1. Max Baak1 Impact of Tag-side Interference on Measurement of sin(2  +  ) with Fully Reconstructed B 0  D (*)  Decays Max Baak NIKHEF, Amsterdam For the BaBar Collaboration APS Meeting Philadelphia, 8 April 2003

2. Max Baak2 CP Violation in B 0  D (*)  Four final states: D -  +, D +  - ; D *-  +, D *+  - (not CP eigenstates) Each pair accessible to B 0 and B 0  CP violation through interference Expected CP violation small (2%) Suppressed amplitude through b  u transition Dominant amplitude  strong phase difference  (  3 ) CKM Unitarity Triangle

3. Max Baak3 Time-Dependent sin(2  +  ) Measurement: Old School Time evolution for B 0 decays (R unmix ) and B 0 decays (R mix ) to D -  + For D +  - : sin(2  +  -  )  sin(2  +  +  ) r = 0.0 r = 0.1,  = 0 Simultaneous determination of r and  challenging Estimate (and fix) r from B 0  D s +  - [1] r (D  ) = 0.021  0.005 r (D *  ) = 0.017  0.007 Similar for D*  [1] hep-ex/0211053 – submitted to PRL

4. Max Baak4 Common Analysis Technique in BaBar Fully reconstruct one B in state D or D *  Determine flavor of other B meson B TAG (“tagging”) Reconstruct vertex of B TAG and compute proper time difference  t (4s) Tag B Reco B K+K+ ++ zz K+K+ t  z/c = 0.55 At time of B TAG decay, the 2 B’s are in opposite flavor states z Coherent B 0 B 0 production 1. 2. -s-s --

5. Max Baak5 Subtlety of B Flavor Tagging Many B 0  DX modes (X a hadron) ‘kaon tag modes’ At BR levels of O(10 -4 ) intrinsic mistagging because of b  u transitions in B 0 decays Effect always assumed tiny, and accounted for by mistag fractions. Hidden assumption: Individual tagging states dominated Use charge correlation between final state and B flavor by single B 0 decay amplitudes Not True! Works well for lepton tags!

6. Max Baak6 B0B0 B0B0 Doubly-Cabibbo suppressed decays on the tag side 1.  (4s)  B 0 B 0 system symmetric in two B’s 2.System evolves coherently in time 3.On reco-side b  u interference is used for sin(2  +  ) measurement. Induced time-dependent effects of order V ub V cd /V cb V ud = 0.02  b  u Interference at tag-side B induces time-dependent effect, just like reco-side! Lepton tags unaffected. Kaon tags have problems. Change the time-dependent pdf’s! Long, Baak, Cahn, Kirkby hep-ex/0303030  2% for sin2  with J/  K s 100% effect for D (*)  !  (4s)

7. Max Baak7 How the decay distributions change for D (*)  For sin(2  +  ) measement (b  u transition) tag-side problem of similar size compared to signal, cannot be ignored! How do the time-dependent decay distributions change? One kaon tag mode with (unknown!) amplitude ratio r’ and strong phase  ’ Similar for D +  - r=0.1,  =0, r’=0 r=0.1, r’=0.1,  =0,  ’=  r=0, r’=0 Equations pick up sine terms

8. Max Baak8 Change of Variables Flavor-tag symmetric lepton tags Handle on phase  -Only 3 independent parts -The b parameter does not dilute in mistagging! Split off the strong phases  and  ’ for better parametrization set Reco side Tag side (`primed’) r’ unknown

9. Max Baak9 Fit Technique Unbinned maximum likelihood fit to  t spectra of D  and D *  samples. Fit Parameters # a,b,c parameters13 Resolution Function8 Mistag fractions12 Background modelling15  m d and  B fixed (PDG) - Free arameters48 2a(D  ) and a(D*  ) common for all tag. cats. 2c LEP (D  ) and c LEP (D*  ) 3b pars. : for each kaon tag. category, common to D  and D*  6c pars. : for each kaon tagging cat. of D  and D*  Most sensitive to 2  +  BaBar uses 1 lepton and 3 kaon tag. categories! Similar to other mixing measurements In practice numerous kaon tag-modes No reason tag-side parameters r’ and  ’ to be identical for each tag category  Use different b and c tag-parameters for each kaon tag. category

10. Max Baak10  a(0)=0.000  0.002  c(0)=0.001  0.003 r’(generated) c LEP (fit) – c LEP (gen) r’(generated)  (c LEP )  (a) D*  a(fit) – a(gen) Toy MC Validation No observed biases in signal parameters! r = 0.02, ,  ’ = 0.00  a=0.04, c=0.00 Toys correspond to 82 /fb of data+background (D  plus D*  )

11. Max Baak11 Data Sample [1999-2002]: 82 fb -1 on  (4s) Resonance N(D  ) = 5207  87 Purity = 85 % N(D*  ) = 4746  78 Purity= 94 % LeptonKaonIKaonIIOther DD 704  271328  391682  441550  44 D*  644  261197  361427  401492  40 breakdown in tagging categories Fully reconstructed B  D (*)  normally used for mistag fractions in sin2  analysis

12. Max Baak12 Sensitivity to  after tag-side effect Analysis not yet finished  With current D (*)  data set, what is loss & sensitivity to  ? No tag-side interference (c  c LEP ) With tag-side interference Signal parameters:  (a[D  ]) 0.04  (c[D  ]) 0.04  (a[D  ]) 0.04  (c LEP [D  ]) 0.07 Stat. sensitivity  (sin(2  +  )) ~ 0.X loss due to kaon tags Identical errors for D *  sample B A B AR 82 fb  B A B AR 82 fb  Dominant Systematic uncertainties: 1) Uncertainty in r3) Detector effects 2) Monte Carlo4) Background Systematics  (sin(2  +  )) ~ 0.5 x stat.

13. Max Baak13Conclusion Tag-side Doubly-Cabibbo-Suppressed decays sofar neglected in most time-dependent analyses (using coherent B-decays) Complications for sin(2  +  ) measurements using D (*)  /  /a 1 Effect cannot be ignored! Using correct parametrization, can work around problem. Some loss in sensitivity to   First BaBar Result coming soon!  2% for sin2  with J/  K s 100% effect for D (*)  (stay tuned) Long, Baak, Cahn, Kirkby hep-ex/0303030

14. Max Baak14 Backup Slides

15. Max Baak15 B Flavor Tagging Methods In BaBar tagging is handled with Neural Nets Information used: Primary lepton Secondary lepton Kaon(s) Soft pions from D * decays Fast charged tracks Tagging category Fraction of tagged events  (%) Wrong tag fraction w (%) Q =  (1-2w) 2 (%) Lepton 9.1  0.23.3  0.6 7.9  0.3 Kaon+Kpi 16.7  0.29.9  0.710.7  0.4 Kaon+Spi 19.8  0.320.9  0.8 6.7  0.4 Inclusive 20.0  0.331.6  0.9 0.9  0.2 ALL 65.6  0.528.1  0.7 Smallest mistag fraction The errors on a,c LEP scale with quality Q Mistag fraction w determined from cosine coefficients

16. Max Baak16 Multiple tag-side final states In practice there are numerous tag-modes Combining these leads to average, effective r’ eff and  ’ eff No reason to expect r’ and  ’ to be identical for each tag category  Use different b and c parameters for each category Hardly anything known about values of r’ i or  ’ i  Uncertainty on r’ eff : 0 – r’ max No sensitivity to 2  +  from kaon tag-side parameters b and c