S. Leontsinis

Benford’s law predicts the occurrence of the n-th digit of numbers in datasets originating from various sources all over the world, ranging from financial data to atomic spectra. It is intriguing that although many features of Benford’s law have been proven, it is still not fully understood mathematically. In this paper we investigate the distances of galaxies and stars by comparing the first, second and third significant digit probabilities with Benford’s predictions. It is found that the distances of galaxies follow the first digit law reasonable well, and that the star distances agree very well with the first, second and third significant digit.

The ATLAS collaboration at the Large Hadron Collider at CERN has endorsed the resistive-strip micromegas technology for the high luminosity upgrade of the first muon station in the high-rapidity region, the so called “New Small Wheel” project. It requires detectors with a spatial resolution of ∼100μm, fully efficient up to a particle rate of ∼20kHz/cm2. In order to demonstrate that the resistive-strip micromegas technology fulfils these requirements, small resistive bulk micromegas have been studied with radioactive sources and with high energy beams. The micromegas chambers were operated with an Ar+7%CO2 gas mixture and read out using the APV25 chip. Results on the detection efficiency and the position resolution are presented for track impact angles from 0° to 40°. A position reconstruction method has been developed for inclined tracks, called the “micro-TPC method”. A description of the method along with performance studies is presented. In addition, the impact of the unavoidable presence of pillars and the relative alignment of readout and resistive strips on the micromegas performance has been quantified. In view of the fact that the micromegas detectors will also contribute to the trigger in ATLAS their time response has been studied.

Resistive-anode micromegas detectors have been in development for several years, in an effort to solve the problem of sparks when working at high flux and high ionizing radiation like in the HL-LHC (up to ten times the luminosity of the LHC). They have been chosen as one of the technologies that will be used in the ATLAS New Small Wheel project (forward muon system). An ageing study is mandatory to assess their capabilities to handle the HL-LHC environment on a long-term period. A prototype has been exposed to several types of irradiation (X-rays, cold neutrons, 60Co gammas and alphas) above the equivalent charge produced in the detector in five HL-LHC running years without showing any degradation of the performance in terms of gain and energy resolution, and with the characterization of the tracking performance in terms of efficiency and spatial resolution, verifying non degradation on the exposed resistive micromegas.

Five small prototype micromegas detectors were positioned in the ATLAS detector during Large Hadron Collider running at √s = 7 and 8 TeV. A 9 × 4.5 cm2 double drift gap detector was placed in front of the electromagnetic calorimeter and four 9 × 10 cm2 detectors on the ATLAS Small Wheel, the first station of the forward muon spectrometer. The one attached to the calorimeter was exposed to interaction rates of about 70 kHz/cm2 at = 5 × 1033 cm−2s−1 two orders of magnitude higher than the rates in the Small Wheel. We present the results from performance studies carried out using data collected with these detectors and we also compare the currents drawn by the detector installed in front of the electromagnetic calorimeter with the luminosity measurement in ATLAS.

The ATLAS experiment is one of the multi-purpose experiments at the Large Hadron Collider (LHC) at CERN, constructed to study elementary particle interactions in collisions of high-energy proton beams. Twelve different sub detectors as well as the common experimental infrastructure are controlled and monitored by the Detector Control System (DCS) using a highly distributed system of 140 server machines running the industrial SCADA product PVSS. Higher level control system layers allow for automatic control procedures, efficient error recognition and handling, manage the communication with external systems such as the LHC controls, and provide a synchronization mechanism with the ATLAS data acquisition system. Different databases are used to store the online parameters of the experiment, replicate a subset used for physics reconstruction, and store the configuration parameters of the systems. This contribution describes the computing architecture and software tools to handle this complex and highly interconnected control system.

The spatial resolution of a detector, using a reference detector telecscope, can be measured applying the geometric mean method, with tracks reconstructed from hits of all the detectors, including (σin) and excluding (σex) the hit from the detector under study. The geometric mean of the two measured resolution values (σ = √σexσin), is proposed to provide a more accurate estimate of the intrinsic detector resolution. This method has been tested using a Monte Carlo algorithm and is proven to give accurate results, independently of the distance between the detectors used for the track fitting. The method does not give meaningful results if all the detectors do not carry the same characteristics.

The micromegas detectors are proposed as one of the options to upgrade the ATLAS muon spectrometer in the very forward/backward region. One of the problems of all detectors in the LHC and especially the ones near the beam pipe is the high neutron background. A study of a tracking micromegas detector with high flux neutrons, focusing on the sparking properties, is performed for the first time. The neutrons are supplied by the Tandem accelerator, at the N.C.S.R. ``Demokritos'' in Athens, which can provide quasi monochromatic neutrons with energies up to 25.7 MeV. The first results of this study are presented.

In this paper we present a method of reconstructing the circle parameters from a set of datapoints on a plane. The method is based on the geometrical Legendre transform. We test the method under various scenarios using Monte Carlo generated data. These scenarios include variation of the noise hits percentage, uncertainties in the hit position and the number of datapoints. The technique is proven to be robust and provide quickly and efficiently very accurate results. Furthermore, the use of the geometrical Legendre transform method for the identification of two overlapping circles is shown.

The associated production of vector boson + prompt J/ψ is a key observable for understanding of quarkonium production mechanisms. Here we present the first evidence of such process and the measurement of its production rate. Relative contributions to the signal from single and double parton scattering are estimated and possible implications of this novel final state for studying multiple parton interactions are discussed. Finally, we compare Single parton scattering cross-sections to cutting-edge theoretical calculations in the colour singlet and colour octet formalisms.

We present the muon reconstruction algorithms used in ATLAS during the LHC run-1 and their performances in terms of efficiency, muon momentum scale and resolution. These performances have been measured using large calibration samples of J/ψ, ϒ and Z decays, which allow to control the systematic uncertainties on efficiency and on momentum scale at the per-mille level. Corrections to be applied to simulation have been derived from the performances measurements and used in physics analyses. The impact of these correction on physics measurements, and the associated uncertainties, is also presented.

Precision determinations of the flavour sector allow the search for indirect new physics signatures. At the forefront of these studies are the determinations of interference of new physics with known ΔF = 1 and ΔF = 2 processes. The ATLAS collaboration explores this area with competitive results measuring the CP violating phase ϕs from Bs0 → J/ψϕ decays and investigating rare B decays with dileptons in the final state with data collected at the Large Hadron Collider. In this paper, the latest ATLAS results relevant for new physics searches in the heavy flavour sector will be discussed

A group of Early-Career Researchers (ECRs) has been given a mandate from the European Committee for Future Accelerators (ECFA) to debate the topics of the current European Strategy Update (ESU) for Particle Physics and to summarise the outcome in a brief document [1]. A full-day debate with 180 delegates was held at CERN, followed by a survey collecting quantitative input. During the debate, the ECRs discussed future colliders in terms of the physics prospects, their implications for accelerator and detector technology as well as computing and software. The discussion was organised into several topic areas. From these areas two common themes were particularly highlighted by the ECRs: sociological and human aspects; and issues of the environmental impact and sustainability of our research.

We present evidence of associated vector boson + prompt J/ψ production and measure its production rate. This is a key observable to the understanding of quarkonium production mechanisms. We estimate the relative contributions to the signal from single and double parton scattering and discuss possible implications of this novel final state for study of multiple parton interactions. Single parton scattering cross-sections are compared to cutting-edge theoretical calculations in the colour singlet and colour octet formalisms.

We present rare B decays and processes measured with the ATLAS detector. First, the associated production of vector boson + prompt J/ψ that is a key process for understanding of quarkonium production mechanisms, and second, the rare B0s → µ+µ− decay, that due to its small branching fraction, is an excellent probe for physics beyond the standard model.

The ATLAS collaboration has chosen the Micromegas technology along with the small-strip Thin Gap Chambers for the upgrade of the inner muon station in the high-rapidity region, the so called New Small Wheel upgrade project. It will employ eight layers of Micromegas and eight layers of small-strip Thin Gap Chambers per wheel. The New Small Wheel project requires fully efficient Micromegas chambers, able to cope with the maximum expected rate of 15 kHz/cm2 featuring single plane spatial resolution better than 100 μm. The Micromegas detectors will cover a total active area of ~ 1200 m2 and will be operated in a moderate magnetic field (≤ 0.3 T). Moreover, together with their precise tracking capability the New Small Wheel Micromegas chambers will contribute to the ATLAS Level-1 trigger system. Several studies have been performed on small (10 × 10 cm2) and medium (1 × 0.5 m2) size prototypes using medium (1 − 5 GeV/c) and high momentum (120 – 150 GeV/c) hadron beams at CERN. A brief overview of the results obtained is presented.

A large number of detailed measurements of various charm states production (J/ψ,ψ(2S),χc) at the ATLAS experiment at the LHC at centre-of-mass energies of 2.76TeV,7TeV,8TeV, and 13TeV is presented. These measurements extend in reach and precision beyond those currently available, and are compared to a variety of the latest theoretical predictions. Measurements of the associated production of quarkonium with a vector boson using the ATLAS Run-1 dataset are also presented. These rare processes provide new insight into QCD models of quarkonium production, but also provide new opportunities to study double parton scattering, including crosssection measurements in single and double parton scattering dominated regimes and a precise assessment of the σeff parameter governing the effective spatial area of parton–parton interactions at a variety of energy scales. Finally, latest results from the ATLAS experiment on heavy flavour production and decay properties at ATLAS are additionally presented. These results include determination of the decay properties of the Λb baryon and new measurements of Bc production cross-sections and branching ratio measurements of the Bc → J/ψD∗+ decay.

We propose a pattern recognition method that identifies the common tangent lines of a set of ellipses. The detection of the tangent lines is attained by applying the Legendre transform on a given set of ellipses. As context, we consider a hypothetical detector made out of layers of chambers, each of which returns an ellipse as an output signal. The common tangent of these ellipses represents the trajectory of a charged particle crossing the detector. The proposed method is evaluated using ellipses constructed from Monte Carlo generated tracks.

A key observable for understanding the quarkonium production mechanism is the associated production of a vector boson with heavy quarkonia.ATLAS Collaboration at LHC observed the associated production of prompt and non-prompt J/ψ mesons with Z boson with 5σ and 9σ signifance, respectively.In this poster the measurement of the production rate of Z + J/ψ over inclusive Z is discussed.Additionally, contributions from single and double parton interactions are evaluated and the results are compared to latest theoretical calculations in the colour singlet and colour octet formalisms.Finally, a lower limit of the double parton scattering effective cross section is extracted.

We present rare B decays and processes measured with the ATLAS detector. First, the associated production of vector boson + prompt J/ψ that is a key process for understanding of quarkonium production mechanisms, and second, the rare B0s → µ+µ− decay, that due to its small branching fraction, is an excellent probe for physics beyond the standard model.

We present the muon reconstruction algorithms used in ATLAS during the LHC run-1 and their performances in terms of efficiency, muon momentum scale and resolution. These performances have been measured using large calibration samples of J/ψ, ϒ and Z decays, which allow to control the systematic uncertainties on efficiency and on momentum scale at the per-mille level. Corrections to be applied to simulation have been derived from the performances measurements and used in physics analyses. The impact of these correction on physics measurements, and the associated uncertainties, is also presented.

Resistive-anode Micromegas detectors are in development since several years, in an effort to solve the problem of sparks when working in high flux and high radiations environment like in the HL-LHC (ten times the luminosity of the LHC). They have been chosen as one of the technologies that will be part of the ATLAS New Small Wheel project (forward muon system). An ageing study is mandatory to assess their capabilities to handle the HL-LHC environment on a long-term period. A prototype has been exposed to several types of irradiations (X-rays, cold neutrons, 60 Co gammas) up to an equivalent HL-LHC time of more than five years without showing any degradation of the performances in terms of gain and energy resolution. Beam test studies took place in October 2012 to assess the tracking performances (efficiency, spatial resolution,...). Results of ageing studies and beam test performances are reported in this paper.

We calculate the leading order cross section for the associated production of Z and J/{\psi}. Processes that include associated production of electroweak bosons and heavy quarlonium can give valuable insight to the production mechanism of quarkonia. We conclude that this process is accessible by the LHC statistics.

The first observation of the three J/ψ meson production in proton-proton collisions at a center-of-mass energy of 13 TeV in final states with three µ +µ − pairs is reported. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 133 fb−1 . The pp → J/ψ J/ψ J/ψ X process is observed with a significance in excess of five standard deviations. The fiducial cross section for this process is found to be σ(pp → J/ψ J/ψ J/ψ X) = 272+141 −104(stat)±17(syst) fb. The result is compared to theoretical expectations for the production of three J/ψ mesons in single (SPS), double- (DPS), and triple- (TPS) parton scattering processes. Under the most economical assumption of factorization of multiple hard scattering probabilities in terms of SPS cross sections, the measured final state is found to be dominated by DPS and TPS contributions. A value of the associated DPS effective cross section parameter of σeff,DPS = 2.7 +1.4 −1.0 (exp)+1.5 −1.0 (theo) mb, related to the transverse distribution of partons in the proton, is derived.

The observation of the $\mathrm{Z}$ boson rare decay to a $\psi$ meson and two oppositely charged same-flavour leptons, $\ell^+ \ell^-$, where $\psi$ represents the sum of $\mathrm{J}/\psi$ and $\psi(\mathrm{2S})\to\mathrm{J}/\psi\, X$, and $\ell=\mu,\mathrm{e}$, is presented. The data sample used corresponds to an integrated luminosity of $35.9\,\mathrm{fb}^{-1}$ of proton-proton collisions at a center-of-mass energy of $13\,\mathrm{TeV}$ accumulated by the CMS experiment at the LHC. The signal is observed with a significance in excess of 5 standard deviations. Removing contributions from $\psi(\mathrm{2S})$ decays to $\mathrm{J}/\psi$, the signal is interpreted as being entirely from $\mathrm{Z}\to\mathrm{J}/\psi\,\ell^+\ell^-$, with its fiducial branching fraction relative to that of the decay $\mathrm{Z}\to\mu^+\mu^-\mu^+\mu^-$ measured to be $$\frac{\mathcal{B}(\mathrm{Z}\to\mathrm{J}/\psi\,\ell^+\ell^-)}{\mathcal{B}(\mathrm{Z}\to\mu^+\mu^-\mu^+\mu^-)}=0.70\pm 0.18\, \mathrm{(stat)} \pm 0.05\, \mathrm{(syst)}.$$ This result is obtained with the assumption of no $\mathrm{J}/\psi$ polarisation, where extreme polarisation scenarios can create $-24\%$ to $+22\%$ variations.

Recent results on quarkonia production, using proton-proton collision datasets at √ s = 8 TeV and √ s = 13 TeV from the ATLAS and CMS experiments at the LHC are presented.

The CMS and ATLAS detectors will face challenging conditions after the upgrade of the LHC to the High Luminosity LHC.In particular, the granularity of the pixel detectors should increase to mitigate the effect of pileup.Two possible sensor geometries are being investigated, 50 × 50 µm 2 and 25 × 100 µm 2 , to handle these conditions.One of the main factors in choosing the pixel geometry is inter-channel charge induction or crosstalk, defined as the ratio of charge induced into neighboring pixels relative to the total charge.This charge induction will affect the data rates, position resolution, and track reconstruction efficiencies.Therefore, it should be investigated carefully.The effect of crosstalk is expected to depend on the chosen pixel geometry, threshold of the signal, and readout front-end.The readout chip in this study is RD53A, developed by the RD53 Collaboration, which is a prototype investigated by both the CMS and ATLAS collaborations implementing three different analog front-end designs.Crosstalk effects are larger for the 25 × 100 µm 2 geometry, given the larger sensor capacitance.Both have been studied in the lab through direct charge injection, and also at DESY test beam facility by charge deposition of 5.6 GeV electrons in 150 µm thick silicon pixels.The effects on the cross-talk due to varying the front-end, threshold, and the impinging position of the electrons will be presented.