Wed·Oct 23, 2019Wednesday·October 23, 2019

1. 01*

   Measurement of the (anti-)${}^3$He elliptic flow in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The elliptic flow ($v_2$) of (anti-)${}^3$He is measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV in the transverse-momentum ($p_{\mathrm{T}}$) range of 2-6 GeV/$c$ for the centrality classes 0-20%, 20-40%, and 40-60% using the event-plane method. This measurement is compared to that of pions, kaons, and protons at the same center-of-mass energy. A clear mass ordering is observed at low $p_{\mathrm{T}}$, as expected from relativistic hydrodynamics. The violation of the scaling of $v_2$ with the number of constituent quarks at low $p_{\mathrm{T}}$, already observed for identified hadrons and deuterons at LHC energies, is confirmed also for (anti-)${}^3$He. The elliptic flow of (anti-)${}^3$He is underestimated by the Blast-Wave model and overestimated by a simple coalescence approach based on nucleon scaling. The elliptic flow of (anti-)${}^3$He measured in the centrality classes 0-20% and 20-40% is well described by a more sophisticated coalescence model where the phase-space distributions of protons and neutrons are generated using the iEBE-VISHNU hybrid model with AMPT initial conditions.

   nucl-exhep-exPLB(2020)·29 citations
2. 02*

   Cross section of $\alpha$-induced reactions on ${}^{197}$Au at sub-Coulomb energies

   T. Szücs🇩🇪 · P. Mohr🇭🇺 · Gy. Gyürky🇭🇺 · Z. Halász🇭🇺 · R. Huszánk🇭🇺 · G. G. Kiss🇭🇺 · T. N. Szegedi🇭🇺 · Zs. Török · Zs. Fülöp🇭🇺

   Statistical model calculations have to be used for the determination of reaction rates in large-scale reaction networks for heavy-element nucleosynthesis. A basic ingredient of such a calculation is the a-nucleus optical model potential. Several different parameter sets are available in literature, but their predictions of a-induced reaction rates vary widely, sometimes even exceeding one order of magnitude. This paper presents the result of a-induced reaction cross-section measurements on gold which could be carried out for the first time very close to the astrophysically relevant energy region. The new experimental data are used to test statistical model predictions and to constrain the a-nucleus optical model potential. For the measurements the activation technique was used. The cross section of the (a,n) and (a,2n) reactions was determined from g-ray counting, while that of the radiative capture was determined via X-ray counting. The cross section of the reactions was measured below E${}_a=20.0$~MeV. In the case of the ${}^{197}$Au(a,2n)${}^{199}$Tl reaction down to 17.5~MeV with 0.5-MeV steps, reaching closer to the reaction threshold than ever before. The cross section of ${}^{197}$Au(a,n)${}^{200}$Tl and ${}^{197}$Au(a,g)${}^{201}$Tl was measured down to E${}_a=13.6$ and 14.0~MeV, respectively, with 0.5-MeV steps above the (a,2n) reaction threshold and with 1.0-MeV steps below that. The new dataset is in agreement with the available values from the literature, but is more precise and extends towards lower energies. Two orders of magnitude lower cross sections were successfully measured than in previous experiments which used g-ray counting only, thus providing experimental data at lower energies than ever before. The new precision dataset allows us to find the best-fit a-nucleus optical model potential and to predict cross sections in the Gamow window with smaller uncertainties.

   nucl-exPRC(2019)·13 citations
3. 03*

   Ultraperipheral vs ordinary nuclear interactions

   I.M. Dremin🇷🇺

   It is argued that the cross sections of ultraperipheral interactions of heavy nuclei can become comparable in value to those of their ordinary hadronic interactions at high energies. Simple estimates of corresponding "preasymptotic energy thresholds" are provided.The~method of equivalent photons is compared with the perturbative approach. The~situation at NICA/FAIR energies is discussed.

   ↳ nucl-thhep-exhep-phnucl-exUniverse(2019)·5 citations
4. 04*

   Extraction of gluon distributions from structure functions at small x in holographic QCD

   Akira Watanabe🇨🇳 · Takahiro Sawada🇯🇵 · Mei Huang🇨🇳

   We investigate the nucleon and pion gluon distribution functions in the framework of holographic QCD, focusing on the small Bjorken x region. Based on an approximate relation, the gluon distributions are extracted from structure functions of the unpolarized deep inelastic scattering which can be calculated with a holographic QCD model, assuming the Pomeron exchange. All the adjustable parameters of the model are determined with the HERA data of the proton structure functions. We explicitly show that the extracted proton gluon distribution is consistent with results of the recent global QCD analysis. The structure functions of the pion can be computed without any additional parameter, which enables us to predict its gluon distribution also. We find that the resulting pion gluon density is smaller than the proton's, and agrees with the recent global QCD analysis result within the uncertainties.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2020)·29 citations
5. 05*

   Power Counting the Small-$x$ Observables

   Zhong-Bo Kang🇺🇸 · Xiaohui Liu🇨🇳

   We emphasize the importance of applying power counting to the small-$x$ observables, which introduces novel soft contributions usually missing and allows for a unified treatment of the Balitsky-Kovchegov (BK) evolution and various Sudakov logarithms. We use $pA\to h(p_{h\perp })X$ at forward rapidity to highlight how the power counting yields a partonic cross section with collinear and soft sectors. We show how the kinematic constraints can be obtained in the soft sector without violating the power counting. We further show how one can resum the threshold Sudakov logarithms systematically to all orders in a re-factorized framework with additional collinear-soft contributions. Direct applications to other small-$x$ processes involving heavy particles, jet (sub-)observables and EIC physics are straightforward.

   ↳ hep-phhep-exnucl-exnucl-th13 citations
6. 06*

   Accurately accounting for effects on times-of-flight caused by finite field-transition times during the ejection of ions from a storage trap: A study for TOF and MRTOF mass spectrometry

   M. Rosenbusch🇩🇪 · P. Schury🇯🇵 · M. Wada🇺🇸 · S. Iimura · Y. Ito🇨🇦 · H. Wollnik🇺🇸

   In applied forms of time-of-flight mass spectrometry utilizing ion storage devices prior to an analysis device, a non instantaneous electric ejection pulse applied in the region of ion storage is used to accelerate ions into the time-of-flight analyzer. The calculated mass value of the ions from the time-of-flight is dependent on the duration of the field transition up to full strength. For novel applications dedicated to precision measurements, such as multi-reflection time-of-flight mass spectrometry of short-lived isotopes, the goal is to continuously decrease the measurement uncertainty while providing a mass accuracy on the same order. Even though dynamic-field models for time-of-flight mass spectrometry have been considered in the past for technological advances, it is important to study the accuracy of the measured mass in this context. Using a simplified linear model for the field transition, we provide a basic investigation of the scenario, and discuss the deviation from the classical "mass-over-charge" dependency of the ions' time-of-flight, which becomes violated. The emerging mass discrepancy depends on the distance between the mass of the ion used for calibration and that of the ion of interest and, in extreme cases, can increase to about one percent for systems with short times-of-flight. However, for typical conditions in single-reference multi-reflection time-of-flight mass spectrometry, mass deviations caused by this effect typically remain below the 1 ppm level. If a mass calibration using two or more ion species is possible during the measurement, the effect becomes negligible for appropriate choices of reference masses.

   ↳ physics.ins-detnucl-exInt.J.Mass Spectrometry(2020)·1 citation

* 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.