New experimental results on exotic XYZ states
Chang-Zheng Yuan

( yuancz@ihep.ac.cn )IHEP, Beijing

20th Lomonosov Conference On Elementary Particle Physics
online, 19-25 August, 2021
1

Mass (GeV)

Charmonium(like) spectroscopy
4.8➢ Charmonium-like (XYZ) particles➢ New type of hadron (multi-quark …)?
➢ Too many vector states! Exotics?

Y(4660)33 D1(4.52)y(4415)

4.4

4Y(4360)
32Y(4260)
D1(4.19)33y(4160)
S (4.10)31S0(4.06) 1y(4040) 1

321D2(4.21) 2 D2(4.21) 2 D3(4.22)
3

32 P2(3.98)
3(2P)
2 P 1(3.96) 32 P 1(3.95) cc22cc0
P0(2P)(3.92)

y(3770)2y(2S)
S 1(3.68)2h
S0(2S)(3.62)

1 F3(4.10) 13F (4.09)
43c

2005 CLEOc
11h
P 1(3.52)
(1P)

c

1c
Pc1
(1P)
1(3.51)3

1c
P0(3.44)(1P)
3Zc(4430)?

1c
P2(3.55)(1P)
3c2X(4350)
X(4500)X(4700)1974

unpredicted, discovered

3

1 SJ/y(3.10)11h
Sc0(2.97)(1S)
12.8-+0Y(4230)

predicted, discovered--

1+-

1++

0++

1++

2-+

2--

2--

3+-

3

Godfrey & Isgur, PRD 32, 189 (1985)++

3• charmoniumlike XYZstates......

X(4160)c0

3.2

Limit my talk to• States with information
available from two orX(3915)
more experiments
X(3960)3

3

3Zc(4020)

33D ) 1y(1D3)
D3(3.85)
11D2(3.84) 1D2(3.84)
y(12X(3872)

1 D1(3.82)

1

3.6

1 F (4.09)
2015 2019
BESIII LHCb

3Zc(3900)

Zcs(...)

1

1 F2(4.09)

3DD

3charged++

4Y(4390)
X(4140)X(4274)
X(4685)......

• X(3872)• Y(4660)• Zcs(xxxx)
More in a recent review:
N. Brambilla et al.,Phys. Rept. 873 (2020) 1-154.
2

The X(3872):
how many efforts must we make before we understand a particle?

3

Discovery of the X(3872)
Belle, 2003

73090evts

Events/0.01 GeV

PRL91, 262001

367 evts(10.3s)CDF 2004
PRL93, 072001

522100evts

M(J/y) –M(J/y) [GeV]

M = 3872.0 0.6  0.5 MeV,Γ  2.7 MeV
B(B → XK  →π+π− J/ψK )= (6.3  1.2  0.7)%+ −
B(B →ψ'K →π π J/ψK )D0, 2004
PRL93, 162002
4

Mass of the X(3872)

MD0 + MD*0= 3871.69 ± 0.11 MeV
Eb = − 0.04 ± 0.12 MeV
Eb(deuteron) = − 2.2 MeV

𝑟𝑋 = (8𝜇|𝐸𝑏 |)−1/2 > 5 fm

5

Width of the X(3872)
BW width!

sm=2.4~3.0 MeV

Flatté parametrization:

Depends strongly on g, coupling toD0D*0!
FWHM = 0.22+0.06+0.25−0.08−0.17 MeVBESIII may
supply crucial
information ong & line shape.
Mass resolution
sm < 1 MeV!
PRL124, 242001(2020)
6

Production of the X(3872)
Production

CMS, arXiv: 2102.13048

experiments

B decays

BaBar, Belle, CMS, LHCb

Bs decays

CMS, LHCbb decays

LHCbpതp collision

CDF, D0

pp collision

ATLAS, CMS, LHCb

PbPb collisionCMSe+e− → X(3872)

BESIII* → X(3872)

Belle

4.2s

BESIII, PRL 112, 092001 (2014)

PRL122, 232002 (2019)

4.0 fb-1, 205 evts

11.6 fb-1, 799 evts

Belle, PRL 126, 122001 (2021)

3 evts3.2s෩B(X → +−J/ψ)=(5.5+4.1
−3.8 0.7) eV7

Production of the X(3872) in B+→K+X
PRD 97, 012005 (2018)

PRL 124, 152001 (2020)

BaBar
BelleNsignal

Signif.

B(𝐵+ → 𝐾 + 𝑋)

9922852602303.0s
1.1s(2.10.60.3)10−4(1.21.10.1)10−4

These allow a determination of the X(3872) decay
BFs with the product BFs and the BRs.
8

Decay of the X(3872)• Open charm• Transitions– Hadronic transitions– Radiative transitions

D0D*0? Threshold?
D0D00 (nonD0D*0)
D0D0 (nonD0D*0)
D + D −J/y, J/y, ccJ,
ccJ, hc, …

J/y, y(2S)• Hadronic decays• Radiative decays

New measurementsfrom BESIII & Belle.

9Global fit to X(3872) decays
Chunhua Li and CZY, PRD 100, 094003 (2019)10

Chunhua Li and CZY, PRD 100, 094003 (2019)

X(3872) decay BFs
A global fit to BaBar/Belle/LHCb/BESIII data (c2/ndf=25/17):
••
•
•
•
•

𝐵(𝑋 3872 → +−𝐽/𝜓) = (4.1+1.9−1.1 )%𝐵(𝑋 3872 → 𝜔𝐽/𝜓) = (4.4+2.3−1.3 )%𝐵(𝑋 3872 → 𝛾𝐽/𝜓) = (1.1+0.6−0.3 )%ഥ 0 + 𝑐. 𝑐. = (52+25𝐵 𝑋 3872 → 𝐷∗0 𝐷−14 )%𝐵(𝑋 3872 → 𝜋 0 𝜒𝑐1 ) = (3.6+2.2−1.6 )%𝐵 𝑋 3872 → 𝑢𝑛𝑘𝑛𝑜𝑤𝑛 = (32+18−32 )%𝜎(𝑒 + 𝑒 − → 𝛾𝑋 3872 , 𝑋 → +−𝐽/𝜓)=(0.290.11) pb @ 4.226 GeV

𝜎 𝑒 + 𝑒 − → 𝛾𝑋 3872 = (5.5+2.8@ 4.226 GeV−3.6 ) pb
𝜎(𝑒 + 𝑒 − → +−𝐽/𝜓) = (85.15.1) pb @ 4.226 GeV11X 3872 → γψ 2S puzzle
PRL 102, 132001(2009)

B+, 0.4s

B0, 0.3s

PRL 107, 091803(2011), 711/fb

3.5s

PRL124, 242001 (2020)

NPB 886 (2014) 665, 3/fb

Ns=36.4±9.04.4s

It is still not clear if X(3872)→y(2S) exists or not!

1212What is the X(3872)?
•• Width: Very narrow!
• IG(JPC)=0+(1++) [ ➔ cc1(3872) by PDG ]• Production
Mass: Very close toD0D*0 threshold– inpp/pp/PbPb collision, multiplicity dependence– In B, Bs, b decays– e+e−→+X(3872), *→X(3872)• Decay BFs: open charm ~1/2, charmonium~O(%)

Belle 2003,140/fb
PRL 91, 262001

M(J/y) –M(J/y) [GeV]– ~1/3 decays missing– y(2S) needs confirmation• Nature (very likely exotic, theoretical efforts needed)– LooselyD0D*0 bound state (like deuteron)?
– Mixture of excited cc1 andD0D*0 bound state?
– Many other possibilities (if it is not c’c1, where is c’c1?)

Still mind-boggling (crazy)
after all these years!
13The Y(4660):charmonium, f0(980)y(2S), or +c−c molecule?

14

The Y states were discovered via ISR
PRD 89, 111103 (2014)

PRL 99,142002 (2007)

PRL 110,252002
967/fb

PRD 86,051102
454/fb

PRL101,172001
695/fbM(c+c-)15

Y(4630)=Y(4660)? Are there other decay modes?
Y(4660) discovered by Belle in 2007
Y(4630) discovered by Belle in 2008

Belle: PRD91, 112007 (2015), 980/fb
BaBar: PRD89, 111103 (2014), 520/fb
Belle: PRL101, 172001 (2008), 695/fb

Belle: PRD89, 072015 (2014), 980/fb

e+e−→+c−ce+e−→K+K-J/ye+e−→y’Experiment

Mass (MeV)

Width (MeV)

Belle, +c−c4634+8-7+5-892+40-24+10-21

Belle, y’465210868111BaBar, y’4669213104481016

e+e−→+−y’

Recent measurements
arXiv:2107.09210

e+e−→+c−c

BESIII: PRL120, 132001 (2018)

BESIII data available

BESIII data confirmed Belle & BaBar measurements withmuch improved precision!
BESIII has data now covering from threshold to 4.95 GeV,
comparable precision as at 4.6 GeV is expected!
17PRD 100, 111103 (2019)e+ e− → Ds+ Ds1 (2536)− + 𝑐. 𝑐.
𝟖𝟗+𝟏𝟕−𝟏𝟔 𝒆𝒗𝒕𝒔
5.9s

Recent measurements

PRD 101, 091101 (2020)

e+ e− → Ds+ D∗s2 (2573)− + 𝑐. 𝑐.

𝟔𝟔+𝟐𝟔−𝟐𝟎 𝒆𝒗𝒕𝒔
3.4s

18

BESIII has data from threshold to 4.95 GeV, improved measurements are expected!

arXiv: 2106.02298
PRD (in press)

Recent measurementse+ e− → Ds∗+ D∗s0 (2317)− + 𝑐. 𝑐.
Ds∗+ Ds1 (2460)− + 𝑐. 𝑐.
Ds∗+ Ds1 (2536)− + 𝑐. 𝑐.

∗−D∗+s Ds0 (2317) + 𝑐. 𝑐.

−D∗+s Ds1 (2460) + 𝑐. 𝑐.

Clear e+ e− →D∗s DsJ production between 4.6 and 4.7 GeV.

−D∗+s Ds1 (2536) + 𝑐. 𝑐.

No significant Y(46xx)→Ds∗ DsJ signal
19BESIII has data from threshold to 4.95 GeV, improved measurements are expected!

e+e−→DsDs1Y(4630)? Y(4660)?
e+e−→+c−ce+e−→DsD*s2
e+e−→y’Tension between open charm& charmonium modes.
Parametrization affects theresonance parameters.

Experiment

Mass (MeV)

Width (MeV)

Belle, y’465210868111BaBar, y’46692131044810BESIII, y’4651382155251Belle, +c−c 4634+8-7+5-8

92+40-24+10-21

Belle, DsDs1

4625.9+6.2-6.0 0.4 49.8+13.9-11.5 4.0

Belle, DsD*s2

4619.8+8.9-8.0 2.3 47.0+31.3-14.8 4.620

The Zcs states21

Zc(3900)

The famous Zc states
Zc(4020)

Zc(4430)

All are observed in+charmonium (J/y, hc,y(2S)) final states,
candidate c cd utetraquark states➔ Existence of stateswith d→s?

➔ Search for states
decay into KJ/y,D*Ds +DD*s !
22

𝒔=4.4~5.5 GeV

PRD 89, 072015 (2014)

No significant signal in
KJ/y decay mode!
(statistics low!)

PRL 126, 102001 (2021)

PRL 127, 082001 (2021)

Zcs(3985) inD*Ds +DD*s mode!

StateSignif. JP

Mass (MeV)

Width (MeV)

Zcs(3985) 5.3s+5.3?? 3982.5+1.8−2.6 ± 2.1 12.8−4.4 ± 3.0

Zcs(4000)15s

1+4003 ± 6+4−141311526

Zcs(4220) 5.9s

1+4216 ± 24+43−30

233 ± 52+97−73

Zcs(4000) and Zcs(4220)
in KJ/y decay mode!
Widths very different,
not the same state!

Waiting for BESIII result on e+e−→K+K-J/y from the same data sample!

23Summary• Lots of progress in the experimental study of the XYZ states.
• X(3872) width to be refined, still ~30% decays to be discovered• More data available for the Y(4630)/Y(4660) states, still not clear whether
they are the same
• Three Zcs(xxxx) discovered, need confirmation• More results to come, and lots of Opportunities and Challenges ahead

24

The near future

Thank you very much! Большое спасибо!

25