A. Corvaglia

A high performance front end for MEG II tracker

MEG Experiment Upgrade proposes a major improvement [1] of the sensitivity in the μ →eγ decay [2]. In particular the positron tracking will be performed by means of an upgrade of MEG Drift Chamber that consists in a cylindrical wire drift chamber, with the axis parallel to the muon beam, inspired to the one used in the KLOE experiment [3]. The new tracker, currently under costruction, can achieve a resolution of 100 μm in the measurement of the drift distance to the anode wires. Improving the resolution imposes a high speed and high performance Front End Electronics for signal acquisition.

The CluTim algorithm: an improvement on the impact parameter estimates

A Drift Chamber (DC) is a detector used in high energy physics experiments for determining charged particles trajectories. It consists of a gas volume and of an array of thin anode wires at high voltages generating high electric fields. Charged particles passing through the gas ionize it creating electron/ion pairs along their path, which, accelerated by the electric fields, produce signal pulses on the sense wires. The signal pulses from all the wires are then collected and the particle trajectory is tracked assuming that the distances of closest approach (the impact parameter) between the particle trajectory and the wires coincide with the distance between the closest ion cluster and the corresponding nearest wire. The widespread use of helium based gas mixtures, aimed at minimizing the multiple scattering contribution to the momentum measurement for low momentum particles, produces, as a consequence, a low ion ionization clusters density (12cluster/cm in a 90/10helium/isobutanemixture), thus introducing a sensible bias in the impact parameter assumption, particularly for short impact parameters and small cell drift chambers. Recently, it has been proposed an alternative track reconstruction (Cluster Counting/Timing) technique, which consists in measuring the arrival times on the wires of each individual ionization cluster and combining these times to get a bias free estimate of the impact parameter. Typical time separations between consecutive ionization acts, in a He-based gas mixture, range from a few ns, at small impact parameters, to a few tens of ns, at large impact parameters. Therefore, in order to efficiently applying the cluster timing technique, it is necessary to have read-out interfaces capable of processing high speed signals, in which one can easily isolate pulses due to different ionization clusters. The wire signals generated by the drift chamber, before being processed, are converted from analog to digital with the use of flash-ADCs. Requirements on drift chamber performance impose the conversions at sampling frequencies of at least 1 GS/s with at least 8-bit resolution. These constraints, together with the maximum drift times, usually of the order of 1 microsecond, and with the large number of acquisition channels, typically of the order of tens of thousand, mandate some sizeable data reduction, which, however, must preserve all the relevant information. Identifying both the amplitude and the arrival time of each peak associated to each individual ionization cluster is the minimum requirement on the data transfer for storage. More specifically, a fast readout algorithm (CluTim) for identifying, in the digitized drift chamber signals, the individual ionization pulse peaks and recording their time and amplitude has been implemented and tested on a Virtex 6 core FPGA board. The CluTim algorithm, that we have been developed, is able to process the data in real-time and in particular it:  identifies, in the digitized signal, the peaks corresponding to the different ionization cluster;  stores each peak amplitude and timing in an internal memory;  sends the data stored to an external device when specific trigger signals occur. This algorithm has been implemented tested on different xilinx fpga getting a data reduction factors of more than one order of magnitude respect a the older algorithms.

Voltage control system for a Multigap Resistive Plate Chambers telescope

Multigap Resistive Plate Chambers (MRPCs) are gas detectors operating in avalanche saturated mode at a standard voltage ranges around 18 ÷ 20 kV, applied by means of DC Low Voltage to DC High Voltage converters (DC/DC converters). This device is used in the Extreme Energy Events Project (EEE Project), an innovative experiment to study high energy cosmic rays by using a network of tracking detectors, located across the Italian territory plus CERN, over a total area of 105 km2. Each EEE telescope is composed of three MRPCs. A suitable device to supply and control voltage and current for the DC-DC converters and for the MRPCs front-end cards has been developed. This electronic module is interfaced with the DAQ computer, controlled by a dedicated software in LabVIEW and, since computer is permanently online, the LV/HV system can be continuously monitored from remote.

A new assembly technique of full stereo Drift Chamber for high energy physics experiments

Modern High Energy Physics experiments for the search of extremely rare processes require high resolutions (order of 50-200 keV/c) tracking systems for particle momenta in the range of 50-300 MeV/c, dominated by multiple scattering contributions. We will describe a newly developed construction technique for ultra-low mass, high granularity Drift Chambers fulfilling this goal. These techniques have been successfully implemented at INFN-Lecce and University of Salento and are currently being used for the construction of the Drift Chamber of the MEG upgrade experiment.

The DAQ system for CORAM (COsmic RAy Mission) experiment

CORAM (COsmic RAy Mission) is an experiment carried out by INFN and the University of Salento for studying and measuring several properties of the cosmic ray flux. The CORAM detector can be used both for experimental and outreach goals and it is designed also for aereospace applications. The final Data Acquisition system (DAQ) has been implemented in order to create a compact, redundant and user friendly device that can be used for several purposes. In this work we present this DAQ system and the electronics used.