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Probing the B0→D0K0 System: A Quick Update

This update delves into CPV in B0 decays to D0K0, highlighting advantages and disadvantages, with ongoing analysis enhancements for precise measurements and parameter estimations. Experimental data from BaBar and Belle is discussed, along with motivation to study rB, sin(2b+g), and phase differences.

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Probing the B0→D0K0 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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