Nuclear Theory·nucl-th

Wednesday·February 11, 2015

12 papers—7 primary·5 cross-listed

08
[Submitted on 9 Feb 2015] (cross-list from nucl-ex)
The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC
Yasuyuki Akiba (RIKEN)🇯🇵 · Aaron Angerami (Columbia University)🇺🇸 · Helen Caines (Yale University)🇺🇸 · Anthony Frawley (Florida State University)🇺🇸 · Ulrich Heinz (Ohio State University)🇺🇸 · Barbara Jacak (University of California, Berkeley)🇺🇸 · Jiangyong Jia (Stony Brook University)🇺🇸 · Tuomas Lappi (Jyväskylä University)🇫🇮 · Wei Li (Rice University)🇺🇸 · Abhijit Majumder (Wayne State University)🇺🇸 · David Morrison (Brookhaven National Laboratory)🇺🇸 · Mateusz Ploskon (Lawrence Berkeley National Laboratory)🇺🇸 and 8 other authors
The past decade has seen huge advances in experimental measurements made in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and more recently at the Large Hadron Collider (LHC). These new data, in combination with theoretical advances from calculations made in a variety of frameworks, have led to a broad and deep knowledge of the properties of thermal QCD matter. Increasingly quantitative descriptions of the quark-gluon plasma (QGP) created in these collisions have established that the QGP is a strongly coupled liquid with the lowest value of specific viscosity ever measured. However, much remains to be learned about the precise nature of the initial state from which this liquid forms, how its properties vary across its phase diagram and how, at a microscopic level, the collective properties of this liquid emerge from the interactions among the individual quarks and gluons that must be visible if the liquid is probed with sufficiently high resolution. This white paper, prepared by the Hot QCD Writing Group as part of the U.S. Long Range Plan for Nuclear Physics, reviews the recent progress in the field of hot QCD and outlines the scientific opportunities in the next decade for resolving the outstanding issues in the field.
Comments:
110 pages, 33 figures, 429 references. Prepared as part of the U.S. Long-Range Plan for Nuclear Physics
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1502.02730 [pdf]
162 citations
09
[Submitted on 10 Feb 2015] (cross-list from nucl-ex)
Flavor decomposition of the nucleon electromagnetic form factors at low $Q^{2}$
I. A. Qattan🇦🇪 · J. Arrington🇺🇸 · A. Alsaad🇯🇴
The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors. These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions. In this work, we extract the proton and neutron form factors from world's data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we separate the up- and down-quark contributions to the proton form factors. We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parameterization of the neutron form factor data and uncertainties to separate the up- and down-quark contributions to the proton's charge and magnetic form factors. The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavor-separated form factors are extracted and compared to models of the nucleon structure. With the inclusion of the precise new data, the extracted TPE contributions show a clear change ofsign at low $Q^{2}$ , necessary to explain the high- $Q^{2}$ form factor discrepancy while being consistent with the known $Q^{2} \to 0$ limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavor-separated contributions. We also observe that the RMS radius of both the up- and down-quark distributions are smaller than the RMS charge radius of the proton.
Comments:
11 pages, 8 figures, Submitted to Phys. Rev. C
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1502.02872 [pdf]
PRC(2015)·32 citations
10
[Submitted on 10 Feb 2015] (cross-list from astro-ph.HE)
Magnetar superconductivity versus magnetism: neutrino cooling processes
Monika Sinha (ITP, Frankfurt) · Armen Sedrakian (ITP, Frankfurt)
We describe the microphysics, phenomenology, and astrophysical implication of a $B$ -field induced unpairing effect that may occur in magnetars, if the local $B$ -field in the core of a magnetar exceeds a critical value $H_{c 2}$ . Using the Ginzburg-Landau theory of superconductivity, we derive the $H_{c 2}$ field for proton condensate taking into the correction ( $\leq 30%$ ) which arises from its coupling to the background neutron condensate. The density dependence of pairing of proton condensate implies that $H_{c 2}$ is maximal at the crust-core interface and decreases towards the center of the star. As a consequence, magnetar cores with homogenous constant fields will be partially superconducting for "medium-field" magnetars ( $1 0^{15} \leq B \leq 5 \times 1 0^{16}$ G) whereas "strong-field" magnetars ( $B > 5 \times 1 0^{16}$ G) will be void of superconductivity. The neutrino emissivity of a magnetar's core changes in a twofold manner: (i)~the $B$ -field assisted direct Urca process is enhanced by orders of magnitude, because of the unpairing effect in regions where $B \geq H_{c 2}$ ; (ii)~the Cooper-pair breaking processes on protons vanish in these regions and the overall emissivity by the pair-breaking processes is reduced by a factor of only a few.
Comments:
v2: minor changes, matches published version; v1: 10 RevTex two-column pages, 7 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1502.02979 [pdf]
PRC(2015)·51 citations
11
[Submitted on 10 Feb 2015] (cross-list from hep-ph)
Kinematic biases on centrality selection of jet events in pPb collisions at the LHC
Nestor Armesto🇪🇸 · Doga Can Gulhan🇺🇸 · Jose Guilherme Milhano🇵🇹
Centrality selection has been observed to have a large effect on jet observables in pPb collisions at the Large Hadron Collider, stronger than that predicted by the nuclear modification of parton densities. We study to which extent simple considerations of energy-momentum conservation between the hard process and the underlying event affect jets observables in such collisions. We develop a simplistic approach that considers first the production of jets in a pp collision as described by PYTHIA. From each pp collision, the value of the energy of the parton from the proton participating in the hard scattering is extracted. Then, the underlying event is generated simulating a pPb collision through HIJING, but with the energy of the proton decreased according to the value extracted in the previous step, and both collisions are superimposed. This model is able to capture the bulk of the centrality effect for central to semicentral collisions, for the two available sets of data: dijets from the CMS Collaboration and single jets from the ATLAS Collaboration. As expected, the model fails for peripheral collisions where very few nucleons from Pb participate.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1502.02986 [pdf]
PLB(2015)·41 citations
12
[Submitted on 10 Feb 2015] (cross-list from astro-ph.HE)
Cooling of neutron stars and hybrid stars with a stiff hadronic EoS
H. Grigorian · D. Blaschke · D. N. Voskresensky
Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the high masses of the pulsars PSR J1614-2230 and PSR J0348-0432 on the one hand, and of the low masses for PSR J0737-3039B and the companion of PSR J1756-2251 on the other, provide independent proof for the existence of neutron stars with masses in a broad range from $\sim 1.2$ to 2 $M_{⊙}$ . The values $M > 2 M_{⊙}$ call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about $2.4 M_{⊙}$ would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner core. Without readjustment of cooling inputs the mass range required to cover all cooling data for the stiff DD2 equation of state should include masses of $2.426 M_{⊙}$ for describing the fast cooling of CasA while the existence of a quark matter core accelerates the cooling so that CasA cooling data are described with a hybrid star of mass $1.674 M_{⊙}$ .
Comments:
12 pages, 3 figures, typos corrected
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1502.03080 [pdf]
Phys.Part.Nucl.(2015)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE

The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC

Flavor decomposition of the nucleon electromagnetic form factors at low Q2

Magnetar superconductivity versus magnetism: neutrino cooling processes

Kinematic biases on centrality selection of jet events in pPb collisions at the LHC

Cooling of neutron stars and hybrid stars with a stiff hadronic EoS

Affiliations

Flavor decomposition of the nucleon electromagnetic form factors at low $Q^{2}$