Regular Series

Vol. 47 (2016), No. 6, pp. 1357 - 1756

Cracow Epiphany Conference on the Physics in LHC Run 2


Standard Model Results of CMS at 13 TeV

Acta Phys. Pol. B 47, 1365 (2016)

page 1365 •

abstract

The most recent results of Standard Model physics using 13 TeV proton–proton collisions data recorded by CMS detector during the LHC Run 2 are reviewed. This overview includes studies of several results of Forward and Small-\(x\) QCD physics, \(B\) physics and Quarkonia, Standard Model physics and Top physics. The outlined results are compared to the corresponding theoretical predictions and no significant deviation is observed.


First Run 2 Searches for Exotica at CMS

Acta Phys. Pol. B 47, 1379 (2016)

page 1379 •

abstract

An overview of the first results of the experimental searches for exotica at the CMS experiment with 13 TeV collision data is presented. The results cover various models with different topologies such as searches for new heavy resonances, extra space dimensions, black holes and dark matter. The analysis results with 13 TeV data are emphasized, corresponding to an integrated luminosity in the range of 2.1–2.8 fb\(^{-1}\), and the results are presented in comparison to those obtained with 8 TeV data.


Heavy-ion Results of the CMS Experiment

Acta Phys. Pol. B 47, 1397 (2016)

page 1397 •

abstract

An overview of selected heavy-ion results of the CMS experiment is presented. Jet quenching, quarkonia suppression and two-particle angular correlation results are discussed. The measurements have been performed for lead–lead, proton–lead and proton–proton data samples recorded for Run 1 of the LHC accelerator. In the correlation analysis, low pile-up proton–proton collisions at an energy of 13 TeV (from Run 2) have been used as well.


Standard Model Results from ATLAS — Early 13 TeV Data

Acta Phys. Pol. B 47, 1417 (2016)

page 1417 •

abstract

Selected Standard Model measurements obtained with the ATLAS detector at the LHC using the early 13 TeV data are presented.


Past, Present and Future of the LHCb Detector

Acta Phys. Pol. B 47, 1437 (2016)

page 1437 •

abstract

The LHCb experiment has been designed as a high precision experiment devoted to the search of physics beyond the Standard Model through the study of CP violation and rare decays in hadrons containing b and c quarks. During the Run 1 of LHC, the LHCb detector has performed very well producing a large number of physics results on a vast number of subjects. The first Long Shutdown offered the opportunity to further optimise the detector, anticipating in some cases the interventions foreseen for Run 3. Nevertheless, the phase of upgrade of the detector, foreseen for 2019–2020, will be crucial to exploit the full potential of the LHCb experiment. In this context, an overview of the LHCb detector is presented, concerning its past, present, and foreseen future performances.


Performance of the CMS Detector During the LHC Run 2

Acta Phys. Pol. B 47, 1451 (2016)

page 1451 •

abstract

Highlights of the performance of the CMS detector in the LHC Run 2.


Standard Model Higgs Results from ATLAS and CMS Experiments

Acta Phys. Pol. B 47, 1459 (2016)

page 1459 •

abstract

This paper presents an overview of the current status of Higgs boson measurements from the ATLAS and CMS experiments at the LHC. First, the Higgs boson mass, couplings, CP and spin analyses will be discussed. Proton–proton collisions data at the centre-of-mass energies of 7 TeV and 8 TeV have been used for these studies. Finally, preliminary Higgs boson cross-section measurements at the centre-of-mass energy of 13 TeV are presented.


Soft QGP Probes with ALICE

Acta Phys. Pol. B 47, 1473 (2016)

page 1473 •

abstract

In heavy-ion collisions at the LHC, a hot and dense medium of deconfided partons, the Quark–Gluon Plasma (QGP), is created. Its global properties can be characterized by the measurements of particles in the low transverse momentum (or “soft”) regime, which represent the majority of created particles. In this report, we outline a selection of measurements of the soft probes by the ALICE experiment in \(pp\), \(p\)–Pb, and Pb–Pb collisions. The paper focuses on recent flow measurements via angular correlations and femtoscopic studies. The first ever preliminary analysis of \(K^0_{\rm S}K^{\pm }\) femtoscopy is also presented.


Searches for Supersymmetry with the CMS Detector at the LHC

Acta Phys. Pol. B 47, 1489 (2016)

page 1489 •

abstract

Results of the 2015 early searches for supersymmetric particles obtained by the CMS experiment with 13 TeV data are reviewed. With an integrated luminosity of 2.2 fb\(^{-1}\), limits on the gluino mass have been lifted up to higher values with respect to previous limits from 19.5 fb\(^{-1}\) of 8 TeV data.


SUSY Searches with the ATLAS Experiment

Acta Phys. Pol. B 47, 1505 (2016)

page 1505 •

abstract

The Standard Model describes the elementary particles and their interactions. Supersymmetry, a symmetry beyond those included in the Standard Model, could resolve some of its shortcomings. Supersymmetry can provide a solution to the hierarchy problem and a candidate for dark matter. The Large Hadron Collider has the potential to produce some of the particles predicted by supersymmetry. This document presents searches for supersymmetric particles in proton–proton collision data recorded by the ATLAS experiment. The analyses are done using \(\cal {L}=3.2\) fb\(^{-1}\) proton–proton collisions at \(\sqrt {s}=13\) TeV collected in 2015. Also, searches performed using up to \(\cal {L}=20.3\) fb\(^{-1}\) dataset at \(\sqrt {s}=7\) and 8 TeV collected in 2011 and 2012 are presented.


Non-perturbative Bottom PDF and Its Possible Impact on New Physics Searches

Acta Phys. Pol. B 47, 1519 (2016)

page 1519 •

abstract

Heavy quark parton distribution functions (PDFs) play an important role in several Standard Model and new physics processes. Most PDF analyses rely on the assumption that the charm and bottom PDFs are generated perturbatively by gluon splitting and do not include any non-perturbative degrees of freedom. However, a non-perturbative, intrinsic heavy quark PDFs have been predicted in the literature. We demonstrate that to a very good approximation, the scale-evolution of the intrinsic heavy quark content of the nucleon is governed by non-singlet evolution equations, and use this approximation to model the intrinsic bottom distribution and its impact on parton–parton luminosities at the LHC.


Direct Photon and Neutral Mesons Measurements with the ALICE Detector

Acta Phys. Pol. B 47, 1529 (2016)

page 1529 •

abstract

The ALICE experiment at LHC is dedicated to studies of the Quark–Gluon Plasma (QGP) state, which is going to be created in heavy-ion collisions. Both photons and neutral mesons are excellent probes for QGP formation. Photons are produced during the different stages of the expansion of the initial hot matter fireball. They do not interact strongly with the medium and passing through it, they carry information on their emission point. The prompt photons which are formed at the early stage of the collision enable us to test perturbative QCD constraining parton distributions and fragmentation functions. Looking into the regime of thermal photons, one can extract the temperature of the medium. The medium-induced energy loss of particles can be investigated via the measurement of neutral meson spectra for different centrality classes as well as via neutral meson–hadron correlations. A decrease of the nuclear modification factor (\(R_{AA}\)) with centrality of the collision is observed. The suppression of the away side of the per-trigger yield modification factor (\(I_{AA}\)) shows in a similar way the evidence for energy loss in medium. Both direct photons and neutral mesons have been measured by the ALICE experiment. Photons are measured in ALICE directly in the two electromagnetic calorimeters (PHOS and EMCal), as well as via method of photon conversion (PCM) into electron–positon pairs in the inner tracking system (ITS) and the time projection chamber (TPC). Neutral mesons are combined from photon pairs via the invariant mass technique. Results obtained in EMCal, PHOS and PCM are consistent one to the other and allow to measure the spectra of particles with high precision over a wide kinematical range. An overview of the recent results on photon and meson physics from ALICE will be shown.


Measurements of Jets in ALICE

Acta Phys. Pol. B 47, 1543 (2016)

page 1543 •

abstract

The ALICE detector can be used for measurements of jets in \(pp\), \(p\)Pb, and Pb–Pb collisions. Measurements of jets in \(pp\) collisions are consistent with expectations from perturbative calculations and jets in \(p\)Pb scale with the number of nucleon–nucleon collisions, indicating that cold nuclear matter effects are not observed for jets. Measurements in Pb–Pb collisions demonstrate suppression of jets relative to expectations from binary scaling to the equivalent number of nucleon–nucleon collisions.


Selected CPV Results from LHCb Run 1 and Prospects for CKM \(\gamma \) Angle Measurements in Run 2

Acta Phys. Pol. B 47, 1553 (2016)

page 1553 •

abstract

The LHCb detector is a single-arm forward spectrometer that collects data at the LHC, designed for studies of flavour physics with high precision. In this review, a few selected results regarding CP violation are discussed with particular emphasis on the CKM \(\gamma \) angle measurements. This summary covers results based on the data collected by the LHCb detector during 2011 and 2012 proton–proton LHC runs at the centre-of-mass energies of 7 and 8 TeV, respectively. Some remarks on prospects for analyses foreseen in the ongoing LHC Run 2 are also presented.


BSM Higgs Searches with the ATLAS Experiment

Acta Phys. Pol. B 47, 1565 (2016)

page 1565 •

abstract

The searches for evidence of beyond the Standard Model (BSM) Higgs bosons is a crucial part of the LHC physics program. These searches are mainly driven by two approaches: directly from decays of neutral and charged Higgs bosons, indirectly by interpreting measured mass and couplings of light Higgs boson in extensions of the SM. This note reviews the most recent BSM Higgs boson searches performed with ATLAS at the LHC using Run 1 and early Run 2 proton–proton collision data. In particular, limits on new phenomena via coupling measurements, searches for charged and neutral Higgs bosons, double Higgs boson production and scalar particles decaying to \(\gamma \gamma \) are presented. No significant deviations from the SM background expectations are found in any of the searches and thus the resulting exclusion limits are given.


Highlights of LHCb Measurement in Rare Decays and Discovery of First Pentaquark States with Run 1 Data

Acta Phys. Pol. B 47, 1581 (2016)

page 1581 •

abstract

In \(pp\) collisions at the LHC, the LHCb experiment has collected the world’s largest sample of beauty and charmed hadrons. Very precise measurements obtained from these data provide tests of the Standard Model, which are indirect searches for new physics. The highlights obtained using data of an integrated luminosity of 3.0 fb\(^{-1}\) recorded in 2011 and 2012 were shown, concerning the measurements of rare \(B\) and \({\mit \Lambda }_b\) decays. The first observation of two exotic structures in the \(J/\psi p\) channel from \({\mit \Lambda }^0_b \rightarrow J/\psi p K^-\) decays was also presented. Masses of these states are \(4380\pm 8\pm 29\) MeV and \(4449.8\pm 1.7\pm 2.5\) MeV. The preferred \(J^P\) assignments are of opposite parity, one state having spin \(3/2\) and the other \(5/2\). These states are referred to as charmonium pentaquark states.


Exotics Searches at ATLAS

Acta Phys. Pol. B 47, 1595 (2016)

page 1595 •

abstract

A broad range of searches for exotic phenomena has been carried out at the ATLAS experiment at the Large Hadron Collider, using 3.2 fb\(^{-1}\) of \(pp\) collisions at \(\sqrt {s} = 13\) TeV. These searches did not uncover any discrepancies with the Standard Model.


Determination of the CP-violating phase \(\phi _{s}\) in \(B^{0}_{s}\rightarrow J/\psi \phi \) Decays

Acta Phys. Pol. B 47, 1611 (2016)

page 1611 •

abstract

The determination of the CP-violating phase \(\phi _{s}\) in \(B^{0}_{s}\rightarrow J/\psi \phi \) decays is one of the key goals of the LHCb experiment. Its value is predicted to be very small in the Standard Model. However, it can be significantly enhanced by contributions from effects of new physics. The most precise measurements of \(\phi _{s}\) and \(\Delta {\mit \Gamma }_{s}\) to date are presented. Using a dataset corresponding to 3 fb\(^{-1}\) collected at the LHCb during 2011–2012, they are measured to be \(\phi _{s}=-0.010\pm 0.039\) rad and \(\Delta {\mit \Gamma }_{s}=0.0805\pm 0.0091\pm 0.0032\) ps\(^{-1}\).


Hot-spot Method for Alignment of Forward Proton Detectors at the LHC

Acta Phys. Pol. B 47, 1619 (2016)

page 1619 •

abstract

A method for alignment of the forward proton detectors at the LHC based on the characteristic shape of the hit pattern containing a dense region is presented. The precision of the method is discussed, including the systematic uncertainties.


The Flow Harmonics Measurement with the Event Plane and Multi-particle Cumulant Methods in Pb+Pb Collisions at 2.76 TeV in ATLAS

Acta Phys. Pol. B 47, 1625 (2016)

page 1625 •

abstract

The ATLAS results on charged particles flow harmonics in Pb\(+\)Pb collisions at \(\sqrt {s_{NN}} = 2.76 \) TeV are presented. Elliptic flow and higher order flow harmonics, \(v_{n}\) (for \(n = 2\)–\(4\)), are measured using two methods: standard event plane and multi-particle cumulants (up to the 8\(^{\rm th}\) order). Results for elliptic flow are shown in a wide range of pseudorapidity (\(|\eta | \lt 2.5\)), transverse momentum (\(0.5\lt p_{{\rm T}}\lt 20\) GeV) and centrality (\(0\)–\(80\%\)). The measurement techniques are discussed in terms of non-flow effects. It is shown that four-particle correlations suppress most of non-flow contributions.


Flexibility of LHC Optics for Forward Proton Measurements

Acta Phys. Pol. B 47, 1633 (2016)

page 1633 •

abstract

The geometric acceptance of the ATLAS Forward Proton detectors is studied. The elements of the LHC magnetic lattice that are most important for the acceptance are identified. The effects of possible changes of the LHC optics are studied.


Study of Diffractive Bremsstrahlung at 13 TeV LHC

Acta Phys. Pol. B 47, 1639 (2016)

page 1639 •

abstract

Feasibility studies of the diffractive bremsstrahlung measurement at the LHC at \(\sqrt {s} = 13\) TeV are presented. The method considered for this measurement uses the ATLAS detector and, in particular, the Zero Degree Calorimeter and the ATLAS Forward Proton detectors. The signal and background processes were generated with GenEx and PYTHIA 8.2 generators, respectively. The obtained fiducial cross sections are 1.2 \(\mu \)b for the signal and 6 \(\mu \)b for the background. Further reduction of the background is possible by the optimisation of event selection cuts.


Four-lepton Production from Photon-induced Reactions in \(pp\) Collisions at the LHC

Acta Phys. Pol. B 47, 1645 (2016)

page 1645 •

abstract

The cross sections for the reaction \(\gamma \gamma \rightarrow 4\ell \) in proton–proton collisions are calculated at the LHC energies. We show that the purely electroweak process \(\gamma \gamma \rightarrow 4\ell \) can be studied at the LHC and can constitute a background to other processes with \(4\ell \) or \(2\ell \) final states.


A New Approach to the ALFA Trigger Simulator

Acta Phys. Pol. B 47, 1655 (2016)

page 1655 •

abstract

The idea and principle of operation of a device which is used to test the trigger system of the ALFA detectors of the ATLAS experiment at the LHC are discussed. A new approach to the application control is presented. The application runs under control of the ArchLinuxARM operating system. Also, the drawbacks of the new solution are discussed.


Observation of \(B_{s}^{0} \to \mu ^{+} \mu ^{-}\) at CMS and LHCb and Future Plans at LHCb

Acta Phys. Pol. B 47, 1661 (2016)

page 1661 •

abstract

The branching fractions of the decays \(B^{0} \to \mu ^{+} \mu ^{-}\) and \(B_{s}^{0} \to \mu ^{+} \mu ^{-}\) are highly suppressed in the Standard Model but can be modified by contributions from new physics models. The combined result from the CMS and LHCb Run 1 data for the \(B^{0} \to \mu ^{+} \mu ^{-}\) and \(B_{s}^{0} \to \mu ^{+} \mu ^{-}\) branching fractions is presented here. The measured results are \(\mathcal {B}(B_{s}^{0} \to \mu ^{+} \mu ^{-}) = (2.8^{+0.7}_{-0.6})\times 10^{-9}\) at \(6.2 \sigma \) statistical significance and \(\mathcal {B}(B^{0} \to \mu ^{+} \mu ^{-}) = (3.9^{+1.6}_{-1.4})\times 10^{-10}\) at \(3.0 \sigma \) statistical significance, both results are consistent with Standard Model predictions. A brief discussion of the future prospects for the study of \(B^{0} \to \mu ^{+} \mu ^{-}\) and \(B_{s}^{0} \to \mu ^{+} \mu ^{-}\) at the LHCb is also included.


Splitting Functions for High-energy Factorization at Leading Order

Acta Phys. Pol. B 47, 1667 (2016)

page 1667 •

abstract

We report on the recently calculated transverse-momentum-dependent (TMD) splitting functions for the quark channel at leading order (LO) in the high-energy factorization framework of QCD. Our calculations complement earlier results for the gluon channel, which makes a complete set of TMD splitting functions available at LO. They are required to formulate evolution equations for TMD parton distribution functions, to develop TMD parton shower algorithms, and for other applications.


Correcting for Detector Effects in High-multiplicity Events with the HBOM Method

Acta Phys. Pol. B 47, 1677 (2016)

page 1677 •

abstract

Measurements of particle multiplicities in high-energy collisions may be affected by various detector effects which distort the values of measured observables. We present tests of a procedure of correcting for these effects called the HBOM method which is an alternative to unfolding procedures based on inverting the response matrix of the detector. Studies of the method are performed using a sample of high-multiplicity Pb+Pb collisions generated at \(\sqrt {s_{NN}} = 2.76\) TeV with the HIJING generator. The HBOM method is tested on factorial moments of the charged particle distribution distorted by a track reconstruction efficiency similar to those observed in high-energy experiments. Closure tests show that the method is able to correct factorial moments very well in the whole considered pseudorapidity range.


The Latent Meaning of Forcing in Quantum Mechanics

Acta Phys. Pol. B 47, 1685 (2016)

page 1685 •

abstract

We analyze random forcing in QM from the dual perspective of the measure and category correspondence. The dual Cohen forcing allows interpreting the real numbers in a model \(M\) and its Cohen extension \(M[G]\) as absolute subtrees of the binary tree (Cantor space). The trees are spanning non-trivial Casson handles of smooth exotic 4-manifolds, like \(\mathbb {R}^4\). We formulate the consequences for the cosmological model with random forcing where dual smooth non-standard and non-flat Riemannian geometries have to appear.


Higgs \(\tau \)-lepton Yukawa Coupling Measurement and the \(\tau \) Embedding Method for Background Estimation

Acta Phys. Pol. B 47, 1691 (2016)

page 1691 •

abstract

To measure the \(H\rightarrow \tau \tau \) Yukawa coupling the full dataset of the LHC Run 1 period recorded by the ATLAS experiment at the LHC during 2011 and 2012 has been analysed. The data correspond to integrated luminosities of 4.5 fb\(^{-1}\) and 20.3 fb\(^{-1}\) at centre-of-mass energies of \(\sqrt {s} = 7\) TeV and \(\sqrt {s} = 8\) TeV, respectively. Evidence for the coupling of the Higgs boson to tau leptons at 4.5 (3.4) sigma significance was observed (expected). Recently, the combination of the CMS and ATLAS datasets has been published, raising the observed significance to discovery level at 5.5 sigma. One crucial ingredient in the search for the \(H\rightarrow \tau \tau \) decay is the embedding method, which is a data-driven technique to estimate the large and irreducible background from \(Z\rightarrow \tau \tau \) decays that cannot be obtained directly from data control samples. In this paper, the ATLAS search for the Higgs boson decaying to tau leptons is discussed and a detailed explanation of the embedding method is given. Other use cases of the embedding method are also mentioned.


Higgs \(\to \tau \tau \) Analysis in the CMS Experiment

Acta Phys. Pol. B 47, 1697 (2016)

page 1697 •

abstract

In July 2012, the CMS and ATLAS collaborations announced the discovery of a Higgs boson with a mass of about 125 GeV and properties in agreement with expected from the Standard Model. In this note, we review the analysis performed for the \(H \to \tau \tau \) decay mode during the first stage of the LHC operation in the CMS. Further, we present the work done during the First Long Shutdown and the first stage of Run 2 of the LHC on the field of hadronic tau lepton offline reconstruction.


Selected Measurements of Rare Decays at the LHCb Experiment

Acta Phys. Pol. B 47, 1705 (2016)

page 1705 •

abstract

Experimental results of rare decays \(B^0 \rightarrow K^{*0} \mu \mu \), \(B^0 \rightarrow K^{*0} ee\), \({\mit \Lambda }_b \rightarrow {\mit \Lambda } \mu \mu \) and \(B_s^0 \rightarrow \phi \mu \mu \) governed by Flavour Changing Neutral Current transitions are discussed in this paper. The angular distributions and differential branching fractions measurements were performed using data corresponding to an integrated luminosity of \(3.0~{\rm fb}^{-1}\) collected at the LHCb experiment.


Measurement of the \(ZZ\) Production Cross Section in \(pp\) Collisions at \(\sqrt {s} =13\) TeV with the ATLAS Detector

Acta Phys. Pol. B 47, 1713 (2016)

page 1713 •

abstract

The \(ZZ\) production cross section in proton–proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb\(^{-1}\) of data recorded with the ATLAS detector at the Large Hadron Collider. The considered \(Z\) boson candidates decay to an electron or muon pair of mass 66–116 GeV. The cross section is measured to be 29.7\(^{+3.9}_{-3.6}\)(stat.)\(^{+1.0}_{-0.8}\)(syst.)\(^{+1.7}_{-1.3}\)(lumi.) fb in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for \(Z\) bosons in the same mass range and of all decay modes, giving \(16.7^{+2.2}_{-2.0}\)(stat.)\(^{+0.9}_{-0.7}\)(syst.)\(^{+1.0}_{-0.7}\)(lumi.) pb. The results agree with Standard Model predictions. Motivations for the measurement are presented and near-future prospects discussed.


Searches for New Physics with Displaced Vertex Signatures at the ATLAS Experiment in LHC Run 1

Acta Phys. Pol. B 47, 1723 (2016)

page 1723 •

abstract

Results from a selection of \(\sqrt {s} = 8\) TeV ATLAS searches for new physics with displaced signatures are presented. Displaced decays are reconstructed in either the inner detector, hadronic calorimeter, or muon spectrometer. No events over the expected background were observed, and limits as a function of proper lifetime are set.


Four-jet Production in \(k_{\rm T}\)-factorization: Single and Double Parton Scattering

Acta Phys. Pol. B 47, 1731 (2016)

page 1731 •

abstract

We present a preliminary study of both Single and Double Parton Scattering contributions to the inclusive 4-jet production in the \(k_{\rm T}\)-factorization framework at Leading Order and \(E_{\rm CM} = 7\) TeV. We compare our results to collinear results in the literature and to the ATLAS and CMS data at 8 and 7 TeV, respectively. We also discuss the importance of double-parton scattering for relatively soft cuts on the jet transverse momenta and find out that symmetric cuts do not suit quite well to \(k_{\rm T}\)-factorization predictions because of a kinematic effect suppressing the double parton scattering contribution.


ATLAS Inner Tracker Performance at the Beginning of the LHC Run 2

Acta Phys. Pol. B 47, 1739 (2016)

page 1739 •

abstract

The ATLAS experiment performs studies of proton–proton collisions at the Large Hadron Collider (LHC) at CERN. The Inner Detector is a part of the ATLAS apparatus placed nearest the interaction point, designed to measure charged particles momenta and their trajectories, and to reconstruct vertices of decays of physics objects created in collisions. During the LHC technical stop in 2013–2015, the Inner Detector underwent several upgrades and improvements, most notably an additional Pixel Detector layer was installed. This document describes the improvements done in the Inner Detector and its combined performance in the first year of data taking after the LHC restart in 2015.


Exclusive Jet Measurement in Special LHC Runs — Feasibility Studies

Acta Phys. Pol. B 47, 1745 (2016)

page 1745 •

abstract

Feasibility studies of the central exclusive jet production at the LHC using the proton tagging technique are presented. Three classes of the data-taking scenarios are considered: double tag at high and low pile-ups and single tag at low pile-up. Analyses were performed at the center-of-mass energy of 14 TeV for the ATLAS experiment, but are also valid for the CMS/TOTEM detectors.


Exclusive Production at CMS

Acta Phys. Pol. B 47, 1751 (2016)

page 1751 •

abstract

I briefly introduce so-called central exclusive production. I mainly focus on the example analyses that have been performed in the CMS experiment at CERN. I conclude with ideas and perspectives for future work that will be done during Run 2 of the LHC. I pay special attention to the ultra-peripheral collisions.


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