Tue·Sep 3, 2019Tuesday·September 3, 2019

1. 01*

   Measurement of $\Lambda$(1520) production in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The production of the $\Lambda$(1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at $\sqrt{s}$ = 7 TeV and in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel $\Lambda$(1520) $\to$ pK${}^{-}$ and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p-Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons ($\pi$, K, K${}_{\mathrm{S}}^0$, p, $\Lambda$) describes the shape of the $\Lambda$(1520) transverse momentum distribution up to 3.5 GeV/$c$ in p-Pb collisions. In the framework of this model, this observation suggests that the $\Lambda (1520)$ resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of $\Lambda (1520)$ to the yield of the ground state particle $\Lambda$ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p-Pb collisions on the $\Lambda$(1520) yield.

   nucl-exhep-exEPJC(2020)·34 citations
2. 02*

   Low-$Q^2$ empirical parametrizations of the $N^{\ast }$ helicity amplitudes

   G. Ramalho🇧🇷

   The data associated with the electromagnetic excitations of the nucleon (${\gamma }^{\ast }N\to N^{\ast }$) are usually parametrized by helicity amplitudes at the resonance $N^{\ast }$ rest frame. The properties of the ${\gamma }^{\ast }N\to N^{\ast }$ transition current at low $Q^2$ can be, however, better understood when expressed in terms of structure form factors, particularly near the pseudothreshold, when the magnitude of the photon three-momentum vanishes ($|\mathbf{q}|=0$). At the pseudothreshold the invariant four-momentum square became $q^2=(M_R-M_N{)}^2$, well in the timelike region $Q^2=-q^2<0$ [$M_N$ and $M_R$ are the mass of the nucleon and of the resonance, respectively]. In the helicity amplitude representation, the amplitudes have well-defined dependences on $|\mathbf{q}|$, near the pseudothreshold, and there are correlations between different amplitudes. Those constraints are often ignored in the empirical parametrizations of the helicity amplitudes. In the present work, we show that the structure of the transition current near the pseudothreshold has an impact on the parametrizations of the data. We present a method which modifies analytic parametrizations of the data at low $Q^2$, in order to take into account the constraints of the transition amplitudes near the pseudothreshold. The model dependence of the parametrizations on the low-$Q^2$ data is studied in detail.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2019)·16 citations
3. 03*

   The Shape of the Correlation Function

   Jakub Cimerman🇨🇿 · Boris Tomášik🇸🇰 · Christopher Plumberg🇸🇪

   The correlation function measured in ultrarelativistic nuclear collisions is non-Gaussian. By making use of models we discuss and assess how much various effects can influence its shape. In particular, we focus on the parametrisations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as non-spherical shape, resonance decays, event-by-event fluctuations and functional dependence on $Q_{inv}$ or similar.

   ↳ nucl-thhep-phnucl-exPhys.Part.Nucl.(2020)·6 citations
4. 04*

   Color transparency in $\bar{p}d\to {\pi }^{-}{\pi }^{0}p$ reaction

   A.B. Larionov🇩🇪 · M. Strikman🇺🇸

   We consider exclusive two-pion production in antiproton-deuteron interactions at the beam momenta around 10 GeV/c in the kinematics with large momentum transfer in the underlying hard process $\bar{p}n\to {\pi }^{-}{\pi }^0$. The calculations are performed taking into account the antiproton and pion soft rescattering on the spectator proton in the framework of the generalized eikonal approximation. We focus on the color transparency effect that is modeled by introducing the dependence of rescattering amplitudes on the relative position of the struck and spectator nucleons along the momentum of a fast particle. As a consequence of the interplay between the impulse approximation and rescattering amplitudes the nuclear transparency ratio reveals a pretty complicated behaviour as a function of the transverse momentum of the spectator proton and the relative azimuthal angle between the ${\pi }^{-}$-meson and the proton. Color transparency significantly suppresses rescattering amplitudes which leads to substantial modifications of the nuclear transparency ratio moving it closer to the value obtained in the impulse approximation. By performing the Monte-Carlo analysis we determine that this effect can be studied at PANDA with a reasonable statistics.

   ↳ nucl-thhep-exhep-phnucl-exEPJA(2020)·7 citations
5. 05*

   Nucleon axial, tensor and scalar charges and $\sigma$-terms in lattice QCD

   C. Alexandrou (Univ. of Cyprus & The Cyprus Inst.) · S. Bacchio (The Cyprus Inst.) · M. Constantinou (Temple Univ.) · K. Hadjiyiannakou (The Cyprus Inst.) · K. Jansen (DESY-Zeuthen) · G. Koutsou (The Cyprus Inst.) · A. Vaquero Aviles-Casco (Univ. of Utah)

   We determine the nucleon axial, scalar and tensor charges within lattice Quantum Chromodynamics including all contributions from valence and sea quarks. We analyze three gauge ensembles simulated within the twisted mass formulation at approximately physical value of the pion mass. Two of these ensembles are simulated with two dynamical light quarks and lattice spacing $a=0.094$~fm and the third with $a=0.08$~fm includes in addition the strange and charm quarks in the sea. After comparing the results among these three ensembles, we quote as final values our most accurate analysis using the latter ensemble. For the nucleon isovector axial charge we find $1.286(23)$ in agreement with the experimental value. We provide the flavor decomposition of the intrinsic spin $\frac{1}{2}\Delta {\Sigma }^q$ carried by quarks in the nucleon obtaining for the up, down, strange and charm quarks $\frac{1}{2}\Delta {\Sigma }^u=0.431(8)$, $\frac{1}{2}\Delta {\Sigma }^d=-0.212(8)$, $\frac{1}{2}\Delta {\Sigma }^s=-0.023(4)$ and $\frac{1}{2}\Delta {\Sigma }^c=-0.005(2)$, respectively. The corresponding values of the tensor and scalar charges for each quark flavor are also evaluated providing valuable input for experimental searches for beyond the standard model physics. In addition, we extract the nucleon $\sigma$-terms and find for the light quark content ${\sigma }_{\pi N}=41.6(3.8)$~MeV and for the strange ${\sigma }_s=45.6(6.2)$~MeV. The y-parameter that is used in phenomenological studies we find $y=0.078(7)$.

   ↳ hep-lathep-exhep-phnucl-ex+1PRD(2020)·158 citations
6. 06*

   Temperatures and chemical potentials at kinetic freeze-out in relativistic heavy ion collisions from coarse grained transport simulations

   Gabriele Inghirami🇫🇮 · Paula Hillmann🇩🇪 · Boris Tomášik🇸🇰 · Marcus Bleicher🇩🇪

   Using the UrQMD/coarse graining approach we explore the kinetic freeze-out stage in central Au + Au collisions at various energies. These studies allow us to obtain detailed information on the thermodynamic properties (e.g. temperature and chemical potential) of the system during the kinetic decoupling stage. We explore five relevant collision energies in detail, ranging from $\sqrt{s_{NN}}=2.4\mathrm{GeV}$ (GSI-SIS) to $\sqrt{s_{NN}}=200\mathrm{GeV}$ (RHIC). By adopting a standard Hadron Resonance Gas equation of state, we determine the average temperature $⟨T⟩$ and the average baryon chemical potential $⟨{\mu }_{\mathrm{B}}⟩$ on the space-time hyper-surface of last interaction. The results highlight the nature of the kinetic freeze-out as a continuous process. This differential decoupling is an important aspect often missed when summarizing data as single points in the phase diagram as e.g. done in Blast-Wave fits. We compare the key properties of the system derived by using our approach with other models and we briefly review similarities and differences.

   ↳ hep-phnucl-exnucl-thJ.Phys.G(2020)·15 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.