8 research outputs found
The RHIC Spin Program: Achievements and Future Opportunities
This document summarizes recent achievements of the RHIC spin program and
their impact on our understanding of the nucleon's spin structure, i.e. the
individual parton (quark and gluon) contributions to the helicity structure of
the nucleon and to understand the origin of the transverse spin phenomena. Open
questions are identified and a suite of future measurements with polarized
beams at RHIC to address them is laid out. Machine and detector requirements
and upgrades are briefly discussed
The RHIC SPIN Program: Achievements and Future Opportunities
Time and again, spin has been a key element in the exploration of fundamental
physics. Spin-dependent observables have often revealed deficits in the assumed
theoretical framework and have led to novel developments and concepts. Spin is
exploited in many parity-violating experiments searching for physics beyond the
Standard Model or studying the nature of nucleon-nucleon forces. The RHIC spin
program plays a special role in this grand scheme: it uses spin to study how a
complex many-body system such as the proton arises from the dynamics of QCD.
Many exciting results from RHIC spin have emerged to date, most of them from
RHIC running after the 2007 Long Range Plan. In this document we present
highlights from the RHIC program to date and lay out the roadmap for the
significant advances that are possible with future RHIC running
Recommended from our members
The RHIC SPIN Program: Achievements and Future Opportunities
Time and again, spin has been a key element in the exploration of fundamental
physics. Spin-dependent observables have often revealed deficits in the assumed
theoretical framework and have led to novel developments and concepts. Spin is
exploited in many parity-violating experiments searching for physics beyond the
Standard Model or studying the nature of nucleon-nucleon forces. The RHIC spin
program plays a special role in this grand scheme: it uses spin to study how a
complex many-body system such as the proton arises from the dynamics of QCD.
Many exciting results from RHIC spin have emerged to date, most of them from
RHIC running after the 2007 Long Range Plan. In this document we present
highlights from the RHIC program to date and lay out the roadmap for the
significant advances that are possible with future RHIC running
Hyperon Polarization along the Beam Direction Relative to the Second and Third Harmonic Event Planes in Isobar Collisions at <math display="inline"><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>
The polarization of Λ and Λ¯ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at sNN=200  GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild pT dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagrees with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and pT dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy.The polarization of and hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at = 200 GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagree with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy