Trigger counter for p-p measurements at RHIC-PHENIX; t-zero counter

Why p-p measurments needed at RHIC-PHENIX?

High energy heavy ion collision is complicated phenomena which involves space-time evolutions. From the present knowledgeIt of nuclear collisions, it is difficult to predict the heavy ion collisions well enough at totally new energy regime of RHIC. Thus, it is necessary to carry out the systematic comparison of heavy ion collisions with pp and pA collisions in order to clarify the true heavy ion effects as is done before at AGS and SPS.

Why an additional counter needed for pp measurements at PHENIX?

Multiplicities expected in pp collisions will be much smaller than those in AA collisions. Therefore, experimental technology wise, it is easier to measure the pp collision at PHENIX. However, the trigger device of PHENIX is designed for AA collisons and may not be adequate for pp collisions; the trigger device, which accepts leading particles in the beam rapidity region, triggers almost 100% of geometrical cross section in AA collisions, but in pp, it triggers only 50 % of the geometrical cross sections of pp. Unless triggered, no data can be taken. You may assume relations between the cross sections and the multiplicities, you may be able to extrapolate the data to full crosssections. However, unless you actually measure it, you never know the true answer. Thus, it is very much preferable to measure 100% of geometrical cross section of pp collisons. This is especially important to make systematic comparison of soft production of particles. Also, the current trigger counter of PHENIX, BBC, does not provide good timing resolution in pp. Thus, an additional counter in pp should provide good trigger capability and good start timing which is vital for the particle identification of hadrons using time-of flight measurement.

What is t-zero counter?

Univ of Tsukuba team has developed trigger/start counter for pp collsions. This counter is called as t-zero counter. T-zero counter covers acceptance of High-res TOF with 8 plastic scintillation counters. This counter provides the trigger for the identified hadron measurements and the start timing of TOF measurements with resolution of better than 60 ps. T-zero counter will be implemented during the pp measurements only. To avoid the effect of photon conversion in electron measurements, photon conversion rejectors (PCR) are also implemented in front of the t-zero counter.

Status of t-zero counter;

In 2000, the design and prototype construction has been completed and is tested at KEK. By August of 2001, construction has been completed . Check with a beta source, performance test with cosmic ray has been carried out successfully. Also installation procedure has been tested with mockup model of the magnet. All the counters and the mockup model has been shipped to BNL on August 30th, 2001.


Aug.7th,2001A Aug.10th,2001