The BGOOD experiment at ELSA
– multi-quark structures in the uds sector ?

OutlineHartmut Schmieden
Physikalisches Institut
Universität Bonn

• BGOOD experiment• physics case• selected results• conclusions

supported by DFG
PN 50165297 andPN 405882627

This project has received funding from the European Union’s
Horizon 2020 research and innovation programme under grant
agreement No 824093

H. Schmieden – CLUSHIQ 2022 workshop – Sendai, Japan1

located atelectron accelerator
Physikalisches Institut
Universität Bonn2

BGOOD experiment

located atelectron accelerator
Physikalisches Institut
Universität Bonn2

BGOOD experiment

S. Alef et al. [BGOOD collab.], EPJ A 56 (2020) 104
spokespersons:P. Levi Sandri (Frascati) &H.Schmieden (Bonn)• combination of BGO central calorimeter & forward spectrometer• high momentum resolution, excellent neutral & charged particle id

1m

H. Schmieden

3

BGOOD experiment

S. Alef et al. [BGOOD collab.], EPJ A 56 (2020) 104
spokespersons:P. Levi Sandri (Frascati) &H.Schmieden (Bonn)• combination of BGO central calorimeter & forward spectrometer• high momentum resolution, excellent neutral & charged particle id

1m

H. Schmieden

3

BGOOD experiment

S. Alef et al. [BGOOD collab.], EPJ A 56 (2020) 104
spokespersons:P. Levi Sandri (Frascati) & H.S. (Bonn)• combination of BGO central calorimeter & forward spectrometer• high momentum resolution, excellent neutral & charged particle id

1m

H. Schmieden

4

BGOOD experiment

S. Alef et al. [BGOOD collab.], EPJ A 56 (2020) 104
spokespersons:P. Levi Sandri (Frascati) & H.S. (Bonn)• combination of BGO central calorimeter & forward spectrometer• high momentum resolution, excellent neutral & charged particle id

1m

H. Schmieden

5

BGOOD experiment at ELSA

Vorstellung Fachschaft – Dezember 20146

physics case7

Excited states: quark model
N* resonancesexp. values
U. Löring et al.
Eur.Phys.J. A10(2001) 395

H. Schmieden

8

Excited states: quark model
N* resonances

gr
n
i
s
is

es

s"
e
c
n
ona

"m

exp. values
U. Löring et al.
Eur.Phys.J. A10(2001) 395

H. Schmieden

8

Excited states: quark model
N* resonances

S11(1535)P=–
Roper(1440)
P=+
NucleonP=+

H. Schmieden

exp. values
U. Löring et al.
Eur.Phys.J. A10(2001) 395

9

Excited states: quark model
N* resonances

S11(1535)P=–
Roper(1440)
P=+
NucleonP=+

exp. values
U. Löring et al.
Eur.Phys.J. A10(2001) 395• parity pattern lowest states + → + → – !?!
• effective degrees of freedom ??
H. Schmieden

9

Excited states: quark model
Λ* resonancesΛ(1600)P=+Λ(1405)P=–Λ g.s.
P=+••

H. Schmieden

parity pattern OK
masses reversed ??

10

context c-quark sector
X(3872)
Belle PRL91, 262001(2003)
B± → K± π+π– J/ψΨ'X(3872)M(π+π-l+l-)- M(l+l-)

BaBar / SLAC
PRD 77 (2008)
111101

CDF / Tevatron
PRL 103 (2009) 152001

11context c-quark sector
X(3872)
Belle PRL91, 262001(2003)
B± → K± π+π– J/ψΨ'X(3872)M(π+π-l+l-)- M(l+l-)

BaBar / SLAC
PRD 77 (2008)
111101

CDF / Tevatron
PRL 103 (2009) 152001

12

context c-quark sector
PC+(4380, 4450)

X(3872)Ψ'

Belle PRL91, 262001(2003)
B± → K± π+π– J/ψ

R. Aaij et al., PRL 115 (2015) 072001

X(3872)LHCb 2015

p J/ψ

M(π+π-l+l-)- M(l+l-)

BaBar / SLAC
PRD 77 (2008)
111101

CDF / Tevatron
PRL 103 (2009) 152001

PB / VB hidden c predicted frommeson-baryon interactions:
Oset, Zou et al., PRL 105 (2010)"new N*cc states are simply
brothers or sisters of the wellknown N*(1535) and Λ*(1405)... and many other dynamicallygenerated states ..."

13

context c-quark sector
PC+(4380, 4450)

X(3872)Ψ'

Belle PRL91, 262001(2003)
B± → K± π+π– J/ψ

R. Aaij et al., PRL 115 (2015) 072001

X(3872)LHCb 2015
at

at

D* D

D* Σc

thresholdp J/ψthresholdM(π+π-l+l-)- M(l+l-)

BaBar / SLAC
PRD 77 (2008)
111101

CDF / Tevatron
PRL 103 (2009) 152001

PB / VB hidden c predicted frommeson-baryon interactions:
Oset, Zou et al., PRL 105 (2010)"new N*cc states are simply
brothers or sisters of the wellknown N*(1535) and Λ*(1405)... and many other dynamicallygenerated states ..."

14

context c-quark sector
PC+(4380, 4450)

X(3872)Ψ'

Belle PRL91, 262001(2003)
R. Aaij et al., PRL 115 (2015) 072001
B± → K± π+π– J/ψ
• 5-quark structures definitely observed
LHCb 2015
X(3872)p J/ψ
• (hidden) c-quark sector• similar 4-quark
states in meson sector
at
at• structure/binding mechanism under debate
D* DthresholdM(π+π-l+l-)- M(l+l-)

BaBar / SLAC
PRD 77 (2008)
111101

CDF / Tevatron
PRL 103 (2009) 152001

D* Σcthresholdparadigm change in hadron physics
general feature of structure formation in QCD ?
similiar structures in (hidden) s-quark sector ??

PB / VB hidden c predicted frommeson-baryon interactions:
Oset, Zou et al., PRL 105 (2010)"new N*cc states are simply
brothers or sisters of the wellknown N*(1535) and Λ*(1405)... and many other dynamicallygenerated states ..."

15

Parallels in s-quark
sector ?

(* ) Σ
DD*
Σcc
thresholds

16Parallels in s-quark
sector ?
s s̄

D (* ) Σ cK(*) Σ

thresholds

thresholds

s s̄

17

parallels between c and s sector ?

H. Schmieden

18

parallels between c and s sector ?

D

H. Schmieden

X(3872)D*

19

parallels between c and s sector ?

ΣcPC(4380/4450)

D*

3 ⇿ 3

q ➞ [qq]

H. Schmieden

20parallels between c and s sector ?

ΣcΛ*c
H. Schmieden

π

π

D*

D
21

parallels between c and s sector ?

ΣΛ*H. Schmieden(1520)

π

π

K*

K
22

uds sector ?

selected results of BGOOD

H. Schmieden

23uds sector – threshold dynamics
narrow peak& cusp in η n/p

2.08

K* – Λ
K+ –
Λ(15
20)
K*
–Σ

p – η'

p–ϕ

1.96
2.00
7
2.013

1.7

1.68
H. Schmiedenp–ω& node asymmetry

K–Σ

p–η
1.49

1.43

K–N

S11(1535)

1.90

Λ(1405)narrow peakcusp in KΣ
in ϕpcusp in ηp

cm energy / GeV

24

γ + p -> K0 + Σ+

anomaly @ K* threshold
R. Ewald et al. (CB/TAPS), PLB 713 (2012)

most forward bin<cos θKcm> = 0.83

H. Schmieden25γ + p -> K0 + Σ+

anomaly @ K* threshold
R. Ewald et al. (CB/TAPS), PLB 713 (2012)

most forward bin<cos θKcm> = 0.83

K

K*
K
N

π
Λ/Σ

also:
Ramos & Oset,
PLB 727 (2013) 287

H. Schmieden26γ + p -> K0 + Σ+

anomaly @ K* threshold
R. Ewald et al. (CB/TAPS), PLB 713 (2012)

most forward bin<cos θKcm> = 0.83

protonK

K*
K

neutron

N

π
Λ/Σ

also:
Ramos & Oset,
PLB 727 (2013) 287

H. Schmieden27γ + p -> K0 + Σ+

anomaly @ K* threshold
R. Ewald et al. (CB/TAPS), PLB 713 (2012)

N*(2030) / N*(2080)

most forward bin<cos θKcm> = 0.83

protonK

K*
K

neutron

N

π
Λ/Σ

also:
Ramos & Oset,
PLB 727 (2013) 287

H. Schmieden28γ + p -> K0 + Σ+

anomaly @ K* threshold
R. Ewald et al. (CB/TAPS), PLB 713 (2012)

N*(2030) / N*(2080)

most forward bin<cos θKcm> = 0.83

protonK

K*
neutronKπsmoking gunNΛ/Σ“pentaquark“
also:same mechanism
Ramos & Oset,
as LHCb PCPLB
w/ 727 (2013) 287
c s

H. Schmieden29γ n → K0 Σ0
PhD thesis K. Kohl (Bonn 2021)
arXiv:2108.13319

C. Akondi et al. [MAMI-A2]
EPJ A 55 (2019) 202

Eγ / MeV
1500

2000

-0.70<cos(θKCM)<-0.40

0.2

BGOOD, PS
BGOOD, RDA2
Ramos & Oset
KMAID
BnGa

0

1500

2000

BGOOD simulated bg fit

2500

BGOOD real bg fit-0.40<cos(θKCM)<-0.10

0.2

0.1

0

1800

2000

2200

-0.10<cos(θKCM)<0.20

0.2

1800

2000

2200
K
CM

0.20<cos(θ )<0.50

0.2

σ/µb

dσ/d Ω / µ b/sr

0.1

2500

1

0.5
0.1

0.1

0

0

1800

2000

2200

0

1800

2000

2200

W/ MeV

H. Schmieden30γ n → K0 Σ0
PhD thesis K. Kohl (Bonn 2021)
arXiv:2108.13319

C. Akondi et al. [MAMI-A2]
EPJ A 55 (2019) 202

Eγ / MeV
1500

2000

-0.70<cos(θKCM)<-0.40

0.2

BGOOD, PS
BGOOD, RDA2
Ramos & Oset
KMAID
BnGa

0

1500

2000

BGOOD simulated bg fit

2500

BGOOD real bg fit-0.40<cos(θKCM)<-0.10

0.2

see also:
0.1

0

1800

2000

2200

-0.10<cos(θKCM)<0.20

0.2

1800

2000

2200
K
CM

0.20<cos(θ )<0.50

0.2

σ/µb

dσ/d Ω / µ b/sr

0.1

2500

1

0.5
0.1

0.1

0

0

1800

2000

2200

0

1800

2000

“The molecular nature of someexotic hadrons“Ramos, Feijoo, Llorens,Montaña
Few Body Sys. 61 (2020) 4, 34
arXiv:2009.04367 (2020)

smoking gun“pentaquark“same mechanism
as LHCb PC w/
c s

2200

W/ MeV

H. Schmieden30γ n → K0 Σ0
PhD thesis K. Kohl (Bonn 2021)
arXiv:2108.13319

C. Akondi et al. [MAMI-A2]
EPJ A 55 (2019) 202

Eγ / MeV‣ too limited statistics 😕

1500

2500

1500

2000

BGOOD simulated bg fit

2500

BGOOD real bg fit-0.40<cos(θKCM)<-0.10‣ 2x statistics on disc 😀
‣ theory: compare differential cross sections-0.70<cos(θKCM)<-0.40

0.2

0.1

BGOOD, PS
BGOOD, RDA2
Ramos & Oset
KMAID
BnGa

0

0.2

see also:

0.1

0

1800

2000

2200

-0.10<cos(θKCM)<0.20

0.2

1800

2000

2200
K
CM

0.20<cos(θ )<0.50

0.2

σ/µb

dσ/d Ω / µ b/sr

2000

1

0.5
0.1

0.1

0

0

1800

2000

2200

0

1800

2000

“The molecular nature of someexotic hadrons“Ramos, Feijoo, Llorens,Montaña
Few Body Sys. 61 (2020) 4, 34
arXiv:2009.04367 (2020)

smoking gun“pentaquark“same mechanism
as LHCb PC w/
c s

2200

W/ MeV

H. Schmieden30

Λ(1405)

PDG 2010
Historic
remark→Dalitz& TuanTheΛ(1405)
clean Λpredictedhas
in fact
beenastaken to settle the decades-longc spectrumby
composedof Kaon-Nucleon
discussion
about
the nature of the Λ(1405) – true 3-quark state or mere
Dalitz & effect?
S.F. Tuan,
2 (1959) 425 in favor of the first interpretation.
K̅ N R.H.
threshold– PRL
unambiguously→ discovered 1961 in Kp → Σπππ
M.H. Alston et al., PRL 4 (1961) 698

PDG
2016 first “exotic“ hadron→probablyThe Λ(1405) resonance emerges in the meson-baryon scattering amplitudewith the strangeness S = –1 and isospin I = 0. It is the archetype of what iscalled a dynamically generated resonance, as pioneered by Dalitz and Tuan.

31

Λ(1405)

PDG 2010
The clean Λc spectrum has in fact been taken to settle the decades-long
discussion about the nature of the Λ(1405) – true 3-quark state or mere
K̅ N threshold effect? – unambiguously in favor of the first interpretation.
PDG 2016
The Λ(1405) resonance emerges in the meson-baryon scattering amplitudewith the strangeness S = –1 and isospin I = 0. It is the archetype of what iscalled a dynamically generated resonance, as pioneered by Dalitz and Tuan.

32

Λ(1405)

PDG 2010
The clean Λc spectrum has in fact been taken to settle the decades-long
discussion about the nature of the Λ(1405) – true 3-quark state or mere
K̅ N threshold effect? – unambiguously in favor of the first interpretation.
PDG 2016
The Λ(1405) resonance emerges in the meson-baryon scattering amplitudewith the strangeness S = –1 and isospin I = 0. It is the archetype of what iscalled a dynamically generated resonance, as pioneered by Dalitz and Tuan.

32

Λ(1405)

2-pole structure in χPTtaken from Maxim Mai’s
talk at NSTAR 2019
(Baryon ChPT)33

Λ(1405)

Lattice QCD

J.M.M. Hall et al. [Adelaide group],
Phys. Rev. Lett. 114 (2015) 132002
UχPT see also:
R. Molina & M. Döring,PR D94 (2016) 056010& 079901"molecule" as dominating
Fock component

genuine 3q

H. Schmieden34

K+ Λ(1405)

experimental status

Λ(1405) photoproduction – line shape• two pole structure

predicted & confirmed• different line shapes in(Σπ)0 channels
confirmed

2-poles structure should be
visible in pure I=0 channel
Σ0 π0theory: J.A. Oller & U.-G. Meißner, PLB 500 (2001) 263
35

K+ Λ(1405)
Λ(1405) photoproduction – line shape

H. Schmieden

G. Scheluchin et al. [BGOOD collab.]
Phys. Lett B 833 (2022) 137375

36K+ Λ(1405)
Λ(1405) photoproduction – line shape

G. Scheluchin et al. [BGOOD collab.]
Phys. Lett B 833 (2022) 137375

double peak strukture@ 1395 / 1425 MeV ??

H. Schmieden36

K+ Λ(1405)
Λ(1405) photoproduction – line shape

G. Scheluchin et al. [BGOOD collab.]
Phys. Lett B 833 (2022) 137375

double peak strukture@ 1395 / 1425 MeV ??

• K+ in forward spectrometer
H. Schmieden

36photoproduction mechanism – triangle singularity
B
A

1
3
2
C

H. Schmieden

Coleman-Norton theorem,
Il Nuovo Cimento 38 (1965) 438:
1, 2, 3 must be nearly on mass shell

can mimic resonance37

photoproduction mechanism – triangle singularity
B
A

1
3
2
C

Coleman-Norton theorem,
Il Nuovo Cimento 38 (1965) 438:
1, 2, 3 must be nearly on mass shell

can mimic resonanceor drive (dynamically generated) resonance
E. Wang, J. Xie, W. Liang, F. Guo, E. Oset,
PR C 95 (2017) 015205

H. Schmieden

37photoproduction mechanism – triangle singularity
B
A

1
3
2
C

Coleman-Norton theorem,
Il Nuovo Cimento 38 (1965) 438:
1, 2, 3 must be nearly on mass shell

can mimic resonanceor drive (dynamically generated) resonance
E. Wang, J. Xie, W. Liang, F. Guo, E. Oset,
PR C 95 (2017) 015205

K*Σ suspect in K0Σ0 channel
H. Schmieden37

K+ Λ(1405) – photoproduction mechanism
K+ Λ(1405) photoproduction – total x-sec

G. Scheluchin et al. [BGOOD collab.]
Phys. Lett B 833 (2022) 137375

cusp: triangle meachanism significant

E. Wang, J. Xie, W. Liang, F. Guo, E. Oset,
PR C 95 (2017) 015205

H. Schmieden

38

Multi-quark statestaken from Jinlin Fu’s talk
@ HaSP general meeting (Munich 22)

H. Schmieden

39

Multi-quark statestaken from Jinlin Fu’s talk
@ HaSP general meeting (Munich 22)mπ

H. Schmieden39γ p → K+ Σ0 photoproduction
T. Jude et al. [BGOOD collab.]
Phys. Lett B 820 (2021) 136559

cos θKcm > 0.9

H. Schmieden40γ p → K+ Σ0 photoproduction
T. Jude et al. [BGOOD collab.]
Phys. Lett B 820 (2021) 136559

H. Schmieden

41γ p → K+ Σ0 photoproduction
T. Jude et al. [BGOOD collab.]
Phys. Lett B 820 (2021) 136559

S.V. Golovkin et al. [SPHINX collab.]
Z. Phys. C 68 (1995) 585

H. Schmieden

41γ p → K+ Σ0 photoproduction
T. Jude et al. [BGOOD collab.]
Phys. Lett B 820 (2021) 136559

S.V. Golovkin et al. [SPHINX collab.]
Z. Phys. C 68 (1995) 585

H. Schmieden

41

from penta to hexa …

42

→ Dibaryons ?

from penta to hexa …

42

Dibaryons ?
• early SU(6) predictions – NN, NΔ & ΔΔ type dibaryon candidates
Dyson & Xuong, PRL 13 (1964) 815• 3-body calculations NΔ & ΔΔ in good agreement
Gal & Garcilazo, NPA 928 (2014) 73

d*(2380)
observed in pn fusion reaction
at WASA experiment at COSY
P. Adlarson et al. [WASA@COSY],
PRL 106 (2011) 242302• (I) JP = (0) 3+• ΔΔ type object ?
• meanwhile observed in multiple final
states in pn reactions

43

Dibaryons ?
• Microscopic χ quark models:- 2/3 hidden color (compact) configuration- 1/3 molecular component
Huang et al., Chin. Phys. C7 (2015) 071001• d*(2380) in the centre of neutron stars
Vidana et al., PLB 781 (2018) 112• Dark matter ?? – d*(2380) BEC formed in early universe ?
Bashkanov and Watts, J. Phys. G 47 (2020) 03LT01

44

Dibaryons ?
• coherent photoproduction γ d → π π dchallenging: minimal momentum transfer to target deuteron, nbarn x-sec & large qf background• previous data from ELPH

Takatsuku Ishikawa et al., PLB 789 (2019) 413

45

6

ER = 2470 MeV/c2, Γ = 120 MeV/c2
ER = 2630 MeV/c2, Γ = 130 MeV/c2

5}

ELPH@Tohoku

2BW fit: ER = 2615 ± 14 MeV/c ,Γ = 148 ± 29 MeV/c2

4

3

2

20
15
10
5

2300

2400

2500

2600

2700

2800

W [MeV]

2.1

2.2 2.3 2.4 2.5 2.6
π0d invariant mass [GeV/c2](c) 2628 - 2705

30
25
20
15
10
5
0
2

1

0

25

0
2
dσ/d Ωdm [nb/(sr.GeV/c2]

BGOOD data, sequential decay(a) 2523 - 2628

2.1

16

2.2 2.3 2.4 2.5 2.6
π0d invariant mass [GeV/c2](e) 2705 - 2771

14
12
10
8
6
4
2
0
2

2630

2114

2.1

dσ/d Ωdm [nb/(sr.GeV/c2]

ER = 2380 MeV/c2, Γ = 70 MeV/c230

2.2 2.3 2.4 2.5 2.6
π0d invariant mass [GeV/c2]

dσ/d Ωdm [nb/(sr.GeV/c2]

Summed phase space term & 3 BWs:dσ/d Ωdm [nb/(sr.GeV/c2)]7dσ/d Ωdm [nb/(sr.GeV/c2]

dσ/d Ω [nb/sr]

T.C. Jude et al. [BGOOD],
PLB 832 (2022) 137277
arXiv:2202.08594

dσ/d Ωdm [nb/(sr.GeV/c2)]

γ d → d π0 π0 coherent photoproduction @BGOOD
18
16
14
12
10
8
6
4
2
0

22
20
18
16
14
12
10
8
6
4
2
0

(b) 2523 - 2628

0.3

0.4 0.5 0.6 0.7 0.8
π0π0 invariant mass [GeV/c2](d) 2628 - 2705

0.3

0.4 0.5 0.6 0.7 0.8
π0π0 invariant mass [GeV/c2](f) 2705 - 2771

10
8
6
4
2
0

0.3

0.4 0.5 0.6 0.7 0.8
π0π0 invariant mass [GeV/c2]

π0d isovector state: 2114 MeV, Γ≃ 20 MeV
46

Conclusions• multi-quark effects in uds sector observed w/ BGOOD experiment• forward acceptance ⬌ meson-baryon dynamics@ thresholds & low t / pT
Λ(1405) line shape in agreement w/ molecular K̅ N structure•• possible [K*-Σ] configuration N*(2030) in K0Σ0 and K+Λ(1405)
photoproduction (triangle singularity)• possible [K-Σ*(1385)] configuration in K+Σ0
• possible dibaryon transitions in coherent 2π0 d• hadronic structure formation from basic QCD d.o.f. ?
a lot remains to be done, but:meson-baryon & baryon-baryon interactions at thresholds
do play a significant role in uds similar to c sector

H. Schmieden – CLUSHIQ 2022 workshop – Sendai, Japan47

BGOOD collaborationBACKUPγ p → K+ Σ0 photoproduction
T. Jude et al. [BGOOD collab.]
Phys. Lett B 820 (2021) 136559

H. Schmieden

50

Status N* spectroscopy
PDG status instate• missing resonances ?
• relevant degrees of freedom ?

• 3 const. quarks unlikely• quark – diquark ??
• meson d.o.f. ?

JP

N(1860) 5/2+
N(1875) 3/2–
N(1880) 1/2+
N(1895) 1/2–
N(1900) 3/2+
N(1990) 7/2+
N(2000) 5/2+
N(2060) 5/2–
N(2100) 1/2+
N(2120) 3/2–
N(2190) 7/2–
N(2220) 9/2+
N(2250) 9/2–

2010

*

****
**
**
*
****
****
****

2020 (Nγ)

*
**
**
****
****
**
**
***
**
***
**
**
**

e.g.
L.Ya. Glozman and D.O. Riska,
Phys. Rep. 268 (1996) 263
C. Garcia-Recio et al., PLB 582 (2004) 49
M. Lutz, E. Kolomeitsev, PLB 585 (2004) 243

H. Schmieden• inclusion of CLAS, GRAAL, MAMI, ELSA data
• confirmation of known resonances
w/ improved parameters• observation of few (!) new states

51