Nuclear Theory·nucl-th

Wednesday·May 29, 2019

11 papers—5 primary·6 cross-listed

06
Nuclear-matter distribution in the proton-rich nuclei $^{7}$ Be and $^{8}$ B from intermediate energy proton elastic scattering in inverse kinematics
A.V. Dobrovolsky · G.A. Korolev · A.G. Inglessi · G.D. Alkhazov · G. Colò · I. Dillmann · P. Egelhof · A. Estradé · F. Farinon · H. Geissel · S.Ilieva · Y. Ke and 16 other authors
Absolute differential cross sections for elastic $p^{7}$ Be and $p^{8}$ B small-angle scattering were measured in inverse kinematics at an energy of 0.7 GeV/u at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR was used as an active target to detect the recoil protons. The projectile tracking and isotope identification were performed with multi-wire proportional chambers and scintillation detectors. The measured cross sections were analysed using the Glauber multiple-scattering theory. The root-mean-square (rms) nuclear matter radii $R_{m} = 2.42 (4)$ fm for $^{7}$ Be and $R_{m} = 2.58 (6)$ fm for $^{8}$ B were obtained. The radial density distribution deduced for $^{8}$ B exhibits a proton halo structure with the rms halo radius $R_{h} = 4.24 (25)$ fm. A comparison of the deduced experimental radii is displayed with existing experimental and theoretical data.
↳ nucl-exnucl-thNPA(2019)·22 citations
07
On pseudorapidity distribution in p-Pb and Xe-Xe collisions at high energy based on the three-source Landau hydrodynamic model
Li-Na Gao🇨🇳 · Zhen-Hu Li🇨🇳 · Er-Qin Wang🇨🇳
The pseudorapidity distributions of charged particles produced in p-Pb collisions and Xe-Xe collisions at LHC energies are described by the revised Landau hydrodynamic model. The research results are in agreement with the experimental data measured by ALICE collaboration at LHC. The related parameters are obtained and analyzed. And, we extracted the values of the squared speed of sound for central source are between 0.4 and 0.5.
↳ hep-phnucl-thIndian J.Phys.(2021)·0 citations
08
Questioning quark-gluon plasma formation in small collision systems
Thomas A. Trainor🇺🇸
A recent letter published in the journal Nature reports observation at the relativistic heavy ion collider (RHIC) of quark-gluon plasma (QGP) formation in small asymmetric collision systems denoted as $p$ -Au, $d$ -Au and $^{3}$ He-Au. The claimed phenomenon, described as `short-lived QGP droplets,' is inferred from a combination of Glauber Monte Carlo simulations, measurement of two azimuth Fourier amplitudes $v_{2}$ and $v_{3}$ and hydro theory calculations. While that claim follows a trend in recent years to report `signals' conventionally attributed to QGP as appearing also in smaller collision systems, the new result remains surprising in the context of expectations before first RHIC operation that small systems, e.g. $d$ -Au collisions, would provide control experiments in which a QGP was unlikely to appear. An alternative interpretation of the recent RHIC result is that small-system control experiments do convey an important message: The `signals' conventionally attributed to QGP formation in larger A-A collisions do not actually represent that phenomenon in any system. The present study reviews a broad array of experimental evidence for or against QGP formation in several collision systems. It examines in particular hydro theory descriptions of spectra and correlations usually interpreted to support QGP formation. Available evidence suggests that data features conventionally attributed to QGP formation represent either minimum-bias jet production or a nonjet azimuth quadrupole with properties inconsistent with a hydro hypothesis.
↳ hep-phnucl-th6 citations
09
Chiral phase transition in (2 + 1)-flavor QCD
Heng-Tong Ding🇨🇳 · Prasad Hegde🇮🇳 · Olaf Kaczmarek🇨🇳 · Frithjof Karsch🇩🇪 · Anirban Lahiri🇩🇪 · Sheng-Tai Li🇨🇳 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸
The chiral phase transition temperature $T_{c}^{0}$ is a fundamental quantity of QCD. To determine this quantity we have performed simulations of (2 + 1)-flavor QCD using the Highly Improved Staggered Quarks (HISQ/tree) action on $N_{τ} = 6, 8$ and 12 lattices with aspect ratios $N_{σ} / N_{τ}$ ranging from 4 to 8. In our simulations the strange quark mass is fixed to its physical value $m_{s}^{phy}$ , and the values of two degenerate light quark masses $m_{l}$ are varied from $m_{s}^{phy} /20$ to $m_{s}^{phy} /160$ which correspond to a Goldstone pion mass $m_{π}$ ranging from 160 MeV to 55 MeV in the continuum limit. By investigating the light quark mass dependence and the volume dependence of various chiral observables, e.g. chiral susceptibilities and Binder cumulants, no evidence for a first order phase transition in our current quark mass window is found. Two estimators $T_{60}$ and $T_{δ}$ are proposed to extract the chiral phase transition temperature $T_{c}^{0}$ in the chiral and continuum limit and our current estimate for $T_{c}^{0}$ is $13 2_{- 6}^{+ 3}$ MeV.
↳ hep-lathep-phhep-thnucl-thPoS(2019)·14 citations
10
Strong isospin symmetry breaking in light scalar meson production
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
Isospin symmetry breaking is discussed as a tool for studying the nature and production mechanisms of light scalar mesons. We are concerned with isospin breaking effects with an amplitude $\sim m_{d} - m_{u}$ (instead of the usual $\sim m_{d} - m_{u}$ ), where $m_{u}$ and $m_{d}$ are the $u$ and $d$ quark masses, whose magnitude and phase vary with energy in a resonance-like way characteristic of the $K K ˉ$ threshold region. We consider a variety of reactions that can experimentally reveal (or have revealed) the mixing of $a_{0}^{0} (980)$ and $f_{0} (980)$ resonances that breaks the isotopic invariance due to the mass difference between $K^{+}$ and $K^{0}$ mesons. Experimental results on the search for $a_{0}^{0} (980) - f_{0} (980)$ mixing in $f_{1} (1285) \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ and $η (1405) \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ decays suggest a broader perspective on the isotopic symmetry breaking effects due to the $K^{+}$ and $K^{0}$ mass difference. It has become clear that not only the $a_{0}^{0} (980) - f_{0} (980)$ mixing but also any mechanism producing $K K ˉ$ pairs with a definite isospin in an S wave gives rise to such effects, thus suggesting a new tool for studying the nature and production mechanisms of light scalars. Of particular interest is the case of a large isotopic symmetry breaking in the $η (1405) \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ decay due to the occurrence of anomalous Landau thresholds (logarithmic triangle singularities), i.e., due to the $η (1405) \to (K^{*} K ˉ + K ˉ^{*} K) \to (K^{+} K^{-} + K^{0} K ˉ^{0}) π^{0} \to f_{0} (980) π^{0} \to π^{+} π^{-} π^{0}$ transition (where it is of fundamental importance that the $K^{*}$ meson has a finite width).
↳ hep-phhep-exnucl-thPhys.Usp.(2019)·14 citations
11
Time-dependent relaxation of observables in complex quantum systems
Alexander Volya · Vladimir Zelevinsky
We consider time-dependent relaxation of observables in quantum systems of chaotic and regular type. We show that the spread of the wave function in the Hilbert space is determined by the survival probability which is known to have pre-exponential, exponential, and long-term power-law limiting behaviors. This result relies on complexity of the wave functions and thus is generic to many systems. In the chaotic limit modeled by the Gaussian Orthogonal Ensemble we show that the survival probability obtained analytically also fully defines the relaxation timescale of observables. This is not the case in general, using realistic nuclear shell model and the quadrupole moment as an observable we demonstrate that the relaxation time is significantly longer than defined by the survival probability of the initial state. An example of the non-chaotic limit of coherent and squeezed states provides an additional illustration.
↳ quant-phnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Nuclear-matter distribution in the proton-rich nuclei 7Be and 8B from intermediate energy proton elastic scattering in inverse kinematics

On pseudorapidity distribution in p-Pb and Xe-Xe collisions at high energy based on the three-source Landau hydrodynamic model

Questioning quark-gluon plasma formation in small collision systems

Chiral phase transition in (2 + 1)-flavor QCD

Strong isospin symmetry breaking in light scalar meson production

Time-dependent relaxation of observables in complex quantum systems

Affiliations

Nuclear-matter distribution in the proton-rich nuclei $^{7}$ Be and $^{8}$ B from intermediate energy proton elastic scattering in inverse kinematics