Strangeness photoproduction at the BGO-OD experiment Tom Jude On - - PowerPoint PPT Presentation

Strangeness photoproduction at the BGO-OD experiment

Tom Jude On behalf of the BGO-OD Collaboration

Physikalisches Institut University of Bonn Supported by the DFG PN 50165297

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 1 / 35

Strangeness photoproduction at extremely forward angles at the BGO-OD experiment

The BGO-OD experiment at ELSA, Bonn Motivation: Hadron structure - parallels in strange & charmed quark sectors? Strangeness photoproduction - first results:

1

Λ(1405) & access to higher lying hyperons

2

Extreme forward cross sections for K +Λ & K +Σ0 photoproduction

3

K 0 photoproduction off proton & neutron (deuterium) targets

4

Future opportunities - Y-N interaction & hypernuclei studies Summary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 2 / 35

The Electron Stretcher Accelerator (ELSA)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 3 / 35

The BGO-OD experiment at ELSA

BGO calorimeter (central region) & Forward Spectrometer combination High momentum resolution, excellent charged & neutral particle ID

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 4 / 35

The BGO-OD experiment at ELSA

BGO calorimeter (central region) & Forward Spectrometer combination High momentum resolution, excellent charged & neutral particle ID

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 4 / 35

The BGO-OD experiment at ELSA

BGO calorimeter (central region) & Forward Spectrometer combination High momentum resolution, excellent charged & neutral particle ID

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 4 / 35

Motivation - Exotic phenomena in the charmed sector

Pentaquark candidates observed at LHCb - Pc(4450)+ & Pc(4380)+

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

Meson-baryon dynamically generated states in the charmed sector - J.-J. Wu, R. Molina, E. Oset,

and B.S. Zou, Phys. Rev. Lett. 105, 232001 (2010)

Forsaken pentaquark particle spotted at CERN

Nature 523, 267 (2015)

X(3872) - a molecular D0 ¯ D0∗ state?

N.A. T¨

• rnqvist, Phys. Lett. B590, 209 (2004)

Close to D0 ¯ D0∗ threshold, favouring DD∗ decay

• B. Aubert et al (BARBAR Collaboration), Phys. Rev.

D77 111101 (2008)

JPC verified: 1++ R. Aaij et al. (LHCb

Collaboration), PRL 110, 222001 (2013)

X(3872) discovery - most cited paper from Belle, PRL91, 262001 (2003)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 5 / 35

Motivation - Structure of the Λ(1405)

Between the πΣ & ¯ KN thresholds Line shape (invariant mass) depends upon the πΣ decay mode Distorted by interference of Isospin 0 & 1 amplitudes J.C. Nacher et al., Nucl.

• Phys. A 725, 181 (2003)
• K. Moriya et al. (CLAS Collaboration) Phys. Rev. C 87,

035206 (2013)

Λ(1405) - dynamically generated by meson-baryon interactions? J.C.

Nacher, E. Oset, H. Toki, A. Ramos, U.G. Meissner,

• Nucl. Phys. A 725 (2003) 181

LQCD calculations: J.M.M Hall et al., Phys.

• Rev. Lett. 114 (2015) 132002

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 6 / 35

Motivation - Cusp structure in γp → K 0Σ+ cross section

• R. Ewald et al.,Phys. Lett. B 713 (2012) 180 (CBELSA/TAPS Collaboration).

This data: Full squares, Previous CBELSA-TAPS data: open squares, Previous SAPHIR data: triangles (references therein)

Cusp-like structure due to K ∗0 subthreshold production rescattering to π0 & K 0? Grey points - K 0Σ+ + K ∗Σ+ M. Nanova et al., EPJ A35, 333 (2008)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 7 / 35

Motivation - K 0 photoproduction off the neutron

• A. Ramos and E. Oset, Phys. Lett. B 727, (2013) 287 The

role of vector-baryon channels and resonances in the γp → K 0Σ+ and γn → K 0Σ0 reactions near the K ∗Λ threshold K 0Λ Complementary to K +Λ - relate hadronic coupling constants Limited available data, K. Tsukada et al,

• Phys. Rev. C 78, 014001 (2008)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 8 / 35

Motivation - Parallels between charmed and strange sectors

Table and figures from H. Schmieden, private communication

c-sector s-sector

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 9 / 35

Motivation - Threshold dynamics

Figure from H. Schmieden, private communication Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 10 / 35

Λ∗ and Σ∗ spectra

Very limited succss with constituent quark models Models including meson-baryon interactions as degrees of freedom - more successful, L.Ya. Glozman and D.O. Riska, Physics Reports 268 (1996) 263, C. Garcia-Recio et al., Phys. Lett. B

582 (2004) 49, M.F.M. Lutz, E.E. Kolomeitsev, Phys. Lett. B 585 (2004) 243.

Hadronic molecules - predict new Y ∗ states, eg Σ∗ (JP = 1/2−) close to Σ(1385): Jia-Jun Wu et al., Phys. Rev. D 80 (2009) 017503 K −p → Λπ+π− 26 PDG Σ∗ states - 16 are listed as existence poor to fair. C. Patrignani et al.

(Particle Data Group), Chin. Phys. C 40, 100001 (2016) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 11 / 35

Experimental requirements

Charged particle identification at extremely forward angles - reaction dynamics at very low momentum exchange (t-channel) High forward momentum resolution Reconstruction of complicated, mixed charge final states - eg K +Λ(1405) → K +(π0Σ0) → K +π0γpπ−

K N K Λ / Σ π K* γ K+ p K+ Λ(1405) γ

Unique & complementary to existing facilities (eg CBELSA-TAPS neutral particle reconstruction, CLAS charged particle reconstruction). BGO-OD at the ELSA facility, Bonn (Germany)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 12 / 35

Detector performance - central region

1st large data set taken in 2017. Neutral meson reconstruction (lH2 target):

invariant mass [MeV] γ 2 100 200 300 400 500 600 700 800 [MeV] γ missing mass recoiling from 2 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Neutral meson reconstruction in the BGO ball

invariant mass [MeV] γ 2 100 200 300 400 500 600 700 Counts 20 40 60 80 100

10 ×

= 10 MeV σ : mean = 135 MeV, π = 20 MeV σ : mean = 557 MeV, η (scaled x50)

Demonstration (1 of many bench marks) - γp → ωp dσ/dΩ via the mixed charge decay, ω → π0π+π− (G. Scheluchin)

[MeV]

E 1200 1400 1600 1800 2000 2200 2400 2600 2800 b/sr] µ [ Ω /d σ d 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

< -0.60

CM

θ

• 0.67 < cos

[MeV]

E 1200 1400 1600 1800 2000 2200 2400 2600 2800 b/sr] µ [ Ω /d σ d 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

< -0.33

CM

θ

• 0.44 < cos

) γ π → ω CB-ELSA/TAPS ( )

• π

+

π π → ω CLAS ( )

• π

+

π π → ω BGO-OD (

Preliminary

• F. Dietz et al. (CB-ELSA/TAPS),
• Eur. Phys. J. A 51, 6 (2015)
• M. Williams et al. (CLAS), Phys.
• Rev. C 80, 065208 (2009)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 13 / 35

Detector performance - forward spectrometer

Top - Particle identification in the Forward Spectrometer Bottom - “Missing mass” from forward proton (raw counts)

p [MeV] 500 1000 1500 2000 2500 3000 β 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Forward particle reconstructed mass [MeV]

+

e

+

π

+

K protons

Forward proton missing mass [MeV]

Counts 50 100 150 200 250

10 ×

η ω ’ η φ

Forward proton missing mass [MeV] 900 920 940 960 980 1000 1020 1040 1060 Counts 14000 16000 18000 20000 22000 24000 26000

’ η φ

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 14 / 35

Strangeness photoproduction at extremely forward angles at the BGO-OD experiment

BGO-OD experiment at ELSA, Bonn Motivation: Hadron structure - parallels in strange & charmed quark sectors? Strangeness photoproduction - first results:

1

Λ(1405) & access to higher lying hyperons

2

Extreme forward cross sections for K +Λ & K +Σ0 photoproduction

3

K 0 photoproduction off proton & neutron (deuterium) targets

4

Future opportunities - Y-N interaction & hypernuclei studies Outlook and conclusions

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 15 / 35

Mass recoiling from K + in the forward spectrometer

The study of Y ∗ states in an extremely low momentum transfer region

missing mass [MeV]

+

K 1100 1200 1300 1400 1500 1600 missing mass [MeV] π

+

K 900 950 1000 1050 1100 1150 1200 1250 1300

(1116) Λ (1193) Σ (1405) Λ (1385)/ Σ

n γ n+ Λ Σ

) missing mass π

+

Discriminating between states with (K

missing mass [MeV]

+

K 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Counts 200 400 600 800 1000

(1116) Λ (1193) Σ (1405) Λ (1385) Σ (1520) Λ momentum < 1 GeV

+

All events for K

Identify Y ∗ states from K +π0 recoiling mass

K +Λ → K +π0n (Missing neutron mass from K +π0 system) K +Λ(1405) → K +π0Σ0 (Missing Σ0 mass from K +π0 system) K +Σ(1385) → K +π0Λ (Missing Λ mass from K +π0 system) Goal - Λ(1405) lineshape at low momentum transfer region

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 16 / 35

Λ(1405) over a broad kinematic range

• G. Scheluchin

Complements CLAS data - K. Moriya et al., Phys. Rev. C

88, 045201 (2013)

Triangle singularity can describe peak at W = 2110 MeV & cos θ = 0: Full K +Λ(1405) & K +Λ(1520) reconstruction K +Λ(1405) → K +π0Σ0 → K +γγγπ−p

• E. Wang et al., Phys. Rev. C 95, 015205 (2017)

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 17 / 35

Strangeness photoproduction at extremely forward angles at the BGO-OD experiment

BGO-OD experiment at ELSA, Bonn Motivation: Hadron structure - parallels in strange & charmed quark sectors? Strangeness photoproduction - first results:

1

Λ(1405) & access to higher lying hyperons

2

Extreme forward cross sections for K +Λ & K +Σ0 photoproduction

3

K 0 photoproduction off proton & neutron (deuterium) targets

4

Future opportunities - Y-N interaction & hypernuclei studies Outlook and conclusions

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 18 / 35

K +Λ at forward angles - motivation

Not only Y ∗ states at forward angles important - ground state hyperon photoproduction at low t virtually unconstrained by data!

Bydzovsky and D. Skoupil, arXiv:1211.2684v1 (2012) Proceedings of SNP12

Crucial constraint for hypernuclei electroproduction!

• eg Saclay Leon model for p(e, e′K +)Λ
• T. Mizutani, C. Fayard, G.-H. Lamot & B. Saghai, Phys. Rev. C 58, 75 (1998)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 19 / 35

K +Λ at forward angles - motivation

• M. E. McCracken, et. al (CLAS Collaboration),
• Phys. Rev. C 81, 025201 (2010)
• D. Skoupil, P. Bydzovsky, Phys. Rev. C97, 025202 (2018)

At BGO-OD

Forward CM polar angle range approx. 3-260, 0.9 < cos θK +

cm < 1.0

Unprecedented θK +

cm resolution (< 10)

PΛ - recoil Λ polarisation accessed by angular distribution of Λ → π0n & π−p

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 20 / 35

Selecting forward K + at BGO-OD

Mass calculated from momentum and β Red - real data, Blue - simulated data Low mass shoulder from π+ and e+ background

]

Mass [MeV/c 300 350 400 450 500 550 600 650 700 10 20 30 40 50 60

p = 500 - 600 MeV/c

]

Mass [MeV/c 300 350 400 450 500 550 600 650 700 20 40 60 80 100

p = 600 - 700 MeV/c

]

Mass [MeV/c 300 350 400 450 500 550 600 650 700 20 40 60 80 100

p = 700 - 800 MeV/c

]

Mass [MeV/c 300 350 400 450 500 550 600 650 700 20 40 60 80 100 120 140

p = 800 - 900 MeV/c Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 21 / 35

Extracting K +Λ & K +Σ0 signal from background

600 700 800 900 1000 1100 1200 1300 1400 ]

Missing mass [MeV/c

K 10 20 30 40 50 Events / ( 8 )

= 936 MeV

γ

E

600 700 800 900 1000 1100 1200 1300 1400 ]

Missing mass [MeV/c

K 20 40 60 80 100 120 Events / ( 8 )

= 1049 MeV

γ

E

Data - black points )

+

π from beam,

+

Background (e Λ

+

Simulated K Σ

+

Simulated K

600 700 800 900 1000 1100 1200 1300 1400 ]

Missing mass [MeV/c

K 20 40 60 80 100 120 Events / ( 8 )

= 1156 MeV

γ

E

600 700 800 900 1000 1100 1200 1300 1400 ]

Missing mass [MeV/c

K 20 40 60 80 100 120 140 160 Events / ( 8 )

= 1209 MeV

γ

E

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 22 / 35

Extracting K +Λ & K +Σ0 signal from background

To reduce background/ check systematics

Different selection of forward K + masses (1,2,3 σ) Reduce background via Λ → π0n Σ0 → γΛ identification -

600 700 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 70 80 90 Events / ( 8 )

decay photon Σ After selecting

= 1209 MeV

γ

E

20 40 60 80 100 120 140 160 180 200 rest frame) [MeV] Σ energy ( γ 200 400 600 800 1000 1200 1400 1600 1800 2000 Counts

= 77 MeV

Λ

• M

Σ

M

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 23 / 35

Preliminary forward K +Σ0 differential cross sections

High statistics data set - to be binned into 0.01 cos θK +

CM intervals

Ongoing analysis - systematic errors to be determined

Photon beam energy [MeV] 1100 1200 1300 1400 1500 1600 1700 b/sr] µ [ Ω /d σ d 0.05 0.1 0.15 0.2 0.25 Σ

+

K → p γ < 1.00

+

K CM

θ 0.92 < cos BGO-OD (preliminary) CLAS (Bradford ’06) CLAS (Dey ’10) SAPHIR (Glander ’04) BnGa PWA 1450-1700 MeV BGO-OD data in preparation

Preliminary

• R. Bradford et al., Phys. Rev. C73, 035202 (2006), B.Dey et al., Phys.Rev. C82, 025202 (2010),

K.H. Glander et al., Eur. Phys. J. A19, 251 (2004), CLAS data in cos θCM

K+ 0.85 to 0.95 interval

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 24 / 35

Preliminary forward K +Λ differential cross sections

Highest statistics data set - to be binned into 0.01 cos θK +

CM intervals

Ongoing analysis - systematic errors to be determined

Photon beam energy [MeV] 1000 1100 1200 1300 1400 1500 b/sr] µ [ Ω /d σ d 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Λ

+

K → p γ < 1.00

+

K CM

θ 0.92 < cos BGO-OD (preliminary) CLAS (McCracken ’10) CLAS (Bradford ’06) SAPHIR (Glander ’04) BnGa PWA

Preliminary

• R. Bradford et al., Phys. Rev. C73, 035202 (2006), M.E.McCracken et al., Phys.Rev. C81, 025201 (2010),

K.H. Glander et al., Eur. Phys. J. A19, 251 (2004), CLAS data in cos θCM

K+ 0.85 to 0.95 interval

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 25 / 35

Strangeness photoproduction at extremely forward angles at the BGO-OD experiment

BGO-OD experiment at ELSA, Bonn Motivation: Hadron structure - parallels in strange & charmed quark sectors? Strangeness photoproduction - first results:

1

Λ(1405) & access to higher lying hyperons

2

Extreme forward cross sections for K +Λ & K +Σ0 photoproduction

3

K 0 photoproduction off proton & neutron (deuterium) targets

4

Future opportunities - Y-N interaction & hypernuclei studies Outlook and conclusions

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 26 / 35

Preliminary identification of K 0Σ+ with BGO-OD

Study the Cusp-like structure in the cross section. K ∗0 subthreshold production rescattering to π0 & K 0? Access γp → K 0Σ+ via different decay modes at BGO-OD Reduction of background & improved momentum resolution acheivable with the MWPC (analysis underway)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 27 / 35

γn(p) → K 0Σ0 using a deuterium target

Peak predicted from coherent interference of dynamically generated resonances

• A. Ramos and E. Oset, Phys. Lett. B 727, (2013) 287

γn(p) → K 0Σ0 at BGO-OD

Analysis by K. Kohl K 0 → 2π0 in the BGO Proton in the Forward Spectrometer & select missing π− mass from Σ0 → pπ− Photon from Σ0 → γΛ: Σ0 − Λ mass difference in the Σ0 rest frame

]

2

invariant mass [MeV/c π Two

200 300 400 500 600 700 800 500 1000 1500 2000

Real data Σ Simulated K

K

M

candidate rest frame [MeV] Σ energy in γ

50 100 150 200 250 300 350 400 450 500 500 1000 1500 2000 2500 3000 2

= 77 MeV/c

Λ

• M

Σ

M

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28 / 35

Strangeness photoproduction at extremely forward angles at the BGO-OD experiment

BGO-OD experiment at ELSA, Bonn Motivation: Hadron structure - parallels in strange & charmed quark sectors? Strangeness photoproduction - first results:

1

Λ(1405) & access to higher lying hyperons

2

Extreme forward cross sections for K +Λ & K +Σ0 photoproduction

3

K 0 photoproduction off proton & neutron (deuterium) targets

4

Future opportunities - Y-N interaction & hypernuclei studies Outlook and conclusions

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 29 / 35

Future opportunities: Hypernuclei production

Hypernuclei photoproduction, eg γ +12 C → K + +12

Λ B - natural laboratory

to probe the Y − N interaction Forward K +, coherent production, leaving the Λ within the Fermi surface of the residual nuclei

• P. Achenbach, arXiv:1101.4395 (2008)

Opportunities for first real photon beam photoproduction?

In conversation with P. Achenbach & J. Pochodzalla, 2018

Mesic decay (Λ → πN) identification in BGO - favour light nuclei Identify specific states, eg γ +12 C → π0 +12 C ∗ → π0 +12 C + γ′ (4.4 MeV) Can use “sensitive” targets that are spoiled by intense e− beams (eg Li) Hypernuclei lifetime measurements, angular K + distributions, differential cross sections...

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 30 / 35

Future opportunities: Hypernuclei production

Coherent pion production (“non-strange” example)

Method similar to C.M. Tarbert, D.P. Watts et. al (A2 Collaboration) Phys Rev. Lett. 100 (2008) 13 γ +12 C → π0 +12 C ∗ → π0 +12 C + γ′ (4.4 MeV) E2 transition, Jπ : 2+ → 0+, sin2(2α) distr. between nuclear recoil & γ’ ∼ 2 hours of commissing data with BGO-OD:

energy [MeV] π Calculated - measured 300 − 200 − 100 − 100 200 300 Counts 100 200 300 400 500 600 700 800 900

= 297 MeV

γ

E angles π All < 40

π

θ events π

• 1. Search for coherent

Photon energy [MeV] 2 4 6 8 10 Counts 100 200 300 400 500 600 700 800 900

Exponential + Gaussian fn. 4.5 MeV ≈ Mean 0.6 MeV ≈ σ

• 2. Search for additional decay photon

[deg] α 50 100 150

Counts

1 2 3 4 5

) fit α (2

2

sin angular distr. γ

• 3. Verification - decay

Not efficiency corrected Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 31 / 35

Future opportunities: Y-N studies with deuterium targets

Final state interactions for γd → K +Λ + (n) KN, YN & pion mediated θK < 300 - FSI dominated by Y-N Models of YN forces - cusps at ΣN & YN thresholds

• K. Miyagawa, T. Mart, C. Bennhold, W. Gl¨
• ckle, Phys. Rev.

C74 (2006) 034002

Cross section & pol. obs. sensitive to YN interactions at these cusps!

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 32 / 35

Beam asymmetry for γp → η′p near threshold - motivation

• A. Fantini, R. Di Salvo, P. Levi Sandri

Previous GRAAL data: In this beam energy region, the recoil proton is always in the forward spectrometer

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 33 / 35

Beam asymmetry for γp → η′p near threshold - At BGO-OD

Analysis by S. Alef In this beam energy region, the recoil proton is always in the forward spectrometer Preliminary asymmetries:

Forward proton missing mass [MeV] 900 920 940 960 980 1000 1020 1040 1060 Counts 14000 16000 18000 20000 22000 24000 26000

’ η φ

] ° [ φ 150 − 100 − 50 − 50 100 150 Asymmetry 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

= 1460 - 1479 MeV

γ

E

] ° [ φ 150 − 100 − 50 − 50 100 150 Asymmetry 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

= 1467 - 1488 MeV

γ

E

] ° [ φ 150 − 100 − 50 − 50 100 150 Asymmetry 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

= 1477 - 1499 MeV

γ

E

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 34 / 35

Summary

Hadrons - molecular-like structure? BGO-OD - strangeness photoproduction - extreme forward angles Low momentum transfer region 1st preliminary results - K +Y at forward angles Λ(1405), K 0 off protons & neutrons - analyses ongoing Y-N interaction study opportunities - deuterium, hypernuclei...

missing mass [MeV]

K 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Counts 200 400 600 800 1000

(1116) Λ (1193) Σ (1405) Λ (1385) Σ (1520) Λ momentum < 1 GeV

+

All events for K

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 35 / 35