Recent results and prospects of exotic hadrons at B-factory

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1 Recent results and prospects of exotic hadrons at B-factory XiaoLong Wang Virginia Tech & Belle Collaboration XVI International Conference on Hadron Spectroscopy Jefferson Lab, Newport News, Virginia 9/13 9/18/215

2 Introduction Potential model works very well for charmonium states below DD threshold. A lot of charmonum(-like) states above DD threshold were observed in the past decade. XYZ particles Quarkonium-like states with many exotic properties! What is their nature? e + γ ISR e + γ ISR e + e - γ* * Y e + e - γ* * Y -- 1 e - e - γ ISR From A. Esposito et al., Int.J.Mod.Phys. A3, 1532 (214). The charmonium(-like) states observed via ISR: Y (48), Y (426), Y (436), Y (466), X(463), ψ(44), ψ(416), ψ(4415),... Exotics@Belle Hadron215 1 / 25

3 List of XYZ particles From A. Esposito et al., Int.J.Mod.Phys. A3, 1532 (214). Hadron215 2 / 25

4 List of XYZ particles continue 24 structures listed! Only 7 observed in different channels. of the left reported from single experiment. More experimental data are required. BelleII Exotics@Belle Hadron215 3 / 25

5 KEKB and Belle Physics targets: CP Violation, Spectroscopy, τ Physics, New Physics beyond Standard Model,... Belle data samples: On resonances: Υ(5S): 121 fb 1 Υ(4S): 711 fb 1 Υ(3S): 3 fb 1 Υ(2S): 25 fb 1 Υ(1S): 5.8 fb 1 Off reson./scan: fb 1 Total: fb 1 Exotics@Belle Hadron215 4 / 25

6 BelleII BelleII detector improvements: Vertex: Pixel Drift Chamber Particle ID: itop KLM: scintillator BelleII will have better performance than Belle. Latest SuperKEKB Luminosity Profile BelleII data: 1 ab 1 Peak luminosity: 36 cm 2 s 1 ab 1. Data sample: 5 achieve 1 ab 1 data. Will be easy to BelleII data will obviously contribute to the studies on exotic particles. Exotics@Belle Hadron215 5 / 25

7 Update on e + e π + π ψ(2s) via ISR at Belle Exotics@Belle Hadron215 6 / 25

8 First scan on π + π ψ(2s) at BaBar: 298 fb 1 data Y (426) was discovered by BaBar in e + e π + π J/ψ via ISR. B. Aubert et al., PRL95,1421(25) BaBar searched for Y (426) in e + e π + π ψ(2s) final states later. BaBar: B. Aubert et al., PRL98, 2121(27). Exotics@Belle Hadron215 7 / 25

9 Following studies on e + e π + π ψ(2s) Belle scanned on π + π ψ(2s) with 673 fb 1 data. Y (436) was confirmed and Y (466) was discovered at Belle. Y (466) has been confirmed by BaBar with 52 fb 1 data: The charmonium-like state with highest mass but narrowest width. Are Y (466) and Y (463) the same? PRL99,1422(27) 1 events 673 fb 1 PRD89,1113(R)(214) BaBar 52 fb 1 PRL1,1721(28) X(463) Λ + c Λ c Belle has about 1 ab 1 data after 2, and efficiency increases after data reprocessed. What could happen? Many more signal events are expected! Search for possible intermediate state(s) in Y decays. Exotics@Belle Hadron215 8 / 25

10 M π + π vs.m π + π ψ(2s) Two modes used in reconstructing ψ(2s) signals: ψ(2s) π + π J/ψ, ψ(2s) µ + µ Selection criteria improved comparing to previous measurement. M[π + π - ] GeV/c π + π J/ψ mode M[π + π - ] (GeV/c 2 ) µ + µ mode M[π + π - ψ(2s)] GeV/c M[π + π - ψ(2s)] (GeV/c 2 ) Purity: 245 candidate events with a purity of 96% from π + π J/ψ mode, and 118 events with a purity of 6% from µ + µ mode. M π + π : tends to the phase space boundary; f (98) belts. PRD91, 1127(215) Exotics@Belle Hadron215 9 / 25

11 M π + π projections in π+ π J/ψ It s not so clean in µ + µ mode, due to the width of sidebands: Mass resolution: σ π + π J/ψ = 2.7 ±.2 MeV/c2, σ µ + µ = 13.8 ± 2.1 MeV/c2. Y (436) + Y (466) Y (436) Y (466) Entries/2 MeV/c Entries/2 MeV/c 2 5 Entries/2 MeV/c M[π + π - ] GeV/c M[π + π - ] GeV/c M[π + π - ] GeV/c 2 Dots: data; Blank hist: MC simulations; Shaded hist: bkg from ψ(2s) sidebands. (a) with 4. < M π + π ψ(2s) < 5.5 GeV/c2. Y (436): 4. < M π + π ψ(2s) < 4.5 GeV/c2, looks like f (5) Y (466): 4.5 < M π + π ψ(2s) < 4.9 GeV/c2, could only be f (98). MC simulation with an incoherent sum of the f (5) and f (98). Exotics@Belle Hadron215 / 25

12 Fit of M π + π ψ(2s) spectrum with two resonances Unbinned simultaneous maximum likelihood fit for Y (436) and Y (466): Amp = BW 1 + e iφ BW 2. Entries/2 MeV/c π + π J/ψ Entries/2 MeV/c 2 5 µ + µ Entries/2 MeV/c both modes M[π + π - ψ(2s)] (GeV/c 2 ) M[π + π - ψ(2s)] (GeV/c 2 ) M[π + π - ψ(2s)] (GeV/c 2 ) Parameters Solution I Solution II M Y (436) (MeV/c 2 ) 4347 ± 6 ± 3 Γ Y (436) (MeV) 3 ± 9 ± 5 B Γ e+ e Y (436) (ev) 9.2 ±.6 ±.6.9 ±.6 ±.7 M Y (466) (MeV/c 2 ) 4652 ± ± 11 Γ Y (466) (MeV) 68 ± 11 ± 5 B Γ e+ e Y (466) (ev) 2. ±.3 ± ± 1.1 ± 1. φ ( ) 32 ± 18 ± ± 8 ± 7 χ 2 /ndf = 18.7/21. Consistent with previous measurement No obvious signal above Y (466). 12 events accumulate at Y (426), especially the π + π J/ψ mode. If Y (426) is included in the fit,... Exotics@Belle Hadron / 25

13 Fit of M π + π ψ(2s) spectrum with three resonances Entries/2 MeV/c 2 2 Entries/2 MeV/c 2 2 Entries/2 MeV/c 2 2 Entries/2 MeV/c M[π + π - ψ(2s)] (GeV/c 2 ) M[π + π - ψ(2s)] (GeV/c 2 ) M[π + π - ψ(2s)] (GeV/c 2 ) B Γ e+ e Y (426) (ev) 1.5 ±.6 ± ±.7 ±.5.4 ± 1.3 ± ± 1.2 ±.8 M Y (436) (MeV/c 2 ) 4365 ± 7 ± 4 Γ Y (436) (MeV) 74 ± 14 ± 4 B Γ e+ e Y (436) (ev) 4.1 ± 1. ± ± 1.3 ± ± 3.5 ± ± 2.6 ± 1.5 M Y (466) (MeV/c 2 ) 466 ± 9 ± 12 Γ Y (466) (MeV) 74 ± 12 ± 4 B Γ e+ e Y (466) (ev) 2.2 ±.4 ± ±.9 ± ± 1.2 ± ±.5 ±.3 φ 1 ( ) 34 ± 24 ± ± 25 ± ± 4 ± ± 5 ± 4 φ 2 ( ) 26 ± 19 ± 238 ± 14 ± ± 8 ± ± 23 ± M[π + π - ψ(2s)] (GeV/c 2 ) Significance of Y (426) is 2.4σ low, but affects the parameters of Y (436) and Y (466)! FOUR solutions with equally good fit quality, which is χ 2 /ndf = 14.8/19. We may get about 5 Y (426) events from BelleII. In that case, we need to figure out which solution is the one of Physics. There should be about 5, signal events above Y (466) with BelleII more Y state(s)? Mathmatical solutions with n Y states: 2 n 1 Exotics@Belle Hadron / 25

14 σ(e + e π + π ψ(2s)) e + e π + π ψ(2s) cross section is calculated with σ i = nobs i n bkg i L i 2 j=1 ε, ij B j where i indicates the mass bin and j indicates the ψ(2s) decay mode. Other cross sections from ISR: PRL1, 2522(213) e + e π + π J/ψ PRD91, 1127(215) peaks 75 pb! PRD87,511(R)(213) e + e ηj/ψ The σ(e + e π + π J/ψ) at Y (426), σ(e + e π + π ψ(2s)) at Y (436) and σ(e + e ηj/ψ) at ψ(44) are almost the same!!! WHY? Need BelleII data, or more BESIII data. Exotics@Belle Hadron / 25

15 Tetra-quark state candidate: Z c Z (443) ± observed in π ± ψ(2s) final states. Z c (39) observed in Y (426) decay. Both Z (443) and Z c (39) are candidates of tetra-quark states. Here are two Y s, and π ± ψ(2s) final states. What can we get in Y (436)/Y (466) decays? PRL1,2522(213) PRL, 1421(28) PRL1,2521(213) Exotics@Belle Hadron / 25

16 Search for intermediate states in Y (436) decays M[π - ψ(2s)] (GeV/c 2 ) π + π J/ψ M[π - ψ(2s)] (GeV/c 2 ) µ + µ M[π + ψ(2s)] (GeV/c 2 ) M[π + ψ(2s)] (GeV/c 2 ) Entries/12.5 MeV/c π + π J/ψ Entries/12.5 MeV/c µ + µ M[π ± ψ(2s)] GeV/c M[π ± ψ(2s)] (GeV/c 2 ) M π ± ψ(2s): sum of the M π + ψ(2s) and M π ψ(2s) An excess at both π + π J/ψ and µ + µ modes, and both M π + ψ(2s) and M π ψ(2s)! A new Z c at 4.5 GeV/c 2? No excess found at previous measurement of Belle, because only 1 signal events observed then. Exotics@Belle Hadron / 25

17 Z c (45)? An unbinned maximum-likelihood fit is performed simultaneously. M max (π ± ψ(2s)): the maximum of M(π + ψ(2s)) and M(π ψ(2s)) π + π J/ψ + µ + µ M = (454 ± 3(stat.) ± 1(syst.)) MeV/c 2 Γ = (45 ± 11(stat.) ± 6(syst.)) MeV About 45 signal events. The significance is 3.5σ. Bias between M max [πψ(2s)] and M π ± ψ(2s) is corrected according to MC simulation. Exotics@Belle Hadron / 25

18 Search for intermediate states in Y (466) decays No obvious excess found in Y (466) decays. M[π - ψ(2s)] (GeV/c 2 ) π + π J/ψ M[π - ψ(2s)] (GeV/c 2 ) µ + µ M[π + ψ(2s)] (GeV/c 2 ) M[π + ψ(2s)] (GeV/c 2 ) Entries/2 MeV/c 2 5 π + π J/ψ Entries/2 MeV/c µ + µ M[π ± ψ(2s)] (GeV/c 2 ) M[π ± ψ(2s)] (GeV/c 2 ) f (98)ψ(2S) dominates in Y (466) decays. However, looks no-f (98) component exists as shown in the scatter plot (p.9). Relationship between Z c and Y (466) would be interesting at BelleII. Exotics@Belle Hadron / 25

19 Summary Belle updates the measurement on e + e γ ISR π + π ψ(2s) with 98 fb 1 data. Resonance parameters of Y (436) and Y (466) are updated. Y (426) π + π ψ(2s) is studied. The significance of Y (426) is < 3σ, but it has significant affect on Y (436) and Y (466) parameters. Comparison between Y (466) and X(463): X(463) from Λ + c Λ c : M = MeV/c2, Γ = MeV. Y (466) from 2R fit: M = 4652 ± ± 11 MeV/c 2, Γ = 68 ± 11 ± 5 MeV. Y (466) from 3R fit: M = 466 ± 9 ± 12 MeV/c 2, Γ = 74 ± 12 ± 4 MeV. Evidence of a structure in M max (π ± ψ(2s)) in Y (436) decays with significance of 3.5σ. M = (454 ± 3(stat.) ± 1(syst.)) MeV/c 2 ; Γ = (45 ± 11(stat.) ± 6(syst.)) MeV The BelleII will help to understand the nature of many exotic states in the future. Thank you! Exotics@Belle Hadron / 25

20 Back-up Hadron / 25

21 ψ(2s) signals 3 Entries/1 MeV/c 2 2 Entries/7 MeV/c M[π + π - J/ψ] (GeV/c 2 ) M[µ + µ - ] (GeV/c 2 ) ψ(2s) π + π J/ψ mode: selection criteria optimized. M ψ(2s) = M π + π l + l M l + l + m J/ψ ψ(2s) µ + µ mode: a new mode. ψ(2s) e + e mode is not used due to high background level. Mass resolution: σ π + π J/ψ = 2.7 ±.2 MeV/c2, σ µ + µ = 13.8 ± 2.1 MeV/c2. Exotics@Belle Hadron215 2 / 25

22 ISR characteristics Entries/.1 (GeV/c 2 ) M 2 rec[ππψ(2s)] ((GeV/c 2 ) 2 ) ψ(2s) π + π J/ψ mode Entries/.1 GeV Evis (GeV) Entries/ cosθ Entries/.2 (GeV/c 2 ) M 2 rec[ππψ(2s)] ((GeV/c 2 ) 2 ) ψ(2s) µ + µ mode Entries/.1 GeV Evis (GeV) Entries/ cosθ Missing mass: signal of γ ISR. 2 < M 2 rec(π + π ψ(2s)) < 2 (GeV/c 2 ) 2 is required. Visible energy: Only -2% γ ISR can be detected. Angular distribution: γ ISR highly forward/backward. PRD91, 1127(215) Exotics@Belle Hadron / 25

23 e + e γ ISR + e + e DD scanned by both BaBar and Belle. The results are consistent. Clear ψ(44), ψ(416) and ψ(4415). But no evidence for Y states in these channels. Exotics@Belle Hadron / 25

24 ηj/ψ via ISR Belle: Search for hadronic transition via emitting η. (η γγ/π + π π ) This is the first time to found ψ states in charmonium transition. (> 6.σ for ψ(44); > 6.5σ for ψ(416).) Large B(ψ ηj/ψ)! B(ψ(2S) ηj/ψ) = (3.28 ±.7)% Unlike π + π transition, no significant Y signal!!! Γ e + e (ψ(44)) = (.86 ±.7) kev from PDG B(ψ(44) ηj/ψ) = (.56 ±. ±.18)% or B(ψ(44) ηj/ψ) = (1.3 ±.15 ±.26)%. Γ e + e (ψ(416)) = (.83 ±.7) kev from PDG B(ψ(416) ηj/ψ) = (.48 ±. ±.17)% or B(ψ(416) ηj/ψ) = (1.66 ±.16 ±.29)%. Belle: X. L. Wang et al., PRD87,511(R)(213). Exotics@Belle Hadron / 25

25 Other fit results on M π + π ψ(2s) Published Belle results: Current BaBar results: π + π J/ψ only: Exotics@Belle Hadron / 25

26 Fit with three resonance using π + π J/ψ mode Exotics@Belle Hadron / 25