In the CMS experiment, sub-detectors may send special trigger signals, called
“Technical Triggers”, for special purposes like test and calibration during the
off-beam periods. The Resistive Plate Chambers are part of the Muon Trigger system of
the experiment, but might also be used to produce a cosmic muon trigger to be used
during the Commissioning of the detectors to check the efficiency of the installed
chambers and, as Technical Trigger, during the Cosmic Challenge and the later running
Since this project started only few months ago, when the electronics and cabling in
the experimental hall were frozen, this RPC trigger system for the detection of
cosmic muons must use as much as possible the existing functionalities and
infrastructures and don’t introduce major modifications to the existing electronics.
Another constraint is the capability to generate a trigger signal both locally and
globally. The local trigger involves the chambers of one Barrel sector and can be
used during the Commissioning of the RPCs and the Cosmic Challenge. The global
trigger, used as Technical Trigger, involves the whole Barrel and requires
infrastructures in the counting room.
In the proposed scheme, the RPC-based Technical Trigger will be implemented by two
types of electronic boards: the RPC Balcony Collector (RBC) housed in the cavern and
Technical Trigger Unit (TTU) housed in the Counting Room.
Since the RPC signal cables are connected to the Link Boards (LB) for
synchronization, data compression and optical conversion, the RBC could access
only an OR signal of 96 strips produced by each LB. So each RBC collects the Ors from
two Barrel sectors, produces two independent sector-based cosmic trigger as “local”
triggers and transmit optically the input Ors to the Counting Room, where the TTU
will produce a wheel-level cosmic trigger, to be sent as technical trigger to the
Global Trigger of the experiment.
The most convenient position for the RBC is inside the crate housing the LBs. In fact
from the backplane can take the power supplies and the slow control signals, while
the ORs can be easily taken from the LBs by means of Front-Planes.
The RBC has been designed using FPGA to allow easy upgrades of its firmware by means
of JTAG bus. Three prototypes of RBC have been produced, tested and used during the
Cosmic Challenge to provide a cosmic trigger from the two barrel sectors equipped
In this work the overall scheme of the proposed implementation, the RBC project
design, the prototype tests and their performance during the Cosmic Challenge will be