toru iijima & koji ikado (talk presented by t.i.) nagoya university

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

2006/05/15 Toru Iijima @ Flavour in the LHC era 2

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 3

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


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


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


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 !


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


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%


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.


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%


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


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


B Candidate Event

BB++ D D0 0 ++

KK++ - - ++ --

BB-- --

ee--


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


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


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


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%


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

2006/05/15 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

fB = 0.216 0.022 GeV

[HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ]

14% 11% = 8%(exp.) + 8%(Vub)


Constraints on |Vub|/|Vtd|

Constraint in the (,) plane from the branching fraction and md

Constraint for( ) 0Br B

Improved measurement will help.


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


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:

2006/05/15 23

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


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


fD measurements


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


Backup Slides


Fit Result (2)

Likelihood fit results for each decay mode.

Signal

Background

Signal +

background


Fit Results (3)

Likelihood distributions for each decay mode.


Future Prospect (5ab-1)

fB(LQCD) = 5%

fB(LQCD) = 10%

95.5%C.L. exclusion boundaries

2

rH

tan / Hm

2

rH


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


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


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


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.

toru iijima & koji ikado (talk presented by t.i.) nagoya university

Documents

b decaysleptonic

signal decay

nonsignal b tagging

rare b decays

reconstruction b d

b tn decaytagging

b factorieslepfirst

reconstructed b tagpros