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Probing The B 0  D 0 K 0 System: A Quick Update

Probing The B 0  D 0 K 0 System: A Quick Update. Vivek Sharma University of California San Diego. Motivation: sin(2 b + g ) From B  D (*)0 K (*)0 Decays. CPV due to Interference between decay and mixing as in B  D (*) p system Advantages:

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Probing The B 0  D 0 K 0 System: A Quick Update

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  1. Probing The B0 D0 K0 System:A Quick Update Vivek Sharma University of California San Diego

  2. Motivation: sin(2b+g) From B D(*)0K(*)0 Decays CPV due to Interference between decay and mixing as in B D(*)p system • Advantages: • Expect large CP Violation since two processes of comparable strength (?) • Experimentally probe rB in self-tagging final state BDK*0 with K*0K+p- • Disadvantages: • CKM suppressed, Color suppressed decays, Br (B0 ->DK0) 2 Br(B0 ->D0 ) • Much smaller decay rates (x 102) than B  D(*)p Strong phase difference crucial parameter

  3. Estimating B0 D (*)0K(*)0Rates From Measured Rates BaBar Naively

  4. Improved B0/ B0 D(*)0K(*)0Rate Measurements • Analysis described in BAD 484V8 improves over analysis described in past ICHEP04 conf paper BAD 884 • Current analysis  Runs1-4, 205.5 fb-1 at (4S) • Largely eliminate reliance on MC for unobserved modes which can contribute to “peaking” background in mES but don’t peak near E=0 • Analysis tuned towards measurement/constraint on rB • 2-dimensional fit to mES and E distributions • Signal and background model: Five free parameters: Nsig ,argus ,slope pE ,Npeak ,Ncomb

  5. B D(*)0K0Yields andRates: Combining 3 D0 Modes D0 Sidebands N104 ± 14 D0 Sidebands N17 ± 5 BaBar * Comb./0.01 GeV Comb./0.01 GeV E(GeV) E(GeV) BAD 484 V8 205 million BB Preliminary Signal Yields are as expected * The E fits shown above are for illustration only Actual fits are per D decay mode and in mes Vs DE

  6. 7814 -0.2 E 0.2 B0/B0 D(*)0KS Yields & Rates From Belle Belle 196 hep-ex/0408108 274 million BB Preliminary ICHEP04

  7. Motivation for rB : Study of B DK Sensitivity to sin(2+) • Study based on Toy MC reported by Shahram Rahatlou @ CKM Angles Workshop 2003, assumptions in the study still valid • http://www.slac.stanford.edu/BFROOT/www/Organization/CollabMtgs/2003/workshops/ckm2003/Thur2/rahatlou.pdf • Fit simulated proper time distribution of BD0 K0 events expected in 500 fb-1 to simultaneously extract amplitude ratio rB , sin(2+), phase diff  Too few data! fit converges always when rB is input/constrained from elsewhere

  8. Al3(r+ih)eig Al2 u c b b D0 D0 c u B0 B0 l s s K*0 K*0 d d d d Isolating Vub and V cb Driven Amplitudes in B D0K*0 • Vcb only: • B0 D0bar K*0 D0bar K+p-,p-p0,3p K*0K+p- • Same sign kaons • Vub only: • B0 D0 K*0 D0K-p+,p+p0,3p K*0K+p- • Kaons with opposite sign

  9. Vcbtransition N=77 ± 13 Probing rB From Self-Tagging B0 D0K*0 & B0 D0K*0 Kaon Charge correlation to separate Vcb & Vub driven modes Vub transition BaBar  E (GeV) E (GeV) 205 million BB Preliminary BAD 484V8 See SR’s talk at next Breco meeting

  10. Belle Search For The Self-Tagging B0 D0K*0 Vub Vcb Br<0.5x10-5@90%CL Br<1.9x10-5 @90%CL Belle 274 million BB (Preliminary hep-ex/0408108 Belle do not quote a rB limit in ICHEP04 conf paper: unlikely to be better than Babar’s

  11. Near Term Plans • The main aim in the first analysis phase was to map out the decays rates and probe rB • This is now done as well as one can with 200 fb-1 data, have comparable precision to Belle with smaller data sample • need to finish the paperwork • BAD484 V9, the final version of the analysis BAD expected out by 7th Oct, together with a PRD-RC draft • Hope to send to journal well before Xmas holidays • Related Documents not explored in this 10’ talk: • Study of Time-dependent CPV in BD0K0 • http://www.slac.stanford.edu/BFROOT/www/Organization/CollabMtgs/2003/ • workshops/ckm2003/Thur2/rahatlou.pdf • Viola Sordini’s exercise at CKM2005 combining phenomenology and exptal results to obtain constraints on rB and projected sensitivity to Sin2+ from B  D(*)0K0 decays : • http://ckm2005.ucsd.edu/WG/WG5/thu2/Sordini-WG5-S3.pdf

  12. Bottom Line: B  DKS • Like with most pursuits of , knowing the bu amplitude is key • So far no observation, only limits on rB from B0D(*)0K*0 modes, rB <0.42 (BaBar) • Playing with measured B -> DK rates and constraining various contributing amplitudes suggests rBDKs=0.260.16. Is this approach theoretically kosher? • ToyMC based time-dependent CPV studies indicate that with 500 fb-1 samples, mild information only on sin(2b+g) provided rB obtained from elsewhere • More B modes need to be added • Self tagging decay B  D**0 KS decays (poor Br. for self tagging modes) • B  DKs, D Ks  mode not prolific (yield ~4x smaller than DKp mode) • Precise measurements require > ab-1 data samples • There are no shortcuts in clean measurements of  !

  13. Unused Slides

  14. rB from fits to 2D fit to mES and DE • Ratio rB defined as • Signal yields measured with separate 2D fits to distributions of mES and DE for Vub (B0D0K*0) and Vcb (B0D0K*0) modes • Each D0 mode fitted seperately • Modify fit to determine directly rB • Fix yield and efficiency of Vcb mode • Use uncertainties assigned as systematic error • Fit provides ‘raw’ likelihood versus rB2 for each D0 mode • Convolve with Gaussian to account for systematic errors • Total likelihood given by product of likelihoods from 3 D0 modes • Determine limit on rB2 by integrating the convolved likelihood function Shahram Rahatlou

  15. Upper Limit on rB2 with Bayesian Approach • Upper limit x at 90% confidence level computed as • Two different priors used to determine the limit L(rB2): likelihood functionconvoluted with systematic error p0(rB2): prior with differenthypothesis Shahram Rahatlou

  16. Likelihood functions including systematic error Kp Kpp0 All modes Kppp Shahram Rahatlou

  17. Shahram’s TD Sensitivity Studies (Angles03 WS)

  18. Time-Dependent Decay Distributions S+ • Similar to BD*p time-distribution • But r expected to be much larger (x 10-20) • Linear dependency on r: can it be measured in the fit (?) • Tag-side DCS effects are small compared to signal amplitude • But there are other potential complications due to DCS decays on reco side (20%) S- One solution: sin2(2b+g) The other one: cos2D fit for rB and sin(2b+g-d) and sin(2b+g+d)

  19. Assumptions Used In This Toy Study • Signal Yield:  0.3 events / fb-1 160 reconstructed events (BD0Ks only for now) • Yields can be 50% higher (Br. Ratio knowledge, better event selection) • Additional modes can increase signal yield but wont be as clean • No combinatorial or peaking background • Signal asymmetries expected to be weakly correlated with background parameters • b=23±3, g=59±19 2b+g=105±20 (1.83 rad) • Use 3 values in toys: 0.9, 1.88, and 2.8 rad • No Knowledge of strong phase • Use different values d = 0.0, 0.8, 2.4 rad • Realistic BaBar Flavor Tagging circa ‘03 • 105 tagged events in 500 fb-1 • Vertexing: realistic resolution function • 10% tail and 0.2% outliers with category dependent bias • Parameters fixed in the fit

  20. Summary of Signal efficiencies and yields circa 2003 • K*0Ksp0: • Expected events: N(K+p-) x 0.5 (BF) x 0.5 (p0 eff) x 0.75 (Ks eff) ~ 50 events • But more background from p0 • D0Kspp: done but not included for technical reason. Fewer events than D0K mode • D0KK, pp: Branching fraction ~ 10 smaller than BF(Kp) • B0 D**0K(*)0: similar to B0 D*0K(*)0 but reduced by intermediate branching fraction Yields for 500 fb-1 withBF = 4 x 10-5 Assuming D*0reco. efficiencyof 50%

  21. Fit Validation with 50 ab-1: rB • Validate fit with 500 experiments of 50 ab-1 • rB(gen) = 0.4, 2b+g = 1.88, d=0.0 Slightly better errors for larger rB rB(fit) – rB(gen) rB(fit) uncertainty rB(fit) uncertainty vs. rB(fit) Mean: 0.014 RMS: 0.001 m: -0.002±0.006 s: 0.013±0.006 rB No bias in the fitted values for any parameter

  22. First ToyFit Attempt for 500 fb-1 sample: fit 3 parameters rB, sin(2b+g±d) • Problem with fit convergence • Small values of rB are problematic • rB constrained to be positive in the fit • ~10% of fits with rB close to the limit 2b+g=1.88d=0.8 2b+g=1.88d=0.0

  23. Plan B  Sensitivity for sin(2b+g±d) with rB=0.4 (fixed) • All fits successful! • Problems with MINOS errors in some fits • Under investigation Not perfect Gaussian shape Bad errors mostlyfor the positive errorProbably hitting non-physicalregion in LL

  24. Summary of Preliminary Toy Study • Sensitivity with 0.5 ab-1? • Simultaneous determination of rB, and sin(2b+g±d) probably not be feasible with current method with  500 fb-1 samples  (too few data) • With 500 fb-1, expected uncertainty on sin(2b+g±d) ~ 0.6-0.7 provided rB known from elsewhere. • ignoring DCS effects which at ~22% is small compared to expected errors and where CLEO-c can help ? • Sensitivity with 5 ab-1? • No problem measuring rB and sin(2b+g±d) • All simultaneous fits successful • Uncertainty on rB: ~ 0.04-0.05 • Uncertainty on sin(2b+g): ~0.15-0.20 • The errors now scale with luminosity

  25. Estimating rB “by Hook or by Crook” Viola Sordini

  26. Getting to rB “By Hook or By Crook” ! : Exercise@CKM2005 by Viola Sordini et al Learning Today From Data on B  DK Family of Decays

  27. Getting to rB “ By Hook or By Crook” ! : Exercise@CKM2005 by Viola Sordini

  28. Viola Sordini et al sin(2+) Relative Error

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