Speaker
Description
Summary
The goal of the NA62 experiment at CERN SPS is a precision measurement
of the branching ratio of the ultra-rare kaon decay $K^+ \rightarrow
\pi^+\,\nu\,\bar{\nu}$ with 100 expected events and 10% background in
two years of data taking. A system of different detectors is needed
to achieve an high rejection factor for photons coming from the $K^+
\rightarrow \pi^+\,\pi^0$ decay, one of the main background sources.
As part of the photon veto, in the 1-10 mrad angular region, the NA48
liquid krypton high-performance electromagnetic calorimeter is reused
with an upgrade of both the detector and the trigger electronics.
The object of this contribution is the level-0 trigger for the
electromagnetic calorimeter: it identifies electromagnetic clusters in
the calorimeter and sends to the Level 0 Trigger Processor a
time-ordered list of reconstructed clusters with their arrival time,
position, and energy measurements. The trigger is designed to sustain
the instantaneous hit rate of 30 MHz, to process data with a maximum
latency of 100 us, and to achieve a time resolution of 1.5 ns on the
single cluster.
The trigger design is based on a system of custom readout boards of
the experiment (TEL62), 9U size, which can host various mezzanine
cards thanks to five 200-pins high-speed connectors. Each TEL62 board
is controlled by an on-board PC with fast Ethernet connection. In
total, the calorimeter trigger system will be composed of 36 TEL62
boards, 108 mezzanines and 215 high-performance FPGAs. They are
combined in a three layers parallel system, divided in front end and
concentrator boards.
The readout electronics of the liquid krypton electromagnetic
calorimeter reads and sums together the energy deposits in
tiles of 16 calorimeter cells. Digitized data are then
transmitted from the readout boards to the Level 0 Trigger over
shielded copper twisted pair cables on 864 digital channels. The first
(front-end) layer of 28 boards deserializes the incoming data (trough
the TELDES mezzanine boards) and performs a parabolic fit to obtain an
accurate estimate of the peak amplitude, and then applies a
constant-fraction discriminator to measure the cluster arrival time.
Since clusters may hit more than one calorimeter tile, the second
(concentrator) layer of 7 boards performs cluster reconstruction by
merging the information transmitted (trough a custom 4.8 Gbps link)
by the first layer and implements additional peak finding algorithms.
The final concentrator board is connected to the L0 Trigger Processors
and generates and transmits the time-ordered list of the reconstructed
clusters.
Since the first data taking is scheduled for October 2014 and the
whole trigger system will be commissioned by then, we aim at
presenting the whole system and the first performance results obtained
at the experimental site.
