Post on 04-Feb-2022
transcript
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|
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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)
BELLE2-CONF-PH-2020-007
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
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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
The Belle II Physics Book, PTEP 2019, 123C01
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
The Belle II Physics Book, PTEP 2019, 123C01
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 !
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
BELLE2-CONF-PH-2020-011
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
BELLE2-CONF-PH-2020-012
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
The Belle II Physics Book, PTEP 2019, 123C01
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
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