3,586 research outputs found

    Can the "standard" unitarized Regge models describe the TOTEM data?

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    The standard Regge poles are considered as inputs for two unitarization methods: eikonal and U-matrix. It is shown that only models with three input pomerons and two input odderons can describe the high energy data on pppp and pˉp\bar pp elastic scattering including the new data from Tevatron and LHC. However, it seems that the both considered models (eikonal and U-matrix) require a further modification (e.g., to explore nonlinear reggeon trajectories and/or nonexponential vertex functions) for a more satisfactory description of the data at 19.0 GeVs\leq \sqrt{s}\leq 7 TeV and 0.01 t\leq |t|\leq 14.2 GeV2^{2}.Comment: 11 pages, 7 figures, typos are corrected, minor corrections in the text, No changes in results and conclusion. To appear in EP

    Impact analysis of TOTEM data at the LHC: black disk limit exceeded

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    We discuss the profile of the impact--parameter dependent elastic scattering amplitude. Extraction of impact-parameter dependence from the dataset with inclusion of the experimental data on elastic scattering at the LHC energies helps to reveal the asymptotics of hadron interactions. Analysis of the data clearly indicates that the impact-parameter elastic scattering amplitude exceed the black disk limit at the LHC energy 7TeV and the inelastic overlap function reaches its maximum value at b>0b>0Comment: 5 pages, 5 figure

    Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76$ TeV

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    In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow v2v_2 reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in Pb-Pb collisions at sNN=2.76\sqrt{s_{_{\rm NN}}} =2.76 TeV. The two-particle correlator cos(φαφβ)\langle \cos(\varphi_\alpha - \varphi_\beta) \rangle, calculated for different combinations of charges α\alpha and β\beta, is almost independent of v2v_2 (for a given centrality), while the three-particle correlator cos(φα+φβ2Ψ2)\langle \cos(\varphi_\alpha + \varphi_\beta - 2\Psi_2) \rangle scales almost linearly both with the event v2v_2 and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on v2v_2 points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10-50% centrality interval is found to be 26-33% at 95% confidence level.Comment: 20 pages, 6 captioned figures, 1 tables, authors from page 15, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/382

    Measurement of the production of charm jets tagged with D0^{0} mesons in pp collisions at s\sqrt{s}= 7 TeV

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    The production of charm jets in proton-proton collisions at a center-of-mass energy of s=7\sqrt{s}=7 TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is based on a data sample corresponding to a total integrated luminosity of 6.236.23 nb1{\rm nb}^{-1}, collected using a minimum-bias trigger. Charm jets are identified by the presence of a D0^0 meson among their constituents. The D0^0 mesons are reconstructed from their hadronic decay D0^0\rightarrowKπ+^{-}\pi^{+}. The D0^0-meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-kTk_{\mathrm{T}} algorithm in the jet transverse momentum range 5<pT,jetch<305<p_{\rm{T,jet}}^{\mathrm{ch}}<30 GeV/c{\rm GeV/}c and pseudorapidity ηjet<0.5|\eta_{\rm jet}|<0.5. The fraction of charged jets containing a D0^0-meson increases with pT,jetchp_{\rm{T,jet}}^{\rm{ch}} from 0.042±0.004(stat)±0.006(syst)0.042 \pm 0.004\, \mathrm{(stat)} \pm 0.006\, \mathrm{(syst)} to 0.080±0.009(stat)±0.008(syst)0.080 \pm 0.009\, \rm{(stat)} \pm 0.008\, \rm{(syst)}. The distribution of D0^0-meson tagged jets as a function of the jet momentum fraction carried by the D0^0 meson in the direction of the jet axis (zchz_{||}^{\mathrm{ch}}) is reported for two ranges of jet transverse momenta, 5<pT,jetch<155<p_{\rm{T,jet}}^{\rm{ch}}<15 GeV/c{\rm GeV/}c and 15<pT,jetch<3015<p_{\rm{T,jet}}^{\rm{ch}}<30 GeV/c{\rm GeV/}c in the intervals 0.2<zch<1.00.2<z_{||}^{\rm{ch}}<1.0 and 0.4<zch<1.00.4<z_{||}^{\rm{ch}}<1.0, respectively. The data are compared with results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and with a Next-to-Leading-Order perturbative Quantum Chromodynamics calculation, obtained with the POWHEG method and interfaced with PYTHIA 6 for the generation of the parton shower, fragmentation, hadronisation and underlying event.Comment: 29 pages, 8 captioned figures, 3 tables, authors from page 24, published version, figures at http://alice-publications.web.cern.ch/node/525

    The politicisation of evaluation: constructing and contesting EU policy performance

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    Although systematic policy evaluation has been conducted for decades and has been growing strongly within the European Union (EU) institutions and in the member states, it remains largely underexplored in political science literatures. Extant work in political science and public policy typically focuses on elements such as agenda setting, policy shaping, decision making, or implementation rather than evaluation. Although individual pieces of research on evaluation in the EU have started to emerge, most often regarding policy “effectiveness” (one criterion among many in evaluation), a more structured approach is currently missing. This special issue aims to address this gap in political science by focusing on four key focal points: evaluation institutions (including rules and cultures), evaluation actors and interests (including competencies, power, roles and tasks), evaluation design (including research methods and theories, and their impact on policy design and legislation), and finally, evaluation purpose and use (including the relationships between discourse and scientific evidence, political attitudes and strategic use). The special issue considers how each of these elements contributes to an evolving governance system in the EU, where evaluation is playing an increasingly important role in decision making
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