PHENIX EMCal Trigger Study for pp Collision

In the baseline construction project of the PHENIX detector, it is proposed to descope EMCal trigger. The EMCal trigger is an extremely important item for spin (high p_T) physics with pp collision even in the first year of the pp run (year-2 of the RHIC run). The current EMCal triggger is designed for heavy ion physics. For the spin physics, we can consider simpler (and cheaper) trigger logic implementation.

The current design of the EMCal trigger is composed of 4x4 towers ('tile'). This tile is overlapped half with the next tile each other. Energy sum of the tile is made to judge trigger condition. A simplified trigger is to use super-module (SM) without overlap each other to calculate energy sum. We compared these two triggers, 4x4 overlap trigger and SM non-overlap trigger, using PYTHIA event generator to estimate trigger rate and trigger efficiency for each case.

The simulation was performed using PYTHIA 5.7 with GRV94LO parton distribution function. The acceptance and the performance (energy resolution, position resolution) of the PHENIX EMCal detector was taken account of, but the shower profile was not considered. Trigger rate for prompt photon process and QCD jet process were estimated for sqrt(s)=200GeV full luminosity (8E+31/cm^2/sec) with 8 sectors (all) of EMCal. For year-2 estimation, we devided the ratio by 20 for 10% luminosity (8E+30) with 4 sectors of EMCal.

p_T threshold
event type trigger 1GeV/c 2GeV/c 5GeV/c 10GeV/c
prompt photonSM non-overlap 1.7Hz 0.43Hz0.023Hz0.0015Hz
4x4 overlap 1.7Hz 0.43Hz0.023Hz0.0015Hz
QCD jet SM non-overlap1.4kHz 58Hz 0.79Hz 0.016Hz
4x4 overlap 1.3kHz 53Hz 0.44Hz 0.008Hz

By setting p_T threshold about 2GeV/c, we can realize reasonable event rate for the EMCal. We definitely need some trigger for the EMCal and the SM non-overlap trigger is enough for this. The threshold value 2GeV/c is low enough to collect prompt photon data higher than 5-10GeV/c.

Figures to show trigger efficiencies for pi0, eta (by QCD jet process) and J/Psi (J/Psi and Chi_Jc production process) are presented below. (This is the result for 8 sectors of EMCal. The result for 4 sectors will be different and it depends on the selection of the 4 sectors.) The efficiencies for eta and J/Psi are low at the threshold, because of larger openning angle of the decay. The difference between two trigger scheme is small for 2GeV/c threshold.

To conclude, the EMCal trigger is necessary in year-2 for the spin physics and the SM non-overlap scheme works well enough for it.

Go to PHENIX EMCal Subsystem Home Page
Created: 1 October 1998
Last updated: 1 October 1998
Comments to: Yuji Goto