The multiplicities of positive and negative pions, kaons and unidentified hadrons produced in deep-inelastic scattering are measured in bins of the Bjorken scaling variable x, the relative virtual-photon energy y and the fraction of the virtual-photon energy transferred to the final-state hadron z. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam of both electric charges and a liquid hydrogen target. These measurements cover the kinematic domain with photon virtuality Q^2 > 1 (GeV/c)^2, 0.004 < x < 0.4, 0.1 < y < 0.7 and 0.2 < z < 0.85, in accordance with the kinematic domain used in earlier published COMPASS multiplicity measurements with an isoscalar target. The calculation of radiative corrections was improved by using the Monte Carlo generator DJANGOH, which results in up to 12% larger corrections in the low-x region.

Owing to a change in the scope of physics research, the AMBER spectrometer at CERN is undergoing an update on its instrumentation and trigger strategy for the data acquisition system. One of the key updates is the adoption of a free-running and trigger-less operation, which differs from the predecessor of AMBER, COMPASS, by working in a continuous mode but in an event-based triggered way. In this article, we present a multichannel data-acquisition platform developed in line with the next generation of trigger-less and free-running data acquisition systems. The platform is based on a pre-existing Mezzanine Sampling ADC board for the analog-to-digital conversion and a Xilinx Zynq Ultrascale+ System on Module for online real-time data processing. We also present the evaluation of the system operating in continuous mode, taking data from a 25-element electromagnetic calorimeter prototype with a muon beam, during the first AMBER pilot run. The acquired data were used for noise and pulse shape studies required for the design of the algorithms for lossless compression and data feature extraction needed for trigger-less operation.

New results are presented on a high-statistics measurement of Collins and Sivers asymmetries of charged hadrons produced in deep inelastic scattering of muons on a transversely polarised $^6$LiD target. The data were taken in 2022 with the COMPASS spectrometer using the 160 \gevv\ muon beam at CERN, balancing the existing data on transversely polarised proton targets. The first results from about two-thirds of the new data have total uncertainties smaller by up to a factor of three compared to the previous deuteron measurements. Using all the COMPASS proton and deuteron results, both the transversity and the Sivers distribution functions of the $u$ and $d$ quark, as well as the tensor charge in the measured $x$-range are extracted. In particular, the accuracy of the $d$ quark results is significantly improved.

A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised 6LiD (deuteron) and NH3 (proton) targets is presented. All available data collected in the years 2003–2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160GeV/c at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from e+e− annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of π+π− pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range x>0.032, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of π+π− measured on the 6LiD target can be interpreted as indication for a cancellation of u and d-quark transversity distributions.

We present a method for diagnostics analysis for pixelated particle detectors. The method is based on extracting information from the detector in the form of model parameters by using a representative mathematical model. To illustrate the procedure we analyzed real experimental data obtained with the electromagnetic calorimeter ECAL2 of the COMPASS experiment at CERN. Having observed the data, the typical pulses were fitted with a mathematical model. Heat maps were drawn to visualize the distribution of the mean values of each of the fitted parameters. This data visualization technique is useful for highlighting areas with similar behavior and detecting abnormal responses in single cells.

COMPASS RICH-1 has used high-purity perfluorobutane as radiator gas since 2001. The operation and control of the radiator gas has evolved over years with continuous improvements. We report on the experience gained in the 20 year-long operation of perfluorobutane as COMPASS RICH radiator.Very accurate values for the radiator gas refractive index are needed for high-performance particle identification. The procedure has evolved over years and the one presently in use, which provides refractive index estimate at the 1 ppm level, is discussed. Perfluorobutane procurement is becoming challenging, and the minimization of material waste is now a priority for the protection of the environment. Commercially available perfluorobutane needs dedicated filtering before usage and typical material losses in the filtering procedure were around 30%. Recent efforts allowed us to reduce them to about 5%. A potential alternative to fluorocarbon radiators in gaseous RICHes is also presented.

The production of vector mesons in deep inelastic scattering is an interesting yet scarcely explored channel to study the transverse spin structure of the nucleon and the spin-dependence of fragmentation. The COMPASS collaboration has performed the first measurement of the Collins and Sivers asymmetries for inclusively produced rho(0) mesons. The analysis is based on the data set collected in deep inelastic scattering in 2010 using a 160 GeV/c mu(+) beam impinging on a transversely polarized NH3 target. The rho(0) mesons are selected from oppositely charged hadron pairs, and the asymmetries are extracted as a function of the Bjorken-xvariable, the transverse momentum of the pair and the fraction of the energy z carried by the pair. Indications for positive Collins and Sivers asymmetries are observed. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).

We present the study of the production of double J/ψ mesons using COMPASS data collected with a 190 GeV/c π^- beam scattering off NH_3, Al and W targets. Kinematic distributions of the collected double J/ψ events are analysed, and the double J/ψ production cross section is estimated for each of the COMPASS targets. The results are compared to predictions from single- and double-parton scattering models as well as the pion intrinsic charm and the tetraquark exotic resonance hypotheses. It is demonstrated that the single parton scattering production mechanism gives the dominant contribution that is sufficient to describe the data. An upper limit on the double intrinsic charm content of pion is evaluated. No significant signatures that could be associated with exotic tetraquarks are found in the double J/ψ mass spectrum.

The COMPASS RICH-1 detector has undergone a major upgrade in 2016 with the installation of four novel MPGD-based photon detectors. They consist of large-size hybrid MPGDs with multi-layer architecture composed of two layers of Thick-GEMs and bulk resistive MicroMegas. A dedicated high voltage power supply system, based on CAEN HV modules, has been built and put in operation: it controls more than 100 HV channels. The system is required to protect the detectors against errors by the operator, monitor voltages and currents at a 1 Hz rate and automatically react to detector misbehavior. It includes also a HV compensation system against environmental pressure and temperature variation to grant the detector stability. The operation of a MPGD based single photon detector poses challenging requirements to the high voltage power supply systems employed in terms of high-resolution diagnostic features and dynamic voltage control. Systems satisfying all the needed features are not commercially available; for this reason a novel single channel high voltage system matching the MPGD needs has been designed and realized. In this article the COMPASS RICH-1 MPGD HV system implementation is described as well as its performance in terms of stability of the novel MPGD-based photon detectors during the physics data taking at COMPASS. The design, implementation and performance of a novel HV power supply system based on DC to DC converters and controlled by a FPGA device is presented. The capabilities of the first prototype of the new single HV channel power supply are illustrated when operated with a MPGD based single photon detector during a test beam exercise. The preliminary result of the multi channel system are briefly discussed.

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ρ ^0 meson muoproduction at COMPASS using 160 GeV/c polarised μ ^+ and μ ^- beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/c^2 < W < 17.0 GeV/c^2, 1.0 (GeV/c)^2 < Q^2 < 10.0 (GeV/c)^2 and 0.01 (GeV/c)^2 < p_T^2 < 0.5 (GeV/c)^2. Here, W denotes the mass of the final hadronic system, Q^2 the virtuality of the exchanged photon, and p_T the transverse momentum of the ρ ^0 meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons (γ^*_T → V^_L) indicate a violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive ρ ^0 production.

We present an open hardware/software architecture for remote control of Field Programmable Gate Array (FPGA) based Systems on Chip (SoC). These systems, which integrate embedded processors, FPGA fabric, memory blocks and other resources, usually need to be controlled from a computer. The proposed architecture comprises a set of commands, instructions for data movement, and standardized data packets. A minimal set of specifications and design guidelines will effectively separate hardware and software developments granting compatibility to the different subsystems. A simple architectural approach ensures compatibility of computer resident software, embedded processor software, and FPGA designs. The implicit structured design methodology associated with the proposed architecture facilitates remote control as well as maintenance, debugging, and portability among SoC-FPGA vendors. We describe a concrete implementation in order to show how data and instructions can be moved across the whole system.

In this study, we present a procedure to optimize a set of finite impulse response filter (FIR) coefficients for digital pulse-amplitude measurement. Such an optimized filter is designed using an adapted digital penalized least mean square (DPLMS) method. The effectiveness of the procedure is demonstrated using a dataset from a case study on high-resolution X-ray spectroscopy based on single-photon detection and energy measurements. The energy resolutions of the Kα and Kβ lines of the Manganese energy spectrum have been improved by approximately 20%, compared to the reference values obtained by fitting individual photon pulses with the corresponding mathematical model.

A simplified correlation index is proposed to be used in real-time pulse shape recognition systems. This index is similar to the classic Pearson's correlation coefficient, but it can be efficiently implemented in FPGA devices with far fewer logic resources and excellent performance. Numerical simulations with synthetic data and comparisons with the Pearson's correlation show the suitability of the proposed index in applications such as the discrimination and counting of pulses with a predefined shape. Superior performance is evident in signal-to-noise ratio scenarios close to unity. FPGA implementation of Person's method and the proposed correlation index have been successfully tested and the main results are summarized.

We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen target and confirm the $\pi_1(1600) \to \rho(770) \pi$ amplitude, which interferes with a nonresonant $1^{-+}$ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile their experimental findings. We study the nonresonant contributions to the $\pi^-\pi^-\pi^+$ final state using pseudo-data generated on the basis of a Deck model. Subjecting pseudo-data and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the $J^{PC} = 1^{-+}$ amplitude and also for amplitudes with other $J^{PC}$ quantum numbers. We investigate for the first time the amplitude of the $\pi^-\pi^+$ subsystem with $J^{PC} = 1^{--}$ in the $3\pi$ amplitude with $J^{PC} = 1^{-+}$ employing the novel freed-isobar analysis scheme. We reveal this $\pi^-\pi^+$ amplitude to be dominated by the $\rho(770)$ for both the $\pi_1(1600)$ and the nonresonant contribution. We determine the $\rho(770)$ resonance parameters within the three-pion final state. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the $J^{PC} = 1^{-+}$ amplitude.

Configuring and setting up a remote access laboratory for an advanced online school on fully programmable System-on-Chip (SoC) proved to be an outstanding challenge. The school, jointly organized by the International Centre for Theoretical Physics (ICTP) and the International Atomic Energy Agency (IAEA), focused on SoC and its applications to nuclear and scientific instrumentation and was mainly addressed to physicists, computer scientists and engineers from developing countries. The use of e-learning tools, which some of them adopted and others developed, allowed the school participants to directly access both integrated development environment software and programmable SoC platforms. This facilitated the follow-up of all proposed exercises and the final project. During the four weeks of the training activity, we faced and overcame different technology and communication challenges, whose solutions we describe in detail together with dedicated tools and design methodology. We finally present a summary of the gained experience and an assessment of the results we achieved, addressed to those who foresee to organize similar initiatives using e-learning for advanced training with remote access to SoC platforms.

This paper describes a custom made high voltage isolated bidirectional network interface for communication among FPGA devices, which are in different power domains. Preliminary performance test and measurements of noise tolerance and stability are presented. A case study of an application regarding a network of multiple single-channel power supply systems for Micro Pattern Gaseous Detectors is portrayed. In order to match the specific system needs of dynamic voltage control, the network interface provides a reliable high voltage decoupling up to 2 kV with reasonable noise tolerance and data transmission rate up to 100 Mbps. The flexibility of the interface allows the implementation of different communication protocols.

The requirements posed to high voltage power supply systems by the operation of Micro Pattern Gaseous Detectors are specific in terms of high resolution diagnostic features and intelligent dynamic voltage control. These requirements are needed both when technology development is performed and when extended detector systems are supplied and monitored. Systems satisfying all the needed features are not commercially available. A single channel high voltage system matching the Micro Pattern Gaseous Detector needs has been designed and realized, including its hardware and software components. The system employs a commercial DC/DC converter and is coupled to a custom high resolution ammeter. Local intelligence, flexibility and high speed inter-connectivity are provided by a System on Chip Board and the use of a powerful FPGA. The single channel system has been developed, as critical milestone towards the realization of a multi-channel system. The design, implementation and performance of the system are reported in detail in this article, as well as the performance of the single channel power supply when connected to a Micro Pattern Gaseous Detector in realistic working condition during a test beam exercise.

A pulse drive system capable of converting an arbitrary input signal into a delta sigma encoded pulse code stream in real time has been demonstrated. This system is based on the use of analog and digital hardware controlled by a Field Programmable Gate Array (FPGA) rather than using software to produce the delta sigma code and then loading it into the memory of a commercial Pulse Pattern Generator (PPG). The results of using the system to drive a Josephson junction array to synthesize quantum-accurate voltage waveforms are presented. The advantage of such a system includes the significant reduction in time required to change waveform parameters. This provides an easily tunable source of high-fidelity stable voltage waveforms at low temperature for future applications including validation of components for use in quantum technologies.

A portable architectural design strategy is described for the implementation of reconfigurable virtual instrumentation based on programmable Systems-on-Chip integrating microprocessors and FPGA in the same physical device. The key role is played by a general purpose communication block as a means to efficiently separate the activities carried out in the microprocessor and in the FPGA. Both parts interact according to simple logic protocols by reading and writing data on the common memory resources of the communication block. The architecture of the proposed communication system can be easily implemented in practically any modern programmable System-on-Chip. With the proposed strategy, the porting of embedded software programs and associated FPGA designs among different device families and vendors is facilitated. A structured methodology is proposed for handling complex real-time systems based on these programmable Systems-on-Chip. We described a concrete communication block that has been successfully implemented and utilized for a quick implementation of a data acquisition system based on a Xilinx Zynq-7030 FPGA Mezzanine Card (FMC) and a custom FMC module with an 8-bit 500 MSPS ADC.