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Understanding Unitarity Problem in the CKM Matrix: Results from NA48 Experiment

Explore the significance of CKM matrix unitarity and the impact of measurements on Vus using the NA48 experiment at CERN. Discover how deviations from expected values may hint at new physics developments.

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Understanding Unitarity Problem in the CKM Matrix: 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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