Nuclear Theory·nucl-th

Tuesday·May 12, 2020

25 papers—12 primary·13 cross-listed

13
Dark matter or correlated errors: Systematics of the AMS-02 antiproton excess
Jan Heisig🇧🇪 · Michael Korsmeier🇮🇹 · Martin Wolfgang Winkler🇸🇪
Several studies have pointed out an excess in the AMS-02 antiproton spectrum at rigidities of 10-20 GV. Its spectral properties were found to be consistent with a dark-matter particle of mass 50-100 GeV which annihilates hadronically at roughly the thermal rate. In this work, we reinvestigate the antiproton excess including all relevant sources of systematic errors. Most importantly, we perform a realistic estimate of the correlations in the AMS-02 systematic error which could potentially "fake" a dark-matter signal. The dominant systematics in the relevant rigidity range originate from uncertainties in the cross sections for absorption of cosmic rays within the detector material. For the first time, we calculate their correlations within the full Glauber-Gribov theory of inelastic scattering. The AMS-02 correlations enter our spectral search for dark matter in the form of covariance matrices which we make publicly available for the cosmic-ray community. We find that the global significance of the antiproton excess is reduced to below 1 $σ$ once all systematics, including the derived AMS-02 error correlations, are taken into account. No significant preference for a dark-matter signal in the AMS-02 antiproton data is found in the mass range 10-10000 GeV.
↳ astro-ph.HEhep-phnucl-thPRResearch(2020)·102 citations
14
Non-perturbative Enhancement of Heavy Quark-Antiquark Pair Annihilation in the Quark-Gluon Plasma
Xin Wu🇨🇳 · Min He🇨🇳
The annihilation of heavy particles close to thermal equilibrium, which plays a prominent role in the chemical equilibration of heavy quarks in the Quark-Gluon Plasma (QGP) as well as in many classic dark matter scenarios, is reexamined. We derive a scattering amplitude that resums near-threshold attractive interaction of the annihilating particles in terms of the non-relativistic scattering $T$ -matrix and Green's function, thereby capturing the pertinent Sommerfeld enhancement from both nonperturbative scattering state and bound state solutions. The derived formula is of such generality that it applies to arbitrary partial wave processes of two-particle annihilation, and enables to incorporate finite widths of the annihilating particles. In a screened potential model, the non-perturbative scattering amplitude is computed and the Sommerfeld enhancement is identified for heavy quark-antiquark annihilation in the QGP.
↳ hep-phnucl-exnucl-thPRD(2020)·0 citations
15
A Search for the Quark-Hadron Phase Transition in pp collisions at $s$ = 13 TeV using UrQMD model
Swarnapratim Bhattacharyya🇮🇳
Charged particle multiplicity fluctuations in pp collisions at $s$ = 13 TeV have been studied by the method of scaled factorial moment for the minimum bias events generated by Ultra Relativistic Quantum Molecular Dynamics (UrQMD) model in the pseudo-rapidity ({\eta}), azimuthal angle ( $ϕ$ ) and two dimensional anisotropic ( $η$ - $ϕ$ ) phase space. Strong intermittent type of fluctuations have been observed for the UrQMD simulated data. Systematic studies of intermittent fluctuations in terms of scaled factorial moments was utilized to extract the anomalous fractal dimension in the pseudo-rapidity ({\eta}), azimuthal angle ( $ϕ$ ) and two dimensional anisotropic ( $η$ - $ϕ$ ) phase space. Search for the quark-hadron phase transition in the framework of Ginzburg-Landau theory of second-order phase transition by the analysis with the factorial moment method has also been performed.
↳ nucl-exnucl-th0 citations
16
Dense Baryonic Matter and Applications of QCD Phase Diagram Dualities
T. G. Khunjua🇬🇪 · K. G. Klimenko🇷🇺 · R. N. Zhokhov🇷🇺
Recently it has been found that quantum chromodynamics (QCD) phase diagram possesses a duality between chiral symmetry breaking and pion condensation. For the first time this was revealed in the QCD motivated toy model. Then it was demonstrated in effective models as well and new additional dualities being found. We briefly recap the main features of this story and then discuss its applications as a tool to explore the QCD phase structure. The most appealing application is the possibility of getting the results on the QCD phase diagram at large baryon density. Taking the idea from large $1/ N_{c}$ universalities it was argued that the scenario of circumventing the sign problem with the help of dualities seems plausible. It is also discussed that there is a persistent problem about whether there should be catalysis or anti-catalysis of chiral symmetry breaking by chiral imbalance. One can probably say that the issue is settled after lattice results (first principle approach), where the catalysis was observed. But they used an unphysically large pion mass so it is still interesting to get additional indications that this is the case. It is shown just by the duality property that there exists catalysis of chiral symmetry breaking. So, having in mind our results and the earlier lattice simulations, one can probably claim that this issue is settled. It is demonstrated that the duality can be used to obtain new results. As an example, it is showcased how the phase structure of dense quark matter with chiral imbalance (with possibility of inhomogeneous phases) can be obtained from the knowledge of a QCD phase diagram with isopin asymmetry.
↳ hep-phhep-thnucl-thParticles(2020)·14 citations
17
Dense baryonic matter with chiral imbalance and charged pion condensation
T. G. Khunjua🇺🇸 · K. G. Klimenko🇷🇺 · R. N. Zhokhov🇷🇺
After the first predictions in seventies that in dense nuclear matter, for example, in neutron stars there could be pion condensation phenomenon, it was shown that at least s-wave pion condensation is unlikely to occur in such a medium in different approaches including NJL model consideration with neutrality and $β$ -equilibrium condition. Then it has been found a condition that can promote this phenomenon in dense baryonic matter, it is chiral imbalance, so now it is interesting if this generation can survive rather strict requirement of electric neutrality and $β$ -equilibrium. Here in this paper the generation of pion condensation in dense baryonic matter by chiral imbalance is investigated. It is shown that electric neutrality and $β$ -equilibrium conditions do not spoil this phenomenon and this leads to interesting applications for physics of neutron stars. There are several possible mechanisms of generation of chiral imbalance in dense matter. In a view of latest and forthcoming NICER results and the first observed and possibly new events of neutron star mergers it is rather interesting to explore how possible chiral imbalance in neutron star can influence and change EOS and, hence, mass-radius relation. It is a first step in that direction.
↳ hep-phhep-thnucl-thActa Phys.Polon.Supp.(2021)·8 citations
18
Spectroscopy of low spin states in 157Dy: Search for evidence of enhanced octupole correlations
S. N. T. Majola🇿🇦 · R. A. Bark🇿🇦 · L. Bianco🇨🇦 · T. D. Bucher🇿🇦 · S. P. Bvumbi🇿🇦 · D. M. Cullen🇫🇮 · P. E. Garrett🇨🇦 · P. T. Greenlees🇫🇮 · D. Hartley🇺🇸 · J Hirvonen🇫🇮 · U. Jakobsson🇫🇮 · P. M. Jones🇿🇦 and 31 other authors
Low-spin states of 157Dy have been studied using the JUROGAM II array, following the 155Gd ({\alpha}, 2n) reaction at a beam energy of 25 MeV. The level scheme of 157Dy has been expanded with four new bands. Rotational structures built on the [523]5/2- and [402]3/2+ neutron orbitals constitute new additions to the level scheme as do many of the inter- and intra-band transitions. This manuscript also reports the observation of cross I- to (I-1)- and I- to (I-1)+ E1 dipole transitions inter-linking structures built on the [523]5/2- (band 5) and [402]3/2+ (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s = -i related to possible octupole correlations.
↳ nucl-exnucl-thPRC(2019)·6 citations
19
Smooth flux-sheets with topological winding modes
A. Bakry🇨🇳 · M. Deliyergiyev🇵🇱 · A. Galal🇪🇬 · M. Khalil Williams🇩🇪
The inclusion of the Gaussian-curvature term in the bulk of Polyakov-Kleinert string action renders new boundary terms and conditions by Gauss-Bonnet theorem. Within a leading approximation, the eigenmodes of smooth worldsheets and the free-energy of a gas of open rigid strings appears to be altered at second order in the coupling by the topological term . In analogy to the topological $θ$ term, the Gauss-Bonnet term is introduced into the effective action with a complex coupling to implement signed energy shifts. We investigate the rigid color flux-sheets between two static color sources near the critical point in the light of the topologically induced shifts. The Yang-Mills lattice data of the potential of static quark-antiquark $Q Q ˉ$ in a heatbath is compared to the string potential. The Monte-Carlo data correspond to link-integrated Polyakov-loop correlators averaged over SU(3) gauge configurations at $β = 6.0$ . Substantial improvement in the fit behavior is displayed over the nonperturbative source separation distance $0.2$ fm to $1.0$ fm. Remarkably, the returned coupling parameter of the topological term from the fit exhibits a proportionality to a quantum number. These findings suggest that the manifested modes are the winding number of a topological particle on the string's worldsheet.
↳ hep-lathep-phhep-thnucl-th4 citations
20
First candidates for {\gamma} vibrational bands built on the [505]11/2- neutron orbital in odd-A Dy isotopes
S.N.T. Majola🇿🇦 · M.A. Sithole🇿🇦 · L. Mdletshe🇿🇦 · D. Hartley🇺🇸 · J. Timar🇭🇺 · B.M. Nyako🇭🇺 · J.M. Allmond🇺🇸 · R.A. Bark🇿🇦 · C. Beausang🇺🇸 · L. Bianco🇨🇦 · T.D. Bucher🇿🇦 · S.P. Bvumbi and 58 other authors
Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the 155Gd({\alpha},2n)157Dy and 148Nd(12C, 5n)155Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a K{\pi}= 2+ {\gamma} vibrational band, built on the [505]11/2- neutron orbital, in both odd-A 155, 157Dy isotopes. The coupling of the first excited K=0+ states or the so-called \b{eta} vibrational bands at 661 and 676 keV in 154Dy and 156Dy to the [505]11/2- orbital, to produce a K{\pi}=11/2- band, was not observed in both 155Dy and 157Dy, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei 154Dy and 156Dy are also discussed.
↳ nucl-exnucl-thPRC(2020)·5 citations
21
Observation of $γ$ -vibrations and alignments built on non-ground-state configurations in 156Dy
S. N. T. Majola🇿🇦 · D. J. Hartley🇺🇸 · L.L. Riedinger🇺🇸 · J.F. Sharpey-Schafer🇿🇦 · J. M. Allmond🇺🇸 · C. Beausang🇺🇸 · M.P. Carpenter🇺🇸 · C.J. Chiara🇺🇸 · N. Cooper🇺🇸 · D. Curien🇫🇷 · B. J. P. Gall🇫🇷 · P.E. Garrett🇨🇦 and 16 other authors
The exact nature of the lowest $K^{π} = 2_{γ}^{+}$ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the $γ$ degree of freedom perpendicular to the nuclear symmetry axis. Very few such $γ$ -bands have been traced past the usual back-bending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus 156Dy, using the 148Nd(12C,4n)156Dy reaction at 65 MeV, observing the resulting $γ$ -ray transitions with the Gammasphere array. The even- and odd-spin members of the $K^{π} = 2_{γ}^{+}$ $γ$ -band are observed to 32+ and 31+ respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible $γ$ -vibration built on the aligned yrast S-band are observed to spins 28+ and 27+. An even-spin positive-parity band, observed to spin 24+, is a candidate for an aligned S-band built on the seniority-zero configuration of the $0_{2}^{+}$ state at 676 keV. The crossing of this band with the $0_{2}^{+}$ band is at $ℏ ω$ = 0.28(1) MeV and is consistent with the configuration of the $0_{2}^{+}$ band not producing any blocking of the monopole pairing.
↳ nucl-exnucl-thPRC(2015)·25 citations
22
Unconventional superconductivity as a synchronization problem in nuclear oscillator networks
V. Velasco · M. B. Silva Neto
We formulate the problem of unconventional $d -$ wave superconductivity, with phase fluctuations, pseudogap phenomenon, and local Cooper pairs, in terms of a synchronization problem in random, quantum dissipative, elasto-nuclear oscillator networks. The nodes of the network correspond to {\it localized, collective quadrupolar vibrations} of nuclei-like, elastic inhomogeneities embedded in a dissipative medium. Electrons interacting with such vibrations form local Cooper pairs, with a superfluid $d -$ wave pseudogap $Δ_{P G}$ , due to an effective, short range attractive interaction of $d_{x^{2} - y^{2}}$ character. Phase coherent, bulk superconductivity, with a $d -$ wave gap $Δ$ , is stabilized when the oscillator network is asymptotically entangled in a nearly decoherence-free environment. Phase coherence will in turn be destroyed, at $T_{c}$ , when the thermal noise becomes comparable to the coupling between oscillators, the superfluid density $K$ . The $2Δ/ k_{B} T_{c}$ ratio is a function of Kuramoto's order parameter, $r = 1 - K_{c} / K$ , for the loss of synchronization at $K_{c}$ , and is much larger than the nonuniversal $2 Δ_{P G} / k_{B} T^{*}$ ratio, where $T^{*}$ is the temperature at which $Δ_{P G}$ is completely destroyed by thermal fluctuations. We discuss our findings in connection to the available data for various unconventionally high-temperature superconductors.
↳ cond-mat.supr-connlin.AOnucl-thJ.Phys.Comm.(2021)·1 citation
23
$F_{K} / F_{π}$ from Möbius domain-wall fermions solved on gradient-flowed HISQ ensembles
Nolan Miller🇺🇸 · Henry Monge-Camacho🇺🇸 · Chia Cheng Chang🇯🇵 · Ben Hörz🇺🇸 · Enrico Rinaldi🇯🇵 · Dean Howarth🇺🇸 · Evan Berkowitz🇺🇸 · David A. Brantley🇺🇸 · Arjun Singh Gambhir🇺🇸 · Christopher Körber🇺🇸 · Christopher J. Monahan🇺🇸 · M. A. Clark🇺🇸 and 6 other authors
We report the results of a lattice quantum chromodynamics calculation of $F_{K} / F_{π}$ using Möbius domain-wall fermions computed on gradient-flowed $N_{f} = 2 + 1 + 1$ highly-improved staggered quark (HISQ) ensembles. The calculation is performed with five values of the pion mass ranging from $130 ≲ m_{π} ≲ 400$ MeV, four lattice spacings of $a \sim 0.15, 0.12, 0.09$ and $0.06$ fm and multiple values of the lattice volume. The interpolation/extrapolation to the physical pion and kaon mass point, the continuum, and infinite volume limits are performed with a variety of different extrapolation functions utilizing both the relevant mixed-action effective field theory expressions as well as discretization-enhanced continuum chiral perturbation theory formulas. We find that the $a \sim 0.06$ fm ensemble is helpful, but not necessary to achieve a subpercent determination of $F_{K} / F_{π}$ . We also include an estimate of the strong isospin breaking corrections and arrive at a final result of $F_{K^{\pm}} / F_{π^{\pm}} = 1.1942 (45)$ with all sources of statistical and systematic uncertainty included. This is consistent with the Flavour Lattice Averaging Group average value, providing an important benchmark for our lattice action. Combining our result with experimental measurements of the pion and kaon leptonic decays leads to a determination of $∣ V_{u s} ∣/∣ V_{u d} ∣ = 0.2311 (10)$ .
↳ hep-lathep-exhep-phnucl-thPRD(2020)·57 citations
24
Excitation function of initial temperature of heavy flavor quarkonium emission source in high energy collisions
Qi Wang🇨🇳 · Fu-Hu Liu🇨🇳
The transverse momentum spectra of $J / ψ$ , $ψ (2 S)$ , and $Υ (n S, n = 1, 2, 3)$ produced in proton-proton ( $p$ + $p$ ), proton-antiproton ( $p$ + $p ˉ$ ), proton-lead ( $p$ +Pb), gold-gold (Au+Au), and lead-lead (Pb+Pb) collisions over a wide energy range are analyzed by the (two-component) Erlang distribution, the Hagedorn function (the inverse power-law), and the Tsallis-Levy function. The initial temperature is obtained from the color string percolation model due to the fit by the (two-component) Erlang distribution in the framework of multisource thermal model. The excitation functions of some parameters such as the mean transverse momentum and initial temperature increase from dozens of GeV to above 10 TeV. The mean transverse momentum and initial temperature decrease (increase slightly or do not change obviously) with the increase of rapidity (centrality). Meanwhile, the mean transverse momentum of $Υ (n S, n = 1, 2, 3)$ is larger than that of $J / ψ$ and $ψ (2 S)$ , and the initial temperature for $Υ (n S, n = 1, 2, 3)$ emission is higher than that for $J / ψ$ and $ψ (2 S)$ emission, which shows a mass-dependent behavior.
↳ hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2020)·10 citations
25
$ϕ$ meson mass and decay width in strange hadronic matter
Rajesh Kumar🇮🇳 · Arvind Kumar🇮🇳
The in-medium mass and decay width of the $ϕ$ meson in the hot asymmetric strange hadronic matter are calculated using an effective Lagrangian approach for $ϕ$ $K K ˉ$ interaction. The in-medium contributions of $K K ˉ$ loop to the $ϕ$ meson self-energy are computed by the medium modified kaon and antikaon mass which is evaluated using the chiral SU(3) model. To deal with the ultraviolet divergence, we regularize the loop integral of self-energy with a dipole form factor, and present the results for cut-off mass, $Λ_{c}$ =3 GeV. In chiral model calculations, for strange matter, we find that the mass of kaons and antikaons decreases with the increase in baryonic density whereas the finite temperature causes an increase in the mass. We observed that the in-medium $ϕ$ meson mass decreases slowly with baryonic density whereas the decay width increases rapidly. The results in the present investigation support result in the literature which indicate a small downward shift in mass and a large broadening in the decay width. In the asymmetric strange hadronic matter, the study of the $ϕ$ mesons can be relevant for the compressed strange baryonic matter and experimental observables such as dilepton spectra which can result from the experiments in the future FAIR facility at GSI.
↳ hep-phnucl-thPRC(2020)·20 citations

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