J.R.M Annand

Publications (3)0 Total impact

• Article: A high-resolution, large acceptance scintillation time-of-flight spectrometer

  P Grabmayr, T Hehl, A Stahl, J.R.M Annand, R.O Owens
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  ABSTRACT: A high-resolution detector array has been developed for the measurement of momenta of charged and uncharged particles via the time-of-flight method. This spectrometer represents one detector arm of a system used to study the photoabsorption mechanisms of (γ, NN) and (γ, πN) reactions. It is comprised of 112 plastic scintillators (NE110) of dimensions 5 × 20 × 300 cm3 with a photomultiplier attached to each end. A mean time resolution of ≲400 ps (FWHM) and a position resolution of ≲6 cm have been achieved. The modularity and flexibility of the array encouraged its use in other electron-and photo-induced reaction measurements.
  Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
• Source

  Available from: Martin Schumacher

  Article: Helicity dependence of the γ→p→→nπ+π0 reaction in the second resonance region

  J Ahrens, S Altieri, J.R.M Annand, G Anton, H.-J Arends, K Aulenbacher, R Beck, C Bradtke, A Braghieri, N Degrande, [......], T Speckner, N Takabayashi, G Tamas, A Thomas, R van de Vyver, A Wakai, W Weihofen, F Wissmann, F Zapadtka, G Zeitler
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  ABSTRACT: The helicity dependence of the total cross section for the reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D13 resonance.
  Physics Letters B.
• Article: Double π0 photoproduction off the proton at threshold

  M Kotulla, J Ahrens, J.R.M Annand, R Beck, D Hornidge, S Janssen, B Krusche, J.C McGeorge, I.J.D MacGregor, J.G Messchendorp, V Metag, R Novotny, M Pfeiffer, R.O Owens, M Rost, S Schadmand, D.P Watts
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  ABSTRACT: The reaction γp→π0π0p has been measured using the TAPS BaF2 calorimeter at the tagged photon facility of the Mainz Microtron accelerator. Chiral perturbation theory (ChPT) predicts that close to threshold this channel is significantly enhanced compared to double pion final states with charged pions. In contrast to other reaction channels, the lower order tree terms are strongly suppressed in 2π0 photoproduction. The consequence is the dominance of pion loops in the 2π0 channel close to threshold—a result that opens new prospects for the test of ChPT and in particular its inherent loop terms. The present measurement is the first which is sensitive enough for a conclusive comparison with the ChPT calculation and is in agreement with its prediction. The data also show good agreement with a calculation in the unitary chiral approach.
  Physics Letters B.