Recent Achievements of Belle experiment

Kenkichi Miyabayashi (Nara Women’s Univ.)for Belle collaboration

KEKPH07

2007/Mar./2nd

As of 2007/Feb./28,…

http://belle.kek.jp/bdocs/b_journal.html

During 2006/2007, 40 papers have been published or submitted (more than 200 from the beginning).

↓Apparently it is impossible to mention all of them, so …

Outline

• CP violation measurements for unitarity angles

• B decays with “Missing Energy”

• Activities on other Υ states

• Future prospect and Summary

KM scheme & Unitarity triangle

In the quark mixing matrix, an irreducible complex phase is there.→ CP violation.

On complex plane, a triangle is formed.B meson is a good probe.

Angle measurements

Decay via b → c (tree)

Decay via b → u(tree)

B-B mixing(box)

How about b → s (penguin)??

b → d (penguin) is also participating in some cases → direct CPV.

In order to perform such study, …

The B decay modes for CP violation studies have small branching fraction(i.e. B is so heavy that there are so many decay modes).

→ Need quite a lot of B.→ Need to measure time evolution of B.

PDG2006

KEKB accelerator

700fb-1

1fb-1/day

Int. lum.

Lum./day

8GeV(e-)X3.5GeV(e+)3km double ring Peak lum.>1.7X1034cm-2s-1

535M BBby 2006 summer

Silicon Vertex Detector

Central Drift Chamber

Aerogel CerenkovTime Of Flight CsI calorimeter

S.C. solenoid

1.5T

KL μ system

8GeV e-

3.5GeV e+

Belle detector

Time dependent CPVCP side(B to fCP)

Tag side(the other B)zz=ct, =0.425

In order to see CPV by interference between decay and mixing.

Measurement of sin21

(1) Decay

(2) Decay with mixing

Interference between (1) and (2) results in CP violation.We have to wait to let (2) contribute, i.e. t=0.

In SM, SfCP=-CP sin21,where CP =-1 for CP odd, +1 for CP even,AfCP=0. Theoretical uncertainty is ~0.01.

Vtd*

Vtd*

Reconstruction of B0 → J/ K0

Nsig = 7482Purity 97 %

CP odd

Nsig = 6512Purity 59 %

CP even

KL; only direction known.B0 → J/ KL has less purity.

In Υ(4S) rest frame,Mbc = { (ECM/2)2 - ( Pi)2}1/2

PRL98,031802(2007)

Time-dependent decay rates

B0 tag_B

0 tag

Asymmetry=-CP sin21sin(mt)Opposite asymmetry corresponding to CP ! PRL98,031802(2007)

sin21; J/ KS & J/ KL combined

B0 tag_B

0 tag

sin21 = +0.642±0.031±0.017AJ/K = +0.018±0.021±0.014

PRL98,031802(2007)

Before/After

B factories

Before B factories

Recent World Average

1 in penguin decays

as well as

New Physics in the loop;CPV deviation from J/ K0?

SM penguin; No complex phase in decay.

Look time-dependent CPV in such decay modes!A series of this kind of B decays;’K0, K0, KSKSKS, KS, KS0, K+K-KS.

B0 → ’ KS, KS, KSKSKS

Plots show signal enriched sample by event shape variables.

Mbc(GeV/c2)

Nsig=1421±46

Nsig=307±21

Nsig=185±17

PRL98,031802(2007)

Reconstruction of B0 → ’ KL, KL

After background subtraction.

Nsig=454±39

Nsig=114±17

PRL98,031802(2007)

B0 → ’ K0

sin21eff = +0.64±0.10±0.04

A’K = -0.01±0.07±0.05

CPV in 5.6!First CPV observation in penguin decays!

PRL98,031802(2007)

See other modes

sin21eff = +0.50±0.21±0.06

A = +0.07±0.15±0.05sin21

eff = +0.30±0.32±0.08A = +0.01±0.20±0.07

PRL98,031802(2007)

See other modes(cont.)

KS f0(980)KS

KS0 K+K-KS

(excl. KS)

hep-ex/0609006

Compare tree and penguin

Theory predicts positive shift,while measurements tend to benegative shift(av. 2.6 deviation).

More statistics needed to have conclusive results.

Another tree: B0 → D+D-

Tree (a) dominant → SDD becomes -sin21, ADD = 0.Penguin (b) is b → d, complex phase due to Vtd → may cause Direct CPV.

From 535M BB, Nsig = 150±15 has been obtained.

hep-ex/0702031

caused by b → ccd

B0 → D+D-; t distribution

hep-ex/0702031

B0(t)→ D+D-B0(t)→ D+D-

SDD=-1.13±0.37±0.09ADD=+0.91±0.23±0.06 Evident Direct CPV(3.2)!

Need to update all the b → ccd modes(D*+D*-, J/0, etc)to have a comprehensive understanding of this transition.

2 measurement

B0

d

b–

d–

bt

–tB0

–V*

tb Vtd

V*tbVtd

Mixing diagram Decay diagram (tree)

B0

b–

d du–

d–u

/

/Vud

V*ub

There are 3 possibilities; ,, .

If tree only, Sf is directly connected to sin22 and Af=0.

Large Direct CPV A=0 ; Not only Tree but also Penguin→S=(1-A

)1/2 sin2(2+) , how to solve?

B0→+ -

(Background subtracted)

S=-0.61±0.10±0.04A=+0.55±0.08±0.05

Nsig=1464±65

C.L. contour

Extract 2; isospin analysisM. Gronau and D. London, PRL 65, 3381 (1990)

B0→+-, 00, B±→±0 branching fractions,and B0→ 00 Direct CPV are used as inputs to solve this relation.SU(2) braking effect is still much smaller than measurements’ errors.

2 constraint only with B→

Constraint is not stringentby alone.→ need and .

2

B→ BV1

V2

Transverse polarization(CP-odd)H+

H−

H0 Longitudinal polarization(CP-even)

There are two miracles;•fL=0.968±0.023, i.e. almost pure CP eigenstate. •B0→ 00 is small, i.e. small penguin pollution.

|H0|2 + | H+ |2 + | H−|2 =1

It is B→ VV decay, admixture of CP-odd and CP-even, in general.

Quite high ability to constrain 2!

B0→

B0(t)B0(t)S=+0.19±0.30±0.07A=+0.16±0.21±0.07

Note; CPV is small, but consistent with 2=90°because S = sin22 in “tree dominance”.

hep-ex/0702009

2 by B→

This region is ruled out.

Time-dependent Dalitz Plot Analysis (TPDA) of B0→ (

Since decays into , ther ethree possibilities; B0→ +-(+), -+(-) and 00(0). Final state commonly + - 0

→ resolve by Dalitz distribution(26 parameter fit!).

Then, 2 is extracted by the amplitudes;

With 449M BB,Nsig=971±42(B0→ + - 0)

hep-ex/0701015

TDPA of B0→ (

68°< 2 < 95°at the 68% C.L.

(=m)

+-(+)

-+(-)

00(0)

hep-ex/0701015

Isospin relation results in“pentagon” in this mode.

About 2

All the measurements favor about 90° as 2.• B→ sets window around 90°.• B→ pinpoints the favored value inside t

he window.• B→ isexpected to rule out solutions o

f 2~0 and ~180° with higher statistics.

3 by B±→ D(*)K(*)± Dalitz analysis

D(*)0 and D (*)0decay into common final state→Vcb and Vub interfere ： 3

Here, select D→KS+−,B+ decay amplitude = f(m+

2, m−2) + r exp(+i3+i f(m−

2, m+2)

B− decay amplitude = f(m−2, m+

2)+ r exp( i− 3+i f(m+2, m−

2) (m+= KS+, m−=KS − inv. mass)

→ extract r, 3, by B+ and B −Dalitz Plots.

B±→ D(*)K(*)± reconstruction

B±→ D(KS+−)K±

Nsig=331±23B±→ D*0[(KS+−)0]K±

Nsig=81±11B±→ D(KS+−)K(*)±

Nsig=54±8

Dalitz Plot

B±→ D(KS+−)K±B−B+

B+ B−

B±→ D*0[(KS+−)0]K±

After background subtractionand acceptance correction,these distributions are fitted withthe model taking 18 resonantand non-resonant amplitudes.

3=53° +15°/-18° ±3°±9°

Model uncertainty ： Can be reduced by charm meson data.(Eventually ~2°)

B±→ ±

In SM, caused by annihilation diagram; → determination of B decay constant fB.

tan cotb um m +

b

u H/W

tanm

While, charged Higgs can interfere helicity-suppressed W exchange.

⎛ ⎞⎜ ⎟⎝

×⎠

222

SMB

H H 2H

mr , r = 1- tan â

mBr =Br

Full reconstruction technique

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 tool for B decays with neutrinos!Note that it can be done only at e+e- B-factories.

One of the Bs is fully reconstructed (by D, D, etc. )to tag B production/flavor(charge)/momentum.

Evidence of B±→ ± Try to reconstruct by the particles other than the fully reconstructed B daughters via , e, , 0and modes. Remove the calorimeter(ECL) hits associated with daughters.

The remained ECL energy(EECL) becomes zero for the signal(only (s) remain).

fB=PRL97,251802(2006)

Constraint on charged Higgs

⎛ ⎞⎜ ⎟⎝ ⎠

=

222B

H 2H

exp

SM

mR = 1- tan â

m

Br=1.13±0.53

Br

fB from HPQCD

Much stronger constraint than those from energy frontier exp’s.

|Vub|fB

|Vub| from HFAG

BrSM=(1.59±0.32±0.24)×10-4

Excluded Using SM estimation;

Running on Υ(3S)

Try to hunt Υ(3S)→ Υ(1S)

to see Υ(1S) decays into a light dark matter. invisible

Recoil mass distribution

Peak is consistent with the background due to Υ(1S) → l+l- escaping detector acceptance

Dashed line: expectation withBr(Υ(1S) → )=6×10-3

Br(Υ(1S)→ invisible)<2.5×10-3

@90% C.L.

hep-ex/0611041, to appear in PRL

Running on Υ(5S)PRL98, 052001(2007)

Ds

J/

Histograms:continuum

Bs(*)Bs(*) production ratio,inclusive Ds, D and J/ measurements have been done.

Future prospect

Example of physics reach

LHC find mass spectrum of SUSY particles, while SUSY breaking scenario would be identified by CPV, i.e. measurement of coupling and its phase!

Summary

• Three angles (1, 2, 3) are fairly well-measured to perform quantitative test of KM scheme, more efforts to be continued to hunt New Physics effect.

• With full reconstruction technique, rare decays with missing are to be measured. Evidence of B±→ ±has been obtained.

• Running on other Υ states have been done successfully, accumulating more in future upon a good idea.

• In LHC era, Super B-factory could identify SUSY breaking scenario through its program of measurements of Phases from CPV New Physics.

Backup slide

Decay angle definition

Reconstruction of CP side B meson

Mbc(GeV)

E(GeV)

Utilize Υ(4S)→ BB kinematics

Mbc = { (ECM/2)2 - ( Pi)2}1/2

→ Signal peaks at B mass (5.28GeV).

E = Ei - ECM/2→ Signal peaks at zero.

Example; B0→ J/ KS

Vertex reconstructiont measurement)

BB is boosted with =0.425: t is obtained by z.

CP side vertex· J/ 、 +-,etc. charged tracks.· In KS→+- case, extrapolate

momentum vector toward IP-profile. Tag side vertex

· Tracks with impact parameter w.r.t. CP side vertex < 500m

· Veto KS daughters, remove poorly reconstructed tracks by2.

Resolution function· Detector resolution, D(*) life, B momentum into account.

Utilize IP-profile a lot.

Lepton chargehigh-p l b c l intermed-p l+ s l

Hadron chargehigh-p + B0D(*) +, D(*) +, etc.intermed-p K+ K+ X,

low-p D0

Flavor tagging (B or B?)

By calculating Likelihood, q =+1(B0) , − 1 (B0) (Tag side)r = 0(no flavor info.) 〜 1(perfectly confident tagging).

Validation of flavor tagging

B0 D*-l+ decay is self tagging;reconstructed with high purity

Good tag

Poor tag

OF-SF asymmetry ~ (1-2w)cos(mt)w is also investigated.

1-2w

CP fit : unbinned max. likelihood fitSignal probability density function(PDF) is;Psig(t, q, wl, wl)= exp(-|t|/B)/4B{1-qwl+q(1-2wl)[SfCPsin(mt)+AfCPcos(mt)]}

here, l is flavor tagging class(1,2,…6).

For i-th event, likelihood value is;Pi(ti, SfCP, AfCP)=(1-fol)[fsig Psig(t, q, wl, wl) X Rsig(ti) + fbg Pbg X Rbg (ti)]

+ fol Pol(ti)

Free parameters : SfCP and AfCP Proper resolution func. : R**

B life and mixing : PDG values Fraction of each component : f**