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e'/e Measurement by NA48: History, Analysis, Results

Explore the direct CP violation in neutral kaon decays, detailed analysis of the 2001 data sample, final results, and conclusions from the NA48 Collaboration. Learn about the measurement method, uncertainties, and event losses.

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e'/e Measurement by NA48: History, Analysis, Results

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  1. Final measurement of e’/e by NA48 • Direct CP violation in neutral kaon decays • History of the e’/e measurement by NA48 • Analysis of the 2001 data sample • Final result and conclusions G.Unal, LAL-Orsay On behalf of the NA48 Collaboration: Cagliari,Cambridge,CERN,Dubna,Edinburgh,Ferrara,Firenze, Mainz,Orsay,Perugia,Pisa,Saclay,Siegen,Torino,Vienna,Warsaw G.Unal, ICHEP02 Amsterdam

  2. CP violation in neutral kaon decays • CP violation in mixing (« indirect ») KL = K2 +e K1 KS = K1 + e K2 (K1,K2 = CP eigenstates) |e| = (2.28±0.02)10-3 • CP violation in p p decay A(KLp+p-)/A(KSp+p-) = e + e’ A(KLp0p0)/A(KSp0p0) = e – 2 e’ e’ = «direct » CP violation (interference between I=0 and I=2 amplitudes) Standard Model: both e and e’ Quantitative predictions difficult:e’/e (-10 to +30) 10-4 G.Unal, ICHEP02 Amsterdam

  3. The double ratio R • need to measure small deviation of R from 1 • reduce to event counting if at least 2 modes taken simultaneously • NA48 method: • take the 4 modes • simultaneously (cancellation of dead time, inefficiencies, …) • fromsame decay region • KL events are weighted to have same decay distribution as KS(minimise detector acceptance correction) • high resolution detectorsminimise residual backgrounds • KS/KL identification by « tagging » the proton creating the KS G.Unal, ICHEP02 Amsterdam

  4. The Simultaneous KS and KL beams not to scale G.Unal, ICHEP02 Amsterdam

  5. The NA48 detector p0p0 detection ( 4 g) LKr calorimeter s(E)/E=0.032/E0.09/E0.0042 < 1% for E=25 GeV p+p- detection magnetic spectrometer s(p)/p = 0.5%0.9%(p/100 GeV) G.Unal, ICHEP02 Amsterdam

  6. History of the e’/e measurement by NA48 Year:19971998 199920002001 N(KL2p0) 0.5 M 1 M 2 M - 1.5 M improvements in LKr, triggers, DAQ,efficiency Beam tube implosion Cross-checks with neutrals (+rare Ks decays) Drift chambers rebuilt Lower beam intensity e’/e = (15.32.6)10-4 (published in 2001) Result today ! G.Unal, ICHEP02 Amsterdam

  7. Summary of uncertainties on R for 98-99 data related to beam intensity effects smaller uncertainties for 2001 data Example: p+p- trigger efficiency increased from 97.78% to 98.70% smaller uncertainty in efficiency measurement G.Unal, ICHEP02 Amsterdam

  8. 1998-1999spill=2.4s every 14.4s 2001 spill=5.2s every 16.8s => 80 % higher duty cycle Instantaneous beam intensity reduced by 30% Dead time in drift chamber readout: 20%  11% (this dead time condition is recorded and applied in the analysis to all events) G.Unal, ICHEP02 Amsterdam

  9. 2001 1998-1999 slightly better efficiency Performances of rebuilt DCH similarp+p- mass resolution G.Unal, ICHEP02 Amsterdam

  10. Analysis of the 2001 data sample (some selected topics…) p0p0p+p- G.Unal, ICHEP02 Amsterdam

  11. p0p0 reconstruction Decay region definition  Energy scale 1 cm on decay vertex  10-4 on E-scale D(vertex-LKr) = 1/M(K) Ei Ej dij (from K mass constraint) Cross-check: use p0p0 hadronic production from p- beam striking two thin targets during special runs Adjust E-scale to reproduce nominal position of AKS KSp0p0 Total uncertainty (E-scale+non linearities+…) =  5.3 10-4 on R G.Unal, ICHEP02 Amsterdam

  12. Acceptance Weight KL events to equalize decay vertex distribution and make detector acceptance the same Residual correction (beam geometry) D(R) = (21.93.54.0) 10-4 Does not rely on detailed detector simulation G.Unal, ICHEP02 Amsterdam

  13. KS-KL identification R sensitive top+p-p0p0differences DaSL =(00.5)10-4  DR = (03)10-4 DaLS =(3.41.4)10-4 DR =(6.92.8)10-4 From vertex-identifiedp+p-: aSL=(1.12±0.03)10-4(KS tagging inefficiency) aLS=(8.115±0.010)%(KL accidental tagging) Higher losses related to beam intensity in p+p- Can be predicted using overlay technique Time in spill (s) G.Unal, ICHEP02 Amsterdam

  14. Accidental effects • Accidental effectevent losses induced by (KL) beam activity • Miminised by simultaneous data collection in 4 modes • DR = D(p0p0-p+p-) * D(KL-KS) • D(p0p0-p+p-) minimised by applying to all events the recorded • dead time conditions • main tool: overlay pp events with random events (  beam intensity) • D(KL-KS)small by design of the experiment: • simultaneous beam • KS and KL decays see the same beam intensity • deviation =« intensity difference effect » • lifetime weighting • KS and KLdecays illuminate the same part of the detector • residual effect =« illumination difference effect » G.Unal, ICHEP02 Amsterdam

  15. Event losses(from overlay): D(p+p--p0p0)=(1.0±0.5)% for 2001 data Better check of linearity of losses in 2001 (better beam monitors) Measure accidental activity (  KL beam intensity) in KS and KLevents  DI/I = (0±1)% G.Unal, ICHEP02 Amsterdam

  16. Uncertainties from accidental effects: • Intensity difference effect: • from estimates ofD(p+p--p0p0)andDI/I • DR = ± 1.1 10-4 • (was ±3 10-4 for 98-99 data) • Illumination difference effect: • overlaying « random » events to KS and KL decays • DR = ± 3.0 10-4 • (limited by statistical uncertainty of overlay sample) G.Unal, ICHEP02 Amsterdam

  17. Summary of corrections and uncertainties on R for 2001 data G.Unal, ICHEP02 Amsterdam

  18. Cross-checks of the stability of the result 2001 data published 98-99 data G.Unal, ICHEP02 Amsterdam

  19. The double ratio result (2001 data) The analysis is performed in Kaon energy bins to be insensitive to KS-KL differences in energy spectra R = 0.99181 ± 0.00147 stat ± 0.00110 syst G.Unal, ICHEP02 Amsterdam

  20. Final result From 2001 data: e’/e = (13.7±2.5±1.8)10-4 =(13.7±3.1) 10-4 in very good agreement with 97-98-99 published result e’/e = (15.3±2.6)10-4 Final combined result from NA48: e’/e = (14.7±2.2)10-4 (correlated systematic uncertainty is ±1.4 10-4) G.Unal, ICHEP02 Amsterdam

  21. e’/e vs data taking year G.Unal, ICHEP02 Amsterdam

  22. Comparison of experimental results NA31: (23.0±6.5)10-4 E731: (7.4±5.9)10-4 KTeV: (20.7±2.8)10-4 (preliminary) NA48: (14.7±2.2)10-4 World averagee’/e = (16.6±1.6)10-4c2=6.2/3 (prob=10%) G.Unal, ICHEP02 Amsterdam

  23. Conclusions NA48 measurement of e’/e is completed: e’/e = (14.7±2.2) 10-4 proposed accuracy is reached papers: - V.Fanti et al, Phys. Lett. B465, 335(1999) 97 data result - A.Lai et al, Eur. Phys. Jour.C83,22(2001) 98-99 data - coming out soon on 2001 data KTeV still to analyse 1999 data (same stat as 96-97 data) Kloe with different method (need luminosity) The ball is now on the theory side … G.Unal, ICHEP02 Amsterdam

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