Light Meson Spectroscopy at BESIII Tianjue Min Institute of High Energy Physics, Chinese Academy of Sciences On Behalf of f th the BESIII Collaboration th International Workshop on Meson Production, 14 th 14 , Properties and Interaction nd - 7 th th Ju 2 nd June 2016, , KRAKÓW, , POLAND
2 Outline • BEPCII and BESIII • Light Meson Spectroscopy at BESIII • Summary Light Meson Spectroscopy at BESIII
3 BEPCII and BESIII Beam energy: 1.0 ~ 2.3 GeV LINAC Luminosity: 1.0×10 33 cm -2 s -1 (reached in April 5 th , 2016) 2004: BEPCII upgrade, BEPCIII construction BESIII 2008: test run 2009 ~ now: physics run Light Meson Spectroscopy at BESIII
4 BEPCII and BESIII Super-Conducting Magnet 1.0 T (2009) 0.9 T(2012) Main Drift Chamber (MDC MDC) σ P /P = 0.5% (1 GeV) σ dE/dx = 6% Electromagnetic Calorimeter (EMC) CsI (Tl) σ E / E = 2.5% (1 GeV) σ z, φ = 0.5 - 0.7 cm/ E Time of Flight (TOF) σ T : 90 ps (barrel) μ Counter ( MUC MUC) 110 ps (endcap) 8 - 9 layers RPC δ RΦ = 1.4 cm ~ 1.7 cm Light Meson Spectroscopy at BESIII
5 BEPCII and BESIII World la largest t J/ J/ ψ , , ψ (3686), , ψ(3770), … Produced directly from e + e - collision Light Meson Spectroscopy at BESIII
6 Light Meson Spectroscopy at BESIII • Light meson spectroscopy plays an important role in testing the QCD theory • J/ ψ decays is an ideal place to study light meson spectroscopy • BESIII collected the largest J/ ψ sample (~1.3 billion events) in the world • 225 million in 2009 • 1086 million in 2012 • Recent progress in light meson spectroscopy at BESIII • Observation of X(1835) in J/ ψ→γ K S K S η • Anomalous line shape of η′π + π - near p p mass threshold in J/ ψ→γη′π + π - • Model independent partial wave analysis of J/ ψ→γπ 0 π 0 • Partial wave analysis of J/ ψ→γϕϕ Light Meson Spectroscopy at BESIII
7 X( 𝐪 X(1835) and X( 𝐪 ) ) • X(1835) • Discovered by BESII in J/ ψ→γη′π + π - • Confirmed by BESIII in J/ ψ→γη′π + π - +5.6 MeV/𝑑 2 M = 1836.5 ± 3.0 −2.1 +38 MeV/𝑑 2 Γ = 190 ± 9 −36 Angular distribution is consistent with 0 - Light Meson Spectroscopy at BESIII
8 X(1835) and X( 𝐪 𝐪 ) ) • X( p p ) • Discovered by BESII in J/ ψ→γp p • Confirmed by BESIII and CLEO-c in ψ (3686) →π + π - J/ ψ , J/ ψ→γp p • Confirmed by BESIII in J/ ψ→γp p 0 -+ Not fr from FSI +19 +18 ± 19 MeV/𝑑 2 M = 1832 −5 −17 Γ = 13 ± 19 MeV/𝑑 2 ( < 76 MeV/𝑑 2 @ 90% C.L.) Light Meson Spectroscopy at BESIII
9 X(1835) and X( 𝐪 𝐪 ) ) X(1835) X( X( 𝐪 𝐪 ) +𝟔.𝟕 MeV/𝑑 2 +𝟐𝟘 +𝟐𝟗 ± 𝟐𝟘 MeV/𝑑 2 M = 𝟐𝟗𝟒𝟕. 𝟔 ± 𝟒. 𝟏 −𝟑.𝟐 M = 𝟐𝟗𝟒𝟑 −𝟔 −𝟐𝟖 +38 MeV/𝑑 2 Γ = 13 ± 19 MeV/𝑑 2 ( < 76 MeV/𝑑 2 @ 90% C.L.) Γ = 190 ± 9 −36 Probably 0 -+ 0 -+ η′ excitation? p p bound state? glueball? … … SAME sta tate? Light Meson Spectroscopy at BESIII
10 Observation of X(1835) in J/ ψ→γ K S K S η PRL 115, , 091803 (2015) • Use 1.3×10 9 J/ ψ events collected by BESIII in 2009 and 2012 • Clear structure on mass spectrum of K S K S η around 1.85 GeV/𝑑 2 • Strongly correlated to f 0 (980) • PWA for M(K S K S ) < 1.1 GeV/𝑑 2 Light Meson Spectroscopy at BESIII
11 Observation of X(1835) in J/ ψ→γ K S K S η PRL 115, , 091803 (2015) • X(1560) • 0 -+ ; X(1560) → K S K S η (> 8 .9σ) +0 MeV/𝑑 2 • M = 1565 ± 8 −63 +14+21 MeV/𝑑 2 • Γ = 45 −13−28 • Consistent with η (1405)/ η (1475) within 2.0 σ • X(1835) • 0 -+ ; X(1835) → K S K S η (> 12.9 𝜏 ), dominated by f 0 (980) production +16 MeV/𝑑 2 • M = 1844 ± 9 −25 +20+62 MeV/𝑑 2 • Γ = 192 −17−43 • Consis from J/ ψ→γη’π + π - istent wit ith th the valu lues obtain ined fr +0.33+1.96 ) × 10 −5 • (J/ ψ→γ X(1835)) ∙ (X(1835) → K S K S η )= (3.31 −0.30−1.29 Light Meson Spectroscopy at BESIII
Anomalous line shape of η′π + π - near 𝐪 𝐪 12 mass threshold in J/ ψ→γη′π + π - • Use 1.09×10 9 J/ ψ events collected by BESIII in 2012 • Two decay modes of η′ • η′→γπ + π - • η′→ηπ + π - , η→γγ • Clear peaks of X(1835), X(2120), X(2370), η c , and a structure near 2.6 GeV/𝑑 2 the η′π + π - li • A sig ignificant dis istortion of f th line shape near th the 𝐪 𝐪 mass th threshold arXiv:1603.0 .09653v2 Light Meson Spectroscopy at BESIII
Anomalous line shape of η′π + π - near 𝐪 𝐪 13 mass threshold in J/ ψ→γη′π + π - arXiv:1603.0 .09653v2 • Simultaneous fits to two η′ decay modes • Simple Breit-Wigner function fails in describing the η′π + π - line shape near the p p mass threshold • Two typical circumstances where an abrupt distortion of a resonance’s line shape shows up • Threshold str tructure caused by th the openin ing of f an addit itional l 𝐪 𝐪 decay mode • Use the Flatté formula for the line shape • In lo log 𝓜 = 630503.3 Interference betw tween tw two resonances • Use coherent sum of two Breit-Wigner amplitudes for the line shape Light Meson Spectroscopy at BESIII
Anomalous line shape of η′π + π - near 𝐪 𝐪 14 mass threshold in J/ ψ→γη′π + π - arXiv:1603.0 .09653v2 • Use the Flatté formula for the line shape 𝜍 𝑝𝑣𝑢 • 𝑈 = 2 𝜍 𝑙 ℳ 2 −𝑡−𝑗 𝑙 𝑙 2 𝑞 2 𝜍 𝑙 ≃ 0 𝑞 • 𝑙 𝑙 2 (𝜍 0 + 2 𝜍 𝑞 𝑞 ) 0 2 is the ratio between the coupling strength to the p 2 • p channel 𝑞 0 𝑞 and the summation of all other channels The state around 1.85 GeV/ c 2 ℳ (MeV/ c 2 ) +121.9 +127.8 1638.0 −121.9 −254.3 2 ((GeV/ c 2 ) 2 ) +35.4 +47.6 0 93.7 −35.4 −43.9 log 𝓜 = 630549.5 2 +0.37 +0.83 2 𝑞 0 2.31 −0.37 −0.60 𝑞 A 𝐪 𝐪 M pole (MeV/ c 2 ) * +15.9 +9.4 𝟑 being 1909.5 −15.9 −27.5 𝟑 Significance of 𝒉 𝐪 𝒉 𝟏 mole lecule- 𝒒 Γ pole (MeV/ c 2 ) * +21.4 +6.1 273.5 −21.4 −64.0 non-zero is larger than 7 σ like sta lik tate? Branching Ratio +0.38 +0.31 ) × 10 −4 (3.93 −0.38 −0.84 X(1920) is needed with 5.7 σ * The pole nearest to the p p mass threshold Light Meson Spectroscopy at BESIII
Anomalous line shape of η′π + π - near 𝐪 𝐪 15 mass threshold in J/ ψ→γη′π + π - arXiv:1603.0 .09653v2 • Use coherent sum of two Breit-Wigner amplitudes 𝛾⋅𝑓 𝑗𝜄 ⋅ 𝜍 𝑝𝑣𝑢 𝜍 𝑝𝑣𝑢 2 −𝑡−𝑗𝑁 1 Γ 1 + • 𝑈 = 2 −𝑡−𝑗𝑁 2 Γ 2 𝑁 1 𝑁 2 X(1835) M (MeV/ c 2 ) +2.4 +17.3 1825.3 −2.4 −2.4 Γ (MeV/ c 2 ) +14.2 +4.6 245.2 −12.6 −9.6 B.R. (constructive interference) +0.17 +0.26 ) × 10 −4 (3.01 −0.17 −0.28 B.R. (destructive interference) +0.21 +0.18 ) × 10 −4 (3.72 −0.21 −0.35 X(1870) log 𝓜 = 630540.3 M (MeV/ c 2 ) +2.2 +2.3 1870.2 −2.3 −0.7 A 𝐪 𝐪 Significance of X(1870) Γ (MeV/ c 2 ) +7.1 +2.1 13.0 −5.5 −3.8 bound sta tate? is larger than 7 σ B.R. (constructive interference) +0.12 +0.43 ) × 10 −7 (2.03 −0.12 −0.70 B.R. (destructive interference) +0.09 +0.49 ) × 10 −5 X(1920) is not significant (1.57 −0.09 −0.86 Light Meson Spectroscopy at BESIII
Anomalous line shape of η′π + π - near 𝐪 𝐪 16 mass threshold in J/ ψ→γη′π + π - • A significant distortion of the η′π + π - line shape near the p p mass threshold is observed in J/ ψ→γη′π + π - • Simple Breit-Wigner function fails in describing the line shape near the p p mass threshold • Two models have been used • MODEL I: threshold structure due to the opening of the p p decay mode • Use the Flatté formula • Strong 𝐪 𝐪 coupling, with significance larger than 7 σ +𝟐𝟔.𝟘 +𝟘.𝟓 MeV/ c 2 • M pole = 𝟐𝟘𝟏𝟘. 𝟔 −𝟐𝟔.𝟘 −𝟑𝟖.𝟔 +𝟑𝟐.𝟓 +𝟕.𝟐 MeV/ c 2 • 𝚫 pole = 𝟑𝟖𝟒. 𝟔 −𝟑𝟐.𝟓 −𝟕𝟓.𝟏 • MODEL II: interference between two resonances • Use coherent sum of two Breit-Wigner amplitudes • A narrow resonance below the 𝐪 𝐪 mass threshold, with significance larger than 7 σ +𝟑.𝟑 +𝟑.𝟒 MeV/ c 2 • M = 𝟐𝟗𝟖𝟏. 𝟑 −𝟑.𝟒 −𝟏.𝟖 +𝟖.𝟐 +𝟑.𝟐 MeV/ c 2 • 𝚫 = = 𝟐𝟒. 𝟏 −𝟔.𝟔 −𝟒.𝟗 Light Meson Spectroscopy at BESIII
Anomalous line shape of η′π + π - near 𝐪 𝐪 17 mass threshold in J/ ψ→γη′π + π - • Both models fit the data well with almost equally good quality • Cannot distinguish them with current data • Suggest the existence of a state, either a broad state with strong couplings to 𝐪 𝐪 , or a narrow state just below the 𝐪 𝐪 mass threshold • Support the existence of a 𝐪 𝐪 molecule-like state or bound state • To elucidate further the nature of the state • More J/ ψ data • Study line shapes in other decay modes • J/ ψ→γ p p • J/ ψ→γ K S K S η • … Light Meson Spectroscopy at BESIII
18 Structures around 1.8 𝐇𝐟𝐖/𝒅 𝟑 3( π + π - ) J/ J/ ψ→γ 3( Phys. . Rev. . D 88, , 091502(R) (2013) J PC of X(1840) and X(1870): PWA Search and study those states in more channels J/ ψ→ωηπ + π - J/ Phys. . Rev. . Lett tt. . 107, , 182001 (2011) Light Meson Spectroscopy at BESIII
Recommend
More recommend
