BNM Tsukuba (KEK) Sep 13-14 2006 Antonio Limosani KEK Slide 1 Antonio Limosani JSPS Fellow (KEK-IPNS...

BNM Tsukuba (KEK) Sep 13-14 2006 Antonio Limosani KEK Slide 1

The Future of Vub Antonio Limosani

JSPS Fellow (KEK-IPNS JAPAN)

BMN 2006

2006

2010


Motivation• Fundamental parameter in SM

• CKM mixing matrix element

• Unitarity Triangle Side-length

Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb

L SM ... gWbL

VubuL ...

3() 1()

2 ( )

VcdVcb*

VtdVtb*

VudVub*

Directly test the mechanism for CP Violation in SM


Measurement type - InclusiveMX

hadrons

Charged lepton

neutrino

q2

plepton

1. Cuts to avoid B Xc l

2. Measure

3. Extract Vub

pl (M B

2 M D2 )

2M B

2.3 GeV/c ( : 10% phase space)

q2 (M B M D )2 11 GeV2 /c2 ( : 30%)

M X M D 1.8 GeV/c2 ( : 80%)

B(B Xul) NSelected NBackground

Quark level

B


HFAG Vub AverageSource Error

(%)Stat 2.2Exp 2.8Bkgd model 1.9Signal model 1.6HQE: mb 4.2SSF/matching 3.8WA 1.9Total 7.3


Fully reconstructed B sample• Dedicated exclusive channels are searched

for in reconstruction– 180 decay chains – Clean environment but small sample – Reconstruction Efficiency ~ 0.3%

• Reconstructed modes


Fully reconstructed B analysis• Fully reconstruct the event 4-momenta of both B’s are known

• Identify lepton from BXl on the signal side

• Use Particle ID to reconstruct the hadronic system and calculate

• Estimate the signal BXul


Belle Mx Analysis @ 253/fb

B=(1.24±0.11(stat) ±0.09(sys) ± 0.08(b->u) ±0.03(b->c))x10-3

Vub=4.09 x10-3 (1 ±0.049 (stat) ±0.035 (sys) ±0.031 (b->u) ±0.011 (b->c) ±0.045 (SF) ±0.038 (theory))

Mx < 1.7 GeV/c2

Phys.Rev.Lett.95:241801,2005 (hep-ex/0505088)


Mx Analysis : StatisticalError projections

Luminosity(/ab) 0.25 1.0 5.0 50.0Signal to Noise 0.65 1.5 2.0 2.0B tag efficiency 0.3 0.4 0.6 0.6|Vub| stat % 4.9 2.0 0.7 0.2


Luminosity(/ab) 0.25 1.0 5.0 50.0

Detector simulation 3.5 3.5 3.5 3.5

Background model (charm)

1.1 1.0 0.5 0.5

Signal model Depends of HQE parameters : b-quark mass, mb, dominates

Extrapolating to full branching fraction (SF)Theory |Vub| :Matching scales, SSFTheory/Exp |Vub| :Weak Annihilation |Vub| stat %

Mx Analysis : Systematic & TheoryError projections


b-quark mass, mb

(4.60 +/- 0.04) GeV/c2

Luminosity(/ab) 0.25 1.0 5.0 50.0

Exp error:Moments data

0.025 0.02 0.01 0.01

Theory errorVary s, mb, mc

0.03 0.03 0.03 0.03

Total error 0.04 0.04 0.03 0.03

Mx Analysis : b-quark mass

Precision on mb hits theory floor!


Mx Analysis : Systematic & TheoryError projections

Luminosity(/ab) 0.25 1.0 5.0 50.0



1.1 1.0 0.5 0.5

Signal model 3.1 2.8 2.6 2.4

Extrapolating to full branching fraction (SF)

4.5 4.2 3.9 3.7

Theory |Vub| :Matching scales, SSF

3.6 3.6 3.6 3.6

Theory/Exp |Vub| :Weak Annihilation

3.0 2.0 1.0 1.0


Mx Analysis : TotalError projections

Luminosity(/ab) 0.25 1.0 5.0

|Vub| total % 9.4 7.7 7.0 6.8

|Vub| exp % 6.1 4.1 3.6 3.6

|Vub| theory % 7.2 6.5 6.0 5.8


Mx Analysis : TotalError projections


Vub with Reduced Model dependencePhys.Rev.Lett. 96 (2006) 221801 (hep-ex/0601046 ) (BABAR Collaboration)

Mx < 2.5 GeV/c2

Vub=3.84 x10-3 (1 ±0.182 (stat) ±0.036 (sys) ±0.056 (b->u) ±0.038 (b->c) ±0.000 (SF) ±0.026 (theory))


Error projectionsLuminosity(/ab) 0.1 1.0 5.0 50.0

Statistics 18.2 5.7 2.6 0.8



3.8 3.5 2.0 2.0

Signal model 3.1 2.9 2.7 2.5

Extrapolating to full branching fraction (SF)

0.0 0.0 0.0 0.0

Theory |Vub| :Perturbative

3.6 3.6 3.6 3.6

Total 19.5 8.9 6.6 6.1


Error projections


Measurement types - Exclusive

dB(B0 l )dq2d(cosWl )

Vub

2

B0

GF2 k

3

32 3 sin2Wl f (q2 )2

Vub B(B ( / )l

thy B

,

thy Form factor normalisation

Theoretical description parameterised by a single form factor

pion

Charged lepton

neutrino

q2

plepton

B Experimentally less ambiguous than the inclusive decay

Determine using unquenched lattice QCD calculations.

• Model independent• Limited to q2>16 GeV2/c2


Current status - Exclusive


Vub from B(B->lv:q2>16) Three methods 1. Untagged: Systematic error 4% @ 0.2ab-1 (BABAR)

• Previous to this study consensus was one couldn’t get lower than 8%

2. Semileptonic tag : Systematic error 10% @ 0.25ab-1 (Belle)• Systematic dominated by statistics of control sample• Total error 2.9% @ 5ab-1 and 2.1% @ 50ab-1

3. Full B reconstruction tag : Systematic error 2.1% @0.5ab-1 (Belle)• Total error : 40% @0.5ab-1 (statistics dominated)• Total error : 27% @1.0ab-1 • Total error : 15% @5.0ab-1 (improvement in full recon efficiency)• Total error : 5% @50ab-1

Theoretical uncertainties (Lattice QCD) Phys. Rev. D73:074502 (2006)Currently error is at 12%, but it’s anticipated that it will reach 5%.


Future of Exclusive Vub


Future of Vub

•Tagged analyses are essential

•At logged luminosities of 5/ab and 50/ab precision is limited by systematic and theoretical uncertainties ~ 5%

•Co-ordinated experimental and theory studies are needed to reduce this error further

•b-quark mass


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