Toru Iijima Nagoya University
description
Transcript of Toru Iijima Nagoya University
Toru Iijima
Nagoya University
December 19, 2006BNM-II Workshop, Nara-WU
Tauonic and Leptonic Decays
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Contents
Introduction
BBD, X Bl
Bll (ee, , )BK(*)
Technical issues;- Tagging- Background
’s in the final state(missing energy)
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Hunting Rare Decays
Observation of BK l+ l-
CPV in B decay
Beginning of B->K0 saga
Direct CPV in B0K+
FB asymmetry in BK* l+l-
Evidence of B
Observation of bd
High luminosity Good detector (PID, vertex…) Analysis techniques
– qq background suppression– Fully reconstructed tag
Success of B factories brought rare B decays in leptonic and neutrino modes on the stage !Success of B factories brought rare B decays in leptonic and neutrino modes on the stage !
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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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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)]
2006/05/15 6
BX as a Probe to Charged Higgs
Charged Higgs contribution to B decays
In two Higgs doublets model, charged Higgs exchange interferes with the helicity suppressed W-exchange.
tan cotb um m
b
u H/W
tanm
Br(SM) ~ 9 x 10-5
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SMB
H H 2H
mr , r = 1- tan β
mBr =Br
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The final results are deduced by unbinned likelihood fit to the obtained
EECL distributions.
The First B Evidence
Signal shape : Gauss + exponentialBackground shape : second-order polynomial
+ Gauss (peaking component)
Signal +
background
Background
B
Signal
Observe 17.2 events in the signal region. Significance decreased to 3.5 after including systematics
+ 5.3 - 4.7
: Statistical Significance
To appear in Phys. Rev. Lett.hep-ex/0604018v3
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Results (Br & fB Extraction)
Measured branching fraction;
Product of B meson decay constant fB and CKM matrix element |Vub|
Using |Vub| = (4.39 0.33)×10-3 from HFAG
fB = 216 22 MeV
[HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ]
15% 16% = 14%(exp.) + 8%(Vub)
+0.56 +0.46 -4-0.49 -0.51Br B 1.79 ×10
+1.6 +1.3 -4B ub -1.4 -1.4f V =10.1 ×10 GeV
+0.036 +0.034B -0.031 -0.0370.229f = GeV
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Constraints on Charged Higgs
+0.56 +0.46 -4exp -0.49 -0.51
-4SM
Br =(1.79 )×10
Br =(1.59 ±0.32 0.24)×10
222B
H 2H
exp
SM
mR = 1- tan β
m
Br=1.13±0.53
Br
fB from HPQCD
These regions are excluded.
Much stronger constraint than those from energy frontier exp’s.
|Vub|
stat. syst.
fB
|Vub| from HFAG
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Future Prospect: B Br(B) measurement:
More luminosity help to reduce both stat. and syst. errors.– Some of the syst. errors limited by statistics of 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%
My assumption fB(LQCD) = 5%5ab-1
50ab-1
If |Vub| = 0 & fB = 0
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Cont’d
Charged Higgs Mass Reach (95.5%CL exclusion @ tan=30)
Only exp. error(Vub=0%, fB=0%)
Vub=5%, fB=5%
Vub=2.5%, fB=2.5%
Mass
Reach
(G
eV
)
Luminsoity(ab-1)
Constraints at Super-B (cont.)
fB(LQCD) = 5%
rH
5
rH
5ab -1
50ab -1
tan / Hm
5 potential
5
Charged Higgs Mass Reach with 5
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Ratio may help ?
Ratio to cancel out fB (G.Isidori&P.Paradisi, hep-ph/0605012)
Deviation of Br.
expH
SM
BrR =1.13±0.53=1.13 0.45 0.23 0.17
Br exp. |Vub|fB
d
d
exp
B B
SM
B B
Br(B )M
R = 1.23 0.49 0.10 0.12Br(B )
Mexp. |Vub|BBd
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B D(*) Semileptonic tauonic decays
cb
H/W
tan cotb cm m
tanm
( )
( )
B D vB
B D v
Br(SM)~ 8 x 10-3
– Ratio (/) is modified by the charged Higgs effect.– Provide good cross check to B– Y.Okada
• H-b-u vertex by B• H-b-c vertex by BD• H-b-t vertex by LHC direct search.
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LoI
5ab-1 50ab-1
Mode Nsig Nbkg dB/B Nsig Nbkg dB/B
280 55012.7 7.9%
2800 550040.3 2.5%
620 3600 6200 36000
0 ( )D
0 ( )D h
Expectation at 5 / 50 ab-1 for B+ decay
5 observation possible at 1ab-1
Signal selection efficiency0
0
( )
( )
e
e
D e
D
0
0
( )
( )
D
D
10.2%2.6%
26.1%13.3%
Major background sourceMissing charged and tracks from BD(*) l X (incl. slow )
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Sensistivity to H±
Similar to B
5ab-1
FF=15%50ab-1
FF=5%
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Be
B is the next milestone decay.
When do we see the signal ?Precision at Super-B ?
Precise B/ data provide lepton universality test.– Higgs effect itself is universal.
RH = RH
– Good probe to distinguish NP models.
Br()=1.6x10-4
Br()=7.1x10-7
Br(e)=1.7x10-11
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Belle Results
Inclusive reconstruction– Reconstruct the accompanying B via a 4-vector sum
of everything else in the event.– Efficiency: 2.18±0.06% (), 2.39±0.06% (e)– NSM: 2.8±0.2 (), (7.3±1.4)x10-5 (ev)
hep-ex/0611045, submitted to Phys. Lett. B
e
Br() < 1.7x10-6@90%CL Br(e) < 9.8x10-7
253fb -1
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Future Prospect: B
Method?S.Robertson at CERN WS (May 2006)– Inclusive-recon method has high efficienc
y but poor S/N.
– Hadronic tag will provide very clean and ambiguous signals, but very low efficiency.
Luminosity (ab-1)
Sta
ndard
Devia
tion
3 at 1.3ab-1
5 at 3.7ab-1
Extrapolation from the present Belle analysis(inclusive-recon.)
limit 1/ L
limit 1/ L
Extrapolation from the present Belle analysis.K.Ikado at BNM1 (Sep. 2006)
~50 events @ 5ab-1~500 events @ 50ab-1
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d l
l
Proceeds via box or penguin annihilationSM Branching fractions
Flavor violating channel (B0 e +–, etc.) are forbidden in SM.
B0l+l-
0 + - -15d
0 + - -10d
0d
Br(B e e ) ~10
Br(B ) ~10
Br(B ) =zero
d l
l
New Physics can enhance the branching fractions by orders of magnitude.
ex.) loop-induced FCNC Higgs coupling
b
dA0,Hh0
6
4A
tan βm
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B0l+l- (e+e-,+-,e+-)
B(B0 e+e–) < 6.1 × 10-8 (90%CL) B(B0 +–) < 8.3 × 10-8 (90%CL)
B(B0 e+ –) < 18 × 10-8 (90%CL)
e+e– +–
e-+
Signal regions Events observed
Phys. Rev. Lett. 94, 221803 (2005)
B(B0 e+e–) < 1.9 × 10-7 (90%CL) B(B0 +–) < 1.6 × 10-7 (90%CL)
B(B0 e+ –) < 1.7 × 10-7 (90%CL)
B(B0d) < 2.3×10-8 (90% CL)
Phys. Rev. D 68, 111101 (2003)
78 fb-1
780 pb-1
111 fb-1
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B0l+l- at B factories ?
Pre-LHC era Present CDF limit;Br(Bs) < 2.3x10-8 (90%CL) is equivalent to Br
(Bd) < 1x10-9. Interesting to see results with full Belle/BaBar data.
LHC era Who knows the background at LHC ? Bs from (5S) runs at Super-B ?
– We can study background using the present (5S) data! Bd is an unique opportunity at B factories.
But, how clean are they ?
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τ
μ
mBr(B )= 300
Br(B ) m
2
s ts
d td
Br(B ) V= 25
Br(B ) V
See talk by E. Baracchini
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B0+ - (BaBar @ 210fb-1)
Experimentally very very challenging (2-4 neutrinos in the final state ! )
High sensitive to NP Bs at hadron machines
Analysis• Reconstruct one B in a fully
hadronic final state B D(*) X=>280k events
• In the event remainder, look fortwo decays (l, , )
• Kinematics of charged partilcemomenta and residual energyare fed into a neutral networkto separate signal and BG
Data Controlsample
Nobs=263±19 Nexpect=281±48
Phys. Rev. Lett. 96, 241802 (2006)
-3Br(B ) <4.1×10 @90%C.L.
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Plots to be made…
Region in tan-mH for 5 evidence.– B + BD – LHC direct search for the same 5 effect– Other measurements from B decays
• BXs• Bll
Combine B and D(*) to show– mH reach at tan=30 as a function of L.
– Significance at tan=30 and mH=500GeV as a function of L.
Precision for Br(), Br() and their ratio as a function of L
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Need to study… Tagging strategy for neutrino modes
– Inclusive recon.– Semileptonic tag.– Hadronic tag.
Data quality in large L environment– Tagging efficiency– Beam background– Neutrino reconstruction
BaBar’s B search (324x106 BB)Tag by BDlXTag B recon. eff.=0.7%
Extra energy distribution inBelle’s B search
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Backup
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New Physics in large tan Leptonic decays (Bl, ll) are theoretically clean, free from hadronic
uncertainty. In particular, they are good probes in large tanregion, together with
other measurements; mBS, Bs, BXs and also decays (, ). Ex.) G.Isidori & P.Paradisi, hep-ph/0605012
b
uH
b
dA0,Hh0
Charged Higgs
Neutral Higgs
tan
MH(GeV)See talk by A.Weiler
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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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Future Prospect: BK
Belle @ 250fb-1 (preliminary)Fully reconstructed tag (by modifying the PID criteria used in B analysis).
Consistent with BG expected
Belle preliminary
Signif. Lum (ab-1)3 12
5 33
Need Super-B !
cf.) K.Ikado @ BNM2006