Etothi Trigger Efficiencies


The Etothi part of the neutral trigger is designed to tag events were 80% of the available lab energy is deposited in the CCAL. The signals from the 1280 lead glass blocks first go through the level 1 summers where the signals for each block in a ring are summed. Thus, 20 signals leave the level one summers (one from each ring). These signals then enter the Etot summer.

At the Etot summer the 20 signals from each ring are summed, after which they go through an integrator and finally split. One set goes through the Etotlo discriminator and the other set goes through the Etothi discriminator. The Etothi discriminator is set to pass signals showing a energy deposit in the CCAL at least 80% of the available lab energy from the p pbar collision. If a signal passes the discriminator for Etothi, bit 8 of the NMLU is set. At the MMLU, if bit 8 of the NMLU was set as well as bits showing a veto on H1*H2' OR and Fch OR from the charged trigger, the Etothi bit is set.

To calculate the Etothi efficiencies, the signals from the 1280 CCAL blocks are used to duplicate offline what happens in the hardware during data taking. For efficiency calculations real physics events must be used and accordingly, pi0pi0 events from the Etotlo data stream were chosen. The events were chosen with the following selection:

  • trigger id 80 (Etotlo with the neutral veto)
  • Exactly 4 clusters
  • Acopl = | | phi forward - phi backward | - pi | < 25 mrad
  • Akin = | thetaf - thetaf theoretical | < 12 mrad
  • | mpi0 - mpi0 theoretical | < 30 Mev

  • Once the pi0pi0 events were selected the energies for the blocks were summed and compared with the 80% value of the available lab energy. If the total energy was at least that big, an etothi software trigger was recorded. A hardware trigger is present when the MMLU input bit 3 is set. The calculated efficiency is a ratio of the number of events with both the hardware and software trigger to the number of events with a software trigger only.