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: Λ(1405) & access to higher lying hyperons 1 Extreme forward cross sections for K + Λ & K + Σ 0 photoproduction 2 K 0 photoproduction off proton & neutron (deuterium) targets 3 Future opportunities - Y-N interaction & hypernuclei studies 4 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 X (3872) - a molecular D 0 ¯ D 0 ∗ state? Pentaquark candidates observed at LHCb - P c (4450) + & P c (4380) + N.A. T¨ ornqvist, Phys. Lett. B590, 209 (2004) Close to D 0 ¯ D 0 ∗ threshold, favouring R. Aaij et al, PRL 115, 072001 (2015) DD ∗ decay 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 B. Aubert et al (BARBAR Collaboration), Phys. Rev. D77 111101 (2008) J PC verified: 1 ++ R. Aaij et al. (LHCb Collaboration), PRL 110, 222001 (2013) X(3872) discovery - most cited paper from Belle, PRL91, 262001 (2003) Nature 523, 267 (2015) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 5 / 35
Motivation - Structure of the Λ(1405) Between the π Σ & ¯ KN thresholds Λ(1405) - dynamically generated by Line shape (invariant mass) meson-baryon interactions? J.C. depends upon the π Σ decay mode Nacher, E. Oset, H. Toki, A. Ramos, U.G. Meissner, Nucl. Phys. A 725 (2003) 181 Distorted by interference of Isospin 0 & 1 amplitudes J.C. Nacher et al. , Nucl. LQCD calculations: J.M.M Hall et al., Phys. Phys. A 725, 181 (2003) Rev. Lett. 114 (2015) 132002 K. Moriya et al. (CLAS Collaboration) Phys. Rev. C 87 , 035206 (2013) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 6 / 35
Motivation - Cusp structure in γ p → K 0 Σ + 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 π 0 & K 0 ? Grey points - K 0 Σ + + 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 γ p → K 0 Σ + and γ n → K 0 Σ 0 reactions near the K ∗ Λ threshold K 0 Λ 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 s-sector c-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 ∗ ( J P = 1 / 2 − ) close to Σ(1385): Jia-Jun Wu et al., Phys. Rev. D 80 (2009) 017503 K − p → Λ π + π − 26 PDG Σ ∗ states - 16 are listed as existence poor to fair. C. Patrignani et al. Tom Jude (University of Bonn) (Particle Data Group), Chin. Phys. C 40 , 100001 (2016) 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 + ( π 0 Σ 0 ) → K + π 0 γ p π − K + γ K γ K* K + K π Λ / Σ Λ(1405) p N 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 (lH 2 target): Neutral meson reconstruction in the BGO ball 1500 6 [MeV] × 10 Counts 1400 5 10 100 γ 1300 missing mass recoiling from 2 1200 4 10 π 0 : mean = 135 MeV, σ = 10 MeV 80 1100 10 3 1000 60 900 η : mean = 557 MeV, σ = 20 MeV 10 2 800 40 (scaled x50) 700 10 20 600 500 1 0 100 200 300 400 500 600 700 800 0 2 γ invariant mass [MeV] 100 200 300 400 500 600 700 2 γ invariant mass [MeV] Demonstration (1 of many bench marks) - γ p → ω p d σ /dΩ via the mixed charge decay, ω → π 0 π + π − (G. Scheluchin) Preliminary 1 1 b/sr] b/sr] -0.44 < cos θ < -0.33 -0.67 < cos θ < -0.60 0.9 0.9 CM CM µ µ [ [ - Ω Ω BGO-OD ( ω → π 0 π + π ) 0.8 0.8 /d /d σ σ 0.7 0.7 0 d d CB-ELSA/TAPS ( ω → π γ ) F. Dietz et al. (CB-ELSA/TAPS), 0.6 0.6 - CLAS ( ω → π 0 π + π ) 0.5 0.5 Eur. Phys. J. A 51 , 6 (2015) 0.4 0.4 0.3 0.3 M. Williams et al. (CLAS), Phys. 0.2 0.2 0.1 0.1 Rev. C 80 , 065208 (2009) 0 0 1200 1400 1600 1800 2000 2200 2400 2600 2800 1200 1400 1600 1800 2000 2200 2400 2600 2800 E [MeV] E [MeV] γ γ 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) 3 1.1 × 10 100 β e + 1 protons 10 4 + π 80 0.9 0.8 3 10 60 0.7 0.6 2 10 40 0.5 0.4 10 20 + K 0.3 0 1 500 1000 1500 2000 2500 3000 0 200 400 600 800 1000 1200 1400 p [MeV] Forward particle reconstructed mass [MeV] 3 × 10 Counts Counts 26000 η η ’ 250 24000 ω 200 22000 150 20000 φ η ’ 18000 100 φ 16000 50 14000 0 900 920 940 960 980 1000 1020 1040 1060 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Forward proton missing mass [MeV] Forward proton missing mass [MeV] 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: Λ(1405) & access to higher lying hyperons 1 Extreme forward cross sections for K + Λ & K + Σ 0 photoproduction 2 K 0 photoproduction off proton & neutron (deuterium) targets 3 Future opportunities - Y-N interaction & hypernuclei studies 4 Outlook and conclusions Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 15 / 35
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