(Roughly) Bending Effects of Magnetic Field in VELO & TT S. Blusk June 17, 2009

Question Issue: In trigger, we don’t want to consider low momentum tracks, since they undergo large multiple scattering and thus have degraded resolution. Would like to avoid doing tracking in T stations, as this is likely CPU intensive. Can we use tracking station(s) at Z=2.5 m (such as TT), to select tracks of sufficient momentum for triggering?

Basic Idea Bending in xz plane due to B y LL

LHCb Magnetic Field Parameterization CHEP 07 Use = 1.8x10 -4 T,  L=0.7 m Use = 0.02 T  L = 2.5 m (Based on Hall probe measurements)

Displacement from linear projection at TT 60 um

Displacement from linear projection at end of VELO

Preliminary Conclusions A station at TT could provide a “momentum selection” Need a real simulation to see if we pick up too many hits in current TT –Maybe finer granularity needed –No gaps, obviously Will do a more realistic GEANT simulation vs luminosity Perhaps slightly higher field can be obtained in region between VELO and TT?