Semileptonic Decays from Belle Youngjoon Kwon Yonsei Univ. / Belle

2 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Contents n Introduction n Analyses for V ub –Inclusive B  X u l n with full-recon. –Inclusive B  X u l n with end-point –Exclusive B  X u l n with semileptonic tag. (prelim.) n Analyses towards precise V cb –Inclusive B  X e n with full-recon. –B  X l n hadronic mass moments (prelim.) –B  X l n lepton energy moments (prelim.) PRL submitted, hep-ex/ PLB accepted, hep-ex/ PLB 614, 27 (2005)

3 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Motivation n Fundamental free parameters –Majority of free parameters in the SM are related to quark (and lepton) flavors : masses and mixings –Quark flavor mixing through CKM matrix n Unitarity triangle –Direct test of CP violation mechanism in SM –V ub : still a weak link in CKM test –V cb : as fundamental as V ub Super-high precision, experimentally A good testing ground of strong int. theory

4 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Issues in V ub measurement Use B  X u l n (semileptonic) –Cleaner, better understood than B  hadronic –More accessible than B  leptonic –Inclusive and Exclusive n Experimentally challenging n Tight selection criteria results in Limited phase space  Extra theoretical uncertainties (from extrapolation)

5 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Variables to suppress b  c l n (10% phase sp.) (~80%) (~30%)

Inclusive B  X u l n with End-point

7 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Main features OPE breaks down  need shape ftn.! Measure D B (B  X u e n, p e > p cut ) Kinematic selection  p e > p cut  p cut = 1.9, 2.0, 2.1, 2.2, 2.3 and 2.4 GeV/c No requirement other than on the signal electron  high statistics Large background from B  X c e n  bkg. sys. uncertainty

8 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) b-quark Shape Function n What is it? –b-quark Fermi motion inside the B-meson n How to get it? –Universal at leading order for all b  light quark transitions –Use E( g ) in B  X s g

Three models for SF Neubert & Paz, hep-ph/

10 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

12 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Event Selection Hadronic events Electrons in the barrel region  eff. ~ 94%; fake rate ~ 0.13%  J/ y, y (2S), g, p 0 veto Continuum suppression  Fox-Wolfram moment  Fisher disc. for energy-flow variables  |cos q th | < 0.75  as q 2 independent as possible Background estimated by  b  c MC and Off-resonance Data  low-p region for check 1.5 < p e < p cut (GeV/c)

13 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) E(e) spectrum for B  X u e n

D B – partial BF Two methods for D B  V ub –Standard method (DFN, JHEP 9906, 017) –New method (BLNP, NP B699 (2004))

V ub from D B DFN BLNP

Inclusive B  X u l n with Full-Recon.

17 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 4.2  10 5 evts./253 fb -1 effic. = 0.33% purity = 62% 2.5  10 5 evts./253 fb -1 effic. = 0.21% purity = 59% Full Reconstruction

18 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Signal selection Lepton Selection p > 1 GeV/c leptons in the barrel region  J/ y, g, p 0 veto Correct charge for B+ candidate No other lepton For b  u Total charge = 0 No reconstructed K S or K  N sl = (9.15  0.05) x 10 4

19 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Kinematic selections (New)

(1) M X < 1.7 GeV –Each bin content is calculated from Mbc fit –2-component fit to extract N(b  u)

21 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle)

(2) M X 8 GeV 2

(3) P + < 0.66 GeV –First measurement using P +

24 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Signal Yield & D B

25 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) V ub from D B n New method –V ub directly from D B R by Bosch, Lange, Neubert, Paz, NPB699 (2004) with an improved treatment of shape-function effects + weak annihilation effects estimated

Exclusive B  X u l n with S.L. tag

Experimental Strategy B   l /  l  (140fb -1 ) ICHEP04 preliminary hep-ex/ B   l  (78fb -1 ) PRL 93, (2004) lowmiddlehigh poor mod. good S/N Eff. trad. recon. Full recon. advanced recon. D (*) l tag Lum. How well can we measure the q 2 dist. (for p l n ) ? +  l /  l (preliminary) Unique opportunity at e+e- B-factory!

Analysis Method 4 decay modes 7 decay modes Tag side reconstruction To have intersection, need Kinematics of double semileptonic decay Back-to-back correlation of the two B’s constrains their direction to the intersection of the 2 cones. or Signal side reconstruction 2-fold ambiguity  q 2 calculated neglecting the B motion in U (4S) q 2 resolution = 0.75 GeV 2

The ratio N obs /N expected = 0.89  0.08 is used to correct the MC efficiency for p l n and r l n detection. Calibration with B sig → D*l Decays n Validity of the method for double semileptonic decay detection has been tested with M(K +  -  - ) on the signal side x B 2 distribution N obs =147  12 The method works ! Dots: Data Histo: MC ( N expected =165) M(K  ) GeV/c 2 xB2xB2

30 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Signal Extraction n q 2 distribution is extracted by fitting the (m X,x 2 ) distrib. for three q 2 intervals. m X (GeV/c 2 ) ■ Fitting components: p l n, r l n, other Xu l n, and BB ■ PDF’s are based on MC. ■ Constraint for extracted Br: Br( p l n ) + Br( r l n ) + Br(other X u l n ) = Br(X u l n ) q 2 <8GeV 2 q 2 :8-16GeV 2 q 2 >16GeV 2 82   20

Results

V ub from exclusive B  X u l n 140 fb -1

Analyses towards precise V cb Inclusive B  X e n (0 th moment) B  X l n hadronic mass moments (prelim.) B  X l n lepton energy moments (prelim.) PLB 614, 27 (2005)

35 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) B  X l n moments n Leptonic and hadronic moments –Needed for global fit for precise V cb n Common features –Preliminary with 140 fb -1 –Full-recon. in the tag side –Boost from B tag –QED correction by PHOTOS –Mixing correction –Unfolded by SVD method

Leptonic moments

37 Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) Hadronic moments

Belle V ub Summary