2004/8/17 ICHEP2004 1
Measurement of |Vub| at Belle
Toru Iijima
Nagoya University
for
Belle Collaboration
August 17, 2004
32nd International Conference on High Energy Physics
2004/8/17 ICHEP2004 2
Introduction|Vub| measurement
Crucial to test the standard model of the CP violation.
Both inclusive/exclusive B→Xu l decays are useful.
Belle explores B tagging technique to extract B→Xu l in good quality.
Good signal-to-noise
Sufficient statistics
low middle high
poor
mod.
goodS/N
Eff.
trad. recon.
Full recon.
advanced recon.
Semilep. decay
Belle (mX,q2)PRL92,071802
Lum.
with 140fb-1 (152M BB)Results are preliminary
In this talk, we report measurements of
Inclusive B→Xu l
with fully reconstructed tag.
Exclusive B→Xu l with semileptonic decay tag.
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Inclusive B→Xu l w/ Fully Reconstructed Tag
Tagging side: Full reconstruction of Btag using hadronic decay modes.
Signal side: Lepton Detection
Neutrino reconstruction using Pmiss, Emiss.
Reconstruction of (mX, q2)
Υ(4S)e- e+
Btag
Bsig
K
mX: Hadronic inv. mass
v
Tagging side Btag→D(*) etc.
q2: Leptonic inv. mass 2Signal side Bsig→Xu l
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Full Reconstruction of Btag
Reconstructed modes (180 in total)
7 modes
6 modes
0 (*) (*)1/ / / SB D a D
(*)0 (*)1/ / / SB D a D
0 0/D D
0 0 0/D D sD
sD 0D
D
sD 2 modes
B0 tag.1.58 ×105 eff.=0.21% purity = 47%
B0 tag.1.58 ×105 eff.=0.21% purity = 47%
B+ tag.2.47 ×105 eff.=0.33% purity = 50%
B+ tag.2.47 ×105 eff.=0.33% purity = 50%
Inclusive B→Xu l
Mbc (beam constrained mass) distribution 140fb-1 data
Signal region: Mbc > 5.26GeV/c2, -0.2 GeV < E < 0.05 GeV
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Reconstruction of Signal Side
Semileptonic lepton selectionLepton momentum Pl > 1.0 GeV/c
Lab. angle 26 ~ 140deg.
+ J/ veto, conversion veto etc.
Normalization to B→X l
Inclusive B→Xu l
mX < 1.7 GeV/c2, q2 > 8 GeV2
Phase space cut to minimize theory error
※ same as our previous (mX,q2) measurement with simulated annealing [PRL 92, 071802 (2004)]
Reduction of bc background• Number of leptons Nl = 1• Total net charge ∑Qi=0• Missing mass -1.0<MM 2<0.5 Ge
V2
• Missing mom. Direction cosMM < 0.95• Number of kaons NK+ = NKS = 0
0 2 4 6 8 141210-4 -2MM2 (GeV2/c2)
Expected MM2 dist. b→u b→c
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Signal Yield ExtractionFit Mbc distribution in each mX region with Gaussian+’Argus’ to subtract the combinatorial background in the Btag sample.
Fit the obtained mX distribution with expected b → u and b → c distribution.
Nb→ u = 174±26
Nsl = (5.07±0.4)×104
Inclusive B→Xu l
The number of semileptonic leptons is extracted by similar fitting on Mbc before the b → u selection cut.
mX<1.7GeV/c2
q2>8GeV2
Mbc distribution for each mX region mX distribution with Btag bkg. Subtracted.
Expected dist. of b→u b→c
Btag background
0 0.5 1.0 1.5 2.0mX (GeV/c2)
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Event Distribution in mX and q2
Event distribution in mX and q2 with the normalization fixed to the fitting with the coarse bin.
Inclusive B→Xu l
140fb-1
q2 distribution (mX>1.7GeV/c2)
Expected dist. of b→u b→c
-5 0 5 10 15 20q2(GeV2)
mX distribution (q2>8GeV2)
Expected dist. of b→c b→u
0 0.5 1.0 1.5 2.0 2.5 3.0mX (GeV/c2)
Subtracted with the Expected b→c bkg.
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Fraction of semileptonic leptons with Pl > 1.0GeV/c
Partial Branching FractionRelative partial branching fraction
( )
( )
1b us
sll
b u
slfrec
b ufrec
b
l ls l
u u
e
FB B X N
B B X N
b→ u selection efficiency: 0.274
Full recon. efficiency ratio:
Corrections: Unfolding the mX /q2 resol. 0.984±0.014
3( ) 0.99 0.15 0.18 0.04 0.07 10uB B X
( ) 0.1073 0.0028Br B X (PDG2004)
stat. syst. b→u b → c
Partial branching fraction
140fb-1 preliminary
mX < 1.7 GeV/c2, q2 > 8 GeV2
Inclusive B→Xu l
0.75±0.048
2004/8/17 ICHEP2004 9
|Vub| Determination
Extrapolation to the total br.
New determination of b-quark shape function (SF)
parameters from Belle’s B → Xs photon spectrum.
( ) ( ) /u u uB B X B B X f
0.294 0.044uf
+ Higher order correction (FN → BLL)+ Contribution from sub-leading SF + W.A.
Inclusive B→Xu l
A.Limosani, T.NozakiHep-ph/0407052
3( ) 3.37 0.50 0.60 0.14 0.24 0.50 10uB B X
from fu error1/ 2( ) 1.61
| | 0.004240.002
uub
B
B B X psV
+latest HQ parametersPDG formula
3| | 5.54 0.42 0.50 0.12 0.19 0.42 0.27 10ubV stat. syst. b→u. b → c. fu Br→|Vub
|140fb-1 preliminary
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Exclusive B→Xu l w/ Semileptonic Decay Tag
New method for clean extraction of
B→ l l decays.
Υ(4S)e- e+
Btag
Bsig
v
Tagging side Btag→D(*) l
Signal side Bsig→ l
v
D(*)
“Double semileptonic”decay.
2004/8/17 ICHEP2004 11
Analysis Method
* /tagB D D 0 0/D D
decay modesdecay modes
Tag side reconstruction
o have intersection,must be 20 1Bx
Kinematics of double semileptonic decay Back-to-back correlation of the two B constrains their direction to the intersection of the 2 cones.
Exclusive B→Xu l
sig uB X
0( ) 1, ( ) 1N N 0 or
Signal side reconstruction0.8 /P GeV c
2004/8/17 ICHEP2004 12
The ratio Nobs/Nexpected = 0.89 ±0.08 is used to correct the MC efficiency for l and l detection.
Calibration with Bsig→D*l Decays
Validity of the method for double semileptonic decay detection has been tested with *
sigB D 0D
K
M(K+--) on the signal side x2 distribution
Nobs=147±12
The method works !
Dots: DataHisto: MC
Exclusive B→Xu l
( Nexpected =165)
M(K) GeV/c2 x2
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Signal ExtractionWe extract l / l signals simultaneously by fitting 2D
(mX, x2) distribution.
Fitting components: l , l , other Xu l , BB background.
PDF’s are based on MC.
Constraint for extracted Br: Br( l +Br( l +Br(other Xu l )=Br(Xu l )
Exclusive B→Xu l
Fitting results for all q2 data.l (82±13)
l (65±20)other Xul
BB
x2 dist. for mass region (I)
x2 dist. for mass region (II)
I II
mX GeV/c2 x2 x2
ldecays are cleanly extracted !
140fb-1
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Extraction of q2 Distributionq2 distribution is extracted by fitting the (mX,x2) distribution for three q2 intervals.
Exclusive B→Xu l
△ UKQCD○Ball’01□ ISGW IIl+
△ UKQCD○Ball’01□ ISGW II
◇ Melikhov’98
l+
At the present accuracy, the obtained q2 dist. does not exclude any tested models
32.54 0.78 0.85 0.30 10totalB 31.76 0.28 0.20 0.03 10totalB
Extracted q2 dist.
FF-dep.
140fb-1
Preliminary
q2<8GeV2 q2:8-16GeV2 q2>16GeV2mX dist. for three q2 intervals
mX (GeV/c2)
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|Vub| from B0→ l+
|Vub| determined from B>16GeV2 (B0→ l+ ) with lattice QCD.
0.62 30.48(3.90 0.71 0.23 ) 10
0.320.121.92 0.47thy
Exclusive B→Xu l
( )ub
phy B
B BV
w/ quenched LQCD [FNAL/JLQCD/APE/UKQCD]
Average
4th error fromFF-dep. in Br is small for l data
w/ unquenched LQCD [FNAL/HPQCD]
Preliminary results reported at Lattice’04.
FNAL’04
HPQCD
1.96 0.51 0.39thy
1.31 0.33thy
0.85 30.51(3.87 0.70 0.22 ) 10
0.74 30.50(4.73 0.85 0.27 ) 10
140fb-1, preliminary thy
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Summary
We have obtained preliminary |Vub| results from
Inclusive B→Xu l w/ fully reconstructed tag.
Results are compatible and consistent
with the previous exp’s.
Exclusive B→Xu l (B0 → l )
w/ semileptonic decay tag.Results are compatible and consistent
with the previous exp’s and inclusive results.
New method for clean signal extraction
has been demonstrated.
These measurements are promising
approach at B-factories in the coming years !
Belle |Vub|
2004/8/17 ICHEP2004 18
Systematic Uncertainties
bu MC statistics = 4%model dep. = 4.2%
Detector sim. for bc & bu MC = 6.5%Correlated errors, added/subtracted in linear for the two MC’s
Subtracting:Lept. sel. = 1% clusters = 1%
Adding:Kaon ID = 6%tracking = 2%
Systematic error of Refreco and Re
lept ... 6.4%
bc MC statistics = 15%model dep. = 5%
Variate inclusive parameters within errors
Dl (D =1.19±0.19)D*l (A1=1.51±0.13)D**l
... 5.6%
... 3.9%
... 1.6%
Inclusive B→Xu l
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Systematic UncertaintyMajor contribution
D*lcalibration
Statistics of detected D*l8.3%
Error of Br(B0D*l) 4.3%
BB background shape
tested B(l) (B( l )) in MC by
removing charged track by 1%
-4.2(+23.5) %
removing by -1.1(+12.8) %
Replacing K with by 2%
-0.5(+16.6) %
Exclusive B→Xu l
Significant change in B( l ), due to the broad width of meseon.
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Four quenched calculations from FNAL, JLQCD, APE and UKQCD (used in CLEO2003).
Average
Preliminary unquenched results from FNAL and HPQCD
(reported at Lattice’04).
FNAL (M.Okamoto)
HPQCD(J.Shigemitsu)
B Form-Factor from LQCD
0.320.121.92 0.47thy Include 15%
quenching error
1.96 0.51 0.39thy
1.31 0.33thy
( given for q2>16GeV2 )thy
Exclusive B→Xu l
2004/8/17 ICHEP2004 21
FNAL’04Statistical ~10%
Lattice-continuum matching ~7%
Chiral extrapolation ~6%
Discritization ~5%
HPQCDStatistical ~5%
Higher oder operator matching ~9%
Chiral extrapolation ~5%
Relativistic+discritization ~5%
Error of FF from Unquenched LQCD
1.96 0.51( .) 0.39( .)phy stat syst
1.31 0.33[0.13( ) 0.30( )]phy stat syst
2
Number given by M.Okamoto (FNAL) and J.Shigemitsu (HPQCD) in private communications.
2
Exclusive B→Xu l