Review of Vcb and Vub measurements Fabrizio Bianchi

Review of |Vcb| and |Vub| measurements Fabrizio Bianchi University of Torino and INFN-Torino Rencontres de Moriond EW 2009 La Thuile, 7 -14 March 2009

Outline n Introduction to the measurement of |Vcb| and |Vub| n Results from the B-factories: n n |Vcb| from Spectral Moment n FF x|Vcb| from B n Inclusive |Vub| n |Vub|from exclusive SL charmless B decays D(*)ln Summary and outlook 2

Constraints on Unitarity Triangle h a g b r A precise determination of |Vub/Vcb| is crucial to be able to observe deviations from the CKM mechanism due to New Physics 3

Semileptonic B Decays |Vcb| and |Vub| are determined from semileptonic B decays. At tree level everything is nice and clean. QCD corrections must be included. • Inclusive measurements: OPE • Exclusive measurements: Form Factors from LQCD |Vcb| , |Vub| B Xc , X u 4

|Vcb| from Spectral Moments 5

OPE: Semileptonic Width Wilson coefficients f, k, g, d, l can be calculated in perturbation theory. Non-perturbative parameters μπ , μG , ρD , ρLS are matrix elements of local operators in HQET. 6

OPE: Other Observables OPE for moments involves same matrix elements and different, calculable Wilson coefficients. 7

Moment Analysis Moment Measurements Fit OPE Expressions |Vcb| μπ mb mc μG ρD ρLS External input: average B lifetime t. B = (1. 585 +/- 0. 006) ps • Kinetic running mass • P. Gambino, N. Uraltsev, Eur. Phys. J. C 34, 181 (2004) • D. Beson, I. Bigi, N. Uraltsev, Nucl. Phys. B 710, 371 (2005) • 1 S mass • C. Bauer, Z. Ligeti, M. Luke, A. Manohar, M. Trott, Phys. Rev. D 70, 094017 (2004) 8

Belle Results Fit in the Kinetic Scheme Phys. Rev. D 78, 032016 (2008) 9

Belle Results 10

Bell Moment Analysis not included |Vcb| - HFAG Average Adding Xsg Moments lowers m. B Belle result don’t show this effect m. B is input to |Vub| extraction !!! Kinetic Scheme Low c 2/ndf Are theoretical correlation properly accounted ? 11

FF x|Vcb| from B D(*)ln 12

VCB & Form Factors: HQET expansion of width: Caprini et al. Parametrization of FF (Nucl. Phys. B 530 (1998), 153): Experiments measure: • |Vcb|*FF(w→ 1) • � r 2 D, r 2 D* ( slopes of FF ) • R 1, R 2 : form factor ratios (D*) 13

ar. Xiv: 0810. 1657 [hep-ex] 140 fb-1 Untagged Analysis • Decay chain: • Measure helicity angles (Ql, QV, c) • Fit: 14

Phys. Rev. D 79: 012002, 2009 207 fb-1 Untagged Analysis • Select D 0(Kp)ln. X, D+(Kpp)ln. X events with pl > 1. 2 Ge. V/c • Get D/D* rates with a binned 3 -d fit to pl, p. D, cos. QBY • Relate BR(B 0) to BR(B+) using lifetime ratio • Extract from the fit: r 2 D, r 2 D*, BF • Compute: |Vcb|*F(1), |Vcb|*G(1) 15

ar. Xiv: 0807. 4978 [hep-ex] 417 fb-1 Hadronic Tag Analysis D 0 • Select D 0 ln, D+ln decays on the recoil of a fully reconstructed B • Event yields from a fit to MM 2 in 10 w bins D+ • G(1) |Vcb| and r 2 G from a fit to w distribution MM 2 = (PB−PD−Pl)2 [Ge. V 2/c 4] 16

ar. Xiv: 0808. 0528 [hep-ex] 417 fb-1 Hadr Tag Analysis Important to reduce systematic in |Vcb| excl. measurements. Discrepancy between B ->Xcln inclusive rate and sum of exclusive modes. M(D(*)p – m(D(*)) [Ge. V/c 2] 17

C. Bernard et al. , ar. Xiv: 0808. 2519[hep. lat] M. Okamoto et al. , Nucl. Phys. Proc. Suppl. 140, 461 (2005) VCB & Form Factors: Averages 18

Open Issues on |Vcb| Measurements |Vcb| from Moment Analysis • Belle recent results in good agreement with HFAG average • Open questions on HFAG global fit: • Inclusion of the B ->Xs g data lowers the b-quark mass mb • c 2/ndf = 29. 7/57 (24. 1/46) Too small ? F(1)|Vcb| and G(1)|Vcb| from B->D(*)ln • Good agreement between experiments • |Vcb| extracted using LQCD 2 s lower than result from Moment Analysis 19

|Vub| from Inclusive Semileptonic B Decays 20

Inclusive |Vub| Measurement I Charm background ~50 x larger than signal Use kinematics to distinguish Xu signal from Xc BG (mc >> mu) ● ELEP = lepton energy ● q 2 = momentum transfer squared = (p. B-p. X)2 = (pl+pn)2 ● m. X = mass of the hadronic system ● P+ = EX-|p. X| = light-cone component of X momentum 21

Inclusive |Vub| Measurement II Cut away B Xcln loose some B Xuln signal We measure: total rate fraction of signal that pass the cut Must be corrected for QCD BLNP - B. O. Lange, M. Neubert and G. Paz, Phys. Rev. D 72: 073006 (2005) DGE - J. R. Andersen and E. Gardi, JHEP 0601: 097 (2006) GGOU - P. Gambino, P. Giordano, G. Ossola, N. Uraltsev, JHEP 0710: 058, 2007 BLL - C. W. Bauer, Z. Ligeti and M. E. Luke, Phys. Rev. D 64: 113004 (2001) cut dependent constant predicted by theory Use HQE parameters from B Xcln and B sg to extrapolate to full phase space and extract |Vub| 22

PRL 100, 171802 (2008) Ba. Bar: Hadronic tag technique B → Xu l n B → Xc l n (bkgd) B → Xu l n (outside selected region) Background subtracted Mx<1. 55 Ge. V/c 2 P+<0. 66 Ge. V/c 2 Mx<1. 7 Ge. V/c 2 Q 2>8. 0 Ge. V 2/c 2 BLNP DGE BLL 23

Presented at CKM Belle Multivariate Analysis • Hadronic Tag • Boosted decision tree based selection, use ~20 event parameters • 2 D fit to Mx, q 2 with backgrounds and signal floated 24

Belle multivariate analysis not included Inclusive |Vub|: HFAG averages Different |Vub| values from different calculations Nice agreement of |Vub| measurements 25

|Vub| from Exclusive SL Charmless B Decays 26

Exclusive |Vub| Measurements = p, h, h’, r, w Complementary exp approaches: • Untagged (with n reconstruction) • Semileptonic tag • Hadronic tag Different form factor calculations Different systematic errors and independent samples Perform measurement in q 2 bins to reduce model dependency See Talk of R. Sommer 27

Still most precise measurement PRL 98, 091801 (2007) 206 fb-1 B pln untagged Reconstruct neutrino from full event: Extract signal yield in 12 q 2 bins from fit to ΔE vs. m. ES distributions Used by FNAL (ar. Xiv: 0811. 3640 [hep-lat]) to extract |Vub| = (3. 38 +/- 0. 36)x 10 -3 28

ar. Xiv: 0805. 2408 [hep-ex] 348 fb-1 B p, h, h’ l n Semileptonic Tag Analysis Strategy: • Tag one B in D(*)ln and look for signal in the recoil; • Identify a signal lepton (right charge) and search for a: • p+ , p− , p 0 • h → g g , h → p+ p− p 0 , h → p 0 p 0 • h´ → h p+ p− • No additional tracks and low neutral energy; • Extract signal yields with unbinned maximum likelihood fit to cos 2 ϕ B. 29

ar. Xiv: 0805. 2408 [hep-ex] 348 fb-1 B p, h, h’ l n Semileptonic Tag Using isospin relation 3. 2 s significance (90% CL) CLEO (PRL 99, 041802(2007): 30

ar. Xiv: 0812. 1414 [hep-ex] 605 fb-1 B p, (r, w) l n Hadronic Tag • Fully reconstruct the Breco • Know kinematics and flavor of signal B • Extract signal yields from M 2 miss≈ M 2ν distribution in 3 q 2 bins 31

|Vub| from B pln: HFAG average Consistent results Form Factor systematic dominates More exp q 2 data to constraint FF 32

Open Issues in |Vub| Measurements Inclusive measurements: • Nice consistency of |Vub| measurements extracted using the same calculations • Different |Vub| values are obtained when using different calculations • (d|Vub|/|Vub|)exp ~ 4% (d|Vub|/|Vub|)Th ~ 6 -7% Exclusive measurements: • Uncertainties from Form Factors are the dominant systematic • (d|Vub|/|Vub|)exp ~ 5% (d|Vub|/|Vub|)FF=+17% -11% • Need more data to constraint different calculations • Looking for progress from Lattice. QCD Exclusive measurements give a lower |Vub| than inclusive ones 33

Conclusions • Progressing in the understanding of B SL decays • Inclusive |Vcb| precision now at 2% level • Still remaining issues on global fit and B->Xsg data inclusion • Many new results on B->D(*)ln decays • Precision on |Vcb| measurements limited by form factor knowledge • Lower value (2 s) than from inclusive analysis • Inclusive |Vub| measurements now at 8% precision • Limited by calculation of theoretical phase space acceptances • Exclusive |Vub| measurements limited by form factor knowledge • Need more data and progress on theoretical calculation • Puzzle of exclusive vs inclusive |Vub| values not yet solved 34

Backup Slides

BABAR Detector 36

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Experimental Methods 38

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ar. Xiv: 0805. 2408 [hep-ex] 348 fb-1 |Vub| from B pln SL Tag DB is the partial branching fraction Dz calculated using: • LCSR for q 2<16 Ge. V 2 • Lattice QCD for q 2>16 Ge. V 2 40

B p, r, w l n Hadronic Tag 41

ar. Xiv: 0812. 1414 [hep-ex] 605 fb-1 |Vub| from B pln Hadr. Tag To extract |Vub| use: LCSR for q 2<16 Ge. V 2 Lattice QCD for q 2>16 Ge. V 2 42