Benedetto Gorini

The direct CP violation parameter Re(epsilon'/epsilon) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The new data yield the result: Re(epsilon'/epsilon) = (13.7 +/- 3.1) times 10^{-4}. Combining this result with that published from the 1997, 98 and 99 data, an overall value of Re(epsilon'/epsilon) = (14.7 +/- 2.2) times 10^{-4} is obtained from the NA48 experiment.

We report test beam studies of 11% of the production ATLAS Tile Calorimeter modules. The modules were equipped with production front-end electronics and all the calibration systems planned for the final detector. The studies used muon, electron and hadron beams ranging in energy from 3 to 350 GeV. Two independent studies showed that the light yield of the calorimeter was ∼70pe/GeV, exceeding the design goal by 40%. Electron beams provided a calibration of the modules at the electromagnetic energy scale. Over 200 calorimeter cells the variation of the response was 2.4%. The linearity with energy was also measured. Muon beams provided an intercalibration of the response of all calorimeter cells. The response to muons entering in the ATLAS projective geometry showed an RMS variation of 2.5% for 91 measurements over a range of rapidities and modules. The mean response to hadrons of fixed energy had an RMS variation of 1.4% for the modules and projective angles studied. The response to hadrons normalized to incident beam energy showed an 8% increase between 10 and 350 GeV, fully consistent with expectations for a noncompensating calorimeter. The measured energy resolution for hadrons of σ/E=52.9%/E⊕5.7% was also consistent with expectations. Other auxiliary studies were made of saturation recovery of the readout system, the time resolution of the calorimeter and the performance of the trigger signals from the calorimeter.

The ATLAS Phase-I upgrade (2019) requires a Trigger and Data Acquisition (TDAQ) system able to trigger and record data from up to three times the nominal LHC instantaneous luminosity. The Front-End LInk eXchange (FELIX) system provides an infrastructure to achieve this in a scalable, detector agnostic and easily upgradeable way. It is a PC-based gateway, interfacing custom radiation tolerant optical links from front-end electronics, via PCIe Gen3 cards, to a commodity switched Ethernet or InfiniBand network. FELIX enables reducing custom electronics in favour of software running on commercial servers. The FELIX system, the design of the PCIe prototype card and the integration test results are presented in this paper.

The ATLAS experiment at CERN is planning full deployment of a new unified optical link technology for connecting detector front end electronics on the timescale of the LHC Run 4 (2025). It is estimated that roughly 8000 GBT (GigaBit Transceiver) links, with transfer rates up to 10.24 Gbps, will replace existing links used for readout, detector control and distribution of timing and trigger information. A new class of devices will be needed to interface many GBT links to the rest of the trigger, data-acquisition and detector control systems. In this paper FELIX (Front End LInk eXchange) is presented, a PC-based device to route data from and to multiple GBT links via a high-performance general purpose network capable of a total throughput up to O(20 Tbps). FELIX implies architectural changes to the ATLAS data acquisition system, such as the use of industry standard COTS components early in the DAQ chain. Additionally the design and implementation of a FELIX demonstration platform is presented and hardware and software aspects will be discussed.

The response of pions and protons in the energy range of 20–180 GeV, produced at CERN's SPS H8 test-beam line in the ATLAS iron–scintillator Tile hadron calorimeter, has been measured. The test-beam configuration allowed the measurement of the longitudinal shower development for pions and protons up to 20 nuclear interaction lengths. It was found that pions penetrate deeper in the calorimeter than protons. However, protons induce showers that are wider laterally to the direction of the impinging particle. Including the measured total energy response, the pion-to-proton energy ratio and the resolution, all observations are consistent with a higher electromagnetic energy fraction in pion-induced showers. The data are compared with GEANT4 simulations using several hadronic physics lists. The measured longitudinal shower profiles are described by an analytical shower parametrization within an accuracy of 5–10%. The amount of energy leaking out behind the calorimeter is determined and parametrized as a function of the beam energy and the calorimeter depth. This allows for a leakage correction of test-beam results in the standard projective geometry.

The NA48 collaboration is preparing a new experiment at CERN aiming to study CP violation in the K0-K0 system with an accuracy of 2 × 10−4 in the parameter Re(ϵ′/ϵ). Decays in two π0's will be recorded by a quasi-homogeneous liquid krypton calorimeter. A liquid krypton calorimeter has been chosen to combine good energy, position and time resolution with precise charge calibration and long-term stability. The prototype calorimeter incorporating the final design of the electrode read-out structure is presented in this paper. An energy resolution of ≃3.5%√E with a constant term smaller than 0.5% has been obtained. The time resolution was found to be better than 300 ps above 15 GeV.

The decay rate of KL→π0γγ has been measured with the NA48 detector at the CERN SPS. A total of 2558 KL→π0γγ candidates have been observed with a residual background of 3.2%. The branching ratio is determined to be (1.36±0.03(stat)±0.03(syst)±0.03(norm))×10−6 and the vector coupling constant av=−0.46±0.03(stat)±0.04(syst). This result suggests that the CP-violation effects are dominating in the KL→π0e+e− decay. An upper limit for the KL→π0γγ decay rate in the two photon mass region mγγ<mπ0 is also given.

The semileptonic decay of the neutral K meson, KL -> pi e nu (Ke3), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f_+(q^2)), scalar (f_S) and tensor (f_T) interactions were measured. The linear slope of the vector form factor lambda_+ = 0.0284+-0.0007+-0.0013 and values for the ratios |f_S/f_+(0)| = 0.015^{+0.007}_{-0.010}+-0.012 and |f_T/f_+(0)| = 0.05^{+0.03}_{-0.04}+-0.03 were obtained. The values for f_S and f_T are consistent with zero. Assuming only Vector-Axial vector couplings, lambda_+ = 0.0288+-0.0004+-0.0011 and a good fit consistent with pure V-A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M = 859+-18 MeV, consistent with the K^*(892) mass.

New measurements of the $\eta$ and $K^0$ masses have been performed using decays to 3$\pi^0$ with the NA48 detector at the CERN SPS. Using symmetric decays to reduce systematic effects, the results $M(\eta) = 547.843\pm0.051$ MeV/c$^2$ and $M(K^0) = 497.625\pm0.031$ MeV/c$^2$ were obtained.

For new detector and trigger systems to be installed in the ATLAS experiment after LHC Run 2, a new approach will be followed for Front-End electronics interfacing. The FELIX (Front-End LInk eXchange) system will function as gateway connecting: on one side to detector and trigger electronics links, as well as providing timing and trigger information; and on the other side a commodity switched network built using standard technology (either Ethernet or Infiniband). The new approach is described in this paper, and results achieved so far are presented.

The effects of space charge due to slowly drifting ions can be relevant for detectors operated at high intensity, or for relatively low values of the bias voltage. Accurate measurements have been obtained with the liquid krypton calorimeter of the NA48 experiment, from data collected in 1997. The build-up of space charge takes place during the first part of the beam extraction burst, and causes a dependence of the response on the transverse coordinate of the axis of electromagnetic showers, and a small reduction of average amplitude. The effects are well reproduced by a computation, where the only free parameter is the value of the ion mobility. The model can be applied a wide range of operating conditions, and generalized to detectors with different geometry and active medium.

The base-line design and implementation of the ATLAS DAQ DataFlow system is described. The main components of the DataFlow system, their interactions, bandwidths, and rates are discussed and performance measurements on a 10% scale prototype for the final ATLAS TDAQ DataFlow system are presented. This prototype is a combination of custom design components and of multithreaded software applications implemented in C++ and running in a Linux environment on commercially available PCs interconnected by a fully switched gigabit Ethernet network.

The ATLAS readout subsystem is the main interface between ∼ 1600 detector front-end readout links and the higher-level trigger farms. To handle the high event rate (up to 100 kHz) and bandwidth (up to 160 MB/s per link) the readout PCs are equipped with four ROBIN (readout buffer input) cards. Each ROBIN attaches to three optical links, provides local event buffering for approximately 300 ms and communicates with the higher-level trigger system for data and delete requests. According to the ATLAS baseline architecture this communication runs via the PCI bus of the host PC. In addition, each ROBIN provides a private Gigabit Ethernet port which can be used for the same purpose. Operational monitoring is performed via PCI. This paper presents a summary of the ROBIN hardware and software together with measurements results obtained from various test setups.

Using data taken during the year 2000 with the NA48 detector at the CERN SPS, a search for the CP violating decay K_S -> 3 pi0 has been performed. From a fit to the lifetime distribution of about 4.9 million reconstructed K0/K0bar -> 3 pi0 decays, the CP violating amplitude eta_000 = A(K_S -> 3 pi0)/A(K_L -> 3 pi0) has been found to be Re(eta_000) = -0.002 +- 0.011 +- 0.015 and Im(eta_000) = -0.003 +- 0.013 +- 0.017. This corresponds to an upper limit on the branching fraction of Br(K_S -> 3 pi0) < 7.4 x 10^-7 at 90% confidence level. The result is used to improve knowledge of Re(epsilon) and the CPT violating quantity Im(delta) via the Bell-Steinberger relation.

A novel type of particle detector based on scintillation, with precise spatial resolution and high radiation hardness, is being studied. It consists of a single microfluidic channel filled with a liquid scintillator and is designed to define an array of scintillating waveguides each independently coupled to a photodetector. Prototype detectors built using an SU-8 epoxy resin have been tested with electrons from a radioactive source. The experimental results show a light yield compatible with the theoretical expectations and confirm the validity of the approach.

The ATLAS ReadOut System (ROS) receives data fragments from ∼1600 detector readout links, buffers them and provides them on demand to the second-level trigger or to the event building system. The ROS is implemented with ∼150PCs. Each PC houses a few, typically 4, custom-built PCI boards (ROBIN) and a 4-port PCIe Gigabit Ethernet NIC. The PCs run a multi-threaded object-oriented application managing the requests for data retrieval and for data deletion coming through the NIC, and the collection and output of data from the ROBINs. At a nominal event fragment arrival rate of 75 kHz the ROS has to concurrently service up to approximately 20 kHz of data requests from the second-level trigger and up to 3.5 kHz of requests from event building nodes. The full system has been commissioned in 2007. Performance of the system in terms of stability and reliability, results of laboratory rate capability measurements and upgrade scenarios are discussed in this paper.

From the ATLAS Phase-I upgrade and onward, new or upgraded detectors and trigger systems will be interfaced to the data acquisition, detector control and timing (TTC) systems by the Front-End Link eXchange (FELIX). FELIX is the core of the new ATLAS Trigger/DAQ architecture. Functioning as a router between custom serial links and a commodity network, FELIX is implemented by server PCs with commodity network interfaces and PCIe cards with large FPGAs and many high speed serial fiber transceivers. By separating data transport from data manipulation, the latter can be done by software in commodity servers attached to the network. Replacing traditional point-to-point links between Front-end components and the DAQ system by a switched network, FELIX provides scaling, flexibility uniformity and upgradability and reduces the diversity of custom hardware solutions in favour of software.

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Ξ0→Λγ have been found with an estimated background of 58±8 events. From these events the Ξ0→Λγ decay asymmetry has been determined to α(Ξ0→Λγ)=−0.78±0.18stat±0.06syst, which is the first evidence of a decay asymmetry in Ξ0→Λγ. The branching fraction of the decay has been measured to be Br(Ξ0→Λγ)=(1.16±0.05stat±0.06syst)×10−3.

In the ATLAS experiment at the LHC, the ROD Crate DAQ provides a complete software framework to implement data acquisition functionality at the boundary between the detector specific electronics and the common part of the data acquisition system. Based on a plugin mechanism, it allows selecting and using common services (like data output and data monitoring channels) and developing software to control and acquire data from detector specific modules providing the infrastructure for control, monitoring and calibration. Including also event building functionality, the ROD Crate DAQ is intended to be the main data acquisition tool for the first phase of detector commissioning. This paper presents the design, functionality and performance of the ROD Crate DAQ and its usage in the ATLAS data acquisition system and during detector tests.

In this paper are presented the Work Items on Energy saving that are in the ETSI standardization work programme. An overview of the activities on energy consumption in other standardization bodies having links with ETSI is also provided together with a brief overview of the European regulation 2005/32/EC.

The processes of coherent bremsstrahlung (CB) and coherent pair production (CPP) based on aligned crystal targets have been studied in the energy range 20 -170 GeV.The experimental arrangement allowed for measurements of single photon properties of these phenomena including their polarization dependences.This is significant as the theoretical description of CB and CPP is an area of active debate and development.With the approach used in this paper, both the measured cross sections and polarization observables are predicted very well.This indicates a proper understanding of CB and CPP up to energies of 170 GeV.Birefringence in CPP on aligned crystals is applied to determine the polarization parameters in our measurements.New technologies for high-energy photon beam optics including phase plates and polarimeters for linear and circular polarization are demonstrated in this experiment.Coherent bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger enhancement for hard photons than CB for the channeling orientations of the crystal.Our measurements and our calculations indicate low photon polarizations for the high-energy SOS photons.

A measurement of the KS lifetime is presented using data recorded by the NA48 experiment at the CERN-SPS during 1998 and 1999. The KS lifetime is derived from the ratio of decay time distributions in simultaneous, collinear KS and KL beams, giving a result which is approximately independent of the detector acceptance and with reduced systematic errors. The result obtained is τS=(0.89598±0.00048±0.00051)×10−10 s, where the first error is statistical and the second systematic.

A search for the decay KS→π0e+e− has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching fraction B(KS→π0e+e−)<1.4×10−7 at 90% confidence level has been obtained.

The CERN-NA-59 experiment examined a wide range of electromagnetic processes for multi-GeV electrons and photons interacting with oriented single crystals. The various types of crystals and their orientations were used for producing photon beams and for converting and measuring their polarisation. The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised photon beams. A new crystal polarimetry technique was established for measuring the linear polarisation of the photon beam. The polarimeter is based on the dependence of the coherent pair production (CPP) cross section in oriented single crystals on the direction of the photon polarisation with respect to the crystal plane. Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set of synthetic Diamond crystals were used as analyzers of the linear polarisation. A birefringence phenomenon, the conversion of the linear polarisation of the photon beam into circular polarisation, was observed. This was achieved by letting the linearly polarised photon beam pass through a 10 cm thick Silicon single crystal that acted as a “quarter wave plate” (QWP) as suggested by Cabibbo et al.

Event data from proton-proton collisions at the LHC will be selected by the ATLAS experiment in a three-level trigger system, which, at its first two trigger levels (LVL1+LVL2), reduces the initial bunch crossing rate of 40 MHz to ~ 3 kHz. At this rate, the Event Builder collects the data from the readout system PCs (ROSs) and provides fully assembled events to the Event Filter (EF). The EF is the third trigger level and its aim is to achieve a further rate reduction to ~ 200 Hz on the permanent storage. The Event Builder is based on a farm of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (100) PCs, interconnected via a gigabit Ethernet to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (150) ROSs. These PCs run Linux and multi-threaded software applications implemented in C++. All the ROSs, and substantial fractions of the Event Builder and EF PCs have been installed and commissioned. We report on performance tests on this initial system, which is capable of going beyond the required data rates and bandwidths for event building for the ATLAS experiment.

The ATLAS Level-1 Central Trigger Processor (CTP) combines information from calorimeter and muon trigger processors as well as other sources and makes the final Level-1 Accept (L1A) decision. Due to the increasing luminosity of the LHC and the growing demands of physics and monitoring placed on the ATLAS Level-1 trigger system, the current CTP has reached its design limits. Therefore and in order to provide some margin for future operation, the CTP will be upgraded during the LHC shutdown of 2013/14.

Microfluidic channels obtained by SU-8 photolithography and filled with liquid scintillators were recently demonstrated to be an interesting technology for the implementation of novel particle detectors. The main advantages of this approach are the intrinsic radiation resistance resulting from the simple microfluidic circulation of the active medium and the possibility to manufacture devices with high spatial resolution and low material budget using microfabrication techniques.

A prototype electromagnetic calorimeter containing 180 litres of liquid krypton has been tested in electron and muon beams at the CERN SPS. The main features of this detector are its active shower medium, a granularity of 2 cm with tower readout, and the use of the initial current readout technique with an effective shaping time of about 60 ns. An energy resolution for electrons of 4.1%√E[GeV] with a constant term of 0.4% and a noise contribution of 50 MeV has been achieved. The calorimeter has a spatial resolution of 4.5 mm√E[GeV] with a constant term of 0.3 mm and a time resolution of about 0.5 ns for energies larger than 10 GeV.

The trigger used for the collection of the samples of K0→π0π0 decays in the NA48 experiment at CERN uses a novel pipeline design in order to satisfy the demanding specifications of a high rate kaon beam. The trigger algorithms, architecture and performance are described.

The ATLAS trigger reduces the rate of interesting events to be recorded for off-line analysis in three successive levels from 40 MHz to /spl sim/100 kHz, /spl sim/2 kHz and /spl sim/200 Hz. The high level triggers and data acquisition system are designed to profit from commodity computing and networking components to achieve the required performance. In this paper, we discuss data flow aspects of the design of the second level trigger (LVL2) and present results of performance measurements.

Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates with an estimated background of 13.7 +- 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory predictions.

In the ATLAS experiment at the LHC, the output of read-out hardware specific to each subdetector will be transmitted to buffers, located on custom made PCI cards ("ROBINs"). The data consist of fragments of events accepted by the first-level trigger at a maximum rate of 100 kHz. Groups of four ROBINs will be hosted in about 150 Read-Out Subsystem (ROS) PCs. Event data are forwarded on request via Gigabit Ethernet links and switches to the second-level trigger or to the Event builder. In this paper a discussion of the functionality and real-time properties of the ROS is combined with a presentation of measurement and modelling results for a testbed with a size of about 20% of the final DAQ system. Experimental results on strategies for optimizing the system performance, such as utilization of different network architectures and network transfer protocols, are presented for the testbed, together with extrapolations to the full system.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Event data from proton-proton collisions at the LHC will be selected by the ATLAS experiment by a three level trigger system, which reduces the initial bunch crossing rate of 40 MHz at its first two trigger levels (LVL1+LVL2) to <formula formulatype="inline"><tex>$\sim$</tex></formula>3 kHz. At this rate the Event-Builder collects the data from all Read-Out system PCs (ROSs) and provides fully assembled events to the the Event-Filter (EF), which is the third level trigger, to achieve a further rate reduction to <formula formulatype="inline"> <tex>$\sim$</tex></formula>200 Hz for permanent storage. The Event-Builder is based on a farm of <formula formulatype="inline"><tex>$O(100)$</tex></formula> PCs, interconnected via Gigabit Ethernet to <formula formulatype="inline"><tex>$O(150)$</tex> </formula> ROSs. These PCs run Linux and multi-threaded software applications implemented in C++. All the ROSs and one third of the Event-Builder PCs are already installed and commissioned. Performance measurements have been exercised on this initial system, which show promising results that the required final data rates and bandwidth for the ATLAS event builder are in reach. </para>

The ATLAS experiment is located at the European Center for Nuclear Research (CERN) in Switzerland. It is designed to observe collisions at the Large Hadron Collider (LHC): the world's largest and highest-energy particle accelerator. Event triggering and Data Acquisition is one of the extraordinary challenges faced by the detectors at the high luminosity LHC collider upgrade. During 2011, the LHC reached instantaneous luminosities of 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and produced events with up to 24 interactions per colliding proton bunch. This places stringent operational and physical requirements on the ATLAS Trigger in order to reduce the nominal 40MHz collision rate to a manageable event storage rate up to 400Hz and, at the same time, select those events considered interesting. The Level-1 Trigger is the first rate-reducing step in the ATLAS Trigger, with an output rate of 75kHz and decision latency of less than 2.5μs. It is primarily composed of the Calorimeter Trigger, Muon Trigger, the Central Trigger Processor (CTP) and by 2014 a complete new electronics module: the Topological Processor (TP). The TP will make it possible, for the first time, to concentrate detailed information from sub-detectors in a single Level-1 module. This allows the determination of angles between jets and/or leptons, or even more complex observables such as muon isolation or invariant mass. This requires to receive on a single module a total bandwidth of about 1Tb/s and process the data within less than 100 ns. In order to accept this new information from the TP, the CTP will be upgraded to process double the number of trigger inputs and logical combinations of these trigger inputs. These upgrades also address the growing needs of the complete Level-1 trigger system as LHC luminosity increases. During the LHC shutdown in 2013, the TP and the upgraded CTP will be installed. We present the justification for such an upgrade, the proposed upgrade to the CTP, and tests on the TP demonstrator and prototype, emphasizing the characterization of the high speed links and tests of the topological algorithm's latency and logic utilization.

A search for the decay KS→π0γγ has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching ratio BR(KS→π0γγ,z⩾0.2)<3.3×10−7 has been obtained at 90% confidence level, where z=mγγ2/mK02.

We present a measurement of the relative branching ratio of the decay K0→π±e±νγ (Ke3γ) with respect to K0→π±e±ν (Ke3+Ke3γ) decay. The result is based on observation of 19 000 Ke3γ and 5.6×106 Ke3 decays. The value of the branching ratio is Br(Ke3γ0,Eγ*>30MeV, θeγ*>20°)/Br(Ke30)=(0.964±0.008−0.009+0.011)%. This result agrees with theoretical predictions but is at variance with a recently published result.

The ATLAS collaboration at CERN operated a combined test beam (CTB) from May until November 2004. The prototype of ATLAS data acquisition system (DAQ) was used to integrate other subsystems into a common CTB setup. Data were collected synchronously from all the ATLAS detectors, which represented nine different detector technologies. Electronics and software of the first level trigger were used to trigger the setup. Event selection algorithms of the high level trigger were integrated with the system and were tested with real detector data. The possibility to operate a remote Event Filter farm synchronized with the ATLAS Trigger and Data Acquisition System (TDAQ) was also tested. Event data, as well as detector conditions data, were made available for offline analysis

A novel liquid scintillation detector with high spatial resolution is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by filling microfluidic channels with an organic liquid scintillator and optically coupled to a pixellated photodetector. Such a microfluidic device can be designed and processed to meet the requirements of a wide range of applications like medical imaging, homeland security and high-energy physics. High-spatial resolution miniaturized detectors as well as large-area detectors can easily be fabricated. The fabrication process of a prototype detector and experimental results are presented in this paper.

The NA48 experiment at the CERN SPS accelerator is making a measurement of the direct CP violation parameter /spl epsiv/'//spl epsiv/ by comparing the four rates of decay of K/sub S/ and K/sub L/ into 2/spl pi//sup 0/ and /spl pi//sup +//spl pi//sup -/. To reconstruct the decays into 2/spl pi//sup 0/ the information from the almost 13500 channels of a quasi-homogeneous liquid krypton electromagnetic calorimeter is used. The readout electronics of the calorimeter has been designed to provide a dynamic range from a few MeV to about 50 GeV energy deposition per cell, and to sustain a high rate of incident particles. The system is made by cold charge preamplifiers (working at 120/spl deg/K), low-noise fast shapers followed by digitizer electronics at 40 MHz sampling rate that employs a gain switching technique to expand the dynamic range, where the gain can be selected for each sample individually (i.e. every 25 ns). To reduce the amount of data collected the system contains a zero suppression circuit based on halo expansion.

In the ATLAS experiment at the LHC, the ROD Crate DAQ provides a complete framework to implement data acquisition functionality at the boundary between the detector specific electronics and the common part of the data acquisition system. Based on a plugin mechanism, it allows selecting and using common services (like data output and data monitoring channels) and developing simple libraries to control, monitor, acquire and/or emulate detector specific electronics. Providing also event building functionality, the ROD Crate DAQ is intended to be the main data acquisition tool for the first phase of detector commissioning. This paper presents the design, functionality and performance of the ROD Crate DAQ and its usage in the ATLAS DAQ and during detector tests

The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS High-Level Trigger (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests with the full detector in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, integration of selection algorithms, testing, software distribution, installation and improvements.

The Central Trigger Processor (CTP) is the final stage of the ATLAS first level trigger system which reduces the collision rate of 40 MHz to a Level-1 event rate of 100 kHz. An upgrade of the CTP is currently underway to significantly increase the number of trigger inputs and trigger combinations, allowing additional flexibility for the trigger menu. We present the hardware and FPGA firmware of the newly designed core module (CTPCORE+) module of the CTP, as well as results from a system used for early firmware and software prototyping based on commercial FPGA evaluation boards. First test result from the CTPCORE+ module will also be shown.

The NA48 experiment for a precision measurement of the CP violation parameter ϵ′ϵin K0 → 2 π decays will require a fast electromagnetic calorimeter with excellent energy and time resolution. A quasi homogeneous calorimeter using liquid krypton and a fast readout with 40 MHz FADCs is proposed. A prototype with 400 kg of liquid krypton was built and tested in an electron beam. Results for the energy, space and time resolution of this prototype are given.

The decay rate of KS → γγ has been measured with the NA48 detector at the CERN SPS. A total of 149 KS → γγ events have been observed. The branching ratio is determined to be (2.58±0.36(stat)±0.22(sys))×10−6.

The ATLAS experiment under construction at CERN is due to begin operation at the end of 2007. The detector will record the results of proton-proton collisions at a center-of-mass energy of 14 TeV. The trigger is a three-tier system designed to identify in real-time potentially interesting events that are then saved for detailed offline analysis. The trigger system will select approximately 200 Hz of potentially interesting events out of the 40 MHz bunch-crossing rate (with 109 interactions per second at the nominal luminosity).

An outlook of the experiments needs for Heavy Ion physics for the next ten years is given, including a summary of required beam types and configurations (e.g. p-Pb and collision energies other than the nominal 13 TeV). We discuss which, if any, other ion species than Pb are being considered. The experiment expectations in terms of integrated luminosities are discussed, along with the impact usefulness, or otherwise, of different scheduling options for the Ion physics program. Different ion running scenarios, as well as the interest of an extended ion run, in light of the upgrade plans and goals are discussed in terms of integrated luminosity and physics targets.

Na59 Experiment at CERN-SPS aims for obtaining circularly polarized high energy photons (~100GeV) starting from an unpolarized electron beam. The basic principle of operation was predicted in 1962 by Cabbibo and has remained untested up to now. Among other physics goals, Na59 collaboration investigates usage of crystals for high energy photon polarimetry. This paper presents the experiment and summarizes some of the results obtained as of Autumn 2000.

The KL→π±π0e∓νe(ν̄e) decay was investigated with the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The branching ratio Br(KL→π±π0e∓νe(ν̄e))=(5.21±0.07stat±0.09syst)×10−5 was fixed from a sample of 5464 events with 62 background events. The form factors f̄s, f̄p, λg and h̄ were found to be in agreement with previous measurements but with higher accuracy. The coupling parameter of the chiral Lagrangian L3=(−4.1±0.2)×10−3 was evaluated from the data.

A first level trigger system based on a 40 MHz digital pipeline has been developed for the CERN NA48 experiment, aiming at measuring CP violation in K/sup 0//spl rarr/2/spl pi/ decays. The outputs of the 13340 cells of the 10 m/sup 3/ liquid krypton calorimeter are summed into 64 X and 64 Y projection strips and continuously digitised with 40 MHz FADCs. This information is used to reconstruct at each clock cycle and for the two calorimeter projections, the number of clusters, the impact time of each of them (with a precision of about 3 ns), their total energy and the first and second moments of the energy distribution. Based on the quantities listed above, a programmable look-up table system subsequently computes online the longitudinal position of the kaon decay vertex and performs an event selection. The system is described.

This paper presents the study of a novel scintillation detector based on standard microfabrication techniques. It consists of a fine pitch array of hollow waveguides filled with a liquid scintillator and optically coupled to photodetectors. The detector has been fabricated by patterning the SU-8 photoresist on silicon wafers. Experimental studies have been performed by exciting the liquid scintillator contained in the SU-8 waveguides with electrons. The scintillation light produced was read out by an external photodetector. The results obtained with this set-up demonstrate the concept of microfluidic scintillation detection and are very encouraging for future developments.

A novel scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by filling microfluidic channels with an organic liquid scintillator. Such a microfluidic device can be designed and processed to meet the requirements of a wide range of applications like medical imaging, homeland security and high-energy physics. High-spatial resolution miniaturized detectors as well as large-area detectors can easily be fabricated. This paper presents the fabrication process of a prototype detector with 200 μm × 50 μm microchannels obtained by photolithography of the SU-8 photoresist. Preliminary experimental results are presented.

The PeakSum Processing System (PSS) is an element of the neutral trigger of the NA48 experiment at CERN. The PSS is a pipelined processor based on a VLSI semi-custom device, containing all the processing blocks needed in the system. The PSS provides information on the energy pattern released in the electromagnetic calorimeter of the NA48 experiment, used to identify K/sub 0//spl rArr//spl pi//sup 0//spl pi//sup 0//spl rArr/4/spl gamma/ decays.

Event data from proton-proton collisions at the LHC will be selected by the ATLAS experiment in a three-level trigger system, which, at its first two trigger levels (LVL1+LVL2), reduces the initial bunch crossing rate of 40 MHz to ~3 kHz. At this rate, the Event Builder collects the data from the readout system PCs (ROSs) and provides fully assembled events to the Event Filter (EF). The EF is the third trigger level and its aim is to achieve a further rate reduction to ~200 Hz on the permanent storage. The Event Builder is based on a farm of 0(100) PCs, interconnected via a Gigabit Ethernet to 0(150) ROSs. These PCs run Linux and multi-threaded software applications implemented in C++. All the ROSs, and substantial fractions of the Event Builder and Event Filter PCs have been installed and commissioned. We report on performance tests on this initial system, which is capable of going beyond the required data rates and bandwidths for Event Building for the ATLAS experiment.

The ATLAS readout subsystem (ROS) is the main interface between 1600 detector front-end readout links (ROL) and the high level (HLT) trigger farms. Its core device, the readout-buffer input (ROBIN), accepts event data on 3 readout links (ROLs) with a maximum rate of 100 kHz and a bandwidth of up to 160MB/s per link. Incoming event data is temporarily buffered and delivered via PCI or Gigabit Ethernet on request. Two devices, a XILINX XC2V2000 FPGA and an IBM PowerPC 440, are present, implementing the ROBIN’s functionality. Furthermore one 64 MB SDRAM event data buffer is available per ROL. The device supports the ATLAS baseline implementation, which foresees the PCI bus as the main communication path inside the ROS, as well as an optional data path using Gigabit Ethernet to increase scalability when needed. The paper presents the final design of the ATLAS ROBIN. Measurement results, obtained with a prototype device in PCI bus and Gigabit Ethernet setups, show the usability and approve the design choices.

The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS high-level triggers (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, selection algorithms, testing, software distribution, installation and improvements

In the ATLAS experiment at the LHC, the output of readout hardware specific to each subdetector will be transmitted to buffers, located on custom made PCI cards ("ROBINs"). The data consist of fragments of events accepted by the first-level trigger at a maximum rate of 100 kHz. Groups of four ROBINs will be hosted in about 150 read-out subsystem (ROS) PCs. Event data are forwarded on request via Gigabit Ethernet links and switches to the second-level trigger or to the event builder. In this paper a discussion of the functionality and real-time properties of the ROS is combined with a presentation of measurement and modeling results for a testbed with a size of about 20% of the final DAQ system. Experimental results on strategies for optimizing the system performance, such as utilization of different network architectures and network transfer protocols, are presented for the testbed, together with extrapolations to the full system

The “neutral” trigger system for the selection of K0→2π0→4γ decays of the NA48 CP-violation experiment is described. The trigger system has been implemented in a 40 MHz “dead-time free” pipeline to allow large rate reduction and high-trigger efficiency. The trigger decision is based on the information from 13 340 cells of the electro-magnetic calorimeter. Every 25 ns the energy, the centre of gravity, the kaon lifetime and the number of peaks in calorimeter projections are calculated in the trigger. The pipeline system is described and the performance of the trigger during the 1997 data-taking period is discussed.

The Atlas RobIn Prototype is an FPGA and Processor based PCI device, which receives event data fragments on two HOLA SLink ports, buffers and delivers or deletes them on request. Thus it is one of the core devices of the Atlas Readout System (ROS). To study various PCI-Bus and Ethernet based ROS implementations the board offers two interface flavours for data requests: PCI and Gigabit Ethernet. This paper presents a study of a ROS System based on an ordinary PC, hosting up to 3 RobIn Prototypes using the PCI-Bus for data exchange. The multithreaded host software uses an asynchronous messaging scheme optimizing the communication with the RobIns. First measurements indicate that a PCI-Bus based ROS can satisfy Atlas Data-Flow needs.

The ATLAS collaboration at CERN operated a combined test beam (CTB) from May until November 2004. The prototype of ATLAS data acquisition system (DAQ) was used to integrate other subsystems into a common CTB setup. Data were collected synchronously from all the ATLAS detectors, which represented nine different detector technologies. Electronics and software of the first level trigger were used to trigger the setup. Event selection algorithms of the high level trigger were integrated with the system and were tested with real detector data. A possibility to operate a remote event filter farm synchronized with ATLAS TDAQ was also tested. Event data, as well as detectors conditions data were made available for offline analysis

A new type of scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by coupling microfluidic channels filled with a liquid scintillator to photodetectors. Easy manipulation of liquid scintillators inside microfluidic devices allow their flushing, renewal, and exchange making the active medium intrinsically radiation hard. Prototype detectors have been fabricated by photostructuration of a radiation hard epoxy resin (SU-8) deposited on silicon wafers and coupled to a multi-anode photomultiplier tube (MAPMT) to read-out the scintillation light. They have been characterized by exciting the liquid scintillator in the 200 micrometers thick microchannels with electrons from a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{90}{\rm Sr}$</tex> </formula> yielding approximately 1 photoelectron per impinging Minimum Ionizing Particle (MIP). These promising results demonstrate the concept of microfluidic scintillating detection and are very encouraging for future developments.

In early 2012, the Large Hadron Collider (LHC) reached instantaneous luminosities of 6.7·1033 cm−2s−1 and produced events with up to 40 interactions per colliding proton bunch. This places stringent operational and physical requirements on the ATLAS trigger in order to reduce the collision rate of up to 40 MHz when operating with design parameters to a manageable event storage rate of about 400 Hz without discarding those events considered interesting. The Level-1 trigger is the first rate-reducing step in the ATLAS trigger and primarily composed of the Calorimeter Trigger, Muon Trigger, and the Central Trigger Processor which are implemented in custom built VME electronics. The Central Trigger Processor collects trigger information from all Level-1 systems and produces a Level-1 trigger decision that initiates the readout of all ATLAS detectors. After 2014, the LHC will run at a centre of mass energy of up to 14 TeV, compared to the current 8 TeV, and the luminosity will exceed 1034 cm−2s−1. With higher luminosities, the required number and complexity of Level-1 triggers will increase in order to satisfy the physics goals of ATLAS while keeping the total Level-1 rates at a maximum of 100 kHz. To provide this added functionality, the Central Trigger Processor will be upgraded during the planned LHC shutdown that begins in 2013.

About 600 custom-built ReadOut Buffer INput (ROBIN) PCI boards are used in the DataCollection system of the ATLAS experiment at CERN. They are plugged into the PCI slots of about 150 PCs of the ReadOut System (ROS). In the standard busbased setup of the ROS requests and event data are passed via the PCI interfaces. The performance meets the requirements, but may need to be enhanced for more demanding use cases. Modifications in the software and firmware of the ROBINs have made it possible to improve the performance by using the onboard Gigabit Ethernet interfaces for passing part of the requests and of the data in the so called switch-based scenario. Details of these modifications as well as measurement results are presented in this paper.

We present new results regarding the features of high energy photon emission by an electron beam of 178 GeV penetrating a 1.5 cm thick single Si crystal aligned at the Strings-Of-Strings (SOS) orientation. This concerns a special case of coherent bremsstrahlung where the electron interacts with the strong fields of successive atomic strings in a plane and for which the largest enhancement of the highest energy photons is expected. The polarization of the resulting photon beam was measured by the asymmetry of electron-positron pair production in an aligned diamond crystal analyzer. By the selection of a single pair the energy and the polarization of individual photons could be measured in an the environment of multiple photons produced in the radiator crystal. Photons in the high energy region show less than 20% linear polarization at the 90% confidence level.

We present the first experimental results on the use of a thick aligned Si crystal acting as a quarter wave plate to induce a degree of circular polarisation in a high energy linearly polarised photon beam. The linearly polarised photon beam is produced from coherent bremsstrahlung radiation by 178 GeV unpolarised electrons incident on an aligned Si crystal, acting as a radiator. The linear polarisation of the photon beam is characterised by measuring the asymmetry in electron-positron pair production in a Ge crystal, for different crystal orientations. The Ge crystal therefore acts as an analyser. The birefringence phenomenon, which converts the linear polarisation to circular polarisation, is observed by letting the linearly polarised photons beam pass through a thick Si quarter wave plate crystal, and then measuring the asymmetry in electron-positron pair production again for a selection of relative angles between the crystallographic planes of the radiator, analyser and quarter wave plate. The systematics of the difference between the measured asymmetries with and without the quarter wave plate are predicted by theory to reveal an evolution in the Stokes parameters from which the appearance of a circularly polarised component in the photon beam can be demonstrated. The measured magnitude of the circularly polarised component was consistent with the theoretical predictions, and therefore is in indication of the existence of the birefringence effect.

The cross section for coherent pair production by linearly polarised photons in the 20-170 GeV energy range was measured for photon aligned incidence on ultra-high quality diamond and germanium crystals. The theoretical description of coherent bremsstrahlung and coherent pair production phenomena is an area of active theoretical debate and development. However, under our experimental conditions, the theory predicted the combined cross section and polarisation experimental observables very well indeed. In macroscopic terms, our experiment measured a birefringence effect in pair production in a crystal. This study of this effect also constituted a measurement of the energy dependent linear polarisation of photons produced by coherent bremsstrahlung in aligned crystals. New technologies for manipulating high energy photon beams can be realised based on an improved understanding of QED phenomena at these energies. In particular, this experiment demonstrates an efficient new polarimetry technique. The pair production measurements were done using two independent methods simultaneously. The more complex method using a magnet spectrometer showed that the simpler method using a multiplicity detector was also viable.

The PeakSum Processing System (PSS) is an element of the neutral trigger of the NA48 experiment at CERN. The PSS is a pipelined processor based on a semi-custom device. It provides information on the energy pattern released. In the electromagnetic calorimeter of the experiment, used to discriminate K/sub S/ and K/sub L/ events.

The NA48 collaboration goal is to measure the CP violation parameter Re(ɛl/ɛ) at the level of 2 × 10−4. The neutral Kaon decays will be reconstructed by an electromagnetic liquid Krypton calorimeter with fine granularity and a volume almost totally sensible, to obtain excellent position and energy resolution, as well as time resolution. A description of the detector, results from tests of a prototype and the status of the final calorimeter are reported.