Spectra and nuclear modification factor of charged hadrons produced in lead-lead collisions at sqrt(s_NN)=2.76TeV with the ATLAS detector at the LHC

The measurement of charged particle spectra in heavy ion collisions is a way to study properties of hot and dense matter created in these interactions. The centrality dependence of the spectral shape is an important tool to understand the energy loss mechanism. The ATLAS detector at the LHC accumulated integrated luminosity equal to 0.15nb^{-1} of lead-lead data at 2.76TeV per nucleon-nucleon pair. Due to the excellent capabilities of the ATLAS detector, and its stable operation in 2010 and 2011 heavy ion physics runs, these data allow measurements of the charged particle spectra and their ratios in different centrality bins over a wide range of transverse momenta (0.5-150GeV) and pseudorapidity (|eta|<2.5). The measured ratio central to peripheral events shows a suppresion by a factor of 5 at pT=7GeV. At higher pT the ratio increases

Measurement of the nuclear modification factor for high-pTp_{\mathrm{T}} charged hadrons in pp+Pb collisions with the ATLAS detector

The charged hadron spectra in $p$+Pb and $pp$ collisions at $\sqrt{s_{NN}}=\sqrt{s}=5.02$TeV are measured with the ATLAS experiment at the LHC. The measurements are performed with $p$+Pb data recorded in 2013 with an integrated luminosity of 25nb${}^{-1}$ and $pp$ data recorded in 2015 with an integrated luminosity of 28pb${}^{-1}$. The $p$+Pb results are compared to $pp$ spectra, presented as a ratio of transverse momentum distributions in the two systems scaled by the number of binary nucleon-nucleon collisions, the nuclear modification factor $R_{p \mathrm{Pb}}$. The study of $R_\mathrm{pPb}$ allows a detailed comparison of the collision systems in different centrality intervals and in a wide range of transverse momentum. It is shown that the nuclear modification factor does not have any significant deviation from unity in the high transverse momentum region.Comment: 4 pages, 4 figures, presented at Hard Probes 201

Studium srážek protonů a těžkých iontů v experimentu ATLAS na LHC

Název práce: Studium srážek protonů a těžkých iontů v experimentu ATLAS na LHC Autor: Mgr. Petr Balek Katedra: Ústav částicové a jaderné fyziky Vedoucí disertační práce: Doc. RNDr. Jiří Dolejší, CSc. Abstrakt: Presentované výsledky jaderného modifikačního faktoru ukazují potla- čení produkce nabitých hadronů ve srážkách těžkých iontů v porovnání s produkcí v proton-protonových srážkách. Data použitá pro tuto práci byla nabrána de- tektorem ATLAS na LHC v letech 2010 a 2011 ve srážkách Pb+Pb o těžišťové energii √ sNN = 2.76 TeV a o celkové integrované luminositě 0.15 nb−1 . Proton- protonová data byla nabrána v letech 2011 a 2013 ve srážkách o těžišťové energii√ s = 2.76 TeV a mají celkovou integrovanou luminositu 4.2 nb−1 . Výsledky jsou presentovány v intervalech příčné hybnosti (0.5 &lt; pT &lt; 150 GeV) a pseudora- pidity (|η| &lt; 2), a též v různých centralitách srážek těžkých iontů. Jaderný modifikační faktor RAA ukazuje jasnou závislost na pT s minimem okolo 7 GeV, avšak nad 60 GeV je téměř nezávislý na pT. Jakožto funkce |η| je RAA ploché v celém intervalu příčné hybnosti. Klíčová slova: detektor ATLAS, srážky těžkých iontů, spektra nabitých hadronů, jaderný modifikační faktor RAATitle: Study of proton-proton and heavy-ion collisions with the ATLAS experi- ment at the LHC Author: Mgr. Petr Balek Department: Institute of Particle and Nuclear Physics Supervisor: Doc. RNDr. Jiří Dolejší, CSc. Abstract: The presented results show a suppression in a production of charged hadrons in heavy-ion collisions with respect to the production measured in proton- proton collisions. Lead-lead data at √ sNN = 2.76 TeV were recorded by the AT- LAS experiment at the LHC in 2010 and 2011 and they have a total integrated luminosity of 0.15 nb−1 , and proton-proton data at √ s = 2.76 TeV were recorded in 2011 and 2013 having an integrated luminosity of 4.2 nb−1 . The results are presented in wide transverse momentum (0.5 &lt; pT &lt; 150 GeV) and pseudorapid- ity (|η| &lt; 2) ranges, and also in different centrality intervals of Pb+Pb collisions. Nuclear modification factor RAA shows a clear pT-dependence with a minimum at around 7 GeV, however above 60 GeV, it reaches a plateau with no significant pT-dependence. As a function of |η|, the RAA is flat over whole pT region. Keywords: ATLAS detector, heavy-ion collisions, charged-hadron spectra, nuclear modification factor RAAÚstav částicové a jaderné fyzikyInstitute of Particle and Nuclear PhysicsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Studium pp a PbPb srážek na LHC

V předložené práci studujeme identifikaci částic za pomoci náboje deponovaného v Pixelovém detektoru (součást detektoru ATLAS), který je schopen vyčítat deponovaný náboj téměř analogově. Nejprve popíšeme závislost deponovaného náboje na jednotkovou délku na hybnosti pomocí řady parametrů, abychom snížili objem zpracovávaných dat. Poté použijeme tyto parametry jakožto vstupní data pro identifikaci částic. Vypracujeme postup identifikace na jehož konci můžeme ve většině případů rozhodnout, zda částice prolétnuvší detektorem byla pion, kaon, nebo proton. Tento postup je snadno zopakovatelný pomocí Athena tool, který byl pro tento účel napsán.In the present work we study the identification of the particle using deposited charge per unit length in the Pixel detector (part of the ATLAS detector) wich can offer an almost analogous read-out of the deposited charge. First, we parametrically describe the dependences of the deposited charge to reduce the volume of the data used in further analysis. Then we use these parameters as an input for particle identification. We elaborate the method of the identification that allows us to say in most of the cases whether the particle passing through the detector was pion, kaon, or proton. This method can be reproduced using Athena tool that has been written.Institute of Particle and Nuclear PhysicsÚstav částicové a jaderné fyzikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Role of electric charge in shaping equilibrium configurations of fluid tori encircling black holes

Astrophysical fluids may acquire non-zero electrical charge because of strong irradiation or charge separation in a magnetic field. In this case, electromagnetic and gravitational forces may act together and produce new equilibrium configurations, which are different from the uncharged ones. Following our previous studies of charged test particles and uncharged perfect fluid tori encircling compact objects, we introduce here a simple test model of a charged perfect fluid torus in strong gravitational and electromagnetic fields. In contrast to ideal magnetohydrodynamic models, we consider here the opposite limit of negligible conductivity, where the charges are tied completely to the moving matter. This is an extreme limiting case which can provide a useful reference against which to compare subsequent more complicated astrophysically-motivated calculations. To clearly demonstrate the features of our model, we construct three-dimensional axisymmetric charged toroidal configurations around Reissner-Nordstr\"om black holes and compare them with equivalent configurations of electrically neutral tori.Comment: 14 pages, 7 figure

Equatorial circular orbits in the Kerr-de Sitter spacetimes

Equatorial motion of test particles in the Kerr-de Sitter spacetimes is considered. Circular orbits are determined, their properties are discussed for both the black-hole and naked-singularity spacetimes, and their relevance for thin accretion discs is established.Comment: 24 pages, 19 figures, REVTeX

Validity and reliability of drought reporters in estimating soil water content and drought impacts in central Europe

Increasing drought is considered one of the major threats associated with climate change in central Europe. To provide an objective, quantitative tool that represents current drought conditions, the Czech Drought Monitor System (CzechDM) was established in 2012. Like other drought monitoring systems worldwide, the CzechDM uses several approaches to provide drought data. However, the CzechDM is unique internationally due to its utilization of a network of voluntary reporters (farmers) who complete a weekly online questionnaire to provide information about soil water content and the impacts of drought on crop yield. In this study, the results from the questionnaires from individual farms were aggregated by district. Reporters’ data were compared and validated with the outputs of the SoilClim model (a core tool of the CzechDM) and with other drought monitoring tools, such as the water balance model, the soil water index and the evaporative stress index. The soil water content estimated by the reporters was significantly correlated (on average r = 0.8) with the outputs of the SoilClim model. Conversely, the correlation between the drought impacts on yield estimated by the reporters and the SoilClim outputs was lower (on average r = 0.4), suggesting that in situ observations by farmers provide additional insights into the occurrence of drought impacts. Importantly, it was found that farmers reported significant drought impacts on yield earlier in the season than any other methods (models or remote sensing). The main findings of this study are that the drought monitoring provided by reporters is a useful and reliable component of the CzechDM. We conclude that weekly reports by farmers represent a significant enhancement to drought monitoring and have potential for use in developing automated approaches that combine in situ, modeling and remote sensing data within a data fusion or machine learning framework

Mitigation efforts will not fully alleviate the increase in water scarcity occurrence probability in wheat-producing areas.

Global warming is expected to increase the frequency and intensity of severe water scarcity (SWS) events, which negatively affect rain-fed crops such as wheat, a key source of calories and protein for humans. Here, we develop a method to simultaneously quantify SWS over the world's entire wheat-growing area and calculate the probabilities of multiple/sequential SWS events for baseline and future climates. Our projections show that, without climate change mitigation (representative concentration pathway 8.5), up to 60% of the current wheat-growing area will face simultaneous SWS events by the end of this century, compared to 15% today. Climate change stabilization in line with the Paris Agreement would substantially reduce the negative effects, but they would still double between 2041 and 2070 compared to current conditions. Future assessments of production shocks in food security should explicitly include the risk of severe, prolonged, and near-simultaneous droughts across key world wheat-producing areas