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CKM unitarity problem: results from NA48 experiment

CKM unitarity problem: results from NA48 experiment. Evgueni Goudzovski (JINR) JINR Scientific Council January 20, 2005. The CKM matrix. The Cabibbo-Kobayashi-Maskawa matrix connects the eigenstates d’,s’,b’ of weak interaction with the quark flavour eigenstates d,s,b :. =.

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CKM unitarity problem: results from NA48 experiment

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  1. CKM unitarity problem:results from NA48 experiment Evgueni Goudzovski (JINR) JINR Scientific Council January 20, 2005

  2. The CKM matrix • The Cabibbo-Kobayashi-Maskawa matrix connects the eigenstates d’,s’,b’ of weak interaction with the quark flavour eigenstates d,s,b: = • Conservation of probability: • CKM matrix has to be unitary: VCKMVCKM+=I • If unitary not fulfilled: • New Physics (e.g. 4th quark generation) E. Goudzovski  JINR SC  January 20, 2005

  3. CKM unitarity problem • CKM unitarity requires for the 1st row: |Vud|2 +|Vus|2+ |Vub|2 = 1 • Particle Data Group (PDG) 2004 review: • |Vub|=(3.67 ± 0.47)∙10-3[negligible contribution into unitarity relation, ~10-5] • |Vud|=0.9738 ± 0.0005[well measured, e.g. neutron lifetime] • |Vus|= 0.2200 ± 0.0026 (≈sinCabibbo)[old measurements: semileptonic kaon decays] |Vud|2+|Vus|2+|Vub|2 = 1(4.3±1.9)∙10-3 (2.2deviation from unitarity) E. Goudzovski  JINR SC  January 20, 2005

  4. CKM unitarity: |Vus| measurement • Best way to determine |Vus|: semileptonic (neutral and charged) kaon decays Ke (Ke3); • A few recent measurements of BR(Ke3) lead to |Vus| values significantly above PDG 2004 values; • New measurements of |Vus| are desirable. E. Goudzovski  JINR SC  January 20, 2005

  5. 1283Br(Ke3())/K 1 |Vus|= where • Br(Ke3())  experimentally measured value; • K kaon lifetime, measured by other experiments; • f+(0)  form-factor, evaluated theoretically; • SEW=1.0232 short distance enhancement factor; • IK  phase space integral; • C2=1 for K0, C2=1/2 for K. f+K(0) C2GF2MK5SEWIK Form-factor calculation (Cirigliano, Neufeld, Pichl, EPJC35,53,2004) Precisions • Kaon lifetimes: • (KL)/(KL)=0.8%; • (K)/(K)=0.2%; • Desirable BR(Ke3) precision: • BR/BR<1% f+K0+(0) = 0.981  0.010 f+K+0(0) = 1.002  0.010 (evaluated with 1% precision) Determination of |Vus|from BR(Ke3) E. Goudzovski  JINR SC  January 20, 2005

  6. NA48 experiment at CERN SPS • Main detector components: • Magnetic spectrometer (4 DCHs) • redundancy  high efficiency; • Δp/p = 0.5% + 0.009%*p [GeV/c]. LKr HOD • Liquid Krypton EM calorimeter (LKr) • High granularity, quasi-homogenious; • ΔE/E = 3.2%/√E + 9%/E + 0.42%; • electron/pion discrimination; •  registration. DCH • Hodoscope • high granularity multiplicity trigger; • precise time measurement (150ps). E. Goudzovski  JINR SC  January 20, 2005

  7. |Vus| measurements by NA48 • NA48/2: Semileptonic K± decays: K±0e (Ke3) • Data: 90k events in 8 hours of low intensity run 2003; • Loose hodoscope trigger (1 charged track); • NA48: Semileptonic KLdecays: KLe (Ke3) • Data: 6.8 mln events in 2 days of special run 1999; • Trigger on 2 charged particles in DCH or hodoscope; • NA48/1: Semileptonic 0 decays: 0+e • Data: whole high intensity run 2002 (6.2k events); • Approach different to the one for kaon decays; • These preliminary results are not discussed in this talk. E. Goudzovski  JINR SC  January 20, 2005

  8. Br(K0e) measurement • Measurement method: normalize Ke3 events to K0 events (Br=0.21130.0014); • Signal practically background free; • Statistics selected from the minimum bias run: E. Goudzovski  JINR SC  January 20, 2005

  9. K0e:Data/MC comparison With radiative corrections Without radiative corrections Data/MC Data/MC E. Goudzovski  JINR SC  January 20, 2005

  10. Preliminary NA48/2 result: Br(K0e) = (5.140.02stat0.06syst)% NA48/2 BNL E865 K+ K K PDG 2004 Br(K0e): result … confirms the deviation from PDG observed by BNL E865! … the most precise measurement of Br(Ke3)! • Main systematics: Branching ratio E. Goudzovski  JINR SC  January 20, 2005

  11. N(Ke3)/acceptance(Ke3) (KLe) = R= (KL all two-track) N(2-track)/acceptance(2-track) Br(KLe) measurement Phys.Lett. B602 (2004) 41 • Measurement method: • Use minimum bias trigger to collect KL2-track events; • Normalization to Br(2-track) = 1.0048  Br(30) • Best input precision:ΔBr(2-track)/Br(2-track)<0.9% • Exactly the same selection for signal (Ke3) and normalization events, but electron identified by energy deposit in the LKr calorimeter; • Measured quantity: E. Goudzovski  JINR SC  January 20, 2005

  12. Data sample and selection • Data sample: • ~80 million 2-track triggers taken during 2 days of minimum bias run with pure KL beam; • Selection criteria: • Conditions on track geometry and kinematics; • Leave a sample of 12.6 million 2-track events; • Additional criterion for Ke3: • Electron ID: E(LKr)/P>0.93for 1 track; • 6.8 mln candidates selected. E. Goudzovski  JINR SC  January 20, 2005

  13. Quality of electron ID can be estimated from the data itself! Electron/pion separation Background to Ke3 sample: • K3/K3 with ± misidentified as e± • Estimated from Ke3 data with identified e±(E/p>1): Prob(e)=5.8·10-3 Inefficiency of electron ID: • Estimated from data with identified ± (0.3<E/p<0.7): Prob(e)=4.9·10-3 E. Goudzovski  JINR SC  January 20, 2005

  14. Monte Carlo simulation • To determine acceptances, Monte Carlo simulation of 5 significant 2-track modes involved (radiative corr. included): • For average 2-track acceptance use ratios of BR: averages from PDG + KTeV (B3/Be3, B3/Be3, …) • Absolute BR’s are not used! • Acceptance(2-track events) = 0.2412  0.0004 • Small normalization uncertainty: ΔA/A=0.16% E. Goudzovski  JINR SC  January 20, 2005

  15. Errors on R=(Ke3)/(2-track) • Statistical errors are negligible; • Dominating systematic uncertainty: due to inexact knowledge of beam energy spectrum; • Summary of systematic errors: E. Goudzovski  JINR SC  January 20, 2005

  16. Data/Monte Carlo comparison Kaon energy spectrum: major uncertainty Profiles at drift chamber E. Goudzovski  JINR SC  January 20, 2005

  17. (KLe) = 0.4978  0.0035 R = (KL all two-track) Br(KLe): result Phys.Lett. B602 (2004) 41 • Experimental result: • To compute Br(KLe) we use Br(KL30): Br(KL30)=0.19920.0070 (inconsistent data; scale factor applied to error) • Result on Ke3 branching ratio: Br(KLe) = 0.4010  0.0028(exp)  0.0035(norm) = 0.4010  0.0045 E. Goudzovski  JINR SC  January 20, 2005

  18. |Vus|∙f+(0) ~ Br(Ke3)/K From BR’s to unitarity test • Br(K) = (5.14  0.06)% • Br(KL) = 0.4010  0.0045 • K:f+(0)|Vus| = 0.2245  0.0013 • KL: f+(0)|Vus| = 0.2146  0.0016 • K: |Vus| = 0.2241  0.0026 • KL:|Vus| = 0.2187  0.0028 (PDG: 0.2200  0.0026) [accuracy 1.1%] [1.1%] [0.6%] [0.7%] [1.3%] [1.2%] E. Goudzovski  JINR SC  January 20, 2005

  19. NA48/2: K± NA48: KL 0.2 0.21 0.22 0.23 0.24 0.25 0.26 |Vus|·f+(0) Results on |Vus|·f+(0) (preliminary) (2003) PL B602 (2004) 41 E. Goudzovski  JINR SC  January 20, 2005

  20. Conclusions • Values of |Vus| obtained by experiments before 2003 are in poor agreement with CKM unitarity; • Recent NA48 measurements of |Vus|: • From K: • In agreement with new BNL result and CKM unitarity; • In disagreement with the old measurements; • From KL: • In agreement with new KTeV and KLOE measurements; • In better agreement with CKM unitarity than the old measurements. • More precise calculations of f+(0) are desirable. E. Goudzovski  JINR SC  January 20, 2005

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