View
24
Download
0
Category
Preview:
DESCRIPTION
Semileptonic Decays from Belle. Youngjoon Kwon Yonsei Univ. / Belle. Contents. Introduction A nalyses for V ub Inclusive B X u l n with full-recon. Inclusive B X u l n with end-point Exclusive B X u l n with semileptonic tag. ( prelim. ) - PowerPoint PPT Presentation
Citation preview
Semileptonic Decays from Semileptonic Decays from BelleBelle
Youngjoon KwonYonsei Univ. / Belle
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 2
ContentsContents
Introduction
Analyses for Vub
– Inclusive B Xu l with full-recon.– Inclusive B Xu l with end-point– Exclusive B Xu l with semileptonic tag.
(prelim.)
Analyses towards precise Vcb
– Inclusive B X e with full-recon. – B X l hadronic mass moments (prelim.)
– B X l lepton energy moments (prelim.)
PRL submitted, hep-ex/0505088
PLB accepted, hep-ex/0504046
PLB 614, 27 (2005)
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 3
MotivationMotivation Fundamental free parameters
– Majority of free parameters in the SM are related to quark (and lepton) flavors : masses and mixings
– Quark flavor mixing through CKM matrix
Unitarity triangle– Direct test of CP violation mechanism in
SM
– Vub: still a weak link in CKM test
– Vcb : as fundamental as Vub
• Super-high precision, experimentally• A good testing ground of strong int. theory
*VV tbtd
*VV cbcd
1
2
3
*VV ubud
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 4
Issues in VIssues in Vubub measurementmeasurement
Use B Xu l (semileptonic)– Cleaner, better understood than B hadronic– More accessible than B leptonic– Inclusive and Exclusive
Experimentally challenging
Tight selection criteria results inLimited phase space Extra theoretical uncertainties (from
extrapolation)
cbV ubV
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 5
Variables to suppress b Variables to suppress b c l c l
XX pEP
GeV 66.0/ 2 BD MMP
2
222
22
GeV/ 8.1 GeV/ 11
GeV/ 3.22
cMMcMMq
cM
MMp
DX
DB
B
DBl
(10% phase sp.)
(~80%)(~30%)
Inclusive B Inclusive B X Xuu l l with End- with End-pointpoint
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 7
Main featuresMain features
OPE breaks down need shape ftn.!
• Measure B(B Xu e , pe > pcut)
• Kinematic selection pe > pcut
pcut = 1.9, 2.0, 2.1, 2.2, 2.3 and 2.4 GeV/c
• No requirement other than on the signal electron
high statistics
• Large background from B Xc e bkg. sys. uncertainty
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 8
b-quark Shape Functionb-quark Shape Function
What is it?– b-quark Fermi motion
inside the B-meson
How to get it?– Universal at leading
order for all b light quark transitions
– Use E() in B Xs
Three models for Three models for SFSF
Neubert & Paz, hep-ph/0504071
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 10
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 12
Event SelectionEvent Selection
• Hadronic events• Electrons in the barrel region
eff. ~ 94%; fake rate ~ 0.13% J/, (2S), , 0 veto
• Continuum suppression Fox-Wolfram moment Fisher disc. for energy-flow variables |cos th| < 0.75 as q2 independent as possible
• Background estimated by b c MC and Off-resonance Data low-p region for check 1.5 < pe < pcut (GeV/c)
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 13
EE(e) spectrum for B (e) spectrum for B X Xuu e e
BB – partial BF – partial BF
Two methods for B Vub
– Standard method (DFN, JHEP 9906, 017)
– New method (BLNP, NP B699 (2004))
MC2
BB
uu N
lXNB
03.007.00.53 1.016.2 6.24.207.010.01.18 0.916.5 6.23.220.014.02.17 0.916.6 6.22.248.020.03.78 0.917.2 6.21.298.028.05.74 0.917.6 6.20.253.137.08.47 0.918.0 6.29.1
)10(in -4MCCM pBp u
VVubub from from BB
DFN
BLNP
Inclusive B Inclusive B X Xuu l l with Full- with Full-Recon.Recon.
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 17
4.2105 evts./253 fb
effic. = 0.33%purity = 62%
2.5105 evts./253 fb
effic. = 0.21%purity = 59%
Full ReconstructionFull Reconstruction
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 18
Signal selectionSignal selectionLepton Selection• p > 1 GeV/c • leptons in the barrel region
J/, , 0 veto• Correct charge for B+ candidate• No other lepton
For b u• Total charge = 0• • • No reconstructed KS or K
22miss GeV 5.0 0.1 m
95.0cos miss
Nsl = (9.15 0.05) x 104
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 19
Kinematic Kinematic selectionsselections
GeV 66.0 )3(
GeV 8 GeV, 7.1 (2)
GeV 7.1 )1(22
XX
X
X
pEP
qM
M
(New)
(1) M(1) MXX < 1.7 GeV < 1.7 GeV
– Each bin content is calculated from Mbc fit– 2-component fit to extract N(bu)
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 21
(2) M(2) MXX < 1.7 GeV & q < 1.7 GeV & q22 > 8 > 8 GeVGeV22
(3) P(3) P++ < 0.66 GeV < 0.66 GeV
– First measurement using P+
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 24
Signal Yield & Signal Yield & BB
slubr )%28.073.10(
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 25
VVubub from from BB New method
– Vub directly from BR by Bosch, Lange, Neubert, Paz, NPB699 (2004)with an improved treatment of shape-function effects + weak annihilation effects estimated
.)()(8.62.33
.)()(5.79.40
.)()(0.46.21
)ps(3.23.2
2.39.2
4.23.2
1
thySF
thySF
thySF
R
2/ qM X
XM
P
Exclusive B Exclusive B X Xuu l l with S.L. with S.L. tagtag
Experimental StrategyExperimental Strategy
B l / l (140fb-1)ICHEP04 preliminaryhep-ex/0408145
B l (78fb-1)PRL 93, 131803 (2004)
low middle high
poor
mod.
goodS/N
Eff.
trad. recon.
Full recon.
advanced recon.
D(*) l tag
Lum.
-4Br(ωlν) =(1.3±0.4±0.2±0.3)×10
How well can we measure the q2 dist. (for l ) ?
+ l / l (preliminary)
Unique opportunity at e+e- B-factory!
Analysis MethodAnalysis Method
* /tagB D D 0 0/D D
4 decay modes7 decay modes
Tag side reconstruction
To have intersection,need 20 1Bx
Kinematics of double semileptonic decay Back-to-back correlation of the two B’s constrains their direction to the intersection of the 2 cones.
sig uB X
0( ) 1, ( ) 1N N 0 or
Signal side reconstruction0.8 /P GeV c
2-fold ambiguity q2 calculated neglecting the B motion in (4S) q2 resolution = 0.75 GeV2
The ratio Nobs/Nexpected = 0.89 0.08 is used to correct the MC efficiency for l and l detection.
Calibration with Calibration with BBsigsig→D*l→D*l DecaysDecays
Validity of the method for double semileptonic decay detection has been tested with
0D
K M(K+--) on the signal side xB
2 distribution
Nobs=14712
The method works !
Dots: DataHisto: MC
( Nexpected =165)
M(K) GeV/c2 xB2
lDBsig*
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 30
Signal ExtractionSignal Extraction q2 distribution is extracted by fitting the (mX,x2)
distrib. for three q2 intervals.mX (GeV/c2)
■ Fitting components: l, l, other Xu l and BB■ PDF’s are based on MC.■ Constraint for extracted Br:
Br(l) + Br( l) + Br(other Xu l) = Br(Xu l)
q2<8GeV2 q2:8-16GeV2 q2>16GeV2
8213 6520
ResultsResults
VVubub from exclusive B from exclusive B X Xuu l l 140 fb-1
Analyses towards precise Analyses towards precise VVcbcb
Inclusive B X e (0th moment) B X l hadronic mass moments
(prelim.) B X l lepton energy moments
(prelim.)
PLB 614, 27 (2005)
PLB 614, 27 (2005)
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 35
B B X l X l moments moments
Leptonic and hadronic moments– Needed for global fit for precise Vcb
Common features– Preliminary with 140 fb-1
– Full-recon. in the tag side– Boost from Btag
– QED correction by PHOTOS– Mixing correction– Unfolded by SVD method
Leptonic momentsLeptonic moments
cute EEeE
cute EEe ME
2
1
Beauty 2005, June 20-24, 2005 Youngjoon Kwon (Yonsei Univ. / Belle) 37
Hadronic momentsHadronic moments
Hadronic momentsHadronic moments
Belle VBelle Vubub Summary Summary
Recommended