ZGOUBI USERS' GUIDE - HEP

4.4 Optical Elements and related numerical procedures 79©©w>>î––––>¹¹–•©©w––>>É•¥ É>wŽŽ•w–• ÊÊ•• ©• ©>©©î>••>@COLLIMA: CollimatorCOLLIMA acts as a mathematical aperture of zero length. It causes the identification, counting and stopping of particlesthat reach the aperture limits.Physical apertureA physical aperture can be either rectangular (IFORM = 1) or elliptic (IFORM = 2). The collimator is centered at ², ²and has transverse dimensions o å¨ and o}r¨ such that any particle will be stopped if its coordinates , satisfyorif IFORM q ² ² Ž þ¨ŽKv¨> > Ž q if IFORM @ ² ² Longitudinal collimationå¨v¨COLLIMA can act as a longitudinal phase-space aperture, coordinates acted on are selected with IFORM.J. Any particlewill be stopped if its horizontal (h) and vertical (v) coordinates satisfy ÇÇ §¦Ó or § bwherein, is either path length if IFORM=6 or time if IFORM=7, and is either 1+DP/P if J=1 or kinetic energy ifJ=2 (provided mass and charge have been defined using the keyword PARTICUL).If IFORM=11 (respectively 12) Ç then ·(respectively ) is to be specified by the user as well – d •as– d •É , . ¹IfIFORM=14 (respectively ¹ 15) Éthen ¹and É(respectively , ) are computed by zgoubi by prior matchingÊÊof theparticle population, only need be specified by the user.Ê– d •Ç § bX or Ž §FÓ X or Ç ŽPhase-space collimationCOLLIMA can act as a phase-space aperture. Any particle will be stopped if its coordinates satisfyÁ – @å – >if IFORM qq or 14if IFORM qor 15If IFORM=11 (respectively 12) then (respectively ÊIFORM=14 (respectively 15) then ¹ and É (respectively ¹Êparticle population, only need be specified by the user.Ê– d •) is to be specified by the ¹– d •user– d •Éas well as , . If, ) are computed by zgoubi by prior matching of Éthev¥ Á • @When a particle is stopped, its index IEX (see OBJET and section 4.6.8) is set to the value -4, and its actual path length isstored in the array SORT for possible further statistical purposes (e.g. with HISTO).