1. Recent XYZ results from BESIII
Jingzhi Zhang (IHEP)
XYZ seminar

2. In 2013-2014, 4.6 fb-1 at 𝑺 >3.8 GeV collected
At BESIII, intensive XYZ studies start from:
In , 4.6 fb-1 at 𝑺 >3.8 GeV collected
Fasten your seatbelt, let’s begin

3. Zc Zc±(3900) in e+e-p+p-J/y PRL 110,252001
Zc0(3900) in e+e-p0p0J/y paper in n preparation
ZC±(4020) in e+e-p+p-hc PRL, 110,
Zc0(4020) in e+e-p0p0hc PRL, 113,212002
Zc±(3885) in e+e-p(D*D)± PRL,112,
single tag / double tag
Zc±(4025) in e+e-p(D*D*)± PRL,112,
Search for Zclight hadron prepare for publication

4. 1. Observation of Zc±(3900)
PRL

5. CLEOc M = 388551 MeV  = 34124 MeV 81  20 events 6.1
M(π+π−J/ψ) = 4.17
M(π+π−J/ψ) = 4.26
(4.15 <M(π+π−J/ψ) < 4.45 )
CLEOc
PLB 727, 366 (586 pb-1)
PRL,111, (967 fb-1)
PRL,110,252001(525 pb-1)
M = 388551 MeV
 = 34124 MeV
81  20 events
6.1
M = 6.64.5 MeV
 = 632426 MeV
159  49 events
>5.2
M = 3.64.9 MeV
 = 461020 MeV
307  48 events
>8

6. 2. Observation of Zc0(3900) in e+e- p0p0J/y
Oberved Zc0(3900) signal.
Simultaneous fit is performed to the π0J/ψ spectra at the ten energy points.

7. Simultaneous fit to the M(π0J/ψ) for 4230, 4260, 4360 MeV.
Mass = ±2.3 MeV
Width = 29.6±8.2 MeV
Significance = 10.4 s
Simultaneous fit to the M(π0J/ψ) for 4230, 4260, 4360 MeV.
Signal: BW  3-Gaussian
Bg: Argus function
For detector
resolution

8. e+e- p+p-hc Significant p+p-hc production
reported by CLEO at MeV
Correlated with Y(4260)?
hc is spin singlet (s=0) state;
J/y has spin=1
Explore p+p- transitions to hc as a function of E cm
Search for p±hc states
PRL,107,041803

9. 3. Observation of Zc±(4020)p±hc in e+e- p+p-hc
No sharp structure in p+p-hc cross section;
correlation with Y(4260) is unclear
Narrow p±hc structure observed
M[Zc(4020)] =4023 ±3 MeV
G[Zc(4020)] = 8±4 MeV
No significant evidence for
Zc(3900) p±hc
at Ecm =4260 MeV
s(e+e- p Zc(3900)  p+ p-hc) <10 pb
s(e+e- p Zc(3900)  p+ p-J/y) = 13± 5 pb
[ PRL, 110, ]

10. e+e- p0p0hc hcghc, hc-->hadrons [16 exclusive decay modes]
pp, p+p-K+K-, p+p-pp, 2(K+K-), 2(p+p-), 3(p+p-), 2(p+p-)K+K-, KS0K+p-+c.c.,
KS0K+p-p+p-+c.c., K+K-p0, ppp0, K+K-h, p+p-h, p+p-p0p0, 2(p+p-)h, 2(p+p-p0),
~40% of hc decay _ _ _
Observe
p+p-hc
The Ecms = 4.23, 4.26, 4.36 GeV (~2.5fb-1)
PRL. 113,

11. 4. Observation of Zc0(4020)p0hc in e+e- p0p0hc
The s(p0p0hc ) is consistent to be half of s(p+p-hc) within 2s
s(p0p0hc )/s(p+p-hc) =0.63±0.9
Narrow p±hc structure observed
M[Zc(4020)] =4023.3±2.2±3.8 MeV
G[Zc(4020)] is fixed at 8 MeV
No significant evidence for
Zc(3900) p0hc
Very likely the neutral isospin partner of the charged Zc(4020)

12. 5. Observation of Zc± (3885)  (DD*) ± via e+e-  p±(DD*)∓
Single-tag technique
Tag p-D+
Tag p+D0 1- 1+ 0-
Using 525 pb-1 taken at Ecms = 4.26 GeV
M[Zc(3885)] = 3884 ±4 MeV; G[Zc(3885)] =25±11MeV
The p angular distribution establishes JP= 1+
If Zc(3885) is Zc(3900) , _
(𝑍𝑐(3900)→𝐷𝐷∗) (𝑍𝑐 3900 → 𝐽/ ) = 6.2 ± 2.9

13. Double-tag Simultaneous Fit
𝑒 + 𝑒 − →𝜋 + 𝐷 0 𝐷 ∗−
𝑒 + 𝑒 − →𝜋 + 𝐷 − 𝐷 ∗0
1090
Signal: mass dependent width Breit-Wigner (BW)
Background: Shape from PHSP MC
1090
BW i m D D ∗ ∝ m D D ∗ Γ i m Z c 2 − m D D ∗ 2 −i 1 2 m Z c ( Γ 1 + Γ 2 ) ,
Where Γ i = Γ Z c q i ∗ q i l+1 ( m Z c m D D ∗ ) ( f l ( q i ∗ ) f l ( q i 0 ) ) 2 ,
the subscript i denotes the 𝑒 + 𝑒 − →𝜋 + 𝐷 0 𝐷 ∗− (i =1)
and 𝑒 + 𝑒 − →𝜋 + 𝐷 − 𝐷 ∗0 (i = 2) processes.
BESIII preliminary
827
827

14. Angular Distribution BESIII preliminary BESIII preliminary
𝑒 + 𝑒 − →𝜋 + 𝐷 0 𝐷 ∗−
𝑒 + 𝑒 − →𝜋 + 𝐷 − 𝐷 ∗0
BESIII preliminary
BESIII preliminary
Dots with error bars: Combined data at 𝒔 =4.23GeV and at 𝒔 =4.26GeV;
Solid Lines: Fits to the data using 𝐽 𝑃 = 1 + ;
Dashed curves: Fits to the data using 𝐽 𝑃 = 0 − ;
Dotted curves: Fits to the data using 𝐽 𝑃 = 1 − ;
The data agrees well with 𝑱 𝑷 = 𝟏 + and disagrees with 𝑱 𝑷 = 𝟎 − / 𝟏 − .

15. BESIII previous observation
Double D tags
BESIII previous observation
𝑀 pole (MeV/ 𝑐 2 )
3884.3±1.2 𝑠𝑡𝑎𝑡. ±1.5 𝑠𝑦𝑠𝑡.
3883.9±1.5 𝑠𝑡𝑎𝑡. ±4.2 𝑠𝑦𝑠𝑡.
Γ pole (MeV)
23.8±2.1 𝑠𝑡𝑎𝑡. ±2.6 𝑠𝑦𝑠𝑡.
24.8±3.3 𝑠𝑡𝑎𝑡. ±11.0 𝑠𝑦𝑠𝑡.
𝜎(𝑒 + 𝑒 − → 𝜋 ± 𝑍 𝑐 (3885) ∓ )
×𝐵 𝑍 𝑐 (3885) ∓ → (𝐷 𝐷 ∗ ) ∓ 𝑍 𝑐 (3885) ∓ → (𝐷 𝐷 ∗ ) ∓ (pb)
PRL 112, (2014)
The Results are consistent with but more precise than BESIII previous observation.

16. 6. Observation of Zc±(4020) ( 𝐷 ∗ 𝐷 ∗ )± in e+e-→p±( 𝐷 ∗ 𝐷 ∗ )∓ at 𝑠 =4.26GeV
Deviation from phase spde decay
Could de described by a charged state decaying to 𝐷 ∗ 𝐷 ∗
M[Zc(4025)] =4026 ±3 MeV
G[Zc(4025)] = 25±6 MeV
Compare to p±hc structure
M[Zc(4020)] =4023 ±3 MeV
G[Zc(4020)] = 8±4 MeV0
If Zc(4025) ± is the Zc(4020),
PRL,112,132001
(𝑍𝑐(4020)→ 𝐷 ∗ 𝐷 ∗ ) (𝑍𝑐 4020 →ℎ𝑐) = 12±5

17. Y(4360) p
Y(4260)
Zc±/0(4020)
y(3S)
p±/0
Zc±/0(3900)
D*D*
p±/0
DD*

18. 7. No Zcwπ signals found in e+e- wπ π
[BESIII Preliminary]
[BESIII Preliminary]
Fitting with acceptance weighted S-wave BW folded with Gaussian + ARGUS BGNo interference is considered
1094 pb-1 @4230
827
The non-observation of Zc ω π (a typical decay mode of a 1+ resonance) may indicate that the annihilation of ccbar in Zc is suppressed.

19. u c c d
Charged Zc+ charmonium-like state is smoking guns for exotic state with at least four quarks.
Many proposals
Hadronic molecules,
arXiv: , ,
Tetraquark states
arXiv: ,
arXiv: ,
Meson loop (arXiv: )
ISPE model (arXiv: )
Smoking guns for
4-quark states

20. X
Y(4260) gX(3872) RPL,112,092001
X(3823) (𝝍( 𝟏 𝟑 𝑫 𝟐 )) arXiv:
Some slides from Li Ke

21. e+e- gX(3872)
Search for gX(3872) with X(3872) ppJ/y at Ecm=4.23, 4.26 and 4.36 GeV
Left: summed over all data X(3872) significance = 6.3 s
Production in Y(4260) decay suggestive, but not conclusive
If from Y(4260)
𝐵(𝑌 4260 → g𝑋 3872 ) 𝐵(𝑌 4260 →p+−J/)  0.1
[BESIII RPL112,092001]

22. 𝒆 + 𝒆 − → 𝝅 + 𝝅 − 𝑿, 𝑿→𝜸 𝝌 𝒄𝑱 , 𝝌 𝒄𝑱 →𝜸𝑱/𝝍
𝒆 + 𝒆 − → 𝝅 + 𝝅 − 𝑿, 𝑿→𝜸 𝝌 𝒄𝑱 , 𝝌 𝒄𝑱 →𝜸𝑱/𝝍
4.230 GeV
4.260 GeV
4.360 GeV
4.420 GeV
4.600 GeV
Sum up
arXiv:

23. Simultaneous fit of 𝛾 𝜒 𝑐1 (left) and 𝛾 𝜒 𝑐2 (right) events
𝑀 𝑋 = ±1.3(𝑠𝑡𝑎𝑡)±0.7(𝑠𝑦𝑠𝑡) MeV/ 𝑐 2
Γ 𝑋 <16 MeV at 90% C.L. consist with Belle
D-wave is expected.
Limited statistics
limited informations

24. X-section 𝝈 𝒆 + 𝒆 − → 𝝅 + 𝝅 − 𝑿 𝟑𝟖𝟐𝟑 ⋅𝓑(𝑿 𝟑𝟖𝟐𝟑 →𝜸 𝝌 𝒄𝟏 )
𝜎 𝑒 + 𝑒 − → 𝜋 + 𝜋 − 𝑋 ⋅ℬ(𝑋 3823 →𝛾 𝜒 𝑐1 ) 𝜎 𝑒 + 𝑒 − → 𝜋 + 𝜋 − 𝜓 ′ ⋅ℬ( 𝜓 ′ →𝛾 𝜒 𝑐1 )
= 0.20 − (4.36 GeV)
= 0.39 − (4.42 GeV)
ℬ 𝑋 3823 →𝛾 𝜒 𝑐2 ℬ(𝑋 3823 →𝛾 𝜒 𝑐1 )
<0.42 at 90% C.L.
≈0.24 (PRD 55,4001)

25. Y Cross section of 𝒆 + 𝒆 − →𝝅𝝅𝑱/𝝍 ( 𝒉 𝒄 ) e+e-  wcc0 PRL,114,092003
e+e-  h J/y arXiv:
e+e-  h’J/y preliminary
Search for Y(4140)f J/y via e+e-  g f J/y, f  K+K- /KSKL/p+p-p PRD 92,032002
e+e-  g ccJ at 𝒔 > 4GeV CPC, 39(4) (2015)
Search for the isospin violating decay Y(4260)J/yηp arXiv:
Borrowed slides from Li Ke

26. 1. Study the x-section of e+e-ppJ/y, pphc , DDp , DS(*)DS(*)
The analyses are in progress.

27. 2. Study of 𝝎 𝝌 𝒄𝟎 from 4.21 to 4.42 GeV 𝜔→ 𝜋 + 𝜋 − 𝜋 0
𝜔→ 𝜋 + 𝜋 − 𝜋 0
𝜒 𝑐0 → 𝐾 + 𝐾 − / 𝜋 + 𝜋 −
4.26 GeV
4.26 GeV

28. Simultaneous unbinned LH fit to 𝜋 + 𝜋 − / 𝐾 + 𝐾 −
4.23 GeV
4.26 GeV

29. Fit to 𝝈( 𝒆 + 𝒆 − →𝝎 𝝌 𝒄𝟎 ) Phase-space modified Breit-Wigner
with significance >9𝜎
Γ 𝑒𝑒 ℬ 𝜔 𝜒 𝑐0 = 2.7±0.5 eV
𝑀 𝑌 = 4230±8 MeV/ 𝑐 2
Γ 𝑡 =(38±12) MeV
Not consistent with Y(4260)𝜋𝜋𝐽/𝜓

30. 3. Cross section of 𝐞 + 𝒆 − →𝜼𝑱/𝝍
4.23 GeV
𝜂→𝛾𝛾
𝐽/𝜓→ 𝜇 + 𝜇 − / 𝑒 + 𝑒 −
4.26 GeV

31. 𝒆 + 𝒆 − →𝜼𝑱/𝝍
𝒆 + 𝒆 − →𝝅 𝟎 𝑱/𝝍
No signal
No signal

32. Born cross section of 𝒆 + 𝒆 − →𝜼𝑱/𝝍?

33. 4. Cross section of 𝐞 + 𝒆 − →𝜼′𝑱/𝝍
Preliminary
4.23GeV
4.26GeV
Simultaneous fit to 𝜂 ′ →𝛾 𝜋 + 𝜋 − /𝜂 𝜋 + 𝜋 − , 𝐽/𝜓→ 𝜇 + 𝜇 − / 𝑒 + 𝑒 −

34. The cross-section

35. 5. Search for Y(4140)f J/y f  K+K-
PRD 92,032002
e+e-  g f J/y; J/y e+e-/m+m-
f  K+K-
Partial reconstruction, only require one K
f  KSKL
Partial reconstruction, only require KS; the KL not reconstructed.
fp+p-p0
Full reconstruction.

37. Combine 6 modes ( 3 f modes  2 J/y modes)
eff. curve
Sum of all data sets

38. No Y(4140) signal found @ BESIII
Set upper limit at the 90% CL. for
𝜎 𝐵 ×ℬ= 𝜎 𝐵 𝑒 + 𝑒 − →𝛾𝑌 ×ℬ(𝑌 4140 →𝜙𝐽/𝜓)
𝑠 (GeV/ 𝑐 2 )
Luminosity (pb-1)
(1+𝛿)
𝜎 𝐵 ×ℬ
4.23
1094
0.840
<0.35
4.26
827
0.847
<0.28
4.36
545
0.944
<0.33
Systematic error included
Compared with the 𝐗(𝟑𝟖𝟕𝟐) product ion
𝜎 𝐵 𝑒 + 𝑒 − →𝛾𝑋 ×ℬ(𝑋 3872 → 𝜋 + 𝜋 − 𝐽/𝜓)
Take ℬ 𝑋 3872 → 𝜋 + 𝜋 − 𝐽/𝜓 = 5%. arXiv:
And ℬ(𝑌 4140 →𝜙𝐽/𝜓) = 30%, molecular calculation, PRD 80,
𝜎 𝐵 ( 𝑒 + 𝑒 − →𝛾𝑌 𝜎 𝑒 + 𝑒 − →𝛾𝑋 ≤0.1 at 𝑠 =4.23 and 4.26 GeV.

39. 6. Evidence for e+e−gccJ fit to M(gJ/y)
Signal: a double-Gaussian with shape parameters determined from MC at 4260 MeV
Background: radiative dimu MC shape
Data:
limited statistics
is not consistent with being background
4009
4230
4260
4360

40. e+e−gccJ the statistical significance is 1.2σ, 3.0σ, 3.4σ for
A simultaneous fit to M(gJ/y) at 4 CME points with assuming the production s(e+e− gccJ ) at different 𝑠 follows the lineshape of Y(4260)
Fit to M(gJ/y) for summing the events in the 4 CME points
cc2
cc1
cc0
cc2
cc1
the statistical significance
is 1.2σ, 3.0σ, 3.4σ for
cc0, cc1, cc2 respectively.
the stat. significance
is 0, 2.4, 4.0 s for
cc0, cc1, cc2 , respectively

41. The measured Born corss-section s(e+e− gccJ )∎ ∎ ∎ s s s ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ 𝑠 𝑠 𝑠
The upper limits on the cross section of e+e-  gccJ
are compatible with the theoretical predication.
Ref: arXiv:

42. 8. Search for Y(4260)J/yηp0 yields no signal
Scatter Plot of M(gg) and M(l+l-) (combination closest to p0 and η)
arXiv:

43. unanswered questions FROM Changzheng
pi+pi-J/psi, there is dip at 4.17 GeV and a sharp increase at 4.23 GeV, we can know better where is the turning point;
omega chi_c0, we are lack of data points close to threshold for claiming a narrow structure;
KKJ/psi, seems there is a narrow structure at around 4.23 GeV;
pi+pi-hc, there is a narrow structure at around 4.23 GeV;
eta J/psi, line shape different from pi+pi-J/psi, peak at 4.23 GeV, but no data point on the left side;
Zc(3900) production vs. Ecm, is the line shape of pi Zc the same as pi pi J/psi?
eta hc, is there a structure at ~4.23 GeV?
eta'J/psi close to threshold
Are gamma chi_cJ signals from psi(4160) or Y(4260) or something else?
Is gamma X(3872) from Y(4260)
Search for F-wave states via psi(4160) decays?
Gamma chi_c(2P), gamma XYZ(3940), X(3915) from psi(4160)? ….
FROM Changzheng

44. Benefits from the 4.6 fb-1 data The data have attracted many colleagues from every physics group within BESIII (charmonium, light hadron, charm, QCD); Yielded very interesting results; Bring (experimentalist + theorist) together to have disccussions What’s the next? We deadly need more data at 𝒔 > 4 GeV high statistical scan: ~10 MeV Step ~500 pb-1/each

45. Summary
Have listed the recent results on XYZ studies; some (not released) still in working progress.
A few observations (7 PRL + x PRD + x talks….);
seems lots more unanswered questions.
A high statistical scan is desirable.

46. Y(4360) p
Y(4260) g
Zc±(4020)
y(3S) p
Zc±(3900)
3872 g
D*D*
DD*

47. The Zc states presented in last workshop
Zc(3900) M(+J/)
Zc(4020) M(+hc)
PRL,111,252002
PRL, 110,
Zc(3885) M(DD*)
Zc(4025) M(D*D*)
PRL,112,022001
PRL,112,132001