Nuclear Theory·nucl-th

Thursday·July 2, 2020

6 papers—4 primary·2 cross-listed

01
Study of freeze-out dynamics of strange hadrons
Sushant K. Singh🇮🇳 · Purabi Ghosh🇮🇳 · Jajati K. Nayak🇮🇳
We study the chemical freeze-out dynamics of strange particles ( $K, Λ, Σ$ ) from a homogeneous and isotropically expanding hadronic system of $π, K, ρ, N, Λ$ and $Σ$ with zero net baryon density. We use the momentum integrated Boltzmann equation and study their evolution over the bulk hadronic matter, a condition being similar to the one created at top RHIC and LHC energies. The cross-sections, which are input to the equations, are taken either from phenomenological models or parameterized by comparing against experimental data. From this microscopic calculation we find that these strange particles freeze-out near transition temperature $\approx T_{c}$ due to large relaxation time. The continuous cease of the inelastic processes due to gradual fall in the temperature and decrease in the number density, thus lead to early freeze out of strange hadrons $K, Λ$ and $Σ$ which happens sequentially near $T_{c}$ . However, freeze-out of these strange species near Tc appears as a sudden and simultaneous process, which is mostly predicted by thermal model while explaining the yield of identified particles at RHIC and LHC energies.
nucl-thhep-exhep-phnucl-exPRD(2021)·8 citations
02
Spin tensor and pseudo-gauges: from nuclear collisions to gravitational physics
Enrico Speranza🇩🇪 · Nora Weickgenannt🇩🇪
The relativistic treatment of spin is a fundamental subject which has an old history. In various physical contexts it is necessary to separate the relativistic total angular momentum into an orbital and spin contribution. However, such decomposition is affected by ambiguities since one can always redefine the orbital and spin part through the so-called pseudo-gauge transformations. We analyze this problem in detail by discussing the most common choices of energy-momentum and spin tensors with an emphasis on their physical implications, and study the spin vector which is a pseudo-gauge invariant operator. We review the angular momentum decomposition as a crucial ingredient for the formulation of relativistic spin hydrodynamics and quantum kinetic theory with a focus on relativistic nuclear collisions, where spin physics has recently attracted significant attention. Furthermore, we point out the connection between pseudo-gauge transformations and the different definitions of the relativistic center of mass. Finally, we consider the Einstein-Cartan theory, an extension of conventional general relativity, which allows for a natural definition of the spin tensor.
nucl-thhep-phhep-thEPJA(2021)·122 citations
03
Analytical Results for the Classical and Quantum Tsallis Hadron Transverse Momentum Spectra: the Zeroth Order Approximation and beyond
Trambak Bhattacharyya🇷🇺 · Alexandru S. Parvan🇷🇺
We derive the analytical expressions for the first and second order terms in the hadronic transverse momentum spectra obtained from the Tsallis normalized (Tsallis-1) statistics. We revisit the zeroth order quantum Tsallis distributions and obtain the corresponding analytical closed form expressions. It is observed that unlike the classical case, the analytical closed forms of the zeroth order quantum spectra do not resemble the phenomenological distributions used in the literature after $q \to q^{- 1}$ substitution, where $q$ is the Tsallis entropic parameter. However, the factorization approximation increases the extent of similarity.
nucl-thhep-exhep-phEPJA(2021)·7 citations
04
Electromagnetic fields and directed flow in large and small colliding systems at ultrarelativistic energies
Lucia Oliva🇩🇪
The hot and dense QCD matter produced in nuclear collisions at ultrarelativistic energy is characterized by very intense electromagnetic fields which attain their maximal strength in the early pre-equilibrium stage and interplay with the strong vorticity induced in the plasma by the large angular momentum of the colliding system. A promising observable keeping trace of these phenomena is the directed flow of light hadrons and heavy mesons produced in symmetric and asymmetric heavy-ion collisions as well as in proton-induced reactions. In particular, the splitting of the directed flow between particles with the same mass but opposite electric charge as a function of rapidity and transverse momentum gives access to the electromagnetic response of medium in all collision stages and in the different colliding systems. The highest influence of electromagnetic fields is envisaged in the pre-equilibrium stage of the collision and therefore a significant imprint is left on the early-produced heavy quarks. The aim of this review is to discuss the current developments towards the understanding of the generation and relaxation time of the electromagnetic fields embedded in both large and small systems and their impact on the charge-odd directed flow of light and heavy particles, highlighting the experimental results and the different theoretical approaches. Since it is possible to perform realistic simulations of high-energy collisions that incorporate also the generated electromagnetic fields and vorticity, the study of the directed flow can provide unique insight into the early nonequilibrium phase and the ensuing QGP formation and transport properties.
nucl-thEPJA(2020)·27 citations
05
Active-sterile neutrino mixing constraint using reactor antineutrinos with the ISMRAN set-up
S. P. Behera🇮🇳 · D. K. Mishra🇮🇳 · L. M. Pant🇮🇳
In this work, we present an analysis of the sensitivity to the active-sterile neutrino mixing with the Indian Scintillator Matrix for Reactor Anti-Neutrino (ISMRAN) experimental set-up at very short baseline. In this article, we have considered the measurement of electron antineutrino induced events employing a single detector which can be placed either at a single position or moved between near and far positions from the given reactor core. Results extracted in the later case are independent of the theoretical prediction of the reactor anti-neutrino spectrum and detector related systematic uncertainties. Our analysis shows that the results obtained from the measurement carried out at a combination of the near and far detector positions are improved significantly at higher $Δ m_{41}^{2}$ compared to the ones obtained with the measurement at a single detector position only. It is found that the best possible combination of near and far detector positions from a 100 MW $_{t h}$ power DHRUVA research reactor core are 7 m and 9 m, respectively, for which ISMRAN set-up can exclude in the range 1.4 $e V^{2} \leq Δ m_{41}^{2} \leq$ 4.0 $e V^{2}$ of reactor antineutrino anomaly region along with the present best-fit point of active-sterile neutrino oscillation parameters. At those combinations of detector positions, the ISMRAN set-up can observe the active sterile neutrino oscillation with a 95 $%$ confidence level provided that $sin^{2} 2 θ_{14} \geq 0.09$ at $Δ m_{41}^{2}$ = 1 eV $^{2}$ for an exposure of 1 ton-yr. The active-sterile neutrino mixing sensitivity can be improved by about 22\% at the same exposure by placing the detector at near and far distances of 15 m and 17 m, respectively, from the compact proto-type fast breeder reactor (PFBR) facility which has a higher thermal power of 1250 MW $_{t h}$ .
↳ hep-phnucl-exnucl-thphysics.ins-detPRD(2020)·15 citations
06
Sensitivity of $^{229}$ Th nuclear clock transition to variation of the fine-structure constant
Pavel Fadeev🇩🇪 · Julian C. Berengut🇦🇺 · Victor V. Flambaum🇩🇪
Peik and Tamm [Europhys. Lett. 61, 181 (2003)] proposed a nuclear clock based on the isomeric transition between the ground state and the first excited state of thorium-229. This transition was recognized as a potentially sensitive probe of possible temporal variation of the fine-structure constant, $α$ . The sensitivity to such a variation can be determined from measurements of the mean-square charge radius and quadrupole moment of the different isomers. However, current measurements of the quadrupole moment are yet to achieve an accuracy high enough to resolve non-zero sensitivity. Here we determine this sensitivity using existing measurements of the change in the mean-square charge radius, coupled with the ansatz of constant nuclear density. The enhancement factor for $α$ variation is $K = - (0.82 \pm 0.25) \times 1 0^{4}$ . For the current experimental limit, $δ α / α ≲ 1 0^{- 17}$ per year, the corresponding frequency shift is $\sim 200$ Hz per year. This shift is six orders of magnitude larger than the projected accuracy of the nuclear clock, paving the way for increased accuracy of the determination of $δ α$ and interaction strength with low-mass scalar dark matter. We verify that the constant-nuclear-density ansatz is supported by nuclear theory and propose how to verify it experimentally. We also consider a possible effect of the octupole deformation on the sensitivity to $α$ variation, and calculate the effects of $α$ variation in a number of Mössbauer transitions.
↳ physics.atom-phhep-phnucl-thPRA(2020)·65 citations

Affiliations

first authorsco-authorsvia INSPIRE

Study of freeze-out dynamics of strange hadrons

Spin tensor and pseudo-gauges: from nuclear collisions to gravitational physics

Analytical Results for the Classical and Quantum Tsallis Hadron Transverse Momentum Spectra: the Zeroth Order Approximation and beyond

Electromagnetic fields and directed flow in large and small colliding systems at ultrarelativistic energies

Active-sterile neutrino mixing constraint using reactor antineutrinos with the ISMRAN set-up

Sensitivity of 229Th nuclear clock transition to variation of the fine-structure constant

Affiliations

Sensitivity of $^{229}$ Th nuclear clock transition to variation of the fine-structure constant