M. Oldenburg

Novel integrated CMOS sensor circuits

Three novel integrated CMOS active pixel sensor circuits for vertex detector applications have been designed with the goal of increased signal-to-noise ratio and speed. First, a large-area native epitaxial silicon photogate sensor was designed to increase the charge collected per hit pixel and to reduce charge diffusion to neighboring pixels. High charge to voltage conversion is maintained by subsequent charge transfer to a low capacitance readout node. Second, a per-pixel correlated double sampling kT/C reset noise reduction circuit was tested. It requires only one read, as compared to two for typical double sampling in active pixel sensors, and no off-pixel storage or subtraction is needed. The technique reduced input-referred temporal noise by a factor of 2.5 to a measured 15.6 e/sup -/, rms. Finally, a column-level active reset technique was designed that suppresses kT/C reset noise. It reduced noise by up to a factor of 7.6, to an estimated 8.3 input-referred electrons, rms. The technique also dramatically reduces fixed pattern (pedestal) noise, by up to a factor of 21. This may reduce pixel-by-pixel pedestal differences enough to permit sparse data scan without per-pixel offset corrections.

A Heavy Flavor Tracker for STAR

We propose to construct a heavy flavor tracker for the STAR experiment at RHIC in order to measure the elliptic flow of charmed hadrons in the low p T region and identify B-meson contributions in the region p T > 4 xa0GeV/c . In this talk, we will present the design of the detector in-depth and its expected performance as studied in detailed simulations and analytic calculations. Physics potentials of the detector will also be discussed.

Scaling of anisotropic flow in the picture of quark coalescence

Measurements of anisotropic flow at low (pT < 1.5 GeV/c) and intermediate (1.5 < pT < 5 GeV/c) transverse momentum from the STAR collaboration are reviewed. While at low pT an ordering of elliptic flow strength with particle mass is observed, the measured signals appear to follow number-of-constituent quark scaling at intermediate pT. The observations of higher harmonics support this picture qualitatively, and are sensitive to specific model assumptions.

Measurement of charm flow with the STAR Heavy Flavour Tracker

In order to understand the partonic EOS of matter created at RHIC, one needs to study both the collectivity of the produced matter and the degree of thermalization. Anisotropic flow measurements have already demonstrated the development of partonic collectivity at RHIC (Ackermann K et al 2001 Phys. Rev. Lett. 86 402), and now it is necessary to address the issue of quark thermalization. Since the masses of the heavy flavour quarks are larger than the possible excitations of the system created in the collision, their collective motion could be used to indicate the degree of thermalization of the light flavour quarks (u, d, s). The Heavy Flavour Tracker (HFT), a tracking upgrade of the STAR experiment, is being designed to provide an unambiguous measurement of charm quark flow through the direct reconstruction of the D0. The current design of our detector uses a novel CMOS-based sensor, allowing for a low mass and high resolution detector element.

ANISOTROPIC FLOW IN ULTRA-RELATIVISTIC HEAVY-ION COLLISIONS

The analysis of anisotropic flow of particles created in high energy heavy-ion collisions gives insight into the early stage of these reactions. Measurements of directed flow (v1), elliptic flow (v2) and flow of 4th and 6th order (v4 and v6) are presented. While the study of v2 for multi-strange particles establishes partonic collectivity the results for higher order anisotropies constrain the initial conditions of hydrodynamic model calculations.