1. Toru Iijima & Koji Ikado (Talk presented by T.I.) Nagoya University
The First Evidence of Bt n from Belle
& Future Prospect
As a contribution to WG2 (neutrino modes)
Ref: K.Ikado’s talk at FPCP06
hep-ex/
Toru Iijima & Koji Ikado
(Talk presented by T.I.)
Nagoya University
May 15, 2006
“Flavour in the LHC CERN

2. Toru Iijima @ Flavour in the LHC era
Bt n (within the SM)
Proceed via W annihilation in the SM.
Branching fraction is given by
Provide information of fB|Vub|
|Vub| from BXu l n fB cf) Lattice (d~10%)
Br(Btn)/Dmd |Vub| / |Vtd|
Expected branching fraction
HFAG [hep-ex/ ]
HPQCD [PRL95,212001(2005)]
2006/05/15
Toru Flavour in the LHC era

3. Bt X as a Probe to Charged Higgs
Charged Higgs contribution to B decays
Leptonic: Bt n
Semileptonic: BD t n
H+/W+
t +
Br(SM)
~ 9 x 10-5 c b
t +
H+/W+ nt
Br(SM)
~ 8 x 10-3
Decay amplitude
Tauonic decay is the most sensitive !
2006/05/15

4. Toru Iijima @ Flavour in the LHC era
Search for Btn
B tn is important for both SM and BSM.
Purely leptonic  Theoretically very clean
More than two n’s  Experimentally very challenging.
Its detection is a milestone of B physics.
B factories
LEP
First Evidence !
April 2006
2006/05/15
Toru Flavour in the LHC era

5. Btn Analysis Concepts
B decays with missing neutrinos lack the kinematic constraints which are used to separate signal events from backgrounds (Mbc and DE).
Reconstruct the decay of the non-signal B (tagging), then look for the signal decay in whatever is left over
More than 2 neutrinos appear in B tn decay
Tagging side :
Fully reconstruct
hadronic modes
Y(4S) B- B+ n p+
Signal side :
Reconstruct particles
from t decay
2006/05/15
Toru Flavour in the LHC era

6. Features with Fully Reconstructed B Tag
Pros: Offline B meson Beam
B momentum is known.
 Resolution of Mmiss2 can be significantly improved.
B-flavor/charge is known.
 We can treat charged & neutral B separately
 Large background reduction
Cons: Low statistics
Tagging efficiency : %
Mmiss2 for B-D0 m- n (MC)
w/o B momentum
with B momentum
 Large lum. required !
2006/05/15
Toru Flavour in the LHC era

7. Fully Reconstructed Tag at Belle (447M BB)
7 modes
6 modes
~ 180 channels used
2 modes
Beam constrained mass
N= 680k
eff.= 0.29%
purity = 57%
N = 412 k
eff.= 0.19%
purity = 52%
m ~ 5.28 GeV/c2
s~ 3 MeV/c2 due to 　　　　　　　s(Ebeam)
~10% for feed-across between B+ and B0
Charged B
Neutral B
Signal region : < DE < 0.06 GeV, Mbc > 5.27 GeV/c2
2006/05/15
Toru Flavour in the LHC era

8. Toru Iijima @ Flavour in the LHC era
Signal Selection (1)
t lepton is identified in the 5 decay modes.
Signal selection criteria.
Signal-side efficiency including t decay br.)
All selection criteria were optimized before examining the signal region (blind analysis).
81% of all t decay modes
32.92 0.12%
2006/05/15
Toru Flavour in the LHC era

9. Toru Iijima @ Flavour in the LHC era
Signal Selection (2)
Extra neutral energy in calorimeter EECL
Most powerful variable for separating signal and background
Total calorimeter energy from the neutral clusters which are not associated with the tag B
Minimum energy threshold
Barrel : 50 MeV
For(Back)ward endcap : 100(150) MeV
Zero or small value of EECL arising only from beam background
Higher EECL due to additional neutral clusters
MC includes overlay of random trigger
data to reproduce beam backgrounds.
2006/05/15
Toru Flavour in the LHC era

10. Toru Iijima @ Flavour in the LHC era
Signal Selection (3)
Extra neutral energy EECL Validation by double tagged sample (control sample);
Btag is fully reconstructed
Bsig is semileptonic decays
B+ D(*)0 X+ (fully reconstruction)
B- D*0 l-n
　　　　　　D0 p0
　　　　　　 K- p+
K- p+ p- p+
B+B-
494  18
B0B0
7.9  2.2
Total
502  18
Data
458
Purity ~ 90%
2006/05/15
Toru Flavour in the LHC era

11. Background Estimation
MC : 94.2  8.0 Data : 96
MC : 89.6  8.0 Data : 93
MC : 41.3  6.2 Data : 43
MC : 23.3  4.7 Data : 21
MC : 18.5  4.1 Data : 21
Sideband Total
MC : 267  14 Data : 274
Large MC samples for e+e- BB, qq, Xuln, Xu tn, t+ t- , and rare B decays are used (including beam-background).
Majority come from BD(*) X l n (~90%) + Xu l n/rare (~10%).
2006/05/15
Toru Flavour in the LHC era

12. Result: Opening the Box !
The signal regions are examined after finalizing all of the selection criteria.
414 fb-1
# estimated background and observed events in the signal region
Observe excess in signal region !
2006/05/15
Toru Flavour in the LHC era

13. Toru Iijima @ Flavour in the LHC era
Btn Candidate Event
B+ g D0 p+
K+ p- p+ p-
B- g t - n
e-nn
2006/05/15
Toru Flavour in the LHC era

14. Verification of the Signal (1)
For events in the EECL signal region, distribution of event selection variables other than EECL are verified.
They are consistent with MC expectation for Btn signal + background.
Btn signal
Background
Mbc
Pmiss
2006/05/15
Toru Flavour in the LHC era

15. Verification of the Signal(2)
About 30% of background have neutral cluster in the KLM detector (KL candidates).
The excess remains after requiring KL veto.
KL in coincidence.
KL in veto
EECL
EECL
We do not use this cut in the result, to avoid introducing large systematic error due to KL detection efficiency uncertainty.
2006/05/15
Toru Flavour in the LHC era

16. Toru Iijima @ Flavour in the LHC era
Fit Results
The final results are deduced by unbinned likelihood fit to the obtained EECL distributions.
Signal +
background
S : Significance with systematics
Btn
Signal
Background
Observe events with
a significance of 4.2s
Signal shape : Gauss + exponential
Background shape : second-order polynomial
2006/05/15
Toru Flavour in the LHC era

17. Systematic Uncertainty
Signal selection efficiencies
Tag reconstruction efficiency : 10.5%
Difference of yields between data and MC in the B- D*0l-n control sample
Number of BB : 1%
Signal yield :
signal shape ambiguity estimated by varying the signal PDF parameters
BG shape : changing PDF
Total systematic uncertainty
+12% %
+17% %
2006/05/15
Toru Flavour in the LHC era

18. Btn Branching Fraction
Branching fractions are calculated by
All t decay modes combined
Extracted branching fraction for each t decay mode
SM : B(Btn)=(1.59  0.40)×10-4
Result is consistent with SM　
prediction within error
2006/05/15
Toru Flavour in the LHC era

19. fB Extraction
Product of B meson decay constant fB and CKM matrix element |Vub|
Using |Vub| = (4.39  0.33)×10-3 from HFAG
14%
11% = 8%(exp.) + 8%(Vub)
fB =  GeV
[HPQCD, Phys. Rev. Lett. 95, (2005) ]
2006/05/15

20. Constraints on |Vub|/|Vtd|
Constraint in the (r,h) plane from the Btn branching fraction and Dmd
Constraint for
Improved measurement
will help.
2006/05/15
Toru Flavour in the LHC era

21. Constraints on Charged HiggsrH
95.5%C.L. exclusion boundaries B A A
2006/05/15
Toru Flavour in the LHC era

22. Toru Iijima @ Flavour in the LHC era
Future Prospect (1)
Br(Bt n) measurement:
Further accumulation of luminosity help to reduce both statistical and systematic errors errors.
Some of the major systematic errors come from limited statistics of the control sample.
|Vub| measurement:
< 5% in future is an realistic goal.
fB from theory
~10% now  5% ?
Note:
Lum.
DB(Btn) exp
D|Vub|
414 fb-1
36%
7.5%
5 ab-1
10%
5.8%
50 ab-1 3%
4.4%
Assumption in the following
plots
2006/05/15
Toru Flavour in the LHC era

23. Future Prospect (2) 5ab -1 50ab -1 If D|Vub| = 0 & DfB = 0
95.5%C.L. exclusion boundaries
DfB(LQCD) = 5%
5ab -1 rH 2s
If D|Vub| = 0 & DfB = 0
50ab -1 rH
2006/05/15

24. Future Prospect (3) Charged Higgs Mass Reach (95%CL @ tanb=30) 1TeV
Only exp. error
(DVub=0%, DfB=0%)
DVub=2.5%, DfB=2.5%
Mass Reach (GeV)
DVub=5%, DfB=5%
Luminsoity(ab-1) 5 10 20 30 40 50
2006/05/15
Toru Flavour in the LHC era

25. Toru Iijima @ Flavour in the LHC era
fD measurements
2006/05/15
Toru Flavour in the LHC era

26. Toru Iijima @ Flavour in the LHC era
Summary
We have seen the evidence of B t n with 414fb-1 data at Belle.
The first evidence of purely leptonic B decays.
Branching fraction
B decay constant
Constraint on charged Higgs.
O(ab-1) data, together with improved fB and |Vub|, will allow us to probe large tanb-mass space of charged Higgs.
Probe up to ~200GeV at tanb=30
2006/05/15
Toru Flavour in the LHC era

27. Toru Iijima @ Flavour in the LHC era
Backup Slides
2006/05/15
Toru Flavour in the LHC era

28. Toru Iijima @ Flavour in the LHC era
Fit Result (2)
Likelihood fit results for each t decay mode.
Signal +
background
Background
Signal
2006/05/15
Toru Flavour in the LHC era

29. Toru Iijima @ Flavour in the LHC era
Fit Results (3)
Likelihood distributions for each t decay mode.
2006/05/15
Toru Flavour in the LHC era

30. Toru Iijima @ Flavour in the LHC era
Future Prospect (5ab-1)
95.5%C.L. exclusion boundaries
DfB(LQCD) = 10% rH 2s
DfB(LQCD) = 5% rH 2s
2006/05/15
Toru Flavour in the LHC era

31. Full Reconstruction Method
Fully reconstruct one of the B’s to tag
B production
B flavor/charge
B momentum
Decays of interests
BXu l n,
BK n n
BDtn, tn B
e- (8GeV)
e+(3.5GeV)
Υ(4S) p
full (0.1~0.3%)
reconstruction
BDp etc. B
Single B meson beam in offline !
Powerful tools for B decays w/ neutrinos
2006/05/15
Toru Flavour in the LHC era

32. Search for Charged Higgs
BDtn (semileptonic decay) c b
t +
H+/W+ nt
Band width from form-factor uncertainty
Full reconstruction tag
Signal  large missing mass
Expected at 5ab-1
Mode
Nsig
Nbkg
dB/B
280
550
7.9%
620
3600
2006/05/15
Toru Flavour in the LHC era

33. Constraint to Charged Higgs
Once branching fraction is measured, we can constrain R.
Form factor error
M.Tanaka,
Z.Phys. C67 (1995) 321
r can be determined experimentally
by B semiletonic decays
at 5ab-1
2006/05/15
Toru Flavour in the LHC era

34. Sensitivity for Charged Higgs
Constraint from BXs g
BDtn
D(Form-factor) ~5%
D(Form-factor) ~15%
Btn
(present)
LHC
100fb-1
D(form-factor) can be reduced with the present BDmn data.
2006/05/15
Toru Flavour in the LHC era