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Nuclear Theory·nucl-th

Monday·April 27, 2015

10 papers—3 primary·7 cross-listed

All10Primary3Cross-lists7
  1. 04

    [Submitted on 23 Apr 2015] (cross-list from hep-ph)

    Axial anomaly effects in finite isospin PT in a magnetic field

    Prabal Adhikari🇺🇸

    In this paper, we consider finite isospin chiral perturbation theory including the effects of the axial anomaly (through the Wess-Zumino-Witten term) in a strong magnetic field. We firstly prove that in a strong external magnetic field () or more precisely the Schwinger limit, where photon back-reactions are suppressed, only neutral pions can condense and the condensation of charged pions is forbidden. Secondly, we find that the domain wall is an example of a phase that can exist in a strong magnetic field and suggest the existence of a new phase transition line from the normal vacuum state to the domain wall state. This phase transition exists for non-zero pion masses if the baryon chemical potential exceeds a critical value . The phase transition line persists away from the Schwinger limit when the photons can back-react to the external magnetic field.

    Comments:
    7 pages, 3 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1504.06349 [pdf]
    4 citations
  2. 05

    [Submitted on 23 Apr 2015] (cross-list from hep-ph)

    Small- evolution of jet quenching parameter

    Raktim Abir🇺🇸

    Concept of transverse deflection probability of a parton that travels through strongly interacting medium, recently introduced by D'Eramo, Liu and Rajagopal, have been used to derive high energy evolution equation for the jet quenching parameter in stochastic multiple scatterings regime. Jet quenching parameter, , appears to evolve with , with an exponent , which is slightly less than that of where is the gluon distribution function.

    Comments:
    Version accepted in Phys. Lett. B
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1504.06356 [pdf]
    PLB(2015)·11 citations
  3. 06

    [Submitted on 24 Apr 2015] (cross-list from hep-ph)

    A compression algorithm for the combination of PDF sets

    Stefano Carrazza🇮🇹 · Jose I. Latorre🇪🇸 · Juan Rojo🇬🇧 · Graeme Watt🇬🇧

    The current PDF4LHC recommendation to estimate uncertainties due to parton distribution functions (PDFs) in theoretical predictions for LHC processes involves the combination of separate predictions computed using PDF sets from different groups, each of which comprises a relatively large number of either Hessian eigenvectors or Monte Carlo (MC) replicas. While many fixed-order and parton shower programs allow the evaluation of PDF uncertainties for a single PDF set at no additional CPU cost, this feature is not universal, and moreover the a posteriori combination of the predictions using at least three different PDF sets is still required. In this work, we present a strategy for the statistical combination of individual PDF sets, based on the MC representation of Hessian sets, followed by a compression algorithm for the reduction of the number of MC replicas. We illustrate our strategy with the combination and compression of the recent NNPDF3.0, CT14 and MMHT14 NNLO PDF sets. The resulting Compressed Monte Carlo PDF (CMC-PDF) sets are validated at the level of parton luminosities and LHC inclusive cross-sections and differential distributions. We determine that around 100 replicas provide an adequate representation of the probability distribution for the original combined PDF set, suitable for general applications to LHC phenomenology.

    Comments:
    45 pages, 24 figures, version accepted for publication in the European Journal of Physics C
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1504.06469 [pdf]
    EPJC(2015)·108 citations
  4. 07

    [Submitted on 24 Apr 2015] (cross-list from hep-ph)

    A possible evidence of the hadron-quark-gluon mixed phase formation in nuclear collisions

    V.A. Kizka🇺🇦 · V.S.Trubnikov🇺🇦 · K.A. Bugaev🇺🇦 · D.R. Oliinychenko🇺🇦

    The performed systematic meta-analysis of the quality of data description (QDD) of existing event generators of nucleus-nucleus collisions allows us to extract a very important physical information. Our meta-analysis is dealing with the results of 10 event generators which describe data measured in the range of center of mass collision energies from 3.1 GeV to 17.3 GeV. It considers the mean deviation squared per number of experimental points obtained by these event generators, i.e. the QDD, as the results of independent meta-measurements. These generators and their QDDs are divided in two groups. The first group includes the generators which account for the quark-gluon plasma formation during nuclear collisions (QGP models), while the second group includes the generators which do not assume the QGP formation in such collisions (hadron gas models). Comparing the QDD of more than a hundred of different data sets of strange hadrons by two groups of models, we found two regions of the equal quality description of data which are located at the center of mass collision energies 4.4-4.87 GeV and 10.8-12 GeV. At the collision energies below 4.4 GeV the hadron gas models describe data much better than the QGP one and, hence, we associate this region with hadron phase. At the collision energies between 5 GeV and 10.8 GeV and above 12 GeV we found that QGP models describe data essentially better than the hadron gas ones and, hence, these regions we associate with the quark-gluon phase. As a result, the collision energy regions 4.4-4.87 GeV and 10.8-12 GeV we interpret as the energies of the hadron-quark-gluon mixed phase formation. Based on these findings we argue that the most probable energy range of the QCD phase diagram (tri)critical endpoint is 12-14 GeV.

    Comments:
    33 pages, 6 figures and 11 tables
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1504.06483 [pdf]
    8 citations
  5. 08

    [Submitted on 24 Apr 2015] (cross-list from hep-ex)

    CMS physics highlights in the LHC Run 1

    David d'Enterria (for the CMS Collaboration)🇨🇭

    The main physics results obtained by the CMS experiment during the first three years of operation of the CERN Large Hadron Collider (2010--2013, aka. Run 1) are summarized. The advances in our understanding of the fundamental particles and their interactions are succinctly reviewed under the following physics topics: (i) Quantum Chromodynamics, (ii) Quark Gluon Plasma, (iii) Electroweak interaction, (iv) Top quark, (v) Higgs boson, (vi) Flavour, (vii) Supersymmetry, (viii) Dark Matter, and (ix) other searches of physics beyond the Standard Model.

    Comments:
    14 pages, 9 figures. Proceedings Bormio'2015. PoS, to appear. Typo corrected
    Subjects:
    High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1504.06519 [pdf]
    PoS(2015)·5 citations
  6. 09

    [Submitted on 24 Apr 2015] (cross-list from hep-ph)

    Double-quarkonium production at a fixed-target experiment at the LHC (AFTER@LHC)

    Jean-Philippe Lansberg🇫🇷 · Hua-Sheng Shao🇨🇭

    We present predictions for double-quarkonium production in the kinematical region relevant for the proposed fixed-target experiment using the LHC beams (dubbed as AFTER@LHC). These include all spin-triplet S -wave charmonium and bottomonium pairs, i.e. Psi(n_1S) + Psi(n_2S), Psi(n_1S) + Upsilon(m_1S) and Upsilon(m_1S) + Upsilon(m_2S ) with n_1,n_2 = 1,2 and m_1,m_2 = 1,2,3. We calculate the contributions from double-parton scatterings and single-parton scatterings. With an integrated luminosity of 20 fb-1 to be collected at AFTER@LHC, we find that the yields for double-charmonium production are large enough for differential distribution measurements. We discuss some differential distributions for J/Psi + J/Psi production, which can help to study the physics of double-parton and single-parton scatterings in a new energy range and which might also be sensitive to double intrinsic c-bar(c) coalescence at large negative Feynman x.

    Comments:
    Latex, 24 pages, 23 figures, 12 tables. v2: published version: complete analysis of the colour-octet contributions for psi+Y production added and the impact of the NLO corrections discussed
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1504.06531 [pdf]
    NPB(2015)·68 citations
  7. 10

    [Submitted on 24 Apr 2015] (cross-list from hep-ph)

    Quark and Glue Components of the Proton Spin from Lattice Calculation

    Keh-Fei Liu🇺🇸

    The status of lattice calculations of the quark spin, the quark orbital angular momentum, the glue angular momentum and glue spin in the nucleon is summarized. The quark spin calculation is recently carried out from the anomalous Ward identity with chiral fermions and is found to be small mainly due to the large negative anomaly term which is believed to be the source of the `proton spin crisis'. We also present the first calculation of the glue spin at finite nucleon momenta.

    Comments:
    Plenary talk presented at SPIN2014, the 21st International Symposium on Spin Physics, 16 pages, 6 figures, references added and typos corrected. arXiv admin note: text overlap with arXiv:1504.04052
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1504.06601 [pdf]
    Int.J.Mod.Phys.Conf.Ser.(2016)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE