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Register a new userLocal strong parity violation and new possibilities in experimental study of non-perturbative QCD
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Sergei A. Voloshin
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Quark interaction with topologically non-trivial gluonic fields, instantons and sphalerons, violates P and CP symmetry. In the strong magnetic field of a non-central nuclear collision such interactions lead to the charge separation along the magnetic field, the so called chiral magnetic effect, which manifests local parity violations. An experimental observation of the chiral magnetic effect would be a direct proof for the existence of such physics. Recent STAR results on charge and the reaction plane dependent correlations are consistent with theoretical expectations for the chiral magnetic effect. IIn this paper I discuss different approaches to experimental study of the local parity violation, and propose future measurements which can clarify the picture. In particular I propose to use central body-body U+U collisions to disentangle correlations due to chiral magnetic effect from possible background correlations due to elliptic flow. Further more quantitative studies can be performed with collision of isobaric beams.
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Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in non-central collisions. To study this effect, we investigate a three particle mixed harmonics azimuthal correlator which is a P-even observable, but directly sensitive to the charge separation effect. We report measurements of this observable using the STAR detector in Au+Au and Cu+Cu collisions at $sqrt{s_{NN}}$=200 and 62~GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators, and discuss in detail possible contributions from other effects that are not related to parity violation.
This PhD dissertation is devoted to a non-perturbative study of QCD correlators. The main tool that we use is lattice QCD. We concentrated our efforts on the study of the main correlators of the pure Yang - Mills theory in the Landau gauge, namely the ghost and the gluon propagators. We are particularly interested in determining the $Lqcd$ parameter. It is extracted by means of perturbative predictions available up to NNNLO. The related topic is the influence of non-perturbative effects that show up as appearance of power-corrections to the low-momentum behaviour of the Green functions. A new method of removing these power corrections allows a better estimate of $Lqcd$. Our result is $Lambda^{n_f=0}_{ms} = 269(5)^{+12}_{-9}$ MeV. Another question that we address is the infrared behaviour of Green functions, at momenta of order and below $Lqcd$. At low energy the momentum dependence of the propagators changes considerably, and this is probably related to confinement. The lattice approach allows to check the predictions of analytical methods because it gives access to non-perturbative correlators. According to our analysis the gluon propagator is finite and non-zero at vanishing momentum, and the power-law behaviour of the ghost propagator is the same as in the free case.
A key question in understanding the structure of nucleons involves the role of sea quarks in their ground state electromagnetic properties such as charge and magnetism. Parity-violating electron scattering, when combined with determination of nucleon electromagnetic form factors from parity-conserving e-N scattering, provides another degree of freedom to separately determine the up, down and strange quark contributions to nucleon electromagnetic structure. Strange quarks are unique in that they are exclusively in the nucleons sea. A program of experiments using parity violating electron scattering has been underway for approximately a decade, and results are beginning to emerge. This paper is a brief overview of the various experiments and their results to date along with a short-term outlook of what can be anticipated from experiments in the next few years.
We show that local parity violation due to chirality imbalance in relativistic nuclear collisions can be revealed by measuring the projection of the polarization vector onto the momentum, i.e. the helicity, of final state baryons. The proposed method does not require a coupling to the electromagnetic field, like in the Chiral Magnetic Effect. By using linear response theory, we show that, in the presence of a chiral imbalance, the spin 1/2 baryons and anti-baryons receive an additional contribution to the polarization along their momentum and proportional to the axial chemical potential. The additional, parity-breaking, contribution to helicity can be detected by studying helicity-helicity azimuthal angular correlation.
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