Light Hadron Spectroscopy at BESIII Haolai TIAN On

Light Hadron Spectroscopy at BESIII Haolai TIAN (On behalf of the BESIII Collaboration) Institute of High Energy Physics, Beijing 23 rd Rencontre de Blois Particle Physics and Cosmology 29 th May. -3 rd June. , 2011, Blois, France

Outline • pp mass threshold enhancement study in the radiative decays of J/ψ and ψ’ • Confirmation of X(1835) and observation of two new resonances in J/ψ → γη’π+π • Observation of X(1870) in J/ψ → ωηπ+π • Direct measurements of a 0 -f 0 mixing via J/ψ → ϕf 0 → ϕa 0 and χc 1→π0 a 0→π0 f 0 Haolai TIAN, Blois, France 2

Remarks of BESII on light hadron spectroscopy • The multi-quark states, glueballs and hybrids have been experimentally searched for a very long time. • During the last few decades, a lot of unexpected experimental evidence for hadrons are reported: Ø pp threshold enhancement observed in J/ψ → γpp; Ø X(1835) observed in J/ψ → γX, X → η’ππ; 0 0. 1 0. 2 0. 3 Mpp-2 mp (Ge. V) Haolai TIAN, Blois, France M(η’ππ) (Ge. V/c 2)

The BEPCII/BESIII Project 225 M J/ψ 106 M ψ’ Double-ring collider Designed Luminosity: 1× 1033 cm-2 s-1 Record Luminosity : ~6. 49× 1032 cm-2 s-1 @3770 Ge. V The construction started in 2004: Apr. 14, 2009: ~106 M ψ’ events 42. 3 pb-1 at 3. 65 Ge. V July 28, 2009: ~225 M J/ψ events We have opportunities to confirm the existence of pp mass threshold enhancement and X(1835) at BESIII … and to search new observations ! Haolai TIAN, Blois, France 4

pp mass threshold enhancement 3 -body phase space BESII X(1860) 0 acceptance 0. 1 0. 2 No similar structure is observed in relative channels Mpp-2 mp (Ge. V) Υ(1 S)→γpp @CLEO PRD 73 (2006) 032001 0. 3 Theoretical speculations: • Pure FSI effect (disfavored by fit) • Baryonium: pp bound state • … J/ψ→ωpp @BESII EPJ C 53 (2008) 15 Haolai TIAN, Blois, France ψ’→γpp @BESII PRL 99 (2007) 011802 5

pp mass spectrum in ψ’ → π+π-J/ψ, J/ψ → γpp 3 -body phase space BESIII results: • M = 1861+6 -13+7 -26 Me. V/c 2 • Γ < 38 Me. V/c 2 at 90% C. L. BESII results: Chinese Physics C, 34 421 (2010) • M = 1859+3 -10+5 -25 Me. V/c 2 • Γ < 30 Me. V/c 2 at 90% C. L. Consistence within the error Haolai TIAN, Blois, France 6

pp mass spectrum in J/ψ → γpp BES III Preliminary BESII results: BES III Preliminary • M = 1859+3 -10+5 -25 Me. V/c 2 • Γ < 30 Me. V/c 2 at 90% C. L. BESIII preliminary results: • M = 1861± 0. 8 Me. V/c 2 • Γ < 8 Me. V/c 2 at 90% C. L. Consistence within the error PWA is on going. Haolai TIAN, Blois, France 7

pp mass spectrum in ψ’ radiative decay ψ’ → γpp BES III BESII Preliminary PRL 99 (2007) 011802 No obvious narrow threshold enhancement No significant narrow strong enhancement near threshold (~2 if fitted with X(1860)) Haolai TIAN, Blois, France 8

Observation of X(1835) in J/ψ → γη’ππ BESII result (PRL 95, 262001 (2005) ) • M = 1833. 7± 6. 1(stat)± 2. 7(syst) Me. V/c 2 • Γ = 67. 7± 20. 3(stat)± 7. 7(syst) Me. V/c 2 • Significance: ~7. 7σ Theoretical interpretations: pseuodscaler glueball / radial excitation of η’ ? • A 0 -+ glueball is expected to have similar decay properties of ηc, which decays primarily via η’ππ. • LQCD predicts that the 0 -+ glueball lies around 2. 3 Ge. V. The confirmation of X(1835) is necessary with higher statistics data sample and better detector like BESIII. Haolai TIAN, Blois, France 9

Mass spectrum of η’π+π- • X(1835) and ηc are evident. • Two additional structures are observed at ~2. 1 and 2. 3 Ge. V. • There exists a small peak at 1. 5 Ge. V. Combination for to + - and Haolai TIAN, Blois, France 10

Fit of the combined mass spectrum Ø Ø Fitting with four resonances Three background components: 1. 2. 3. η’ mass sideband J/ψ → π0η’π+π- with reweighting “PS background” The angular distribution of the events in X(1835) ∝ 1+cos 2(Ѳ) , which agrees with JPC=0 -+ Red line: estimated contribution of 1. + 2. Black line: total background PRL 106, 072002 (2011) Haolai TIAN, Blois, France 11

Summary of J/ψ → γη’π+π • The existence of X(1835) is confirmed at BESIII, with a much higher statistical significance ( >20σ ). • Two additional resonances, X(2120) and X(2370), are observed with significance larger than 7. 2σ and 6. 4σ, respectively. • PWA is needed not only to determine the spin-parities of the above three resonances, but also to make more precise measurement of masses, widths and BRs by taking possible interference into account. • The study of the decay pattern is of crucial importance, i. e. in relative channels (ηππ, …) and with other decay mode (ω, ϕ, …) Haolai TIAN, Blois, France 12

Analysis of J/ψ → ωηππ M(ηππ), with a 0(980) a 2(1320 ) BES III Preliminary f 1(1285) M(ηππ), veto a 0(980) ? h’ h(1405) BES III Preliminary • In addition to the well-known η’, f 1(1285) and η(1405), an unknown structure (denoted as X(1870)) around 1. 87 Ge. V/c 2 is observed. • The f 1(1285), η(1405) and X(1870) decay primarily via a 0(980)π mode. Haolai TIAN, Blois, France 13

Mass spectrum fitting results Signal peak: acceptance weighted BW⊗Gauss Background: 4 th-order polynomial Fitted result of X(1870): BES III Preliminary • M = (1877. 3± 6. 3) Me. V/c 2 • Γ = (57± 12) Me. V/c 2 • Significance: 7. 1σ • The fit is performed under the assumption that the interference between the resonances and background can be ignored. • Current results cannot settle down whether X(1870) is actually η 2(1870) (Γ =225± 14 Me. V/c 2)or a new resonance. Haolai TIAN, Blois, France 14

Studying a 0(980)-f 0(980) mixing • Interpretation of a 0/f 0: qq, four quarks, KK molecule, hybrids, … • Study of the mixing of a 0 and f 0 will shed new light on the enigmatic light scalars. No firm experimental determination yet. • Signature of the mixing signal: a narrow peak (8 Me. V) between the charged and neutral kaon thresholds (987~995 Me. V). π0 ϕ J/ψ η f 0 → a 0 χc 1 a 0 → f 0 π0 J. Wu, Q. Zhao, B. Zou PRD 75 114012, π+ π- J. Wu, B. Zou PRD 78 074017 C. Hanhart etc. PRD 76 074028, etc. Haolai TIAN, Blois, France 15

a 0(980)-f 0(980) mixing: f 0 → a 0 transition PRD 83 032003(2011) J/ψ → ϕf 0 → ϕa 0 → ϕηπ0 Significance: 3. 4σ …. Mixing signal --- a 0(980) contribution from J/ψ → γ*/K*K → ϕa 0(980) --- Background polynomial Haolai TIAN, Blois, France 16

a 0(980)-f 0(980) mixing: a 0 → f 0 transition PRD 83 032003(2011) ψ→γχc 1, χc 1→a 0π0→ f 0π0→ π+π-π0 Significance: 1. 9σ …. Mixing signal --- f 0(980) contribution from other process --- Background polynomial Haolai TIAN, Blois, France 17

Comparison with different models PRD 83 032003(2011) a 0 -f 0 mixing: a sensitive probe Shaded region: BESIII measurements Red Line: BESIII upper limits Dots: various predictions Haolai TIAN, Blois, France 18

Summary • pp mass threshold enhancement and X(1835) are confirmed at BESIII. • In addition to X(1835), two new resonances, X(2120) and X(2370) are observed in the channels of J/ψ → γη’π+π-. • A new process is observed in J/ψ → w. X(1870) → wηπ+π. • The transition of a 0 ↔ f 0 is studied and the mixing intensity is extracted. Haolai TIAN, Blois, France 19

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