T.C. Jude D.I. Glazier, D.P. Watts The University of Edinburgh Strangeness Photoproduction At Threshold Energies

Hyperon photoproduction Crystal Ball detector at the MAMI-C facility A new method of K + meson detection Cross section measurements Search for rare   decays Future plans

Hyperon Photoproduction  p  K + +  p +  - (~ 64%) n +  0 (~ 36%)   p  K + +    Important for investigations of nucleon resonances. Predicted nucleon resonances which have not been observed experimentally may couple to strange decay channels [1] A crucial test of QCD based chiral perturbation theories in the strange quark sector [1] S Capstick and W Roberts, Phys. Rev. D58, (1998) T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Cross-Section Measurements Significant discrepancies exist between cross-sections measured at JLab [2] and ELSA [3] Fits to these data sets reveal large differences in the roles of nucleon resonances when describing the photoproduction process [4] 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 T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Experimental Apparatus The Crystal Ball detector NaI crystals covering ~93% of 4  steradians Edinburgh PID - 24 Plastic Scintillators parallel to the beam TAPS - Segmented BaF2 detector. Used as a forward wall for the Crystal Ball The Crystal Ball (Edinburgh PID and target in the centre) TAPSGlasgow Photon Tagger Beam direction T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Experimental Apparatus The Crystal Ball detector NaI crystals covering ~93% of 4  steradians Edinburgh PID - 24 Plastic Scintillators parallel to the beam TAPS - Segmented BaF2 detector. Used as a forward wall for the Crystal Ball T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

K + meson detection in segmented calorimeters K +     ( ~ 63%) Mean lifetime of K + ~ 12 ns     (~ 21%) First cluster from K + < 3ns Secondary cluster from K +      decay > 10ns Identify the K + decay within the crystals of the Crystal Ball and TAPS Eliminates the need of expensive magnetic spectrometers T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

(a) Energy of the Second Cluster (a) Time difference between first and second clusters T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

2D cut on K + loci in the  E-E analysis T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Detection of  0 decay Measure missing masses from K +  final states Select the photon giving closest missing mass to the  mass Further 2D cuts on the photon polar angle and energy in the lab frame (simulation) T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Photon energy in the  0 rest frame (after 2D cuts) From the K + events identified (in simulation): ~ 40% of K +  0 events correctly identified by detection of the decay photon ~ 10% of K +  events misidentified (Still in progress) Simulation Real Data Detection of  0 decay T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Fitting to K + Missing Mass Plots Fit To K + missing mass plots to measure  (p,K + )  &  (p,K + )    contributions For determining K + yield for particular energy and polar angle ranges, integrate over the Lambda peak (blue) T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Fitting to K + Missing Mass Plots Further cuts on K + cluster size (< 3) and K + punch through energy (< 340 MeV & reconstructed from polar angle) T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009 K + cluster size < 3, punch through K + rejected K+ cluster size < 3 K+ cluster size < 3, punch through K+ and events with photon from  0 decay rejected

 (p,K + )  Cross Section Measurements ~ 0.6 Target pressure ~ kgm -3 ~ x protons m -3 Target length = m  = x protons m -2 Detection Efficiency: 20 million  (p,K + )  events with phase space generation and A2 GEANT4 simulation. Approximately 10% July 2007 data, ~36500 K + events that pass cuts 350 MeV Crystal Ball energy sum, Multiplicity 2+ T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009 Next Slide: Black points: this data Blue Points: JLab data (2006)[2] Red Points: ELSA data (2004)[3]

Preliminary Black points: this data, Blue Points: JLab data, Red Points: SAPHIR data T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Cross sections for forward angles (K + centre of mass polar angle < 76 0 ) Approaching region of cross section discrepancy with previous data Future beam times : greater proportion of K + in forward directions (change of electronic triggers) Reduce statistical error by ~2 Preliminary T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Branching ratio of the decay:  0  e + e -  [5] H. Courant et. al. Phys Rev Lett 10, 409 (1963) Select e + and e - from 2D graphical cuts in  E-E analysis For multiple events, select combinations giving the best missing mass of  (from K +, e + and e - momenta) Boost into  0 rest frame and sum the energies of the e + and e - First measured in the 1960s to measure relative parity between  0 and  [5] Accepted branching ratio < 0.5% T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Branching ratio of the decay:  0  e + e -   p  K +  0 simulation with branching ratio for decay  0  e + e -  set at 0.5% Red Fit:     e + e -  contributions Blue Fit: Background from  p  K +  and  p  K +  0 Total Background  0  e + e decay [5] H. Courant et. al. Phys Rev Lett 10, 409 (1963) First measured in the 1960s to measure relative parity between  0 and  [5] Accepted branching ratio < 0.5% T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

TotalBackground  0  e + e decay Real Data: Sim:Total  0  e + e decay Background Branching ratio of the decay:  0  e + e -  T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Future Plans More data: resolve  (p,K + )  cross sections at an unprecedented resolution Increased beam energy: measure the  (1405) structure Circular polarised beam: measure polarisation observables, C X and C Z at threshold Preliminary Asymmetry of  decay distribution with circular polarised beam 1.0 – 1.2 GeV  [deg]cos(  ) T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April – 1.2 GeV

Future Plans Deuterium target: study the reaction:  (n(p s ),K + )  - Energy [MeV] Missing mass from K + Photoproduction for beam energies < 1.05 GeV (peak observed at the  mass) Very preliminary! T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009

Future Plans Strangeness photoproduction with transversely polarised target [6] Measure the beam-target polarisation observables E and G (longitudinal pol. target), and H and F (transversely pol. target) Sensitive to missing nucleon resonances, for example D 13 (1900) [6] A. Thomas, Helicity Dependence of Meson Photoproduction on the Proton, 13 th Crystal Ball Meeting, Mainz, Germany, March 2009 G E T. C. Jude Strangeness Photoproduction At Threshold Energies NSTAR, Beijing, April 2009 KAON-MAID

T.C. Jude D.I. Glazier, D.P. Watts The University of Edinburgh Strangeness Photoproduction At Threshold Energies