Implementation of the DCS System for the validation of MM HV Boards and the DCS System of the new BIS78 Chambers for the upgrade of muon system of the ATLAS Experiment

The ATLAS Muon Spectrometer is going through upgrades on the Phase I in order to achieve higher rates for the upcoming LHC runs. The two main projects of this Phase I upgrade are the New Small Wheels (NSW), which are expected to complement the ATLAS muon spectrometer in the end-cap regions and a smaller size project, known as BIS78 (Barrel Inner Small sectors). The NSW is expected to replace the Small Wheel (SW) and it will be installed in the ATLAS underground cavern during the summer by the end of the LHC Long Shutdown 2. This new system will be consisted by two prototype detectors, the sTGC (small Thin Gas Chambers) and the resistive Micromegas (MM). In order to cope with higher LHC luminosities, the installation of NSW will help the reduction of the trigger rate in the forward region. With half of the rate in the barrel-endcap transition region reduced by the existing TGCs, the other half of the fake trigger rate in transition region will be reduced by the new BIS78 stations. The BIS78 subproject foresees the replacement of the existing Monitored Drift Tubes (MDTs), used for the precise position measurement in this area, with muon stations formed by integrated smaller diameter tubes (sMDT) and a new generation of RPCs, capable of withstanding the higher rates and provide a robust standalone muon confirmation. The existing BIS7 and BIS8 MDT Chambers will be replaced by 16 new muon stations of one small (sMDT) chamber and two RPC triplets, and it will be the pilot project for the Phase II BI Upgrade. This work is divided into two parts. First will be presented the development and the implementation of a Detector Control System (DCS) for the HV system for the MM detectors of NSW and specifically the validation of a new type of HV Boards (A7038AP). Second, the development of the DCS for the monitoring and operation of the new sMDT chambers of the MDT Sub-System will be presented.

Towards the Large-Eddy Simulation of a full engine: Integration of a 360 azimuthal degrees fan, compressor and combustion chamber. Part II: Comparison against stand-alone simulations

Unsteady simulations of various components of a gas-turbine engine are often carried out independently and only share averaged quantities at the component interfaces. In order to study the impact and interactions between components, this work compares results from sectoral stand-alone simulations of a fan, compressor and annular combustion chamber of the DGEN-380 demonstrator engine at take-off conditions against an integrated 360 azimuthal degrees large-eddy simulation with over 2.1 billion cells of all previously listed components. Note that, at take-off conditions the compressor works at transonic conditions and generates an upstream-propagating shock that interacts with the fan modifying the shape of its wake with respect to the stand-alone simulation. Furthermore, the shock is seen as a tone in the pressure spectra at half the impeller blade passing frequency in the forward region of the engine. In the aft region, time-averaged fields are overall similar between stand-alone and integrated simulations but show a deviation in the azimuthal position of the hot-spot at the exit of the combustion chamber due to the addition of the diffuser. Pressure fluctuations generated in the compressor are captured in the combustion chamber as tones in the temperature and pressure spectra at the impeller blade-passing frequency and harmonics as well as an increase in the root-mean-square pressure.

The history of LHCb

In this paper, we describe the history of the LHCb experiment over the last three decades, and its remarkable successes and achievements. LHCb was conceived primarily as a $${b} $$ b -physics experiment, dedicated to $$CP$$ CP violation studies and measurements of very rare $${{b}} $$ b decays; however, the tremendous potential for $${c} $$ c -physics was also clear. At first data taking, the versatility of the experiment as a general-purpose detector in the forward region also became evident, with measurements achievable such as electroweak physics, jets and new particle searches in open states. These were facilitated by the excellent capability of the detector to identify muons and to reconstruct decay vertices close to the primary $${{p}} {{p}} $$ pp interaction region. By the end of the LHC Run 2 in 2018, before the accelerator paused for its second long shut down, LHCb had measured the CKM quark mixing matrix elements and $$CP$$ CP violation parameters to world-leading precision in the heavy-quark systems. The experiment had also measured many rare decays of $${b} $$ b and $${c} $$ c quark mesons and baryons to below their Standard Model expectations, some down to branching ratios of order 10$$^{-9}$$ - 9 . In addition, world knowledge of $${{b}} $$ b and $${{c}} $$ c spectroscopy had improved significantly through discoveries of many new resonances already anticipated in the quark model, and also adding new exotic four and five quark states. The paper describes the evolution of the LHCb detector, from conception to its operation at the present time. The authors’ subjective summary of the experiment’s important contributions is then presented, demonstrating the wide domain of successful physics measurements that have been achieved over the years.

Forward Higgs production within high energy factorization in the heavy quark limit at next-to-leading order accuracy

We use Lipatov’s high energy effective action to determine the next-to-leading order corrections to Higgs production in the forward region within high energy factorization making use of the infinite top mass limit. Our result is based on an explicit calculation of real corrections combined with virtual corrections determined earlier by Nefedov. As a new element we provide a proper definition of the desired next-to-leading order coefficient within the high energy effective action framework, extending a previously proposed prescription. We further propose a subtraction mechanism to achieve for this coefficient a stable cancellation of real and virtual infra-red singularities in the presence of external off-shell legs. Apart from its relevance for direct phenomenological studies, such as high energy resummation of Higgs $$+$$ + jet configurations, our result will be further of use for the study of transverse momentum dependent factorization in the high energy limit.

Measurement of differential $$ b\overline{b} $$- and $$ c\overline{c} $$-dijet cross-sections in the forward region of pp collisions at $$ \sqrt{s} $$ = 13 TeV

The inclusive $$ b\overline{b} $$ b b ¯ - and $$ c\overline{c} $$ c c ¯ -dijet production cross-sections in the forward region of pp collisions are measured using a data sample collected with the LHCb detector at a centre-of-mass energy of 13 TeV in 2016. The data sample corresponds to an integrated luminosity of 1.6 fb−1. Differential cross-sections are measured as a function of the transverse momentum and of the pseudorapidity of the leading jet, of the rapidity difference between the jets, and of the dijet invariant mass. A fiducial region for the measurement is defined by requiring that the two jets originating from the two b or c quarks are emitted with transverse momentum greater than 20 GeV/c, pseudorapidity in the range 2.2 < η < 4.2, and with a difference in the azimuthal angle between the two jets greater than 1.5. The integrated $$ b\overline{b} $$ b b ¯ -dijet cross-section is measured to be 53.0 ± 9.7 nb, and the total $$ c\overline{c} $$ c c ¯ -dijet cross-section is measured to be 73 ± 16 nb. The ratio between $$ c\overline{c} $$ c c ¯ - and $$ b\overline{b} $$ b b ¯ -dijet cross-sections is also measured and found to be 1.37 ± 0.27. The results are in agreement with theoretical predictions at next-to-leading order.

A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: detector concept, description and R&D and beam test results

The particle flux increase (pile-up) at the HL-LHC with luminosities of L = 7.5 × 1034 cm−2 s−1 will have a significant impact on the reconstruction of the ATLAS detector and on the performance of the trigger. The forward region and the end-cap where the internal tracker has poorer longitudinal track impact parameter resolution, and where the liquid argon calorimeter has coarser granularity, will be significantly affected. A High Granularity Time Detector (HGTD) is proposed to be installed in front of the LAr end-cap calorimeter for the mitigation of the pileup effect, as well as measurement of luminosity. It will have coverage of 2.4 to 4.0 from the pseudo-rapidity range. Two dual-sided silicon sensor layers will provide accurate timing information for minimum-ionizing particles with a resolution better than 30 ps per track (before irradiation), for assigning each particle to the correct vertex. The readout cells are about 1.3 mm × 1.3 mm in size, which leads to a high granular detector with 3 million channels. The technology of low-gain avalanche detectors (LGAD) with sufficient gain was chosen to achieve the required high signal-to-noise ratio. A dedicated ASIC is under development with some prototypes already submitted and evaluated. The requirements and general specifications of the HGTD will be maintained and discussed. R&D campaigns on the LGAD are carried out to study the sensors, the related ASICs and the radiation hardness. Both laboratory and test beam results will be presented.

An overview of the ATLAS New Small Wheel Micromegas construction project at Aristotle University

The upcoming luminosity upgrade of the LHC will impose new requirements for the detector installations. To perform under these conditions the Micromegas (MM) technology was selected to be adopted in the New Small Wheel (NSW) upgrade, dedicated to precision tracking. A large surface of the forward regions of the Muon Spectrometer will be equipped with 8 layers of MM modules forming a total active area of 1200 m2. The NSW is planned to be installed in the forward region of [Formula: see text] of ATLAS. This new system will have to operate in a high background radiation region, while reconstructing muon tracks as well as furnishing information for the Level-1 trigger. The project requires fully efficient MM chambers with spatial resolution down to 100 [Formula: see text]m, a rate capability up to about 15 kHz/cm2 and operation in a moderate (highly inhomogeneous) magnetic field up to [Formula: see text][Formula: see text]T. The required tracking is linked to the intrinsic spatial resolution in combination with the demanding mechanical accuracy. An overview of the design, construction and QA/QC procedures followed at the Aristotle University of Thessaloniki for the Micromegas LM2 Drift panels production will be presented.