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.
We present measurements of the pseudorapidity distribution of primary charged particles produced in Au+Au collisions at three energies, sqrts(NN)=19.6, 130, and 200 GeV, for a range of collision ...centrali-ties. The distribution narrows for more central collisions and excess particles are produced at high pseudorapidity in peripheral collisions. For a given centrality, however, the distributions are found to scale with energy according to the "limiting fragmentation" hypothesis. The universal fragmentation region described by this scaling grows in pseudorapidity with increasing collision energy, extending well away from the beam rapidity and covering more than half of the pseudorapidity range over which particles are produced. This approach to a universal limiting curve appears to be a dominant feature of the pseudorapidity distribution and therefore of the total particle production in these collisions.
The nfkb2 gene is a member of the Rel/NF-kappa B family of transcription factors. COOH-terminal deletions and rearrangements of this gene have been associated with the development of human cutaneous ...T cell lymphomas, chronic lymphocytic leukemias, and multiple myelomas. To further investigate the function of NF-kappa B2, we have generated mutant mice carrying a germline mutation of the nfkb2 gene by homologous recombination. NF-kappa B2-deficient mice showed a marked reduction in the B cell compartment in spleen, bone marrow, and lymph nodes. Moreover, spleen and lymph nodes of mutant mice presented an altered architecture, characterized by diffuse, irregular B cell areas and the absence of discrete perifollicular marginal and mantle zones; the formation of secondary germinal centers in spleen was also impaired. Proliferation of NF-kappa B2-deficient B cells was moderately reduced in response to lipopolysaccharide, anti-IgD-dextran, and CD40, but maturation and immunoglobulin switching were normal. However, nfkb2 (-/-) animals presented a deficient immunological response to T cell-dependent and -independent antigens. These findings indicate an important role of NF-kappa B2 in the maintenance of the peripheral B cell population, humoral responses, and normal spleen architecture.
RelB, a member of the NF-κB/Rel family of transcription factors, has been implicated in the constitutive expression of KB-regulated genes in lymphoid tissues. We have generated mice carrying a ...germline mutation of the
relB gene, resulting in the absence of RelB protein and a dramatic reduction of constitutive κB-binding activity in thymus and spleen. Mice homozygous for the disrupted
relB locus had phenotypic abnormalities including multifocal, mixed inflammatory cell infiltration in several organs, myeloid hyperplasia, splenomegaly due to extramedullary hematopoiesis, and a reduced population of thymic dendritic cells. ReIB-deficient animals also had an impaired cellular immunity, as observed in contact sensitivity experiments. Thus, ReIB plays a decisive role in the hematopoietic system, and its absence cannot be functionally compensated by any other member of the NF-κB/Rel family.
Transgenic mice overexpressing the chemokine monocyte chemoattractant protein-1 (MCP-1) in the thymus and central nervous system have a higher number of mononuclear cells in those tissues than do ...control littermates. In the thymus, there is a modest increase in the number of Mac-1 and F4/80 positive cells, but no apparent change in the number of lymphoid cells. A more pronounced mononuclear infiltrate is detected in transgenic mice expressing MCP-1 in the brain. The vast majority of the recruited cells in the brain are monocytes and macrophages, as defined by light microscopy, and ultrastructural and immunohistochemical criteria. Such cells are found in a perivascular orientation with minimal parenchymal infiltration, possibly as a consequence of the accumulation of MCP-1 in the vessels, as shown by immunohistochemistry. The mononuclear cell infiltrate in the brain can be significantly amplified by LPS treatment, suggesting that the recruitment properties of MCP-1 can be potentiated by additional factors.
We present the first measurement of the pseudorapidity density of primary charged particles in Au+Au collisions at root squares(NN) = 200 GeV. For the 6% most central collisions, we obtain ...dN(ch)/d(eta)/(/eta/<1) = 650+/-35(syst). Compared to collisions at root squares(NN) = 130 GeV, the highest energy studied previously, an increase by a factor of 1.14+/-0.05 at 90% confidence level, is found. The energy dependence of the pseudorapidity density is discussed in comparison with data from proton-induced collisions and theoretical predictions.
The PHOBOS detector at RHIC Back, B.B; Baker, M.D; Barton, D.S ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2003, Letnik:
499, Številka:
2
Journal Article
Recenzirano
This manuscript contains a detailed description of the PHOBOS experiment as it is configured for the Year 2001 running period. It is capable of detecting charged particles over the full solid angle ...using a multiplicity detector and measuring identified charged particles near mid-rapidity in two spectrometer arms with opposite magnetic fields. Both of these components utilize silicon pad detectors for charged particle detection. The minimization of material between the collision vertex and the first layers of silicon detectors allows for the detection of charged particles with very low transverse momenta, which is a unique feature of the PHOBOS experiment. Additional detectors include a time-of-flight wall which extends the particle identification range for one spectrometer arm, as well as sets of scintillator paddle and Cherenkov detector arrays for event triggering and centrality selection.
Transgenic mice expressing the chemokine N51/KC in thymus, skin, and tongue showed a marked infiltration of a single class of inflammatory cells (neutrophils) in the sites of transgene expression. In ...the thymus, neutrophils were most numerous in the cortex and juxta-medullary regions, often forming aggregates or clusters. A similar, but less intense, neutrophilic infiltrate occurred in close proximity to the epidermal basal layer of the tongue and skin. No morphologic evidence of injury was observed in the thymus, skin, or tongue of these transgenic mice, indicating that N51/KC expression induces recruitment but not inflammatory activation of neutrophils. The lack of activation in the thymus resulted in a large senescent neutrophilic population that was phagocytosed by thymic macrophages and epithelial-reticular cells. These results indicate that N51/KC is a neutrophil chemoattractant in vivo and establish these transgenic mice as effective models to study the phenomena of recruitment and clearance of neutrophils, events that are critical for the initiation and resolution of the inflammatory response.
Mice with a targeted disruption of RelB, a member of the Rel/NF-kappaB family of transcription factors, have multifocal, mixed inflammatory cell infiltration in several organs, myeloid hyperplasia, ...and splenomegaly due to extramedullary hemopoiesis. To elucidate the cellular requirements for this complex phenotype, we have bred RelB-deficient (RelB(kappaO)) animals to two strains of immunodeficient mice, recombinase-activating gene-1-deficient (RAG-1(kappaO), lacking B and T cells), and Nur77/N10-transgenic mice (Nur77/N10(TG), lacking only T cells). We also generated mutant mice deficient in both RelB and the p50 subunit of NF-kappaB (p50(kappaO), multiple defects in B cell function). RelB(kappaO)RAG-1(kappaO) and RelB(kappaO)Nur77/N10(TG) mice are disease-free, while RelB(kappaO)p50(kappaO) double-mutant animals develop an even more severe phenotype despite the absence of B cells in the inflammatory infiltrates. Thus, both multiorgan inflammation and myeloid hyperplasia in RelB-deficient mice are T cell dependent, whereas B cells are not crucially involved.
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