Nuclear Theory·nucl-th

Tuesday·September 15, 2015

14 papers—7 primary·7 cross-listed

01
Nuclear medium effect on nuclear modification factor of protons and pions in intermediate-energy heavy ion collisions
Ming Lv🇨🇳 · Yu-Gang Ma🇨🇳 · Jin-Hui Chen🇨🇳 · De-Qing Fang🇨🇳 · Guo-Qiang Zhang🇨🇳
Nuclear modification factor ( $R_{c p}$ ) of protons and pions are investigated by simulating Au + Au collisions from 0.8 to 1.8 $A$ GeV in a framework of an isospin-dependent quantum molecular dynamics (IQMD) model. $R_{c p}$ of protons rises with the increase of \pt~ at different beam energies owing to radial flow and Cronin effect. The rate of increase of \rcp~ is suppressed at higher beam energies. The significant difference of $R_{c p}$ between protons and pions indicates different medium effects between protons and pions. By changing the in-medium nucleon-nucleon cross section, the $R_{c p}$ of protons changes a lot, while the $R_{c p}$ of pions does not. Taking the pion absorption into account, the $R_{c p}$ of pions becomes close to unity without $p_{T}$ dependence after deactivating the reaction $π N \to Δ$ , while there is nearly no change on proton. This suggests that the pion absorption plays a dominant role on pion dynamics and have slight effect for proton dynamics.
nucl-thnucl-exPRC(2017)·5 citations
02
Theory of electromagnetic reactions in light nuclei
Tianrui Xu · Mirko Miorelli · Sonia Bacca · Gaute Hagen
We briefly review the theory for electromagnetic reactions in light nuclei based on the coupled-cluster formulation of the Lorentz integral transform method. Results on photodisintegration reactions of 22O and 40Ca are reported on and preliminary calculations on the Coulomb sum rule for 4He are discussed.
nucl-th0 citations
03
Double Lambda He-6 in cluster effective field theory
S.-I. Ando (Sunmoon U.)🇰🇷 · Y. Oh (Kyungpook National U.)🇰🇷
The bound state of \nuclide[6][\Lambda\Lambda]{He} is studied as a three-body ( $ΛΛ α$ ) system in a cluster effective field theory at leading order (LO). We find that the system exhibits the limit cycle which is associated with the formation of bound states called the Efimov states. This implies that the three-body contact interaction should be promoted to LO. The relationship of the binding energy and the $ΛΛ$ scattering length is discussed as well as the role of the scale in this system.
nucl-thhep-phEPJ Web Conf.(2016)·0 citations
04
Electromagnetic fields and anomalous transports in heavy-ion collisions --- A pedagogical review
Xu-Guang Huang🇨🇳
The hot and dense matter generated in heavy-ion collisions may contain domains which are not invariant under P and CP transformations. Moreover, heavy-ion collisions can generate extremely strong magnetic fields as well as electric fields. The interplay between the electromagnetic field and triangle anomaly leads to a number of macroscopic quantum phenomena in these P- and CP-odd domains known as the anomalous transports. The purpose of the article is to give a pedagogical review of various properties of the electromagnetic fields, the anomalous transports phenomena, and their experimental signatures in heavy-ion collisions.
nucl-thhep-phnucl-exRept.Prog.Phys.(2016)·359 citations
05
Reduction of the $K^{*}$ meson abundance in heavy ion collisions
Sungtae Cho🇰🇷 · Su Houng Lee🇰🇷
We study the $K^{*}$ meson reduction in heavy ion collisions by focusing on the hadronic effects on the $K^{*}$ meson abundance. We evaluate the absorption cross sections of the $K^{*}$ and $K$ meson by light mesons in the hadronic matter, and further investigate the variation in the meson abundances for both particles during the hadronic stage of heavy ion collisions. We show how the interplay between the interaction of the $K^{*}$ meson and kaon with light mesons in the hadronic medium determines the final yield difference of the statistical hadronization model to the experimental measurements. For the central Au+Au collision at $s_{N N} = 200$ GeV, we find that the $K^{*} / K$ yield ratio at chemical freeze-out decreases by $36%$ during the expansion of the hadronic matter, resulting in the final ratio comparable to STAR measurements of 0.23 $\pm 0.05$ .
nucl-thhep-phnucl-exPRC(2018)·27 citations
06
Pseudorapidity correlations in heavy ion collisions from viscous fluid dynamics
Akihiko Monnai🇺🇸 · Bjoern Schenke🇺🇸
We demonstrate by explicit calculations in 3+1 dimensional viscous relativistic fluid dynamics how two-particle pseudorapidity correlation functions in heavy ion collisions at the LHC and RHIC depend on the number of particle producing sources and the transport properties of the produced medium. In particular, we present results for the Legendre coefficients of the two-particle pseudorapidity correlation function in Pb+Pb collisions at 2760 GeV and Au+Au collisions at 200 GeV from viscous hydrodynamics with three dimensionally fluctuating initial conditions. Our results suggest that these coefficients provide important constraints on initial state fluctuations and the transport properties of the quark gluon plasma.
nucl-thhep-phnucl-exPLB(2016)·43 citations
07
Two-particle correlations in pseudorapidity in a hydrodynamic model
Piotr Bozek🇵🇱 · Wojciech Broniowski🇵🇱 · Adam Olszewski🇵🇱
Two-particle pseudorapidity correlations of hadrons produced in Pb+Pb collisions at 2.76 TeV at the CERN Large Hadron Collider are analyzed in the framework of a model based on viscous 3+1-dimensional hydrodynamics with the Glauber initial condition. Based on our results, we argue that the correlation from resonance decays, formed at a late stage of the evolution, produce significant effects. In particular, their contribution to the event averages of the coefficients of the expansion in the Legendre basis explain 60-70% of the experimental values. We have proposed an accurate way to compute these <a_n a_m> coefficients, independent of the binning in pseudorapidity, and tested a double expansion of the two-particle correlation function in the azimuth and pseudorapidity, which allows us to investigate the pseudorapidity correlations between harmonics of the collective flow. In our model, these quantities are also dominated by non-flow effects from the resonance decays. Finally, our method can be used to compute higher-order cumulants for the expansion in orthonormal polynomials which offers a suitable way of eliminating the non-flow effects from the correlation analyses.
nucl-thhep-phnucl-exPRC(2015)·21 citations
08
Scaling properties of inclusive W $^{\pm}$ production at hadron colliders
François Arleo🇫🇷 · Émilien Chapon🇫🇷 · Hannu Paukkunen🇫🇮
We consider the hadroproduction of W gauge bosons in their leptonic decay mode. Starting from the leading-order expressions, we show that by defining a suitable scaling variable the centre-of-mass dependence of the cross sections at the LHC energies can be essentially described by a simple power law. The scaling exponent is directly linked to the small- $x$ behaviour of parton distribution functions (PDF) which, at the high virtualities involved in W production, is largely dictated by QCD evolution equations. This entails a particularly simple scaling law for the lepton charge asymmetry and also predicts that measurements in different collision systems (p-p, p- $p ˉ$ , p-Pb Pb-Pb) are straightforwardly related. The expectations are compared with the existing data and a very good overall agreement is observed. It is shown that the PDF uncertainty in certain cross-section ratios between nearby centre-of-mass energies can be significantly reduced by taking the ratios at fixed value of scaling variable instead of fixed rapidity.
↳ hep-phhep-exnucl-exnucl-thEPJC(2016)·12 citations
09
Symmetry violations in nuclear and neutron $β$ decay
K.K. Vos🇳🇱 · H.W. Wilschut🇳🇱 · R.G.E. Timmermans🇳🇱
The role of $β$ decay as a low-energy probe of physics beyond the Standard Model is reviewed. Traditional searches for deviations from the Standard Model structure of the weak interaction in $β$ decay are discussed in the light of constraints from the LHC and the neutrino mass. Limits on the violation of time-reversal symmetry in $β$ decay are compared to the strong constraints from electric dipole moments. Novel searches for Lorentz symmetry breaking in the weak interaction in $β$ decay are also included, where we discuss the unique sensitivity of $β$ decay to test Lorentz invariance. We end with a roadmap for future $β$ -decay experiments.
↳ hep-phhep-exnucl-exnucl-thRMP(2015)·71 citations
10
Pentaquarks and Tetraquarks at LHCb
Sheldon Stone🇺🇸
Exotic resonant structures found in $Λ_{b}^{0}$ and $B^{0}$ decays into charmonium in the LHCb experiment are discussed. Examination of the $J / ψ p$ system in $Λ_{b}^{0} \to J / ψ K^{-} p$ decays shows two states each of which must be composed of $uu d c c$ quarks, and thus are called charmonium pentaquarks. Their masses are $4380 \pm 8 \pm 29$ ~MeV and $4449.8 \pm 1.7 \pm 2.5$ ~MeV, and their corresponding widths ( $Γ$ ) are $205 \pm 18 \pm 86$ MeV, and $39 \pm 5 \pm 19$ MeV. The preferred $J^{P}$ assignments are of opposite parity, with one state having spin 3/2 and the other 5/2. Models of internal binding of the pentaquark states are discussed. Finally, another mesonic state is discussed, the $Z (4430)^{-}$ that decays into $ψ^{'} π^{-}$ and was first observed by the Belle collaboration in $B^{0} \to ψ^{'} K^{+} π^{-}$ decays. Using a sample of approximately 25,000 signal events, LHCb determines the $J^{P}$ to be $1^{+}$ .
↳ hep-exhep-phnucl-exnucl-thPoS(2015)·13 citations
11
Heavy flavor in nucleus-nucleus and proton-nucleus: quenching, flow and correlations
M. Nardi🇮🇹 · A. Beraudo🇮🇹 · A. De Pace🇮🇹 · M. Monteno🇮🇹 · F. Prino (INFN Torino)🇮🇹
We present recent results for heavy-flavor observables in nucleus-nucleus collisions at LHC energies, obtained with the POWLANG transport setup. The initial creation of c-cbar and b-bbar pairs is simulated with a perturbative QCD approach (POWHEG+PYTHIA); their propagation in the medium (created in the nucleus-nucleus or in proton-nucleus collision) is studied with the relativistic Langevin equation, here solved using weak-coupling transport coefficients. Successively, the heavy quarks hadronize in the medium. We compute the nuclear modification factor and the elliptic flow parameter of the final D mesons both in nucleus-nucleus and in (for the first time, in the POWLANG setup) proton-nucleus collisions and compare our results to experimental data.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2016)·7 citations
12
Transition form factors $γ^{*} \to γ f_{2} (1270)$ and $γ^{*} \to γ a_{2} (1320)$ in the $e^{+} e^{-}$ collisions
N.N. Achasov🇷🇺 · A.V. Kiselev🇷🇺
The predictions for transition form factors $γ^{*} \to γ f_{2} (1270)$ and $γ^{*} \to γ a_{2} (1320)$ and corresponding $e^{+} e^{-} \to γ^{*} \to f_{2} γ$ and $e^{+} e^{-} \to γ^{*} \to a_{2} γ$ cross sections are obtained for the energy region up to $2$ GeV. These predictions are coordinated with the recent Belle data on the $γ^{*} (Q^{2}) γ \to f_{2}$ transition. It is shown that the QCD asymptotics of the amplitudes of the reactions $e^{+} e^{-} \to γ^{*} \to f_{2} γ$ and $e^{+} e^{-} \to γ^{*} \to a_{2} γ$ can be reached only by taking into account a compensation of contributions of $ρ (770)$ , $ω (782)$ with contributions of their radial excitations. The relation $σ (e^{+} e^{-} \to γ^{*} \to f_{2} γ) / σ (e^{+} e^{-} \to γ^{*} \to a_{2} γ) \approx 25/9$ , obtained with the help of the $q q ˉ$ model of $a_{2}$ and $f_{2}$ and QCD, is used to determine the $σ (e^{+} e^{-} \to γ^{*} \to a_{2} γ)$ at high energies. Recent BABAR measurement of the $e^{+} e^{-} \to f_{2} γ \to π^{+} π^{-} γ$ cross section at $10.58$ GeV gives hope for detailed investigation of the $γ^{*} (s) \to f_{2} γ$ and $γ^{*} (s) \to a_{2} γ$ transition form factors at high energy region.
↳ hep-phhep-exnucl-thEPJ Web Conf.(2016)·2 citations
13
Proton-lambda correlation functions at the LHC with account for residual correlations
V. M. Shapoval🇺🇦 · Yu. M. Sinyukov🇺🇦 · V. Yu. Naboka🇺🇦
The theoretical analysis of $p ˉ - Λ \oplus p - Λ ˉ$ correlation function in 10% most central Au+Au collisions at RHIC energy $s_{N N} = 200$ GeV shows that the contribution of residual correlations is the necessary factor to obtain a satisfactory description of the experimental data. A neglecting of the residual correlation effect, leads to unrealistically low source radius, about 2 times smaller than the corresponding value for $p - Λ \oplus p ˉ - Λ ˉ$ case, when one fits the experimental correlation function within Lednicky-Lyuboshitz analytical model. Recently an approach accounting effectively for residual correlations for the baryon-antibaryon correlation function was proposed, and a good RHIC data description was reached with the source radius extracted from the hydrokinetic model (HKM). The $p ˉ - Λ$ scattering length, as well as the parameters characterizing the residual correlation effect --- annihilation dip amplitude and its inverse width --- were extracted from the corresponding fit. In this paper we use these extracted values and simulated in HKM source functions for Pb+Pb collisions at the LHC energy $s_{N N} = 2.76$ TeV to predict the corresponding $p Λ$ and $p Λ ˉ$ correlation functions.
↳ hep-phhep-exnucl-exnucl-thPRC(2015)·2 citations
14
Photon and dilepton production from a non-equilibrium quark-gluon plasma
Lusaka Bhattacharya🇺🇸 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸
We calculate leading-order medium photon and dilepton yields from a quark-gluon plasma using (3+1)-dimensional anisotropic hydrodynamics. In the case of dileptons, at leading-order it is sufficient to take into account non-equilibrium corrections to the rate through the use of anisotropic distribution functions. In the case of photons, non-equilibrium corrections to the rate are taken into account using a self-consistent modification of the distribution functions and the corresponding anisotropic hard-loop quark self-energies. We present predictions for the high-energy photon and dilepton spectrum and the photon elliptic flow as a function of invariant mass, transverse momentum, shear viscosity, and initial momentum-space anisotropy. Our findings indicate that both high-energy photon and dilepton production are sensitive to the assumed level of initial momentum-space anisotropy of the quark-gluon plasma. In addition, we find that the photon elliptic flow depends on the initial momentum-space anisotropy.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2016)·3 citations

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