arXiv subjects

Christine Nattrass

Publications and source records attributed to Christine Nattrass.

25 records · Page 2Linked to original sources

arXiv2016

Background subtraction methods for precision measurements of di-hadron and jet-hadron correlations in heavy ion collisions

Di-hadron correlations and jet-hadron correlations are frequently used to study interactions of the Quark Gluon Plasma with the hard partons that form jets. The existing background subtraction methods for these studies depend on several assumptions and independent measurements of the Fourier coefficients of the combinatorial background. In this paper, we present two background subtraction methods which use the observation that the near-side correlation signal is negligible for large separations between the associated particle and the trigger. The combinatorial background is fit in this background-dominated region. Including the reaction plane dependence of the raw correlation improves these results. To test the accuracy of these methods, a simple model is used to simulate di-hadron and jet-hadron correlations with a combinatorial background similar to that observed in the data. The true signal is compared to the extracted signal. The results are compared to results from two variants of the Zero-Yield-At-Minimum (ZYAM) method. We test these methods for mid-peripheral and central collisions and for di-hadron and jet-hadron correlations. These methods are more precise than the ZYAM method with fewer assumptions about the shape and level of the combinatorial background, even in central collisions where the experimental resolution on the measurement of the reaction plane dependence is poor. These methods will allow more accurate studies of modifications of the away-side jet and will be particularly useful for studies of jet-hadron correlations, where the combinatorial background is poorly constrained from previous studies.

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arXiv2011

Results from ALICE

The ALICE experiment at the Large Hadron Collider at CERN is optimized to study the properties of the hot, dense matter created in high energy nuclear collisions in order to improve our understanding of the properties of nuclear matter under extreme conditions. In 2009 the first proton beams were collided at the Large Hadron collider and since then data from proton-proton collisions at $\sqrt{s}$ = 0.9, 2.36, 2.76, and 7 TeV have been taken. Results from pp collisions provide significant constraints on models. In particular, results on strange particles indicate that Monte Carlo generators still have considerable difficulty describing strangeness production. In 2010 the first lead nuclei were collided at $\sqrt{s_{NN}}$ = 2.76 TeV. Results from Pb+Pb demonstrate suppression of particle production relative to that observed in pp collisions, consistent with expectations based on data available at lower energies.

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arXiv2010

Di-hadron correlations at RHIC

Di-hadron correlations have been used to study jets at RHIC and have yielded rich insight into the properties of the medium. Studies show that the near-side peak of high-pT triggered correlations can be decomposed into two parts, a jet-like correlation and the ridge. The jet-like correlation is narrow in both azimuth and pseudorapidity and has properties consistent with vacuum fragmentation, while the ridge is narrow in azimuth but broad in pseudorapidity and roughly independent of pseudorapidity. The energy, system, and particle composition of the jet-like correlation and the ridge are discussed. Data indicate that the jet-like correlation is dominantly produced by vacuum fragmentation. Attempts have been made to explain the production of the ridge component as coming from recombination, momentum kicks, and QCD magnetic fields. However, few models have attempted to quantitatively calculate the characteristics of the ridge. The wealth of data should help distinguish models for the production mechanism of the ridge. Implications for studies of the jet-like correlation and the ridge at the LHC are discussed.

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arXiv2010

System size and energy dependence of the near-side of high-$p_T$ triggered di-hadron correlations in STAR

Previous studies have indicated that the near-side peak of high-pT triggered di-hadron correlations can be decomposed into two parts, a jet-like correlation and the ridge. We present data from Cu+Cu and Au+Au collisions at sqrt(sNN)=62 and 200 GeV, which should allow more robust tests of models. The jet-like correlation is narrow in both azimuth and pseudorapidity and has properties similar to those expected from vacuum fragmentation. The yield of particles in the jet-like correlation are presented for both systems and at both energies and compared to the yields expected from di-hadron correlations in PYTHIA 8.1. The ridge is narrow in azimuth but broad in pseudorapidity and roughly independent of pseudorapidity within STAR's acceptance. Attempts have been made to explain the production of the ridge component as coming from recombination, momentum kicks, Glasma flux tubes, and a plasma instability. However, few models have attempted to quantitatively calculate the characteristics of the ridge. The yield in the ridge is compared for all systems and energies. The implications for measurements at the LHC are discussed in context of the data and models.

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arXiv2008

Energy and system dependence of high-$p_T$ triggered two-particle near-side correlations

Previous studies have indicated that the near-side peak of high-$p_T$ triggered correlations can be decomposed into two parts, the \textit{Jet} and the \textit{Ridge}. We present data on the yield per trigger of the \textit{Jet} and the \textit{Ridge} from $d+Au$, $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}$ = 62.4 GeV and 200 GeV and compare data on the \textit{Jet} to PYTHIA 8.1 simulations for $p+p$. PYTHIA describes the \textit{Jet} component up to a scaling factor, meaning that PYTHIA can provide a better understanding of the \textit{Ridge} by giving insight into the effects of the kinematic cuts. We present collision energy and system dependence of the \textit{Ridge} yield, which should help distinguish models for the production mechanism of the \textit{Ridge}.

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arXiv2008

System and energy dependence of strange and non-strange particle correlations in STAR at RHIC

Two-particle high-$p_T$ triggered correlations in $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}$ = 62 $GeV$ and $\sqrt{s_{NN}}$ = 200 $GeV$ in STAR at RHIC are presented. The $N_{part}$, $p_T^{associated}$, and $p_T^{trigger}$ dependence of the yield per trigger in the \textit{Jet} and \textit{Ridge} components of the near-side is investigated for h, $K^0_S$, $Λ$, and $Ξ$ trigger and associated particles. The system and energy dependence of these components is a potentially powerful tool to distinguish between models used to describe their production.

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arXiv2008

System size dependence of strange particle correlations in Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR at RHIC

Two particle azimuthal correlations with strange trigger particles ($K^0_S,Λ,Ξ$) are presented in Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR at RHIC. The near-side associated yield is investigated as a function of centrality, $p_T$, and strangeness content of the trigger to investigate possible flavour or meson/baryon differences. The system size dependence of both the jet-like correlations and the long range pseudorapidity correlations is studied to give insight into the origin of these two components.

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