Semileptonic B Decays at the B Factories Concezio Bozzi INFN Sezione di Ferrara Representing Babar and Belle At the XL Rencontres de Moriond LaThuile, Italy - March 2006

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi2 Why? Measurements of |V ub | and |V cb | from tree level processes –Constraints on new physics in loops –Treatment of theoretical uncertainties is mature c,u V cb,V ub Probe the structure of B mesons –Inclusive decays: b quark mass, momentum distributions –Exclusive decays: form factors

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi3 How? Inclusive measurements: |V cb | & |V ub | –A glimpse on b→s  Exclusive measurements: |V cb | & |V ub | –A glimpse on charm SL decays

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi4 Inclusive decays: |V cb | Heavy Quark Expansion (HQE): double expansion in  s and m b -1 Fit moments of inclusive distributions –lepton energy, hadron invariant mass –Determine HQ parameters and |V cb | Many measurements from B Factories, CDF, Delphi Recent measurements from Belle: Depend on scheme, order of expansion Benson, Bigi, Mannel, Uraltsev, hep-ph/ Gambino, Uraltsev, hep-ph/ Benson, Bigi, Uraltsev, hep-ph/ Electron energy, hep-ex/ Hadronic mass, hep-ex/ fb -1

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi5 b→s  helps too… CLEO Belle Babar semi Babar full Photon Moments Warning: Some debate going on: Spectrum? Moments? Normalization Scheme? OPE? DGE? Buchmueller, Flaecher hep-ph/ th moment 2 nd moment

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi6 Results Global fit in the kinetic scheme |V cb 2% m b < 1% m 5% Buchmüller, Flächer hep-ph/ |V cb | =(41.96± 0.23± 0.35± 0.59) m b = 4.590± 0.025± 0.030GeV m c = 1.142± 0.037± 0.045GeV μ π 2 = 0.401± 0.019± 0.035GeV 2 μ G 2 = 0.297± 0.024± 0.046GeV 2 ρ D 3 = 0.174± 0.009± 0.022GeV 3 ρ LS 3 =-0.183± 0.054± 0.071GeV 3 BR clv = 10.71± 0.10± 0.08% exp HQE Γ SL b→sγ b→clν combined b→clν combined Based on: Babar: PRD69, (2004) PRD69, (2004) PRD72, (2005) hep-ex/ Belle: PRL93, (2004) hep-ex/ CLEO: PRD70, (2004) PRL87, (2001) CDF: PRD71, (2005) DELPHI: EPJ C45, 35 (2006)

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi7 Inclusive decays: |V ub | Unfortunately: Kinematic cuts needed: Smaller acceptances, theory uncertainties increase –OPE breaks down –“shape function” to resum non-perturbative physics Strategy to minimize theory uncertainties: –maximize acceptance, or –choose “smart” regions/variables measure partial branching ratio  B get predicted partial rate  (  p) from theory Theoretical uncertainty ~5% Not to scale! q 2 = dilepton mass squared m X = hadron system mass E l = lepton energy Close friends to the previous ones

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi8 Electron endpoint First |V ub | measurement –CLEO, November 1989 –E ℓ > 2.3 GeV,  (  p)~8% Precise knowledge of BB backgrounds –Belle: E ℓ > 1.9GeV,  (  p)~30% –Babar: E ℓ > 2.0GeV,  (  p) ~25% –Smaller uncertainties from theory Typical requirements: missing momentum, event shape S/B~1/10,  ~40% Predicted partial rate from HQE fits Bosch et al. hep-ph/ , hep-ex/ PRD73 (012006), hep-ex/ M BB 2.0 GeV < E l <2.6 GeV fully corrected spectrum

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi9 Hadronic B tag Fully reconstruct one B Study the recoiling B –Known momentum and flavour Access to all kinematic variables B reco B recoil XuXuXuXu l e-e-e-e- D*D*D*D*  e+e+e+e+ M X <1.7GeV, q 2 >8GeV P + =E X -|p X | >0.66 hep-ex/ hep-ex/ M X 8GeV M X <1,7GeV |V ub |= S/B~2  ~ M BB 210M BB 253M BB |V ub | = (4.70 ± 0.24 stat ± 0.28 syst ± 0.20 SF th ) × |V ub | = (4.09 ± 0.19 stat ± 0.20 syst ± 0.18 SF th ) × |V ub | = (4.19 ± 0.20 stat ± 0.30 syst ± 0.24 SF th ) × 10 -3

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi10 Reducing model dependence Relate charmless SL rate to b→s  spectrum Reduced dependence from shape function Recoil analysis on 88M BB Weight function Leibovich, Low, Rothstein hep-ph/ , m X cut LLR : M X < 1.67 GeV: |V ub | = (4.43 ± 0.38 stat ± 0.25 syst ± 0.29 theo ) OPE: M X < 2.50 GeV: |V ub | = (3.84 ± 0.70 stat ± 0.30 syst ± 0.10 theo ) hep-ex/ theory uncertainties NEW!

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi11 Inclusive |V ub |: summary & outlook Babar (no SF) 4.43 ± 0.45 ± 0.29 Uncertainty on shape function parameters: 4.5% –  m b ~40 MeV –reduce SF dependence? Leibovich-Low-Rothstein hep-ph/ , Lange-Neubert-Paz (JHEP 0510 (2005) 084), Lange (hep- ph/ ) Other theory uncertainties ~5% –Subleading SF: 3.5% –Weak annihilation: 2%, can be studied experimentally –Different theory approaches? Andersen-Gardi JHEP 0601 (2006) 097 Aglietti, Ferrara, Ricciardi hep-ph/ , , Experimental uncertainties: –Statistics: 2% –Detector systematics: 2.6% –Background modeling: 2% –Signal modeling: 2.2% hep-ex/ not included yet in HFAG average WARNING values and errors adjusted by HFAG. HQ parameters from hep-ex/ , predicted partial rates from hep-ph/ , |V ub ~8%

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi12 How? Inclusive measurements: |V cb | & |V ub | –A glimpse on b→s  Exclusive measurements: |V cb | & |V ub | –A glimpse on charm SL decays

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi13 Exclusive |V cb | Well-established method: F(1)=1 in the heavy quark limit; lattice QCD says: Shape of F(w) unknown Parametrized with  2 (slope at w = 1) and form factor ratios R1, R2 ~ independent on w use Caprini-Lellouch-Neubert Determine  2, R1, R2 via multi-dimensional fit to helicity amplitudes: H +,-,0 are functions of  2, R1, R2 Phase space Form factor D * boost in B rest frame Hashimoto et al, PRD 66 (2002) Nucl. Phys. B 530, 153 (1998)

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi14 New Babar measurement stat. MC stat. syst. Factor 5 improvement on FF uncertainty from previous CLEO measurement (1996!) Reduced uncertainty on |V cb | +2.9% -2.6%  ± 0.5% Total systematic error on |V cb | 4.5%  3.5% Systematic uncertainty on |V ub | for endpoint analyses is also reduced hep-ex/ NEW! 1D projections of fit result: 80 fb -1

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi15 Exclusive |V ub | Experimentally: –Good S/B ratio, untagged analyses –Small branching fractions –Measure q 2 dependence, compare to theory Theoretically: –Uncertainties complementary to inclusive approach –FF normalization dominates the error on |V ub | (~10% for all models) Calculations of f + (q 2 ): –LQCD (q 2 >16) –Light-cone sum rules (q 2 <14) –Quark models (ISGW2) M ES for <  E < 0.25 GeV Continuum cl ul crossfeed B  l 83 x 10 6 BB = missing of the event Fit of signal yield using B mass and  E in bins of q 2. Babar untagged analysis: hep-ex/

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi16 (Selected) results 253 fb -1   l  — Ball’01  — ISGW2  — UKQCD d  /dq 2 /  tot x 10 4   l q2q2 q2q2 D*lv tag hep-ex/ hep-ex/ Lattice and LCSR favored over ISGW2 untagged 80 fb -1

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi17 Summary of exclusive |V ub | Tagged: S/B~3, untagged: S/B~1 Comparable precision Tagged measurements will improve –statistical component in significant systematic uncertainties |V ub | averages based on different models

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi18 Validate theory with D→K/  l 80 fb -1 NEW! More results from CLEO-c this afternoon

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi19 Conclusion Semileptonic B decays: very active area for both theory and experiment Substantial progress in HQE fits to inclusive decays: –precise measurements of |V cb |, m b and HQ parameters relevant to other decays Exclusive/inclusive determinations of |V cb | in agreement Increased precision in inclusive |V ub | –improved measurements, –more comprehensive theoretical treatment –better determination of m b. Studies of exclusive charmless decays are improving as datasets increase. –Reducing the theoretical uncertainties to a comparable level is challenging.

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi20 Backup

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi21 Inclusive decays: |V cb | Heavy Quark Expansion (HQE): double expansion in  s and m b -1 Fit moments of inclusive distributions –lepton energy, hadron invariant mass –Determine HQ parameters and |V cb | Depend on scheme, order of expansion Lepton Moments Hadron Moments E cut (GeV) Buchmueller, Flaecher hep-ph/ Benson, Bigi, Mannel, Uraltsev, hep-ph/ Gambino, Uraltsev, hep-ph/ Benson, Bigi, Uraltsev, hep-ph/

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi22 Results Global fit (in the kinetic scheme) gives: |V cb 2% m b < 1% m 5% hep-ph/ |V cb | =(41.96± 0.23± 0.35± 0.59) m b = 4.590± 0.025± 0.030GeV m c = 1.142± 0.037± 0.045GeV μ π 2 = 0.401± 0.019± 0.035GeV 2 BR clv = 10.71± 0.10± 0.08% exp HQE Γ SL E ℓ, hep-ex/ Hadronic mass, hep-ex/ Recent measurements from Belle (to be included) unfolded 0.4 GeV! Stat. errors only!

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi23 Hadronic B tag Fully reconstruct one B Study the recoiling B –Known momentum and flavour Access to all kinematic variables B reco B recoil XuXuXuXu l e-e-e-e- D*D*D*D*  e+e+e+e+ M X <1.7GeV, q 2 >8GeV P + =E X -|p X | >0.66 hep-ex/ hep-ex/ M X 8GeV M X <1,7GeV |V ub |= S/B~2  ~ M BB 210M BB 253M BB

Moriond EW, March 2006Semileptonic B decays - Concezio Bozzi24 Validate FF calculations with D→K/  l