hep-ex updates on arXiv.org


Bayesian probability for leptonic CP phase with strong CP prior. (arXiv:2103.03262v1 [hep-ph])

In a world devoid of axions, the smallness of the strong CP phase can have implications for leptonic CP violation being probed by neutrino experiments. For example, if nature adopted an axionless solution to the strong CP problem, the same symmetries that set the strong CP phase to zero at the tree-level, may also set the leptonic $CP$ phases to zero (mod \pi). This automatically happens in the left-right symmetric model when it is extended minimally to solve the strong CP problem by imposition of both P and CP. In the Nelson Barr solution the needed symmetries can be assigned so that leptonic CP violation is not generated. In the minimal left-right symmetric model with P (and not CP), where the strong CP problem remains, leptonic CP phases radiatively generate the strong CP phase in one loop, and therefore they may be absent (negligibly small) in large regions of parameter space. All these results motivate us to consider a Bayesian prior for leptonic Dirac CP phase \delta_{CP} of the PMNS matrix that has delta function like peaks at CP conserving values of 0 and \pi on top of a uniform distribution. We evaluate the posterior probability distribution for \delta_{CP} using the current global fit to neutrino experiments and find significant enhancements for the probability that \delta_{CP} is at or negligibly close to \pi. We also provide useful tables for the posterior probability considering present and future experimental sensitivities.

Extraction of the Sivers function from SIDIS, Drell-Yan, and $W^\pm/Z$ boson production data with TMD evolution. (arXiv:2103.03270v1 [hep-ph])

We perform a global fit of the available polarized Semi-Inclusive Deep Inelastic Scattering (SIDIS), polarized pion-induced Drell-Yan (DY) and $W^\pm/Z$ boson production data at N$^3$LO and NNLO accuracy of the Transverse Momentum Dependent (TMD) evolution, and extract the Sivers function for $u$, $d$, $s$ and for sea quarks. The Qiu-Sterman function is determined in a model independent way via the operator product expansion from the extracted Sivers function. The analysis is supplemented by additional studies, such as the estimation of applicability region, the impact of the unpolarized distributions' uncertainties, the universality of the Sivers functions, positivity constraints, the significance of the sign-change relation, and the comparison with the existing extractions

Scanning force sensing at $\mu$m-distances from a conductive surface with nanospheres in an optical lattice. (arXiv:2103.03420v1 [physics.optics])

The center-of-mass motion of optically trapped dielectric nanoparticles in vacuum is extremely well-decoupled from its environment, making a powerful tool for measurements of feeble sub-attonewton forces. We demonstrate a method to trap and manuever nanoparticles in an optical standing wave potential formed by retro-reflecting a laser beam from a metallic mirror surface. We can reliably position a $\sim 170$ nm diameter silica nanoparticle at distances of a few hundred nanometers to tens of microns from the surface of a gold-coated silicon mirror by transferring it from a single-beam tweezer trap into the standing wave potential. We can further scan the two dimensional space parallel to the mirror surface by using a piezo-driven mirror. This method enables three-dimensional scanning force sensing near surfaces using optically trapped nanoparticles, promising for high-sensitivity scanning force microscopy, tests of the Casimir effect, and tests of the gravitational inverse square law at micron scales.