The Belle II prospects for charmonium
and bottomonium studies
Pavel Krokovny
Budker INP
Experiment status●Charmonia results●
Bottomonia results●Summary●

19-27 August

Lomonosov 2021

Moscow

SuperKEKB collider●

Asymmetric e+e- collider●

Energy limit 11.02 GeV (up to 11.24)●

Luminosity goal: 6✕1035 cm-2s-1●

Belle II goal: collect 50 ab-1

Higher beam current

Very strong vertical focusing at the interaction point

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Belle II detector

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Data taking status

New luminosity world record 3.1 x 1034 cm-2s-1 (KEKB: 2.1 x 1034cm-2s-1).
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Data taking efficiency is achieved almost 90%.
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Double available statistics up to 213 fb-1 by 2021a/b physics run.
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Charmonia
Observed States:●

Conventional Charmonium●

Unconventional neutral states●

Unconventional charged states●

Pentaquark candidates

Below kinematic threshold:
mostly bound states of mesons/baryons.
Above threshold:zoo of complex XYZ states.

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Charmonia production at B factory
B decay: B →K Xcc̅JPC = 0-+, 1--, 1++
Initial-state Radiation (ISR)
JPC = 1-Two-photon Process
JPC = 0-+, 0++, 2++ ,2-+
Double charmoniume.g. e+e- →J/ψX[PRL 98, 082001 (2007)]

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X(3872)
Most interesting particle in charm sector
Observed by Belle
Phys.Rev.Lett. 91 (2003) 262001
Studied by B-Factories, LHCb
Still many puzzles:
decays ratios?
lineshape?
real nature?
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X(3872)

Data Sample: 62.8 fb-1
Reconstruction of final states: B ±→π+π- J/ψ(l+l-) K±andB0→π+π- J/ψ(l+l-) KS

Selection: Continuum suppression,
Particle Identification,
Kinematics criteria: Mππ , Mbc = √(E2beam — pB2) , |ΔE| = EB - Ebeam
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X(3872) rediscovery at Belle IICalibration: B → ψ(2S) K.
First X(3872) at Belle II:14.4±4.6 events (4.6σ)
Consistent with Belle[BELLE2-NOTE-PL-2021-002]

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Charmonium production by ISR
Reconstruction: e+e- ƔISR →π+π-J/ψ(l+l-)●Nominal PID requirements,●|M(l+l-) - mJ/ψ | < 75 MeV/c2,●|M2recoil(π+π-J/ψ)| < 2 GeV/c2.

Clear observation of ISR ψ(2S) signals.
Next step is Y(4260) rediscovery.
Expecting ~60 total events per 100 fb-1.

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Bottomonia
How to produce bb at e+e- collider:●

Directly from e+e- : JPC=1-- : Υ(nS),●ISR production : JPC=1-- : Υ(nS),●

Hadronic transitions from Υ(nS) through η,ππ
JPC=1--, 0-+, 1+- ... : Υ(nS), hb(nS), ηb(nS), ...

●Radiative transitions from Υ(nS) JPC = 0++,1++,2++ : cb,●

Electric dipole transition (E1) JPC = 0-- : ηb,●

Hindered magnetic dipole (M1) transitions.

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Bottomonia
Search exotics by pp, g, h transitions

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Belle II progress in dipion transitions

Early Belle II data, 72 fb-1●
Verification of analysis chain for p+p-l+l●
Future studies: M(p+p-) in Y(4S) transitions●

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Belle II potential●●Run at Υ(6S) and Υ(5S) and high energy scan:•Search for new, predicted, resonances such missing bottomonia, exotic states,•Improve precision of already known process and states: e.g. Zb’s,•Measure the effect of the coupled channel contribution,•

Study B(*)B(**) and Bs(*)Bs(**) threshold regions (challenging for Super-KEKb).

Run at Υ(3S) and Υ(2S):•Search for missing ππ/η transitions to constrain further theoretical models,•

Search for new physics: LFV, LFU, new scalars...

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Main focus to collect Y(4S) on-peak data.
●Upcoming non-Y(4S) plans (Nov 2021):•
10.751 GeV (10 fb-1): to study Yb(10753) on-peak,•
10.657, 10.706, 10.810 (1+2+3 fb-1): additional points for BBdecomposition.
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Expected data: ~400 fb-1 by end of 2021, ~750 fb-1 by summer 2022.
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9 month upgrade, then data taking till 2026, expected O(10 ab -1).
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After upgrade: 11 GeV (30 fb-1): to study Y(6S) on-peak.
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Future proposals: options for larger Y(6S), Y(3S), Y(5S) datasets.
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Summary●Belle II: next generation B-Factory.

●Charmonia / bottomonia / XYZ is a significant component of the physics program.

●Advantages with unique production, decay modes related to neutrals.

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Planning for non-Y(4S) energies.

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Analysis of early data.

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Rediscoveries of 1-- bb states.

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Statistics soon comparable to BaBar/Belle.

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Input welcome from community on 10.75 GeV and other bb studies.

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