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

Hyperon Photoproduction  p  K + +  p +  - (~ 64%) n +  0 (~ 36%)   p  K + +    Important for investigations of nucleon resonances A crucial test of QCD based chiral perturbation theories in the strange quark sector T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008 Threshold Energy ~ 911 MeV Threshold Energy ~ 1046 MeV

Polarisation observables Spin observables – constrains reaction models and baryon resonance structure Circularly polarised photons - polarisation transferred to the recoiling hyperon C X and C Z : P X = -P  C X, P y = P, P Z = -P  C z  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] T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008 [1] R. Bradford et al., Phys Rev. C 75, (2007)

Cross-Section Measurements Significant discrepancies between cross-sections measured at JLab [2] and ELSA [3]. T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008 E  [GeV] [2] R. Bradford et al., Phys Rev. C 73, (2006) [3] K.H. Glander et al., Eur Phys. J. A 19, 251 (2004) [4] T. Mart arXiv: v1 [nucl-th] (2008) 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 No detailed measurements of  p  K +  at threshold

Identifying strange mesons K +     (~ 63%) Mean lifetime of K + ~ 12 ns     (~ 21%) First cluster from K + < 3ns Secondary cluster from K +      decay > 10ns A new method of tagging a strange meson reaction channel Identify the K + decay within the crystals of the Crystal Ball T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

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

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

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

Kinematic corrections Distinguishing between K +  0 and K +  events by: (a) Differences in missing mass and reconstructed energies (b) Identification of the photon from the decay:  0    (c) Direct detection of the neutron and momentum measurement T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008 Correcting for the vertex position of the decay:   n +  0 Before Correction After Correction Invariant mass of two photons in coincidence K +  K +  Missing mass from K + and photon in coincidence (simulation) Reconstructed K + energy vs. difference between measured and reconstructed energy K+0K+0 K+K+

 z Asymmetry Measurements Measuring the polar angle of the neutron from the decay of the  Reference frames consistent with [1] Can extract C Z and C X Can include more data from the   p  0 decay [1] R. Bradford et al., Phys Rev. C 75, (2007) T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008

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

T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September < cos(  K+ ) < < cos(  K+ ) < < cos(  K+ ) < < cos(  K+ ) < 2.5 Preliminary

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 C X and C Z Preliminary cross-section measurements close to threshold T C Jude, The University of Edinburgh, Strangeness Photoproduction A2 Collaboration meeting, Mainz, September 2008