1. Recent experimental results and Opportunities in Exotic Hadrons
Chengping Shen (Beihang University)
Peking University, Nov. 30, 2015

2. INT Workshop INT-15-60W: Modern Exotic Hadrons
November 2-13, 2015 (two weeks)
University of Washington, Seattle
~20 participants
Two talks in the morning
1 talk + discussion in the afternoon
A white paper on arXiv:
Organizers:
Jozef Dudek Jefferson Laboratory
Ryan Mitchell Indiana University
Eric Swanson University of Pittsburgh

3. Topics Experiments (BESIII, Belle(II), LHCb)
LQCD (spectroscopy, scattering length)
Theories (phenomenology)
Key points
There are hopes, but still long way to go on lattice
More experimental measurements are desired
Hard to tell among models: molecule, multiquark, cusp, resonance, FSI, …
Wish lists are given in white paper
Today I just review some experimental results and point
out some opportunities.

4. Outline Belle results BESIII results LHCb results
Some discussions during the workshop

5. The Belle experiment World record: L = 2.1 x 1034/cm2/sec 1999-2010
e+ source
Ares RF
cavity
Belle detector
SCC RF(HER)
World record:
L = 2.1 x 1034/cm2/sec
ARES(LER)
~ 1 km in diameter
Mt. Tsukuba
KEKB
Belle
8 x 3.5 GeV
22 mrad crossing
1014/fb
The KEKB Collider

6. 10.865 1 121.4 , hb, B(*)B(*) 10.63-11.02 6+16 ~1 Rb, , hb
Ecm (GeV)
Npoints
Lum per point (fb-1)
Physics analyses
10.865 1
121.4
, hb, B(*)B(*)
6+16 ~1
Rb, , hb 61
~0.05 Rb
10.52
1.03
Continuum bkg. est.

7. e+e- annihilation to vector bottomonia}
JPC = 1--
(nS), Yb…

8. ISR production of vector charmonia}
JPC = 1--
’, ’’, Y…

9. 𝑅 𝑏 = 𝜎( 𝑒 + 𝑒 − →𝑏 𝑏 ) 𝜎 0 ( 𝑒 + 𝑒 − → 𝜇 + 𝜇 − )
𝑅 𝑏 = 𝜎( 𝑒 + 𝑒 − →𝑏 𝑏 ) 𝜎 0 ( 𝑒 + 𝑒 − → 𝜇 + 𝜇 − )
Procedure:
Count hadronic events
Subtract scaled cont. (udsc)
Subtract ISR (1S,2S,3S)
Do efficiency correction
Divided by lum & 0()
No ISR corr.; no VP corr.
Fit with constant width BW in small energy range.
Need better model to fit
Agree with BaBar:PRL102, (2009) with improved precision
Ecm= GeV, 5 MeV step for >300 points, 3.9 fb-1 in total
Belle: arXiv:

10. Rb
(5S):
Mass = ( 1.0 1.2) MeV
Width = (49.8 1.9 2.12.8) MeV
(6S):
Mass = ( 1.1 0.80.9) MeV
Width = (38.5  1.32.4) MeV
=-1.86  0.10 rad
Results agree with previous measurements
Suffers from model uncertainties (signal, background parametrization, interference, thresholds, coupled channel effect)
Belle: arXiv:

11. Ecm=10.54-11.20 GeV, 5 MeV step for >300 points, 3.9 fb-1 in total
No Ali state !
No ISR corr.; no VP corr.
BaBar:PRL102, (2009)

12. e+e−+−(nS) tag (nS) and select +−, fit to |A5S+eiA6S|2
Mass = ( 3.2 0.61.5) MeV
Width = (53.7  0.95.4) MeV
(6S):
Mass = (  2.22.1) MeV
Width = (61 919 220) MeV
=-1.0 0.4  rad
+−(1S)
+−(2S)
Results agree with previous measurements
Also agree with fit with Rb reasonably well
Still room for improvement
+−(3S)
Belle: arXiv:

13. Zb in (5S)+−(nS) 121 fb-1 data, tag (nS) and select +−
Born cross section
121 fb-1 data, tag (nS) and select +−
+−(1S)
+−(2S)
+−(3S)
Belle: PRD91, (2015)

14. Zb in (5S)+−(nS) Full partial wave analysis of (5S)+−
Mass, width, fraction, and JP=1+ of Zb states determined
+−(1S)
+−(2S)
+−(3S)
Belle: PRD91, (2015)

15. Zb in (5S)+−(nS) Relative BR of Zb decays
Belle: PRD91, (2015)

16. e+e−+−hb(nP) Using scan data between Y(5S) and Y(6S)
Belle: arXiv:
Using scan data between Y(5S) and Y(6S)
Reconstruct +−, require +/− recoil mass in Zb region: < Mmiss(π) < GeV/c2
check the +− recoil mass for hb(nP)
+−hb(1P)
+−hb(2P)

17. e+e−+−hb(nP) (5S): Mass = (10884.7 3.22.98.60.6) MeV +−hb(1P)
Width = (44.2   ) MeV
(6S):
Mass = ( 6.1 ) MeV
Width = (29 2012 27) MeV
=0.64   rad
+−hb(1P)
+−hb(2P)
Resonant parameters agree with from e+e−+−(nS)
e+e−+−hb(nP) at the same level as e+e−+−(nS)
1st obs. of (6S)+−hb(nP)
Belle: arXiv:

18. Zb in (6S)+−hb(nP) Events mainly from Zb intermediate states
not clear if only one Zb or both.
Belle II will tell us.
+−hb(1P)
+−hb(2P)
Belle: arXiv:

19. Zb in (5S)[B(*)B(*)]+−+c.c.
BB =B0B+−+c.c.
BB* =B*0B+−+c.c./B0B*+−+c.c.
B*B* =B*0B*+−+c.c.
One B is reconstructed
Select a bachelor ±
Check B recoil mass B B* π e+ e-
Belle preliminary
qq background
B background
BB* BB
B*B*
B sidebands
18 B decay modes combined
B(*)B(*)π +BBγ _
12263±168
B signals

20. Zb in (5S)[B(*)B(*)]+−+c.c.
BB =B0B+−+c.c.
BB* =B*0B+−+c.c./B0B*+−+c.c.
B*B* =B*0B*+−+c.c.
One B is reconstructed
Select a bachelor ±
Check B recoil mass B B* π e+ e-
Belle preliminary
qq background
B background
BB* BB
B*B*
B sidebands
18 B decay modes combined
B(*)B(*)π +BBγ _
12263±168
B signals
the possibility of measuring the open bottom cross section with the Rb scan data ???

21. Zb in (5S)[B(*)B(*)]+−+c.c.
Combine the B with a charged pion
 calculate recoil mass of B B B* π e+ e-
rM(Bπ), GeV/c2
RS data
WS data
Fit
BB threshold
signal MC
BB*
BB
For Zb study!
B*B*
N(BB) = 13 ± N(BB*) = 357 ± N(B*B*) = 161 ± 21
Cross sections are not available yet!
Belle preliminary

22. Zb in (5S)[B(*)B(*)]+−+c.c.
Check recoil mass of bachelor π±
Belle preliminary
Zb(10610) saturates BB*π and Zb(10650) saturates B*B*π
Assuming Zb decays are saturated by observed channels, B(*)B* channels dominate the Zb decays
rM(π), GeV/c2
background
Zb(10610) only
Zb(10610) + NR
Zb(10610) + Zb(10650)
Zb(10650) only
BB*π
B*B*π
Belle PRELIMINARY arXiv:
BB*
B*B*

23. BRs of Zb decays
Belle preliminary

24. Zc(4050)’
arXiv:
PRD91,
An unbinned maximum-likelihood fit is performed on the distribution of Mmax(π±ψ(2S)), the maximum of M(π+ψ(2S)) and M(π−ψ(2S)), simultaneously with both modes.
Y(4360) signal region
M(Zc) = 4054 ± 3 ± 1 MeV/c2
Γ = 45 ± 11 ± 6 MeV
Significance: >3.5

25. No significant Zc in Y(4660) decays!
’ J/ 
’ 
Need more statistics ?
Belle: arXiv: , PRD91,

26. e+e- K+K-J/ via ISR 4-6 GeV: 213 events 35 bkg, 17816 signals
Event selections are almost the same as in Phys. Rev. D 77, (R) (2008)
Shaded hist.: J/ mass sidebands
+one resonance.
Fit with (4415)
980fb-1
Y(4260)
2/ndf=30/11
M=4747117MeV
=67186 MeV
4-6 GeV: 213 events
35 bkg, 17816 signals
7.8% sys. error was
not included.
PRD 89, (2014)

27. Search for ZcsKJ/ states
PRD 89, (2014)
Large data samples at BelleII are needed to understand KJ/ and KKJ/ structures !
No evident structure in K±J/ mass distribution under current statistics

28. Charmonium region at Belle II
ISR produces events at all CM energies BESIII can reach
At 4.26 GeV for +-J/
BESIII = 46%
Belle = 10%

34. Evidence for the X(3823) at Belle
arXiv: (PRL111, (2013))
711 fb-1
3.8σ
B χc1γK
The measured mass and width are consistent with the missing Ψ2(1D) state
BESIII may search for it!
Mχc1γ (GeV/c2)

35. Hunt D-wave charmonium at BESIII
Both E705 and Belle observed evidence.
[Phys. Rev. D 50, 4258 (1994); Phys. Rev. Lett. 111, (2013).]
Potential model: 13D2gcc1,gcc2 with large width.
Use p+p- transition to produce 13D2 with JPC= 2- -; D-wave (L=2) transition is expected.
PRL 115, (2015)
gcc1
gcc2
X(3823)
M[X(3823)]=3821.7±1.3±0.7 MeV (calibrate by y(2S)).
Statistical significance: 6.2s (>5.9s including sys.), observation!
Good candidate of y(13D2), confirms X(3872)≠y(13D2)

36. Production mechanics of X(3823)
PRL 115, (2015)
Whether from Y(4360) or y(4415) decay
Favor the Y(4360) ? [M. B. Voloshin, PRD 91, (2015)]
Y(4360)p+p-X(3823)? New decay model of Y(4360)?

37. Good candidate for y(13D2)
Assume pp system is dominant by f0(500)
Scattering angle distribution of y(2S) and X(3823) in e+e- CM frame.
Kolmogorov-Smirnov test p-value is given.
(Left) p+p-y(2S): S-wave (p=0.791), D-wave (p=0.451)S-wave seems to be better.
(right) p+p-X(3823): S (p=0.928), D (p=0.978)Can’t distinguish

38. Good candidate for y(13D2)
Mass: D-wave ~ GeV by potential model.
X(3823) mass agree with y(13D2) prediction.
Width: narrow
X(3823) should be narrow (<16 90% C.L.).
Production ratio:
90% C.L.
Agree with prediction R~0.2.
Exclusions: 11D2gcc1 forbidden; 13D3gcc1 amplitude=0.

39. Search X(4140)fJ/y
PRD91, (2015)
PRL 102, (2009)
~2.4 fb-1
The X(4140) was reported by CDF with
M=(4143.0±2.9±1.2) MeV, Width= ±3.7 MeV
Controversial: CMS (Yes), Belle (No), LHCb (No), BaBar (no)
BESIII: different process e+e-gfJ/y
No signal, cross section 4.26 GeV

41. Observation of e+e- ’J/
BESIII
Preliminary
4.23 GeV:  = 3.1±0.6±0.3 pb
4.26 GeV:  = 3.9±0.8±0.4 pb
First observation, cannot tell the line shape due to statistics

42. Isospin violation Y(4260)p0hJ/y
BESIII preliminary
No significant signal observed with current BESIII data !
Can not provide effective constraint to models…
BESIII preliminary

43. Discovery of Zc(3900)± BESIII: PRL 110, 252001 (2013)
A 4-quark particle?!
Belle with ISR data (PRL 110, )
CLE0c data at 4.17 GeV (PLB 727, 366) 43

44. Neutral isospin partner: Zc(3900)0
e+e-p0p0J/y
A neutral structure on p0J/y invariant mass is observed !
M = ±2.3±3.2 MeV
G = 29.6±8.2±8.2 MeV
Significance = 10.4s
PRL 115, (2015)
An iso-spin triplet is established !
Mass near DD* threshold
Molecules? Tetraquark?
CLEO’s 4.17 GeV
3.5s
PLB 727(2013) 366

45. e+e-(DD*)+p-+c.c. ? Double tag @ 4.23 GeV Single π+D0 tag @ 4.26 GeV
arXiv:
PRL 112, (2014)
Double 4.23 GeV
Single π+D0 tag
@ 4.26 GeV
Double 4.26 GeV
Single π-D+ tag
@ 4.26 GeV
Single tag
M=3883.9±1.5±4.2 MeV
G=24.8±3.3±11.0 MeV
JP=1+
Double tag
M=3881.7±1.6±2.1 MeV
G=26.6±2.0±2.3 MeV
JP=1+
Good agreement between ST & DT method
Zc(3900) vs. Zc(3885)  Same resonance ?!

47. Neutral iso-spin e+e-(DD*)0p0+c.c.
Partial reconstruction method - Single tag
M= ±8.4 MeV
G= ±15 MeV
Significance: >10s
arXiv:
Good agreement between neutral state and charged state
An iso-spin triplet established in DD* channel
Might be same as Zc(3900)
Molecule state? Tetraquark?

48. e+e-p+p-hc & p0p0hc p+p-hc p0p0hc Charged Zc(4020)±
PRL111,242001(2013)
p+p-hc
p0p0hc
Charged Zc(4020)±
Mass=(4022.9±0.8±2.7) MeV
Width=(7.9±2.7±2.6) MeV
Significance: >8.9s
Neutral Zc(4020)0
Mass=(4023.9±2.2±3.8) MeV
Width: fixed to charged partner
Significance: 5s
PRL 113,212002(2014)
Mass near D*D* threshold
Partner of Zc(3900)?
Molecules? Tetraquark?
An spin triplet is established !

49. e+e--(D*D*)+/p0(D*D*)0+c.c.
PRL115, (2015)
PRL112,132001(2014)
Neutral Zc(4025)0:
M=( 3.1) MeV
=(23.06.01.0) MeV
Significance: >5.9
Charged Zc(4025):
M=(4026.32.63.7) MeV
=(24.85.67.7) MeV
Significance: >10
Agrees !
New isospin triplet?
Zc(4025) and Zc(4020) have similar mass, but different width.

50. preliminary

51. preliminary
4.23 GeV
4.26 GeV

54. preliminary

74. On LQCD There are many LQCD calculations Potential problems
Volume is too small
Not all channels are included
m is too large
(if no ZcsKJ/, it is normal no ZcJ/ on the Lattice)
In LQCD papers
“We conclude that at least with the diquark anti-diquark and meson-meson operators used here our abinitio study shows no exotic state below 4.2 GeV”
“… were established, while Zc(3900), X(4140) and bound ccdu tetraquarks were not found (yet).”

75. What we may contribute Publish upper limits for negative searches
Confirm marginal states
X(3940), Y(4008), Z1(4050), X(4160), Z2(4250), and X(4350)
Unravel the excited cJ(2P) spectrum
Measure e+e- cross sections
Search for flavor analog exotic states (Zs, Xb, …)
Search for flavor analogs of the Pc (Ps, Tcc, …)
Pursue properties of the X(3872) -- X(4013)?
Search for quantum number partners of Y(4260) --if Y is a hybrid

76. Search for more hybrids

77. What we may contribute Search for pp in decays of any states
Study exclusive e+e- cross sections using better coupled-channel formalism
Develop tests for the dynamical diquark picture
cp0 for Psp
Zcc
Develop experimental tests for tetraquarks
Relative strength of Zcc, J/, ’, hc, open charm
X(3872)…
Revisit conventional meson models
Especially for states above open flavor threshold
Search for missing conventional states, c2, hc(2P), …

78. Theory-experiment Collaboration
Improve parameterizations of the data
when appropriate and beneficial, experimentalists and theorists directly work together
theorists, when possible, to publish complete functional forms
Make experimental results more accessible for subsequent interpretation.
Supply also efficiency curve, background subtraction
Publish Dalitz plot in text format
(should not be too complicated …)
Preview upcoming analysis results
We are working on this mode, may you predict?
May theorists predict e+e-J/ Dalitz plot vs. Ecm?

79. University of Washington

80. The campus

81. Physics/Astrophysics building

82. 1st Starbucks

83. The end