Fri·Sep 23, 2016Friday·September 23, 2016

1. 01*

   Evolution of the longitudinal and azimuthal structure of the near-side jet peak in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV

   ALICE Collaboration

   In two-particle angular correlation measurements, jets give rise to a near-side peak, formed by particles associated to a higher $p_{\mathrm{T}}$ trigger particle. Measurements of these correlations as a function of pseudorapidity ($\Delta \eta$) and azimuthal ($\Delta \phi$) differences are used to extract the centrality and $p_{\mathrm{T}}$ dependence of the shape of the near-side peak in the $p_{\mathrm{T}}$ range $1<p_{\mathrm{T}}<$ 8 GeV/c in Pb-Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. A combined fit of the near-side peak and long-range correlations is applied to the data and the peak shape is quantified by the variance of the distributions. While the width of the peak in the $\Delta \phi$ direction is almost independent of centrality, a significant broadening in the $\Delta \eta$ direction is found from peripheral to central collisions. This feature is prominent for the low $p_{\mathrm{T}}$ region and vanishes above 4 GeV/c. The widths measured in peripheral collisions are equal to those in pp in the $\Delta \phi$ direction and above 3 GeV/c in the $\Delta \eta$ direction. Furthermore, for the 10\% most central collisions and $1<p_{\mathrm{T},\mathrm{assoc}}<$ 2 GeV/c, $1<p_{\mathrm{T},\mathrm{trig}}<$ 3 GeV/c a departure from a Gaussian shape is found: a depletion develops around the centre of the peak. The results are compared to AMPT model simulations as well as other theoretical calculations indicating that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.

   nucl-exhep-exPRC(2017)·27 citations
2. 02*

   Charmonium production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 and 5.02 TeV with ALICE

   Biswarup Paul (for the ALICE Collaboration)🇮🇹

   The production of charmonium states, J/$\psi$ and $\psi$(2S), in heavy-ion collisions, is an important probe to investigate the formation of a plasma of quarks and gluons (QGP). In a hot and deconfined medium, quarkonium production is, indeed, expected to be significantly modified, with respect to the pp yields, due to a balance of color screening and charm-quark recombination mechanisms. The ALICE Collaboration at the LHC has measured charmonium production in Pb-Pb collisions at ${\sqrt{s}}_{\mathrm{NN}}=$ 2.76 and 5.02 TeV. The nuclear modification factor of inclusive J/$\psi$, evaluated at forward ($-4<\eta <-2.5$) rapidity, is measured as a function of the centrality of the collision and of the J/$\psi$ kinematic variables as transverse momentum and rapidity. In this article, we report on the new J/$\psi$ results, obtained at forward rapidity, at ${\sqrt{s}}_{\mathrm{NN}}=5.02$ TeV. These new results are compared to the J/$\psi$ nuclear modification factor obtained at ${\sqrt{s}}_{\mathrm{NN}}=$ 2.76 TeV and to the available theoretical predictions.

   nucl-exJ.Phys.Conf.Ser.(2017)·1 citation
3. 03*

   Double polarisation experiments in meson photoproduction

   Jan Hartmann (for the CBELSA/TAPS Collaboration)🇩🇪

   One of the remaining challenges within the standard model is to gain a good understanding of QCD in the non-perturbative regime. A key step towards this aim is baryon spectroscopy, investigating the spectrum and the properties of baryon resonances. To gain access to resonances with small $\pi N$ partial width, photoproduction experiments provide essential information. Partial wave analyses need to be performed to extract the contributing resonances. Here, a complete experiment is required to unambiguously determine the contributing amplitudes. This involves the measurement of carefully chosen single and double polarisation observables. In a joint endeavour by MAMI, ELSA, and Jefferson Laboratory, a new generation of experiments with polarised beams, polarised proton and neutron targets, and $4\pi$ particle detectors have been performed in recent years. Many results of unprecedented quality were recently published by all three experiments, and included by the various partial wave analysis groups in their analyses, leading to substantial improvements, e.g. a more precise determination of resonance parameters. An overview of recent results is given, with an emphasis on results from the CBELSA/TAPS experiment, and their impact on our understanding of the nucleon excitation spectrum is discussed.

   nucl-exEPJ Web Conf.(2016)·1 citation
4. 04*

   On the pi pi continuum in the nucleon form factors and the proton radius puzzle

   M. Hoferichter🇺🇸 · B. Kubis🇩🇪 · J. Ruiz de Elvira🇩🇪 · H.-W. Hammer🇩🇪 · U.-G. Meißner🇩🇪

   We present an improved determination of the $\pi \pi$ continuum contribution to the isovector spectral functions of the nucleon electromagnetic form factors. Our analysis includes the most up-to-date results for the $\pi \pi \to \bar{N}N$ partial waves extracted from Roy-Steiner equations, consistent input for the pion vector form factor, and a thorough discussion of isospin-violating effects and uncertainty estimates. As an application, we consider the $\pi \pi$ contribution to the isovector electric and magnetic radii by means of sum rules, which, in combination with the accurately known neutron electric radius, are found to slightly prefer a small proton charge radius.

   ↳ hep-phhep-latnucl-exnucl-th+1EPJA(2016)·107 citations
5. 05*

   The Validity of the Weizsacker-Williams Approximation and the Analysis of Beam Dump Experiments: Production of a New Scalar Boson

   Yu-Sheng Liu🇺🇸 · David McKeen🇺🇸 · Gerald A. Miller🇺🇸

   Beam dump experiments have been used to search for new particles with null results interpreted in terms of limits on masses $m_{\varphi }$ and coupling constants $ϵ$. However these limits have been obtained by using approximations [including the Weizsäcker-Williams (WW) approximation] or Monte-Carlo simulations. We display methods, using a new scalar boson as an example, to obtain the cross section and the resulting particle production numbers without using approximations or Monte-Carlo simulations. We show that the approximations cannot be used to obtain accurate values of cross sections. The corresponding exclusion plots differ by substantial amounts when seen on a linear scale. In the event of a discovery, we generate pseudodata (assuming given values of $m_{\varphi }$ and $ϵ$) in the currently allowed regions of parameter space. The use of approximations to analyze the pseudodata for the future experiments is shown to lead to considerable errors in determining the parameters. Furthermore, a new region of parameter space can be explored without using one of the common approximations, $m_{\varphi }\gg m_e$. Our method can be used as a consistency check for Monte-Carlo simulations.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2017)·73 citations
6. 06*

   Strangeness production in p-Pb and Pb-Pb collisions with ALICE at LHC

   Domenico Colella (for the ALICE Collaboration)🇨🇭

   The main goal of the ALICE experiment is to study the properties of the hot and dense medium created in ultra-relativistic heavy-ion collisions. The measurement of the (multi-)strange particles is an important tool to understand particle production mechanisms and the dynamics of the quark-gluon plasma (QGP). We report on the production of K${}_S^0$, $\Lambda$($\overline{\Lambda }$), ${\Xi }^{-}$(${\overline{\Xi }}^{+}$) and ${\Omega }^{-}$(${\overline{\Omega }}^{+}$) in proton-lead (p-Pb) collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV and lead-lead (Pb-Pb) collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV measured by ALICE at the LHC. The comparison of the hyperon-to-pion ratios in the two colliding systems may provide insight into strangeness production mechanisms, while the comparison of the nuclear modification factors helps to determine the contribution of initial state effects and the suppression from strange quark energy loss in nuclear matter.

   ↳ hep-exnucl-exJ.Phys.Conf.Ser.(2017)·2 citations
7. 07*

   Measurement of the ${}^{20-22}$Ne ${}^3$P${}_2$-${}^3$D${}_3$ transition isotope shift using a single, phase modulated laser beam

   Ben Ohayon🇮🇱 · Gal Gumpel · Guy Ron🇮🇱

   We develop a simple technique to accurately measure frequency differences between far lying resonances in a spectroscopy signal using a single laser. This technique was used to measure the isotope shift of the cooling transition of metastable neon for the result of $1626.264(79)$ MHz. The most accurate determination of this value to date.

   ↳ physics.opticsnucl-exphysics.atom-phJ.Phys.B(2017)·1 citation

* 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.