Mon·Apr 20, 2020Monday·April 20, 2020

1. 01*

   Investigations of $p$+Pb Collisions at Perturbative and Non-Perturbative QCD Scales

   Kurt Hill🇺🇸

   High energy nuclear collisions manifest a variety of interesting phenomena over a broad range of energy scales. Many of these phenomena are related to the formation of a hot and dense state of deconfined quarks and gluons known as the quark gluon plasma (QGP). Chief among these are the observed near inviscid hydrodynamic expansion of the QGP, as measured through azimuthal anisotropy coefficients of low-$p_{\mathrm{T}}$ final state hadrons $v_{\mathrm{n}}$, and the loss of energy of high-$p_{\mathrm{T}}$ color charges as they traverse the QGP which is observed as a quenching of strongly-interacting final state objects like jets. Observations of these phenomena in Au+Au and Pb+Pb collisions at RHIC and the LHC provide compelling evidence of QGP formation. Small collision systems, like $p$+Pb, also show evidence for the creation droplets of QGP through the observation of anisotropic flow; however, these systems show no signs of the energy loss observed in large collision systems. Thus, small systems are an ideal venue to explore the relationship between high- and low-$p_{\mathrm{T}}$ QGP phenomena. Furthermore, the low ambient energy of $p$+Pb compared to A+A collisions allow for the precise determination of perturbative process rates which can be used to understand the nuclear modification of nucleon parton densities. This dissertation explores $p$+Pb data collected with the ATLAS detector at the LHC. The cross section and nuclear modification factor for prompt, isolated photons are measured and compared to predictions from perturbative QCD calculations and a model of initial state energy loss. Additionally, the charged hadron azimuthal anisotropy coefficients, are measured via two-particle correlations as a function of particle $p_{\mathrm{T}}$ and event centrality. Results are shown from minimum bias events and events selected because of the presence of a high-$p_{\mathrm{T}}$ jet.

   nucl-ex2 citations
2. 02*

   Search for a common baryon source in high-multiplicity pp collisions at the LHC

   ALICE Collaboration

   We report on the measurement of the size of the particle-emitting source from two-baryon correlations with ALICE in high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV. The source radius is studied with low relative momentum p-p, $\bar{\mathrm{p}}$-$\bar{\mathrm{p}}$, p-$\Lambda$ and $\bar{\mathrm{p}}$-$\bar{\Lambda }$ pairs as a function of the pair transverse mass $m_{\mathrm{T}}$ considering for the first time in a quantitative way the effect of strong resonance decays. After correcting for this effect, the radii extracted for pairs of different particle species agree. This indicates that protons, antiprotons, $\Lambda$, and $\bar{\Lambda }$ originate from the same source. Within the measured $m_{\mathrm{T}}$ range (1.1-2.2) GeV/$c^2$ the invariant radius of this common source varies between 0.85 and 1.3 fm. These results provide a precise reference for studies of the strong hadron-hadron interactions and for the investigation of collective properties in small colliding systems.

   nucl-exhep-exPLB(2020)·144 citations
3. 03*

   Two-Pion production in the second resonance region in ${\pi }^{-}p$ collisions with HADES

   J. Adamczewski-Musch · O. Arnold · E. T. Atomssa · C. Behnke · A. Belounnas · A. Belyaev · J. C. Berger-Chen · J. Biernat · A. Blanco · C. Blume · M. Böhmer · S. Chernenko and 108 other authors

   Pion induced reactions provide unique opportunities for an unambiguous description of baryonic resonances and their coupling channels by means of a partial wave analysis. Using the secondary pion beam at SIS18, the two pion production in the second resonance region has been investigated to unravel the role of the $N(1520){\frac{3}{2}}^{-}$ resonance in the intermediate $\rho$ production. Results on exclusive channels with one pion (${\pi }^{-}p$) and two pions (${\pi }^{+}{\pi }^{-}n$, ${\pi }^0{\pi }^{-}p$) in the final state measured in the ${\pi }^{-}-p$ reaction at four different pion beam momenta (0.650, 0.685, 0.733, and 0.786 GeV/c) are presented. The excitation function of the different partial waves and $\Delta \pi$, $N\sigma$ and $N\rho$ isobar configurations is obtained, using the Bonn-Gatchina partial wave analysis. The $N(1520){\frac{3}{2}}^{-}$ resonance is found to dominate the $N\rho$ final state with the branching ratio $BR=12.2\pm 1.9\%$.

   nucl-exPRC(2020)·33 citations
4. 04*

   Discrete symmetries in the cluster shell model

   A.H. Santana-Valdés · R. Bijker🇲🇽

   The role of discrete (or point-group) symmetries is discussed in the framework of the Cluster Shell Model which describes the splitting of single-particle levels in the deformed field of cluster potentials. We discuss the classification of the eigenstates for the cases of a triangular and tetrahedral configuration of alpha-particles in terms of the irreducible representations of the double point groups D'(3h) and T'(d), respectively, and show how the discrete symmetry of a given eigenstate can be determined. Finally, we derive the Coriolis coupling for each one of these geometrical configurations.

   ↳ nucl-thnucl-exEur.Phys.J.ST(2020)·4 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.