Forward Beamline Simulation (short overview) 1. Introduction 2. Dead material description 3. Active detectors 4. Summary Antwerpen 09 December 2005 Diffraction and the (V)FPS V.Andreev LPI, Moscow

List of persons who gave contribution to H1SIM (Forward beamline): M.Kapishin, H.Mahlke-Krueger, A.Kutov, B.List, A.Fedotov, A.Zhokin, V.Solochenko, P.Van Michelen, U.Duenger, K.H. Hiller, V.Andreev. Two important things need to take into account: a) dead material description (“close” as possible to reality) for active detectors (FTS and FNC); b) correct magnet's position and field description for right particle's trajectory reconstruction (FPS and VFPS detectors). Introduction

Dead material Example of quadrupoles description

Such “detailed” description was done only up to ~ 110 m with inserting correct beampipe shape, quadrupoles, dipoles, flanges and all others dead material (this is important for FTS and FNC). Behind FNC calorimeter very simple dead material description was used (like “tube” shape for beampipe and also for magnet elements) because the very precise magnet field description is more important for VFPS.

Active Detectors (FTS and FNC) Forward Tagging System (FTS)

View of two FTS stations FTS 28 m

example of H1SIM simulation (present setup) and comparison with real data ( R.Weber – diffractive rho production with DIFFVM generator)

Xv=0.0 cm Yv=0.0 cm Xv=0.23 cm Yv=0.67 cm Xv=0.23 cm Yv=0.67 cm tilt_x=-0.8 mrad tilt_y=0.8 mrad ela diss sum eladiss sum ela diss sum

Tuning procedure (decreasing GEANT energy cuts in some dead material and put two scintillator counters of 90-th FTS station into correct position ) present “tuned” ela diss sum ela diss sum

Short conclusion for this part H1SIM (at least forward part ) is tuning for the nominal vertex (Xv=0.0 cm and Yv=0.0 cm) for electron case and (Xv=0.75 cm and Yv=0.0 cm) for positron case and for zero tilt in IP. In real life there are vertex shift (Xv=0.23 cm, Yv=0.68 cm) and beam tilt (tilt_x= -0.8 mrad,tilt_y = 0.8 mrad). Simple possibility to “resolve” this problem was suggested by B.List : put all “forward” particles into nominal simulation vertex (with Xv=0.0 cm, Yv=0.0 cm and zero beam tilt).

FPS and VFPS stations Slice at 100 m from IP (inline generator p= GeV, theta= deg and phi= deg) for events with dP > 0.1 MeV standart JGDO “improve” JGDO

Slice at 220 m for the same inline generator and dP < 0.01 MeV and presence hit in VFPS station (influence of the kick magnet) present JBPS “improve” JBPS

Slice at 220 m for the same inline generator and dP < 0.01 MeV and presence hit in VFPS station (different vertex position ) Vx = 0.75 cm Vx = 0.37 cm

the problem which was realized in present description of magnet's position behind 100 m is z s z1 z2 z1 z2 s1 s2 H1 illustrated by the next scetch: real magnet position we have (z1,z2) magnet position coordinates instead of (z1,z2) which should be and shift about several cm at 220 m

Summary Present H1SIM version doesn't give full relevant description of the Forward beamline. Problem with response of FTS stations (could be solved by the simple way). Need to revise magnet's position behind 100 m (VFPS). Absence description of PToF, FTi1 and Fti2 in present H1SIM version.