No abstract

Charge separation (∆S) measurements, obtained relative to the 2 nd -order (Ψ2) and 3 rd -order (Ψ3) event planes with a new charge-sensitive correlator RΨ m (∆S), are presented for p(d)+Au and Au+Au collisions at √ sNN = 200 GeV. The correlator, which is sensitive to the hypothesized Chiral Magnetic Effect (CME), show the expected patterns of background-driven charge separation for the measurements relative to Ψ3 and those relative to Ψ2 for the p(d)+Au systems. By contrast, the Au+Au measurements relative to Ψ2, show event-shape-independent RΨ 2 (∆S) distributions consistent with a CME-driven charge separation, quantified by widths having an inverse relationship to the Fourier dipole coefficient ã1, which evaluates the CME. The extracted values of these widths and their dependencies on centrality and event-shape give new constraints for a possible CME-driven charge separation in relativistic heavy ion collisions.

The strong force, as one of the four fundamental forces at work in the universe, governs interactions of quarks and gluons, and binds together the atomic nucleus. Notwithstanding decades of progress since Yukawa first developed a description of the force between nucleons in terms of meson exchange 1 , a full understanding of the strong interaction remains a major challenge in modern science. One remaining difficulty arises from the non-perturbative nature of the strong force, which leads to the phenomenon of quark confinement at distance scales on the order of the size of the proton. Here we show that in relativistic heavy-ion collisions, where quarks and gluons are set free over an extended volume, two species of produced vector (spin-1) mesons, namely φ and K * 0 , emerge with a surprising pattern of global spin alignment. In particular, the global spin alignment for φ is unexpectedly large, while that for K * 0 is consistent with zero. The observed spin-alignment pattern and magnitude for the φ cannot be explained by conventional mechanisms, while a model with strong force fields 2,3 accommodates the current data. This is the first time that the strong force field is experimentally supported as a key mechanism that leads to global spin alignment. We extract a quantity proportional to the intensity of the field of the strong force. Within the framework of the Standard Model, where the strong force is typically described in the quark and gluon language of Quantum Chromodynamics, the field being considered here is an effective proxy description. This is a qualitatively new class of measurement, which opens a new avenue for studying the behaviour of strong force fields via their imprint on spin alignment.

We present an update to the analysis of fully reconstructed jets in heavy ion collisions by the STAR Collaboration at RHIC. We analyse the response of the anti-k T algorithm in the presence of background, and present a new observable for the measurement of inclusive jet production that is expected to be more robust against background model assumptions than previous jet analyses at RHIC and LHC.

No abstract

With the successful runs of the multi-gap resistive plate chamber (MRPC)-based time-of-flight (TOF) prototypes in the solenoid tracker at RHIC (relativistic heavy ion collider) (STAR) for the past several years, a full barrel TOF is being built to take part in data taking in late 2008. Together with other sub-detectors in STAR this TOF will greatly enhance the reach of the STAR scientific programme significantly by extending the particle identification (PID) capability. It will allow STAR to extract the maximum amount of information available from soft physics measures on an event-by-event basis. It will also extend its power to the heavy flavour sector by increasing the signal-to-noise ratios for charm hadron reconstructions for D0, D+, D+s, J/ψ, enabling STAR to make systematic studies of charm thermalization and charm meson flow. The physics results achieved by the TOF prototypes as well as the goal of the full TOF expectable are presented.

Abstract. We present the centrality dependence of Λ andΛ hyperon global polarization in Au+Au collisions at √ s N N = 62 GeV and 200 GeV measured with the STAR detector at RHIC. Within the precision of the measurement, we observe no centrality dependence of Λ andΛ hyperon global polarization and within our acceptance it is consistent with zero. Different sources of systematic uncertainties (feed down effects, spin precession) are discussed and estimated. The obtained upper limit, |P Λ,Λ | ≤ 0.02, is compared to theoretical predictions discussed recently in literatures.

No abstract