Recent results on
B meson rare decays from Belle

M. Iwasaki
University of Tokyo
For the Belle Collaboration
特定領域「質量起源と超対称性物理の研究」

Introduction(I)FCNC processes
In SM forbidden at tree level .. One loop or box
Æ Sensitive to the New physics
Rare-decay … require very high statistics andsuperb background
B-Factory experiments
The best experiment to measure FCNCHigh luminosity (Belle: >350 fb-1!!)e+e- collider Æ Clean environment

Introduction (II)•Observables
Æ Branching fraction, Acp
Kinematical distributions q2, AFB , …
-----------------------------In this talk, we cover bÆsll, bÆdγ and bÆsγ1) Semi-inclusive BÆXsl+l- (Br, q2 and Mxs spectrum)2) Exclusive BÆK(*)l+l(Br, q2 spectrum, e/μ, AFB)
3) Search for bÆdγ
(Br)4) Exclusive bÆsγ modes (Br)5) Inclusive BÆXsγ(Br, Eγ spectrum)bÆsll and bÆ dγ
b→sl+l−, dγ decays proceed via FCNC like bÆsγ
Br ratio … 1/100 of the bÆsγ very rare decaysl+l−αEMb → sl+l− penguin~1/100b → sγ penguinb → dγ penguinbÆsll measurements

Br is low (bÆsγ: 10-4 bÆsll: 10-6)
Exists the contribution from Z0*
Br, q2 (=mll2) distribution, AFB(q2).. Sensitive to the New Physics
Two analysis approaches:•Semi-inclusive BÆXsll•Exclusive BÆK(*)ll

AFB (K* l+ l- )SMSUSY(C7>0)

Ali et al. PRD61 (2000) 074024

Semi-inclusive BÆXsl+l(Semi-)inclusive BÆ Xsl+l- as a sum of exclusive modes

Inclusive analysis
Æ theoretical uncertainty is smaller than exclusive analysis
 Reconstructed Xs system…1 (K+ or Ks0) + 0-4π (at most 1π0) Backgrounds
Dominant sources … 1) continuum 2) BBÆl+νX + l-νX
 Ali et al.

SM prediction (Mll>0.2GeV)
Br(BÆXsll) = (4.2 ± 0.7) x 10-6

Semi-inclusive BÆXsll
Mbc unbinned likelihood fits, after all cuts

32±10 signals

36±9 signals

68±14 signals

From continuum
and semileptonic B decays

140fb-1BÆXsll results

140fb-1
68 net signal, significance 5.4σ, Ave. of e+e-, μ+μ−

Br ( B → Xsll ) = [4.11 ± 0.83+0.85− 0.81] ×10−6The result is in agreement with SMBÆXsll results(4.2±0.7)×10-6(mll > 0.2 GeV)

Both Belle and BaBar results are consistent with SMExclusive B→ K(*)l+l79 ±10signals

82 ±11signals

Updated with 253 fb-1 data

B (Kll)= (5.50 ± 0.75
0.70 ± 0.27 ± 0.02)
B (K*ll)= (16.5 ± 2.3
2.2 ± 0.9 ± 0.4 )x 10-7>10σ

preliminary

Consistent with SM

B → K* l+l- :electron/muon ratio

preliminary

253 fb-1

B → K* l+l- :FB Asymmetry
AFB(K*ll ) : very sensitive to new physics
that may not be seen in B(b→sγ)
AFB =253 fb-1

Γ(θ Bl + < π / 2) − Γ(θ Bl + > π / 2)

Γ(θ Bl + < π / 2) + Γ(θ Bl + > π / 2)

Raw AFBK*First Look !
q2bÆdγ measurements :Exclusive BÆ(ρ,ω)γ
bÆdγ: more suppressed than bÆsγ
Measurements of bÆsγ & bÆdγÆ Sensitive to Vtd/Vts … constraints the SM

Exclusive BÆρ0/ρ+/ωγ measurements(ρ0Æπ+π−,ρ+Æπ0π+, ωÆπ+π−π0)
Simultaneous fit to 3 signal + 2 K*γ assuming isospin:Br(BÆ(ρ,ω)γ) ≡ Br(B+ Æ ρ+γ)
= 2(τ(B+)/τ(B0))Br(B0 -> ρ0γ)= 2(τ(B+)/τ(B0))Br(B0 -> ωγ)Exclusive BÆρ/ωγ : BG suppression
BG source of BÆρ0/ρ+/ωγ (ρ0Æπ+π−,ρ+Æπ0π+, ωÆπ+π−π0)… BÆK*γ feed down, BÆρ/ωπ0, continuum
BG from K*γ

signalBG from BÆρπ0signalBG

K*γ

Apply Mkπ cut

Apply helicity angle cut

continuum rejection : by Fisher, vertexing, flavor-tag

Exclusive BÆρ/ωγ : results
Projection of the Simultaneous fit in Mbc and ΔE

Simultaneous fit : Γ(B→(ρ,ω)γ) = Γ(B+→ρ+γ) = 2Γ(B0→ρ0γ) = 2Γ(B0→ωγ)

253 fb-1

SignalBG(K*γ)BG(continuum)

Significance = 1.9σ (from simultaneous fit)

B(BÆ(ρ,ω)γ) < 1.4 x 10-6 @90% CL

preliminary

B(BÆ(ρ,ω)γ) / B(BÆK*γ) <0.035 … |Vtd/Vts|<0.21 @90%CLbÆsγ measurements
1) Exclusive bÆ sγ measurements BÆK*γ BÆK*2(1430)γ BÆK* πγ and Kργ BÆKφγ BÆKηγ BÆKππγ and K1(1270)γ

New measurements BÆΛpγ2) Inclusive bÆsγ analysis
Measure the Eγ spectrum from 1.8GeVBÆKηγ (K+ηγ and K0sηγ)
BÆKηγ, ηÆγγ and ηÆπ+π−π0, M(kη) < 2.4GeV-1253
fb++00B ÆK ηγB ÆK ηγ
s21±7 signal

81±14 signal

Br ( B + → K +ηγ ) = [8.4 ± 1.5+−10..29 ] ×10 −6 (6.8σ 1st observation)
Br ( B 0 → K 0ηγ ) = [8.7 −+32..17+−11..96 ] ×10 −6(3.4σ 1st evidence)BÆK+ηγ : ACP measurementBÆKηγ, ηÆγγ and ηÆπ+π−π0, M(kη) < 2.4GeV-1253fb++B ÆK ηγB ÆK ηγ

N − = 34.0 +−99..80.5
N + = 46.7 +−109.8

Acp = −0.16 ± 0.09 ± 0.06BÆKππγBelle 140fb-1

BÆK1γK*2(1430)ÆKππ BG is fixedK1(1270)γ enhanced sample

140fb-1
totalK1(1270)γ &Κ1(1400)γTotal BG
Total BG
wo K*2γ
qq + bÆcBr ( B + → K1 (1270) + γ ) = [4.28 ± 0.94 ± 0.86] × 10 −5
Br ( B + → K1 (1400) + γ ) < 1.48 × 10 −5 @90%C.L.

(9.2σ)(1.3σ)

BÆΛpγBelle 140fb-1

bÆsγ summary

6% less missing than the last yearbÆsγ is now precision physics
Need to seek for small
new physics signaturesInclusive BÆXsγ
Analysis of BÆ Xsγ

 Fully inclusive reconstruction: see only the γ spectrum

Measure Eγ spectrum (single high-energy photon) Huge BG … Subtract BG Eγ spectrum
 Eγ > 1.8 GeV(CLEO… 2.0GeV BaBar … 2.1GeV)
Æ reduce theoretical model error

Inclusive BÆXsγ

Belle 140fb-1

Subtract BG
ε correction

Br (b → sγ ) = (3.59 ± 0.32+0.30 +0.11− 0.31 − 0.07) ×10 −4

Eγ = 2.289 ± 0.026 ± 0.034(GeV )
Eγ

2− Eγ

2= 0.0311 ± 0.073 ± 0.063(GeV 2 )1.8<Eγ<2.8GeV

Inclusive BÆXsγ results

Summary
With the world highest luminosity provided
by KEKB, Belle is continually updating the results.
• Can access very rare decays of bÆ sll and bÆdγ• bÆ K*ll : First measurement of AFB• Can measure the bÆsγ process very precisely• Exclusive bÆ sγ : many new measurements