1 Quarkonium studies at Belle II Y. Kato (KMI, Nagoya) 2019/4/9 DIS 2019 Paradigm shift in the hadron spectroscopy 2 Before the B-factory era, charmonium are well understood by the constituent quark model. B-factories discovered many charmonium-like hadrons deviated from quark model 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 particles not understood. ・ Missing “conventional” quarkonium. How well quark model works? 2019/4/9 DIS 2019 B-factory = hadron factory! 3 Xcc Xcc B meson decay Initial state radiation Two photon 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 mesons/baryons Zb states 2019/4/9 DIS 2019 “New hadrons” from B-factories 4 Hadron Type Charmonium (-like) Bottomonium (-like) D, D(s) Charmed baryon Hyperon 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! 5 - O(10 ) 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 Proton 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? Tetraquark? 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 .. PC - Measure properties of already observed states (J , 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 PC ++ - J = 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. molecule? - 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 B meson 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. M(J/ψη) ・ C-odd partner: - 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 J/ψπ+π- ・ States needs confirmation - 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 Zc(3900) ・ 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? P ・ Full amplitude analysis at Belle II is awaited for J 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 PC ++ ・ J =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.