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UPC and Sti

UPC and Sti. V. Perevoztchikov Brookhaven National Laboratory,USA. What is the problem?. UPS (Ultra Peripheral Collision) represented by few low energy tracks. Typical case is a ρ meson into Pi+ Pi-. Yury Gorbunov found very big difference between TPT and STI for these events.

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UPC and Sti

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  1. UPC and Sti V. Perevoztchikov Brookhaven National Laboratory,USA

  2. What is the problem? UPS (Ultra Peripheral Collision) represented by few low energy tracks. Typical case is a ρmeson into Pi+ Pi-. Yury Gorbunov found very big difference between TPT and STI for these events. Then, to avoid real life problems, he made comparison for simulated events. He found: • Hollow in rapidity distribution of ρmeson; • Asymmetry in +- Z; • Big inefficiency of primaries StarSoft local

  3. TPT and std STI StarSoft local

  4. Std STI and last STI StarSoft local

  5. Wrong Sti geometry. StarSoft local

  6. What was done • First guess was that something wrong with energy loss and multiple scattering. • Multiple scattering accounted now not only to angle but to position as well. For TPC it gives additional 10 microns for each padrow, so for 25 rows it gives 50 microns; • In addition to influence of the energy loss to momentum, influence to angle and position was added. • Fluctuation of energy loss was also accounted. As a result efficiency increased. But no more. • Second guess was that asymmetry is related to asymmetry of detectors. • Geant geometry is symmetrical but according Sti geometry could be wrong. And it is wrong. At the beginning I thought that bug in Geant -> Sti conversion. But it is very old Sti bug in detector tree. StarSoft local

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