arxiv:1005.3288 submitted to phys. rev. d
DESCRIPTION
arXiv:1005.3288 submitted to Phys. Rev. D. Motivation. ℓ -. V ub. W -. q. u. b. B. , . ¯. q. q. ¯. β known within 1º. ¯. Data sample: 377 million BB pairs. Motivation. ℓ -. V ub. W -. q. u. b. B. , . ¯. q. q. ¯. | V ub | uncertainty. ¯. - PowerPoint PPT PresentationTRANSCRIPT
arXiv:1005.3288 submitted to Phys. Rev. D
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 2
Motivation
q̄
b u
ℓ-
B ,
Vub
q
W-
β known within 1º
Data sample: 377 million BB pairs
q̄
¯
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 3
|Vub
| uncertainty
Motivation
q̄
b u
ℓ-
B ,
Vub
q
W-
Data sample: 377 million BB pairs
q̄
¯
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 4
Sample components
• Signal: very small relative to bkgd.
• B→Xu
lν (Xu
≠ π,ρ): similar to signal
• other BB: B→Xclν control samples used as cross-check
• e+e-→qq (q=u,d,s,c) continuum: off-resonance data used to correct fit variable shapes
Signal candidate selectionUntagged
non-signal B is not
reconstructed
Y(4S)
e+ e-
Bsignal
ℓ
Xu
= , →
X1
X2
Xn
Bgeneric
B0→π-ℓ+ after preselection
¯
¯
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 5
Neural net background suppression• Neural nets trained against each of 3 backgrounds, in each q2 bin• Sample plots shown for B0→-ℓ+ in 3 selected q2 bins
0<q2<4 GeV2
Continuum background
Jet-like events differ from isotropic B
decays
B→Xclν background
largest background,
Γ(b→clν) ~ 50×Γ(b→ulν)
B→Xu
lν background
Mostly at high q2,
hard to separate
4<q2<8 GeV2 20 GeV2 <q2 signal
B→Xu
lν
other BB
¯
¯cut cut
cut
B0→-ℓ+ S/B before NN = 3%
B0→-ℓ+ S/B after NN = 12%
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 6
B→ℓ yields
Low q2 Mid q2 High q2
2
s
s
ppE Bbeams
Signal peaks at ΔE = 0
Signal peaks at
mES
≈ mB
= 5.28 GeV/c2
2
22/
Bbeams
BbeamsES p
E
ppsm
Backgrounds vary with q2.
Single mode yields
4-mode yield used to find BF
σstat
= 3.5%; σsyst
= 5.0%; σtot
= 6.1%
signal
B→Xu
lν
other BB
¯
¯
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 7
B→ρℓ yields
Large B→Xu
lν background is highly
correlated with signal and must be fixed in
the fit.
Smaller yield than
B→πlν
σstat
= 8.6%; σsyst
= 15%; σtot
= 18%
signal
B→Xu
lν
other BB
¯
¯
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 8
Shaded band indicates uncertainty on BGL fit.
Form factor parameterizations
All 4 parameterizations agree with each other and are consistent with the
data.
q2 spectrum corrected for detector efficiency &
resolution, bremsstrahlung, and radiative effects
• BCL and BGL expansions avoid ad hoc assumptions and are
based on fundamental QCD concepts.
• We use BGL 3-parameter fit as default (consistent with BGL
2-parameters).
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 9
• Probabilities exclude theory errors and use
full q2 range.
• Calculations valid only for partial q2 range.
Theory curves scaled to area of
the data.
Comparison with theory
Errors too large to distinguish between B→ρℓ
predictions.
LCSR
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 10
Theory needed to calculate
form factor.
• Probabilities exclude theory errors and use
full q2 range.
• Calculations valid only for partial q2 range.
|Vub| from partial q2 range
σexp
= 3-5%; σthy
= ~15%
Theory error dominates
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 11
|Vub| from full q2 range
Simultaneous fit to data and theory
• 3 parameters: BGL quadratic polynomial
• 4th parameter: relative normalization between theory and
data, α |Vub
|2
• Theory points are correlated, so not all are used in fit.
σ(data BF) = 3%
σ(data q2 shape) = 5%
σ(theory FF norm.) = 8.5%
σtotal
= 10.5%
Errors reduced compared to
|Vub
| from partial q2 range
PRD 79, 054507 (2009)
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 12
UT Fit Values
✚ average exclusive
average inclusive
Global “all other” fit =
(3.48 ± 0.16) × 10-3
Conclusion• Most precise branching fraction measurements:
– BF(B0→-ℓ+) = (1.41 ± 0.05 ± 0.07) × 10-4
– BF(B0→ρ-ℓ+) = (1.75 ± 0.15 ± 0.27) × 10-4
• Tests of q2 spectrum agreement with theoretical predictions.
• Determination of |Vub
|:
• LCSR, low q2 = (3.63 ± 0.12 +0.59-0.40
) × 10-3
• HPQCD, high q2 = (3.21 ± 0.17 +0.55-0.36
) × 10-3
• FNAL/MILC, full q2 = (2.95 ± 0.31) × 10-3
BF(B0→-ℓ+) [× 10-4]
BF(B0→ρ-ℓ+) [× 10-4]
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 13
Backup
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 14
Form factor parameterizations
Red-highlighted variables vary in the fit.
¯
ICHEP 24 July 2010 W. Wulsin, B→(π/ρ)ℓν at BaBar 15
Systematic uncertaintiesFrom combined 4-mode fit