arXiv subjects

David Kettler

Publications and source records attributed to David Kettler.

3 recordsLinked to original sources

arXiv2010

The azimuth quadrupole in nuclear collisions

We present measurements of both $p_t$-integral and $p_t$-differential azimuth quadrupole components of two-particle correlations on azimuth ($ϕ$) and pseudorapidity ($η$) for unidentified hadrons in Au-Au collisions at $\sqrt{s_{NN}}=62$ and 200 GeV. The azimuth quadrupole component is distinguished from $η$-localized same-side correlations by taking advantage of the $η$ dependence. The quadrupole component is related to conventional $v_2$ measures. Both $p_t$-integral and $p_t$-differential results are presented as functions of Au-Au centrality. We observe simple universal energy and centrality trends for the $p_t$-integral quadrupole component. $p_t$-differential results are constructed using $v_{2}^{2}$ marginal distributions on $p_t$. These results can be transformed to reveal quadrupole $p_t$ spectra that are nearly independent of centrality. A parametrization of the $p_t$-differential quadrupole shows a simple $p_t$ dependence that can be factorized from the centrality and collision energy dependence above 0.75 GeV/c.

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arXiv2010

Azimuth Quadrupole Systematics in Au-Au Collisions

We have measured $p_t$-dependent two-particle number correlations on azimuth and pseudorapidity for eleven centralities of $\sqrt{s_{NN}} = 62$ and 200~GeV Au-Au collisions at STAR. 2D fits to these angular correlations isolate the azimuth quadrupole amplitude, denoted $2 v_2^2 \{ 2D \} ( p_t )$, from localized same-side correlations. Event-plane $v_2 ( p_t )$ measurements within the STAR TPC acceptance can be expressed as a sum of the azimuth quadrupole and the quadrupole component of the same-side peak. $v_2 \{ 2D \} ( p_t )$ can be transformed to reveal quadrupole $p_t$ spectra which are approximately described by a fixed transverse boost and universal Lévy form nearly independent of centrality. A parametrization of $v_2 \{ 2D \} ( p_t )$ can be factored into centrality and $p_t$-dependent pieces with a simple $p_t$ dependence above 0.75 GeV/c. Results from STAR are compared to published data and model predictions.

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arXiv2009

Universal Centrality and Collision Energy Trends for $v_2$ Measurements From 2D Angular Correlations

We have measured the $p_t$-integrated quadrupole component of two-particle azimuth correlations (related to quantity $v_2$, denoted in this case by $v_2 \{2D\}$) via two-dimensional (2D) angular autocorrelations on $(η, ϕ)$ for unidentified hadrons in Au-Au collisions at 62 and 200 GeV. The 2D autocorrelation provides a method to remove non-quadrupole contributions to $v_2$ (conventionally termed ``nonflow'') under the assumption that such processes produce significant dependence on pair-wise relative $η$ within the detector acceptance. We hypothesize, based on empirical observations, that non-quadrupole contributions are dominated by minijets or minimum-bias jets. Using the optical Glauber eccentricity model for initial-state geometry we find simple and accurate universal energy and centrality trends for the quadrupole component. Centrality trends are determined only by the initial state (impact parameter $b$ and center-of-mass energy $\sqrt{s_{NN}}$). There is no apparent dependence on evolving system dynamics (e.g., equation of state or number of secondary collisions). Our measurements of the quadrupole and non-quadrupole components have implications for the contributions to $v_2$. They suggest that the main source of the difference between $v_2 \{2\}$ and $v_2 \{4\}$ (or $v_2 \{2D\}$) is measured properties of minijets.

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