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Sarah Campbell

Publications and source records attributed to Sarah Campbell.

4 recordsLinked to original sources
arXiv2016

Recent results on collective effects in small systems from PHENIX at RHIC

Collisions of simple systems, such as $p$+$p$, or $p$+Nucleus have been used as benchmarks for our understanding of heavy ion collsions, since it was assumed they would be free of the effects from hot nuclear matter. Recently long range correlations and anisotropies of momentum spectra have been seen in such collisions, challenging this assumption. Such phenomena have been understood to be the result of the collective motion, which can best be described by hydrodynamics, whose initial conditions are set by the geometry of the colliding systems, together with their fluctuations. This talk will discuss the recent results from the PHENIX experiment at RHIC using a variety of colliding species ($p$+Au, $d$+Au, $^{3}$He+Au) that give a better understanding of the origin of the observed correlations and anisotropies, thus providing insight as to whether a quark gluon plasma is formed in these simple systems.

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arXiv2016

sPHENIX: The next generation heavy ion detector at RHIC

sPHENIX is a new collaboration and future detector project at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC). It seeks to answer fundamental questions on the nature of the quark gluon plasma (QGP), including its temperature dependence and coupling strength, by using a suite of precision jet and upsilon measurements that probe different length scales of the QGP. This will be achieved with large acceptance, $|η| < 1$ and $0$-$2π$ in $ϕ$, electromagentic and hadronic calorimeters and precision tracking enabled by a $1.5$ T superconducting magnet. With the increased luminosity afforded by accelerator upgrades, sPHENIX will perform high statistics measurements extending the kinematic reach at RHIC to overlap the LHC's. This overlap with the LHC will facilitate better understanding of the role of temperature, density and parton virtuality in QGP dynamics and for jet quenching in particular. This talk will focus on key future measurements and the current state of the sPHENIX project.

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arXiv2015

Photon production from gluon mediated quark-anti-quark annihilation at confinement

Heavy ion collisions at RHIC produce direct photons at low transverse momentum, $p_{T}$ from 1-3 GeV/c, in excess of the $p$$+$$p$ spectra scaled by the nuclear overlap factor, $T_{AA}$. These low $p_{T}$ photons have a large azimuthal anisotropy, $v_{2}$. Theoretical models, including hydrodynamic models, struggle to quantitatively reproduce the large low $p_{T}$ direct photon excess and $v_{2}$ in a self-consistent manner. This paper presents a description of the low $p_{T}$ photon flow as the result of increased photon production from soft-gluon mediated $q$-$\bar{q}$ interactions as the system becomes color-neutral. This production mechanism will generate photons that follow constituent quark number, $n_{q}$, scaling of $v_{2}$ with an $n_{q}$ value of two for direct photons. $χ^{2}$ comparisons of the published PHENIX direct photon and identified particle $v_{2}$ measurements finds that $n_{q}$-scaling applied to the direct photon $v_{2}$ data prefers the value $n_{q}=1.8$ and agrees with $n_{q}=2$ within errors in most cases. The 0-20% and 20-40% Au$+$Au direct photon data are compared to a coalescence-like Monte Carlo simulation that calculates the direct photon $v_{2}$ while describing the shape of the direct photon $p_{T}$ spectra in a consistent manner. The simulation, while systematically low compared to the data, is in agreement with the Au$+$Au measurement at $p_{T}<3$ GeV/c in both centrality bins. Furthermore, this model predicts that higher order flow harmonics, $v_{n}$, in direct photons will follow the modified $n_{q}$-scaling laws seen in identified hadron $v_{n}$ with an $n_{q}$ value of two.

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