Zahra Haddadi, KVI-CART (University of Groningen) for the BESIII collaboration 1 Sep EUNPC 2015, Groningen

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1 Zahra Haddadi, KVI-CART (University of Groningen) for the BESIII collaboration 1 Sep EUNPC 2015, Groningen

2 Outline: Charmonium spectroscopy spin-singlet states puzzle BESIII & precision measurements

1 QCD bound systems QCD: Is well tested at high

In low-energy region, many aspects are not

Charmonium: The mesonic bound state of cc.

4 GeV : Non-relativistic potential model.

3 1 QCD bound systems QCD: Is well tested at high energies. In low-energy region, many aspects are not understood. Charmonium: The mesonic bound state of cc. Simplest bound state of QCD. m c 1.4 GeV : Non-relativistic potential model. Charmonium spectroscopy: Precise measurements on basic properties of known states. Clean system to study non-perturbative QCD dynamics. 1 fm C C

4 2 Charmonium spectrum Potential model describes spectrum very well; Below the open-charm threshold Narrow states Good agreement between theory and experiment XYZ states: Talk by Landdiao Liu Hadron Structure, Spectroscopy and dynamics II

5 2 Charmonium spectrum Vsdcvsdhsd chv,ejsd Db cb dcvm Mndsb cmnd b Dnbcv N bdfvcjb Nb dcvkjvfdbk hc csd Potential model describes spectrum very well; Below the open-charm threshold Narrow states Good agreement between theory and experiment

6 2 Charmonium spectrum Vsdcvsdhsd chv,ejsd Db cb dcvm Mndsb cmnd b Dnbcv N bdfvcjb Nb dcvkjvfdbk hc csd Potential model describes spectrum very well; Experiment Lattice QCD Phys. Rev. D 87, (2013)

7 2 Charmonium spectrum Vsdcvsdhsd chv,ejsd Db cb dcvm Mndsb cmnd b Dnbcv N bdfvcjb Nb dcvkjvfdbk hc csd Potential model describes spectrum very well; Experiment Lattice QCD Phys. Rev. D 87, (2013)

8 Mass & Width of the ground state: η c Mass Width radiative transition γ γ processes, pp, B Kη c 3

9 Mass & width of the ground state: η c Mass Width After 30 years: We still have problem with the basic properties of η c. radiative transition γ γ processes, pp, B Kη c 3

10 η c studies from e + e - annihilation η c ψ h c Open-charm χ χ c2 c1 ψˊ decay & e + e - annihilation: clean and simple environment 3.4 χ c0 3.2 J/ψ 3.0 η c 2.8 L = J PC =

11 η c studies from e + e - annihilation η c γ ψ J/ψ h c Open-charm χ χ c2 c1 χ c0 ψˊ decay & e + e - annihilation: clean and simple environment η c : Mass and width and lineshape ψˊ γη c suppressed M1 transition! 3.0 η c 2.8 L = J PC =

12 η c studies from e + e - annihilation η c η c γ ψ γ J/ψ π h c Open-charm χ χ c2 c1 χ c0 ψˊ decay & e + e - annihilation: clean and simple environment η c : Mass and width and lineshape ψˊ γη c suppressed M1 transition! ψˊ π h c, h c γη c Isospin forbidden! 2.8 L = J PC =

η c studies from e + e - annihilation 3.8 3.6 3.4 3.2 3.0 2.

13 η c studies from e + e - annihilation η c η c γ ψ J/ψ γ γ π h c Open-charm χ c0 χ c1 χ c2 L = J PC = ψˊ decay & e + e - annihilation: clean and simple environment η c : Mass, width and lineshape ψˊ γη c Suppressed M1 transition! ψˊ π h c, h c γη c Isospin forbidden! J/ψ γη c Suppressed M1 transition! 4

14 5 BESIII: BEijing Linac Spectrometer : 200 m (BES) Magnet yoke SC magnet : 1T BES III Detector e + IP e - Time of Flight Storage ring : 240 m Main Drift Chamber Electromagnetic Calorimeter

15 5 BESIII: BEijing Spectrometer (BES) Magnet Yoke SC magnet : 1T Collected data by BESIII Time of flight e + e - By the end of 2012 : 450 ˣ 10 6 ψˊ Main drift chamber Electromagnetic Calorimeter We are well equipped for measuring these transitions.

16 ψˊ γη c η c γ ψ h c η c J/ψ exclusive decay modes 6

BES III (2012) 106 M ψˊ ψˊ γη c, η c 2K2ππ 1 of 6 decay modes Obviously asymmetric lineshape: Long tail on the low mass side. The signal drops rapidly on the high-mass side.

17 BES III (2012) 106 M ψˊ ψˊ γη c, η c 2K2ππ 1 of 6 decay modes Obviously asymmetric lineshape: Long tail on the low mass side. The signal drops rapidly on the high-mass side. Interference between η c and nonresonant background is significant: Interference was found to be 15σ. Simultaneous fit to 6 modes Phases are consistent within 3σ M ηc = ± 0.6 ± 0.6 MeV/c 2 Γ ηc = 32.0 ± 1.2 ±1.0 MeV PRL 108, (2012) 7

18 BES III (2012) M ηc = ± 0.6 ± 0.6 MeV/c 2 BESIII Lattice 2012 ΔM hf (1S) = ± 0.8 MeV/c 2 Agrees well with recent lattice computations! arxiv:

19 BES III (2012) M ηc = ± 0.6 ± 0.6 MeV/c 2 BESIII Question : Can we see this distortion in the other radiative transition like h c γη c Lattice 2012 ΔM hf (1S) = ± 0.8 MeV/c 2 Agrees well with recent lattice computations! arxiv:

9 ψˊ π h c, h c γη c 3.8 3.6 η c ψ π h c 3.

20 9 ψˊ π h c, h c γη c η c ψ π h c γ J/ψ 3.0 η c exclusive decay modes

described by a simple Breit-Wigner M ηc = 2984.40 ± 1.16 ± 0.52 MeV/c 2 Γ ηc = 36.4 ± 3.2 ± 1.

21 10 η c lineshape in E1 transition h c γη c Sum of 16 η c decay modes 106 M ψˊ B(ψˊ γη c ) = 0.3% B(h c γη c ) = 50% Weaker interference Larger amplitude Background subtracted 106 M ψˊ Signal can be described by a simple Breit-Wigner M ηc = ± 1.16 ± 0.52 MeV/c 2 Γ ηc = 36.4 ± 3.2 ± 1.7 MeV PRD 86, compared with the result from ψˊ γη c : M ηc = ± 0.6 ± 0.6 MeV/c 2 Γ ηc = 32.0 ± 1.2 ±1.0 MeV Statistic error is dominated!

22 11 Comparison of the latest results: Understanding the nature of interference is the key point! Ke Li

23 11 Comparison of the latest results: Ongoing analysis related to η c : ψˊ γη c : 450ˣ10 6 ψˊ h c γη c : 450ˣ10 6 ψˊ Ј/ψ γη c : 1ˣ10 9 J/ψ Understanding the nature of interference is the key point! Ke Li

24 12 ψˊ γη cˊ η c γ ψ h c 3.4 KsKπ KKπ 3.2 J/ψ 3.0 η c 2.8

First observation of the ψˊ γηˊ Experimental challenge : search for photon of 50 MeV. Found no signal : CLEOc (25M ψˊ) M ηcˊ = 3637.6 ± 2.9 ± 1.6 MeV/c 2 Γ ηcˊ = 16.

25 First observation of the ψˊ γηˊ Experimental challenge : search for photon of 50 MeV. Found no signal : CLEOc (25M ψˊ) M ηcˊ = ± 2.9 ± 1.6 MeV/c 2 Γ ηcˊ = 16.9 ± 6.4 ± 4.8 MeV PRL 109, (2012) Signal : Significance is larger than 10σ B( ψˊ γη cˊ) = (6.8 ± 1.1 ± 4.5)ˣ10-4 CLEO-c < (7.6 ± 1.1) ˣ10-4 PRD81, (2012) 13

26 14 Comparison in different production mechanisms: Fhnmcn mn mcn bv BESIII : PRD (2013) BESIII : PRL (2012) BaBar : PRD (2011) Belle : PLB (2011) BaBar : PRD (2005)

27 14 Comparison in different production mechanisms: Fhnmcn mn mcn bv BESIII : PRD (2013) BESIII : PRL (2012) BaBar : PRD (2011) Belle : PLB (2011) BaBar : PRD (2005)

28 14 Comparison in different production mechanisms: Fhnmcn mn mcn bv BESIII will be able to improve mass and width values with more statistic. BESIII : PRD (2013) BESIII : PRL (2012) BaBar : PRD (2011) Belle : PLB (2011) BaBar : PRD (2005)

15 Radiative partial decay widths: Long-standing puzzle on the radiative transition rates of J/ψ and ψˊ γη c : Initial meson J/ψ ψˊ ψˊ Final meson η c η c η cˊ 2.9 9.7 0.21 1.58 ± 0.37 PDG2014 0.

29 15 Radiative partial decay widths: Long-standing puzzle on the radiative transition rates of J/ψ and ψˊ γη c : Initial meson J/ψ ψˊ ψˊ Final meson η c η c η cˊ ± 0.37 PDG ± 0.14 CLEO-c ± ± BESIII 2.51 ± ± arxiv: v2 Finding a procedure to understand interference seems crucial to be able to extract the exact values.

Outlook precise η c and η cˊ studies was done at BESIII: ψˊ γη c : precise measurement on basic properties like mass and width improving the hyperfine splitting value considering the interference for

30 Outlook precise η c and η cˊ studies was done at BESIII: ψˊ γη c : precise measurement on basic properties like mass and width improving the hyperfine splitting value considering the interference for the first time ψˊ π h c, h c γη c interference free lab for η c lineshape promising channel to measure the basic properties of η c ψˊ γη cˊ first observation even with 106M ψˊ Nature of interference : More interesting result will come very soon! 16

Charmonium Radiative Transitions

Charmonium Radiative Transitions Jielei Zhang Institute of High Energy of Physics (for the BESIII collaboration) QWG2016 1 What to measure What have done with old datasets 1.06 10 8 ψ(3686) 2009 What will