D0 Note 1680 Triggering on Large Tiles with the Level 1 Calorimeter Trigger Daniel Edmunds, Steve Gross, and Philippe Laurens Department of Physics and Astronomy Michigan State University East Lansing, MI 48824-1116 I. Motivation for the Large Tile Upgrade ---------------------------------------- Currently, the D0 Level 1 Calorimeter Trigger uses jet Trigger Towers which are very small (0.2 [in eta] x 0.2 [in phi]) compared to the size of a jet (size of order 1.4 x 1.4, taking a cone size of 0.7). The detector is tiled by 1280 non-overlapping Trigger Towers, arranged in a matrix 40 [in eta] by 32 [in phi]. Typically, a Trigger Tower contains only 30% of the total jet energy, and this percentage shows large fluctuations on an event-by- event basis. We propose to provide jet triggering on larger towers in the D0 Level 1 Calorimeter Trigger (in addition to the current Trigger Tower-based jet triggering service). These larger towers (which we call Large Tiles) would be 0.8 [in eta] x 1.6 [in phi], which is approximately the size of a jet. The detector would be tiled by 40 non-overlapping Large Tiles, arranged in a matrix 10 [in eta] by 4 [in phi]. Jet triggering using these Large Tiles would be analogous to the Trigger Tower-based jet triggering system. That is, we would provide 8 independent Large Tile Reference Sets to which the total transverse energy of each Large Tile would be compared. Triggering would be done on the count of Large Tiles with transverse energy above the reference energy. As an example, a trigger of 2 or more Large Tiles with Et greater than 7 GeV could be specified as LT(2,7). II. Detailed Description of Large Tile Upgrade ---------------------------------------------- Triggering on Large Tiles is possible because of certain "hooks" that were built into the Level 1 Calorimeter Trigger. Specifically, the sum of total transverse energy in 32 contiguous trigger towers (arranged 4 [in eta] x 8 [in phi], covering an area 0.8 [in eta] x 1.6 [in phi]) is available in hardware. This transverse energy can be compared to 8 different reference values for each of the 40 Large Tiles. Each of the 8 sets of 40 reference values is called a Large Tile Reference Set (by analogy with the Trigger Tower Reference Sets). These 8 Large Tile Reference Sets would be individually programmable for each of the 40 Large Tiles, and are independent of the Trigger Tower EM Et and Total Et Reference Sets. Three differences exist between the computation of transverse energy for Large Tiles and for Trigger Towers: 1. The Trigger Towers have a low energy cut (i.e. the magnitude of the Et in a given tower must be above a minimum energy cut before the tower is considered to have an Et other than zero. This applies to both Global Sums and EM Et and Total Et Reference Set comparisons). The Large Tiles would not have this low energy cut. 2. The transverse energy for the Trigger Towers can be calculated based on the z-vertex interaction position obtained from Level 0. The Large Tile transverse energy would be computed as if the interaction z-vertex was at 0 (the center of the detector). 3. The transverse energy for the Trigger Towers is broken down into two components: EM and hadronic. These two components are summed to provide the total transverse energy. Triggering is available both on EM Et and Total Et for these Trigger Towers. For Large Tiles, only the total transverse energy would be available for triggering. Note that the Large Tile Reference Sets, like the Trigger Tower Reference Sets, could be programmed for triggering in any region (e.g. CC, ECN, ECS, EC and not CC, etc.) of the detector. We would build 8 of these Large Tile Reference Sets so that we would have the capability to trigger with both "shaped" and "flat" Large Tile Reference Sets (as well as Trigger Tower Reference Sets) simultaneously. Also note that the Large Tile Reference Sets can be tuned to modify the response of individual Large Tiles (again, this functionality mirrors the functionality of the Trigger Tower Reference Sets). For each Large Tile Reference Set, the count of Large Tiles with total transverse energy above the reference value would be computed. This count of Large Tiles with total transverse energy above the reference value would then be compared to each of three thresholds (>=1, >=2, >=3 Large Tiles with transverse energy above reference value) for each Large Tile Reference Set. The results of this count threshold comparison would be the terms available for triggering (as Level 1 Trigger Framework And-Or Input Terms). A fundamental difference exists between the count thresholds for the Large Tile Reference Sets and the count thresholds for the Trigger Tower Reference Sets. The count thresholds for the Trigger Tower Reference Sets are programmable to ANY arbitrary value; the count thresholds for the Large Tile Reference Sets are programmable ONLY to the >=1, >=2, and >=3 values (specifically, a count threshold of >=4 Large Tiles above the reference energy value IS NOT available). The quantities related to Large Tiles which will be added to the Level 1 Data Block are: 1. For each Large Tile Reference Set, a mask of Large Tiles with transverse energy greater than the reference transverse energy value (40 Large Tiles * 8 Large Tile Reference Sets * 1 bit = 320 bits). 2. For each Large Tile Reference Set, a mask of Specific Triggers programmed to use the Large Tile Reference Set (8 Large Tile Reference Sets * 32 Specific Triggers * 1 bit = 256 bits). The quantities related to Large Tiles which are already present (or have reserved space) in the Level 1 Data Block are: 1. For each Large Tile Reference Set, the results of the comparisons of the count of Large Tiles above reference energy value to the count thresholds (8 Large Tile Reference Sets * 3 count thresholds * 1 bit = 24 bits). 2. Sufficient information to calculate the transverse energy deposited in each Large Tile. III. Timescale for Implementation --------------------------------- The effort required to implement Large Tile triggering is reduced by the presence of the above-mentioned "hooks" in the D0 Level 1 Calorimeter Trigger. Only one new species of circuit board must be designed. On the order of 10 units of this species of circuit board must be built and tested. Appropriate cabling must be designed and built. The required software must also be written and tested. Much of this effort can be pursued in parallel. We believe that we can implement Large Tile triggering in time to be of use during Run Ib. IV. Conclusion -------------- We have proposed a mechanism for more efficient jet triggering at Level 1. This mechanism is complementary to, rather than a replacement for, the current jet triggering. We propose to build this jet trigger, as described in this note, in time to be used during Run Ib.