Measurements of branching fractions and q 2 distributions for B→πℓν and B→ρℓν Decays with B→ D (∗) ℓν Decay Tagging
Abstract
We report measurements of the charmless semileptonic decays
B
0
→
π
−
/
ρ
−
ℓ
+
ν
and
B
+
→
π
0
/
ρ
0
ℓ
+
ν
, based on a sample of
2.75×
10
8
B
B
¯
events collected at the
Υ(4S)
resonance with the Belle detector at the KEKB
e
+
e
−
asymmetric collider. In this analysis, the accompanying
B
meson is reconstructed in the semileptonic mode
B→
D
(∗)
ℓν
, enabling detection of the signal modes with high purity. We measure the branching fractions
B(
B
0
→
π
−
ℓ
+
ν)=(1.38±0.19±0.14±0.03)×
10
−4
,
B(
B
0
→
ρ
−
ℓ
+
ν)=(2.17±0.54±0.31±0.08)×
10
−4
,
B(
B
+
→
π
0
ℓ
+
ν)=(0.77±0.14±0.08±0.00)×
10
−4
and
B(
B
+
→
ρ
0
ℓ
+
ν)=(1.33±0.23±0.17±0.05)×
10
−4
, where the errors are statistical, experimental systematic, and systematic due to form-factor uncertainties, respectively. For each mode we also present the partial branching fractions in three
q
2
intervals:
q
2
<8
,
8≤
q
2
<16
, and
q
2
≥16
GeV
2
/
c
2
. From our partial branching fractions for
B→πℓν
and recent results for the form factor from unquenched Lattice QCD calculations, we obtain values of the CKM matrix element
|
V
ub
|
.