Centrality dependence of limiting fragmentation

We investigate the centrality-dependent validity of the limiting-fragmentation hypothesis in relativistic heavy-ion collisions at energies reached at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). A phenomenological analysis of Au–Au and Pb–Pb collisions within a three-source relativistic diffusion model (RDM) is performed at $$\sqrt{s_{NN}}=19.6, 62.4, 130, 200, 2760$$ s NN = 19.6 , 62.4 , 130 , 200 , 2760 and 5023 GeV using four centrality cuts at each energy. Linear and nonlinear expressions for the rapidity drift function are tested and their physical relevance is discussed. Our results are compatible with the limiting-fragmentation conjecture for the investigated centralities in the full energy range. The number of particles in the fragmentation and fireball sources are found to depend on $$\sqrt{s_{NN}}$$ s NN logarithmically and cubic-logarithmically, respectively.

H II regions and high-mass starless clump candidates

Context. The role of ionization feedback on high-mass (>8 M⊙) star formation is still highly debated. Questions remain concerning the presence of nearby H II regions changes the properties of early high-mass star formation and whether H II regions promote or inhibit the formation of high-mass stars. Aims. To characterize the role of H II regions on the formation of high-mass stars, we study the properties of a sample of candidates high-mass starless clumps (HMSCs), of which about 90% have masses larger than 100 M⊙. These high-mass objects probably represent the earliest stages of high-mass star formation; we search if (and how) their properties are modified by the presence of an H II region. Methods. We took advantage of the recently published catalog of HMSC candidates. By cross matching the HMSCs and H II regions, we classified HMSCs into three categories: (1) the HMSCs associated with H II regions both in the position in the projected plane of the sky and in velocity; (2) HMSCs associated in the plane of the sky, but not in velocity; and (3) HMSCs far away from any H II regions in the projected sky plane. We carried out comparisons between associated and nonassociated HMSCs based on statistical analyses of multiwavelength data from infrared to radio. Results. We show that there are systematic differences of the properties of HMSCs in different environments. Statistical analyses suggest that HMSCs associated with H II regions are warmer, more luminous, more centrally-peaked and turbulent. We also clearly show, for the first time, that the ratio of bolometric luminosity to envelope mass of HMSCs (L∕M) could not be a reliable evolutionary probe for early massive star formation due to the external heating effects of the H II regions. Conclusions. We show HMSCs associated with H II regions present statistically significant differences from HMSCs far away from H II regions, especially for dust temperature and L∕M. More centrally peaked and turbulent properties of HMSCs associated with H II regions may promote the formation of high-mass stars by limiting fragmentation. High-resolution interferometric surveys toward HMSCs are crucial to reveal how H II regions impact the star formation process inside HMSCs.

Comparative study for target fragmentation in 4He and 6Li interactions with emulsion nuclei at Elab = 3.7A GeV

The multiplicity characteristics of the grey and black particles are studied in 3.7A GeV 4He and 6Li interactions with emulsion nuclei. The dependence on the system size is examined. The data are classified according the emission direction in the 4π space. The forward or backward emitted grey particle multiplicities distributions are approximated by exponential decay law. The black particle distributions also have the decay shapes, except for the CNO target nuclei; they are shoulder-shaped curves. The production probabilities and average multiplicities increase linearly with the target size. Multiplicity correlations are carried out. Regarding the nuclear limiting fragmentation hypothesis, the grey and black particle productions are independent of the projectile size.

Small-x saturation in forward hadronic interactions

After a brief introduction of parton saturation in hadrons at small Bjorken's x, we recapitulate its phenomenological implications in high-energy particle production, such as longitudinal correlation, particle mulctiplicity, limiting fragmentation and charm quark production, which may have relevance to study of highenergy cosmic ray physics.

Diffusion-model analysis of pPb and PbPb collisions at LHC energies

We present an analysis of centrality-dependent pseudorapidity distributions of produced charged hadrons in pPb and PbPb collisions at the Large Hadron Collider (LHC) energy of [Formula: see text] = 5.02 TeV, and of minimum-bias pPb collisions at 8.16 TeV within the non-equilibrium-statistical relativistic diffusion model (RDM). In a three-source approach, the role of the fragmentation sources is emphasized. Together with the Jacobian transformation from rapidity to pseudorapidity and the limiting fragmentation conjecture, these are essential for modeling the centrality dependence. For central PbPb collisions, a prediction at the projected FCC energy of [Formula: see text] = 39 TeV is made.

Multisource Evidence for Final State Hadrons in 3.7A GeV 16O–Nucleus Interactions

In 3.7A GeV 16O interactions with emulsion nuclei, the shower particle multiplicity characteristics are investigated. Data are presented in terms of the number of emitted particles in both forward and backward angular zones. The dependence on the target size and emission direction is presented. The target separation of events depends on Glauber's multiple scattering theory approaches. A decay mechanism seems to be a characteristic of the backward production. This production may be during the de–excitation of the excited target nucleus, regarding the nuclear limiting fragmentation hypothesis. The forward emitted particle is due to a creation system. The target size is an effective parameter as well as the projectile size in this system, considering the geometrical concept regarded in the nuclear fireball concept. The data are simulated in the framework of the modified FRITIOF model. The multisource thermal model can predict source numbers responsible for particle production.