4 the Beam-Beam Counters (BBC) [21]. The BBCs are segmented scintillator rings covering the region 3 . 3 < | η | < 5 . 0. The STAR p + p minimum-bias trigger requires the coincidence of hits in the BBCs on opposite sides of the interaction region, and is used to monitor the integrated luminosity for measuring absolute cross sections. The BBC acceptance and efficiency were studied previously [22], and it was found from simulations that for p + p non–singly diffractive (NSD) events the BBC trigger was 87 ± 8% efficient. The absolute p + p cross section seen by the BBC trigger was measured via a van der Meer scan to be 26.1 ± 0.2 (stat.) ± 1.8 (syst.) mb. The TPC and BEMC have a large acceptance at midra- pidity: the single track coverage of the TPC+BEMC in pseudorapidity is | η | < 1 and complete in azimuth. The BEMC is divided in η and ϕ into 4800 towers. The size of each tower in η × ϕ is 0 . 05 × 0 . 05 rad. The geomet- rical acceptance of the STAR BEMC for detecting both electrons from an Υ decay is about ≈ 30% over all phase space, and ≈ 60% for Υ’s in the kinematic range | y | < 0 . 5 and p$_{⊥}$ < 5 GeV /c . We focus on this kinematic range, where the acceptance of the detector is optimal. The capability of the TPC+BEMC for electron iden- tification and the triggering capabilities of the BEMC are the two pillars of the STAR quarkonium program. In particular, the BEMC trigger allows us to sample the full luminosity delivered by RHIC to look for the high-mass dielectron signals characteristic of the Υ → e $^{+}$e − decay. The STAR quarkonia trigger is a two-stage system comprising a Level-0 (L0) hardware component [23] (de- cision time of ≈ 1 µ s) and a Level-2 (L2) software com- ponent (decision time of ≈ 100 µ s in p + p , and ≈ 400 µ s in Au+Au). There were two separate Υ triggers used during the 2006 run; in the following we refer to them as Trigger I and Trigger II. They were identical in concept, with the only difference being an increase in thresholds, which was necessary to reduce the trigger rate and re- duce deadtime while data-taking. We discuss the triggers next, and list all the parameters and thresholds. These were chosen based on simulations and on expected trigger rates based on calorimeter data taken in 2003. The L0 trigger is a minimum-bias p + p trigger with the additional requirement of signals in the BEMC con- sistent with a high energy electron. The energy deposited in the calorimeter towers is measured by collecting scin- tillation light from the electromagnetic shower. The sig- nal is digitized, pedestal subtracted, and sent to the L0 Data Storage and Manipulation (DSM) hardware as a 6- bit ADC value for triggering. The calorimeter calibration Once a L0 HTTP trigger is issued, the information for all detectors in STAR begins to be digitized. During this time, the L2 system can use the information from the 4800 individual calorimeter towers to decide whether to keep the event or to abort the readout. The L2 system can use the full energy resolution of the calorimeter (a 10-bit ADC value, in contrast to the 6-bit ADC used at is done such that tower ADC values are proportional to deposited electromagnetic transverse energy ( E$_{⊥}$ ), mak- ing it useful for triggering on high- p$_{⊥}$ electrons. The L0 trigger decision is made for every bunch crossing. For the Υ analysis, the L0 decision was based on two quantities. The first is related to the signal in distinct towers. The tower with the highest E$_{⊥}$ , as represented by the DSM-ADC value, is called the “High Tower” (HT) in the event. The second quantity is a sum of towers in fixed η - ϕ regions of the BEMC, where each region comprises 4 × 4 towers. Each of these regions is named a “Trigger Patch” (TP). Since each tower covers 0.05 units in η and 0.05 radians in ϕ , the TP coverage is 0 . 2 × 0 . 2 rad. The L0 trigger is issued for Trigger I (Trigger II) if all of the following three conditions are met: ( i ) an event has a High Tower with a DSM-ADC value > 12 (16), corresponding to E$_{⊥}$ ≈ 2.6 (3.5) GeV deposited in the tower; ( ii ) the Trigger Patch containing the High Tower has a total DSM-ADC sum over the 16 towers in the patch with a value > 17 (19), corresponding to E$_{⊥}$ ≈ 3.8 (4.3) GeV, and ( iii ) the STAR p + p minimum-bias trigger is met. The minimum-bias trigger is based on a BBC coincidence and is described elsewhere [22]. The coincidence of High-Tower and Trigger Patch triggers will be referred to as “HTTP” in the remainder of the paper. Figure 1 shows the p$_{⊥}$ distribution for simulated elec- trons and positrons from Υ decays in which both daugh- ters are within the STAR acceptance. For each decay, we plot the p$_{⊥}$ distribution of the electron (filled circles) or positron (open squares) with the highest p$_{⊥}$ (the abscissa is simulated p$_{⊥}$ ). The electron and positron distribu- tions are identical, as expected for a two-body decay into daughters with identical masses. The histogram in the figure is the sum, i.e., the p$_{⊥}$ distribution for the hard- est of the two daughters. The corresponding DSM-ADC values used in the L0 trigger (which are proportional to p$_{⊥}$ ) are shown in Fig. 2. The L0 HT Trigger II threshold of 16 is shown by the vertical dashed line. From the p$_{⊥}$ and ADC distributions for the hardest Υ daughter in Figs. 1 and 2, the average values are 〈 p$_{⊥}$ 〉 = 5.6 GeV/c and 〈 ADC 〉 = 18.0 counts. Since the trigger threshold is placed at 16 ADC counts, the hardest daugh- ter will typically fire the trigger. We find that 25% of the Υ’s produced at midrapidity have both daughters in the BEMC acceptance and at least one of them can fire the L0 trigger. The details of the HTTP trigger efficiency and acceptance are discussed in Sec. IV. B. Υ L2 Trigger A. Υ L0 Trigger III. THE STAR QUARKONIA TRIGGERS