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Quarkonium studies at Belle II Y. Kato (KMI, Nagoya)

2019/4/9 DIS 2019 Paradigm shift in the spectroscopy 2

Before the B-factory era, charmonium are well understood by the constituent model.

B-factories discovered many charmonium-like deviated from

Some states have charge, which can not be achieved by cc

X(3872)→J/ψπ+π- X(3915)→J/ψω Y(4260)→J/ψπ+π- Z(4430)+→ψ(2S)π+

arXiv:1511.01589 Phys. Rev. Lett. 91.262001 Phys. Rev. D 88, 074026 (2013) Homeworks from B-factory experiments (= Belle, BaBar): ・ Nature of XYZ not understood. ・ Missing “conventional” . How well quark model works?

2019/4/9 DIS 2019 B-factory = hadron factory! 3

Xcc

Xcc

B decay Initial state radiation Two collision ・X(3872), Z(4430)…. ・JPC=1-- ・JPC=0++, 2++..... ・Open charm hadrons ・Y(4260) ・Extract two photon width

Double charmonium e+e-→ cc Bottomonium transition

・C-even charmonium Charm / Zb states

2019/4/9 DIS 2019 “New hadrons” from B-factories 4 Hadron Type

Charmonium (-like) Bottomonium (-like) D, D(s) Charmed

B-decay ηc(2S) ψ2(3823) D*0(2400) D1(2430) Ξc(2930) X(3872) X(3915) Belle

Zc(4050) Zc(4250) BaBar Zc(4430) Zc(4200) Initial Y(4260) Z(3900) State Y(4008) Y(4360) Radiation Y(4660)

Double X(3860) ≒ χc0(2P) charmonium X(3940) X(4160)

Two-photon χc2(2P)

Reaction + - bar * e e →cc D s0 (2317) D0(2550) Σc(2800) Λc(2940) * DJ (2600) DJ(2740) Ξc(2980) Ξc(3080) * * D3 (2750) D s1(2700) Ωc(2770) Ξc(3055) * D s1(2860) DsJ(3040)

Y(nS) decay Zb(10610) Zb(10650) Ω(2012) ηb(2S) hb(1P) hb(2P) Charm baryon Ξ(1620) decay

2019/4/9 ~40 new hadronsDIS 2019 discovered! Next generation: SuperKEKB 5

Nano-beam scheme

7 GeV

4 GeV

Crossing angle: ~40mrad

2019/4/9 (x2 DISbeam 2019 current, 1/20 beam size) Belle II experiment 6

・ General purpose 4π detector ・ Upgraded to cope with beam BG ・ Better momentum/vertex ・ Improved PID with RICH technique More2019/4/9 than 900 Physicists from ~ DIS100 2019 institutes in 26 countries/region Belle II computing 7

20k jobs

・ Big data → huge computing resource needed! - O(105) CPU cores, O(100 PB) storage ・ Belle II adapted distributed computing model ・ MC production on-going with ~50 sites by automated system.

2019/4/9 DIS 2019 Global schedule 8

50 ab-1

Here

・ Plan to accumulate 50 ab-1 (x50 times of Belle)

- Phase1: SuperKEKB commissioning w/o final focusing and w/o Belle II detector but beam background detectors (=BEAST) installed

- Phase2: Collision data taking w/ final focusing. No VXD (2018 Apr-Jul, Achieved peak luminosity: 5x1033/cm2/s. Collected 0.0005 ab-1 )

- Phase3: Collision data taking w/ full Belle II detector (2019 Mar): Just started! 2019/4/9 DIS 2019 Highlights in these 2 years 9 Belle II roll-in First collisions at phase2! qq e+e-→γ*→BB

Apr 11, 2017 Apr 26, 2018 VXD installation Phase 3 started

Nov 26, 2018 DIS 2019 Mar 25th, 2019 2019/4/9 Physics performance 10

EECL/p(recoil) in e+e-→e+e-γ Track impact parameter

Kaon ID ID φ→K+K- Λ→pπ-

w/o PID w/ PID 2019/4/9 DIS 2019 Re-discoveries in Phase 2 data 11 π0→γγ D*+→D0π+ J/ψ→e+e-

+ - + - + - + e e →π π γ Λc →pK π B→hadronic

2019/4/9 DIS 2019 Role of Belle II for quarkonium physics 12

Molecule? ? Hybrid? Mixing? ・ Nature of each XYZ? D c c c c D* u d g D D* + c c

・ Understand (part of) XYZ in a unified way? New multiplet?

・ Understand charm and bottom in a unified way?

Further new multiplet? ・ What Belle II can do is .. - Measure properties of already observed states (JPC, decay, production…) - Establish the states whose evidence was not very strong. - Discover new states.

・2019/4/9 Many topics covered by Belle II PhysicsDIS 2019 book B-decays: X(3872) 13

JHEP01(2017)117 ・ Firstly observed by Belle in B+→K+ (J/ψπ+π-). The poster boy - JPC = 1++ - Decay into both of J/ψρ (I=1) and J/ψω (I=0): isospin breaking DD* - Mass consistent with DD* with O(0.1) MeV presicion. ?

- Differential cross section for prompt production cross section at LHC cc?

consistent with χc1(2P) χc1(2P)

Decays and production play essential role

Many things missing in the decay property K+ + ・Total width: B only the upper limit of 1.2 MeV is determined. X

+ + × ・Branching fraction: Br(B →K X(3872)) Br(X(3872)→f) Only the product of two branching fractions are measured.

2019/4/9 DIS 2019 Importance of decay width and branching fraction 14

2019/4/9 DIS 2019 Total width with X(3872)→DDπ0 decay mode 15

・ The mass resolution is important to measure narrow width.

・ As the Q-value becomes smaller, the mass resolution becomes better. Decay Q-value + - ・ Q-value of DDπ0 decay has significantly smaller Q-value than J/ψππ J/ψπ π ~500 DDπ0 7 ・ The mass resolution is 680 keV: ~3 times better than J/ψπ+π- mode. - No width measurement at Belle (1) due to poor statistics

・ No bias seen up to O(100 keV) in the simulation. 5σ sensitivity 3σ sensitivity ・ Huge improvement is expected. 90% UL

current UL

2019/4/9 DIS 2019 Br(B+→K+X(3872)) 16

+ + ・Extract Br (B →X(3872) K ) → Do not look for X(3872) decay Belle1 full statistics result 2 2 -4 - Reconstruct X from Missing mass:Mx = (Pbeam-PBTag-PK+) < 2.6×10

Reconstruct Detect Hadronic decay K+ B- B+

X Phys. Rev. D 97, 012005

・ Measurement only possible at e+e- B-factory.

・ There is a lower limit of 1.0×10 -4 from the constraint that all the product of branching fractions to be smaller than 1

・ Even in this lower bound 7σ measurement is possible at Belle II (naïve expectation)

・ Measurement for X(3915) is also important to determine Br(X(3915)→J/ψω)

・ Better reconstruction should improve sensitivity. 2019/4/9 DIS 2019 More realistic simulation on going. Search for partner states 17

・ Molecule/tetra-quark scenarios predict existence of X(3872) partner states.

・ C-odd partner: M(J/ψη) - No structure observed in J/ψη by Belle. The upper limit is around half of X(3872)→J/ψπ+π-

・ Spin partner: - B→K DD and K D*D* not studied in detail yet.

10.1093/ptep/ptu043

2019/4/9 DIS 2019 B decays: States need confirmation 18

+ B+→K+Z(4050), Z(4250) →χ π+ BaBar reported m(χc1π ) can be described c1 by resonances in Kπ channel only

+ Phys. Rev. D 78, 072004 M(χc1π ) (in different M(Kπ) bins Confirmation by Belle II is needed 2019/4/9 DIS 2019 Initial State Radiation 19 e- Effective luminosity/10 MeV γ

M(J/ψπ+π-) + e Y(4260)

・ One of the best probes to study 1-- quarkonium states.

・ Many “Y” states are reported from B-factories and BES III.

・ Also many “Z” states from “Y” decay.

・ 50 ab-1 data corresponds to 2000-2300 pb-1/10 MeV at 4-5 GeV. → Compatible with BES III

・ Belle2019/4/9 II has advantage to access energy higherDIS 2019 than 4.6 GeV, and take data simultaneously. Initial State Radiation golden modes 20 ・ States needs confirmation J/ψπ+π- - Y(4008): inconsistent between Belle/BaBar - Many states observed by BES III only. Y(4008)? ・ State needs further studies

- Z(3900): Resonance or cusp? Phys. Rev. Lett. 99, 182004 DD*Cusp reproduce the peak? Need Argan diagram with amplitude analysis Z (3900) c ・ New States? + - - J/ψ K K for Zcs search. - ISR events are observed, but no structure. - Need more statistics. Phys. Rev. Lett. 117, 242001 M(J/ψK+K-) M(K+ J/ψ) ・ And many more..

Phys. Rev. D 89, 072015 2019/4/9 DIS 2019 Double charmonium production 21 J/ψ missing mass

Reconstruct

・ Large cross section revealed importance of Phys. Rev. Lett. 98, 082001 next order correction in NRQCD. J/ψ D missing mass

・ Observation of two new states - X(3940): observed both inclusive and exclusive DD - X(4160): Observed in exclusive DD*

DD* mass D*D* mass

X(3940) X(4160)

2019/4/9 DIS 2019 Phys. Rev. Lett. 100, 202001 Interpretation of X(3940/4160) and beyond 22

・ All the known states observed in missing mass are J=0. X(3940/4160) should be J=0?

・ If J=0, C-parity = +1 and decay into DD* indicate they are ηc family.

・ However, the mass of X(3940) is ~100 MeV lower than quark model prediction.

2 ・ Also, the predicted mass of ηc(4S) is 4400 MeV/c .

・ Could be a exotic candidate?

・ Full amplitude analysis at Belle II is awaited for JP determination.

・ Recoiling against other charmonium (ηc, χc … ) is also very interesting.

2019/4/9 DIS 2019 Two photon collision (1) X(3915) 23 Xcc Observed in both B-decay and two-photon B-decay Two photon

Phys. Rev. Lett. 94, 182002 Phys. Rev. D 86, 072002 ・ JPC=0++ by BaBar from two photon (good S/N ratio!)

・ Difficult to identify as χc0(2P) - The width 20±5 MeV is too narrow for the state above DD - Not observed in DD, but OZI suppressed J/ψω only: Br(X(3915)→DD)/Br(X(3915)→J/ψω) < 1.2 - J/ψω partial width > O(1 MeV): too large as a OZI suppressed decay. 2 - χc0(2P) candidate recently observed by Belle at mass of ~3860 MeV/c

・Molecule is also difficult as exchange is not allowed for DD or DsDs.

・cscs tetraquark ? Look2019/4/9 for decay modes including η should be veryDIS 2019 interesting. Two photon collision (J/ψ φ) 24 Phys. Rev. Lett. 104, 112004

・ Belle reported evidence of X(4350) in J/ψφ (3.2σ). This needs to be confirmed together with JP determination.

・ LHCb observed four states: X(4140), X(4274), X(4500), X(4700). Measurement of two-photon width must be useful. Note X(4140) and X(4274) with JPC=1++ can not be produced. This may make analysis simpler.

Phys. Rev. Lett. 118, 022003

2019/4/9 DIS 2019 Bottomonium: Digest Belle achievements 25

Υ(5S)→Zbπ, Zb→Y(nS)π Υ(5S)→ππ h (2P)→η (2P)γ Υ(5S)→ππX b b

ηb(2S)

Phys. Rev. Lett. 109, 232002 Phys. Rev. Lett. 108, 032001

Phys. Rev. Lett. 117, 142001 2000 2015

・Fruitful results from 120 fb-1 Υ(5S) and energy scan data.

- Two Zb states observed: - Three conventional bottomonium states

・ So many transitions observed.

2019/4/9 Figures by U. Tamponi DIS 2019 Conventional bottomonium below threshold 26

Figures by U. Tamponi

・ In contrast to charmonium, up to n=3 states or D, F waves are still below the BB threshold.

・ SuperKEKB can reach Υ(6S): Many opportunities from transition other than π

・ Beam schedule still under discussion. 2019/4/9 DIS 2019 Bottom partner of X(3872)? 27 Y(4260)→γ X(3872) Y(5S) →γ ( ωΥ(1S) )

No Xb

Phys. Rev. Lett. 112, 092001 Phys. Rev. Lett. 113, 142001

・ BB* molecule with isospin=0 (isospin breaking is expected to be suppressed). Primary decay mode should be ωΥ(1S).

・ Observation of Y(4260)→γ X(3872), but no Xb in Υ (5S)→γ (ωΥ(1S)) - Not enough statistics ? Br(Y(4260)→γX(3872)/Br(Y(4260)→J/ψπ+π-) ~ 0.1 - Y(4260) and Υ(5S) are not the analogue states (next page)?

- X(3872) comes from accidental coincidence of DD* mass and χc1(2P)?

・ C-parity Partner of Zb (= Wb) also predicted in various decay modes such as Υ(nS)ρ, ηbπ 2019/4/9 DIS 2019 Energy scan 28

・ Dip in Rb and suggesting structure in Y(nS)ππ: Υ(1S)ππ Another Yb? Leading another Zb?

・ Final state other than Y(nS)/h ππ. Υ(2S)ππ b - May shed light on the anomalous Y(5S)→Υ(1-3S)ππ

(*) (*) (*) (*) Υ(3S)ππ ・ Scan with open bottoms: B B , Bs Bs indivisually. are expected have many features.

・ Belle statistics: < 1 fb-1 per point with ~ 10 MeV step. 10 fb-1/10 MeV will be very helpful.

hb(1P)ππ

hb(2P)ππ Phys. Rev. D 93, 011101(R)

2019/4/9 DIS 2019 Summary 29

・ Belle II has started!

・ Many rediscoveries, good physics performances.

・ 50 times statistics opens new door to reveal nature of XYZ exotics: - Discover new states - Confirmation of - JPC determination - Production/decay properties

Stay tuned for the coming result for Belle II !

2019/4/9 DIS 2019 30

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2019/4/9 DIS 2019