Nuclear Theory·nucl-th

Tuesday·November 20, 2018

28 papers—12 primary·16 cross-listed

13
Vector mesons and electromagnetic form factor of the $Λ$ hyperon
Xu Cao🇨🇳 · Jian-Ping Dai🇨🇳 · Ya-Ping Xie🇨🇳
The measured electromagnetic form factors of $Λ$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $ϕ$ (2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p p ˉ$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.
↳ hep-phnucl-thPRD(2018)·31 citations
14
The spin parity of $Z_{c}^{-}$ (4100), $Z_{1}^{+}$ (4050) and $Z_{2}^{+}$ (4250)
Xu Cao🇨🇳 · Jian-Ping Dai🇨🇳
We conjecture that $Z_{c}^{-}$ (4100) found by LHCb group from a Dalitz plot analysis of $B^{0} \to η_{c} K^{+} π^{-}$ decay is the charge conjugate of $Z_{1}^{+}$ (4050) observed in $χ_{c 1} π^{+}$ distribution from Belle collaboration. Some interesting conclusions are inferred from this assumption. The $Z_{2}$ (4250) would be assigned to be a $J^{P} = 1^{+}$ or $1^{-}$ state because of its absence in $η_{c} π^{-}$ invariant mass distribution, while $Z_{1}^{+}$ (4050)/ $Z_{c}^{-}$ (4100) could be a $0^{+}$ or $1^{-}$ state but $2^{+}$ is unfavored because it would be coupled to $η_{c} π$ in $D$ -wave. The null observation of $Z_{1} Z_{2}$ , $Z_{1} Z_{1}$ and $Z_{2} Z_{2}$ production in $e^{+} e^{-}$ annihilation and $Υ (1 S, 2 S)$ decay by Belle collaboration would further allocate the spin parity combination of $Z_{1}^{+}$ (4050)/ $Z_{c}^{-}$ (4100) and $Z_{2}$ (4250). Our deductions can be used to exclude a set of proposed models and could be further tested by future experiment, e.g. in $γ γ$ collisions.
↳ hep-phnucl-thPRD(2019)·16 citations
15
Soft drop groomed jet angularities at the LHC
Zhong-Bo Kang🇺🇸 · Kyle Lee🇺🇸 · Xiaohui Liu🇨🇳 · Felix Ringer🇺🇸
Jet angularities are a class of jet substructure observables where a continuous parameter is introduced in order to interpolate between different classic observables such as the jet mass and jet broadening. We consider jet angularities measured on an inclusive jet sample at the LHC where the soft drop grooming procedure is applied in order to remove soft contaminations from the jets. The soft drop algorithm allows for a precise comparison between theory and data and could be used to extract the QCD strong coupling constant $α_{s}$ from jet substructure data in the future. We develop a framework to realize the resummation of all relevant large logarithms at the next-to-leading logarithmic (NLL) accuracy. To demonstrate that the developed formalism is suitable for the extraction of $α_{s}$ , we extend our calculations to next-to-next-to-leading logarithm (NNLL) for the jet mass case. Overall, we find good agreement between our NLL numerical results and Pythia simulations for LHC kinematics and we observe an improved agreement when the NNLL components are included. In addition, we expect that groomed jet angularities will be a useful handle for studying the modification of jets in heavy-ion collisions.
↳ hep-phhep-exnucl-exnucl-thPLB(2019)·80 citations
16
Quarkonium In-Medium Transport Equation Derived from First Principles
Xiaojun Yao🇺🇸 · Thomas Mehen🇺🇸
We use the open quantum system formalism to study the dynamical in-medium evolution of quarkonium. The system of quarkonium is described by potential non-relativistic QCD while the environment is a weakly coupled quark-gluon plasma in local thermal equilibrium below the melting temperature of the quarkonium. Under the Markovian approximation, it is shown that the Lindblad equation leads to a Boltzmann transport equation if a Wigner transform is applied to the system density matrix. Our derivation illuminates how the microscopic time-reversibility of QCD is consistent with the time-irreversible in-medium evolution of quarkonium states. Static screening, dissociation and recombination of quarkonium are treated in the same theoretical framework. In addition, quarkonium annihilation is included in a similar way, although the effect is negligible for the phenomenology of the current heavy ion collision experiments. The methods used here can be extended to study quarkonium dynamical evolution inside a strongly coupled QGP, a hot medium out of equilibrium or cold nuclear matter, which is important to studying quarkonium production in heavy ion, proton-ion, and electron-ion collisions.
↳ hep-phnucl-thPRD(2019)·128 citations
17
Leading Order $k_{F} a$ Corrections to the Free Energy and Phase Separation in Two-component Fermion Systems
Heron Caldas🇧🇷
We study phase separation in a dilute two-component Fermi system with attractive interactions as a function of the coupling strength and the polarization or number density asymmetry between the two components. In weak and strong couplings with a finite number density asymmetry, phase separation is energetically more favorable. A heterogeneous phase containing a symmetric superfluid component and an asymmetric normal phase has lower energy than a homogeneous normal phase. We show that for a small number density asymmetry, taking into consideration the leading order corrections at order $k_{F} a$ of the interaction parameter, phase separation is stable against the normal phase in the whole BCS range. We investigate the consequences of the consideration of the leading order $k_{F} a$ corrections to the thermodynamic potentials of the normal and BCS phase on the Chandrasekhar-Clogston limit. We have also investigated the stability of a Bose-Fermi mixture in the far-BEC limit. We find that the molecular BEC is locally stable against an external magnetic field $h$ , provided $∣ h ∣$ is smaller than the pairing gap $Δ_{g a p}$ .
↳ cond-mat.quant-gascond-mat.othercond-mat.supr-connucl-thJ.Stat.Mech.(2019)·0 citations
18
Search for the $Σ^{*}$ state in $Λ_{c}^{+} \to π^{+} π^{0} π^{-} Σ^{+}$ decay by triangle singularity
Ju-Jun Xie🇨🇳 · Eulogio Oset🇪🇸
A $Σ^{*}$ resonance with spin-parity $J^{P} = 1/ 2^{-}$ and mass in the vicinity of the $K ˉ N$ threshold has been predicted in the unitary chiral approach and inferred from the analysis of CLAS data on the $γ p \to K^{+} π^{0} Σ^{0}$ reaction. In this work, based on the dominant Cabibbo favored weak decay mechanism, we perform a study of $Λ_{c}^{+} \to π^{+} π^{0} Σ^{*}$ with the possible $Σ^{*}$ state decaying into $π^{-} Σ^{+}$ through a triangle diagram. This process is initiated by $Λ_{c}^{+} \to π^{+} K ˉ^{*} N$ , then the $K ˉ^{*}$ decays into $K ˉ π$ and $K ˉ N$ produce the $Σ^{*}$ through a triangle loop containing $K ˉ^{*} N K ˉ$ which develops a triangle singularity. We show that the $π^{-} Σ^{+}$ state is generated from final state interaction of $K ˉ N$ in $S$ -wave and isospin $I = 1$ , and the $Λ_{c}^{+} \to π^{+} π^{0} π^{-} Σ^{+}$ decay can be used to study the possible $Σ^{*}$ state around the $K ˉ N$ threshold. The proposed decay mechanism can provide valuable information on the nature of the $Σ^{*}$ resonance and can in principle be tested by facilities such as LHCb, BelleII and BESIII.
↳ hep-phhep-exnucl-exnucl-thPLB(2019)·27 citations
19
Fate of the charm baryon $Λ_{c}$ in cold and hot nuclear matter
Shigehiro Yasui🇯🇵
I discuss the properties of the $Λ_{c}$ baryon in nuclear matter at zero or finite temperature. Starting from the Lagrangian based on the heavy-quark effective theory, I derive the effective Lagrangian for the $Λ_{c}$ baryon existing as an impurity particle. Adopting the one-loop calculation for nucleons, I derive the effective potential as the quantity for measuring the stability of the $Λ_{c}$ baryon in nuclear matter. The parameters in the Lagrangian are fitted to reproduce the scattering length of the nucleon and the $Λ_{c}$ baryon estimated in the lattice QCD simulations and the chiral extrapolations. I present that the $Λ_{c}$ baryon is bound in nuclei with the binding energy of about 20 MeV at normal nuclear-matter density. I discuss the case that the $Λ_{c}$ baryon moves with a constant velocity. I also discuss an increase of the nucleon number density near the $Λ_{c}$ baryon in nuclear matter, and show that the $Λ_{c}$ baryon is a useful probe to research the nuclear systems at high density.
↳ hep-phnucl-thPRC(2019)·7 citations
20
Nucleon form factors and root-mean-square radii on a (10.8 fm $)^{4}$ lattice at the physical point
Eigo Shintani🇯🇵 · Ken-Ichi Ishikawa🇯🇵 · Yoshinobu Kuramashi🇯🇵 · Shoichi Sasaki🇯🇵 · Takeshi Yamazaki🇯🇵
We present the nucleon form factors and root-mean-square (RMS) radii measured on a (10.8 fm $)^{4}$ lattice at the physical point. We compute the form factors at small momentum transfer region in $q^{2} \leq 0.102$ GeV $^{2}$ with the standard plateau method choosing four source-sink separation times $t_{sep}$ from 0.84 to 1.35 fm to examine the possible excited state contamination. We obtain the electric and magnetic form factors and their RMS radii for not only the isovector channel but also the proton and neutron ones without the disconnected diagram. We also obtain the axial-vector coupling and the axial radius from the axial-vector form factor. We find that these three form factors do not show large $t_{sep}$ dependence in our lattice setup. On the other hand, the induced pseudoscalar and pseudoscalar form factors show the clear effects of the excited state contamination, which affect the generalized Goldberger-Treiman relation.
↳ hep-lathep-phnucl-exnucl-thPRD(2019)·132 citations
21
Light pseudoscalar meson and doubly charmed baryon scattering lengths with heavy diquark-antiquark symmetry
Lu Meng🇨🇳 · Shi-Lin Zhu🇨🇳
We adopt the heavy baryon chiral perturbation theory (HBChPT) to calculate the scattering lengths of $ϕ B_{cc}^{(*)}$ up to $O (p^{3})$ , where $ϕ$ is the pseudoscalar mesons. The recoil effect and the mass splitting between the spin- $\frac{1}{2}$ and spin- $\frac{3}{2}$ doubly charmed baryons are included. In order to give the numerical results, we construct the chiral Lagrangians with heavy diquark-antiquark (HDA) symmetry in a formally covariant approach. Then, we relate the low energy constants (LECs) of the doubly charmed baryons to those of $D^{(*)}$ mesons. The LECs for the $ϕ D^{(*)}$ scattering are estimated in two scenarios, fitting lattice QCD results and using the resonance saturation model. The chiral convergence of the first scenario is not good enough due to the the large strange quark mass and the presence of the possible bound states, virtual states and resonance. The final results for two scenarios are consistent with each other. The interaction for the $[π Ξ_{cc}^{(*)}]^{(1/2)}$ , $[K Ξ_{cc}^{(*)}]^{(0)}$ , $[K Ω_{cc}^{(*)}]^{(1/2)}$ , $[η Ξ_{cc}^{(*)}]^{(1/2)}$ , $[η Ω_{cc}^{(*)}]^{(0)}$ and $[K ˉ Ξ_{cc}^{(*)}]^{(0)}$ channels are attractive. The most attractive channel $[K ˉ Ξ_{cc}^{(*)}]^{(0)}$ may help to form the partner states of the $D_{s 0}^{*} (2317)$ ( $D_{s 1} (2460)$ ) in the doubly heavy sector.
↳ hep-phhep-exhep-latnucl-thPRD(2019)·27 citations
22
Zero point energy of composite particles: The medium effects
Toru Kojo🇨🇳
We analyze the zero point energy of composite particles (or resonances) which are dynamically created from relativistic fermions. We compare the zero point energies in medium to the vacuum one, taking into account the medium modification of the constituent particles. Treating composite particles as if quasi-particles, their zero point energies contain the quadratic and logarithmic UV divergences even after the vacuum subtraction. The coefficients of these divergences come from the difference between the vacuum and in-medium fermion propagators. We argue that such apparent divergences can be cancelled by consistently using fermion propagators to compute the quasi-particle contributions as well as their interplay, provided that the self-energies of the constituents at large momenta approach to the vacuum ones sufficiently fast. In the case of quantum chromodynamics, mesons and baryons, which may be induced or destroyed by medium effects, yield the in-medium divergences in the zero point energies, but the divergences are assembled to cancel with those from the quark zero-point energy. This is particularly important for unified descriptions of hadronic and quark matter which may be smoothly connected by the quark-hadron continuity.
↳ hep-phastro-ph.HEhep-thnucl-thPRD(2020)·5 citations
23
Studying parton correlations via double parton scatterings in associated quarkonium production at the LHC and the Tevatron
Nodoka Yamanaka🇫🇷 · Jean-Philippe Lansberg🇫🇷 · Hua-Sheng Shao🇫🇷 · Yu-Jie Zhang🇨🇳
Quarkonium production in proton-proton (pp) collision provides interesting means to study the parton content and their correlations in the proton. Recent LHC and Tevatron data of J/psi + Z, J/psi + W and J/psi +J/psi production suggest the relevance of double parton scatterings (DPSs) as opposed to single parton scatterings (SPSs). In this proceedings contribution, we review the corresponding SPS contributions and discuss their upper limits set up by quark-hadron duality. These allow us to perform an improved extraction of the DPS yields and of their implications.
↳ hep-phhep-exnucl-exnucl-thPoS(2019)·1 citation
24
Dilepton production and elliptic flow from an anisotropic quark-gluon plasma
Babak S. Kasmaei🇺🇸 · Michael Strickland🇺🇸
We calculate the yield and elliptic flow of mid-rapidity dileptons emitted from the quark-gluon plasma generated in Pb-Pb collisions at LHC. We use relativistic anisotropic hydrodynamics for the 3+1 dimensional evolution of the quark-gluon plasma and convolve this with the momentum-anisotropic local rest frame production rate for dileptons. The effects of momentum anisotropy of the quark distribution functions, viscosity to entropy density ratio, centrality of the collisions, and initial momentum anisotropy on the results are investigated and discussed.
↳ hep-phnucl-thPRD(2019)·39 citations
25
Searching for the Odderon in the diffractive $f_{2} (1270)$ photoproduction at $p A$ collisions
V. P. Goncalves🇧🇷
Although the Odderon is an unambiguous prediction of Quantum Chromodynamics, its existence still was not confirmed experimentally. One of the processes where the Odderon contribution is expected to be dominant is the diffractive photoproduction of tensor mesons. In this paper we study the diffractive $f_{2} (1270)$ photoproduction in $p A$ collisions at LHC and RHIC considering the model of the stochastic vacuum to treat the non - perturbative process. We demonstrate that this process dominates the $f_{2}$ production at mid - rapidities, and large values for the cross section are predicted. Our results indicate that the experimental analysis of this final state is, in principle, feasible and can be used to probe the Odderon.
↳ hep-phhep-exnucl-thEPJC(2019)·8 citations
26
Correction to the energy spectrum of $^{1} S_{0}$ heavy quarkonia due to two-gluon annihilation effect
Hui-Yun Cao🇨🇳 · Hai-Qing Zhou🇨🇳
In this work, the non-relativistic asymptotic behavior of the transition $q q \to 2 g \to q q$ in the $^{1} S_{0}$ channel is discussed. Different with the usual calculation which expands the physical amplitude around the quark anti-quark threshold, we take the quark anti-quark pairs as off shell and only expand the expression on the three-dimensional momenta of the quarks and anti-quarks. We calculate the results to order 6. The imagine part of the results after applying the on shell conditions can reproduce the non-relativistic QCD (NRQCD) results in leading order of $α_{s}$ . The real part of the results can be used to estimate the mass shift of the $^{1} S_{0}$ heavy quark anti-quark system due to the $2 g$ annihilation effect. The results can also be used to estimate the energy shifts of the positronium system due to the two-photon annihilation.
↳ hep-phnucl-thPRD(2019)·2 citations
27
Centrality and energy dependence of charged particles in p+A and A+A collisions from running coupling $k_{T}$ -factorization
Adrian Dumitru🇺🇸 · Andre V. Giannini🇧🇷 · Matthew Luzum🇧🇷 · Yasushi Nara🇯🇵
We extend the numerical analysis of the energy and centrality dependence of particle multiplicities at midrapidity in high-energy p+A and A+A collisions from a running coupling $k_{T}$ -factorization formula made in~\cite{Dumitru:2018gjm} by considering two unintegrated gluon distributions that were left out. While a good agreement with the experimental data in A+A collisions is achieved, improving the description of those observables in p+A collisions calls for a better understanding of the proton unintegrated gluon distribution at larger values of $x$ and also the use of a realistic impact parameter dependence.
↳ hep-phnucl-thActa Phys.Polon.Supp.(2019)·3 citations
28
Three-loop formula for quark and gluon contributions to the QCD trace anomaly
Kazuhiro Tanaka (Juntendo Univ.)🇯🇵
In the QCD energy-momentum tensor $T^{μν}$ , the terms that contribute to physical matrix elements are expressed as the sum of the gauge-invariant quark part and gluon part. Each part undergoes the renormalization due to the interactions among quarks and gluons, although the total tensor $T^{μν}$ is not renormalized thanks to the conservation of energy and momentum. Recently it has been shown that, through the renormalization, each of the quark and gluon parts of $T^{μν}$ receives a definite amount of anomalous trace contribution, such that their sum reproduces the well-known QCD trace anomaly, $T_{μ}^{μ} = (β /2 g) F^{μν} F_{μν} + m (1 + γ_{m}) ψ ˉ ψ$ , and the corresponding formulas have been derived up to two-loop order. We extend this result to the three-loop order, working out all the relevant three-loop renormalization structure for the quark and gluon energy-momentum tensors in the (modified) minimal subtraction scheme in the dimensional regularization. We apply our three-loop formula of the quark/gluon decomposition of the trace anomaly to calculate the anomaly-induced mass structure of nucleons as well as pions.
↳ hep-phhep-exnucl-exnucl-thJHEP(2019)·49 citations

Affiliations

first authorsco-authorsvia INSPIRE