Semileptonic and leptonic B and Bs decays at Belle

Semileptonic and leptonic B and B s decays at Belle

Robin Glattauer

for the Belle Collaboration

B X

Outline and Motivation

●

B→Dlν (exclusive)

●

New analysis

●

Determination of |V

|

●

First measurement of the channel with full Belle data sample

●

Inclusive – exclusvie measurements: 3σ discrepancy

●

B

→D

*

Xlν (semi-inclusive)

●

New analysis

●

Measurement of branching fractions

Worlds largest B meson sample

~772 million BB events

Unique Y(5S) data sample at a lepton collider

Belle luminosity

B→D ν ℓ

●

Differential decay width:

●

Kinematics:

constants electroweak form factor

correction

CKM matrix

Parametrization from Caprini et al (arXiv:hep-ph/9712417)

B→D ν: Tagging ℓ

●

Y(4S) decays into two B mesons

●

Reconstruct one of them in a hadronic mode (B

)

●

Reduces background

●

Allows full kinematic

reconstruction

B→D ν: reconstruction ℓ

● 4 samples:

● Tracks and photons from B_tag are removed

● Reconstruct D in multiple hadronic channels

● Combine D with a lepton (e,μ) to B_sig

● Determine the missing mass

● If only the neutrino is missing (i.e. genuine reconstruction)

(MC)

B→D ν: Signal yields extraction and final fit ℓ

● Extract signal yield in 10 different w-bins (from 1.0 to 1.6)

● Use MC distribution as template

● Floating: signal, D*- and wrong tag background

● Fixed to MC: other bg (e.g. fake- and non prompt leptons etc.)

● χ² fit of predicted yield (based on differential decay width) to measured yield

Belle preliminary

Belle preliminary

B→D ν: results ℓ (preliminary)

Belle preliminary Belle preliminary

● This results in

● Current HFAG averages:

Belle preliminary Belle preliminary

B s →D s Xlν and B s →D s *Xlν

●

X = feed down from higher D

states

●

D

* and D

** for B

→D

Xlν

●

D

** for B

→D

*Xlν

●

D

→Φ(K

K

)π

●

D

*→D

γ

●

Combine D

*

with lepton of opposite charge

●

Determining the number of D

*

:

●

D

: fit m(KKπ)

●

D

*: fit ∆m = m(KKπγ)-m(KKπ)

B s →D s

*

Xlν

● Determine number of genuine Bs→Ds(*)Xlnu events with X_mis distribution

● E_vis* and p_vis*: visible energy and momentum

● E_B* and p_B*: energy and momentum of Bs meson. Approximated from beam.

● To avoid model dependence of X_mis: use counting experiment with 3 regions:

Wrong side (lepton and Ds⁽*⁾ from different Bs)

Secondary and fake leptons Signal

B s →D s

*

Xlν

●

3 components:

●

Wrong side

(lepton and D

*

from different B

)

●

Secondary and fake leptons

●

Signal

●

Each region enhances one component

●

Measure D

*

in each region (with m(KKπ) or ∆m fit)

●

3 unknowns and 3 equations

→solve to know N

B s →D s

*

Xlν: results (preliminary)

●

Theory predictions don't include "X"

→are lower than our results

Theory predictions:

Combined:

Summary

●

B→Dlnu (exclusive)

● Full reconstruction of events using hadronic tag

● M_miss² allows extraction of B→Dlν signal

● Measure in 10 bins of w and fit differential decay width

●

● Most precise single measurement of

● in agreement with world average, is ~2σ lower.

●

B

→D

*

Xlν (semi-inclusive)

● Determine yields with fits to m(KKπ) and ∆m

● Using 3 seperate regions for counting experiment separated by X_mis and p*(l)

●

Thank you!

Back Up

1999 – 2010: B factory at KEK (Japan)

Linac KEKB double ring

e+e- collider

e+e- → Y(4S) → BB

B→D ν: e ℓ xtracting |Vcb|G(1)η

and ρ²

●

Measured the signal yield in each w-bin

●

Calculate the predicted signal yield for given

|V

|G(1)η

and ρ²:

(relative to MC)

●

χ² fit of predicted yield to measured yield

Predicted

signal in bin i differential decay width using MC parameters

Belle preliminary

B→D ν: systematic errors ℓ

B s →D s Xeν

B s →D s Xμν

B s →D s *Xeν

B s →D s *Xμν

B s →D s

*

Xlν relative systematic

errors