Mon·Sep 18, 2017Monday·September 18, 2017

1. 01*

   J/$\psi$ elliptic flow in Pb-Pb collisions at $\sqrt{{\mathbf{s}}_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   We report a precise measurement of the J/$\psi$ elliptic flow in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ALICE detector at the LHC. The J/$\psi$ mesons are reconstructed at mid-rapidity ($|y|<0.9$) in the dielectron decay channel and at forward rapidity ($2.5<y<4.0$) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow $v_2$ of the J/$\psi$ is studied as a function of transverse momentum and centrality. A positive $v_2$ is observed in the transverse momentum range $2<p_{\mathrm{T}}<8$ GeV/$c$ in the three centrality classes studied and confirms with higher statistics our earlier results at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV in semi-central collisions. At mid-rapidity, the J/$\psi$ $v_2$ is investigated as a function of transverse momentum in semi-central collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low $p_{\mathrm{T}}$ the elliptic flow of the J/$\psi$ originates from the thermalization of charm quarks in the deconfined medium, but suggests that additional mechanisms might be missing in the models.

   nucl-exhep-exPRL(2017)·102 citations
2. 02*

   Laser spectroscopic characterization of the nuclear clock isomer ${}^{229m}$Th

   Johannes Thielking · Maxim V. Okhapkin · Przemyslaw Glowacki · David M. Meier · Lars von der Wense · Benedict Seiferle · Christoph E. Düllmann · Peter G. Thirolf · Ekkehard Peik

   The isotope ${}^{229}$Th is the only nucleus known to possess an excited state ${}^{229m}$Th in the energy range of a few electron volts, a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than common nuclear excitation energies. A number of applications of this unique nuclear system, which is accessible by optical methods, have been proposed. Most promising among them appears a highly precise nuclear clock that outperforms existing atomic timekeepers. Here we present the laser spectroscopic investigation of the hyperfine structure of ${}^{229m}$Th${}^{2+}$, yielding values of fundamental nuclear properties, namely the magnetic dipole and electric quadrupole moments as well as the nuclear charge radius. After the recent direct detection of this long-searched-for isomer, our results now provide detailed insight into its nuclear structure and present a method for its non-destructive optical detection.

   nucl-exNature(2018)·115 citations
3. 03*

   Global analysis of color fluctuation effects in proton- and deuteron-nucleus collisions at RHIC and the LHC

   Massimiliano Alvioli🇮🇹 · Leonid Frankfurt🇮🇱 · Dennis Perepelitsa🇺🇸 · Mark Strikman🇺🇸

   We test the hypothesis that configurations of a proton with a large-$x$ parton, $x_p\gtrsim 0.1$, have a smaller than average size. The QCD $Q^2$ evolution equations suggest that these small configurations also have a significantly smaller interaction strength, which has observable consequences in collisions with nuclei. We perform a global analysis of jet production data in proton- and deuteron-nucleus collisions at RHIC and the LHC. Using a model which takes a distribution of interaction strengths into account, we quantitatively extract the $x_p$-dependence of the average interaction strength, $\sigma (x_p)$, over a wide kinematic range. By comparing the RHIC and LHC results, our analysis finds that the interaction strength for small configurations, while suppressed, grows faster with collision energy than does that for average configurations. We check that this energy dependence is consistent with the results of a method which, given $\sigma (x_p)$ at one energy, can be used to quantitatively predict that at another. This finding further suggests that at even lower energies, nucleons with a large-$x_p$ parton should interact much more weakly than those in an average configuration, a phenomenon in line with explanations of the EMC effect for large-$x_p$ quarks in nuclei based on color screening.

   ↳ hep-phhep-exnucl-exPRD(2018)·38 citations
4. 04*

   Isospin effect on baryon and charge fluctuations from the pNJL model

   He Liu🇨🇳 · Jun Xu🇨🇳

   We have studied the possible isospin corrections on the skewness and kurtosis of net-baryon and net-charge fluctuations in the isospin asymmetric matter formed in relativistic heavy-ion collisions at RHIC-BES energies, based on a 3-flavor polyakov-looped Nambu-Jona-Lasinio model. With typical scalar-isovector and vector-isovector couplings leading to the splitting of $u$ and $d$ quark chiral phase transition boundaries and critical points, we have observed dramatic isospin effects on the susceptibilities, especially those of net-charge fluctuations. Reliable experimental measurements at even lower collision energies are encouraged to confirm the observed isospin effects.

   ↳ nucl-thhep-exnucl-exUniverse(2020)·13 citations
5. 05*

   Electromagnetic fields in small systems from a multiphase transport model

   Xin-Li Zhao🇨🇳 · Yu-Gang Ma🇨🇳 · Guo-Liang Ma🇨🇳

   We calculate the electromagnetic fields generated in small systems by using a multiphase transport (AMPT) model. Compared to $A+A$ collisions, we find that the absolute electric and magnetic fields are not small in $p$+Au and $d$+Au collisions at energies available at the BNL Relativistic Heavy Ion Collider and in $p$+Pb collisions at energies available at the CERN Large Hadron Collider. We study the centrality dependencies and the spatial distributions of electromagnetic fields. We further investigate the azimuthal fluctuations of the magnetic field and its correlation with the fluctuating geometry using event-by-event simulations. We find that the azimuthal correlation $⟨\cos 2({\Psi }_B-{\Psi }_2)⟩$ between the magnetic field direction and the second harmonic participant plane is almost zero in small systems with high multiplicities, but not in those with low multiplicities. This indicates that the charge azimuthal correlation, $⟨\cos ({\varphi }_{\alpha }+{\varphi }_{\beta }-2{\Psi }_{RP})⟩$, is not a valid probe to study the chiral magnetic effect (CME) in small systems with high multiplicities. However, we suggest searching for possible CME effects in small systems with low multiplicities.

   ↳ hep-phnucl-exnucl-thPRC(2018)·28 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.