Fri·Aug 10, 2018Friday·August 10, 2018

1. 01*

   Reaction rates for the ${}^{39}$K(p,$\gamma$)${}^{40}$Ca reaction

   Richard Longland🇺🇸 · John Dermigny · Caleb Marshall🇺🇸

   The magnesium-potassium anti-correlation observed in globular cluster NGC2419 can be explained by nuclear burning of hydrogen in hot environments. The exact site of this nuclear burning is, as yet, unknown. In order to constrain the sites responsible for this anti-correlation, the nuclear reactions involved must be well understood. The ${}^{39}$K+p reactions are one such pair of reactions. Here, we report a new evaluation of the ${}^{39}$K(p,$\gamma$)${}^{40}$Ca reaction rate by taking into account ambiguities and measurement uncertainties in the nuclear data. The uncertainty in the ${}^{39}$K(p,$\gamma$)${}^{40}$Ca reaction rate is larger than previously assumed, and its influence on nucleosynthesis models is demonstrated. We find the ${}^{39}$K(p,$\gamma$)${}^{40}$Ca reaction cross section should be the focus of future experimental study to help constrain models aimed at explaining the magnesium-potassium anti-correlation in globular clusters.

   nucl-exastro-ph.SRPRC(2018)·7 citations
2. 02*

   A novel invariant mass method to isolate resonance backgrounds from the chiral magnetic effect

   Hanlin Li🇨🇳 · Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸

   The Chiral Magnetic Effect (CME) refers to charge separation along a strong magnetic field, due to topological charge fluctuations in QCD. Charge correlation ($\Delta \gamma$) signals consistent with CME have been first observed almost a decade ago. It has also been known since then that the $\Delta \gamma$ is contaminated by a major background from resonance decays coupled with elliptic flow. In this contribution, we propose differential $\Delta \gamma$ measurements as function of the pair invariant mass ($m_{\mathrm{inv}}$). The $\Delta \gamma$ in the high $m_{\mathrm{inv}}$ region is essentially free of resonance backgrounds. In the low $m_{\mathrm{inv}}$ region, the $\Delta \gamma$ backgrounds show resonance peaks. The CME signal, presumably smooth in $m_{\mathrm{inv}}$, may thus be extracted from a two-component model fit. We demonstrate the feasibility and effectiveness of this novel method by using the AMPT and toy-model Monte-Carlo simulations. We also discuss an application of the method in data analysis.

   nucl-exnucl-thNPA(2019)·8 citations
3. 03*

   Contribution of the $a_1$ meson to the axial nucleon-to-$\Delta$ transition form factors

   Y. Unal🇹🇷 · A. Kucukarslan🇹🇷 · S. Scherer🇩🇪

   We analyze the low-$Q^2$ behavior of the axial form factor $G_A(Q^2)$, the induced pseudoscalar form factor $G_P(Q^2)$, and the axial nucleon-to-$\Delta$ transition form factors $C_5^A(Q^2)$ and $C_6^A(Q^2)$. Building on the results of chiral perturbation theory, we first discuss $G_A(Q^2)$ in a chiral effective-Lagrangian model including the $a_1$ meson and determine the relevant coupling parameters from a fit to experimental data. With this information, the form factor $G_P(Q^2)$ can be predicted. For the determination of the transition form factor $C_5^A(Q^2)$ we make use of an SU(6) spin-flavor quark-model relation to fix two coupling constants such that only one free parameter is left. Finally, the transition form factor $C_6^A(Q^2)$ can be predicted in terms of $G_P(Q^2)$, the mean-square axial radius $⟨r_A^2⟩$, and the mean-square axial nucleon-to-$\Delta$ transition radius $⟨r_{AN\Delta }^2⟩$.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2019)·6 citations
4. 04*

   Updating spin-dependent Regge intercepts

   Steven D. Bass🇵🇱 · Magdalena Skurzok🇵🇱 · Pawel Moskal🇵🇱

   We use new high statistics data from CLAS and COMPASS on the nucleon's spin structure function at low Bjorken x and low virtuality, Q^2 < 0.5 GeV^2, together with earlier measurements from the SLAC E-143, HERMES and GDH experiments to estimate the effective intercept(s) for spin dependent Regge theory. We find alpha_{a_1} = 0.31 \pm 0.04 for the intercept describing the high-energy behaviour of spin dependent photoabsorption together with a new estimate for the high-energy part of the Gerasimov-Drell-Hearn sum-rule, -15 \pm 2 mu b from photon-proton centre-of-mass energy greater than 2.5 GeV. Our value of alpha_[a_1} suggests QCD physics beyond a simple straight-line a_1 trajectory.

   ↳ hep-phnucl-exnucl-thPRC(2018)·15 citations
5. 05*

   Molière Scattering in Quark-Gluon Plasma: Finding Point-Like Scatterers in a Liquid

   Francesco D'Eramo🇮🇹 · Krishna Rajagopal🇺🇸 · Yi Yin🇺🇸

   By finding rare (but not exponentially rare) large-angle deflections of partons within a jet produced in a heavy ion collision, or of such a jet itself, experimentalists can find the weakly coupled short-distance quark and gluon particles (scatterers) within the strongly coupled liquid quark-gluon plasma (QGP) produced in heavy ion collisions. This is the closest one can come to probing QGP via a scattering experiment and ultimately learning how a strongly coupled liquid emerges from an asymptotically free gauge theory. The short-distance, particulate, structure of liquid QGP can be revealed in events in which a jet parton resolves, and scatters off, a parton from the droplet of QGP. The probability for picking up significant transverse momentum via a single scattering was calculated previously, but only in the limit of infinite parton energy which means zero angle scattering. Here, we provide a leading order perturbative QCD calculation of the Molière scattering probability for incident partons with finite energy, scattering at a large angle. We set up a thought experiment in which an incident parton with a finite energy scatters off a parton constituent within a "brick" of QGP, which we treat as if it were weakly coupled, as appropriate for scattering with large momentum transfer, and compute the probability for a parton to show up at a nonzero angle with some energy. We include all relevant channels, including those in which the parton that shows up at a large angle was kicked out of the medium as well as the Rutherford-like channel in which what is seen is the scattered incident parton. The results that we obtain will serve as inputs to future jet Monte Carlo calculations and can provide qualitative guidance for how to use future precise, high statistics, suitably differential measurements of jet modification in heavy ion collisions to find the scatterers within the QGP liquid.

   ↳ hep-phnucl-exnucl-thJHEP(2019)·79 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.