Semen Turchikhin

The cross section of associated production of a $Z$ boson with heavy flavor jets in $pp$ collisions is calculated using the Sherpa Monte Carlo generator and the analytical combined QCD approach based on ${k}_{\mathrm{T}}$ factorization at small $x$ and conventional collinear QCD at large $x$. A satisfactory description of the ATLAS and CMS data on the ${p}_{\mathrm{T}}$ spectra of $Z$ bosons and $c$ jets in the whole rapidity, $y$, region is shown. Searching for the intrinsic charm (IC) contribution in these processes, which could be visible at large $y>1.5$, we study observables very sensitive to nonzero IC contributions and less affected by theoretical QCD scale uncertainties. One of such observables is the so-called double ratio, the ratio of the differential cross section of $Z+c$ production in the central region of $|y|<1.5$ and in the forward region $1.5<|y|<2.5$, divided by the same ratio for $Z+b$ production. These observables could be more promising for the search of IC at LHC as compared to the observables considered earlier.

This proceeding contribution presents the recent highlights of charm physics programme of the ATLAS experiment at the Large Hadron Collider. These include measurements of charmonia production both in pp and nuclear collisions, charmonium pair production, studies of exotic states and B c mesons. Most of the shown results are obtained with the data collected during the LHC Run-1.

The paper presents a review of recent heavy-flavour spectroscopy studies performed with the ATLAS experiment using the data collected during the LHC Run 1. This includes the first observation of an excited state of the B + meson and a search for Xb and other hidden-beauty states in + (1S) channel.

Recent results on Λ 0 b baryon and B + c meson decay studies from the ATLAS experiment at the LHC are presented.These include measurements of the parity-violating asymmetry parameter α b and the helicity amplitudes for the Λ 0 b → J/ψΛ 0 decay, the first observation of the Λ 0 b → ψ(2S)Λ 0 decay and a measurement of its rate relative to the Λ 0 b → J/ψΛ 0 decay, and a study of the B + c → J/ψD ( * )+ s decay properties.

This paper presents an overview of muon trigger and B-physics trigger of the ATLAS experiment. Main updates done during the preparation for Run 2 data-taking are outlined. Trigger performance results obtained with new experimental data and modelling are shown.

The Flavour Changing Neutral Current processes are sensitive to New Physics contributions, in particular through additional electroweak loop amplitudes. The angular analysis of the decay of B0 → μ+μ−K*0 is presented. A number of angular coefficients are measured as a function of the invariant mass squared of the dimuon system using data collected by the ATLAS experiment at the LHC. Comparison is made to theoretical predictions, including for the observable P′5, for which there has been recent tension between theory and experiment. ATLAS result on the study of the rare decays is also presented.

Recent results from the ATLAS experiment at the LHC on the charmonium production and on the production and decays are presented.These include studies of the associated production of the / meson and boson, the measurement of / and (2S) mesons differential production cross-sections, the measurement of the differential ratios of the + and + production crosssections, and the new results on the + decays to / ( * ) final states.The results are obtained with collision data collected at centre-of-mass energies √ = 8 and 13 TeV.

We consider the production of $Z$ bosons associated with heavy (charm and beauty) jets at the LHC energies using two scenarios based on the transverse momentum dependent (TMD) parton densities in a proton. The first of them employs the Catani-Ciafaloni-Fiorani-Marchesini gluon evolution and is implemented in the Monte Carlo event generator pegasus. Here, the heavy quarks are always produced in the hard partonic scattering. The second scheme is based on the parton branching approach, currently implemented into the Monte Carlo event generator cascade. In this scenario, the $Z+\text{jets}$ sample is generated and then events containing the heavy flavor jet in a final state are selected. We compare the predictions obtained within these two TMD-based approaches to each other, investigate their sensitivity to the TMD gluon densities in a proton, and estimate the effects coming from parton showers and double parton scattering mechanism. Additionally, we compare our predictions with the results of traditional (collinear) pQCD calculations performed at NLO accuracy. It is shown that the TMD-based results agree with the LHC experimental data collected at $\sqrt{s}=8$ and 13 TeV. We discuss the sensitivity of observables to the quark distributions in a proton and present predictions to search for the intrinsic charm signal in forthcoming analyses of the LHC experimental data.

We consider the production of $Z$ bosons associated with heavy (charm and beauty) jets at the LHC energies using two scenarios based on the transverse momentum dependent (TMD) parton densities in a proton. The first of them employs the Catani-Ciafaloni-Fiorani-Marchesini gluon evolution and is implemented in the Monte-Carlo event generator PEGASUS. Here, the heavy quarks are always produced in the hard partonic scattering. The second scheme is based on the parton branching approach, currently implemented into the Monte-Carlo event generator CASCADE. In this scenario, the $Z$ + jets sample is generated and then events containing the heavy flavor jet in a final state are selected. We compare the predictions obtained within these two TMD-based approaches to each other, investigate their sensitivity to the TMD gluon densities in a proton and estimate the effects coming from parton showers and double parton scattering mechanism. Additionally, we compare our predictions with the results of traditional (collinear) pQCD calculations performed at NLO accuracy. It is shown that the TMD-based results agree with the LHC experimental data collected at $\sqrt s = 8$ and $13$ TeV. We discuss the sensitivity of observables to the quark distributions in a proton and present predictions to search for the intrinsic charm signal in forthcoming analyses of the LHC experimental data.

The proceeding contribution presents recent results of the ATLAS experiment at the LHC on heavy flavour measurements sensitive to possible contributions of the new physics. Two measurements are overviewed: the angular analysis of $B^0\to\mu^+\mu^- K^{*0}$ decay and measurement of relative width difference of the $B^0$-$\bar{B}^0$ system. The first one uses a data sample with an integrated luminosity of 20.3 fb$^{-1}$ collected by ATLAS at a centre of mass energy $\sqrt{s} = 8$ TeV, and the second one benefits from the full ATLAS Run-1 dataset with additional 4.9 fb$^{-1}$ collected at $\sqrt{s} = 7$ TeV.

This proceedings contribution presents recent results of the ATLAS experiment at the LHC on measurements of heavy quarkonium production. These include a study of exotic state X(3872), measurement of prompt J/ψ pair production in pp collisions, and heavy quarkonium production measurements with p+Pb and Pb+Pb collision data.

This proceedings contribution is devoted to studies of heavy flavour hadrons spectroscopy and exotic hadron states in the ATLAS experiment at the LHC.It presents in details the result of a recent study of resonances in / system using collision data collected during LHC Run-1 at √ = 7 and 8 TeV performed to test the existence of the pentaquark states observed earlier by the LHCb experiment.