Strangeness photoproduction at the BGO-OD experiment Tom Jude, on behalf of the BGO-OD collaboration Physikalisches Institut University of Bonn THEIA, 27th Nov 2019 Supported by the DFG PN 388979758 & 405882627 Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 1 / 35
Strangeness photoproduction at the BGO-OD experiment Introduction & motivation - parallels in strange & charmed quark sectors? 1 The BGO-OD experiment at ELSA, Bonn 2 Strangeness photoproduction - first results: 3 K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K + Y and excited hyperons Future opportunities with BGO-OD Supported by the DFG PN 50165297 Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 2 / 35
1. Introduction - N ∗ spectrum: CQM vs. experiment Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 3 / 35
1. Introduction - Status of N ∗ spectroscopy hadronic structure & relevant degrees of freedom - 3 quark states only? Molecule-like states, meson-baryon degrees of freedom? 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. How would this manifest in reaction mechanisms & excitation spectra? BnGa - E. Klempt, A. Sarantsev, U. Thoma, V. Nikonov Wealth of data from ELSA, MAMI, GRAAL & CLAS facilities Much improved understanding of known resonances, but few new states observed Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 4 / 35
1. Motivation - Exotic phenomena in the charmed sector Pentaquark candidates observed at LHCb P c (4450) + & P c (4380) + at Σ c ¯ D ∗ threshold X (3872) → π + π − J /ψ - most cited paper from Belle, PRL91, 262001 (2003) R. Aaij et al, PRL 115, 072001 (2015) Very close to D 0 ¯ D 0 ∗ threshold 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) - molecular D 0 ¯ D 0 ∗ state? N.A. T¨ ornqvist, Phys. Lett. B590, 209 (2004) Nature 523, 267 (2015) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 5 / 35
1. Motivation - Similarities in the uds sector? Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 5 / 35
1. Motivation - Structure of the Λ(1405) K. Moriya et al. (CLAS) Phys. Rev. C 87 , 035206 (2013) Well established since the 1960’s but peculiar features! Difficult to reconcile within a CQM Mass too low compared to N ∗ (1535) Large spin orbit splitting to Λ(1520) Lies between the π Σ & ¯ KN thresholds Λ(1405) - dynamically generated by meson-baryon interactions? Line shape (invariant mass) depends upon the decay mode J.C. Nacher, E. Oset, H. Toki, A. Ramos, U.G. ( → π 0 Σ 0 , π + Σ − , π − Σ + ) Meissner, Nucl. Phys. A 725 (2003) 181 LQCD: J.M.M Hall et al., PRL 114 (2015) 132002 Distorted by interference of Isospin 0 & 1 amplitudes U χ PT: R. Molina & M. D¨ oring, Phys. Rev. D 94, 056010 & 079901 (2016) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 6 / 35
1. Motivation - Cusp 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 THEIA, 27th Nov 2019 7 / 35
1. Motivation - K 0 photoproduction Off the proton: A. Ramos and E. Oset, Phys. Lett. B 727 , (2013) 287 The role of vector-baryon channels & resonances in the γ p → K 0 Σ + & γ n → K 0 Σ 0 reactions near the K ∗ Λ threshold The same model that predicted P c states as meson-baryon dynamically generated! Cusp - destructive interference of dynamically generated N ∗ states Predict constructive interference & peak in γ n → K 0 Σ 0 Off the neutron (bottom) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 8 / 35
1. Motivation - Parallels between charmed & strange sectors Table from H. Schmieden, private communication (2018) Charmed-sector Strange-sector Meson Baryons Meson Baryons State(s) X (3872) P ∗ c (4380 / 4450) f 1 (1285) N ∗ (2030 / 2080) D ∗ 0 ¯ D 0 / D 0 ¯ K ∗ ¯ Λ ∗ ¯ c ¯ D + Σ c ¯ K / K ¯ K + Σ ¯ D ∗ 0 π exchange transition Λ ∗ D ∗ K ∗ K ∗ J PC = 1 ++ J P = 3 / 2 − J PC = 1 ++ J P = 3 / 2 − Quantum numbers D 0 ¯ c ¯ K ¯ Σ ¯ D 0 π 0 Σ + D 0 π 0 K π 0 3-body threshold K π Closed flavour thresh. J /ψω χ c 1 p φ f 0 (500) φ p s-sector c-sector Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 8 / 35
1. Motivation - Threshold dynamics Figure from H. Schmieden, private communication (2018) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 9 / 35
1. Motivation - 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 + π K 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 Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 10 / 35
Strangeness photoproduction at the BGO-OD experiment Introduction & motivation - parallels in strange & charmed quark sectors? 1 The BGO-OD experiment at ELSA, Bonn 2 Strangeness photoproduction - first results: 3 K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K + Y and excited hyperons Future opportunities with BGO-OD Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 10 / 35
2. The Electron Stretcher Accelerator (ELSA) A 3 stage e − accelerator delivering continuous electron beams up to ∼ 3 . 2 GeV BGO-OD Dipole (horizontal) Dipole (vertical) extraction septa hadron Quadrupole physics Skew Quadrupole superconducting solenoid Sextupole experiments PETRA cavities Combined-Function Magnet Solenoid Crystal Barrel Radio Frequency tune jump quadrupole Compton polarimeter (for internal beam) stretcher ring 0.5 GeV - 3.2 GeV booster synchrotron 0.5 GeV - 1.6 GeV irradiation injektion septa area tune jump DESY cavity quadrupole half cell of stretcher ring synchrotron light Q BPM M diagnosis beam line skew quadrupoles Mott polarimeter - pol. e beam line for electron source gun detector tests (50 keV) LINAC 2 (26 MeV) extraction septa 0 m 5 m 10 m 15 m Figure adapted from W. Hillert et al. , EPJ Web Conf. 134, 05002 (2017) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 11 / 35
2. The BGO-OD experiment at ELSA Spokespersons: H. Schmieden (Bonn) & P. Levi Sandri (Frascati) The BGO-OD experimental setup at ELSA , S. Alef et al. Submitted to EPJA. arXiv:1910.11939v2 BGO calorimeter (central region) & Forward Spectrometer combination High momentum resolution, excellent charged & neutral particle ID T oF BGO ball O pen D ipole magnet fl ux monitoring driftchambers SciFi2 MOMO T agger magnet goniometer forward spectrometer e - -beam central detector beam dump agger ARGUS T Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 12 / 35
2. The BGO-OD experiment at ELSA - Central region Spokespersons: H. Schmieden (Bonn) & P. Levi Sandri (Frascati) The BGO-OD experimental setup at ELSA , S. Alef et al. Submitted to EPJA. arXiv:1910.11939v2 BGO calorimeter (central region) Charged & neutral particle ID excellent time resolution ( ∼ 2 ns) per BGO crystal all combinatorics 8 24.7° 10 bin + charge cut BGO twogammap_invmass_6 twogammap_invmass_6 twogammap_fitted_invmass_6 twogammap_fitted_cut_invmass_6 twogammap_chargecut_invmass_6 twogammap_missmass_cut_invmass_6 Entries 3.037735e+07 + missing mass cut Entries 6.884315e+08 Entries 6.884315e+08 Entries 1.807174e+07 2 7 Entries 1.16354e+08 Counts per 7 MeV/c 10 10.4° Entries 3.037993e+07 Mean Mean Mean Mean 177.7 155 177.7 160.6 Mean 137 MWPC Mean + kinematic fit Std Dev 158.3 106.5 Std Dev Std Dev Std Dev 106.4 128.5 128.5 Std Dev 85.63 Std Dev 100.6 6 10 + confidence level cut 5 10 SciRi MOMO Scintillator Barrel SciFi 4 MRPC 10 3 10 2 10 200 400 600 800 1000 2 Two photon invariant mass [MeV/c ] Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 13 / 35
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