Fri·Dec 16, 2016Friday·December 16, 2016

1. 01*

   Process-independent strong running coupling

   Daniele Binosi🇮🇹 · Cedric Mezrag🇺🇸 · Joannis Papavassiliou🇪🇸 · Craig D. Roberts🇺🇸 · Jose Rodriguez-Quintero🇪🇸

   We unify two widely different approaches to understanding the infrared behaviour of quantum chromodynamics (QCD), one essentially phenomenological, based on data, and the other computational, realised via quantum field equations in the continuum theory. Using the latter, we explain and calculate a process-independent running-coupling for QCD, a new type of effective charge that is an analogue of the Gell-Mann--Low effective coupling in quantum electrodynamics. The result is almost identical to the process-dependent effective charge defined via the Bjorken sum rule, which provides one of the most basic constraints on our knowledge of nucleon spin structure. This reveals the Bjorken sum to be a near direct means by which to gain empirical insight into QCD's Gell-Mann--Low effective charge.

   ↳ nucl-thhep-lathep-phnucl-exPRD(2017)·178 citations
2. 02*

   Shear viscosity from nuclear stopping

   Brent Barker (Roosevelt U) · Pawel Danielewicz (NSCL MSU)🇺🇸

   Within a Boltzmann transport model, we demonstrate correlation between stopping observables and shear viscosity in central nuclear collisions at intermediate energies (on the order of 10 to 1000 MeV/nucleon). The correlation allows us to assess the viscosity of nuclear matter, by tuning the in-medium nucleon-nucleon cross section in our transport model to agree with nuclear stopping data. We also calculate the ratio of shear viscosity to entropy density to determine how close the system is to the universal quantum lower limit proposed in the context of ultrarelativistic heavy ion collisions.

   ↳ nucl-thnucl-exPRC(2019)·30 citations
3. 03*

   $p_t$-Angular power spectrum in ALICE events

   Felipe J. Llanes-Estrada🇪🇸 · Jose L. Muñoz Martinez (Univ. Complutense de Madrid)🇪🇸

   We study the particles emitted in the fireball following a Relativistic Heavy Ion Collision with the traditional angular analysis employed in cosmology and earth sciences, producing Mollweide plots of the p_t distribution of a few actual, publically released ALICE-collaboration events and calculating their angular power spectrum. With the limited statistics at hand, we do not find evidence for acoustic peaks but a decrease of C_l that is reminiscent of viscous attenuation, but subject to a strong effect from the rapidity acceptance which probably dominates (so we also subtract the m=0 component). As an exercise, we still extract a characteristic Silk damping length (proportional to the square root of the viscosity over entropy density ratio). The absence of acoustic-like peaks is also compatible with a crossover from the QGP to the hadron gas (because a surface tension at domain boundaries would effect a restoring force that could have driven acoustic oscillations). Presently an unexpected depression appears in the l=6 multipole strength, which should be revisited by the ALICE collaboration with full statistics to confirm or discard it.

   ↳ hep-phnucl-exnucl-thNPA(2018)·8 citations
4. 04*

   The $d^{\ast }$(2380) dibaryon resonance width and decay branching ratios

   Avraham Gal🇮🇱

   Attempts to reproduce theoretically the relatively small width, ${\Gamma }_{d^{\ast }}=80\pm 10$ MeV, of the $I(J^P)=0(3^{+})$ $d^{\ast }$(2380) dibaryon resonance established by the WASA-at-COSY Collaboration are discussed. The validity of associating the $d^{\ast }$(2380) in quark-based models primarily with a tightly bound $\Delta \Delta$ configuration is questioned. The $d^{\ast }$(2380) width and decay branching ratios into $NN\pi \pi$, $NN\pi$ and $NN$ final states are studied within the Gal-Garcilazo hadronic model in which the $d^{\ast }$(2380) is a $\pi N\Delta$ resonance embedded in the $NN\pi \pi$ continuum some 80 MeV below the $\Delta \Delta$ threshold. In particular, predictions are made for the branching ratios of the unobserved yet $d^{\ast }(2380)\to NN\pi$ decays which are suppressed in a purely-$\Delta \Delta$ dibaryon model. Comments are also made on a possible connection of the ABC effect observed in the $pn\to d^{\ast }\to d{\pi }^0{\pi }^0$ resonance reaction to the $d^{\ast }$(2380) dibaryon.

   ↳ nucl-thhep-phnucl-exPLB(2017)·50 citations
5. 05*

   Correlated stopping, proton clusters and higher order proton cumulants

   Adam Bzdak🇵🇱 · Volker Koch🇺🇸 · Vladimir Skokov🇺🇸

   We investigate possible effects of correlations between stopped nucleons on higher order proton cumulants at low energy heavy-ion collisions. We find that fluctuations of the number of wounded nucleons $N_{\mathrm{part}}$ lead to rather nontrivial dependence of the correlations on the centrality; however, this effect is too small to explain the large and positive four-proton correlations found in the preliminary data collected by the STAR collaboration at $\sqrt{s}=7.7$ GeV. We further demonstrate that, by taking into account additional proton clustering, we are able to qualitatively reproduce the preliminary experimental data. We speculate that this clustering may originate either from collective/multi-collision stopping which is expected to be effective at lower energies or from a possible first-order phase transition, or from (attractive) final state interactions. To test these ideas we propose to measure a mixed multi-particle correlation between stopped protons and a produced particle (e.g. pion, antiproton).

   ↳ nucl-thhep-exhep-phnucl-exEPJC(2017)·47 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.