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T. Djobava

Publications and source records attributed to T. Djobava.

At least 19 recordsLinked to original sources
arXiv2025

Study of the Radiation Hardness of the ATLAS Tile Calorimeter Optical Instrumentation with Run 2 data

This paper presents a study of the radiation hardness of the hadronic Tile Calorimeter of the ATLAS experiment in the LHC Run 2. Both the plastic scintillators constituting the detector active media and the wavelength-shifting optical fibres collecting the scintillation light into the photodetector readout are elements susceptible to radiation damage. The dedicated calibration and monitoring systems of the detector (caesium radioactive sources, laser and minimum bias integrator) allow to assess the response of these optical components. Data collected with these systems between 2015 and 2018 are analysed to measure the degradation of the optical instrumentation across Run 2. Moreover, a simulation of the total ionising dose in the calorimeter is employed to study and model the degradation profile as a function of the exposure conditions, both integrated dose and dose rate. The measurement of the relative light output loss in Run 2 is presented and extrapolations to future scenarios are drawn based on current data. The impact of radiation damage on the cell response uniformity is also analysed.

physics.ins-det↗
arXiv2018

Study of Azimuthal Correlations in the Target Fragmentation Region in p, d, He, C+C, Ta and C+Ne, Cu Collisions at a Momentum of 4.2, 4.5 and 10 AGeV/c

Azimuthal correlations between the same type of particles (protons or pions) in the target fragmentation region was studied in d, He, C + C, Ta (4.2 AGeV/c), C + Ne, Cu (4.5AGeV/c) and p + C, Ta (10 GeV/c) interactions. The data were obtained from the SKM-200-GIBS streamer chamber and from Propane Bubble Chamber (PBL-500) systems utilized at JINR. Study of multiparticle azimuthal correlations offers unique information about space-time evolution of the interactions. Azimuthal correlations were investigated by using correlation function C($Δϕ$)=dN/d($Δϕ$), where $Δϕ$ represents the angle between the sums of transverse momenta vectors for particles emitted in the forward and backward hemispheres. For protons a "back-to back" ("negative") azimuthal correlations were observed in the above mentioned interactions. The absolute values of the correlation coefficient $|ξ|$ -- the slope parameter of C($Δϕ$), strongly depend on the mass number of the target ($A_T$) nuclei in the nucleon-nucleus and nucleus-nucleus collisions. Namely, $|ξ|$ -- decreases with increase of $A_T$ in p+C and p+Ta collisions, while $|ξ|$ decreases from d+C up to C+Ne and then almost does not change with increase of $A_P$, $A_T$ in (d+He)Ta, C+Cu and C+Ta collisions. For pions a "back-to-back" correlations were obtained for a light targets (C, Ne), and a "side-by-side" ("positive") correlations for a heavy targets (Cu, Ta). The $|ξ|$ insignificantly changes with increase of the momenta per nucleon and almost does not change with increase of $A_P$ and $A_T$. Models, used for description of the data -- the Ultra relativistic Quantum Molecular Dynamic (UrQMD) and Quark-Gluon String Model (QGSM), satisfactorily describe the obtained experimental results.

nucl-ex↗
arXiv2016

Study of collective flows of protons and $π^{-}$ -mesons in p(C, Ta) and He(Li, C) collisions at momenta of 4.2, 4.5 and 10 AGeV/c

Collective flows of protons and $π^{-}$-mesons are studied at the momenta of 4.2, 4.5 and 10 AGeV/c for p(C, Ta) and He(Li, C) interactions. The data were obtained from the streamer chamber (SKM-200-GIBS) and from the Propane Bubble Chamber (PBC-500) systems utilized at JINR. The method of Danielewicz and Odyniec has been employed in determining the directed transverse flow of particles. The values of the transverse flow parameter and the strength of the anisotropic emission were defined for each interacting nuclear pair. It is found that the directed flows of protons and pions decrease with increase of the energy and the mass numbers of colliding nucleus pairs. The $π^{-}$-meson and proton flows exhibit opposite directions in all studied interactions, and the flows of protons are directed in the reaction plane. The Ultra-relativistic Quantum Molecular Dynamical Model (UrQMD), enlarged by the Statistical Multi-fragmentation Model (SMM), satisfactorily describes obtained experimental results.

nucl-ex↗
arXiv2011

A Layer Correlation technique for pion energy calibration at the 2004 ATLAS Combined Beam Test

A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20 GeV and 180 GeV, the particle energy is reconstructed within 3% and the energy resolution is improved by between 11% and 25% compared to the resolution at the electromagnetic scale.

physics.ins-det↗
arXiv2009

Anisotropic Collective Flow of Lambda Hyperons Produced in C + C Collisions at 4.2 AGeV/c

Features of anisotropic collective flow and spectral temperatures have been determined for lambda hyperons emitted from C + C collisions, at incident momentum of 4.2 AGeV/c, measured using the Propane Bubble Chamber of JINR at Dubna. Moreover, characteristics of protons and of negative pions, emitted from those collisions, have been determined and provided for comparison. The directed and elliptic flows of lambdas both agree in sign with the corresponding flows of protons. Parameters of the directed and elliptic flows for lambdas agree further, within errors, with the corresponding parameters for the co-produced protons. This contrasts an earlier finding by the E895 Collaboration of the directed flow being significantly weaker for lambdas than protons, in the much heavier Au + Au system, at comparable incident momentum. Particle spectral temperatures in the C + C collisions have been determined focusing independently on either center-of-mass energy, transverse energy or transverse momentum distributions. For either protons or negative pions, the temperatures were found to be approximately the same, no matter whether the emission of those particles was associated with lambda production or not. Results of the measurements have been compared to the results of simulations within the Quark-Gluon String Model.

nucl-ex↗
arXiv2007

Study of ATLAS sensitivity to FCNC top decays

The ATLAS experiment sensitivity to top quark Flavour Changing Neutral Current (FCNC) decays was studied at LHC using ttbar events. While one of the top quarks is expected to follow the dominant Standard Model decay t->bW, the other decays through a FCNC channel, i.e. t-> Z u(c), t-> gamma u(c) or t-> g u(c). Different types of analyses, applied to each FCNC decay mode, were compared. The FCNC branching ratio sensitivity (assuming a 5sigma signal significance) and 95% confidence level limits on the branching ratios (in the hypothesis of signal absence) were obtained.

hep-ex↗
arXiv2007

Collective Flow of Protons and Negative Pions in Nucleus-Nucleus Collisions at Momentum of $4.2 ÷4.5$ AGeV/c

Collective flow of protons and negative pions has been studied within the momentum region of $4.2 ÷4.5$ AGeV/c ($E =3.4 ÷3.7$ AGeV) for different projectile-target combinations involving carbon and, specifically, He-C, C-C, C-Ne, C-Cu and C-Ta. The data stem from the SKM-200-GIBS streamer chamber and from Propane Bubble Chamber systems utilized at JINR. The directed flow of protons grows dramatically in the carbon region when the counterpart nucleus grows in mass between He and Ta. The elliptic proton flow points out of the reaction plane and also strengthens as system mass increases. Within the reaction plane, the negative pions flow in the same direction as protons for the lighter of the investigated systems, He-C, C-C and C-Ne, and in the opposite direction for the heavier, C-Cu and C-Ta. The Quark-Gluon String Model reproduces observed changes in the flow with system mass.

nucl-ex↗
arXiv2005

The Flavour-Changing Neutral Currents Decay t-->Hq at ATLAS Experiment

The sensitivity of the ATLAS experiment to the top-quark rare decay via flavour-changing neutral currents t --> Hq (q represents c and u quarks) has been studied at sqrt{s} = 14 TeV in the decay mode of ttbar --> HqWb --> WW*q,Wb -->l νl νj, l^{\pm} νb, (l=e, μ). The Standard Model backgrounds ttbar, ttbar H, WZ and WH have been analysed. The signal and backgrounds were generated via PYTHIA 5.7 and simulated and analysed using ATLFAST 2.51. A branching ratio for t --> Hq -->WW*q as low as 2.0x10^{-3} for m_H=150 GeV and 2.1x10^{-3} for m_H=160 GeV could be discovered at the 5 σlevel with an integrated luminosity of 100 fb^{-1}.

hep-ex↗
arXiv2002

Differential Transverse Flow in Central C-Ne and C-Cu Collisions at 3.7 GeV/nucleon

Differential transverse flow of protons and pions in central C-Ne and C-Cu collisions at a beam energy of 3.7 GeV/nucleon was measured as a function of transverse momentum at the SKM-200-GIBS setup of JINR. In agreement with predictions of a transversely moving thermal model, the strength of proton differential transverse flow is found to first increase gradually and then saturate with the increasing transverse momentum in both systems. While pions are preferentially emitted in the same direction of the proton transverse flow in the reaction of C-Ne, they exhibit an anti-flow to the opposote direction of the proton transverse flow in the reaction of C-Cu due to stronger shadowing effects of the heavier target in thr whole range of transverse momentum.

nucl-ex↗
arXiv2001

Study of Multiparticle Azimuthal Correlations in Central CNe, MgMg, CCu and OPb Interactions at Energy of 3.7 GeV per Nucleon

Azimuthal correlations between protons and between pions have been investigated in central CNe, MgMg, CCu and OPb collisions at energy of 3.7 GeV/nucleon. "Back-to-back" (negative) correlations have been observed for protons in CNe, CCu and for pi^{-}-mesons in CNe and MgMg collisions. For pi^{-}-mesons "side-by-side" (positive) azimuthal correlations have been observed for heavy systems of CCu and OPb. The Quark Gluon String Model satisfactorily describes the experimental results both for protons and pi^{-}-mesons.

nucl-ex↗
arXiv2000

Study of ATLAS Sensitivity to FCNC TOP Quark Decay t--> Zq

The sensitivity of ATLAS experiment to the top-quark rare decay via flavor- changing neutral currents t \to Zq (q represents c and u quarks) have been studied at \sqrt{s}= 14 TeV in two decay modes: 1. The pure leptonic decay of gauge bosons: t\bar{t} \to ZqWb \to l^{+} l^{-} j l^{+-} nu j_{b} (l=e, mu) 2. The leptonic decay of Z bosons and hadronic decay of W bosons t\bar{t} \to ZqWb \to l^{+} l^{-} jjjj_{b} (l=e, mu) The dominant backgrounds Z-jets, Zw and t\bar{t} has been analysed. The signal and backgrounds were generated via PYTHIA 5.7, simulated and analysed using ATLFAST 2.14. A branching ratio for t \to Zq as low as 1.1x1-^{4} for the leptonic mode and 2.3x10^{4} for hadronic mode could be discovered at the 5σlevel with an integrated luminosity of 10^{5} pb^{-1}.

hep-ex↗
arXiv2000

Results from SKM-200-GIBS on multiparticle azimuthal correlations in C-Ne and C-Cu collisions at energy of 3.7 GeV per nucleon

The transverse momentum technique is used to analyse charged-particle exclusive data in central C-Ne and C-Cu interactions at energy of 3.7 GeV per nucleon. Clear evidence of in-plane and out-of-plane (squeeze-out) flow effects for protons and pi^{-} mesons have been obtained. In C-Ne interactions in-plane flow of pi^{-} mesons is in the same direction as for the protons, while in C-Cu collisions pions show antuflow behaviour. From the transverse momentum and azimuthal distributions of protons and pi^{-} mesons with respect to the reaction plane, the flow (the measure of the amount of collective transverse momentum transfer in the reaction plane) and the parameter a_{2} (the measure of the anisotropic emission strength) have been extracted. The flow effects increase with the mass of the particle and the mass number of target A_{T}. The comparison of our in-plane flow results with flow data for various projectile/target configurations was made using the scaled flow F_{S}=F/(A_{P} ^{1/3}+A_{T}^{1/3}). F_{S} demonstrates a common scaling behaviour for flow values from different systems. The Quark Gluon String Model (QGSM) was used for the comparison with the experimental data. The QGSM yields a signature of in-plane and out-of-plane flow effects in C-ne and C-Cu collisions for protons.

nucl-ex↗
arXiv1999

Study of collective matter flow in central C-Ne and C-Cu collisions at energy of 3.7 GeV per nucleon

The transverse momentum technique is used to analyse charged-particle exclusive data in the central C-Ne and C-Cu interactions at energy of 3.7 Gev per nucleon. The clear evidence of in-plane and out-of-plane (squeeze-out) flow effects for protons and $π^{-}$ mesons have been obtained. In C-Ne interactions the $π^{-}$ mesons in-plane flow is in the same direction to the protons, while in C-Cu collisions pions show antiflow behaviour. From the transverse momentum and azimuthal distributions of protons and pi^{-} mesons with respect to the reaction plane the flow F (the measure of the amount of collective transverse momentum transfer in the reaction plane) and the parameter a_{2} (the measure of the strength of the anisotropic emission) have been extracted. The flow effects increase with the mass of the particle and atomic number of target A_{T}. The comparison of our in-plane flow results with flow data of various projectile/target configurations had been done by a scaled flow F_{S}=F/(A_{P}^{1/3}+A_{T}^{1/3}). F_{S} demonstrates a common scaling behaviour among flow values from different systems.

hep-ex↗
arXiv1999

The analysis of pi^{-} mesons produced in nucleus-nucleus collisions at a momentum of 4.5 GeV/c/nucleon in light front variables

The light front analysis of pi^{-} mesons in He(Li,C), C-Ne, C-Cu and O-Pb collisions is carried out. The phase space of secondary pions is divided into two parts in one of which the thermal equilibrium assumption seems to be in a good agreement with the data. Corresponding temperatures T are extracted and their dependence on (A_{P}*A_{T})^{1/2} is studied. The results are compared with the predictions of the Quark-Gluon String Model (QGSM). The QGSM satisfactorily reproduces the experimental data for light and intermediate-mass nuclei.

hep-ex↗
arXiv1998

The Light Front Analysis of pi^{-} Mesons Produced in the Relativistic Nucleus-Nucleus Collisions

The light front analysis of pi^{-} mesons in A_{P} (He, C, Mg, O) + A_{T} (Li,C, Ne, Mg,Cu,Pb) collisions is carried out. The phase space of secondary pions is naturally divided into two parts in one of which the thermal equilibration assumption seems to be in a good agreement with data. Corresponding temperatures are extracted and compared to the results of other experiments. The dependence of the average temperature T on (A_{P}*A_{T})^{1/2} is studied.

hep-ex↗
arXiv1998

Light-Front Analysis of pi^{-} Mesons Produced in Mg - Mg Collisions at 4.3 a Gev/c

Light-front analysis of pi^{-} mesons in Mg-Mg collisions is carried out. The phase space of secondary pions is naturally divided into two parts in one of which the thermal equilibration assumption seems to be in a good agreement with data. Corresponding temperatures are extracted and compared to the results of other experiments. The experimental results have been compared with the predictions of the Quark Gluon String Model (QGSM) and satisfactory agreement between the experimental data and the model has been found.

hep-ex↗
arXiv1998

The comparison of characteristics of pi^{-} mesons produced in central Mg-Mg interactions with the quark gluon string model predictions

A detailed study of pion production in central Mg-Mg collisions at a momentum of 4.3 GeV/c per incident nucleon was carried out with use of the setup GIBS. The average kinematical characteristics of pions (multiplicity n_, momentum P, transverse momentum P_{T}, emission angle Q, rapidity Y) and corresponding distributions have been obtained. The experimental results have been compared with the predictions of the Quark Gluon String Model (QGSM) and satisfactory agreement between the experimental data and the model has been found. The QGSM reproduces also the dependence of average P_{T} on n_{-}. The temperatures of pi^{-} mesons have been estimated in the rapidity interval of 0.5<=Y<=2.1. A satisfactory fit for pi^{-} mesons has been achieved by using a form involving two temperatures T_{1} and T_{2}. It was found that the QGSM underestimates T_{2} by (10-15)%. The data have been analyzed using the transverse momentum technique. The observed dependence of the on Y shows the S-shape behaviour. The slope at midrapidity F had been determined. The QGSM reproduces the distribution satisfactorily, but underestimates the parameter F.

hep-ex↗