Nuclear Theory·nucl-th

Tuesday·October 10, 2017

20 papers—11 primary·9 cross-listed

12
Spectroscopy and decays of the fully-heavy tetraquarks
Muhammad Naeem Anwar🇩🇪 · Jacopo Ferretti🇨🇳 · Feng-Kun Guo🇨🇳 · Elena Santopinto🇮🇹 · Bing-Song Zou🇨🇳
We discuss the possible existence of the fully-heavy tetraquarks. We calculate the ground-state energy of the $bb b ˉ b ˉ$ bound state, where $b$ stands for the bottom quark, in a nonrelativistic effective field theory framework with one-gluon-exchange (OGE) color Coulomb interaction, and in a relativized diquark model characterized by OGE plus a confining potential. Our analysis advocates the existence of uni-flavor heavy four-quark bound states. The ground state $bb b ˉ b ˉ$ tetraquark mass is predicted to be $(18.72 \pm 0.02)$ ~GeV. Mass inequality relations among the lowest $QQ Q ˉ Q ˉ$ state, where $Q \in {c, b}$ , and the corresponding heavy quarkonia are presented, which give the upper limit on the mass of ground state $QQ Q ˉ Q ˉ$ . The possible decays of the lowest $bb b ˉ b ˉ$ are highlighted, which might provide useful references in the search for them in ongoing LHC experiments, and its width is estimated to be a few tens of MeV.
↳ hep-phhep-exnucl-thEPJC(2018)·172 citations
13
Roper resonance -- solution to the fifty year puzzle
Volker D. Burkert🇺🇸 · Craig D. Roberts🇺🇸
For half a century, the Roper resonance has defied understanding. Discovered in 1963, it appears to be an exact copy of the proton except that its mass is 50% greater. The mass is the first problem: it is difficult to explain with any theoretical tool that can validly be used to study quantum chromodynamics [QCD]. In the last decade, a new challenge has appeared, viz. precise information on the proton-to-Roper electroproduction transition form factors, reaching $Q^{2} \approx 4.5$ GeV $^{2}$ . This scale probes the domain within which hard valence-quark degrees-of-freedom could be expected to determine form factor behavior. Hence, with this new data the Roper resonance becomes a problem for strong-QCD [sQCD]. An explanation of how and where the Roper resonance fits into the emerging spectrum of hadrons cannot rest on a description of its mass alone. Instead, it must combine this with a detailed understanding of the Roper's structure and how that is revealed in the transition form factors. Furthermore, it must unify all this with a similarly complete picture of the proton. This is a prodigious task, but a ten-year international effort, drawing together experimentalists and theorists, has presented a solution to the puzzle. Namely, the Roper is at heart the proton's first radial excitation, consisting of a dressed-quark core augmented by a meson cloud that reduces the core mass by approximately 20% and materially alters its electroproduction form factors on $Q^{2} < 2 m_{N}^{2}$ , where $m_{N}$ is the proton's mass. We describe the experimental motivations and developments which enabled electroproduction data to be procured within a domain that is unambiguously the purview of sQCD, thereby providing a real challenge and opportunity for modern theory; and survey the developments in reaction models and QCD theory that have enabled this conclusion to be drawn about the nature of the Roper resonance.
↳ nucl-exhep-lathep-phnucl-thRMP(2019)·161 citations
14
Improved real-time dynamics from imaginary frequency lattice simulations
Jan M. Pawlowski🇩🇪 · Alexander Rothkopf🇩🇪
The computation of real-time properties, such as transport coefficients or bound state spectra of strongly interacting quantum fields in thermal equilibrium is a pressing matter. Since the sign problem prevents a direct evaluation of these quantities, lattice data needs to be analytically continued from the Euclidean domain of the simulation to Minkowski time, in general an ill-posed inverse problem. Here we report on a novel approach to improve the determination of real-time information in the form of spectral functions by setting up a simulation prescription in imaginary frequencies. By carefully distinguishing between initial conditions and quantum dynamics one obtains access to correlation functions also outside the conventional Matsubara frequencies. In particular the range between $ω_{0}$ and $ω_{1} = 2 π T$ , which is most relevant for the inverse problem may be more highly resolved. In combination with the fact that in imaginary frequencies the kernel of the inverse problem is not an exponential but only a rational function we observe significant improvements in the reconstruction of spectral functions, demonstrated in a simple 0+1 dimensional scalar field theory toy model.
↳ hep-latnucl-thEPJ Web Conf.(2018)·2 citations
15
S-matrix analysis of the baryon electric charge correlation
Pok Man Lo🇩🇪 · Bengt Friman🇩🇪 · Krzysztof Redlich🇩🇪 · Chihiro Sasaki🇵🇱
We compute the correlation of the net baryon number with the electric charge ( $χ_{B Q}$ ) for an interacting hadron gas using the S-matrix formulation of statistical mechanics. The observable $χ_{B Q}$ is particularly sensitive to the details of the pion-nucleon interaction, which are consistently incorporated in the current scheme via the empirical scattering phase shifts. Comparing to the recent lattice QCD studies in the $(2 + 1)$ -flavor system, we find that the natural implementation of interactions and the proper treatment of resonances in the S-matrix approach lead to an improved description of the lattice data over that obtained in the hadron resonance gas model.
↳ hep-phnucl-thPLB(2018)·59 citations
16
Average CsI neutron density distribution from COHERENT data
M. Cadeddu🇮🇹 · C. Giunti🇮🇹 · Y.F. Li🇨🇳 · Y.Y. Zhang🇨🇳
Using the coherent elastic neutrino-nucleus scattering data of the COHERENT experiment, we determine for the first time the average neutron rms radius of $^{133} Cs$ and $^{127} I$ . We obtain the practically model-independent value $R_{n} = 5.5_{- 1.1}^{+ 0.9} fm$ using the symmetrized Fermi and Helm form factors. We also point out that the COHERENT data show a $2.3 σ$ evidence of the nuclear structure suppression of the full coherence.
↳ hep-phhep-exnucl-exnucl-thPRL(2018)·158 citations
17
X(3872): propagating in a dense medium
K. Azizi🇹🇷 · N. Er🇹🇷
In cold nuclear matter, the shifts in the mass and current-meson coupling as well the vector self energy of the exotic $X (3872)$ are calculated using the diquark-antidiquark current within the framework of the in-medium two-point QCD sum rule. At the rest frame of the medium, the three momentum of the considered particle is fixed to remove the contributions of the particles with negative energy. In the calculations, we include the in-medium condensates of quark-quark, gluon-gluon and quark-gluon. It is observed that, the shift due to the nuclear matter is negative and is about $25%$ when the saturation density is used. Such shift is considerably large and comparable with the nucleon' mass shift due to the nuclear medium. The negative shift in the current-meson coupling due to nuclear matter is approximately $10%$ . At the saturation density, the vector self energy of the exotic $X (3872)$ state is found to be $Σ_{υ} = 1.31$ GeV. It is shown that the mass, current-meson coupling and vector self energy of $X (3872)$ strongly depend on the density of cold nuclear matter.
↳ hep-phhep-exhep-latnucl-thNPB(2018)·29 citations
18
Derivation of Brown-Rho scaling from scale-chiral perturbation theory
Yan-Ling Li🇨🇳 · Yong-Liang Ma🇨🇳
The medium modified hadron properties are studied by using the scale-chiral perturbation theory $χ$ PT $_{σ}$ in which the lightest scalar meson $f_{0} (500)$ is included as an explicit degree of freedom by regarding it as the Nambu-Goldstone boson of scale symmetry both spontaneously broken and explicitly broken by the QCD trace anomaly. We derive Brown-Rho scaling at the leading order of scale symmetry from $χ$ PT $_{σ}$ and formulate how to make higher-order scale-chiral corrections going beyond the leading order of scale symmetry. By taking into account the intrinsic density dependence given by the dilaton condensate in the "bare" parameters of the Lagrangian, the medium modified hadron properties are investigated. Relying on available experimental information and certain reasonable assumptions, we arrive at the leading order scale symmetric effective theory that can be confronted with nature .
↳ hep-phnucl-th8 citations
19
Rotating Dirac fermions in a magnetic field in 1+2,3 dimensions
Yizhuang Liu🇺🇸 · Ismail Zahed🇺🇸
We consider the effects of an external magnetic field on rotating fermions in 1+2,3 dimensions. The dual effect of a rotation parallel to the magnetic field causes a net increase in the fermionic density by centrifugation, which follows from the sinking of the particle lowest Landau level in the Dirac sea for free Dirac fermions. In 1+d = 2n dimensions, this effect is related to the chiral magnetic effect in 2n-2 dimensions. This phenomenon is discussed specifically for both weak and strong inter-fermion interactions in 1+2 dimensions. For QCD in 1+3 dimensions with Dirac quarks, we show that in the strongly coupled phase with spontaneously broken chiral symmetry, this mechanism reveals itself in the form of an induced pion condensation by centrifugation. We use this observation to show that this effect causes a shift in the chiral condensate in leading order, and to discuss the possibility for the formation of a novel pion super-fluid phase in present heavy ion collisions at collider energies.
↳ hep-phhep-thnucl-thPRD(2018)·25 citations
20
Re-examining the $X (4630)$ resonance in the reaction $e^{+} e^{-} \to Λ_{c}^{+} Λ ˉ_{c}^{-}$
Ling-Yun Dai🇩🇪 · Johann Haidenbauer🇩🇪 · Ulf-G. Meißner🇩🇪
The reaction $e^{+} e^{-} \to Λ_{c}^{+} Λ ˉ_{c}^{-}$ is investigated at energies close to the threshold with emphasis on the role played by the $X (4630)$ resonance. The interaction in the final $Λ_{c}^{+} Λ ˉ_{c}^{-}$ system, constructed within chiral effective field theory and supplemented by a pole diagram that represents a bare $X (4630)$ resonance, is taken into account rigorously. The pole parameters of the $X (4630)$ are extracted and found to be compatible with the ones of the $X (4660)$ resonance that have been established in the reaction $e^{+} e^{-} \to π^{+} π^{-} ψ (2 S)$ . The actual result for the $X (4630)$ is $M = (4652.5 \pm 3.4)$ MeV and $Γ = (62.6 \pm 5.6)$ MeV. Predictions for the $Λ_{c}^{+}$ electromagnetic form factors in the timelike region are presented.
↳ hep-phnucl-thPRD(2017)·48 citations

Affiliations

first authorsco-authorsvia INSPIRE