This paper describes the conclusions that can be drawn from the data taken thus far with the PHOBOS detector at RHIC. In the most central Au
+
Au collisions at the highest beam energy, evidence is ...found for the formation of a very high energy density system whose description in terms of simple hadronic degrees of freedom is inappropriate. Furthermore, the constituents of this novel system are found to undergo a significant level of interaction. The properties of particle production at RHIC energies are shown to follow a number of simple scaling behaviors, some of which continue trends found at lower energies or in simpler systems. As a function of centrality, the total number of charged particles scales with the number of participating nucleons. When comparing Au
+
Au at different centralities, the dependence of the yield on the number of participants at higher
p
T
(
∼
4
GeV
/
c
) is very similar to that at low transverse momentum. The measured values of charged particle pseudorapidity density and elliptic flow were found to be independent of energy over a broad range of pseudorapidities when effectively viewed in the rest frame of one of the colliding nuclei, a property we describe as “extended longitudinal scaling”. Finally, the centrality and energy dependences of several observables were found to factorize to a surprising degree.
Fusion of heavy nuclei remains an area of intense research. Fusion reactions at extremely low energies between carbon and oxygen are important during the late stellar evolution and nucleosynthesis in ...massive stars. The quest to extend the periodic table of the elements relies on heavy-ion fusion to reach superheavy isotopes at the limit of mass and charge. Finally, fusion reactions involving radioactive nuclei elucidate the effects of loosely bound nucleons on many-particle quantum tunneling. In this article, recent experimental and theoretical developments in heavy-ion fusion research, in a wide range from deep sub-barrier energies to energies well above the interaction barrier, are reviewed. As several heavy-ion fusion reactions are of crucial importance in late-stage giant-star evolution, these reactions continue to be studied with better experimental and theoretical tools in order to provide improved input to astrophysical models. Also this area has seen significant progress in several different approaches to the problem of predicting the cross sections for formation and survival of these rare nuclei.
This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the ...Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.
The Back-n white neutron source at China Spallation Neutron Source (CSNS) is designed specifically for nuclear data measurements and multidisciplinary neutron applications. The time of flight (TOF) ...method is deployed to obtain a high resolution of neutron energy. In the normal operation mode of CSNS there are two proton bunches with a time interval of 410 ns in each pulse which has a repetition frequency of 25 Hz. Due to the superposition of the event distributions corresponding to two bunches, the resolution of the TOF measurement at Back-n will be degraded by the double-bunch characteristics if the measured event distribution is used directly without unfolding, especially in the higher neutron energy region. To nearly recover the event distribution corresponding to a single proton bunch, the unfolding methods have been developed to obtain better time resolution and energy resolution. Two kinds of unfolding algorithms based on the iterative Bayesian method and the iterative event re-distribution method, respectively, have been developed and tested with simulated data and experimental data. The developed methods have shown nice performance in unfolding the double-bunch event distributions with high accuracy and fast convergence. With the deploying of the unfolding methods, the data of the first batch experiments conducted at Back-n in the normal double-bunch mode were analyzed and nearly the same time resolution as in the case of the single-bunch mode has been obtained.
In relativistic heavy-ion collisions, anisotropic collective flow is driven, event by event, by the initial eccentricity of the matter created in the nuclear overlap zone. Interpretation of the ...anisotropic flow data thus requires a detailed understanding of the effective initial source eccentricity of the event sample. In this paper, we investigate various ways of defining this effective eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we examine the participant eccentricity, which quantifies the eccentricity of the initial source shape by the major axes of the ellipse formed by the interaction points of the participating nucleons. We show that reasonable variation of the density parameters in the Glauber calculation, as well as variations in how matter production is modeled, do not significantly modify the already established behavior of the participant eccentricity as a function of collision centrality. Focusing on event-by-event fluctuations and correlations of the distributions of participating nucleons, we demonstrate that, depending on the achieved event-plane resolution, fluctuations in the elliptic flow magnitude v{sub 2} lead to most measurements being sensitive to the root-mean-square rather than the mean of the v{sub 2} distribution. Neglecting correlations among participants, we derive analytical expressions for the participant eccentricity cumulants as a function of the number of participating nucleons, N{sub part}, keeping nonnegligible contributions up to O(1/N{sub part}{sup 3}). We find that the derived expressions yield the same results as obtained from mixed-event MCG calculations which remove the correlations stemming from the nuclear collision process. Most importantly, we conclude from the comparison with MCG calculations that the fourth-order participant eccentricity cumulant does not approach the spatial anisotropy obtained assuming a smooth nuclear matter distribution. In particular, for the Cu+Cu system, these quantities deviate from each other by almost a factor of 2 over a wide range in centrality. This deviation reflects the essential role of participant spatial correlations in the interaction of two nuclei.
Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly ...on the reaction rate for 12C+12C fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of 12C+12C fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5–4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate.
The study of fusion reactions at extreme sub-barrier energies has seen an increased interest in recent years, although difficult to measure due to their very small cross sections. Such reactions are ...extremely important for our understanding of the production of heavy elements in various environments. In this article, the status of the field is reviewed covering the experimental techniques, the available data, and the theoretical approaches used to describe such reactions. The fusion hindrance effect, first discovered in medium-mass systems, has been found to be relevant also for lighter systems. In some light systems, resonance structures are found to be important, while for heavy systems, the fission process plays an important role. In the near barrier region, couplings to collective excitations in the fusion participants and transfer reactions have been found to give a good description of the measured fusion cross sections and it results in a distribution of fusion barrier heights. New physics ingredients, related to the overlap process of the two projectiles, have to be introduced to describe the hindrance behavior. In addition, it has recently been found that the fusion cross section in both near-barrier and sub-barrier regions can be described very well in many cases using simple, analytical forms of the barrier-height distributions or a modified version of the classic Wong formula.
Expert communication is essential to high‐quality care for older patients with serious illness. Although the importance of communication skills is widely recognized, formal curricula for teaching ...communication skills to geriatric and palliative medicine fellows is often inadequate or unavailable. The current study drew upon the educational principles and format of an evidence‐based, interactive teaching method to develop an intensive communication skills training course designed specifically to address the common communication challenges that geriatric and palliative medicine fellows face. The 2‐day retreat, held away from the hospital environment, included large‐group overview presentations, small‐group communication skills practice, and development of future skills practice commitment. Faculty received in‐depth training in small‐group facilitation techniques before the course. Geriatric and palliative medicine fellows were recruited to participate in the course and 100% (n = 18) enrolled. Overall satisfaction with the course was very high (mean 4.8 on a 5‐point scale). After the course, fellows reported an increase in self‐assessed preparedness for specific communication challenges (mean increase 1.4 on 5‐point scale, P < .001). Two months after the course, fellows reported a high level of sustained skills practice (mean 4.3 on 5‐point scale). In sum, the intensive communication skills program, customized for the specific needs of geriatric and palliative medicine fellows, improved fellows’ self‐assessed preparedness for challenging communication tasks and provided a model for ongoing deliberate practice of communication skills.
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