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Alexander Milov

Publications and source records attributed to Alexander Milov.

16 recordsLinked to original sources
arXiv2025

The NA60+ experiment at SPS

A new apparatus, NA60+, is proposed for measuring muon pairs in the center-of-mass region from 5 to 17 GeV at CERN SPS in various collisional systems from Pb+Pb and down to $p$+Be. The physics scope of the new detector will cover topics from the measurement of thermal radiation coming from the hot and dense medium to chiral symmetry restoration, strangeness, and charm production. The proposed detector consists of a vertex spectrometer based on novel technology, allowing the production of large silicon sensors and a large-acceptance muon spectrometer based on gaseous detectors. With its high beam intensity, the new apparatus provides access to rare observables that have been scarcely studied until now. The new detector will come into operation after the Long Shutdown 3 of the LHC (past 2029) and is aimed at the first data-taking with Pb and proton beams. In this contribution, we review the project and recent R\&D effort, including the technical aspects and the studies of the physics performances for the observables.

nucl-ex↗
arXiv2022

Missing beauty of proton-proton interactions

From first principles, particles with the same quark content and similar masses should have similar kinematic distributions. Transverse mass scaling may be employed to estimate possible differences in the momentum distribution of such particles. Based on this scaling the excited bottomonium states measured at the LHC are found to be significantly different from $Υ$(1S) to the extent that the integrated yield of $Υ$(2S) is 1.6 times less and $Υ$(3S) 2.4 times less than would be explained by the mass difference. This proceeding explains how the estimate is worked out and relates it to other measurements performed at the LHC.

hep-ph↗
arXiv2022

Can Transverse Mass Scaling Shed Light on the Event-Activity Dependence of $\Upsilon$ Mesons Production at LHC?

Measurements by the CMS experiment [CMS Collaboration, JHEP04 (2014) 103; CMS Collaboration, JHEP11 (2020) 001] reveal a deficit of charged particle tracks in events with higher $\Upsilon$(nS) states. This observation is suggested to be a manifestation of the excited bottomonia suppression in $pp$ interactions. Transverse mass ($m_{\mathrm{T}}$) scaling can be implied to check this assumption in an independent way. The scaling has been observed for a wide range of particle species in proton-proton collisions at various energies from the SPS to RHIC and the LHC. The observed scaling is known to be different for baryons and mesons, and this work presents a comprehensive study of the $m_{\mathrm{T}}$-scaling of mesons at LHC energies with a focus on heavier mesons. The study demonstrates patterns in the scaling properties of mesons, which are related to the particle quark content. In particular, light species and ground-state quarkonia obey the same scaling, whereas open-flavor particles deviate from it because their spectra are significantly harder. The magnitude of deviation depends on the flavor of the heaviest quark in the meson. By extending the $m_{\mathrm{T}}$-scaling assumption to the excited bottomonia states, it is observed that the measured cross sections of $\Upsilon$(2S) and $\Upsilon$(3S) are reduced by factors of 1.6 and 2.4 compared to the expectation from the scaling. This observation is consistent with recently observed differences between the event-activity dependence of different $\Upsilon$(nS) meson states.

hep-ph↗
arXiv2020

Measurement of the ion blocking by the passive bi-polar grid

The ion backflow is the main limiting factor for operating time projection chambers at high event rates. A significant effort is invested by many experimental groups to solve this problem. This paper explores a solution based on operating a passive bi-polar wire grid. In the presence of the magnetic field, the grid more effectively attenuates the ion current than the electron current going through it. Transparencies of the grid to electrons and ions are measured for different gas mixtures and magnitudes of the magnetic field. The results suggest that in a sufficiently strong magnetic field, the bi-polar wire grid can be used as an effective and independent device to suppress the ion backflow in time projection chambers.

physics.ins-det↗
arXiv2018

Electroweak probes with ATLAS

Measuring electroweak bosons in relativistic heavy ion collisions at high energy provide an opportunity to understand temporal evolution of the quark-gluon plasma created in such collisions by constraining the initial state of the interaction. Due to lack of color charges the bosons and or particles produced in their leptonic decays are unaffected by the quark-gluon plasma and therefore preserve the information about the very early stage of the collision when they were born. This singles electroweak bosons as a unique and very interesting class of observables in heavy ion collisions. The ATLAS experiment at LHC measures production of electroweak bosons in pp, p+Pb, and Pb + Pb collisions systems. A review of the existing results is given in this proceeding that includes studies made with isolated photons to constraint kinematic properties and flavour composition of associated jets, measurements of W and Z bosons used to estimate nuclear modification of parton distribution function and the production rates of the bosons used to verify geometric models implied to estimate event centrality. A novel analysis on measuring two-particle correlations in pp collisions where the Z boson is registered is also discussed in the proceeding. This is the first attempt to break into the initial geometry of the pp collisions by constraining the impact parameter with a hard scattering process. It shows that the strength of the two particle correlations in such collision is 1.08+/-0.06 above the inclusive. To make the measurement ATLAS solves the technical problem of measuring the underlying event in high pileup condition.

nucl-ex↗
arXiv2016

Measurement of long-range particle correlations in small systems with the ATLAS detector

The study of particle correlations is an important instrument to understand the nature of relativistic heavy ion collisions. Using a wealth of new data available from the recent heavy ion runs of Large Hadron Collider at CERN it becomes possible to study particle correlations in different collisions systems under the same conditions. The results of several recent measurement performed by the ATLAS experiment are reviewed in this proceeding. Measurements are performed using various techniques in pp, p+Pb and Pb+Pb collisions at the energies $\sqrt{s}$, $\sqrt{s_{_{\rm{NN}}}}$ from 2.76 to 13 TeV. The results are compared between the systems having the same charged particle multiplicities in the final state, but different initial geometries. Results for multiplicity correlations, two-particle and muti-particle correlations measured in different techniques are presented and discussed. The goal of these complementary analyses is to further understanding the nature of fluctuations observed in small collision systems.

nucl-ex↗
arXiv2015

The R_AA and v_2 of muons from heavy-quark decays in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV with the ATLAS detector

The ATLAS experiment measures the production of muons coming from the decays of heavy flavour particles in the kinematic interval 4<p_T<14 GeV and |eta|<1. The measurement is performed in sqrt(s) = 2.76 TeV pp collisions and over the centrality range of 0-60% in sqrt(s_NN) = 2.76 TeV Pb+Pb collisions. The heavy flavour muon differential cross-sections and per-event yields are measured in pp and Pb+Pb collisions, respectively. The nuclear modification factor measured in 0-10% most central collisions is observed to be approximately equal to 0.4 and independent of p_T within uncertainties, which indicates suppressed production of heavy flavour muons in Pb+Pb collisions. The muon yields are also measured as a function of the azimuthal angle with respect to the event plane. Fourier coefficients associated with the second harmonic modulation vary slowly with p_T and show a systematic variation with centrality that is characteristic of other elliptic anisotropy measurements.

nucl-th↗
arXiv2014

A Centrality Detector Concept

The nucleus-nucleus impact parameter and collision geometry of a heavy ion collision are typically characterized by assigning a collision "centrality". In all present heavy ion experiments centrality is measured indirectly, by detecting the number of particles or the energy of the particles produced in the interactions, typically at high rapidity. Centrality parameters are associated to the measured detector response using the Glauber model. This approach suffers from systematic uncertainties related to the assumptions about the particle production mechanism and limitations of the Glauber model. In the collider based experiments there is a unique possibility to measure centrality parameters by registering spectator fragments remaining from the collision. This approach does not require model assumptions and relies on the fact that spectators and participants are related via the total number of nucleons in the colliding species. This article describes the concept of the centrality detector for heavy ion experiment, which measures the total mass number of all fragments by measuring their deflection in the magnetic field of the collider elements.

nucl-ex↗
arXiv2014

Particle production and long-range correlations in p+Pb collisions with the ATLAS detector

The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distribution, charged particle spectra, and the two-particle correlations in p+Pb collisions at a nucleon-nucleon centre-of-mass energy of sqrt(s_NN)=5.02TeV. Charged particles were measured over |eta|<2.7 using the ATLAS detector tracking system. The p+Pb collision centrality was characterized by the total transverse energy deposited over the interval 3.2<eta<4.9 in the direction of the Pb-beam. Three different calculations of the number of participating nucleons, have been carried out using a standard Glauber initial state model as well as two Glauber-Gribov extensions. Charged particle multiplicities per participant pair, and the normalised charged particle spectra are found to vary in shape with eta and also with the model, pointing to the importance of the fluctuating nature of nucleon-nucleon collisions in the modelling of the initial state of p+Pb collisions. The two particle correlation exhibits flow-like modulations for all centrality intervals and particle p_T.

nucl-ex↗
arXiv2012

High-p_T and Jets. A Summary of Results from Quark Matter 2012

A broad range of new experimental data and theoretical results on the properties of hadronic matter under extreme conditions have been reported at Quark Matter 2012 conference. At this conference the scientific community was presented with a variety of measurements from the 2011 lead-lead LHC run using hard probe observables. Many measurements, such as boson-jet correlations, production rates of the b-jets, high precision jet fragmentation and others were shown for the first time. The new data from the LHC was matched by new techniques and analyses coming from RHIC experiments. This proceeding summarises the new measurements with high-p_T particles and jets and attempts to provide a theoretical explanation for the novel results presented at the conference

nucl-ex↗
arXiv2012

Measurement of the W, Z and photon production in lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS detector

The ATLAS experiment measures yields of isolated photons and of Z and W bosons via leptonic decay modes in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV. The data samples used in the analysis were obtained in the year 2010 and year 2011 LHC runs and correspond to 5 ub-1 and 0.15 nb-1 of integrated luminosity respectively. The measured yields of all bosons are consistent with the scaling proportional to the number of nucleon-nucleon collisions. The transverse momentum distributions are measured for isolated photons and for Z bosons for different centrality bins. The shapes of measured distributions do not change with centrality. The transverse momentum and rapidity distributions of Z boson are consistent in shape with Pythia model and the second harmonic coefficient of the azimuthal distribution of Z bosons with respect to the event plane is consistent with zero.

nucl-ex↗
arXiv2011

Centrality dependence of charged particle spectra and RCP in Pb+Pb collisions at \sqrt{s_{NN}}=2.76TeV with the ATLAS detector at the LHC

The ATLAS experiment at the LHC measures the charged particle spectra and the nuclear modification factor in Pb+Pb collisions at the \sqrt{s_{NN}}=2.76TeV in a transverse momentum range up to 30 GeV and a pseudorapidity range up to |η| < 2.5. The measurement reveals the strong suppression of charged hadron production in the most central collisions at a p_T of about 7 GeV. A suppression of more than a factor of 2 is also measured at the upper edge of the analyzed p_T range. The suppression does not show any strong ηdependence.

nucl-ex↗
arXiv2008

Light Vector Mesons

This article reviews the current status of experimental results obtained in the measurement of light vector mesons produced in proton-proton and heavy ion collisions at different energies. The review is focused on two phenomena related to the light vector mesons; the modification of the spectral shape in search of Chiral symmetry restoration and suppression of the meson production in heavy ion collisions. The experimental results show that the spectral shape of light vector mesons are modified compared to the parameters measured in vacuum. The nature and the magnitude of the modification depends on the energy density of the media in which they are produced. The suppression patterns of light vector mesons are different from the measurements of other mesons and baryons. The mechanisms responsible for the suppression of the mesons are not yet understood. Systematic comparison of existing experimental results points to the missing data which may help to resolve the problem.

nucl-ex↗
arXiv2007

Multi-Particle Decays of Light Mesons Measured by PHENIX at RHIC

The PHENIX experiment at RHIC measured K0S, eta and omega-meson production at high pT in p+p, d+Au and Au+Au collisions at sqrt(s_NN)=200 GeV. Measurements performed in different hadronic decay channels give consistent results. This paper presents measured meson-to-pi0 ratios and Nuclear Modification factors in the most central d+Au and Au+Au collisions. No suppression seen in d+Au interactions is in contrast to a strong suppression of meson yields revealed in central Au+Au collisions at the same energy.

nucl-ex↗