Boundary Conditions

First Level Trigger

Si-data is rarely used in a first-level trigger system. As a consequence, the front-end readout systems discussed elsewhere on these pages are not supplying the external output to a trigger system. If we want to implement a microvertex first-level trigger, the requirements are:

• specific data link after preamp to specific  trigger logic
• data to be transferred to the trigger logic within 8 microseconds in order not to intervene with data-taking

External Inputs

The GFLT provides the following information to each component (see also ZEUS note 88/98). For each physics trigger:

• readout type
• bunch crossing number
• FLT-number
• Fast-Clear flag

Besides, the following signals are provided:

• clock
• synchronization signal
• test trigger signals: a warning signal and the test trigger itself

The signals are transmitted over three 17-pair twisted-pair cables at the nominal HERA clock rate: one cable for transmitting clock-related signals, one for control signals and one for transmitting FLT-numbers.

High-Luminosity Upgrade

The present luminosity is about 3*10³⁰ /cm²*s. After the upgrade the luminosity will be around 7*10³¹/ cm²*s. We expect just a limited increase in the trigger rate and data throughput of the ZEUS system, therefore the bandwidth for charm triggers has to be reduced drastically (about a factor 10 or more) to keep high-Q² DIS and EXO triggers.

So, either the charm triggers should select events with higher Pt or a special FLT has to be constructed to keep charm events with tracks in the microvertex.

Please mail suggestion/corrections/updates to Leo Wiggers (wiggers.nikhef.nl)