Nuclear Theory·nucl-th

Friday·March 13, 2015

10 papers—4 primary·6 cross-listed

01
Quantal description of nucleon exchange in stochastic mean-field approach
S. Ayik · O. Yilmaz · B. Yilmaz · A. S. Umar · A. Gokalp · G. Turan · D. Lacroix
Nucleon exchange mechanism is investigated in central collisions of symmetric heavy-ions in the basis of the stochastic mean-field approach. Quantal diffusion coefficients for nucleon exchange are calculated by including non-Markovian effects and shell structure. Variances of fragment mass distributions are calculated in central collisions of $^{40}$ Ca + $^{40}$ Ca, $^{48}$ Ca + $^{48}$ Ca and $^{56}$ Ni + $^{56}$ Ni systems.
nucl-thPRC(2015)·22 citations
02
Proton- $^{3}$ H scattering calculation: Elastic and charge-exchange reactions up to 30 MeV
A. Deltuva · A. C. Fonseca
Proton- $^{3}$ H elastic scattering and charge-exchange reaction $^{3}$ H $(p, n)^{3}$ He in the energy regime above four-nucleon breakup threshold are described in the momentum-space transition operator framework. Fully converged results are obtained using realistic two-nucleon potentials and two-proton Coulomb force as dynamic input. Differential cross section, proton analyzing power, outgoing neutron polarization, and proton-to-neutron polarization transfer coefficients are calculated between 6 and 30 MeV proton beam energy. Good agreement with the experimental data is found for the differential cross section both in elastic and charge-exchange reactions; the latter shows a complicated energy and angular dependence. The most sizable discrepancies between predictions and data are found for the proton analyzing power and outgoing neutron polarization in the charge-exchange reaction, while the respective proton-to-neutron polarization transfer coefficients are well described by the calculations.
nucl-thnucl-exPRC(2015)·14 citations
03
Heavy quark bound states in a quark-gluon plasma: dissociation and recombination
Jean-Paul Blaizot🇫🇷 · Davide De Boni🇬🇧 · Pietro Faccioli🇮🇹 · Giovanni Garberoglio🇮🇹
We present a comprehensive approach to the dynamics of heavy quarks in a quark gluon plasma, including the possibility of bound state formation and dissociation. In this exploratory paper, we restrict ourselves to the case of an Abelian plasma, but the extension of the techniques used to the non Abelian case is straightforward. A chain of well defined approximations leads eventually to a generalized Langevin equation, where the force and the noise terms are determined from a correlation function of the equilibrium plasma, and depend explicitly on the configuration of the heavy quarks. We solve the Langevin equation for various initial conditions, various numbers of heavy quark-antiquark pairs, and various temperatures of the plasma. Results of simulations illustrate various expected phenomena: dissociation of bound states as a result of combined effects of screening of the potential and collisions with the plasma constituent, formation of bound pairs (recombination) that occurs when enough heavy quarks are present in the system.
nucl-thNPA(2016)·121 citations
04
Collective flow in event-by-event partonic transport plus hydrodynamics hybrid approach
Rajeev S. Bhalerao🇮🇳 · Amaresh Jaiswal🇩🇪 · Subrata Pal🇮🇳
Complete evolution of the strongly interacting matter formed in ultrarelativistic heavy-ion collisions is studied within a coupled Boltzmann and relativistic viscous hydrodynamics approach. For the initial nonequilibrium evolution phase, we employ the AMPT model that explicitly includes event-by-event fluctuations in the number and positions of the participating nucleons as well as of the produced partons with subsequent parton transport. The ensuing near-equilibrium evolution of quark-gluon and hadronic matter is modeled within the (2+1)-dimensional viscous hydrodynamics. We probe the role of parton dynamics in generating and maintaining the spatial anisotropy in the preequilibrium phase. Substantial eccentricities epsilon_n are found to be generated in the event-by-event fluctuations in parton production from initial nucleon-nucleon collisions. For ultracentral heavy-ion collisions, the model is able to explain qualitatively the unexpected hierarchy of the harmonic flow coefficients v_n(p_T)(n=2-6) observed at LHC. We find that the results for v_n(p_T) are rather insensitive to the variation (within a range) of the time of switchover from AMPT parton transport to hydrodynamic evolution. The usual Grad and the recently proposed Chapman-Enskog-like (nonequilibrium) single-particle distribution functions are found to give very similar results for v_n(n=2-4). The model describes well both the RHIC and LHC data for v_n(p_T) at various centralities, with a constant shear viscosity to entropy density ratio of 0.08 and 0.12, respectively. The event-by-event distributions of v_{2,3} are in good agreement with the LHC data for midcentral collisions. The linear response relation v_n = k_n epsilon_n is found to be true for n=2,3, except at large values of epsilon_n, where a larger value of k_n is required, suggesting a small admixture of positive nonlinear response even for n=2,3.
nucl-thPRC(2015)·53 citations
05
Light stops, blind spots, and isospin violation in the MSSM
Andreas Crivellin🇨🇭 · Martin Hoferichter🇩🇪 · Massimiliano Procura🇦🇹 · Lewis C. Tunstall🇨🇭
In the framework of the MSSM, we examine several simplified models where only a few superpartners are light. This allows us to study WIMP--nucleus scattering in terms of a handful of MSSM parameters and thereby scrutinize their impact on dark matter direct-detection experiments. Focusing on spin-independent WIMP--nucleon scattering, we derive simplified, analytic expressions for the Wilson coefficients associated with Higgs and squark exchange. We utilize these results to study the complementarity of constraints due to direct-detection, flavor, and collider experiments. We also identify parameter configurations that produce (almost) vanishing cross sections. In the proximity of these so-called blind spots, we find that the amount of isospin violation may be much larger than typically expected in the MSSM. This feature is a generic property of parameter regions where cross sections are suppressed, and highlights the importance of a careful analysis of the nucleon matrix elements and the associated hadronic uncertainties. This becomes especially relevant once the increased sensitivity of future direct-detection experiments corners the MSSM into these regions of parameter space.
↳ hep-phastro-ph.COnucl-thJHEP(2015)·62 citations
06
Anisotropic Propagator for the Goldstone Modes in Color-flavor Locked Phase in the Presence of a Magnetic Field
Srimoyee Sen🇺🇸
We consider the phase diagram of QCD at very high baryon density and at zero temperature in the presence of a strong magnetic field. The state of matter at such high densities and low temperatures is believed to be a phase known as the color-flavor locked phase which breaks color and electromagnetic gauge invariance leaving a linear combination of them unbroken. Of the 9 quarks (three flavors and three colors), five are neutral under this unbroken generator and four are oppositely charged. In the presence of a magnetic field corresponding to the unbroken generator however, the properties of the condensate changes and a new phase known as the magnetic color flavor locked (MCFL)phase is realized. This phase breaks some of the color-flavor symmetry of the Lagrangian spontaneously, giving rise to 6 Goldstone modes, 5 of which are pseudo Goldstone modes. These Goldstone modes are composed of excitations that correspond to both neutral quarks and charged quarks. Hence it is natural to expect that the propagators of these Goldstone modes get affected in the presence of a magnetic field and their speed becomes considerably anisotropic. Although this anisotropy is self-evident from symmetry arguments, it has not been quantified yet. We calculate this anisotropy in the speed of the Goldstone modes using an NJL model type of interaction between the quarks and comment on the impact of such anisotropic modes on the transport properties of the MCFL phase.
↳ hep-phhep-thnucl-thPRD(2015)·2 citations
07
Realistic estimate of valence transversity distributions from inclusive dihadron production
Marco Radici🇮🇹 · A. Courtoy🇧🇪 · Alessandro Bacchetta🇮🇹 · Marco Guagnelli🇮🇹
We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. The e+e- data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.
↳ hep-phhep-exnucl-exnucl-thJHEP(2015)·151 citations
08
Spectroscopy of $η^{'}$ -nucleus bound states at GSI and FAIR --- very preliminary results and future prospects ---
H. Fujioka🇯🇵 · Y. Ayyad🇯🇵 · J. Benlliure🇪🇸 · K.-T. Brinkmann🇩🇪 · S.Friedrich🇩🇪 · H. Geissel🇩🇪 · J. Gellanki🇳🇱 · C. Guo🇨🇳 · E. Gutz🇩🇪 · E. Haettner🇩🇪 · M.N. Harakeh🇳🇱 · R.S. Hayano🇯🇵 and 42 other authors
The possible existence of \eta'-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the \eta' mass at finite density, which is expected to be reduced because of the interplay between the $U_{A} (1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed.
↳ nucl-exnucl-thHyperfine Interact.(2015)·10 citations
09
Rapidity dependence of elliptic and triangular flow in proton-nucleus collisions from collective dynamics
Piotr Bozek🇵🇱 · Adam Bzdak🇵🇱 · Guo-Liang Ma🇨🇳
The rapidity dependence of elliptic, $v_{2}$ , and triangular, $v_{3}$ , flow coefficients in proton-nucleus (p+A) collisions is predicted in hydrodynamics and in a multi-phase transport model (AMPT). We find that $v_{n}$ ( $n = 2, 3$ ) on a nucleus side is significantly larger than on a proton side and the ratio between the two, $v_{n}^{Pb} / v_{n}^{p}$ , weekly depends on the transverse momentum of produced particles.
↳ hep-phhep-exnucl-exnucl-thPLB(2015)·64 citations
10
High-mass twins & resolution of the reconfinement, masquerade and hyperon puzzles of compact star interiors
David Blaschke🇷🇺 · D. E. Alvarez-Castillo🇷🇺
We aim at contributing to the resolution of three of the fundamental puzzles related to the still unsolved problem of the structure of the dense core of compact stars (CS): (i) the hyperon puzzle: how to reconcile pulsar masses of $2$ M $_{⊙}$ with the hyperon softening of the equation of state (EoS); (ii) the masquerade problem: modern EoS for cold, high density hadronic and quark matter are almost identical; and (iii) the reconfinement puzzle: what to do when after a deconfinement transition the hadronic EoS becomes favorable again? We show that taking into account the compositeness of baryons (by excluded volume and/or quark Pauli blocking) on the hadronic side and confining and stiffening effects on the quark matter side results in an early phase transition to quark matter with sufficient stiffening at high densities which removes all three present-day puzzles of CS interiors. Moreover, in this new class of EoS for hybrid CS falls the interesting case of a strong first order phase transition which results in the observable high mass twin star phenomenon, an astrophysical observation of a critical endpoint in the QCD phase diagram.
↳ astro-ph.HEhep-phnucl-thAIP Conf.Proc.(2016)·37 citations

Affiliations

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