ckm measurements at the belle ii experiment

7 - 11 June 2021 FPCP 2021

CKM measurements at the Belle II experiment

Qi-Dong ZHOU　 Institute for Advanced Research (IAR) /

Kobayashi-Maskawa Institute (KMI), Nagoya university

On behalf of Belle II Collaboration

Belle

CKM matrix and unitarity triangle (UT)

2

*

1 *

*

2 *

*

3 *

arg

arg

arg

cd cb

td tb

td tb

ud ub

ud ub

cd cb

V V

V V

V V

V V

V V

V V

f

f

f

æ ö= -ç ÷

è ø

æ ö= -ç ÷

è ø

æ ö= -ç ÷

è ø

( )

( )( )

2 3

2 2 4

2 3 2

1 2

1 2

1 1

ud us ub

cd cs cb

td ts tb

V V V A i

V V V V A O

V V V A i A

l l l r hl l l l

l r h l

æ ö- -æ öç ÷ç ÷

= = - - +ç ÷ç ÷ç ÷ ç ÷- - -è ø è ø

* * *0

ub ud cb cd tb tdV V V V V V+ + =

3 2 31 1l l l l× × ×

V†V = 1

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b row d column

Complex phase cause CP violation

•Search for NP with different processes (tree, loop diagrams) by precise measurement of UT

•Comprehensive test (only Belle II)

•Measure all sides and angles(0,0) (0,1)

(ρ,η)

α/𝜙2

β/𝜙1γ/𝜙3 B→DK B→J/ψKS

B→ππ, ρρ

VubV∗

ud

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VtdV∗

tb

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VcdV∗

cb

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+

+

0

0

The Belle II detector

3

Level-1 trigger system

CDC+ECL+TOP+KLM

L1 trigger latency 5 μsec

Data acquisition (DAQ) system Maximum 30 kHz L1 trigger 1MB/event

Vertex detector (VXD) Inner 2 layers: pixel detector (PXD)Outer 4 layers: strip sensor (SVD)

Central Drift Chamber (CDC) He (50%), C2H6 (50%), small cells, long lever arm

Particle Identification Barrel: Time-Of-Propagation counters (TOP)Forward: Aerogel RICH (ARICH)

ElectroMagnetic Calorimeter (ECL) Barrel: CsI(TI) + waveform samplingEndcap: pure CsI + waveform sampling

KL/μ detector (KLM) Outer barrel: Resistive Plate Counter (RPC)Endcap/inner barrel: Scintillator

e- (7GeV)

e+ (4GeV)

Computing system GRID

Tens of PB / year

This talk focus on: measurements of |Vcb|, |Vub| and 𝜙1,𝜙3

4

𝜙2 : Ching-hua Li ’s talk “Charmless B

decays at Belle II” on 10 June

𝜙1 : details in Radek Zlebcik’s talk

“Rediscovery of the decays for the CP violation measurements at Belle II” on 10 June

Data-set used for the analyses present in this talk:

• 34.6 fb-1 ( |Vcb|, |Vub|, 𝜙1)

• 62.8 fb-1 ( 𝜙3 )

Belle II data taking efficiency = 88.8% Oct. 19 - Dec. 18, 2020

2019-02 - 2019-12

2020-01 - 2020-12

2020-01 -

1.9 fb-1 /day

B decay reconstruction at Belle II

5

Reconstruct ~100 hadronic decay channels, ~10000 decay chains

•ε=0.47% for B± @ purity ~30%

•ε=0.29% for B0 @ purity ~20%

arXiv:2008.06096π+

B0

K-

τ -

ντ

B0

D*+

Υ(4S)ντ

π+

D0

π-

Ks

D+

e-

e+

Tag side reconstruction

Missing energy

Signal side reconstruction

π-

π+

BELLE2-CONF-PH-2020-005

ZLdt = 34.6fb−1

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Data

Untag: only reconstruct signal B decay Tag : reconstruct signal B decay, also the other side B

Mbc =q

(E∗

beam)2 − (p∗

B)2

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arXiv: 1807.08680

BF(B→D*lν) for |Vcb|

6

arXiv:2008.07198arXiv:2008.10299

hadronic tag untagged

w = 1

w = 1.5PLAN: Form factor determination rely heavily on w = 1 (zero recoil)

m2miss [GeV2/c4]

dΓ

dω∝ |V cb|2|F(ω)|2

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BELLE2-CONF-PH-2020-009BELLE2-CONF-PH-2020-008

Unfolded w spectrum to compare with BGL parameterization

B(B0→D*+l-ν)

had. tag ( 4.51 ± 0.41(stat) ± 0.27(sys) ± 0.45(πs))%

untag ( 4.60 ± 0.05(stat) ± 0.17(sys) ± 0.45(πs))%

PDG ( 5.05 ± 0.14)%

Y : D∗l system

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Similar plots for the B→D*eν channel

Similar plots for the B→D*eν channel

BF(B0→πlν) and BF(B→Xulν) for |Vub|

7

Untagged Inclusive B→Xulν measurement

• lepton momentum endpoint

• less B→Xclν (dominant background)

Capable of measuring |Vub| with more data

BELLE2-NOTE-PL-2020-026

Signal

|Vub| determination from exclusive and inclusive measurements differ by ~2σ Measurement of B(B0→π-lν) based on hadronic tag

arXiv:2008.08819

B(B0→π-l+ν) = ( 1.58 ± 0.43(stat) ± 0.07 (sys) ) × 10-4

B(B0→π-l+ν) = ( 1.50 ± 0.06) × 10-4 (PDG)


Next target: q2 distribution for |Vub| determination

Agreement

Prospects of |Vub| and |Vcb|

8

The Belle II Physics Book, PTEP 2019, 123C01

Side Observable Dominant uncertainties

|Vtd|Δmd: BB mixing

frequencyLattice QCD (|Vtd| now is mainly limited by lattice QCD)

|Vcb| Br(b→clν) Exclusive: lattice QCD

Inclusive: experiment vs. phenomenology|Vub| Br(b→ulν)

Effective flavor tagging efficiency:

• Belle II : ( 33.8 ± 3.9 )%

• Belle : ( 30.1 ± 0.4 )%

• Belle II MC : ~37%

BB

9

arXiv: 2008.02707

τB0 = 1.48 ± 0.28 ± 0.06 ps

τB0 = 1.519 ± 0.004 ps (PDG)

Time dependent CPV - Flavor tagging

B0

Ks

D+

π-

π+

e- (7GeV)

e+ (4GeV)𝐽/𝜓 µ+

B0

Ks

π+

µ-

π-

Δt = Δz / βγc

Δz ~ 130 umFlavor non-specific CP eigenstate

Flavor tagger

B → D(∗)h

h : π, ρ

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BELLE2-CONF-PH-2020-004TDCPV measurement:

•Precise measurement of Δt

•B flavor tagger

arXiv: 2005.07507

Details in Radek Zlebcik’s “talk” on 10 June

dilution factor rFBDT = 1-2w w: wrong tagging fraction

εeff =X

i

εi · (1− 2wi)2

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Measurement of sin(2𝜙1)

10

BELLE2-NOTE-PL-2020-011

Sf : indirect (time dependent) CPV parameterAf : direct CP violating asymmetry assumed zero

•b→c : tree diagram dominated golden modes B0→J/ψK0, B0→ψ(2S)K0…

•Theoretically and experimentally precise channel

P (∆t, q) =e−|∆t|τ

B0

4τB0

(1 + (1− 2ω)q[Sfsin(∆m∆t) +Afcos(∆m∆t)])

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sin(2𝜙1) Sf = 0.55 ± 0.21 (stat.) ± 0.04 (syst.)

sin(2𝜙1) = 0.699 ± 0.017 (world average) ≈

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𝜙1 : details with more new results in

Radek Zlebcik’s “talk” on 10 June

Precision aimed at Belle II for sin(2𝜙1):

reduce uncertainty by factor ~5 to reach to 5%

𝜙3 measurement

11

rB : ratio of amplitude δB : strong phase difference

Foreseen precision of 𝜙3

is expected to be 1.6° with 50 ab-1 dataset


arxiv: 2104.03628

• Interference between b→c and b→u (tree level)

Color suppressed

Favored

Asuppr.(B−

→ D̄0K−)

Afavor.(B−

→ D0K−)

= rBei(δB−φ3)

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B-

(Ksπ+π-) K-

D0K-

D0K-

b→c

b→u

• Model-independent binned Dalitz plot approach

• Rely on continuum suppression tool and particle identification technique at Belle II

• Different systematics w.r.t. the LHCb results

Unitarity Triangle fit extrapolation at Belle II

12

3

2

2

dm K

sm & dm

ubV

1sin 2

(excl. at CL > 0.95)

< 01

sol. w/ cos 2

2

13

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

exclu

ded

are

a h

as C

L >

0.9

5

Summer 19

CKMf i t t e r


Standard model (SM) scenario: the central values are chosen such that they satisfy the SM (closed UT)

Current Belle II 50 ab-1

• Tensions existed on |Vub| and 𝜙1

• UT can not close if keeping the central value for 50 ab-1

• Differences between UT determined by tree (|Vub|, 𝜙3) and loop (𝜙1, 𝜙2) can be

discriminated with 50 ab-1 data-set

Zoom

13

Summary and prospects

TOP PMT PXD

RF QCS

• Super B-factory offers good probe for testing SM and searching for NP at luminosity frontier.

• Belle II will play a key role for CKM measurements.

‣First BF measurements of semileptonic B decays with

had. tagged/untagged techniques for |Vcb| and |Vub|.

‣First sin2𝜙1 result has agreement with W.A, aim 5%

precision at Belle II.

‣Decay rate ratio of B→DK/B→Dπ was performed for determination of 𝜙3.

• Looking forward for more interesting results from Belle II. Stay tuned !

Backup

14

15

Belle II - LHCb comparisonRD(*) |Vub|

sin(2𝜙1) 𝜙3

B→Xclv for |Vcb|

16

Hadronic mass moments of inclusive B→Xclν with hadronic tag

arXiv:2009.04493

• |Vcb| calculated based on the parameters extracted from p*l vs <Mnx> distributions

• A new method proposed in JHEP02 (2019)177 to extract |Vcb| from q2 vs <qnx> distributions

• Targeting a publication this summer

Signal


Moments dependence on the lepton momentum cut

sin(2𝜙1) with QCD penguin

17

~

~~

~

• b→qqs : QCD penguin dominated contribution, sensitive to New Physics

• Golden mode, e.g. B→η’K decays

• sin(2𝜙1) measured by b→s and b→c processes used to have ~3.8σ

tension, however now it was reduced to rather small

• Only rediscovery and BR measurement (CP measurement not done yet)

B±→η’K± with η’→ηπ+π- or η’→ργ

B0→η’Ks with η’→ηπ+π- or η’→ργ

𝜙2 measurement (B→ππ)

B-→π-π0B+→π+π0

B+→π+π0 B-→π-π0

Yield 43 +19-20 24 +13-14

ACP -0.268 +0.249-0.322 ± 0.123

ACP(PDG) 0.03 ± 0.04

Sf =

q

1−Af2sin(2φ2 + 2∆φ2)

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Interference between tree and penguin

• B→π0π0 analysis started at Belle II

• 8-fold ambiguity of 𝜙2 can be reduced to

2-fold with TDCPV in B0→π0π0 18

arXiv:2009.09452

penguin pollution

Constraint for 𝜙2

• TDCPV parameter Sf and Af

• Branch fraction of all B→ππ (π+π-, π±π0, π0π0) modes


Diagrams B± →π±π0 B0→π+π- B0→π0π0

Tree ✔ ✔

Color Suppress

Tree

✔ ✔

Penguin ✔ ✔

19

BeIIe II projection Sρ

0ρ

0 = -0.14 Sπ

0π

0 = 0.75

1σ

• Δ𝜙2~0.6° (current 4.2°) with 50 fb-1 data

• B→ππ, B→ρρ isospin analysis and B→ρ(ππ)π

Dalitz analysis of 3 body decays

• LHCb can not measure 𝜙2


B+→ρ+ρ0

Yeild 104 ± 16

Br(10-6) 20.6 ± 3.2 ± 3.1

PDG 24.0 ± 1.9

fL 0.936+0.049-0.041 ± 0.021

fL(PDG) 0.950 ± 0.016

• Compatible with PDG value

• Performance superior to early Belle results

fL = fraction of longitudinally polarized events

B+→ρ+ρ0

𝜙2 measurement (B→ρρ)

Current precision

BELLE2-CONF-DRAFT-2021-005

∆E = E∗

B− E

∗

beam

<latexit sha1_base64="JaVjFWzrRpEzTtMTEfN+pFQzxpY=">AAACB3icbVDLSgMxFM3UV62vUZeCBIsggmVGCupCKNWCywr2Ae04ZNK0Dc1khiQjlKE7N/6KGxeKuPUX3Pk3Zqaz0NYDIYdz7r3JPV7IqFSW9W3kFhaXllfyq4W19Y3NLXN7pymDSGDSwAELRNtDkjDKSUNRxUg7FAT5HiMtb3SV+K0HIiQN+J0ah8Tx0YDTPsVIack197vXhCkEa/AS1u6P3So8Se/Y00MmBdcsWiUrBZwndkaKIEPdNb+6vQBHPuEKMyRlx7ZC5cRIKIoZmRS6kSQhwiM0IB1NOfKJdOJ0jwk81EoP9gOhD1cwVX93xMiXcux7utJHaihnvUT8z+tEqn/uxJSHkSIcTx/qRwyqACahwB4VBCs21gRhQfVfIR4igbDS0SUh2LMrz5Pmackuly5uy8VKNYsjD/bAATgCNjgDFXAD6qABMHgEz+AVvBlPxovxbnxMS3NG1rML/sD4/AGpIpap</latexit>

VXD position resolution

20arXiv:2008.06096

d0

z0

φ0

λ

ex

eyez

IP

pT

pz

d0 resolution:14.2 ± 0.1 μm (Data)12.5 ± 0.1 μm (Simulation)

Detector resolution : difference between d0 and beam profileσx :14.8 μm

σy :1.5 μm

ckm measurements at the belle ii experiment

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