Wed·Aug 13, 2014Wednesday·August 13, 2014

1. 01*

   Collective Expansion at the LHC: selected ALICE anisotropic flow measurements

   Raimond Snellings🇳🇱

   The collective expansion of matter created in collisions of heavy-ions, ranging from collision energies of tens of MeV to a few TeV per nucleon pair, proved to be one of the best probes to study the detailed properties of these unknown states of matter. Collective expansion originates from the initial pressure gradients in the created hot and dense matter. These pressure gradients transform the initial spatial deformations and inhomogeneities of the created matter into momentum anisotropies of the final state particle production, which we call anisotropic flow. These momentum anisotropies are experimentally characterised by so-called flow harmonics. In this paper I review ALICE measurements of the flow harmonics at the CERN Large Hadron Collider and discuss some of the open questions.

   nucl-exnucl-thJ.Phys.G(2014)·36 citations
2. 02*

   Improved version of the PHOBOS Glauber Monte Carlo

   C. Loizides (LBNL)🇺🇸 · J. Nagle (Colorado U.)🇺🇸 · P. Steinberg (BNL)🇺🇸

   Glauber models are used to calculate geometric quantities in the initial state of heavy ion collisions, such as impact parameter, number of participating nucleons and initial eccentricity. Experimental heavy-ion collaboration, in particular at RHIC and LHC, use Glauber Model calculations for various geometric observables. In this document, we describe the assumptions inherent to the approach, and provide an updated implementation (v2) of the Monte Carlo based Glauber Model calculation, which originally was used by the PHOBOS collaboration. The main improvement w.r.t. the earlier version (arXiv:0805.4411) are the inclusion of Tritium, Helium-3, and Uranium, as well as the treatment of deformed nuclei and Glauber-Gribov fluctuations of the proton in p+A collisions. A users' guide (updated to reflect changes in v2) is provided for running various calculations.

   nucl-exnucl-thSoftwareX(2015)·254 citations
3. 03*

   Neutral meson production in pp and Pb-Pb collisions measured by ALICE at the LHC

   A. Marin (for the ALICE Collaboration)🇩🇪

   The midrapidity ${\pi }^0$ nuclear modification factor, $R_{\mathrm{AA}}$, at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV in 6 centrality classes as well as the corresponding ${\pi }^0$ invariant yields in Pb-Pb and in pp collisions are presented. The transverse momentum range covered is 0.6 (0.4) GeV/$c$ $<p_{\mathrm{T}}<$ 12 (10) GeV/$c$ for Pb-Pb (pp) collisions. A suppression of neutral pions increasing with centrality is observed. The yield of charged particles associated with a high $p_{\mathrm{T}}$ neutral pion trigger (8 GeV/$c$ $<p_{\mathrm{T}}<$ 16 GeV/$c$) is measured in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV. The conditional per-trigger yield modification factor in the near and away side is in agreement with the measured one for charged particles.

   nucl-exNPA(2014)·3 citations
4. 04*

   Towards a data-driven analysis of hadronic light-by-light scattering

   Gilberto Colangelo🇨🇭 · Martin Hoferichter🇨🇭 · Bastian Kubis🇩🇪 · Massimiliano Procura🇨🇭 · Peter Stoffer🇨🇭

   The hadronic light-by-light contribution to the anomalous magnetic moment of the muon was recently analyzed in the framework of dispersion theory, providing a systematic formalism where all input quantities are expressed in terms of on-shell form factors and scattering amplitudes that are in principle accessible in experiment. We briefly review the main ideas behind this framework and discuss the various experimental ingredients needed for the evaluation of one- and two-pion intermediate states. In particular, we identify processes that in the absence of data for doubly-virtual pion-photon interactions can help constrain parameters in the dispersive reconstruction of the relevant input quantities, the pion transition form factor and the helicity partial waves for ${\gamma }^{\ast }{\gamma }^{\ast }\to \pi \pi$.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2014)·258 citations
5. 05*

   ${\mathrm{K}}_{\mathrm{S}}^0$ and $\Lambda$ Production in Charged Particle Jets in p--Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with ALICE

   Xiaoming Zhang (for the ALICE Collaboration)🇺🇸

   We study the production of ${\mathrm{K}}_{\mathrm{S}}^0$ mesons and $\Lambda$ baryons in jets in p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with ALICE at the LHC. The $p_{\mathrm{T}}$-differential density of the particles produced in jets is compared to the inclusive distributions and the $\Lambda /{\mathrm{K}}_{\mathrm{S}}^0$ ratio is reported in bins of multiplicity of the collisions. The hard scatterings are selected on an event-by-event basis using the anti-$k_{\mathrm{T}}$ clustering algorithm with resolution parameter $R=0.2,0.3$ and $0.4$, reconstructed from charged particles with a minimum $p_{\mathrm{T},\mathrm{jet}}$ of $10$ (or $20$) GeV/$c$.

   ↳ hep-exnucl-exNPA(2014)·15 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.