Longitudinal Double-Spin Asymmetry of Electrons from Heavy Flavor Decays in Polarized p + p Collisions at s = 200 GeV

This outstanding contribution to the science of particle physics presents ground-breaking results from Japanese researchers with the PHENIX experiment, identifying for the first time the constraint of the gluon polarization in the small Bjorken x region.

In this thesis, the measurement of double-spin asymmetry for electron production from heavy flavor decays was performed in a Relativistic Heavy Ion Collider (RHIC) in the PHENIX experiment at Brookhaven National Laboratory to measure the polarized parton distribution function of gluon in the small Bjorken x region (x~0.01).

For this experiment, for the first time a Hadron Blind Detector (HBD), which is a position-sensitive gas Cherenkov counter with Gas Electron Multiplier whose surface is evaporated by CsI, was employed. This HBD contributes to reducing the background from electron pairs produced by real and virtual photon conversion. Furthermore, the author develops a new analysis method for the background reduction, and the signal-to-background ratio is improved by a factor of roughly 2.0. Using the combination of the HBD and a new analysis method, the double-spin asymmetry of the electron production with transverse momentum ranging 0.5 < pT < 3.0 GeV/c is measured and confirmed to be zero-consistent within the limit of the statistical uncertainty of about 1%. This result identifies the constraint of the gluon polarization in the small Bjorken x region, a worldwide first.

Provides the detailed current states of the gluon polarization measurement, including recent results from the PHENIX and STAR experiment and the global analysis of the DSSV group Introduces the options of rejecting and estimating the photonic electron background using the Hadron Blind Detector. Provides the world-first result of double-spin asymmetry of electrons from heavy flavor decays in protonproton collisions and the constraint of the gluon-polarized parton-distribution function in the small Bjorken x region Nominated as an outstanding contribution by Kyoto University's Physics Department in 2013 Includes supplementary material: sn.pub/extras

Auteur
Dr. Katsuro Nakamura Kyoto University

Contenu
Nucleon Spin Physics.- Experimental Setup.- Electron Analysis.- Results.- Discussion.- Conclusion.