC to: NToT(BG)=K flux x Acc(BG) x Eff x BR(BG) Compute the integral in the region M K ±10MeV BG(3PD)= 192±12.5 stat ± 6 ext BG(2PD)= 75±10 stat ±2.4 ext Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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BG estimate summary table Method3PD2PDTotal TfractionFitter190.5±11100±12290.5±23 Flux norm.195± 13 sta ± 6 ext 75 ± 10 stat ± 2.2ext270.0 ±17stat±7ext 28 August 2013 The BG measurements agree very well on the 3PD The value for PPD is not soo good due to low MC statistics in the plot The value we will use for the BG subtraction is: 280±17stat±7syst The systematic assigned is the 0.5*difference between the 2 estimates 10 Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Flux measurement 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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The Kaon flux measurement Used the decay K ± -> ± D ( ) (PPD) means K ± -> ± e+e- ( ) Same trigger chain of the signal Very similar final state in the charged trigger (e+e- +) MonteCarlo generator used: According to Evgueni suggestion using the KLOE generator (CMC 51) 1 times full 2003 data set 222 Million events generated run by run 165 in the ZV region 1.3 time the data Normalization BR used in the calculation: BR(K->2 ( ))xBR( ->Dalitz)=(20.66*1.174)x10 -2 =(2.425±0.073)x10 -3 No cut applied to minimum E * assuming that generator is fine Flux measurement formula: (N PPD - NBG PPD )/( PPD x Acc PPD x BR PPD ) 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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PPD selection cuts N electrons = 2 (0.9

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T * PPD data BG estimate 28 August 2013 Unknown BG source: NBG=65*(130-85)*4+30*(140-130)*4+734=13634 < 0.1% Systematic on the flux measurement (0.1%) K 3D BG from MC estimate (subtracted from data) NBG=7109 65 events/bin Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy K3DK3D

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Data MC for PPD selection 28 August 2013 Data Mass fit results Mean 493.09 MeV Sigma 3.83 MeV MC Mass fit results Mean 493.18 MeV Sigma 3.93 MeV Mass are very close to each other <100 KeV They are apart from the PDG by 0.5 and 0.4 MeV Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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T* data MC for PPD 28 August 2013 Data T*p fit Mean 1085.56 ±1.23x10 -6 Sigma 3.83 MeV MC T*p fit Mean 108.587 MeV Sigma 3.91 MeV The T*p is perfectly on it’s place 108.5 The difference in data to MC is order 30KeV only The scale of the spectrometer is really in the right place! Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Flux calculation results 2003 QuantityValueRel Error BR( + 0 D ( )) (2.425±0.073)x10 -3 3% Acceptance(8.00± 0.002)%0.02% Trigger efficiency97.15 ± 0.0420.046% BG in PPD sample ??131300.1% (Sys) Ntot events146549940.026% 28 August 2013 KFlux=(N PPD - N BGPPD )/( PPD x Acc PPD x BR PPD )=(7.766±0.23)x10 10 Error completely dominated by external error BR( 0 D )=3% BG in PPD sample set to 0 and added 0.1% systematic Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Trigger efficiency measurement 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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General remarks on trigger Control trigger : CPRE & !WDOG (TRGW) Sample Trigger : 1VTX or 2VTX or 1TRK-P 1TRK-P: NT-PK (LvL 0) and 1TRK-P (Mfake<475 MeV) We expect the trig eff to be different for the 2 decays due to 1TRK-P component in fact: The ppee has 1 more cluster (NT-PK more efficient) The ppee has lower value of T* (Mfake) 1TRK-P is more efficient In the MC the efficiency of LvL0 NT-PK is not simulated correctly Problems of low statistics for signal measurement (27 events) Try to use BG enriched sample (330 events sample) Cannot use efficiency measured using PPD 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Trigger efficiency analysis Control trigger : CPRE & !WDOG (TRGW) Sample Triggers: (1VTX or 2VTX or 1TRKP) (1VTX or 2VTX) Measured with both the signal and the normalization in data and MC with loose and tight cuts Difference in between loose and tight cuts is < 0.1% in MC Data shows the same agreement at least in PPD Can we use the data loose cuts determination for trigger efficiency? 28 August 2013 Trigger Loose cutsPPDPPD MCppeeppee MC 1VTX or 2VTX94.97±0.05597.03±0.004697.7±0.8597.00±0.027 1VTX or 2VTX or 1TRK-P 97.15±0.042 98.48±0.0033 98.7±0.65 98.95±0.016 Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy Trigger Tight cutsPPDPPD MCppeeppee MC 1VTX or 2VTX95.08±0.05697.10±0.004792.6±5.097.44±0.032 1VTX or 2VTX or 1TRK-P97.25±0.04298.55±0.003396.3±3.699.07±0.019

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Trigger efficiency MC vs data PPD Different absolute value due to bad simulation of NT-PK but same behavior as function of Mee (Mee>2MeV) Difference increasing at low Mee 23 April 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy31 Data MC

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Trigger efficiency ppee vs PPD MC This difference is expected and due to MBX cut is small due to electrons in the MC NT-PK is not simulated The difference in data comes from NT-PK (3 clus PPD 4clus ppee) 23 April 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy32 PPD(MC) ppee(MC)

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Trigger efficiency loose to tight 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy Efficiency comparison for ppee MC. Tight 98.95 Loose 99.07 389197 control sample events 247440 control sample events

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Total BR result for 2003 raw value QuantityValue Acceptance(7.80±0.028)x10 -3 Trigger efficiency (raw data value)(98.7±0.65) see systematics N background270±16 Nppee BG subtracted2540±49 K flux (7.766±0.23 ext )x10 10 28 August 2013 Stat: Includes only the error on Nppee External error: only Kflux coming from BR( 0) D Trig: 0.65% error on 98.7% measured from data loose selection What about DE? Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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DE component fitting 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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DE and IB in the Mee spectrum Generated 13 Million events of ppee DE run by run 9.6M in Z V acceptance Acceptance measurement: Acc(DE) = (3.876± 0.006)% Acc(IB) = (0.782± 0.0015)% The ratio of acceptance is Acc(DE)/Acc(IB)~5 which means that the DE is a order ~6% in the data (according to D’Ambrosio prediction 1/77*BR(IB) ) Using G. D’Ambrosio theoretical BR leads to a BG evaluation of: N(ppee) DE =155±20 events ( includes a 10% error on the BR(DE) ) This number can be subtracted as a BG to get the N(ppee) IB N(ppee) IB =N(ppee) TOT N(ppee) DE = 2540 155 = 2385 IB events 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Fitting the DE Fitting the DE using M ee is quite hard for different reasons: Distributions of Mee is really very similar much more that in Regions in which the DE is dominant are populated by 10% BG The low statistics does’nt allow to have a very hard selection cuts Seems that our acceptance spoils the difference even more 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy IB MC GEN DE MC GEN Before the selection After the selection IB MC GEN DE MC GEN

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Real life is even harder… 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy IB MC REC DE MC REC Reconstructed MC after correct DE normalization including higher acceptance factor 5 Mee T* Situation in T*pi looks a bit better but BG has to be taken into account… IB MC DE MC

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T* BG distributions 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy 3pD MC DE MC

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Results of fitting attempts 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy Fit with 3 MC only: IB MC, 3pD, 2pDg MC IB frac (86.9±2.2)% 2445±62 ev BG 3pD frac (9.39±1.2)% 264±34 ev BG 2pDg frac (3.7±1.0)% 104±28 ev Estimate from BG fit measurement are: NBG 3PD 190.5 ± 13.0 NBG 2PD 100.0 ± 9.8 Residuals look quite good even without the DE. The enhancement of the 3PD bg +74 events is masking the presence of the DE Fits with DE does’nt converge!

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Systematic checks 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Cut variation systematics I did many cuts variation that you can see in my April talk M K, M COG, Mee, Mee E min, Pe Min No effect has been seen except for the Pe MIN This has been redone This misses still the correction of trigger efficiency point to point 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Minimum electron energy 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy Max difference (4.34-4.24)/4.24=2.3% max difference Part of this will be due to absence of trigger efficiency I propose to use the 0.5*Max Difference=1.2% systematic I’ll investigate this more soon.

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Errors summary table 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy SystematicValue N of signal events (2450)2.09% sqrt(2811)/2540 Signal acceptance0.2% Total Statistical2.1% Difference of 2 analysis 0.45% Back ground subtraction0.72% (error on BG 18.4/2540) Trigger efficiency0.65% (From data loose sample) Non linearity<1% Energy scaleNo effect Cut Variation1.2% (Pe MIN ) see april talk Total systematics1.74% BR( D ) external 3% Total external3%

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Preliminary BR result Theoretical prediction from G. D’Ambrosio et al (Eur. Phys. J. C (2012) 72:1872): BR(ppee) IB = 4.19 x 10 -6 IB only no isospin correction (PUBLISHED) BR(ppee) IB = 4.10 x 10 -6 IB only isospin breaking correction (PRIVATE) In the IB only BR we considered DE as a BG we subtracted: DE = Kflux*AccDE*Eff*BR DE (Th) =155±20 events (+0.8% syst or EXT) 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Conclusions We performed the first measurement of the BR for K ± ->ppee We reached less than 1% agreement between the two analysis Total and IB only BR can be measured The Background is very well under control (~9.6%) First attempt to fit DE is showing many obstacles Small difference in the spectrum BG domination in favored DE regions Low statistics in the data sample The result is in good agreement with isospin breaking corrected theory First systematic check does’nt reveal important contribution Trigger efficiency to be added to systematic check routine 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Thank you for your attention 28 August 2013

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IB matrix element We discovered that BR quoted in the paper is not including isospin breaking correction! Got new version of table 1 and of the DE part with Isospin breaking 28 August 2013Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Relevant definitions 28 August 2013 Reduced IB relevant T ij Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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Charged energy scales 3pc MC 28 August 2013 MC 3 mass Constant 1305.8 71.207 Mean 0.49365 0.215E-03 Sigma 0.171E-02 0.105E-03 To check the correction I run on a small sample of MC The mass of the Kaon is in its place means that the correction are fine Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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IB vs DE generated Q spectrum 28 August 2013 IB DE (IB+DE)/IB Mauro Raggi - I.N.F.N. - Laboratori Nazionali di Frascati - Italy

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