Charmonium Radiative Transitions

Transcription

1 Charmonium Radiative Transitions Jielei Zhang Institute of High Energy of Physics (for the BESIII collaboration) QWG2016 1

2 What to measure What have done with old datasets ψ(3686) 2009 What will do with new datasets ψ(3686) J/ψ data 5 fb -1 data above 4.0 GeV QWG2016 2

3 What to measure Γ(J/ψ γη c ) PDG2014: 1.58 ± 0.37 kev Error is large η c lineshape Lattice QCD 2.49 ± 0.19 kev PRD 86, large difference among the measurements Interference common phase in ψ 3686 γη c? B(ψ(3686) γη c (2S)) 7 ± 2 ± (PDG2014), The systematic error dominated by B(η c 2S KKπ) B(ψ(3686) γη c ) 0.34 ± (PDG2014) QWG2016 3

4 What have done with old data η c line-shape ψ(3686) M1 transition h c E1 transition M1 transition ψ(3686) γη c (2S) first observation ψ 3686 γγj/ψ 106 M ψ(3686) events QWG2016 4

5 PRL 108, Simultaneous fit with modified Breit-Wigner (hindered M1) Significance of interference is 15σ (may partly explain the discrepancy among measurements) QWG2016 5

6 PDG 12 ave. PDG 14 ave. PDG 12 ave. PDG 14 ave. Suggest a common phase in all the modes. QWG2016 6

7 h c E1 transition to η c Huge interference in ψ 3686 γη c The η c amplitude in h c decays is larger than in ψ(3686) decays Sum of 16 modes PRD 86, Weaker interference in h c γη c Easier and better than ψ 3686 γη c Signal: E γ 3 BW m f d E γ R i (m) Energy of photon in rest frame of h c For convergence Resolution for ith mode M η c = ± 1.16 ± 0.52 MeV/c 2 Γ η c = 36.4 ± 3.2 ± 1.7 MeV QWG2016 7

8 The first observation of the M1 transition ψ 3686 γη c (2S) PRL 109, Significance larger than 10σ M ηc 2S = ± 2.9 ± 1.6 MeV/c 2 Γ ηc 2S = 16.9 ± 6.4 ± 4.8 MeV B ψ 3686 γη c (2S) = 6.8 ± 1.1 ± Systematic error is dominated by B(η c 2S KKπ) QWG2016 8

9 Direct two-photon transition ψ 3686 γγj/ψ Sensitive to the coupling between c c and D D meson pairs PRL 109, E1 transition ψ 3686 γχ cj γγj/ψ B( 10 4 ) γγj/ψ ± σ γ γj/ψ χc0 γ γj/ψ χc1 γ γj/ψ χc ± 0.3 ± ± 0.9 ± ± 0.7 ± 10.2 QWG2016 9

10 What we do with the new data ψ(3686) ψ(3686) J/ψ data 5 fb -1 data above 4.0 GeV QWG

11 Γ(J/ψ/ψ(3686) γη c ) η c lineshape Inclusive Difficult to deal with the interference Exclusive Seems simpler than inclusive method Need to know a branching ratio in high precision How? Use h c γη c inclusive and exclusive Seems small interference QWG

12 ψ 3686 π 0 h c, h c γη c PRL 104, ψ(3686) events E1 tagged Absolute branching fraction B h c γη c = 54.3 ± 6.7 ± 5.2 % dominated by BKG shape Will be improved QWG

13 Now ψ times of old datasets. And 5 fb -1 data above 4.0 GeV ππh c PRL 111, Together we have 9 times h c signals. Measure B(h c γη c ) using inclusive method. B(η c X) for 16 exclusive modes. More precise η c lineshape. B η c K 0 S K ± π = 2.60 ± 0.29(stat) ± 0.34 ± 0.25(syst) % PRD 86, dominant systematic errors reduce to one-third Due to B ψ 3686 π 0 h c B(h c γη c ), Will be improved 2 times with part of data π + π h c N(ψ(3686)): 4% Tracking: 8% Photon: 3% Bkg shape: 4.7% Kinematic fit: 6.8% B J/ψ/ψ 3686 γη c using exclusive method. PWA? Understand the difference. 1% 4% More reliable MC QWG

14 Γ(ψ(3686) γη c (2S)) η c (2S) lineshape Inclusive Seems difficult at BESIII, 50 MeV photon Exclusive B(η c 2S X), error > 60% PDG 2014 Difficult to measure B(η c 2S X) at BESIII Hope this work will be done at Belle or Babar. Try to search other transitions of the η c (2S) η c 2S π + π η c η c 2S γj/ψ η c 2S γh c QWG

15 Summary The η c parameters are measured through M1 transition of ψ(3686) and E1 transition of h c. The most accurate measurement. First observation of M1 transition ψ 3686 γη c (2S). First observation of two-photon transition ψ 3686 γγj/ψ. We can measure Γ(J/ψ/ψ 3686 γη c ) more precisely with new data. More results will come out. QWG

16 Back-up QWG

17 Large uncertainties compared to other charmonium states. 1S Hyperfine splitting. QWG

18 resolution Interference phase Non-resonant component Mass-dependent efficiency Hindered M1 transition QWG

19 QWG

20 PRD 86, QWG

21 η c 2S signal: E γ 3 BW m f d E γ ε m G(δm, σ) M1 transition For convergence Mass shift and detector resolution, fixed to linear extrapolation from γχ cj χ cj : MC shape Gaussian, fixed Background: e + e KKπ(γ ISR/FSR ), MC shape, normalized to the measurements with data e + e π 0 KKπ, Novosibirsk function, measured with data and fixed ωk + K for K + K π 0 mode, double Gaussian, measured with data and fixed. QWG

22 The first observation of the M1 transition ψ 3686 γη c (2S) First observed by Belle in the process B + K ± η c 2S, η c 2S K S 0 K ± π, confirmed in two-photon production and double-charmonium production. Experimental challenge: search for real photon ~50MeV. The branching ratio B ψ 3686 γη c 2S is predicted to be in Chance with ψ(3686) data at BESIII. Two modes: η c 2S K S 0 K ± π, K + K π 0 QWG

23 Lightest charmonium state above open charm threshold, assigned to be a dominant 1 3 D 1 with a small 2 3 S 1 admixture. Non-D D branching fraction, (14.7 ± 3.2)% by BESIII, ( 3.3 ± )% by CLEO Exclusive modes: Hadronic transition: ππj/ψ, ηj/ψ, E1 radiative transition γχ cj (J = 0,1) What about γη c /η c 2S? B ψ 3770 γη c = , B ψ 3770 γη c 2S = Consider the intermediate meson loop (IML). (PRD 84,074005) QWG

24 Background: e + e π 0 K S 0 K ± π, measured with data and fixed e + e γ ISR /γ FSR K S 0 K ± π, fixed, using Born cross section of e + e K S 0 K ± π by BABAR. Tail of the ψ(3686), including γ ISR ψ 3686, ψ 3686 γx b N ψ 3686 = σ s L ε B σ s = 0 x cutw s, x BW s x F x s x dx Relativistic ISR γ-emission probability Phase space factor QWG