arXiv subjects

G. Feofilov

Publications and source records attributed to G. Feofilov.

8 recordsLinked to original sources

arXiv2025

Sensor operating point calibration and monitoring of the ALICE Inner Tracking System during LHC Run 3

The new Inner Tracking System (ITS2) of the ALICE experiment began operation in 2021 with the start of LHC Run 3. Compared to its predecessor, ITS2 offers substantial improvements in pointing resolution, tracking efficiency at low transverse momenta, and readout-rate capabilities. The detector employs silicon Monolithic Active Pixel Sensors (MAPS) featuring a pixel size of 26.88$\times$29.24 $\mu$m$^2$ and an intrinsic spatial resolution of approximately 5 $\mu$m. With a remarkably low material budget of 0.36% of radiation length ($X_{0}$) per layer in the three innermost layers and a total sensitive area of about 10 m$^2$, the ITS2 constitutes the largest-scale application of MAPS technology in a high-energy physics experiment and the first of its kind operated at the LHC. For stable data taking, it is crucial to calibrate different parameters of the detector, such as in-pixel charge thresholds and the masking of noisy pixels. The calibration of 24120 monolithic sensors, comprising a total of 12.6$\times$10$^{9}$ pixels, represents a major operational challenge. This paper presents the methods developed for the calibration of the ITS2 and outlines the strategies for monitoring and dynamically adjusting the detector's key performance parameters over time.

physics.ins-det↗

arXiv2025

Reconstruction of proton relative stopping power with a granular calorimeter detector model

Proton computed tomography (pCT) aims to facilitate precise dose planning for hadron therapy, a promising and effective method for cancer treatment. Hadron therapy utilizes protons and heavy ions to deliver well focused doses of radiation, leveraging the Bragg peak phenomenon to target tumors while sparing healthy tissues. The Bergen pCT Collaboration aims to develop a novel pCT scanner, and accompanying reconstruction algorithms to overcome current limitations. This paper focuses on advancing the track- and image reconstruction algorithms, thereby enhancing the precision of the dose planning and reducing side effects of hadron therapy. A neural network aided track reconstruction method is presented.

physics.comp-ph↗

arXiv2023

Open and hidden strangeness with kaons and $φ$-mesons in Bjorken energy density approach for central A+A collisions from SPS to LHC

We use the available data on $ $ and $<\it{p}_T>$ for the identified hadrons including $π^{+}+π^{-}$, $K^{+}+K^{-}$, $p+\overline{p}$, $K^*(892)^0$ and $φ$-mesons, registered at midrapidity ($\vert y\vert < 0.5)$ in central 0-5% Au-Au, Pb-Pb and Xe+Xe collisions in a broad range of energies in order to compare the relative contributions to the Bjorken energy density. Particles, like strangeness-neutral $φ$-meson (a system of $s\overline{s})$ quarks) and K-meson (containing single s-quark), are of specific interest because they might have different production mechanisms and differ in sensitivity to the properties of the QGP-medium formed in relativistic heavy-ion collisions.

hep-ph↗

arXiv2023

A high-resolution pixel silicon Vertex Detector for open charm measurements with the \NASixtyOne spectrometer at the CERN SPS

The study of open charm meson production provides an efficient tool for the investigation of the properties of hot and dense matter formed in nucleus-nucleus collisions. The interpretation of the existing di-muon data from the CERN SPS suffers from a lack of knowledge on the mechanism and properties of the open charm particle production. Due to this, the heavy-ion programme of the \NASixtyOne experiment at the CERN SPS has been extended by precise measurements of charm hadrons with short lifetimes. A new Vertex Detector for measurements of the rare processes of open charm production in nucleus-nucleus collisions was designed to meet the challenges of track registration and high resolution in primary and secondary vertex reconstruction. A small-acceptance version of the vertex detector was installed in 2016 and tested with Pb+Pb collisions at 150\AGeVc. It was also operating during the physics data taking on Xe+La and Pb+Pb collisions at 150\AGeVc conducted in 2017 and 2018. This paper presents the detector design and construction, data calibration, event reconstruction, and analysis procedure.

physics.ins-det↗

arXiv2021

First demonstration of in-beam performance of bent Monolithic Active Pixel Sensors

A novel approach for designing the next generation of vertex detectors foresees to employ wafer-scale sensors that can be bent to truly cylindrical geometries after thinning them to thicknesses of 20-40$μ$m. To solidify this concept, the feasibility of operating bent MAPS was demonstrated using 1.5$\times$3cm ALPIDE chips. Already with their thickness of 50$μ$m, they can be successfully bent to radii of about 2cm without any signs of mechanical or electrical damage. During a subsequent characterisation using a 5.4GeV electron beam, it was further confirmed that they preserve their full electrical functionality as well as particle detection performance. In this article, the bending procedure and the setup used for characterisation are detailed. Furthermore, the analysis of the beam test, including the measurement of the detection efficiency as a function of beam position and local inclination angle, is discussed. The results show that the sensors maintain their excellent performance after bending to radii of 2cm, with detection efficiencies above 99.9% at typical operating conditions, paving the way towards a new class of detectors with unprecedented low material budget and ideal geometrical properties.

physics.ins-det↗

arXiv2017

Correlation of strange particles production with multiplicity in a multi-pomeron exchange model

We propose a further development of a multi-pomeron exchange model of pp and p$\bar p$ collisions at high energy. The model describes consistently multiplicity, transverse momentum of charged particles and their correlation in wide energy range (from ISR to LHC) by introducing string collectivity effects in pp collisions. The particles species differentiation is implemented according to Schwinger mechanism. Due to the influence of higher resonances on the yields of observed particles, we implement the production of a large set of hadron resonances with cascade decays. We present the results on pion, kaon and proton yields as a function of the collision energy and the correlation of strange and multi-strange hadrons with multiplicity and compare the results with experimental data.

hep-ph↗

arXiv2010

Onset of "ridge phenomenon" in AA and pp collisions and percolation string model

Detailed study of centrality dependence of low-p_t manifestation of so-called "near-side ridge" phenomenon is reported recently by STAR for all charged hadrons with p_t>0.15 GeV/c from AuAu collisions at 62 and 200 GeV at RHIC[1]. It is indicating the existence of the energy-dependent centrality point where some sudden changes in the correlation pattern are observed. In the present work we use the hypothesis of string percolation phase transition for the description of the onset of this ridge. One may assume that the formation of rather large "macroscopic" clusters composed of several overlapped strings extended in rapidity and localized in azimuth could be one of the possible processes leading to the observed phenomenon. This onset is characterized by some definite ("critical") number of participating nucleons. We use also another physical quantity, transverse particle density, to characterize this threshold behavior, this variable brings the transition points for two energies to coincidence [1]. So parameters of the percolation model are defined at these critical points. Also we use results of our previous calculations[2] for energy of collision 17.3 GeV based on observed threshold of anomalous suppression of J/psi. Obtained parameters are extrapolated to AA and pp collisions for energies over the range 17.3 GeV - 7000 GeV.

hep-ph↗

arXiv2009

J/Psi suppression, percolation model and the critical energy density in AA collisions at SPS and RHIC energies with the account of centrality

Experimental data on the onset of a so-called anomalous J/psi suppression in PbPb collisions at the SPS are considered in the framework of string percolation model. This onset is observed at a certain collision centrality, characterized by the number of nucleons-participants (Npart) related to the impact-parameter. Modified Bjorken formula calculations are performed for the local energy densities in AA collisions at different impact-parameters and with detailed account of the latest data available on the charged particles densities at midrapidity. Finally we compare variations of mean local energy and of string densities and match the occurrence of the critical percolation phenomenon with the critical energy density value, considering them at the same values of Npart. Similar analysis was performed for recent RHIC data and the results are discussed.

hep-ph↗