Toru Iijima & Koji Ikado (Talk presented by T.I.) Nagoya University
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Toru Iijima & Koji Ikado
(Talk presented by T.I.)
Nagoya University
May 15, 2006“Flavour in the LHC era” @ CERN
The First Evidence of B from Belle
& Future ProspectAs a contribution to WG2 (neutrino modes)Ref: K.Ikado’s talk at FPCP06
hep-ex/0604018
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B(within the SM)
Proceed via W annihilation in the SM.
Branching fraction is given by
Provide information of fB|Vub|– |Vub| from BXu l fB cf) Lattice (~10%)
– Br(B)/md |Vub| / |Vtd|
Expected branching fraction3| | (4.39 0.33) 10ubV
(0.216 0.022)Bf GeV 5
( )
(1.59 0.40) 10
Br B
HFAG [hep-ex/0603003]
HPQCD [PRL95,212001(2005)]
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BX as a Probe to Charged Higgs
Charged Higgs contribution to B decays Leptonic: B
Semileptonic: BD
cb
H/W
tan cotb cm m
tanm
tan cotb um m
b
u H/W
tanm
Br(SM) ~ 9 x 10-5
Decay amplitude 2tanbm m
( )
( )
B D vB
B D v
Tauonic decay is the most sensitive !
Br(SM)~ 8 x 10-3
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Search for B B is important for both SM and BSM. Purely leptonic Theoretically very clean More than two ’s Experimentally very challenging. Its detection is a milestone of B physics.
B factories
LEP
First Evidence !April 2006
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B Analysis Concepts
B decays with missing neutrinos lack the kinematic constraints which are used to separate signal events from backgrounds (Mbc and E).
Reconstruct the decay of the non-signal B (tagging), then look for the signal decay in whatever is left over
Y(4S)B- B+
+
More than 2 neutrinos appear in B decayTagging side :
Fully reconstruct hadronic modes
Signal side :Reconstruct particles from decay
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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 : 0.2 - 0.3%
w/o B momentum
with B momentum
Mmiss2 for B-D0 (MC)
Large lum. required !
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Fully Reconstructed Tag at Belle (447M BB)
7 modes
6 modes0 (*) (*)1/ / / SB D a D
0 0/D D
(*)0 (*)1/ / / SB D a D
0 0 0/D D sD
sD
0D
D
sD 2 modes
Beam constrained mass
Signal region : -0.08 < E < 0.06 GeV, Mbc > 5.27 GeV/c2
~10% for feed-across between B+ and B0
m ~ 5.28 GeV/c2
~ 3 MeV/c2 due to (Ebeam)
~ 180 channels used
N= 680keff.= 0.29% purity = 57%
N= 680keff.= 0.29% purity = 57%
N = 412 keff.= 0.19% purity = 52%
N = 412 keff.= 0.19% purity = 52%
Charged B Neutral B
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Signal Selection (1) lepton is identified in the 5 decay modes.
Signal selection criteria.
Signal-side efficiency including decay br.)
All selection criteria were optimized before examining the signal region (blind analysis).
81% of all decay modes
32.92 0.12%
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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.
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Signal Selection (3)
Extra neutral energy EECL Validation by double tagged sample (control sample);– Btag is fully reconstructed
– Bsig is semileptonic decays
BB++ D D(*)0(*)0 X X+ + (fully reconstruction)(fully reconstruction) BB-- D D*0 *0 l- DD00 0
KK-- ++ KK-- + + -- ++
B+B- 494 18
B0B0 7.9 2.2
Total 502 18
Data 458Purity ~ 90%
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Background Estimation
MC : 23.3 4.7 Data : 21
MC : 94.2 8.0 Data : 96
Large MC samples for e+e- BB, qq, Xul, Xu , , and rare B decays are used (including beam-background).
Majority come from BD(*) X l (~90%) + Xu l /rare (~10%).
Sideband Total
MC : 267 14 Data : 274
MC : 89.6 8.0 Data : 93
MC : 41.3 6.2 Data : 43
MC : 18.5 4.1 Data : 21
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Result: Opening the Box ! The signal regions are examined after finalizing all of the selection criteria.
Observe excess in signal
region !
414 fb-
1
# estimated background and observed events in the signal region
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B Candidate Event
BB++ D D0 0 ++
KK++ - - ++ --
BB-- --
ee--
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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 signal + background.
MbcPmiss
B signalBackground
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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.
We do not use this cut in the result, to avoid introducing large systematic error due to KL detection efficiency uncertainty.
KL in coincidence. KL in veto
EECLEECL
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The final results are deduced by unbinned likelihood fit to t
he obtained EECL distributions.
Fit Results
Signal shape : Gauss + exponentialBackground shape : second-order
polynomial
Signal +
background
BackgroundB
Signal
: Significance with systematics
Observe 21.2 events with
a significance of 4.2
+6.7 - 5.7
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Systematic Uncertainty
Signal selection efficiencies
Tag reconstruction efficiency : 10.5% Difference of yields between data and MC in the BB-- D D*0*0ll- control sa
mple Number of BB : 1% Signal yield :
– signal shape ambiguity estimated by varying the signal PDF parameters
– BG shape : changing PDF Total systematic uncertainty
+12% -10%
+17% -15%
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B Branching Fraction Branching fractions are calculated by
All decay modes combined
Result is consistent with SM
prediction within error
Extracted branching fraction for each decay mode
SM : B(B)=(1.59 0.40)×10-
4
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fB Extraction
Product of B meson decay constant fB and CKM matrix element |Vub|
Using |Vub| = (4.39 0.33)×10-3 from HFAG
fB = 0.216 0.022 GeV
[HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ]
14% 11% = 8%(exp.) + 8%(Vub)
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Constraints on |Vub|/|Vtd|
Constraint in the (,) plane from the branching fraction and md
Constraint for( ) 0Br B
Improved measurement will help.
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Constraints on Charged Higgs
4( ) (1.59 0.40) 10SMB B
( ) ( )SM HBr B Br B r
2rH
tan / HmA
95.5%C.L. exclusion boundaries
B
A
B
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Future Prospect (1)
Br(B) measurement:Further accumulation of luminosity help to reduce both statistical and systematic errors errors.– Some of the major systematic errors come from limited statistics o
f the control sample.
|Vub| measurement:
< 5% in future is an realistic goal.
fB from theory
~10% now 5% ?Lum. B(B) exp |Vub|
414 fb-1 36% 7.5%
5 ab-1 10% 5.8%
50 ab-1 3% 4.4%
Assumption in the followingplots
2 2ub BBr V f
Note:
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Future Prospect (2)
fB(LQCD) = 5%95.5%C.L. exclusion boundaries
rH
tan / Hm
2
tan / Hm
rH
5ab -1
50ab -1 If |Vub| = 0 & fB = 0
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Future Prospect (3)
Charged Higgs Mass Reach (95%CL @ tan=30)
0
100
200
300
400
500
600
700
800
900
1000
1.000
3.000
5.000
7.000
9.000
11.00
0
13.00
0
15.00
0
17.00
0
19.00
0
21.00
0
23.00
0
25.00
0
27.00
0
29.00
0
31.00
0
33.00
0
35.00
0
37.00
0
39.00
0
41.00
0
43.00
0
45.00
0
47.00
0
49.00
0
Luminosity
Mas
s 5系列6系列7系列
Only exp. error(Vub=0%, fB=0%)
Vub=5%, fB=5%
Vub=2.5%, fB=2.5%
5 10 20 30 40 50 Luminsoity(ab-1)
Mas
s Re
ach
(GeV
)
1TeV
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fD measurements
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Summary
We have seen the evidence of B 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 tan=30
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Backup Slides
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Fit Result (2)
Likelihood fit results for each decay mode.
Signal
Background
Signal +
background
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Fit Results (3)
Likelihood distributions for each decay mode.
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Future Prospect (5ab-1)
fB(LQCD) = 5%
fB(LQCD) = 10%
95.5%C.L. exclusion boundaries
2
rH
tan / Hm
2
rH
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Full Reconstruction Method
Fully reconstruct one of the B’s to tag– B production– B flavor/charge– B momentum
Υ(4S)
e (8GeV)
e+(3.5GeV)
B
B
full (0.1~0.3%)reconstructionBD etc.
Single B meson beam in offline !
Decays of interests BXu l , BK BD,
Powerful tools for B decays w/ neutrinos
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Search for Charged Higgs
BD(semileptonic decay)
cb
H/W
( )tan cotb c um m
tanm
( )
( )
B D vB
B D v
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
0 ( )D
0 ( )D h
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Constraint to Charged Higgs
Once branching fraction is measured, we can constrain R.
tanW
H
MR
M
Form factor error
M.Tanaka, Z.Phys. C67 (1995) 321
11R at 5ab-1 can be determined experimentallyby B semiletonic decays
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Sensitivity for Charged Higgs
(Fo
rm-f
acto
r) ~
5%
(For
m-facto
r) ~15
%
BD
B (present)
Constraint from BXs
LHC100fb-1
(form-factor) can be reduced with the present BD data.