CMS REGIONAL CALORIMETER TRIGGER HIGH SPEED ASICs

The CMS regional calorimeter trigger system detects signatures of electrons/photons, taus, jets, and missing and total transverse energy in a deadtimeless pipelined architecture. This system contains 20 crates of custombuilt electronics. Much of the processing in this system is performed by five types of 160 MHz digital ASICs. These ASICs have been designed in the Vitesse submicron highintegration gallium arsenide gate array technology. The five ASICs perform data synchronization and error checking, implement board level boundary scan, sort ranked trigger objects, identify electron/photon candidates and sum trigger energies. The design and status of these ASICs are presented. 1. CMS CALORIMETER L1 TRIGGER The CMS level 1 trigger decision is based in part upon local information from the level 1 calorimeter trigger about the presence of physics objects such as photons, electrons, and jets, as well as global sums of Et and missing ET (to find neutrinos) [1]. For most of the CMS ECAL, a 5 x 5 array of PbWO4 crystals is mapped into trigger towers. In the rest of the ECAL there is somewhat lower granularity of crystals within a trigger tower. There is a 1:1 correspondence between the HCAL and ECAL trigger towers. The trigger tower size is equivalent to the HCAL physical towers, .087 x .087 in η x φ. The φ size remains constant in ∆ φ and the η size remains constant in ∆η out to an η of 2.1, beyond which the η size increases. The electron/photon trigger uses a 3x3 trigger tower sliding window technique which spans the complete coverage of the CMS electromagnetic calorimeter [2]. Two independent streams are considered, non-isolated and isolated electron/photons. The non-isolated identification requires a large energy deposit in one or two adjacent ECAL trigger cells, a narrow lateral shower profile (the energy spread in η strips of 5 crystals in the central ECAL cell of 3x3 trigger tower window) and small H/E in the central trigger cell of 3x3 window. The isolated electron/photons additionally require small energy in ECAL cells surrounding the central cell of 3x3 window and small energy in HCAL cells surrounding the central cell of 3x3 window. The jet trigger uses the transverse energy sums (ECAL + HCAL) computed in calorimeter regions (4x4 trigger towers). Jets and τs are characterized by the transverse energy ET in 3x3 calorimeter regions (12x12 trigger towers. For each calorimeter region a τ-veto bit is set if there are more than two active ECAL or HCAL towers in the 4x4 region. A jet is defined as ’tau-like’ if none of the 9 calorimeter region τ-veto bits are set. 2. CALORIMETER TRIGGER HARDWARE The calorimeter level 1 trigger system, shown in Figure 1, receives digital trigger sums from the front-end electronics system, which transmits energy on an eight bit compressed scale. The data for two trigger towers will be sent on a single link in eight bits apiece accompanied by five bits of error detection code and a “finegrain” bit for each trigger tower characterizing the energies summed into it, i.e. isolated energy for ECAL or an energy deposit consistent with minimum ionizing particle for HCAL. system. Calorimeter Regional Trigger Crates Data Receiver Electron Isolation Jet/Summary Calorimeter Frontend Electronics Global Trigger Processor Muon Global Trigger Isol. Muon MinIon Tag Cal. Global Trigger Sorting, E t , ΣE t Copper 40 MHz Parallel MinIon Tag for each 4φ x 4η region 4 Highest isol. E t e/γ 4 Highest non-isol. E t e/γ 4 Highest jets, taus E x , E y from each crate Luminosity Monitor E t Sums Luminosity Monitor E t