General Meeting Summary 11/19/14

NPS COLLABORATION MEETING - 19 NOVEMBER 2014

JLAB: S. Abrahamyan, P. Brindza, A. Camsonne, M. Carmignotto, R. Ent, T. Horn, C. Hyde, A. Mkrtchyan, H. Mkrtchyan, C. Munoz-Camacho, R. Novotny, J. Roche, B. Wojtsekhowski, S. Wood, S. Zhamkochyan, J. Zhang

PHONE: D. Day, D. Dutta, P. Nadel-Turonski, V. Tadevosyan, J. Wagner, Z. Zhao

SUMMARY

• TCS theory: Theoretically, the quantity of interest are the transverse target asymmetries A_ux and A_uy. Numerical studies using the VGG model show that these may be sensitive to Htilde. Also of interest if the double asymmetry with polarized beam that can be accessed in double DVCS and is sensitive to the unknown Etilde. DVCS and TCS are complementary (universality, spacelike-timelike crossing) and measuring both reactions is of great interest as well.

• Status on PWO: the PANDA EMC requires ~8000 high-quality PWO crystals for the endcaps. The crystal performance requirements are satisfied by PWO-II and improved version of the PWO-I crystals used for CMS. There are two methods to produce PWO: Czochralsky (used by BTCP and Crytur) and Bridgeman (used by SICCAS). The Bridgeman growing method is slower than the Czochralsky method and requires great care due to evaporation. Crystal quality can be described by three main parameters: optical transmittance, light output and count rate, and radiation hardness. The latter can be defined by the induced absorption coefficient, delta_k, for which values of better than 1.1 m^-1 have been achieved at Panda. The refractive index and so the transmittance is different along each crystal axis. Measuring the light yield as a function of temperature can help identify slow component contribution due to impurities - requirement of a few % of slow component is reasonable. PWO crystals Crystal irradiation tests may best be done at low temperatures since that way the recovery time is reduced.

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