Nuclear Theory·nucl-th

Thursday·December 31, 2015

16 papers—7 primary·9 cross-listed

01
Possible chiral symmetry in $^{138}$ Nd
A. A. Raduta · Al. H. Raduta · C. M. Petrache
The pheomenological Generalized Coherent State Model Hamiltonian is amended with a many body term describing a set of nucleons moving in a shell model mean-field and interacting among themselves with paring, as well as with a particle-core interaction involving a quadrupole-quadrupole and a hexadecapole-hexdecapole force and a spin-spin interaction. The model Hamiltonian is treated in a restricted space consisting of the core projected states associated to the bands ground, $β, γ, γ, 1^{+}$ and $1^{+}$ and two proton aligned quasiparticles coupled to the states of the ground band. The chirally transformed particle-core states are also included. The Hamiltonian contains two terms which are not invariant to the chiral transformations relating the right handed trihedral $(J_{F}, J_{p}, J_{n})$ and the left handed ones $(- J_{F}, J_{p}, J_{n})$ , $(J_{F}, - J_{p}, J_{n})$ , $(J_{F}, J_{p}, - J_{n})$ where $J_{F}, J_{p}, J_{n}$ are the angular momenta carried by fermions, proton and neutron bosons, respectively. The energies defined with the particle-core states form four chiral bands, two of them being degenerate. Electromagnetic properties of the chiral bands are investigated. Results are compared with the experimental data on $^{138}$ Nd.
nucl-th0 citations
02
Thermal Dileptons from Coarse-Grained Transport as Fireball Probes at SIS Energies
Tetyana Galatyuk🇩🇪 · Paul M. Hohler🇺🇸 · Ralf Rapp🇺🇸 · Florian Seck🇩🇪 · Joachim Stroth🇺🇸
Utilizing a coarse-graining method to convert hadronic transport simulations of Au+Au collisions at SIS energies into local temperature, baryon and pion densities, we compute the pertinent radiation of thermal dileptons based on an in-medium $ρ$ spectral function that describes available spectra at ultrarelativistic collision energies. In particular, we analyze how far the resulting yields and slopes of the invariant-mass spectra can probe the lifetime and temperatures of the fireball. We find that dilepton radiation sets in after the initial overlap phase of the colliding nuclei of about 7 fm/c, and lasts for about 13 fm/c. This duration closely coincides with the development of the transverse collectivity of the baryons, thus establishing a direct correlation between hadronic collective effects and thermal EM radiation, and supporting a near local equilibration of the system. This fireball "lifetime" is substantially smaller than the typical 20-30 fm/c that naive considerations of the density evolution alone would suggest. We furthermore find that the total dilepton yield radiated into the invariant-mass window of $M = 0.3 - 0.7$ GeV/ $c^{2}$ , normalized to the number of charged pions, follows a relation to the lifetime found earlier in the (ultra-) relativistic regime of heavy-ion collisions, and thus corroborates the versatility of this tool. The spectral slopes of the invariant-mass spectra above the $ϕ$ mass provide a thermometer of the hottest phases of the collision, and agree well with the maximal temperatures extracted from the coarse-grained hadron spectra.
nucl-thEPJA(2016)·97 citations
03
Anisotropic emission of direct photons from Au+Au collisions at $s_{NN} = 200 GeV$ with EPOS3 and IP-Glasma
Fu-Ming Liu🇨🇳 · Sheng-Xu Liu🇨🇳 · Klaus Werner🇫🇷
The observed large elliptic flow ( $v_{2}$ ) of direct photons in relativistic heavy ion collisions challenges us to explain. In this paper we consider only two sources of direct photons, prompt photons and thermal photons. Prompt photons are calculated with QCD to next leading order, which fits well the spectra at high transverse momentum ( $p_{t}$ ) region. Thermal photons are calculated with AMY rate in a 3+1D viscous hydrodynamical evolution of the collision systems. Two types of initial conditions, EPOS3 and IP-Glasma, are employed. Our results with IP-Glasma initial condition agree with results in published work in most cases, and the difference tells the regions effected by the absence of viscous correction in photon emission rate. Because both models are well constrained with hadron data, the hydrodynamic evolution of collision systems in the two models have many common. However, the transverse velocity of the collective motion are quite different. This makes a big difference in the anisotropic emission of direct photon emission. The observed large elliptic flow of direct photons is reproduced with EPOS3 hydrodynamic evolution.
nucl-thhep-ph7 citations
04
Octet baryon masses and sigma terms in covariant baryon chiral perturbation theory
Xiu-Lei Ren (Beihang U. and IPN Orsay)🇫🇷 · Li-Sheng Geng (Beihang U.)🇨🇳 · Jie Meng (Peking U., SKLNPT and Beihang U. and Stellenbosch U.)🇨🇳
We report on a recent study of the ground-state octet baryon masses and sigma terms in covariant baryon chiral perturbation theory with the extended-on-mass-shell scheme up to next-to-next-to-next-to-leading order. To take into account lattice QCD artifacts, the finite-volume corrections and finite lattice spacing discretization effects are carefully examined. We performed a simultaneous fit of all the $n_{f} = 2 + 1$ lattice octet baryon masses and found that the various lattice simulations are consistent with each other. Although the finite lattice spacing discretization effects up to $O (a^{2})$ can be safely ignored, but the finite volume corrections cannot even for configurations with $M_{ϕ} L > 4$ . As an application, we predicted the octet baryon sigma terms using the Feynman-Hellmann theorem. In particular, the pion- and strangeness-nucleon sigma terms are found to be $σ_{π N} = 55 (1) (4)$ MeV and $σ_{s N} = 27 (27) (4)$ MeV, respectively.
nucl-thhep-lathep-phPoS(2016)·1 citation
05
The R_AA and v_2 of muons from heavy-quark decays in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV with the ATLAS detector
Alexander Milov (for the ATLAS Collaboration)🇮🇱
The ATLAS experiment measures the production of muons coming from the decays of heavy flavour particles in the kinematic interval 4<p_T<14 GeV and |eta|<1. The measurement is performed in sqrt(s) = 2.76 TeV pp collisions and over the centrality range of 0-60% in sqrt(s_NN) = 2.76 TeV Pb+Pb collisions. The heavy flavour muon differential cross-sections and per-event yields are measured in pp and Pb+Pb collisions, respectively. The nuclear modification factor measured in 0-10% most central collisions is observed to be approximately equal to 0.4 and independent of p_T within uncertainties, which indicates suppressed production of heavy flavour muons in Pb+Pb collisions. The muon yields are also measured as a function of the azimuthal angle with respect to the event plane. Fourier coefficients associated with the second harmonic modulation vary slowly with p_T and show a systematic variation with centrality that is characteristic of other elliptic anisotropy measurements.
nucl-thnucl-exNPA(2016)·2 citations
06
New analytical forms of wave function in coordinate space and tensor polarization of deuteron
V. I. Zhaba
Numerically coefficients of the new analytical forms for deuteron wave function in coordinate space for NijmI, NijmII, Nijm93, Reid93 and Argonne v18 potentials are designed. The obtained wave functions do not contain superfluous knots. The designed parameters of a deuteron well agree with the experimental and theoretical data. The tensor polarization t20 designed on wave functions is proportionate to earlier published outcomes.
nucl-thMod.Phys.Lett.A(2016)·18 citations
07
Acceptance dependence of fluctuation measures near the QCD critical point
Bo Ling🇺🇸 · Mikhail A. Stephanov🇺🇸
We argue that a crucial determinant of the acceptance dependence of fluctuation measures in heavy-ion collisions is the range of correlations in the momentum space, e.g., in rapidity, $Δ y_{corr}$ . The value of $Δ y_{corr} \sim 1$ for critical thermal fluctuations is determined by the thermal rapidity spread of the particles at freezeout, and has little to do with position space correlations, even near the critical point where the spatial correlation length $ξ$ becomes as large as $2 - 3$ fm (this is in contrast to the magnitudes of the cumulants, which are sensitive to $ξ$ ). When the acceptance window is large, $Δ y ≫ Δ y_{corr}$ , the cumulants of a given particle multiplicity, $κ_{k}$ , scale linearly with $Δ y$ , or mean multiplicity in acceptance, $⟨ N ⟩$ , and cumulant ratios are acceptance independent. While in the opposite regime, $Δ y ≪ Δ y_{corr}$ , the factorial cumulants, $κ^_{k}$ , scale as $(Δ y)^{k}$ , or $⟨ N ⟩^{k}$ . We demonstrate this general behavior quantitatively in a model for critical point fluctuations, which also shows that the dependence on transverse momentum acceptance is very significant. We conclude that extension of rapidity coverage proposed by STAR should significantly increase the magnitude of the critical point fluctuation signatures.
nucl-thPRC(2016)·118 citations
08
Phenomenological QCD equations of state for neutron stars
Toru Kojo🇨🇳 · Philip D. Powell🇺🇸 · Yifan Song🇺🇸 · Gordon Baym🇯🇵
We delineate the properties of QCD matter at baryon density n_B=1-10n_0 (n_0: nuclear saturation density), through the construction of neutron star equations of state that satisfy the neutron star mass-radius constraints as well as physical conditions on the speed of sound. The QCD matter is described in the 3-window modeling: at n_B < 2n_0 purely nuclear matter; at n_B > 5n_0 percolated quark matter; and at 2n_0 < n_B < 5n_0 matter intermediate between these two which are constructed by interpolation. Using a schematic quark model with effective interactions inspired from hadron and nuclear physics, we analyze the strength of interactions necessary to describe observed neutron star properties. Our finding is that the interactions should remain as strong as in the QCD vacuum, indicating that gluons at n_B =1-10 n_0 remain non-perturbative even after quark matter formation.
↳ hep-phastro-ph.HEnucl-exnucl-thNPA(2016)·24 citations
09
In-medium jet evolution: interplay between broadening and decoherence effects
Liliana Apolinário🇵🇹 · Néstor Armesto🇪🇸 · Guilherme Milhano🇵🇹 · Carlos A. Salgado🇪🇸
The description of the modifications of the coherence pattern in a parton shower, in the presence of a QGP, has been actively addressed in recent studies. Among the several achievements, finite energy corrections, transverse momentum broadening due to medium interactions and interference effects between successive emissions have been extensively improved as they seem to be essential features for a correct description of the results obtained in heavy-ion collisions. In this work, based on the insights of our previous work [1], we explore the physical interplay between broadening and decoherence, by generalising previous studies of medium-modifications of the antenna spectrum [2, 3, 4] - so far restricted to the case where transverse motion is neglected. The result allow us to identify two quantities controlling the decoherence of a medium modified shower that can be used as building blocks for a successful future generation of jet quenching Monte Carlo simulators: a generalisation of the $Δ_{m e d}$ parameter of the works of [2, 4] - that controls the interplay between the transverse scale of the hard probe and the transverse resolution of the medium - and of the $Δ_{co h}$ in [1] - that dictates the interferences between two emitters as a function of the transverse momentum broadening acquired by multiple scatterings with the medium.
↳ hep-phnucl-thNPA(2016)·3 citations
10
Direct-photon+hadron correlations to study parton energy loss with the STAR experiment
Nihar Ranjan Sahoo (STAR collaboration)🇺🇸
We report new results of $γ_{d i r}$ +hadron and $π^{0}$ +hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $s_{N N}$ = 200 GeV in the STAR experiment from years 2011 and 2009 of data taking, respectively. The charged-hadron per-trigger yields at mid-rapidity $(∣ η ∣ < 1)$ and for transverse momenta $p_{T}^{a ssoc} > 1.2$ ~GeV/ $c$ associated with $γ_{d i r}$ ~ and $π^{0}$ ~(for triggers $∣ η ∣ <$ 0.9, 12 $< p_{T}^{t r i g} <$ 20 GeV/ $c$ ) in central Au+Au collisions are compared with p+p collisions. The $z_{T}$ ( $= \frac{p _{T}^{a ssoc}}{p _{T}^{t r i g}}$ ) dependence, now extending down to $z_{T}$ =0.1, of the suppression of the away-side associated yields is presented. We observed that the suppression of away-side associated yields tends to vanish at lower \zT. The dependence of the suppression on both $p_{T}^{a ssoc}$ and $p_{T}^{t r i g}$ is also discussed. Finally, these results are compared with various model predictions.
↳ nucl-exhep-exhep-phnucl-thNPA(2016)·3 citations
11
D mesons in a magnetic field
Philipp Gubler🇮🇹 · Koichi Hattori🇺🇸 · Su Houng Lee🇰🇷 · Makoto Oka🇯🇵 · Sho Ozaki🇯🇵 · Kei Suzuki🇯🇵
We investigate the mass spectra of open heavy flavor mesons in an external constant magnetic field within QCD sum rules. Spectral ansätze on the phenomenological side are proposed in order to properly take into account mixing effects between the pseudoscalar and vector channels, and the Landau levels of charged mesons. The operator product expansion is implemented up to dimension-5 operators. As a result, we find for neutral D mesons a significant positive mass shift that goes beyond simple mixing effects. In contrast, charged D mesons are further subject to Landau level effects, which together with the mixing effects almost completely saturate the mass shifts obtained in our sum rule analysis.
↳ hep-phhep-latnucl-exnucl-thPRD(2016)·89 citations
12
Bose-Einstein Condensation of Bound Pairs of Relativistic Fermions in a Magnetic Field
Bo Feng🇨🇳 · Defu Hou🇨🇳 · Hai-cang Ren🇨🇳 · Ping-ping Wu🇨🇳
The Bose-Einstein condensation of bound pairs made of equally and oppositely charged fermions in a magnetic field is investigated using a relativistic model. The Gaussian fluctuations have been taken into account in order to study the spectrum of bound pairs in the strong coupling region. We found, in weak coupling reagion, the condensation temperature increases with an increasing magnetic field displaying the magnetic catalysis effect. In strong coupling region, the inverse magnetic catalysis appears when the magnetic field is low and is replaced by the usual magnetic catalysis effect when magnetic field is sufficiently high, in contrast to the nonrelativistic case where the inverse magnetic catalysis prevails in strong coupling region regardless of the strength of the magnetic field. The resulting response to the magnetic field is the consequence of the competition between the dimensional reduction by Landau orbitals in pairing dynamics and the anisotropy of the kinetic spectrum of the bound pairs. We thus conclude that dimensional reduction dominates in weak domain and strong coupling one except the small magnetic field region, where the enhanced fluctuations dominates.
↳ hep-phnucl-thPRD(2016)·11 citations
13
Effects produced by multi-parton interactions and color reconnection in small systems
Eleazar Cuautle🇲🇽 · Antonio Ortiz🇲🇽 · Guy Paic🇲🇽
Multi-parton interactions and color reconnection can produce QGP-like effects in small systems, specifically, radial flow-like patterns. For pp collisions simulated with Pythia 8.212, in this work we investigate their effects on different observables like event multiplicity, event shapes and transverse momentum distributions.
↳ hep-phnucl-thNPA(2016)·12 citations
14
Pseudoscalar transition form factors: $(g - 2)$ of the muon, pseudoscalar decays into lepton pairs, and the $η - η^{'}$ mixing
Pere Masjuan🇩🇪 · Pablo Sanchez-Puertas🇩🇪
We present our model-independent and data-driven method to describe pseudoscalar meson transition form factors in the space- and (low-energy) time-like regions. The method is general and conforms a toolkit applicable to any other form factor, of one and two variables, with the potential to include both high- and low-energy QCD constraints altogether. The method makes use of analyticity and unitary properties of form factors, it is simple, systematic and can be improved upon by including new data. In the present discussion, the method is used to show the impact of experimental data for precision calculations in the low-energy sector of the Standard Model. In particular, due to its relevance for New Physics searches, we have considered the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon (the pseudoscalar exchange contribution), the pseudoscalar decays into lepton pairs, and the determination of the mixing parameters of the $η$ and $η^{'}$ system. For all of them we provide the most updated results in a data-driven manner.
↳ hep-phhep-exnucl-thEPJ Web Conf.(2016)·2 citations
15
Pairing Dynamics of Polar States in a Quenched p-wave Superfluid Fermi Gas
Sukjin Yoon · Gentaro Watanabe
We study the pairing dynamics of polar states in a single species p-wave superfluid Fermi gas following a sudden change of the interaction strength. The anisotropy of pair interaction together with the presence of the centrifugal barrier results in profoundly different pairing dynamics compared to the s-wave case. Depending on the direction of quenches, quench to the BCS regime results in a large oscillatory depletion of momentum occupation inside the Fermi sea or a large filling of momentum occupation. We elucidate a crucial role of the resonant state supported by the centrifugal barrier in the pairing dynamics.
↳ cond-mat.quant-gascond-mat.stat-mechcond-mat.supr-connucl-thPRL(2017)·4 citations
16
Two-photon exchange correction to muon-proton elastic scattering at low momentum transfer
O. Tomalak🇩🇪 · M. Vanderhaeghen (JGU Mainz)🇩🇪
We evaluate the two-photon exchange (TPE) correction to the muon-proton elastic scattering at small momentum transfer. Besides the elastic (nucleon) intermediate state contribution, which is calculated exactly, we account for the inelastic intermediate states by expressing the TPE process approximately through the forward doubly virtual Compton scattering. The input in our evaluation is given by the unpolarized proton structure functions and by one subtraction function. For the latter, we provide an explicit evaluation based on a Regge fit of high-energy proton structure function data. It is found that, for the kinematics of the forthcoming muon-proton elastic scattering data of the MUSE experiment, the elastic TPE contribution dominates, and the size of the inelastic TPE contributions is within the anticipated error of the forthcoming data.
↳ hep-phnucl-exnucl-thEPJC(2016)·48 citations

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