Nuclear Theory·nucl-th

Thursday·February 11, 2021

11 papers—5 primary·6 cross-listed

06
[Submitted on 10 Feb 2021] (cross-list from nucl-ex)
The effect of hadronic scatterings on the measurement of vector meson spin alignments in heavy-ion collisions
Diyu Shen🇨🇳 · Jinhui Chen🇨🇳 · Zi-Wei Lin🇨🇳
Spin alignments of vector mesons and hyperons in relativistic heavy-ion collisions have been proposed as signals of the global polarization. The STAR experiment first observed the $Λ$ polarization. Recently, the ALICE collaboration measured the transverse momentum ( $p_{T}$ ) and the collision centrality dependence of $K^{*}$ and $ϕ$ spin alignments in Pb-Pb collisions at $s_{NN}$ = 2.76 TeV. A large signal is observed in the low $p_{T}$ region of mid-central collisions for $K^{*}$ while the signal is much smaller for $ϕ$ , and these have not been understood yet. Since vector mesons have different lifetimes and their decay products have different scattering cross sections, they suffer from different hadronic effects. In this paper, we study the effect of hadronic interactions on the spin alignment of $K^{*}$ , $ϕ$ and $ρ$ mesons in relativistic heavy-ion collisions with a multi-phase transport model. We find that hadronic scatterings lead to a deviation of the observed spin alignment matrix element $ρ_{00}$ away from the true value for $ρ$ and $K^{*}$ mesons (with a bigger effect on $ρ$ ) while the effect is negligible for the $ϕ$ meson. The effect depends on the kinematic acceptance: the observed $ρ_{00}$ value is lower than the true value when the pseudorapidity ( $η$ ) coverage is small while there is little effect when the $η$ coverage is big. Our study thus provides valuable information to understand the vector meson spin alignment signals observed in the experiments.
Comments:
8 pages, 7 figures, submit to Chin. Phys. C
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2102.05266 [pdf]
CPC(2021)·15 citations
07
[Submitted on 10 Feb 2021] (cross-list from hep-ph)
Detecting scale anomaly in chiral phase transition of QCD: new critical endpoint pinned down
Mamiya Kawaguchi🇨🇳 · Shinya Matsuzaki🇨🇳 · Akio Tomiya🇺🇸
Violation of scale symmetry, scale anomaly, being a radical concept in quantum field theory, is of importance to comprehend the vacuum structure of QCD, and should potentially contribute to the chiral phase transition in thermal QCD, as well as the chiral and U(1) axial symmetry. Though it should be essential, direct evidence of scale anomalies has never been observed in the chiral phase transition. We propose a methodology to detect a scale anomaly in the chiral phase transition, which is an electromagnetically induced scale anomaly: apply a weak magnetic field background onto two-flavor massless QCD with an extremely heavy strange quark, first observe the chiral crossover; second, adjusting the strange quark mass to be smaller and smaller, observe the second-order chiral phase transition, and then the first-order one in the massless-three flavor limit. Thus, the second-order chiral phase transition, observed as the evidence of the quantum scale anomaly, is a new critical endpoint. It turns out that this electromagnetic scale anomaly gets most operative in the weak magnetic field regime, rather than a strong field region. We also briefly address accessibility of lattice QCD, a prospected application to dense matter system, and implications to astrophysical observations, such as gravitational wave productions provided from thermomagnetic QCD-like theories.
Comments:
23 pages, 7 figures, some references added, minor corrections made, version accepted in JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2102.05294 [pdf]
JHEP(2021)·7 citations
08
[Submitted on 10 Feb 2021] (cross-list from hep-ph)
Can the nature of $a_{0} (980)$ be tested in the $D_{s}^{+} \to π^{+} π^{0} η$ decay?
Xi-Zhe Ling🇨🇳 · Ming-Zhu Liu🇨🇳 · Jun-Xu Lu🇨🇳 · Li-Sheng Geng🇨🇳 · Ju-Jun Xie🇨🇳
From the amplitude analysis of the $D_{s}^{+} \to π^{+} π^{0} η$ decay, the BESIII Collaboration firstly observed the $D_{s}^{+} \to a_{0} (980)^{+} π^{0}$ and $D_{s}^{+} \to a_{0} (980)^{0} π^{+}$ decay modes, which are expected to occur through the pure $W$ -annihilation processes. The measured branching fraction $B [D_{s}^{+} \to a_{0} (980)^{+ (0)} π^{0 (+)}, a_{0} (980)^{+ (0)} \to π^{+ (0)} η]$ is, however, found to be larger than those of known $W$ -annihilation decays by one order of magnitude. This apparent contradiction can be reconciled if the two decays are induced by internal $W$ -conversion or external $W$ -emission mechanisms instead of $W$ -annihilation mechanism. In this work, we propose that the $D_{s}^{+}$ decay proceeds via both the external and internal $W$ -emission instead of $W$ -annihilation mechanisms. In such a scenario, we perform a study of the $D_{s}^{+} \to π^{+} π^{0} η$ decay by taking into account the contributions from the tree diagram $D_{s}^{+} \to ρ^{+} η \to π^{+} π^{0} η$ and the intermediate $ρ^{+} η$ and $K^{*} K ˉ / K K ˉ^{*}$ triangle diagrams. The intermediate $a_{0} (980)$ state can be dynamically generated from the final state interactions of coupled $K K ˉ$ and $π η$ channels, and it is shown that the experimental data can be described fairly well, which supports the interpretation of $a_{0} (980)$ as a molecular state.
Comments:
14 pages, 8 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2102.05349 [pdf]
PRD(2021)·37 citations
09
[Submitted on 10 Feb 2021] (cross-list from hep-ph)
Analysis of the kinematic boundaries of the quasi-elastic neutrino-nucleus cross section in the superscaling model with a relativistic effective mass
I. Ruiz Simo🇪🇸 · I.D. Kakorin🇷🇺 · V.A. Naumov🇷🇺 · K.S. Kuzmin🇷🇺 · J.E. Amaro🇪🇸
In this work we obtain the analytical expressions for the boundaries of the charged current quasi-elastic double differential cross section in terms of dimensionless energy and momentum transfers, for the Relativistic Fermi Gas (RFG) and the Super-Scaling approach with relativistic effective mass (SuSAM*) models, within the scaling formalism. In addition, we show that this double differential cross section in the scaling formalism has very good properties to be implemented in the Monte Carlo (MC) neutrino event generators, particularly because its peak is almost flat with the (anti)neutrino energy. This makes it especially well-suited for the event generation by the acceptance-rejection method usually used in the neutrino generators. Finally, we analyze the total charged current quasi-elastic (CCQE) cross section $σ (E_{ν})$ for both models and attribute the enhancement observed in the SuSAM* total cross section to the high-momentum components which are present, in a phenomenological way, in its scaling function, while these are absent in the RFG model.
Comments:
28 pages, 20 figures, two appendices. A full reorganization of the whole manuscript has been carried out with respect to the previous version. This version matches published version in Physical Review D. Title and abstract has been changed a bit with respect to the previous version as well
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2102.05510 [pdf]
PRD(2022)·0 citations
10
[Submitted on 10 Feb 2021] (cross-list from hep-th)
The relation between instant and light-front formulations of quantum field theory
Wayne Polyzou🇺🇸
The scattering equivalence of quantum field theories formulated with light-front and instant-form kinematic subgroups is established using non-perturbative methods. The difficulty with field theoretic formulations of Dirac's forms of dynamics is that the free and interacting unitary representations of the Poincaré group are defined on inequivalent representations of the Hilbert space, which means that the concept of kinematic transformations must be modified on the Hilbert space of the field theory. This work addresses this problem by assuming the existence of a field theory with the expected properties and constructs equivalent representations with instant and front form kinematic subgroups. In this construction both the light-front and instant-form formulations share the same vacuum and one-particle states. The free field Fock space plays no role. There is no "quantization" of a classical theory. The property that survives from the perturbative approach is the notion of a kinematic subgroup, which means kinematic Poincaré transformations can be trivially implemented by acting on suitable basis vectors. This non-perturbative approach avoids dealing with issues that arise in perturbative treatments where is it necessary to have a consistent treatment of renormalization, rotational covariance, and the structure of the light-front vacuum. While addressing these issues in a computational framework is important for applications, this work may provide some insight into the nature of the expected resolution and identifies the origin of some of differences between the perturbative and non-perturbative approaches.
Comments:
21 pages, two new sections
Subjects:
High Energy Physics — Theory (hep-th); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th)
arXiv:
2102.05525 [pdf]
PRD(2021)·10 citations
11
[Submitted on 10 Feb 2021] (cross-list from hep-ph)
Transverse $Λ$ Polarization in $e^{+} e^{-}$ collisions
Leonard Gamberg🇺🇸 · Zhong-Bo Kang🇺🇸 · Ding Yu Shao🇺🇸 · John Terry🇺🇸 · Fanyi Zhao🇺🇸
In this paper we study transverse polarization of $Λ$ hyperons in single-inclusive leptonic annihilation. We show that when the transverse momentum of the $Λ$ baryon is measured with respect to the thrust axis, a transverse momentum dependent (TMD) factorization formalism is required and the polarization is generated by the TMD polarizing fragmentation function (TMD PFF), $D_{1 T}^{⊥}$ . However, when the transverse momentum of the $Λ$ baryon is measured with respect to the momentum of the initial leptons, a collinear twist-3 formalism is required and the polarization is generated by the intrinsic collinear twist-3 fragmentation function $D_{T}$ . Thus while these measurements differ from one another only by a change in the measurement axis, they probe different distribution functions. Recently, Belle measured a significant polarization in single-inclusive $Λ$ baryon production as a function of the transverse momentum with respect to the thrust axis. However, this data can in principle be re-analyzed to measure the polarization as a function of the transverse momentum of the $Λ$ baryon with respect to the lepton pair. This observable could be the first significant probe of the function, $D_{T}$ . In this paper, we first develop a TMD formalism for $Λ$ polarization; we then present a recent twist-3 formalism that was established to describe $Λ$ polarization. Using the TMD formalism, we demonstrate that the $Λ$ polarization at OPAL and Belle can be described using the twist-2 TMD factorization formalism. Finally, we make a theoretical prediction for this polarization in the collinear twist-3 formalism at Belle.
Comments:
11 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2102.05553 [pdf]
PLB(2021)·31 citations

Affiliations

first authorsco-authorsvia INSPIRE

The effect of hadronic scatterings on the measurement of vector meson spin alignments in heavy-ion collisions

Detecting scale anomaly in chiral phase transition of QCD: new critical endpoint pinned down

Can the nature of a0​(980) be tested in the Ds+​→π+π0η decay?

Analysis of the kinematic boundaries of the quasi-elastic neutrino-nucleus cross section in the superscaling model with a relativistic effective mass

The relation between instant and light-front formulations of quantum field theory

Transverse Λ Polarization in e+e− collisions

Affiliations

Can the nature of $a_{0} (980)$ be tested in the $D_{s}^{+} \to π^{+} π^{0} η$ decay?

Transverse $Λ$ Polarization in $e^{+} e^{-}$ collisions