LHC and the ATLAS Detector

Based at CERN, the European Organization for Nuclear Research, the Large Hadron Collider (LHC) is the world's largest and most powerful particle accelerator. From 2025, the LHC will be upgraded to allow it to achieve a factor of 10 higher luminosity, which increases the rate of collisions, essential for probing new physics phenomena in the future. The route to high luminosity LHC (HL-LHC) involves various detector upgrades and requires significant infrastructure changes. Recent measurements by CERN Radiation Protection, verifying previous calculations by The University of Sheffield (UoS), has raised awareness about the need to restrict human activity in the HL-LHC experimental, construction and maintenance areas due to exposure from high levels of radiation. Examining the case of the ATLAS detector upgrade, the collaborative partnership between UoS and UK industry is developing state-of-the-art robotic instrumentation, capable of tolerating high radiation levels. The main object of this research is a feasibility study with a TRL (technology readiness level) of three, to determine how materials and sub components of dexterous robotic systems behave after exposure to high levels of radiation. This is evaluation uses novel robotic irradiation equipment, techniques and test methods housed in the Birmingham University (UK) Irradiation Facility. One finger of an unmodified Shadow Robot Company “Hand”, a highly dexterous robotic manipulator, was exposed to specific doses of high radiation in a temperature controlled thermal chamber. Cooled by a liquid nitrogen evaporative system, the irradiation system moves samples continuously through a homogeneous proton beam. Movement is provided by a radiation hard pre-configured XY-Axis Cartesian Robot. The methods and techniques developed as a result of this TRL3 research will further aid the application and deployment of robotic and autonomous systems into highly radioactive environments. Based on preliminary findings it has been concluded that finger materials and basic electrical components can tolerate hazardous radiation environments, with careful selection and substitution of a minimal amount of materials, radiation hardness is also possible. Further work is scheduled for the irradiation of a fully instrumented and powered robotic hand to determine working hour tolerance.

The Large Hadron Collider (LHC), a particle accelerator aimed at exploring deeper into matter than ever before, is currently being constructed at CERN. Beam optics of the LHC, requires stringent control of the field quality of about 8400 superconducting magnets, including 1232 main dipoles and 360 main quadrupoles to assure the correct machine operation. The measurement challenges are various: accuracy on the field strength measurement up to 50 ppm, harmonics in the ppm range, measurement equipment robustness, low measurement times to characterize fast field phenomena. New magnetic measurement systems, principally based on analog solutions, have been developed at CERN to achieve these goals. This work proposes the introduction of digital technologies to improve measurement performance of three systems, aimed at different measurement target and characterized by different accuracy levels. The high accuracy measurement systems, based on rotating coils, exhibit high performance in static magnetic field. With varying magnetic field the system accuracy gets worse, independently from coil speed, due to the limited resolution of the digital integrator currently used, and the restrictions of the standard analysis. A new integrator based on ADC conversion and numerical integration is proposed. The experimental concept validation by emulating the proposed approach on a PXI platform is detailed along with the improvements with respect to the old integrators. Two new analysis algorithms to reduce the errors in dynamic measurements are presented. The first combines quadrature detection and short time Fourier transform (STFT) of the acquired magnetic flux samples; the second approach is based on the extrapolation of the magnetic flux samples. Unlike other algorithms presented in the literature, both the proposals do not require the information about the magnet current and are able to work in real time so, can be easily implemented in firmware on DSP. The performance of the new proposals are assessed in simulation. As far as medium accuracy systems are concerned, at CERN was originally developed a probe to measure the sextupolar and decapolar field harmonics of the superconducting dipoles using a suitable Hall plates arrangement for the bucking of the main dipolar field, which is, 4 orders of magnitude higher than the measurement target. The output signals of each Hall plate belonging to the same measurement ring are mixed using analog cards. The resultant signal is proportional to the field harmonic to measure. A complete metrological characterization of this sensor was carried out, showing the limitation of a fully analog solution. The main problems found were the instability of the analog compensation cards and the impossibility to correct the non linearity effects beyond the first order. An automatic calibration procedure implemented in the new instrument software is presented to guarantee measurement repeatability. In alternative a digital bucking solution, namely the compensation of the main field after the sampling of each hall plate signal by means of numerical sum, is proposed. An implementation of this approach, based on 18 bit ADC converter, over-sampling and dithering techniques as well as compensation of the Hall plates non linearity in real time is analyzed. Finally, as far as the low accuracy measurement systems are concerned, the design of an instrument based on a rotating Hall plate to check the polarity of all LHC magnets is presented. Even if this architecture is characterized by low accuracy in the measurement of field strength and phase, the results are sufficient to identify main harmonic order, type and polarity with practically no errors, thanks to an accurate definition of the measurement algorithm. A complete metrological characterization of the prototype developed and a correction of all the systematic measurement errors was carried out. This instrument, integrated in a test bench developed ad hoc, is become the standard at CERN for the polarity test of all the magnets will compose the machine.

In light of the large quantity of data collected during the second operational run of the Large Hadron Collider (LHC) at CERN, which has made it possible to perform measurements at unprecedented energies with a high degree of statistical precision, the necessity of understanding and constraining the systematic effects on such measurements has become increasingly important. Precision measurements of jet observables in proton-induced collisions have proven instrumental in constraining the parton distribution functions (PDFs) which describe the internal structure of protons, and which remain one of the largest sources of uncertainty in many analyses performed at hadron colliders. This thesis presents the first triple-differential measurement of the dijet production cross section performed in proton-proton collisions at a center-of-mass energy of 13 TeV, based on a data sample of 35.9 fb$^{-1}$ recorded by the CMS experiment at the Large Hadron Collider at CERN. The cross section is measured using anti-$k_\text{T}$ jets with radius parameters of R = 0.4 and R = 0.8 as a function of the dijet rapidity separation $y^{*}$ , the total boost of the dijet system $y_\text{b}$ , and either the average transverse momentum $\langle p_\text{T}\rangle_{1,2}$ or the invariant mass $m_\text{jj}$ of the dijet system as the third variable. This choice of rapidity variables exploits the topology of the dijet system to achieve an increased sensitivity to the proton PDFs. After accounting for detector-induced systematic effects in a three-dimensional unfolding procedure, the measured spectra are compared to fixed-order theory predictions at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics, obtained using several recent PDF sets. While the data are observed to be described by the theory within the experimental and theoretical uncertainties across a large portion of the phase space, potentially significant deviations are observed in areas where a heightened sensitivity to the PDFs is expected.

The strategy for machine protection and quench prevention of the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN) is presently based on the Beam Loss Monitoring (BLM) system. At each turn the BLM system is able to acquire and process in real-time data from approximately 4000 detectors in order to decide if the beams should be permitted to continue circulating or their safe extraction is necessary. At the same time in the system, by making full use of its VME based processing cards, data is continuously recorded from both the acquisition, the processing results as well as the status of the electronics which later will be provided to various systems in the LHC. Part of the recorded data will be used to drive an on-line event display and write an extensive logging database at a refresh rate of 1 Hz. Other parts of the same processing units, initiated by external triggers, will provide fast updates of the loss pattern seen in the last 84 ms by 2.54 ms integrals, necessary for the automated collimator adjustments, 100 ms worth of data for every beam injection and scheduled dump to verify the correctness of those procedures, and the last 1.7 s by 40 us integrals to be used for post-mortem analysis in the event of an unforeseen dump as well as FFT analysis studies. The paper discusses the realization of each of those recording functions and their verification with beam measurements.

Large Hadron Collider (LHC) is the largest scientific instrument ever created. It was built with the intention of testing the most extreme conditions of the matter. Taking into account the significant dangers of LHC operations, European Organization for Nuclear Research (CERN) has developed multi-pronged approach for machine safety, including access control system. This system is based on rolebased access control (RBAC) concept. It was designed to protect from accidental and unauthorized access to the LHC and injector equipment. This paper introduces the new model of the role-based access control developed at CERN and gives detailed mathematical description of it. We propose a new technique called dynamic authorization that allows deploying RBAC gradually in the large systems. Moreover, we show how the protection for the very large distributed equipment control system may be implemented in efficient way. This paper also describes motivation of the project, requirements and overview of the main components: authentication and authorization.

A particle beam is a collection of a large number of charges and represents an electromagnetic potential for other charges, therefore exerting forces on itself (space charge) and other beams (Beam-Beam Interactions, BBIs). The control of the BBIs in particle colliders is fundamental to preserve beam stability and achieve the optimum collider performance. In the case of the Large Hadron Collider (LHC) at CERN, these forces are experienced as localized periodic distortions when the two beams cross each other in the four experimental areas. The forces are most important for high density beams, i.e. high intensity and small beam sizes. Each LHC beam is composed of 2808 bunches, each containing 1011 protons and with a transverse size of 16 µm at the interaction points. These extreme parameters are the key to obtain high "luminosity", i.e. the number of collisions per second needed to study \rare" physics phenomena. The BBI is therefore often the limiting factor for the luminosity of colliders. Within all BB effects, this thesis covers coherent and incoherent beam-beam effects in hadron colliders with particular emphasis on those with a large number of bunches, like the LHC. Complementary numerical tools have been developed to study the effects of BBIs on the particle beams. The use of new parallel algorithms was fundamental to allow the scale of the calculations. The objectives are a better understanding of these effects and if necessary to propose changes to the LHC beam parameters to keep detrimental effects small. We have demonstrated the numerical predictibility of bunch to bunch differences and for the first time compared the results to analytical predictions and experimental data from the Relativistic Heavy Ion Collider (RHIC). Beam-beam transfer function measurements had been reproduced and understood in terms of coherent beam-beam modes. An implementation of the measurement devices had been suggested in order to avoid misinterpreted diagnostics. An emittance growth caused by the BBIs had been observed and characterized with numerical studies and explained with a simple physical picture. A study of the parametrical dependency of this effect defines qualitatively the expected limiting factors to avoid detrimental deterioration of the beams. The variation of the LHC tune spectra for different collision symmetries and in the presence of long range as well as head-on collisions had been presented and explained. This will be of fundamental importance to correctly interprete the observations of single bunch measurements during the operation of the collider and to improve the performances.

In the context of implementing more control and data processing capabilities in new electronic cards at the European Organization for Nuclear Research (CERN), the Smartfusion2 Flash-based Reprogrammable Field Programmable Gate Array (FPGA) has been tested in the CHARM radiation facility at CERN. The CHARM facility was configured to offer a representative radiation environment of the CERN's Large Hardon Collider (LHC) accelerator. The FPGAs were tested during three irradiation campaigns. The observed radiation effects include Single Event Upsets (SEU), Single Event Transients (SET), Single Event Latch-ups (SEL), Single Event Functional Interrupts (SEFI) and failures due to Total Ionizing Radiation (TID). The use of this FPGA is linked to the implementation of appropriate Finite State Machine (FSM) encoding, Printed Circuit Board (PCB) design, and automated power cycling that are here discussed. The suitability of the FPGA in harsh environments and critical applications such as the cryogenics electronics infrastructure in the LHC tunnel is also discussed.

We study a Nb-Ti lay-out for the triplet in the low-beta interaction regions of the Large Hadron Collider, based on a stretched version of the present baseline. The triplet length is increased from the present value of 32 m up to about 60 m. The quadrupoles are based on a two layer coil made with the LHC main dipole cable. A parametric analysis of the dependence of the optics and magnet performances on the triplet length and aperture is carried out.

CARLOSv3 is the third version of a chip that plays a significant role in the data acquisition chain of the A Large Ion Collider Experiment (ALICE) silicon drift detector (SDD). ALICE is one of the foremost high-energy physics experiments (HEPE) conducted within the Large Hadron Collider at CERN, the European Organization for Nuclear Research in Geneva. CARLOSv3 was principally designed and built for the on-line compression of the input dataset originating from a physical bidimensional silicon sensor. To compress a bidimensional dataset, a bidimensional data compressor was required. The compressor was designed for the ALICE SDD Experiment but could be applied to all experiments in which an incoming stream dataset originates from a bidimensional sensor.

The strangeness production ratios [bar wedge]/∧ and [bar wedge]/K0S are measured by the LHCb detector from 0.3 nb-1 of proton-proton collisions delivered by the Large Hadron Collider (LHC) at CERN with centre-of-mass energy √s = 0.9TeV and 1.8 nb-1 at √s = 7TeV. Both ratios are presented as a function of transverse momentum, pT, and rapidity, y, in the ranges 0.15 < pT < 2.50 GeV/c and 2.0 < y < 4.5. The ratios measured at the two energies are in good agreement in an overlapping region of rapidity loss, Δ y = ybeam - y, and are consistent with previous measurements. A review of the Standard Model is presented with emphasis on the diffculties in its application for predictions of physics at the LHC. Phenomenological models are introduced as the current state of the art for such predictions. Accurate models are required as an essential benchmark for future discoveries of physics beyond the Standard Model. LHCb's results represent a powerful test for these models in the soft QCD regime for processes including hadronisation. The ratio [bar wedge]/∧, measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted, particularly at high rapidity. The ratio [bar wedge]/K0 S, measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected. The LHCb experiment is introduced, with particular focus on its Ring Imaging Cherenkov (RICH) detectors. The development and successful implementation of a method to align those RICH detectors is presented, using proton-proton collision data from the early running period of the Large Hadron Collider, which began in November 2009. The performance of the RICH detectors is investigated with preliminary analysis of the Cherenkov photon yield. The RICH mirror positions are monitored using an automated software control system, which has been running successfully since October 2008.

During the CERN Large Hadron Collider (LHC) first long shut down (LS1), a large number of vacuum tests are carried out on consolidated or newly fabricated devices. In such a way, the vacuum compatibility is assessed before installation in the UHV system of the LHC. According to the equipment’s nature, the vacuum acceptance tests consist in functional checks, leak test, outgassing rate measurements, evaluation of contaminants by Residual Gas Analysis (RGA), pumping speed measurements and qualification of the H2 sticking probability of Non-Evaporable-Getter (NEG) coating. In this paper, the methods used for the tests and the acceptance criteria are described. A summary of the measured vacuum characteristics for the tested components is also given.

The article discusses how researchers at the European Organization for Nuclear Research were able to detect a Higgs boson-like particle with the Large Hadron Collider (LHC) in June 2012. Topics include how scientists concealed data from themselves in "blind" analyses in order to prevent bias, how the Higgs-like particle carries several properties researchers anticipated, and how the particle signals the completion of particle physics' Standard Model. Additional information is presented on the engineering and mechanics of the LHC.

Despite burgeoning literature on knowledge transfer, relatively little is known about how strategic knowledge is created and exchanged and, specifically, the influence of leadership in stimulating and marshalling successful innovation. We frame this process as a dynamic capability that is primarily inter-organisational; it is also highly complex, hard to grasp and hard to imitate and calls for knowledge leadership, a qualitatively different kind of leadership from that which characterises more traditional industrial economies. This poses particular challenges for human resource (HR) specialists seeking to promote knowledge leadership across institutional and cultural boundaries. We report on preliminary findings from interviews with scientists working in a global particle physics experiment being conducted in the Large Hadron Collider at CERN (an abbreviation of the French version of European Organisation for Nuclear Research), Switzerland. Given that this collaboration (a global set of loosely coupled, non-hierarchical networks) is prototypical of many international knowledge-based enterprises, the findings will help to inform the HR requirements for successful knowledge leadership.

Effects of thermocapillary forces during welding of 316L-type wrought, cast and powder metallurgy austenitic stainless steels

At high-energy accelerator facilities like the ones that are part of the accelerator complex at the European Organization for Nuclear Research (CERN), Monte Carlo radiation transport codes are widely employed to face the challenges of estimating radionuclide production yields and activities with the aim of performing the radiological characterization of activated components. Indeed, it is of paramount importance to ensure adequate radiation protection during scheduled maintenance, transport, and handling of these components and to establish their proper disposal pathway once they ultimately reach the end of their useful life. This paper summarizes the principles of the fluence conversion coefficients method that was developed as a complementary approach for radiological characterization studies. Then, the Monte Carlo simulations in preparation to the pilot beam run at the Large Hadron Collider at CERN in 2021 are presented as a practical example of possible applications. Finally, the flexibility of the method and the most relevant operational radiation protection implications are discussed in relation to the provided example.