Recent STAR results in high-energy polarized proton-proton collisions at RHIC

The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is carrying out a spin physics program in high-energy polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200-500\,$GeV to gain a deeper insight into the spin structure and dynamics of the proton. One of the main objectives of the spin physics program at RHIC is the extraction of the polarized gluon distribution function based on measurements of gluon initiated processes, such as hadron and jet production. The STAR detector is well suited for the reconstruction of various final states involving jets, $\pi^{0}$, $\pi^{\pm}$, e$^{\pm}$ and $\gamma$, which allows to measure several different processes. Recent results will be shown on the measurement of jet production and hadron production at $\sqrt{s}=200\,$GeV. The RHIC spin physics program has recently completed the first data taking period in 2009 of polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=500\,$GeV. This opens a new era in the study of the spin-flavor structure of the proton based on the production of $W^{-(+)}$ bosons. Recent STAR results on the first measurement of $W$ boson production in polarized $\vec{p}+\vec{p}$ collisions will be shown.Comment: 10 pages, 9 figures, Talk presented at the 26th Winter Workshop on Nuclear Dynamics, Ocho Rios, Jamaica, January 2-9, 2010 to be published in Journal of Physics: Conference Series (JPCS) The author may be contacted via: [email protected]

Recent high pT measurements in STAR

After five years of data taking, the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory provides precise measurements of particle production at high transverse momentum in p-p, d-Au, and Au-Au collisions at sqrt(s) = 200 GeV. We review recent results on the flavor dependence of high pT particle suppression and hadron particle spectra at sqrt(s) = 62.4 GeV. New results on two-particle angular correlations for identified trigger particles and for low momentum associated charged hadrons in p-p and Au-Au as well as near-side $\Delta\eta$ correlations will be presented and discussed.Comment: 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma, Calcutta. 8 pages, 10 figures, submitted to J. Phys. G: Nucl. Part. Phy

Observation of excess J/ψ\psi yield at very low transverse momenta in Au+Au collisions at sNN=\sqrt{s_{\rm{NN}}} = 200 GeV and U+U collisions at sNN=\sqrt{s_{\rm{NN}}} = 193 GeV

We report on the first measurements of J/$\psi$ production at very low transverse momentum ($p_{T} <$ 0.2 GeV/c) in hadronic Au+Au collisions at $\sqrt{s_{\rm{NN}}} =$ 200 GeV and U+U collisions at $\sqrt{s_{\rm{NN}}} =$ 193 GeV. Remarkably, the inferred nuclear modification factor of J/$\psi$ at mid-rapidity in Au+Au (U+U) collisions reaches about 24 (52) for $p_{T} <$ 0.05 GeV/c in the 60-80$\%$ collision centrality class. This noteworthy enhancement cannot be explained by hadronic production accompanied by cold and hot medium effects. In addition, the $dN/dt$ distribution of J/$\psi$ for the very low $p_{T}$ range is presented for the first time. The distribution is consistent with that expected from the Au nucleus and shows a hint of interference. Comparison of the measurements to theoretical calculations of coherent production shows that the excess yield can be described reasonably well and reveals a partial disruption of coherent production in semi-central collisions, perhaps due to the violent hadronic interactions. Incorporating theoretical calculations, the results strongly suggest that the dramatic enhancement of J/$\psi$ yield observed at extremely low $p_{T}$ originates from coherent photon-nucleus interactions. In particular, coherently produced J/$\psi$'s in violent hadronic collisions may provide a novel probe of the quark-gluon-plasma

Beam-Energy Dependence of Charge Balance Functions from Au+Au Collisions at RHIC

Balance functions have been measured in terms of relative pseudorapidity ($\Delta \eta$) for charged particle pairs at the Relativistic Heavy-Ion Collider (RHIC) from Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7 GeV to 200 GeV using the STAR detector. These results are compared with balance functions measured at the Large Hadron Collider (LHC) from Pb+Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV by the ALICE Collaboration. The width of the balance function decreases as the collisions become more central and as the beam energy is increased. In contrast, the widths of the balance functions calculated using shuffled events show little dependence on centrality or beam energy and are larger than the observed widths. Balance function widths calculated using events generated by UrQMD are wider than the measured widths in central collisions and show little centrality dependence. The measured widths of the balance functions in central collisions are consistent with the delayed hadronization of a deconfined quark gluon plasma (QGP). The narrowing of the balance function in central collisions at $\sqrt{s_{\rm NN}}$ = 7.7 GeV implies that a QGP is still being created at this relatively low energy.Comment: 8 pages, 5 figures, submitted to Physical Review

Dancing together: environment, development, aid and faith organisations in climate politics in the United Kingdom

This paper investigates the politics of climate change in the United Kingdom, and in particular, the role of environment non-governmental organisations (ENGOs), aid, faith and development non-government organisations (NGOs). I argue that the drawing together of environment and development concerns is a natural progression in climate politics, given the interdependent nature of development and environmental issues, particularly in developing regions. In addition, this is not surprising given the social justice dimensions to climate change impacts and climate change adaptation, and the pre-existing social justice focus of aid and development organisations. Where other NGO alliances are rare, the combination of a strong civil society, a shared social justice perspective, and a number of important personal connections within the movement laid the groundwork for a strategic joint NGO on climate change. The political result of an alliance between environment groups and aid organisations in the UK context is a strengthened political impact given the wide community support for development and aid organisations and their established voice in politics in that country