T.C. Jude D.I. Glazier, D.P. Watts The University of Edinburgh

1. Strangeness Photoproduction: Polarisation Transfer & Cross-Section Measurements T.C. Jude D.I. Glazier, D.P. Watts The University of Edinburgh

2. g + p g K+ + L p + p- (~ 64%) n + p0(~ 36%) 2g g + p g K+ + S0 g + L Hyperon Photoproduction • Important for investigations of nucleon resonances • A crucial test of QCD based chiral perturbation theories in the strange quark sector Threshold Energy ~ 911 MeV Threshold Energy ~ 1046 MeV T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

3. Polarisation observables • Spin observables – constrains reaction models and baryon resonance structure • Circularly polarised photons - polarisation transferred to the recoiling hyperon • CX andCZ: PX = -PgCX, Py = P, PZ = -PgCz • L decay is a weak decay (parity violating) – measure the polarisation by the distribution of the decay particles (proton or neutron) • Previous measurements found them to be close to one and zero respectively for all measured kinematics [1] [1] R. Bradford et al., Phys Rev. C 75, 035205 (2007) T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

4. Eg [GeV] Cross-Section Measurements • No detailed measurements of g p g K+L at threshold • Significant discrepancies between cross-sections measured at JLab [2] and ELSA [3]. The large angular coverage and intense photon beam over the range ~ 0.9 to 1.4 GeV make the Crystal Ball ideal for strangeness measurements at threshold [2] R. Bradford et al., Phys Rev. C 73, 035202 (2006) [3] K.H. Glander et al., Eur Phys. J. A 19, 251 (2004) [4] T. Mart arXiv:0803.0601v1 [nucl-th] (2008) T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

5. First cluster from K+ < 3ns Secondary cluster from K+gm++ nm decay > 10ns Identifying strange mesons • A new method of tagging a strange meson reaction channel • Identify the K+ decay within the crystals of the Crystal Ball K+ m++nm(~ 63%)Mean lifetime of K+ ~ 12 ns p++p0(~ 21%) T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

6. K+ ID in the Crystal Ball T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

7. K+ K+ ID in the Crystal Ball • DE-E analysis: • Crystal Ball – Identifies ~ 8% of all K+ • Misidentification of non-strange channels ~ 10-5 T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

8. K+ ID in TAPS T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

9. Correcting for the vertex position of the decay:Lg n + p0 Reconstructed K+ energy vs. difference between measured and reconstructed energy Invariant mass of two photons in coincidence Missing mass from K+ and photon in coincidence (simulation) K+L Before Correction After Correction K+S0 K+L K+S Kinematic corrections • Distinguishing between K+S0 and K+Levents by: • (a) Differences in missing mass and reconstructed energies • (b) Identification of the photon from the decay: S0ggL • (c) Direct detection of the neutron and momentum measurement T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

10. qzAsymmetry Measurements • Measuring the polar angle of the neutron from the decay of the L. Reference frames consistent with [1] • Can extract CZand CX • Can include more data from the Lg p p0 decay [1] R. Bradford et al., Phys Rev. C 75, 035205 (2007) T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

11. g p g K+ L Cross-Section Measurements • 5M g p g K+L generated events for the detection efficiency, edetbinned into Eg andq. • For preliminary measurements, assume a tagging efficiency, etagg ~ 0.6 [5] • target density, r ~ 2.023E(27) protons m-2 • Use the JLab convention [2]: (integrate over the q part of the solid angle only) Next slide: CB data JLab data[2] (2006) SAPHIR data[3] (2004) [2] R. Bradford et al., Phys Rev. C 73, 035202 (2006) [3] K.H. Glander et al., Eur Phys. J. A 19, 251 (2004) [5] V.L. Kashevarov, A2 Collaboration meeting, Dubrovnik (2008) T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

12. -5.5 < cos(qK+) < -4.5 -3.5 < cos(qK+) < -2.5 Preliminary Preliminary -0.5 < cos(qK+) < 0.5 1.5 < cos(qK+) < 2.5 Preliminary Preliminary T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

13. Summary • First detection of kaons with the Crystal Ball at MAMI-C • A new technique of strangeness identification – has application for calorimeters elsewhere • Preliminary asymmetry measurements with a circular polarised photon beam – will be used to extract CX and CZ • Preliminary cross-section measurements close to threshold T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008