Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Calculation and hardware base for geomonitoring the state of the array by registering natural electromagnetic radiation

Актуальность исследования обусловлена необходимостью разработки перспективного метода прогноза удароопасности массива по параметрам естественного электромагнитного излучения, возникающего при трещинообразовании в горных породах. Существующие методики интерпретации данных геофизического мониторинга не учитывают связи параметров электромагнитного излучения с основными геомеханическими критериями, определяющими вероятность проявления горного удара: концентрацией напряжений в массиве и расположением их максимума. Цель: установление рациональных параметров для дальнейшего экспериментального обоснования критериев локального прогноза удароопасности методом регистрации электромагнитного излучения на базе экспериментальной аппаратуры «Ангел-М», разработанной в МНЦ ВНИМИ. Объекты: массивы горных пород, склонных к динамическим проявлениям горного давления на горнодобывающих предприятиях Кузбасса (шахта «Таштагольская», глубина 700 м; шахта «Зиминка», глубина 300 м; шахта № 12, глубина 340 м). Методы: анализ физических механизмов электризации пород в поле механических напряжений на основе фундаментальных закономерностей физики твердого тела и электродинамики, экспериментально-теоретические основы метода регистрации электромагнитного излучения в лабораторных и натурных условиях. Результаты. Рассмотрены физические предпосылки возникновения электромагнитного излучения при разрушении твердых тел и горных пород, основные теоретические и экспериментальные результаты, полученные в данной области ведущими научными коллективами. Изложена методика расчета амплитудно-частотной характеристики электромагнитного излучения при трещинообразовании в горных породах, включающая решение волнового уравнения, прямое и обратное преобразование Фурье, эффекты суперпозиции систем трещин и затухания электромагнитного излучения в проводящей среде. Обоснован перспективный метод прогноза удароопасности массива методом регистрации электромагнитного излучения на основе комплексных критериев, косвенно взаимосвязанных с фундаментальными геомеханическими параметрами массива (концентраций напряжений в точке их максимума и расстоянием от контура до этой точки): средняя амплитуда импульсов за интервал регистрации и крутизна графика скорости нарастания импульсов.The relevance of the study is caused by the need to develop a promising method for predicting the impact hazard of the array according to the parameters of natural electromagnetic radiation that occurs during cracking in rocks. The existing methods of interpretation of geophysical monitoring data do not take into account the relationship of electromagnetic radiation parameters with the main geomechanical criteria determining the probability of a mountain impact: the concentration of stresses in the array and the location of their maximum. The main aim is to establish rational parameters for further experimental substantiation of the criteria for local prediction of impact hazard by the electromagnetic radiation registration method based on the experimental equipment «Angel-M» developed at the MNC. Objects: massifs of rocks prone to dynamic manifestations of mountain pressure at Kuzbass mining enterprises (Tashtagolskaya mine, depth 700 m; Ziminka mine, depth 300 m; mine no. 12, depth 340 m). Methods: analysis of the physical mechanisms of electrification of rocks in the field of mechanical stresses based on the fundamental laws of solid state physics and electrodynamics, experimental and theoretical foundations of the method of recording electromagnetic radiation in laboratory and field conditions. Results. The paper considers the physical prerequisites for electromagnetic radiation occurrence during the destruction of solids and rocks, the main theoretical and experimental results obtained in this field by leading scientific teams. A method for calculating the amplitude frequency response of electromagnetic radiation during fracturing in rocks is described, including the solution of the wave equation, the forward and inverse Fourier transform, the effects of superposition of crack systems and electromagnetic radiation attenuation in a conductive medium. A promising method for predicting the impact hazard of an array by the electromagnetic radiation registration method is substantiated on the basis of complex criteria indirectly interrelated with the fundamental geomechanical parameters of the array (stress concentrations at their maximum point and the distance from the contour to this point): the average amplitude of pulses during the registration interval and the steepness of the pulse rate graph

生産增加と貨幣需要

We report on two-particle charge-dependent cor- relations in pp, p\u2013Pb, and Pb\u2013Pb collisions as a function of the pseudorapidity and azimuthal angle difference, \u3b7 and \u3c6 respectively. These correlations are studied using the balance function that probes the charge creation time and the develop- ment of collectivity in the produced system. The dependence of the balance function on the event multiplicity as well as on the trigger and associated particle transverse momentum ( pT ) in pp, p\u2013Pb, and Pb\u2013Pb collisions at 1asNN = 7, 5.02, and 2.76 TeV, respectively, are presented. In the low transverse momentum region, for 0.2 < pT < 2.0 GeV/c, the balance function becomes narrower in both \u3b7 and \u3c6 directions in all three systems for events with higher multiplicity. The experimental findings favor models that either incorporate some collective behavior (e.g. AMPT) or different mecha- nisms that lead to effects that resemble collective behavior (e.g. PYTHIA8 with color reconnection). For higher values of transverse momenta the balance function becomes even narrower but exhibits no multiplicity dependence, indicating that the observed narrowing with increasing multiplicity at low pT is a feature of bulk particle production

Charged–particle multiplicities in proton–proton collisions at s=\sqrt{s}= 0.9 to 8 TeV, with ALICE at the LHC

The ALICE Collaboration has carried out a detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton-proton collisions, at $\sqrt{s} =$ 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range $|\eta| < 2$. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval $|\eta| < 1$. The use of an improved track-counting algorithm combined with ALICE’s measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapidity intervals $|\eta| < 0.5$, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS.A detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton–proton collisions, at $\sqrt{s} =$ 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range $|\eta |<2$ , was carried out using the ALICE detector. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval $|\eta |<1$ . The use of an improved track-counting algorithm combined with ALICE’s measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapidity intervals $|\eta |<$ 0.5, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS.A detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton-proton collisions, at $\sqrt{s} =$ 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range $|\eta|<2$, was carried out using the ALICE detector. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval $|\eta|<1$. The use of an improved track-counting algorithm combined with ALICE's measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapidity intervals $|\eta|<$ 0.5, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS

Measurement of an excess in the yield of J/ψJ/\psi at very low pTp_{\rm T} in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

We report on the first measurement of an excess in the yield of J/ψ at very low transverse momentum (pT<0.3 GeV/c) in peripheral hadronic Pb-Pb collisions at sNN=2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/ψ in the rapidity range 2.5<y<4 reaches about 7 (2) in the pT range 0–0.3 GeV/c in the 70%–90% (50%–70%) centrality class. The J/ψ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/ψ is the underlying physics mechanism. If confirmed, the observation of J/ψ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the quark-gluon plasma

Measurement of electrons from beauty-hadron decays in p-Pb collisions at sNN=5.02 \sqrt{s_{\mathrm{NN}}}=5.02 TeV and Pb-Pb collisions at sNN=2.76 \sqrt{s_{\mathrm{NN}}}=2.76 TeV

The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1<p$_{T}$ < 8 GeV/c in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and in 1.3 < p$_{T}$ < 8 GeV/c in the 20% most central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. The pp reference spectra at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and $\sqrt{s}=2.76$ TeV, needed for the calculation of the nuclear modification factors R$_{pPb}$ and R$_{PbPb}$, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at $\sqrt{s}=7$ TeV. In the p$_{T}$ interval 3 < p$_{T}$ < 8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower p$_{T}$, the R$_{PbPb}$ values increase with large systematic uncertainties. The R$_{pPb}$ is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured R$_{pPb}$ and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of R$_{PbPb}$ below unity at high p$_{T}$ may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions