Stato di Vub e Vcb

1. Stato di Vub e Vcb Concezio Bozzi INFN Ferrara Babar Italia, Trieste 14 Aprile 2005

2. Sommario • Decadimenti semileptonici inclusivi • con charm (Vcb) • senza charm (Vub) • Decadimenti semileptonici esclusivi • pln, rln (nuovi risultati, Moriond&CKM05) • D*ln • NB: ho attinto a piene mani da materiale presentato (da altri ma anche da me!) a CKM2005

3. Misure inclusive

4. Inclusive Decays – the Big Picture

5. Semileptonic B Decays & HQE • contains b- and c-quark masses, mb and mc • mp2 related to kinetic energy of b-quark • mG2 related to chromomagnetic operator: B / B* mass splitting • Darwin term (ρD3) and spin-orbit interaction (ρLS3) enter at 1/mb3 free-quark rate m= scale which separates effects from long- and short-distance dynamics r = mc/mb; z0(r), d(r): phase space factors; AEW = EW corrections; Apert = pert. corrections (asj, askb0) No 1/mb term! Several HQE schemes exist; op’s and coeff’s are scheme dependent

6. Inclusive bcℓν • Measure electron momentum spectrum and mass of hadronic system in SL decay • Determine moments to allow comparison with parton-level calculations (duality assumed) • Calculations exist for the following: • Fit for HQE parameters and |Vcb| Gambino & Uraltsev (hep-ph/0401063, 0403166) Lepton energy spectrum Mass of hadronic system

7. BABAR PRL 93:011803 Fit Results ● = used, ○ = unusedin the nominal fit mX moments BABAR c2/ndf = 20/15 Eℓmoments Red line: OPE fitYellow band: theory errors

8. BABAR PRL 93:011803 Fit Results 2% accuracy! • Impressive agreement between data and theory • ≈ identical results obtained in another renorm. scheme: Bauer, Ligeti, Luke, Manohar, Trott in hep-ph/0408002 precision on |Vcb| = 2% Uncalculatedcorrections to G precision on mb = 1.5% • kinetic mass scheme with μ=1 GeV • Fitted values consistent with external knowledge c2/ndf = 20/15

9. Inclusive |Vcb| status • BaBar result compared with previous measurements: • Agrees with value coming from exclusive BD* ℓν decays (from HFAG):

10. Inclusive bu • Limiting factor in CKM precision tests; known much less well than |Vcb| • CKM suppressed – therefore harder to measure • Challenge for experiment and theory

11. m= scale which separates effects from long- and short-distance dynamics AEW = EW corrections; Apert = pert. corrections (asj, askb0) Starting point: HQE • Just like bcℓν…, and with similar accuracy • …until limited expt’l acceptance is considered • Poor convergence of OPE in region where bcℓν decays are kinematically forbidden • Non-perturbative Shape Function must be used to calculate partial rates

12. Theory input • Reference (ICHEP04, HFAG) results based on triple differential decay rate (Ee, mX, q2) computed to O(as, mb-2) over the entire phase space by de Fazio and Neubert (DFN, JHEP 06:17 (1999)) • Use as input the shape function parameters determined by a fit (hep-ex/0407052) to the Belle b→sg spectrum: Λ= 0.66 GeV,λ1= -0.40 GeV2 + covariance δΛ ~ δmb ≈ 80 MeV Acceptance inb → uℓv Egspectrum inb → sg f(k+) • q2vs mX analysis: take acceptances from Bauer, Ligeti and Luke (BLL,hep-ph/0111387), OPE calculation in a region of the phase space where SF effects are small.

13. Inclusive Vub measurements with BaBar Untagged 4.40 ± 0.24exp± 0.35theo Untagged 4.99 ± 0.48exp± 0.29theo Breco Tags 5.22 ± 0.43exp± 0.33theo Breco Tags 5.18 ± 0.57exp± 0.34theo Current Vub errors: 10-15% Total experimental syst @250-500 ifb: 3-6% Partial Tags exclusive Breco Tags

14. Vub measurements

15. A different theory approach • Bosch, Lange, Neubert and Paz (BLNP) Nucl. Phys. B 699, 335 (2004) • Acceptances computed in BLNP using SF parameters from • Belle b→sg hep-ex/0407052 • BaBar b→cℓn moments (hadronic and leptonic) hep-ex/0404017 • Proper translation into shape function scheme of BLNP hep-ph/0412241 Courtesy of Henning Flächer

16. Results with BLNP and BaBar b→cℓn moments Using mb = 4.63±0.08 GeV and μπ2 = 0.15±0.07 GeV2 (SF scheme) with correlation coefficient -0.4. Errors are: expt ± SF ± theoryexpt ± (SF+theory) b→cℓn moments: significant change in inclusive |Vub| values BLNP: increased sensitivity to SF

17. Misure di Vub esclusive

18. Exclusive B  Xuln Decays Xu = p+, p0, r+, r0, w, h, h’, a00, a0+ low bkg, low stat.: 27p,… (ICHEP’04) Breco Tags p+ Balance between efficiency and purity 3 new pln results Semilep.Tags Y(4S) n l- High statistics, high hackground (b cln) Untagged ▪Goal : Measure Branching Fractions and |Vub| ▪Need FF predictions to describe QCD effects • New unquenched LQCD calculations (HPQCD’04, FNAL’04) • Try to measure q2 dependence of FFwith data

19. Semileptonic Tag Analyses • Reconstruct B D(*)ln and study semileptonic recoil • use both D and D* tags  sizable BF • Tagging efficiency measured with “Double Tags” (two D(*)ln) D(*)ln decays Correct sl. decay  |cosqBY| < 1 ( tag side: cosqBY, signal side: cosqB,pl ) cos2fB < 1 for signal, bkg flat

20. p0ln with SL Tag : Signal Extraction • Cut-and-count analysis in cosqB,pl and mD • Signal region: -1.1 < cosqBpl < 1.0 • Subtract mD sidebands remove cominatoric background • Subtract other background using MC normalized in -10 < cosqBpl < -1.5 82 fb-1 45 p0

21. Mainly B0B0 bkg p+ln with SL Tag : Signal Extraction Extract signal yields by binned c2 fit to cos2fBin3 bins of q2: Fit parameters = signal and background normalizations 14 p+ 26 p+ 21 p+ 211 fb-1 ≈ 30% rln X-feed

22. p+ln with SL Tag : Branching Fractions and q2 • SL tag analyses statistically limited. • Yields not yet large enough to discriminate between FFmodels.

23. Untagged B  pln and B  rln • Neutrino Reconstruction:Reconstruct n from full event & ensure good reco. quality • Cut on missing mass: |M2miss / 2Emiss| < 0.4 GeV • Harsh suppression of b  cln bkg (kinem. cuts, mainly for rln) e+e- qq bkg (topological cuts) • Max-LH fitof signal and background in DE, mES, and q2 • Fit all 4 signal modes simultaneously (p+, p0, r+, r0) • Use isospin relations to reduce number of signal parameters: G (B0 p-l+n) = 2 G (B+ p0l+n) G (B0 r-l+n) = 2 G (B+ r0l+n)

24. 5 bins for pln 3 bins for rln Untagged pln: Fitted DE and mES 76 fb-1 427 p+, 147 p0

25. 5 bins for pln 3 bins for rln Untagged pln: Fitted DE and mES 76 fb-1 101 r+, 104 r0

26. Measured q2 Distributions and Form Factors pln rln • Recent LQCD and LCSR calculations agree well with data • ISGW2 shows marginal agreement for pln • Errors for rln still too large to study 3 form factors.

27. Systematic Uncertainties (Untagged) • Better statistical precision than previous measurements • Syst. error dominated by n reconstruction. Will decrease with improved track/neutral reconstruction. • Results less dependent on theoretical predictions (own FF measurement)

28. Overview: Branching Fraction Measurements pln rln Testing isospin symmetry: Measure p+ln, p0ln separately (untagged)

29. Extraction of |Vub| • Measurement in bins of q2 allows extraction of |Vub| for various q2 regimes and FF calculations: LCSR q2 <15 GeV2, LQCD q2 > 15 GeV2 or extrapolation to whole q2 range Quote LQCD2 as representative

30. Misure di Vcb esclusive

36. Ultimate solution: combined measurement of form factors and Vcb! (work in progress in Trieste)

38. Other ideas? M. Andreotti PhD thesis • D*0ln (little/undermanned efforts) • Yet another measurement of D*+ln • D* partial reconstruction • On the recoil of a fully reconstructed hadronic decay Run1-4

39. Conclusioni • Mole impressionante di risultati sperimentali e teorici • Collaborazione virtuosa tra le due comunità • Effetto complessivo: • Vcb inclusivo: ~1.5% • Accordo impressionante teoria-esperimenti! • Vub inclusivo: 10% → 5% ? • Aggiornare misure con tutta la statistica disponibile • Ampio consenso teorico sulla validità delle relazioni b→cℓν b→sg b→uℓν • Un po’ meno sulle incertezze relative • Vub esclusivo: • Occorre più statistica e migliorare le sistematiche sperimentali • calcolo dei fattori di forma non ancora pienamente maturo • Vcb esclusivo: 4% → ? • Nuove misure (Dln) per limitare incertezze teoriche e per risolvere l’accordo marginale tra le misure esistenti (D*ln)